\ COLLEGE ZOOLOGY THE MACMILLAN COMPANY NEW YORK BOSTON CHICAGO DALLAS SAN FRANCISCO MACMILLAN & CO., LIMITED LONDON BOMBAY CALCUTTA MELBOURNE THE MACMILLAN CO. OF CANADA, LTD. TORONTO f COLLEGE ZOOLOGY //: BY ROBERT W. HEGNER, Pn.D. ASSISTANT PROFESSOR OF ZOOLOGY IN THE UNIVERSITY OF MICHIGAN ff ork THE MACMILLAN COMPANY 1914 All rights reserved COPYRIGHT, 1912, BY THE MACMILLAN COMPANY. Set up and electrotyped. Published July, igit. October, 1917 January, 1913. February, 1914. PREFACE THIS book is intended to serve as a text for beginning students in universities and colleges, or for students who have already taken a course in general biology and wish to gain a more com- prehensive view of the animal kingdom. It differs from many of the college textbooks of zoology now on the market in several important respects: (i) the animals and their organs are not only described, but their functions are pointed out ; (2) the ani- mals described are in most cases native species ; and (3) the relations of the animals to man are emphasized. Besides serv- ing as a textbook, it is believed that this book will be of interest to the general reader, since it .gives a bird's-eye view of the entire animal kingdom as we know it at the present time. Within the past decade there has been a tendency for teachers of zoology to pay less attention to morphology and more to physiology. As a prominent morphologist recently said, " Morphology ... is no longer in favor . . . and among a section of the zoological world has almost fallen into dis- grace " (Bourne). The study of the form and structure of animals is, however, of fundamental importance, and is abso- lutely necessary before physiological processes can be fully understood ; but a course which is built up on the " old-fash- ioned morphological lines " is no longer adequate for the presen- tation of zoological principles. In \vriting this book the author has attempted, not only to describe the most important structural features of the various types of animals, but also to point out the vital phenomena as expressed in the functions of the organs. Furthermore, an endeavor has been made to compare the animals in each phylum with those of the members of nearly related phyla, so that the vi PREFACE student may realize the unity as well as the variety in animal life. So far as possible in a limited space, the relations of the animals to other animals, to plants, and to environmental factors in general are considered, and the animals of special economic importance are emphasized. By this method the student is brought into closer contact with and gains a broader idea of natural phenomena. Questions naturally arise in the student's mind, such as, " Where does the animal live ? " " What does the animal do?" and "What is this or that particular organ for? " and stimulate interest in the work leading to more careful observations and more accurate inferences. Each phylum is introduced by a more or less complete account of the anatomy, physiology, and ecology of one, or in certain cases, two or more types. These types were selected with the following requirements in mind : (i) they must represent as nearly as possible an average of the phylum ; (2) they must illustrate clearly the characteristics of the phylum so as to serve as an introduction to a comparative study of other members of the group ; (3) they must be common native species which can be obtained for direct observations in the laboratory ; (4) they must occupy an important position in the animal series ; and (5) they must be of special importance to man. Very few types fulfill all of these requirements ; in several cases two types have been employed because one was not considered adequate. It is impossible in one small volume to describe as many different animals under each phylum as might be desired, or to give a full classification of each group. However, a general idea of the various kinds of animals and their habitats can be obtained from the short account included in each chapter. The species mentioned are in most cases the commonest and most representative of those living in North America. More space has been devoted to the Chordata than to any other phylum, and the classes under the subphylum Verte- brata have been treated in a somewhat different manner from those of the invertebrates. It is customary in studying the PREFACE Vli vertebrates to select one species as a type to be examined in considerable detail, and then to compare species belonging to the other classes with it. The animal usually chosen for detailed study is the frog, and this form has therefore been treated more fully in this book than any other vertebrate type. The vertebrates are, as a rule, larger than the invertebrates, are fewer in number, and are usually more interesting to be- ginning students ; they are, on the whole, better known than the invertebrates and more easily observed. For these reasons they have been discussed largely from the natural history stand- point, and it is hoped that this treatment will give students a better idea of the everyday events in the lives of the more common vertebrates than can be obtained from a purely morpho- logical course. A book covering such a large field as this one must necessa- rily be more or less of a compilation, and the facts and figures must be selected from numerous textbooks and scientific peri- odicals. The sources from which the author has obtained a large part of his material are as follows :- Bourne, G. C. Comparative Anatomy of Animals, 2 vols., 1909. Bronn, H. G. Klassen und Ordnungen des Tierreichs. Calkins, G. N. Protozoa, 1901. - Protozoology, 1909. Cambridge Natural History, 10 vols. Dean, B. Fishes, Living and Fossil, 1895. Dickerson, M. C. The Frog Book, 1907. Ditmars, R. L. The Reptile Book, 1907. - Reptiles of the World, 1910. Flower, W. H., and Lydekker, R. Mammals, Living and Ex- tinct, 1891. Hertwig, R. Manual of Zoology, 1905. Holmes, S. J. Biology of the Frog, 1906. Jennings, H. S. Behavior of the Lower Organisms, 1906. Jordan, D. S. Guide to the Study of Fishes, 2 vols., 1905. - and Evermann, B. W. Fishes of North America, 4 vols., 1900. Vlll PREFACE Kellogg, V. L. American Insects, 1905. Kingsley, J. S. Textbook of Vertebrate Zoology, 1899. Knowlton, F. H. Birds of the World, 1909. Korschelt, E., and Heider, K. Textbook of the Embryology of Invertebrates, 4 vols., 1895. Lang, A. Comparative Anatomy of Invertebrates. Lankester, E. R. A Treatise on Zoology, 1900-1909. Marshall, A. M., and Hurst, C. H. Practical Zoology, 1905. Matthew, W. D. Evolution of the Horse. American Museum Journal, Vol. III. Guide Leaflet No. 9, 1903. Morgan, T. H. Regeneration, 1901. Osborn, H. F. The Age of Mammals, 1910. Parker, T. J. Zootomy, 1884. - and Parker, W. N. An Elementary Course in Practical Zoology, 1908. - and Haswell, W. A. Textbook of Zoology, 1910. Schmeil, O. Textbook of Zoology, 1901. Sedgwick, A. Student's Textbook of Zoology, 3 vols., 1898-1909. Sedgwick, W. T., and Wilson, E. B. General Biology, 1899. Shipley, A. E., and MacBride, E. W. Zoology, 1904. Simpson, G. B. Anatomy and Physiology' of Poly gyr a Albolabris and Limax Maximus. Bui. N. Y. State Mus., Vol. 8, 1901. Stone, W., and Cram, W. E. American Animals, 1905. United States Department of Agriculture. Circulars and Bul- letins. Verworn, M. General Physiology, 1899. Wiedersheim, R., and Parker, W. N. Comparative Anatomy of Vertebrates, 1907. Wilder, H. H. History of the Human Body, 1909. Willey, A. Amphioxus and the Ancestry of the Vertebrates, 1894. Williams, L. W. Anatomy of the Common Squid. American Museum of Natural History. Wilson, E. B. The Cell in Development and Inheritance, 1900. Zittel, K. von. Textbook of Paleontology, 2 vols., 1903. PREFACE IX In an endeavor to avoid as many errors as possible, the manuscript of most of the chapters has been read by zoologists who are authorities in the special field treated therein. It is a great pleasure to thank these gentlemen in this place for the invaluable assistance they have rendered. I am indebted to Professor A. S. Pearse for reading Chapters I-IX ; to Mr. Peter Okkelberg for reading the entire manuscript ; to Professor G. N. Calkins for reading Chapter II ; to Professor H. V. Wilson for reading Chapter IV ; to Professor Charles W. Hargitt for read- ing Chapters V and VI ; to Professor W. C. Curtis for reading Chapters VII and IX ; to Dr. G. R. La Rue for reading Chapter VII ; to Dr. B. H. Ransom for reading Chapter VIII ; to Dr. Hubert Lyman Clark for reading Chapter X; to Professor J. Percy Moore for reading Chapter XI ; to Mr. H. B. Baker for reading Chapter XII ; to Professor A. E. Ortmann for read- ing the part of Chapter XIII relating to the Crustacea, Ony- chophora, and Myriapoda ; to Professor Vernon L. Kellogg for reading the part of Chapter XIII relating to Insecta ; to Mr. J. H. Emerton for reading the part of Chapter XIII relating to the Arachnida ; to Professor Alexander G. Ruthven for reading Chapters XIV-XIX ; to Professor B. M. Allen for reading Chap- ter XIV ; to Mr. R. E. Richardson for reading Chapters XV- XVII ; to Professor Lynds Jones for reading Chapter XX ; and to Mr. Marcus W. Lyon, Jr., and Mr. N. Hollister for reading Chapter XXI. I am also indebted to Dr. A. F. Shull for read- ing a large part of the proof, and to my wife for her especially valuable assistance in reading proof and preparing the index. ROBERT W. HEGNER. MAY 14, 1912. CONTENTS PAGE PREFACE TABLE OF THE CLASSIFICATION OF THE ANIMAL KINGDOM . xix CHAPTER I INTRODUCTION ... . . . . i 1 . General Survey of the Animal Kingdom i 2. Living Matter contrasted with Non-living Matter 3. The Physical Basis of Life Protoplasm 10 4. The Origin of Life . . 12 5. The Cell and the Cell Theory . ... 12 6. Plants contrasted with Animals . . .18 7. Classification ... .... 21 8. The Principal Phyla of the Animal Kingdom . . 23 9. Zoology and its Subsciences . . . 25 CHAPTER II PHYLUM PROTOZOA 27 1. Class I. Rhizopoda .... 27 a, Ameba proteus, 27 ; b, Rhizopoda in General, 39. 2. Class II. Mastigophora .... 41 a, Euglena viridis, 41 ; b, Mastigophora in General, 45. 3. Class III. Sporozoa ... .48 a. Monocystis, 48 ; b, Plasmodiuni vivax, 50 ; c, Sporo- zoa in General, 52. 4. Class IV. Infusoria . . -53 a, Paramecium caudatiim, 53 ; b, Infusoria in General, 62. 5. Protozoa in General ....... 65 6. Pathogenic Protozoa 70 zi Xll CONTENTS CHAPTER III AN INTRODUCTION TO THE METAZOA 1 . Germ Cells and Somatic Cells . 2. Tissues ...... 3. Organs and Systems of Organs 4. Reproduction . 5. The Forms of Animals . PAGE 73 73 74 76 79 90 CHAPTER IV PHYLUM PORIFERA 1. Structure of a Simple Sponge Leucosolenia . 2. Anatomy and Physiology of Grantia 3. The Fresh-water Sponge Spongilla 4. Sponges in General ...... 92 92 94 98 99 PHYLUM CCELENTERATA CHAPTER V Hydra 1 . The Fresh-water Polyp 2. Class I. Hydrozoa a, A Colonial Hydrozoon Obelia, 119; b, Metagene- sis, 122 ; c, A Jellyfish or Medusa- Gonioneiniis, 122 ; d, Hydroid and Medusa Compared, 124; e, Polymor- phism, 126; f, Reproduction in the Hydrozoa, 127; g, Classification of the Hydrozoa, 128. 3. Class II. Scyphozoa ....... a, A Scyphozoan Jellyfish Aurelia, 129; b, Classifi- cation of the Scyphozoa, 132. 4. Class III. Anthozoa a, A Sea Anemone Metridimn, 134 ; b, A Coral Polyp, 137 ; c, Coral Reefs and Atolls, 138 ; d, Classification of the Anthozoa, 139. 5. Ccelenterates in General . 108 1 08 118 129 133 142 CHAPTER VI PHYLUM CTENOPHORA 145 CONTENTS xiii CHAPTER VII PAGE PHYLUM PLATYHELMINTHES 150 1. A Fresh-water Flatworm Planaria . . . .150 2. Class I. Turbellaria ice 3. Class II. Trematoda . 157 a, The Liver Fluke Fasciola hepatica, 157; b, Tre- matoda in General, 161. 4. Class III. Cestoda 163 a. The Tapeworm Tcenia, 163 ; b, Cestoda in General, 165. 5. Fhtworms in General .166 CHAPTER VIII PHYLUM NEMATHELMINTHES 169 1. A Parasitic Round Worm Ascaris lumbricoides . .169 2. Nemathelminthes in General 173 CHAPTER IX INVERTEBRATES OF MORE OR LESS UNCERTAIN SYSTEMATIC POSITION I7 6 1. Mesozoa I7 6 2. Nemertinea 177 3. Nematomorpha 179 4. Acanthocephala 180 5. Chaetognatha 180 6. Rotifera X 8i 7. Bryozoa ^3 8. Phoronidea 185 9. Brachiopoda . 185 10. Gephyrea . . .186 CHAPTER X PHYLUM ECHINODERMATA . 189 i. Anatomy and Physiology of the Starfish Asterias . 190 3. Class I. Asteroidea Starfishes . 198 XIV CONTENTS . PAGE 3. Class II. Ophiuroidea Brittle Stars .... 199 4. Class III. Echinoidea Sea Urchins .... 202 5. Class IV. Holothurioidea Sea Cucumbers . . . 205 6. Class V. Crinoidea Sea-lilies or Feather-stars . . 208 7. Development of Echinoderms 210 8. Artificial Parthenogenesis 212 9. The Position of Echinoderms in the Animal Kingdom . 213 CHAPTER XI PHYLUM ANNELIDA 215 1. The Earthworm Lumbricus 215 2. Classification of Annelids ...... 231 3. Class I. Archiannelida 232 4. Class II. Chaetopoda 233 5. Class III. Hirudinea ....... 236 6. Annelids in General 240 CHAPTER XII PHYLUM MOLLUSCA 242 1. The Pearly Fresh -water Mussel Anodonta and the Uniones ......... 243 2. Class I. Amphineura 251 3. Class II. Gastropoda 252 a, A Land-snail, 253 ; b, Gastropoda in General, 258. 4. Class III. Scaphopoda 261 5. Class IV. Pelecypoda 261 6. Class V. Cephalopoda 264 a, The Common Squid Loligo, 264 ; b, Cephalopoda in General, 267. 7. Mollusca in General 269 CHAPTER XIII PHYLUM ARTHROPODA 274 I. Introduction ......... t , 274 CONTENTS XV PAGE 2. Class I. Crustacea ... ... 276 a, The Crayfish Cambartis, 276 ; b, Crustacea in General, 292. 3. Class II. Onychophora 305 4. Class III. Myriapoda 308 5. Class IV. Insecta 312 a, The Honey-bee, 312 ; b, The Anatomy and Physi- ology of Insects in General, 328; c. General Survey of the Orders of Insects, 336 ; d, The Economic Im- portance of Insects, 370. 6. Class V. Arachnida . 371 a, The Spiders, 371 ; b, Other Arachnida, 377. CHAPTER XIV PHYLUM CHORDATA: INTRODUCTION 386 1. Subphylum I. ENTEROPNEUSTA 386 2. Subphylum II. TUNICATA 389 3. Subphylum III. CEPHALOCHORDA 393 4. Subphylum IV. VERTEBRATA : INTRODUCTION . . 400 CHAPTER XV SUBPHYLUM VERTEBRATA: Class I. Cyclostomata . . . 414 1. The Lamprey Petromyzon 415 2. Cyclostomata in General 420 CHAPTER XVI SUBPHYLUM VERTEBRATA : Class II. Elasmobranchii ] . . 422 1. The Dogfish -Shark Squalus acanthias . . . . 422 2. Elasmobranchs in General ...... 428 3. The Economic Importance of Elasmobranchs . . . 431 CHAPTER XVII SUBPHYLUM VERTEBRATA: Class III. Pisces .... 432 1 . A Bony Fish The Perch 432 2. An Abridged Classification of Living Fishes . . . 443 xvi CONTENTS 3. The Anatomy and Physiology of Fishes in General 4. General Account of Some of the Principal Groups of Fishes 5. Deep Sea Fishes 6. Fossil Fishes ......... 7. The Economic Importance of Fishes . CHAPTER XVIII SUBPHYLUM VERTEBRATA: Class IV. Amphibia 1 . The Frog 2. A Brief Classification of Living Amphibia 3. Review of the Orders and Families of Living Amphibia 4. General Remarks on Amphibia .... CHAPTER XIX SUBPHYLUM VERTEBRATA: Class V. Reptilia . 1. The Turtle 2. A Brief Classification of Living Reptilia . 3. Review of the Orders and Families of Living Reptiles 4. The Poisonous Snakes of North America 5. The Economic Importance of Reptiles 6. Prehistoric Reptiles ...... CHAPTER XX SUBPHYLUM VERTEBRATA: Class VI. Aves .... 1. The Pigeon . 2. A Brief Classification of Birds . t 3. A Review of the Orders and Families of Birds 4. A General Account of the Class Aves a, Form and Function, 616 ; b. The Colors of Birds, 621 ; c, Bird Songs, 621 ; d, Bird Flight, 621 ; e. Bird Migration, 622 ; f, The Nests, Eggs, and Young of Birds, 624; g, The Economic Importance of Birds, 626 ; h, Domesticated Birds, 630. CONTENTS xvii PAGE CHAPTER XXI SUBPHYLUM VERTEBKATA: Class VII. Mammalia . . . 632 1. The Rabbit . 633 2. A Brief Classification of Living Mammals . . .641 3. A Review of the Principal Orders and Families of Living Mammals ......... 645 4. General Remarks on the Mammalia .... 676 a, Integumentary Structures, 676 ; b, The Teeth of Mam- mals, 678; c, The Development of Mammals. 680; d, Hibernation, 682 ; e, Migration, 683 ; f, Domesti- cated Mammals, 684 ; g, Fossil Mammals, 685 ; h, The Economic Importance of Mammals, 688. CHAPTER XXII THE ANCESTORS AND INTERRELATIONS OF THE VERTEBRATES 691 1. The Relations between Vertebrates and Invertebrates . 691 2. The Phylogenesis of Vertebrates 693 3. The Fossil Remains of Vertebrates 696 a, Succession of Life in General, 696; b, The Evolu- tion of the Horse, 698. SCHEME OF THE CLASSIFICATION ADOPTED IN THIS BOOK PAGE PHYLUM I. PROTOZOA 27 Class I. RHIZOPODA . . . Order i . LOBOSA . . . . " 2. HELIOZOA . . . " 3. RADIOLARIA . . " 4. FORAMINIFERA . Class II. MASTIGOPHORA . Order i . FLAGELLATA . . " 2. CHOANOFLAGEL- LATA . . . . DlNOFLAGELLATA CYSTOFLAGEL- LATA . . . . Class III. SPOROZOA . . . Subclass I . Telosporidia PAGE 27 39 40 Order i. GREGARINIDA " 2. COCCIDIIDEA . " 3. H/EMOSPORIDIA 3- 4- 40 Subclass II. Neosporidia . . 41 Order i. MYXOSPORIDIA 41 '' 2. SARCOSPORIDIA 45 Class IV. INFUSORIA . . . Subclass I. Ciliata . . . 47 Order i. HOLOTRICHA . 47 " 2. HETEROTRICHA " 3. HYPOTRICHA . " 4. PERITRICHA Subclass II. Suctoria . . . 48 48 52 52 52 52 5 2 52 53 53 62 63 63 64 65 65 PHYLUM II. PORIFERA 92 Class I. CALCAREA . . Order i. HOMOCCKLA . . 105 " 2. HETEROCCELA . 105 Class II. HEXACTINELLIDA 105 105 Class III. DEMOSPONGIJE Order i . TETRAXONIDA " 2. MONAXONIDA . >. 3. KERATOSA PHYLUM III. CCELENTERATA . Class I. HYDROZOA . . Order i. ANTHOMEDUS.E 2. LEPTOMEDUS/E 3. TRACHYMEDUS/E 4. NARCOMEUUS^E 5. HYDROCORAL- u u u u 6. SlPHONOPHORA 118 Class II. SCYPHOZOA. 128 Order i. STAUROMEDUS.-E 128 " 2. PEROMEDUS^; . 128 " 3. CUBOMEDUS.K . 128 " 4. DlSCOMEDUS.K Class III. ANTHOZOA . . 129 Subclass!. Alcyonaria . 129 Order i. STOLONIFERA xix 105 105 105 1 08 129 132 132 133 133 133 139 139 XX SCHEME OF THE CLASSIFICATION PAGE Order 2. ALCYONACEA . 139 " 3. GORGONACEA . 139 " 4. PENNATULACEA 140 Subclass II. Zoantharia . .141 Order i. EDWARDSIIDEA 141 PAGE PAGE Order 2. ACTINIARIA . .141 " 3. MADREPORARIA 141 " 4. ZOANTHIDEA . 142 " 5. ANTIPATHIDEA. 142 " 6. CERIANTHIDEA . 142 PHYLUM IV. CTENOPHORA PHYLUM V. PLATYHELMINTHES Class I. TURBELLARIA . Order i. RHABDOCCELIDA " 2. TRICLADIDA . a 3. POLYCLADIDA . 155 Class II. TREMATODA . 156 Order i. MONOGENEA 156 " 2. DIGENEA . . 157 Class III. CESTODA . PHYLUM VI. NEM ATHELMINTHES . . 145 . 150 157 . 161 . 161 . 163 . 169 GROUPS OF INVERTEBRATES OF MORE OR LESS UNCERTAIN SYSTEMATIC POSITION Group i u u MESOZOA . . . 2. NEMERTINEA 3. NEMATOMORPHA 4- ACANTHOCEPHALA 5. CH^TOGNATHA . 176 Group 6. ROTIFERA 177 " 7. BRYOZOA . . 179 " 8. PHORONIDEA 1 80 " 9. BRACHIOPODA 180 " 10. GEPHYREA 176 181 183 185 185 1 86 PHYLUM VII. ECHINODERMATA Class I. ASTEROIDEA Class II. OPHIUROIDEA Class III. ECHINOIDEA 189 198 Class IV. HOLOTHURIOIDEA 205 199 Class V. CRINOIDEA . . .208 202 PHYLUM VIII. ANNELIDA Class I. ARCHI ANNELIDA . Class II. CHJETOPODA . . Subclass I. Polychseta . . Order i. PHANEROCEPH- ALA 232 Order 2. CRYPTOCEPH- 233 ALA . . 234 Subclass II. Oligochaeta . Order i. MICRODRILI 236 " 2. MACRODRILI Class III. HIRUDINEA , 215 236 236 236 236 236 SCHEME OF THE CLASSIFICATION xxi PHYLUM IX. MOLLUSCA 243 PAGE Class I. AMPHINEURA . .251 Order i . POLYPLACO- PHORA . .251 " 2. APLACOPHORA . 252 Class II GASTROPODA . . 252 Subclass I. Streptoneura . 258 Order i. ASPIDOBRAN- CHIA . . . 258 " 2. PECTINIBRAN- CHIA . . . 258 Subclass II. Euthyneura . . 258 Order i . OPISTHOBRAN- CHIA . . . 258 Order 2. PULMONATA . 258 Class III. SCAPHOPODA . . 261 Class IV. PELECYPODA . .261 Order i. PROTOBRAX- CHIA . . . 262 " 2. FlLIBRANCHIA . 262 " 3. EULAMELLI- BRANCHIA . 262 " 4. SEPTIBRANCHIA 262 Class V. CEPHALOPODA . . 264 Order i. TETRABRAN- CHIA . . 268 " 2. DlBRANCHIA 268 PHYLUM X. ARTHROPODA Class I. CRUSTACEA . . Subclass I. Branchiopoda Order i. PHYLLOPODA " 2. CLADOCERA Subclass II. Ostracoda ; ' 3. Copepoda . " 4. Cirripedia " 5. Malacostraca Order i . NEBALIACEA " 2. ANASPIDACEA " 3. MYSIDACEA . " 4- CUMACEA . " 5. TANAIDACEA " 6. ISOPODA . . " 7. AMPHIPODA " 8. EUPHAUSIACEA 297 " 9. DECAPODA . . 297 Suborder i . Nat ant ia 297 2. Reptantia 297 " 10. STOMATOPODA . 297 Class II. ONYCHOPHORA . 305 Class III. MYRIAPODA . .308 2 7 6 292 292 294 294 294 294 294 294 294 294 294 297 297 297 Order i . PAUROPODA " 2. DIPLOPODA . . " 3. CHILOPODA . . " 4 SYMPHYLA . . Class IV. INSECTA . . . Order i. APTERA . . . " 2. EPHEMERIDA . " 3. ODONATA . . " 4. PLECOPTERA . " 5. ISOPTERA . . " 6. CORRODENTIA . " 7. MALLOPHAGA . " 8. THYSANOPTERA " 9. EUPLEXOPTERA " 10. ORTHOPTERA . " 11. HEMIPTERA " 12. NEUROPTERA . " 13. MECOPTERA " 14. TRICHOPTERA . " 15. LEPIDOPTERA . " 1 6. DlPTERA. . . " 17. SlPHONAPTERA 274 309 39 310 3H 312 337 338 339 340 340 342 342 343 345 349 349 35 35 356 359 XXII SCHEME OF THE CLASSIFICATION Order 1 8. COLKOPTERA " 19. HYMENOPTERA Class V. ARACHNIDA . Order i. ARANEIDA . " 2. SCORPIONIDEA " 3. PHALANGIDEA " 4. ACARINA PAGE 360 364 371 371 377 379 379 Orders. PEDIPALPI . u 6. PALPIGRADI " 7. SOLIFUG^E . " 8. CHERNETIDIA " 9. XlPHOSURA . PAGH 38' 382 382 382 383 10. EURYPTERIDA . 384 PHYLUM XI. CHORDATA 386 Subphylum I. ENTEROPNEUSTA 386 Order i. BALANOGLOSSIDA 386 " 2. CEPHALODISCIDA . . . 386 Subphylum II. TUNICATA 389 Order i. ASCIDIACEA 391 " 2. THALIACEA 393 " 3. LARVACEA 393 Subphylum III. CEPHALOCHORDA 393 IV. VERTEBRATA 400 Class I. CYCLOSTOMATA 414 Subclass i. Myxinoidea 420 " 2. Petromyzontia 420 Class II. ELASMOBRANCHII 422 Subclass i. Selachii 428 Order i. SQUALI 428 " 2. RAJI 429 Subclass 2. Holocephali 430 Class III. PISCES . 432 Subclass i. Teleostomi 452 Order i. CROSSOPTERYGII 452 " 2. CHONDROSTEI 452 " 3. HOLOSTEI 454 " 4. TELEOSTEI 455 Subclass 2. Dipnoi 471 Class IV. AMPHIBIA 477 Order i. APODA 512 " 2. CAUDATA 513 " 3. SALIENTIA 517 SCHEME OF THE CLASSIFICATION xxiii PAGE Class V. REPTILIA 527 Order i. TESTUDINATA 540 " 2. RHYNCHOCEPHALIA 546 " 3. CROCODILINI 547 " 4. SQUAMATA 550 Class VI. AVES 575 Subclass i. Archaeornithes 593 '' 2. Neornithes 594 Order i. HESPERORNITHIFORMES 594 " 2. ICHTHYORNITHIFORMES 594 " 3. STRUTHIONIFORMES 595 " 4. RHEIFORMES 596 " 5. CASUARIIFORMES 596 " 6. CRYPTURIFORMES - . 596 " 7. DlNORNITHIFORMES 597 " 8. ^PYORNITHIFORMES 598 " 9. APTERYGIFORMES 598 ' 10. SPHENISCIFORMES 598 " II. COLYMBIFORMES 599 " 12. PROCELLARIIFORMES 600 " 13. ClCONIIFORMES 6oi " 14. ANSERIFORMES 602 " 15. FALCONIFORMES 603 u 16. GALLIFORMES 606 " 17. GRUIFORMES 606 " 18. CHARADRIIFORMES 607 " 19. CUCULIFORMES 6lO " 2O. CORACIIFORMES 6lO " 21. PASSERIFORMES 614 Class VII. MAMMALIA 632 Subclass I. Prototheria 642 Order i. MONOTREMATA 645 Subclass II. Eutheria 642 Division I. DIDELPHIA 642 Order i . MARSUPIALIA 647 Division II. MONODELPHIA 642 Section A. Unguiculata 642 Order i. INSECTIVORA 649 " 2. DERMOPTERA 642 xxiv SCHEME OF THE CLASSIFICATION PAGE Order 3. CHIROPTERA 650 " 4. CARNIVORA 652 " 5. RODENTIA 658 " 6. EDENTATA 660 " 7. PHOLIDOTA 661 " 8. TUBULIDENTATA . . . . . , . . 644 Section B. Primates 644 Order 9. PRIMATES 662 Section C. Ungnlata 644 Order 10. ARTIODACTYLA 667 " ii. PERISSODACTYLA 671 " 12. PROBOSCIDEA 672 " 13. SlRENIA 673 " 14. HYRACOIDEA 645 Section D. Cetacea 645 Order 15. ODONTOCETI 674 " 1 6. MYSTACOCETI 675 COLLEGE ZOOLOGY COLLEGE ZOOLOGY CHAPTER I INTRODUCTION i. GENERAL SURVEY OF THE ANIMAL KINGDOM ONE who is not a naturalist or who does not have access to the apparatus necessary for the examination of minute objects usually becomes acquainted with only a few of the many kinds of animals that inhabit the earth. The most familiar of these are the comparatively large four-footed beasts, the fish, the frogs, the snakes, the birds, and the insects. The majority of animals are never seen by most people, and perhaps never even heard of. This is true of the microscopic parasite which is pres- ent in the blood of malaria patients, of the coral polyp (Fig. 87) which builds up entire islands in the sea, of the Trichindla (Fig. 113), a parasitic worm which sometimes causes a human disease called trichinosis, and of a host of others. Scientists have found it convenient to separate all animals into two groups, the vertebrates and the invertebrates. The ver- tebrates possess a backbone or vertebral column consisting of a linear series of bones called vertebrae (Fig. 418); the inverte- brates have no vertebral column. The vertebrates are better known than the invertebrates, since they are usually large and include most of the domesticated animals. The invertebrates, however, are much more numerous both in regard to the number of kinds and the number of individuals. Thus of the eleven main groups (phyla) of animals recognized in the classification adopted in this book only part of one group, the CHORDATA (Chap. XIV), deals with the vertebrates, whereas the rest of this group and B i 2 COLLEGE ZOOLOGY the other ten chief divisions are composed entirely of inverte- brates. It is therefore of considerable importance at the very beginning to learn something of the characteristics and habitats of the thousands of living creatures that form the basis for the study of zoology. In the following paragraphs a few facts about each main group are presented in such a way as to give a bird's-eye view of the entire animal kingdom. (i) The Vertebrates. - -The members of this group possess a bony axis of vertebrae called the vertebral column or backbone (Fig. 418). They are the most highly developed of all animals, and include man. The vertebrates may be subdivided into seven assemblages, each containing numbers of more or less familiar forms. At the top of the series are placed the MAMMALIA (Chap. XXI), usually known as animals or beasts. Among the repre- sentative mammals are man, the apes, monkeys, bats, moles, rats, mice, rabbits, dogs, cats, cows, sheep, horses, whales, sloths, opossums, and the peculiar duckbill (Fig. 513) and spiny ant- eater of Australia. They are vertebrates which possess hair, and, with a few exceptions, nourish their young with milk se- creted by mammary glands. They breathe air by means of lungs, and are said to be warm-blooded, since their body tem- perature is nearly 100 F., regardless of the temperature of the surrounding medium. The members of the group AVES or BIRDS (Chap. XX) are characterized by the presence of feathers; no other animals possess these structures. Birds are air-breathers and warm- blooded, having a higher body temperature than any other or- ganisms. They are all terrestrial, though many of them are adapted to life on or near the water. The majority of the birds are able to fly long distances, but some of them, like the ostrich and the auk, are flightless. REPTILES (Chap. XIX) are remarkably diversified in form, and occupy many kinds of habitats. Most of them live on land, INTRODUCTION 3 but the turtles and alligators spend much of their existence in the water; the lizards are in many cases arboreal; and the snakes live in almost every conceivable environment. They are all called cold-blooded vertebrates because their body temperature varies with that of the surrounding medium and may drop to the freezing point. They possess lungs, and in most cases are covered with an armor of scales or bony plates. The most familiar AMPHIBIA (Chap. XVIII) are the frogs, toads, and salamanders. They pass the first part of their lives in the water, at which time they breathe by means of gills; but later they become air-breathers, and many of them leave the water and live on land. In form certain AMPHIBIA resemble reptiles, but they usually do not possess scales and are anatomically quite different. They are cold-blooded. The common fishes are members of the group PISCES (Chap. XVII). They are cold-blooded animals, usually covered with scales, and spend their entire existence in the water. They pos- sess gills for breathing, and swim about by means of fins. Some of them, like the sea-horse (Fig. 398), are so modified as to be hardly recognizable as fish; others, called lung- fishes, are able to breathe out of water. Belonging to the vertebrate series, but lower in the scale of life than the common fishes, are two groups of fishlike animals that are comparatively little known. These are the ELASMO- BRANCHII, or sharks and rays (Chap. XVI), and the CYCLOSTO- MATA, or lamprey-eels and hagfishes (Chap. XV; Fig. 352). (2) The Arthropoda. - - The crayfishes, centipedes, insects, and spiders are among the commonest ARTHROPODA (Chap. XIII). All of these animals have jointed appendages, and their bodies are divided into a number of segments which are arranged in a single row and are modified for various purposes. An outer covering of a yellowish substance called chit in gives firmness to the body and also serves as a protection from mechanical injury. The ARACHNIDA are the spiders, scorpions, mites, ticks, etc. They may usually be distinguished from other ARTHROPODA by 4 COLLEGE ZOOLOGY the presence of eight legs. Many of them, like the scorpion, are capable of inflicting severe wounds with their stings. The curious king-crab is now placed by zoologists in the group ARACH- NIDA. The INSECTA are the butterflies, bees, beetles, bugs, etc. They have six legs, and usually possess wings. The MYRIAPODA are long, slender, terrestrial animals with one or two pairs of legs on each body segment; they are known as centipedes (Fig. 233) and millipedes (Fig. 232). The CRUSTACEA are mainly aquatic ARTHROPODA, and breathe with gills; they include the lobsters, crayfishes, crabs, barnacles, sow bugs, and many others. (3) The Mollusca. - - The MOLLUSCA (Chap. XII) most often seen are the snails and clams; the slug, oyster, squid (Fig. 191). nautilus (Fig. 194), cuttlefish, and octopus, are also well known. They are of various shapes and sizes, but most of them possess a ventral muscular structure called the foot, which usually serves as an organ of locomotion. Often a heavy shell of calcium car- bonate covers the body. (4) The Annelida. The ANNELIDA (Chap. XI) are known as segmented worms, since their bodies consist of sometimes over one hundred rings or segments and their shape is wormlike. The earthworm is the commonest representative of the group. There are many marine annelids, and also a number of fresh- water members, like the leech. The medicinal leech (Fig. 169) is famous for its use in sucking blood. (5) The Echinodermata. - - The starfish (Fig. 131) is a well- known echinoderm, and usually serves as a type of the group. Like all echinoderms, it is radially symmetrical, and has five arms extending out from a central disc. The other echinoderms are called brittle stars, sea urchins, sea cucumbers, and sea lilies. Most of these animals have a body-wall supplied with spicules of calcium carbonate; hence their name, which means spiny- skinned. They all live in salt water, and are therefore seldom seen by people who do not visit the sea coast. INTRODUCTION 5 (6) The Nemathelminthes. - - The NEMATHELMINTHES are unsegmented round or thread worms. Most of them are parasitic like the roundworm, Ascaris (Fig. in), which inhabits the alimentary canal of man, the horse, and many other animals. One dangerous parasite is Trichinella (Fig. 113), which spends part of its life in the muscle of the hog, and may attack human beings if infected pork is eaten without being sufficiently cooked. Vinegar usually contains a number of roundworms called -vinegar eels; they can be seen only with the aid of a microscope. (7) The Platyhelminthes. - - The PLATYHELMINTHES or flat- worms are also worm-like and unsegmented. The best known members are the tapeworms, which are parasitic in man and other animals. The liner fluke is a serious pest; it inhabits the bile ducts of sheep and causes the death of large numbers of infected individuals in certain localities. Less widely known are the fresh- water flatworms, like Planaria (Fig. 97), and the terrestrial and marine forms. (8) The Coelenterata. - - The CCELENTERATA are mostly marine animals, and are known as hydroids (Fig. 73) and jelly- fishes (Fig. 82). Their bodies are fundamentally simple sacs, although many modifications give the impression of great com- plexity. Some ccelenterates are famous for the rigid skeletal structures they produce; this is true of the coral polyps (Fig. 86), which have even built up entire islands. There are only a few fresh- water ccelenterates; one of these, Hydra (Fig. 65), is com- paratively common, and is studied as a type of this group by most students of biology. (9) The Porifera. The PORIFERA are sponges. The ordinary bath sponge is the horny skeleton of an animal that lives in the sea (Fig. 63). Venus' s flower basket (Fig. 62) is a sponge skele- ton that is often seen in museums. Most of the sponges secrete a supporting framework of calcium carbonate or silica. Only a few of the sponges live in fresh water, and none lives on land. (10) The Protozoa. - - The PROTOZOA (Chap. II) are in most cases so small as to be visible only with the microscope. They 6 COLLEGE ZOOLOGY are, however, of great importance, especially those which cause diseases such as malaria. PROTOZOA are to be found almost everywhere. If a few dead leaves are placed in a dish of water and left to decay, the scum which forms on the surface will be found to contain thousands of these minute organisms. The simplest animals belong to the PROTOZOA; among these are Ameba (Fig. 9), Paramecium (Fig. 33), and Euglena (Fig. 22), which will be studied in some detail in Chapter II. Few people realize the abundance and variety of animal life. Almost every part of the earth is inhabited by animals of some kind, and these animals 'are more or less restricted to certain kinds of habitats. For example, fishes live in the water, earth- worms in the ground, the polar bear in Arctic regions, the ele- phant in the Tropics, the prairie dog on the prairies, the moun- tain goat on the mountains, and parasites upon or within the bodies of other organisms. Four principal kinds of animals may be recognized according to their mode of existence: (i) ma- rine animals living in the salt waters of the sea, (2) fresh- water animals living in fresh-water streams, ponds, and lakes, (3) ter- restrial animals living on land, and (4) parasites which live on or within the bodies of other animals. The oceans are inhabited by millions of animals of all sizes, ranging from the whale to the microscopic floating organisms known as plankton. Salt-water animals are restricted to certain definite regions; some float on or near the surface, and others live at various distances from the surface, until a depth is reached where the light never penetrates. As a rule, animals living in salt water die almost at once if transferred to fresh water; like- wise salt water is fatal to fresh-water animals. Every pond, lake, brook, creek, and river is inhabited by a host of living animals. A pond, for example, furnishes a home for the early stages in the life history of the mosquito, whose eggs are laid in a raft-like mass on top of the water, and whose young swim about at or near the surface. Frogs and salamanders find a home amid the vegetation common to ponds. Crayfishes INTRODUCTION 7 crawl about on the bottom; wheel animalcules (Fig. 122) and many other extremely small animals swim about in search of food ; and almost every drop of pond water contains a number of microscopic forms. The terrestrial animals are the ones best known to the average person, and every one is aware of the vast numbers of deer, wolves, field-mice, snakes, insects, and other forms that move about on the surface of the earth. Animals like the mole and the earthworm which live underground are said to be subterrestrial, and those like the birds and butterflies that frequent the air are called aerial. Parasites are more widely spread than is generally known. Almost every animal is infested with others which prey upon it. The malarial fever germ is one of the most important, although one of the smallest, parasites. The fleas and lice are called external parasites. The internal parasites of man include the roundworm Ascaris (Fig. in), the tapeworm (Fig. 107), and the Trichinella (Fig. 113). Frequently parasites are preyed upon by other parasites, a condition known as hyperparasitism - and even the hyperparasites may be parasitized. Thus the fol- lowing humorous lines contain a grain of truth: - "Great fleas have little fleas Upon their backs to bite 'em, And little fleas have lesser fleas, And so ad infinititm." The survey of the animal kingdom just concluded attempts to present a few facts about the groups of animals to be studied in the succeeding chapters. The most highly organized and most familiar animals, the mammals, were considered first, and the less complex were successively discussed in a descending series, until the last and simplest organisms were reached. A glance at the table of contents of this book will show that the extended studies of these groups have been arranged in a reversed order, beginning with the simplest animals, the PROTOZOA, and ending with the highest type, the Mammal. This method of presenting 8 COLLEGE ZOOLOGY the facts of zoology has been employed with the idea of organic evolution in mind. Practically every zoologist at the present time believes that the complex animals have evolved from simpler forms at some period in the world's history. How this evolution has taken place is still a moot question. According to the evolution theory the first animals that existed on the earth consisted of a single cell, and all the animals that lived at that time would now be called PROTOZOA (Chap. II). These animals gave rise in some way still unknown to organisms consisting of many cells (Chap. III). In the course of millions of years new and more complex forms were continually being evolved from older and simpler animals, so that all those now existing may be arranged in an ascending series constituting a sort of genealogical tree. Many of the connecting links between the various groups have disap- peared, but in a few cases the remains preserved in the rocks as fossils give us very definite ideas of the order of evolution. Man is no exception in the evolutionary process, but is closely allied to the anthropoid apes, and doubtless arose from an ape- like ancestor. The simpler animals living to-day probably do not represent ancestral forms, since they have become modified in many ways. It is only safe to make general statements, such as, that man has evolved from ape-like ancestors, that the birds have arisen from reptile-like ancestors, and that the insects have descended from worm-like ancestors. 2. LIVING MATTER CONTRASTED WITH NON-LIVING MATTER All living things are either plants or animals, and have certain peculiarities which separate them from non-living things. These peculiarities do not all pertain exclusively to living organisms, but may, to a certain extent, be attributes of non-living bodies; nevertheless, when taken together, they are sufficient to deter- mine whether an object is living or lifeless. The most important peculiarities are as follows: - INTRODUCTION 9 (1) Definite Size. - - The size of living organisms varies within definite limits. The smallest animals known are microscopic blood parasites; the largest living animals are the whales. The difference is great but definite, and each kind of animal has a characteristic size. Non-living bodies, on the other hand, may be of any size; for example, water may exist as a particle of vapor or as an ocean. (2) Definite Form. If animals were not constant in form, we would be unable to distinguish one from another. Non-living bodies usually have no definite form, but may, like water in a lake-bed, assume the shape temporarily forced upon them. (3) Definite Chemical Composition. - - The elements found in living matter are all found in non-living bodies, but in living matter certain elements are combined so as to produce a sub- stance known as protoplasm. These elements are present in a typical animal in the following proportions: - Carbon Oxygen Nitrogen Hydrogen Sulphur Phosphorus Chlorine Potassium Sodium Magnesium Calcium Iron 99 per cent of weight; i per cent of weight. (4) Definite Organization. - - The protoplasm contained in the bodies of animals is not continuous in most cases but is divided up into small units called cells (p. 13, Fig. 2). A cell is a small mass of protoplasm containing a nucleus. The bodies of some animals are composed of only a single cell (PROTOZOA, Chap. II), but all of the more highly organized animals are made 10 COLLEGE ZOOLOGY up of almost countless numbers. Non-living bodies possess no unit of structure comparable to the cell. (5) Metabolism. Animals are able to change food into protoplasm; this process is termed metabolism (p. 19); growth takes place by the addition of these particles of protoplasm among the preexisting particles. This is growth by intussuscep- tion. Non-living bodies are not metabolic, and, if they can be said to grow at all, increase in size by the addition of particles on the outside, that is, growth is by accretion. (6) Reproduction. --Animals are able to produce other ani- mals like themselves. Non-living bodies cannot reproduce their kind. (7) Irritability or Reactiveness. - - Animals have the ability of responding to changes in their environment. The change is termed a stimulus, and the sum total of the animal's movements is known as its behavior. Non-living Directs are not irritable. 3. THE PHYSICAL BASIS OF LIFE - - PROTOPLASM Protoplasm is a term used by both zoologists and botanists to designate the essential substance of which plants and animals are composed. All living organisms are built up of protoplasm, but no non-living object possesses any of this compound. Pro- toplasm has been called by Huxley " the physical basis of life," since all vital phenomena are due to its presence. There are several theories regarding its structure: A, the alveolar theory, B, the reticular theory, and C, the granular theory. According to the alveolar theory (Fig. i), protoplasm consists of two substances, one of which is in the shape of spheres embedded in the other. The reticular theory (B) con- siders protoplasm a network of living anastomosing fibers among which are non-living substances such as water and fat. The third theory (C) maintains that protoplasm is composed of innumerable living granules variously arranged. It is still uncertain which of these theories, if any, is correct. INTRODUCTION II Ninety-seven per cent of protoplasm consists of the following four elements: - Oxygen 65.0 per cent Carbon 18.5 per cent Hydrogen n.o per cent Nitrogen 2.5 per cent These and other elements form rather definite compounds. The principal inorganic constituents of protoplasm are (i) water, which comprises more than 50 per .^____ cent of the weight of most animals, (2) salts, such as the chlorides, car- bonates, and phosphates, and (3) gases, such as oxygen and carbon dioxide. The organic compounds found in pro- toplasm comprise the proteids, carbo- hydrates, and fats. Proteids consist of large molecules which always contain carbon, oxygen, hydrogen, and nitro- gen. They do not dissolve in water, but absorb quantities of this fluid, swelling up like a sponge. Other peculiarities are their inability to pass through animal membranes and their property of coagulation or clotting. Carbohydrates are compounds of car- bon, hydrogen, and oxygen, the last two nearly always occurring in the same ..... . . FIG. i. Alveolar struc- proportion in which they are found in t ure of the protoplasm of an water (H 2 0). Starches and sugars are epidermis cell of an earth- . worm. (From Verworn, after common carbohydrates. Some living Butschli.) substances apparently do not contain this compound. Fats are likewise not invariable constituents of protoplasm. The protoplasm of each species of animal differs from that of every other species, but in all it has similar characteristics. 12 COLLEGE ZOOLOGY 4. THE ORIGIN OF LIFE No one knows when and where life originated on the earth. Many of the ancients believed that animals were created by divine providence, but this theory of special creation is not accepted by present-day zoologists. Historically the special cre- ation theory was followed by that of spontaneous generation. Ac- cording to this theory animals were supposed to originate directly from inorganic substances; for example, frogs and toads from the muddy bottom of ponds under the influence of the sun, and insects from dew. The brilliant experiments of Redi (1668), Pasteur (1864), and Tyndall (1876) overthrew this theory com- pletely, and scientists now believe that living organisms originate only from preexisting organisms. Where life first began is still unknown, but the meeting point of sea and land is the most probable place of origin. From here the fresh water, deep sea, and land were gradually peopled. 5. THE CELL AND THE CELL THEORY (i) Structure. - - It has already been noted that the body of an animal is divided up into microscopic units called cells, and that each cell is a small mass of protoplasm containing a nucleus. Cells vary in size and form; some are extremely small, e.g. blood parasites, whereas others, like the egg of a bird, are very large. They have no definite shape, but may be columnar, flat, spher- ical, or long and thin (Fig. 46). The number of cells in a com- plex animal is enormous; there are about 9,200,000,000 in the gray matter of the human brain. On the other hand, certain animals (PROTOZOA) consist of but a single cell. The size of the animal does not depend upon the size of its cells, but upon their number. Figure 2 shows the essential structure of a cell. The largest part of the contents is the cytoplasm. Within this substance is embedded a nucleus. At certain stages in the life activities of the cell an attraction-sphere enclosing one or two centrosomes is INTRODUCTION visible. Vacuoles, plastids, and non-living bodies (metaplasm) may also be present. The entire cell may or may not be sur- rounded by a membrane. The cell nucleus contains a fluid through which runs a network of thin linin fibers. Scattered about on these fibers are granules Attraction-sphere enclosing two centrosomes 3 X Plasmosome or true nucleolus Chromatin- network Linin-net- work Karyosome, net-knot, or chromatin- nucleolus Plastids lying in the cyto- plasm Vacuole Passive bodies (metaplasm or para plasm) suspended in the cyto- plasmic mesh- work FIG. 2. Diagram of a cell. (From Wilson.) of chromatin, a substance that has a strong affinity for certain dyes. Frequently several granules of chromatin unite to form a net-knot or karyosome. In addition to these regular constit- uents of the nucleus, one or more bodies, known as nucleoli, may be present. In certain cases a cell may possess more than one nucleus, and a few cells have no definite nucleus, but contain chromatin granules which are scattered about in the cytoplasm. (2) Physiology. - -There is a definite division of labor among the parts of a cell. The particular function of the nucleus, aside COLLEGE ZOOLOGY from its important relation to cell division, to be described later, seems to be the control of the activities by which the protoplasm is elaborated. The cytoplasm, from its direct relation to the outside world, is the seat of such functions as irritability, absorption, digestion, excretion, and respiration. The centrosome is of importance during cell division. The cell covering may serve for pro- tection or support, or may be extremely delicate and have sig- nificance only as it helps to control the absorption of certain fluids. Plastids may represent stored food or waste products: some of them, however, have other functions, e.g. the chloro- plasts, which carry on photosynthesis in many plants and a few animal cells. (3) Cell Division. - - Cells multiply either by direct division (amitosis) or indirect division (mitosis). In amitosis (Fig. n) ..TP'^i'fF^^j* FIG. 3. Amitosis. Amitotic nuclear division in the follicle cells of a cricket's egg. (From Dahlgren and Kepner.) the nucleus is either pinched in two in the middle, or a plate is formed in the plane of division, which later be- comes double, and then the two plates separate, or two nuclear membranes are built up inside of the old membrane. The cell body then divides, though in many cases this process does not occur (Fig. 3). Amitosis is characteristic of senescent cells. Mitosis is the usual method of nuclear division. It consists of a series of complex processes that may be arranged into four phases. Constant reference to Figure 4 will make clear the following brief account. (a) During the prophase the chromatin granules that are scat- tered through the nucleus in the resting cell (A) become ar- INTRODUCTION 15 ranged in the form of a long thread or spireme (B). At the same time the centrosomes move apart (A, c ; B, a). The radiating lines that appear about them (B) later give rise to a spindle (C). A B FIG. 4. Mitosis. Diagrams illustrating mitotic cell division. (From Wilson.) A, resting cell; B, prophase showing spireme and nucleolus within the nucleus and the formation of spindle and asters (a); C, la<:er prophase show- ing disintegration of nuclear membrane, and breaking up of spireme into chromosomes; D, end of prophases, showing complete spindle and asters with chromosomes in equatorial plate (ep); E, metaphase each chromosome splits in two; F, anaphase the chromosomes are drawn toward the asters, if = interzonal fibers; G, telophase, showing reconstruction of nuclei; H, later tclophase, showing division of the cell into two While this is going on the nuclear membrane generally disin- tegrates and the spireme segments into a number of bodies called chromosomes (C); these take a position at the equator of the spindle, halfway between the centrosomes (D, ep). The stage shown in Figure 4, D, is known as the am pinaster; at this time I 6 COLLEGE ZOOLOGY all of the machinery concerned in mitosis is present. There are two asters, each consisting of a centrosome surrounded by a num- ber of radiating astral rays, and a spindle which lies between them. The chromosomes lie in the equatorial plate (ep). (b) During the second stage, the metaphase, the chromosomes split in such a way that each of their parts contains an equal amount of chromatin (E, ep). As we shall see later, this is one of the most significant events that takes place during mitosis. (c) During the ana phase (F) the chromosomes formed by split- ting move along the spindle fibers to the centrosomes. As a result every chromosome present at the end of the prophase (D) sends half of its chromatin to either end of the spindle. The mechanism that brings about this migration is as yet somewhat in question. Fibers are usually left between the separating chromosomes; these are known as interzonal fibers (F, if). (d) The telophase (G, H) is a stage of reconstruction from which the nuclei emerge in a resting condition ; the chromatin becomes scattered throughout the nucleus, which is again enveloped by a definite membrane (H) ; the centrosome divides and, with the centrosphere, takes a position near the nucleus. Finally the cycle is completed by the constriction of the cell into two daugh- ter cells. CHROMOSOMES. - - Every species of animal has a definite number of chromosomes that appear when the cells of its body undergo mitosis. Thus sixteen are characteristic of the cells of oxen, guinea pigs, and man; the grasshopper has twelve; and the brine shrimp (Artemia) one hundred and sixty- eight. An even number of chromosomes is characteristic of most animals, but recent researches have demonstrated that some forms, particularly the males of insects, have an odd number. The chromosomes are considered by most zoologists to be the bearers of hereditary qualities from parent to offspring. In concluding this account of cell division two points are worthy of special emphasis. First, with regard to the continuity INTRODUCTION 17 of the chromatin, it may be said that the chromatin is continuous from one cell generation to another. The cells resulting from mitosis may differ greatly in size, but the chromatin seems to be divided equally between them with great exactness. Second, cells are never known to arise except from preexisting cells. These two facts are perhaps the most important for us to keep in mind as we go on to study the more complex problems of fertilization and cell division in the many-celled animals. (4) The Cell Theory. --Cells were first described by Hooke, an Englishman, in 1665. The regular arrangement of the com- FIG. 5. Cells of cork. Facsimile of a figure by Hooke. (From Farmer in Lankester's Zoology.) partments in cork (Fig. 5) reminded him of the cells of the monks in a monastery and suggested the term. In 1833 Brown de- scribed the nucleus as a constant cell element, and a few years later Schleiden (1838) and Schwann (1839) advanced the idea that all plants and animals are composed of cells. For many years the cell-wall was considered the important part of the structure, but later the protoplasm within it was recognized as the principal constituent, and the cell was then defined as a mass of protoplasm containing a nucleus (Max Schultze, 1861). The importance attached to the cell theory may be judged I 8 COLLEGE ZOOLOGY from the following quotation from E. B. Wilson, the foremost investigator of cellular phenomena in this country. ' During the half-century that has elapsed since the enuncia- tion of the cell-theory by Schleiden and Schwann, in 1838-1839, it has become ever more clearly apparent that the key to all ultimate biological problems must, in the last analysis, be sought in the cell. It was the cell-theory that first brought the struc- ture of plants and animals under one point of view, by revealing their common plan of organization. It was through the cell- theory that Kolliker, Remak, Nageli, and Hofmeister opened the way to an understanding of the nature of embryological de- velopment, and the law of genetic continuity lying at the basis of inheritance. It was the cell-theory again which, in the hands of Goodsir, Virchow, and Max Schultze, inaugurated a new era in the history of physiology and pathology, by showing that all the various functions of the body in health and in disease are but the outward expressions of cell activities. And at a still later day it was through the cell-theory that Hertwig, Fol, Van Beneden, and Strasburger solved the long-standing riddle of the fertilization of the egg and the mechanism of hereditary transmission. No other biological generalization, save only the theory of organic evolution, has brought so many apparently diverse phenomena under a common point of view, or has accom- plished more for the unification of knowledge. The cell-theory must therefore be placed beside the evolution-theory as one of the foundation stones of modern biology." 6. PLANTS CONTRASTED WITH ANIMALS It is easy to choose characteristics that will serve to distinguish a tree from a man, but the separation of the simplest animals from the simplest plants is a more difficult problem. In fact, there are at the present time a number of organisms that are claimed by both botanists and zoologists. There is no single peculiarity which can be used in all cases to discriminate between INTRODUCTION 19 these groups of organisms. The view now generally accepted is that plants and animals originated together but have devel- oped along divergent lines. However, certain general features can be indicated in which the two kingdoms differ. These are given in Table I ; but the reader should bear in mind that there are exceptions to every one of these criteria. TABLE I THE CHARACTERISTICS OF PLANTS CONTRASTED WITH THOSE OF ANIMALS 1. Structure 2. Locomotion 3. Irritability 4. Metabolism PLANTS Form of body rather variable ; new organs added externally. Usually none in adult condition. Respond to stimuli slowly ; no nervous system. Possess chlorophyll ; manufacture organic food from CO 2 and H 2 O in the presence of light. 5. Waste products Oxygen, carbon dioxide, water. ANIMALS Form of body usually invariable ; organs compact and mostly internal. Usually well developed. Respond to stimuli quickly ; nervous system present in higher forms. No chlorophyll ; re- quire organic food. Carbon dioxide, water, urea, faeces. One of the principal differences between plants and animals is in their method of obtaining food and changing it into proto- plasm. The processes involved are included under the term metaoolism. Those processes which use energy to build up com- pounds are said to be anabolic, those which destroy substances to produce energy are katabolic. Animals, as shown in Figure 6, 20 COLLEGE ZOOLOGY take in food "which is digested and assimilated, that is, dissolved, absorbed, and changed into protoplasm. Oxygen is also taken in during respiration; this unites with protoplasm (oxidation), OXYGEN _ > *'**^ ^^s^ EXCRETIONS FOOD ^*^\ S**^ FAECES FIG. 6. Metabolism. Diagram showing the various metabolic activities of animals. furnishing energy and producing waste products or excretions. Animals are primarily katabolic organisms, being unable to manufacture organic compounds from simple inorganic substances. CARBON DIOXIDE S^ ^**. OXYGEN WATER S \. / >V STARCH FIG. 7. Metabolism. Diagram showing the manufacture of food by plants (photosynthesis). Plants or other animals are therefore absolutely necessary for their existence. Plants, on the other hand, are able to manufacture food from inorganic matter by a process known as photosynthesis (Fig. 7). INTRODUCTION 21 Carbon dioxide and water are taken into the plant and are changed into starch by means of a green substance known as chlorophyll. Light is necessary for this process. A by-product of photosynthesis is oxygen. The qualities that are usually cited as being peculiarly char- acteristic of animals are locomotion and nervous activity. With the exception of a few extremely sensitive species of which the common sensitive plant, Mimosa pudica, is the most familiar example, plants respond very slowly to external stimuli, and their power of transmitting impulses is poorly developed. Locomo- tion is impossible except in a few simple forms and free swimming reproductive cells. 7. CLASSIFICATION It is natural when a large number of dissimilar objects are collected to attempt to place them in groups according to the presence or absence of certain characteristics. This is known as classification. Animals are not infinitely variable, since only about five hundred thousand species have been described, and they may be classified in several ways. By artificial classification we mean the grouping of animals according to some resemblance in structure, color, habitat, etc. For example, certain animals may be said to be aquatic because they live in the water; others terrestrial, because they live on land. Or certain animals are said to be carnivorous because they eat flesh, others herbivorous because they live on vegetable food, and still others omnivorous because they devour both animal and vegetable matter. It is often convenient to use an artificial classification, but for all scientific work the natural classification is employed. This is an attempt to seek out the relationships of animals and to group them, not because of superficial resemblances, but on a basis of their similarity in structure and probable kinship. A number of large divisions, known as PHYLA, are recognized by zoologists. Each phylum is again divided into CLASSES, each 22 COLLEGE ZOOLOGY class into ORDERS, each order into FAMILIES, each family into GENERA, and each genus into SPECIES. The gray wolf, for example, belongs to the species occidentalis of the genus Canis. This genus, along with others, such as the genus Vulpes, which contains the red fox, constitute the family CANID.E. The CANID.E are included with the bears (family URSHXE), the seals (family PHOCID^E), and a number of other groups of flesh-eating animals in the order CARNIVORA. Fifteen related orders, of which the CARNIVORA forms one, are placed in the class MAMMALIA. Mammals possess hair and mammary giands; these characteristics distinguish them from the five other classes that make up the SUBPHYLUM VERTEBRATA, or ani- mals possessing vertebral columns. The SUBPHYLUM VERTE- BRATA, together with three other SUBPHYLA, usually called primitive vertebrates, are grouped under the PHYLUM CHORDATA, which contains animals possessing at some time in their existence an internal rod-like support known as the notochord. The scientific name of any animal consists of the terms used to designate the genus and species; this is commonly followed by the name of the zoologist who wrote the first authori- tative description of that particular species. The scientific name of the gray wolf is therefore written Canis occidentalis Richardson. The complete classification of the gray wolf may be shown in outline in the following manner: Phylum CHORDATA Subphylum VERTEBRATA Class MAMMALIA Order CARNIVORA Family CANID^E Genus CANIS Species OCCIDENTALIS Richardson. Zoologists do not agree as to the exact meaning of the term species. One authority gives the following definition: "A INTRODUCTION 23 species may be defined as a group of interbreeding individuals which, while they may differ markedly among themselves, yet resemble each other more closely than they do those of any other group; the characters that distinguish the group being consid- erable, not obliterated by intermediate forms, and inherited from generation to generation." 8. THE PRINCIPAL PHYLA OF THE ANIMAL KINGDOM The principal phyla of the animal kingdom as outlined in the following paragraphs are presented in this place since they will be of value for reference purposes during the perusal of the more detailed accounts in the succeeding chapters. The numbers after each phylum indicate approximately the number of living species known at the present time. 1 The groups of animals of more or less uncertain systematic position have been omitted from this outline (see Chap. IX). (1) Protozoa. Single-celled animals; often colonial; sperm and egg cells usually wanting. 8500. (2) Porifera. -- Sponges. Diploblastic (?) ; radially symmet- rical, number of antimeres variable ; body- wall permeated by many pores and usually supported by a skeleton of spicules or spongin. 2500. (3) Coelenterata. - - Jellyfishes, Polyps, and Corals. Diplo- blastic; radially symmetrical, with usually four or six anti- meres; single gastro-vascular cavity; no anus; body-wall con- tains peculiar structures known as nematocysts or stinging cells. 4200. (4) Ctenophora. Sea Walnuts or Comb Jellies. Triplo- blastic; radial combined with bilateral symmetry; eight radially arranged rows of paddle plates. 100. (5) Platyhelminthes. - - Flatworms. Triploblastic ; bilaterally symmetrical; single gastro-vascular cavity; no anus; presence of ccelom doubtful. 4600. *I am indebted to Professor Henry S. Pratt for the numbers given. 24 COLLEGE ZOOLOGY (6) Nemathelminthes. -- Thread Worms. Triploblastic ; bi- laterally symmetrical; possess a tubular digestive system with an anus; ccelom present. 1500. (7) Echinodermata. -- Starfishes, Sea Cucumbers, Sea Ur- chins, Sea Lilies. Triploblastic; radially symmetrical; usually five antimeres; ccelom well developed; anus usually present; locomotion in many species accomplished by characteristic organs known as tube feet; a spiny skeleton of calcareous plates gen- erally covers the body. 3000. (8) Annelida. Jointed Worms. Triploblastic; bilaterally symmetrical; ccelom well developed; anus present; segmented, somites similar. 4000. (9) Mollusca. Clams, Snails, Devilfishes. Triploblastic; bilaterally symmetrical; anus and ccelom present; no segmenta- tion; shell usually present; the characteristic organ is a ventral muscular foot. 60,000. (10) Arthropoda. -- Crabs, Insects, Spiders, Centipedes, Scorpions, Ticks. Triploblastic ; bilaterally symmetrical ; anus present; ccelom poorly developed; segmented, somites usually more or less dissimilar ; paired, jointed appendages present on all or a part of the somites; chitinous exoskeleton. 400,000. (n) Chordata. - - Amphioxus, Sea Squirts, Vertebrates. Triploblastic; bilaterally symmetrical; anus and ccelom present; segmented; gill slits and a rod called the notochord present in some stage of life history; central nervous system on dorsal side of alimentary canal. 30,000. Zoologists do not agree as to the number of phyla into which the animal kingdom should be divided. Some authorities recog- nize only eight, while others maintain that there should be as many as twenty, or even more. Two sub-kingdoms are generally recognized, PROTOZOA (Phylum i) and METAZOA (Phyla 2-11). Recently many zoologists have come to believe that the sponges (Phylum 2) should be separated from other METAZOA and called the PARAZOA. Figure 8 shows by this is modified from II, p. 2. Phylum Ctenophora Phylum Coelenterata INTRODUCTION 25 a diagram one method of classification; Lankester's " Treatise on Zoology," Part ii. Phylum Chordata 10. Phylum Mollusca 9. Phylum Arthropoda 8. Phylum Annelida 7. Phylum Echinodermata 6. Phylum Nemathelminthes 5. Phylum Platyhelminthes I ENTEROOELA ^ (Animals with single body cavity, the enteron) 2. Phylum Porifera I PARAZOA (Sponges) t CCELOMOCCELA (Animals with two body cavities, en- teron and coelom) ENTEROZOA (Primitively a dou- ble-walled sac with a single external opening) Metazoa (Many-celled animals) I i. Phylum Protozoa (One-celled animals) FIG. 8. Classification. Diagram showing one way of classifying animals. 9. ZOOLOGY AND ITS SUBSCIENCES Zoology is the science of animals, but the facts about animals and the methods of studying them have become so numerous that one man in his lifetime can master and become an authority on only one, or at most a few phases of the subject. It has, therefore, been found necessary and convenient to divide Zoology into subsciences. The principal subsciences are named and very briefly defined in Table II. 26 COLLEGE ZOOLOGY o 3 O -3 IH 3 O (10 s * *s a )H T3 <5 rt - g ^ J[ <5 1 , "1 1 1 . o C! "^ " rt x : >-l N _0 3 & -3 M S~ t/5 O &o fl "o -S .2 o . * .-> N g 3 +j v2 G <4H . <^ t o' (D t>0 _o '3 TABLE II ZOOLOGY AND ITS SUBSCIENCES Anatomy (Gr. anatemno, cut up). The study of the structure of organisms as made out by dissection. Histology (Gr. histos, tissue; logos, discourse). The study of the microscopic structure of tissues. Taxonomy (Gr. taxis, arrangement; nomos, law). The study of the laws and principles of classification. Zoogeography (Gr. zoon, animal; geography). The study of the geographical distribution of animals. Paleontology (Gr. palaios, ancient ; onta, beings; logos, discourse). The study of fossil organisms. Teratology (Gr. teras, wonder; logos, discourse). The study of malformations and monstrosities in organisms. Phylogeny (Gr. phylon, tribe; gennao, produce). The study of the ancestral history of organisms. Embryology (Gr. en, in; bruo, bud). The study of the early developmental stages of animals. Pathology (Gr. pathos, suffering; logos, discourse). The study of the nature of diseases, and their causes and symptoms. Physiology (Gr. phusis. nature; logos, discourse). The study of the functions of organisms. Ecology (Gr. oikos, house; logos, discourse). The study of the relations of organisms to their environment. Psychology (Gr. psuche, mind; logos, discourse). The study of the mind. Sociology (L. socius, companion; logos discourse). The study of animal societies. CHAPTER II PHYLUM PROTOZOA THE PROTOZOA (Gr. protos, first; zoo'n, an animal) are mostly microscopic animals, although some of the commonest species, like Paramecium (Fig. 33), are visible to the naked eye. They are the simplest of all animals, consisting of but a single cell. Nevertheless, most of the activities characteristic of the many- celled, complex animals are exhibited by them, usually in a sim- pler form. In many cases PROTOZOA are colonial; that is, a number of individuals of one species are more or less intimately associated into a colony (Fig. 29). The PROTOZOA are separated into classes according to the presence or absence of locomotor organs and the character of these when present. Four classes are usually recognized: Class I. RHIZOPODA (Gr. rhiza, a root; pous, a foot), with pseudopodia (Fig. 9, j); Class II. MASTIGOPHORA, (Gr. mastix, whip; phero, bear) with flagella (Fig. 22); Class III. SPOROZOA (Gr. spora, seed; zoon, animal), with- out locomotor organs in adult stage (Fig. 32) ; and Class IV. INFUSORIA (Lat. infusus, poured into, crowded in), with cilia (Fig. 33). i. CLASS I. RHIZOPODA a. Ameba proteus The fresh-water PROTOZOON, Ameba proteus (Fig. 9), is usually selected as a type of the class RHIZOPODA. It is only about y^ inch in diameter, and is therefore invisible to the naked eye. 27 28 COLLEGE ZOOLOGY Under the compound microscope Ameba looks like an irregular colorless particle of animated jelly. The best way to obtain specimens for laboratory use is to collect a mass of pond weed (preferably Ceratophylium), place it in a flat dish, and immerse in water. The brown scum which appears on the surface in a few days generally contains many Ameba. Anatomy. - - Two regions are distinguishable in the body of the ectosarc and the endosarc. The ectosarc (Fig. 9, 3), FIG. g. Ameba proteus. i, nucleus; 2, contractile vacuole; 3, pseudopodia, dotted line leads to ectoplasm; 4, food vacuoles; 5, grains of sand. (From Shipley and MacBride, after Gruber.) which consists of ectoplasm, is the outer colorless layer. It is firmer than the endosarc and is free from granules. The endo- sarc is the large central mass of granular protoplasm. Within it lies the nucleus (Fig. 9, /), which is difficult to find in living Ameba, but can easily be made out in animals that have been properly killed and stained. The nucleus is necessary for the life of the animal, since if an individual is cut in two the part with the nucleus survives,, whereas the enucleated fragment dies. PHYLUM PROTOZOA 2 9 It probably plays an important role in the metabolic activity of the cell. A clear space rilled with a fluid less dense than the surrounding protoplasm may be seen in favorable specimens. It is called the contractile iiacuole (Fig. 9, 2), since its walls contract at more or less regular intervals and force the fluid contents out of the body. It serves to get rid of the water taken in through the surface of the body, thus regulating the tension between the protoplasm and the surrounding medium. It is also considered a primitive excretory organ. The solid particles of food engulfed by Ameba cause the for- mation of food vacuoles (Fig. 9, 4), which are temporary structures for the digestion of organic material. Besides the nucleus, con- tractile vacuole, and usually one or more food vacuoles, there are often undigested particles, and foreign substances, like grains of sand (Fig. 9, 5), embedded in the endoplasm. Metabolism. - - Metabolism is the term applied to the series of processes concerned with the manufacture and breaking down of protoplasm. The term anabolism is used for the constructive processes such as the ingestion, digestion, absorption, and as- similation of food. The term katabolism means the breaking down of protoplasm into simpler products, and includes the processes of secretion, excretion, and respiration. FOOD. - - The food of A meba consists of very small aquatic plants, such as Oscillaria and diatoms, PROTOZOA, BACTERIA, and other animal and vegetable matter. A certain amount of choice of food is exercised, or the Ameba' 's body would become overloaded with particles of sand and other indigestible mate- rial among which it lives. INGESTION (Fig. 10). - -The ingestion or taking in of food oc- curs without the aid of a mouth. Food may be engulfed at any point on the surface of the body, but it is usually taken in at what may be called the temporary anterior end, that is, the part of the body toward the direction of locomotion. A small amount of water is taken in with the food, so that there is formed a 30 COLLEGE ZOOLOGY vacuole whose contents consist of a particle of nutritive material suspended in water. The whole process of food-taking occupies one or more minutes, depending on the character of the food. No doubt the reactions in food-taking depend upon both me- chanical and chemical stimuli. Imitations of the engulfing of food by Ameba have been de- vised, based on the theory that ingestion depends on the physical FIG. 10. Ameba ingesting a Euglena cyst, i, 2, 3, 4, successive stages in the process. (From Jennings.) adhesion between the liquid protoplasm and the solid food. Drops of water, glycerin, white of egg, etc., will draw into con- tact and engulf solid particles of various kinds. DIGESTION. - - Digestion takes place without the aid of a stomach. After a food vacuole has become embedded in the endoplasm, a secretion of some mineral acid, probably HC1, enters through the walls of the vacuole. This digestive fluid seems to dissolve only proteid substances, having no effect upon fats and carbohydrates. EGESTION. - - Undigested particles, the faeces, are egested at any point on the surface of the Ameba, there being no special opening to the exterior for this waste matter. Usually such particles are heavier than the protoplasm, and, as the animal moves forward, they lag behind, finally passing out at the end PHYLUM PROTOZOA 31 away from the direction of movement; that is, Ameba flows away, leaving the undigested solids behind. ASSIMILATION. - - The peptones, derived from the digestion of proteid substances, together with the water and mineral matter taken in when the food vacuole was formed, are absorbed by the surrounding protoplasm, and pass into the body substance of the animal, no circulatory system being present, so far as we know. These particles of organic and inorganic matter are then assimilated; that is, they are rearranged to form new particles of living protoplasm, which are deposited among the previously existing particles. The ability to thus manufacture protoplasm from unorganized matter, it will be remembered, is one of the fundamental properties of living substance (p. 10). KATABOLISM. - - The energy for the work done by Ameba comes from the breaking down of complex molecules of proto- plasm by oxidation or " physiological burning/' This is known as katabolism or dissimilation. The products of this slow com- bustion are the energy of movement, heat, and residual matter. This residual matter ordinarily consists of solids and fluids, mainly water, some mineral substances, urea and carbon dioxide. Secretions, excretions, and the products of respiration are in- cluded in this list. SECRETION. - - We have already noted that an acid is poured into the gastric vacuole by the surrounding protoplasm. Such a product of dissimilation, which is of use in the economy of the animal, is known as a secretion. EXCRETION. -- Materials representing the final reduction of substances in the process of katabolism are called excretions. These are deposited either within or outside of the body. A large part of the excretory matter, including urea and carbon dioxide, passes through the general surface of the body. The fluid con- tents of the contractile vacuole are known to contain urea, there- fore this organ is excretory in function. RESPIRATION. - -The contractile vacuole is also respiratory, since carbon dioxide probably makes its way to the exterior by 32 COLLEGE ZOOLOGY way of this organ. Oxygen dissolved in water is taken in through the surface of the body. This gas is necessary for the life of the animal ; if replaced by hydrogen, movements cease after twenty- four hours; if air is then introduced, movements begin again; if not, death ensues. GROWTH. - - If food is plentiful, more substance is added to the living protoplasm of the A meba than is used up in its various physical activities. The result is an increase in the volume of the animal. This is growth, and, as in all other living organisms, growth by the addition of new particles among the preexisting particles, i.e. growth by intussusception. Reproduction. - - There is, however, a limit with regard to the size that may be attained by Ameba proteus, as it rarely exceeds .25 mm. ( T ^- - inch) in diameter. When this limit is reached the animal divides into two parts. Why should there be such a limit? The following explanation is given by Herbert Spencer and others. The volume of an organism varies as the cube of its diameter, the surface as the square. Thus, as an animal grows, the ratio between surface and volume decreases; and, since Ameba takes in food, gives off waste material, and carries on respiration through its surface, the activities of the cell must decrease with increase in size until further growth is impossible. The solution of the problem is the division of the animal into two, whereby the ratio of surface to volume is increased. Re- production by binary division, therefore, takes place when growth is no longer possible. It is supposed that this division is inaugurated through some unknown change in the relations between the nucleus and cytoplasm. There are at least two kinds of reproduction in Ameba proteus, but neither has ever been satisfactorily worked out in detail. They are (i) binary division and (2) sporulation. (i) During binary division (Fig. n) the nucleus divides by a primitive sort of mitosis. Then the animal elongates, a constric- tion appears near the center, and division into two daughter cells finally takes place. PHYLUM PROTOZOA 33 (2) Sporulation is apparently a rare process of multiplication in Ameba. First the pseudopodia are drawn in and the animal becomes spherical; a three-layered cyst is then secreted. By successive divisions of the nucleus from five hundred to six hundred daughter nuclei are produced. Cell walls then appear, FIG. ii. Ameba polypodia dividing by binary fusion. Haswell, after F. E. Schulze.) (From Parker and dividing the Ameba into as many cells as there are nuclei. These Amebultz, or pseudopodios pores, as they are sometimes called, break out through the cyst and become recognizable as Ameba proteus in about three weeks. The Behavior of Ameba. - - The sum total of all the move- ments of an animal constitute what is known as its behavior. In Ameba these movements may be separated into those con- 34 COLLEGE ZOOLOGY nected with locomotion and those resulting from external and internal stimuli. LOCOMOTION. -- Ameba moves from place to place by means of finger-like protrusions of the body, known as pseudopodia (Fig. 9, 3). A pseudopodium is formed in the following manner. The ectoplasm bulges out and enlarges until a blunt projection is produced; the endoplasm then flows into it. The result is a movement of the entire animal in the direction of the pseudo- podium. If more than one are formed at the same time, there occurs a struggle for supremacy until finally one survives while the others flow back and gradually disappear. Ameba moves, therefore, by thrusting out pseudopodia and then flowing into them. There are three principal theories which attempt to explain the formation of pseudopodia. (i) The adherence theory holds that the pseudopodium adheres on one side more strongly than on the others, and that the entire animal, therefore, moves to- ward the adhering side. (2) The surface tension theory maintains that local changes in the surface tension cause the currents which initiate movement. (3) According to the contractile theory, Ameba moves by means of a contractile substance in the follow- ing manner. In advancing the Amebce " extend the anterior end free in the water and attach it at or near the tip and then contract. At the same time the posterior end is contracting and the substance thus pushed and pulled forward goes to form the new anterior end (Fig. 12, A, E). . . . In other cases the anterior end is liftedjree and then curves down to the sub- stratum and attaches, forming a long loop. The posterior end is then released, and the substance flows over to the anterior end. At the same time another anterior end is extended (Fig. 12, O-" There are various methods of imitating the movements of Ameba by means of inorganic substances. One of these is as follows: A large drop of mercury is placed in a flat-bottomed watch glass and covered with 10 per cent nitric acid. A piece of PHYLUM PROTOZOA 35 potassium bichromate when placed near the mercury produces a solution which causes local lowering of the surface tension of J FIG. 12. Locomotion of Amcba pro/ens. Photographs in side view. A and B show a specimen attached at two points, a and b, and a pseudopod which projects from one end and bends down to the substratum as in B at d ; C shows the extension of a long pseudopod. (.From Dellinger in Journ. Exp. Zool.) the drop, and results in the formation of projections and move- ment of the mercury in various directions. REACTIONS TO STIMULI. -- A turning of an animal resulting from a change in its environment, for example an increase in the intensity of the light, is known as a " tropism" or "taxis.'' 36 COLLEGE ZOOLOGY The term " tropism " means " a turning "; it is used for purely descriptive purposes. Nothing is known of the psychic phe- nomena of the lower animals, and one must be cautious in at- tributing to them his own mental states. The term " tropism" merely describes an animal's behavior in response to stimuli. The kind of stimulus employed is indicated by a prefix. The principal kinds of tropisms are as follows : - (1) Thigmotropism = reaction to contact. (2) Chemotropism == reaction to a chemical. (3) Thermotropism == reaction to heat. (4) Phototropism == reaction to light. (5) Electrotropism == reaction to electric current. (6) Geotropism == reaction to gravity. (7) Chromo tropism == reaction to color. (8) Rheotropism == reaction to current. ' Taxis " is often employed instead of " tropism," when the terms read " thigmotaxis," " chemotaxis," etc. If the animal reacts by a movement toward the stimulus, such as light, it is said to be positively phototropic or phototactic, etc.; if away from the stimulus, negatively phototropic or phototactic, etc. Ameba has been found to respond to contact with solids, to chemicals, to heat, to light, to colors, and to electricity. Ameba exhibits negative thignwtropism when touched at any point with a solid object; the part affected contracts and the FIG. 13. Thigmotropism of Ameba. The animal moves away when stimulated by a glass rod. (From Jennings.) animal moves away (Fig. 13). When, however, an Ameba is floating freely in the water and a pseudopodium comes in con- PHYLUM PROTOZOA 37 tact with the substratum, the animal moves in the direction of that pseudopodium until the normal creeping position has been attained. Contact with food also results in positive re- actions. Ameba, therefore, reacts negatively to a strong me- chanical stimulus and positively to a weak one. Chemotropic reactions prove that Ameba is sensitive to changes in the chemical composition of the water surrounding it. ' It has been shown to react negatively when the following sub- stances come in contact with one side of its body; methylene blue, methyl green ,-;._.,.-. (Fig. 14), sodium chloride, sodium car- bonate, potassium nitrate, potassium hydroxide, acetic acid, hydrochloric acid, cane sugar, distilled water, tap water, FlG - u- Chemotro- - pism of Ameba. The ani- and water from other cultures than that ma i moves away when a in which the Amoeba under experimenta- little methyl green diffuses ,, against the advancing end. tion lives. ( From Jennings.) Negatively thermotropic reactions result if Ameba is locally affected by heat, since the animal will move away from heat stimuli. Cold and excessive heat retard its activities, which cease altogether between 30 and 35 C. Ameba is negatively phototropic, since it will orient itself in the direction of the rays of a strong light and move away from it (Fig. 15). In Ameba there are no organs that can be compared with what we call sense organs in higher animals, and we must attribute its reactions to stimuli to that fundamental property of protoplasm called irritability. The superficial layer of cytoplasm receives the stimulus and transfers the effects to some other part of the body; thus may be shown the phenomenon of internal irritabil- ity or conductivity. The stimulus causing a reaction seems to be in most cases a change in the environment. The behavior of Ameba in the absence of external stimuli, for example when it is suspended freely in the water (p. 36), show T s that some of its activities are initiated by internal causes. COLLEGE ZOOLOGY The reactions oi Ameba to stimuli are of un- doubted value to the individual and to the preservation of the race, for the negative reaction is in most cases produced by injurious agents such as strong chemicals, heat, and mechanical impacts, whereas posi- tive reactions are produced usually by beneficial agents. The responses, therefore, in the former cases carry the animal out of danger, in the latter, to safety. Ameba is of fundamental interest to animal psy- chologists, since it represents the " animal mind " in its most primitive form. Whether or not the animal is in any degree conscious is a question still unanswered. If Ameba has recognizable sensations, they must be infinitely less in both quality and quantity than those of higher organisms. Further- more, it is unable to learn from the few kinds of experiences it does pass through, and is therefore lacking in memory images. A review of the facts thus far obtained seems to show that factors are present in the behavior of Ameba " comparable to the habits, reflexes, and automatic activities of higher organisms," and " if Amoeba were a large animal, so as to come within the everyday experience of human beings, its behavior would at of Ameba. The arrows indi- . - cate the direction of the light once call forth the attribution to it rays and the numbers the states Q f p l easure and pain, of hunger, successive positions assumed . , by the animal. The Ameba desire, and the like, on precisely always moves away from same basis as we attribute these things the source of light. (From Jennings, after Davenport.) to the dog. PHYLUM PROTOZOA 39 b. Rhizopoda in General The PROTOZOA which are included in the class RHIZOPODA have been grouped into four principal orders according to the character of their pseudopodia and the structure of their shells, if these are present: (i) LOBOSA, (2) HELIOZOA, (3) RADIO- LARIA, (4) FORAMINIFERA. Order i. Lobosa. RHIZOPODA with fingerlike (lobose) pseudo- podia. Most of the LOBOSA occur in fresh water, a few in moist earth, and some are parasites. 1 Examples: Ameba (Fig. 9), Arcella / (Fig. 1 6), and Difflugia (Fig. 17). Arcella (Fig. 16) is common in the FIG. 1 6. Arcella discoides (order LOBOSA) as seen from above, i, shell; 2, pseudopodia ; j, edge of opening into shell; 4, thread attaching animal to interior of shell; 5, nucleus; 6, food vacuole ; 7, gas vacuole. (From Leidy.) FIG. 17. Difflugia urceo- lata (order LOBOSA) as seen from the side, i, shell com- posed of minute particles of sand; 2, pseudopodia. (From Leidy.) ooze on the bottoms of fresh-water ponds and ditches. It has a dome-shaped brownish shell of chitin (/) which it secretes. The lobose pseudopodia (2) protrude from a circular opening (j) in the center of the flattened surface. Difflugia (Fig. 17) is another common member of the order LOBOSA, and is also found in the ooze of ponds. Its shell (/) consists of minute particles of sand and other foreign objects held together by chitin. COLLEGE ZOOLOGY Order 2. Heliozoa. - - RHIZOPODA with thin, radially ar- ranged pseudopodia, which are usually supported by axial threads (Fig. 18, a). Ex- amples: Actinosphcerium, Ac- tinophrys (Fig. 18). Actinophrys (Fig. 18), the sun animalcule, lives among the aquatic plants in fresh- i water ponds and ditches. The body appears vesicular, being crowded with vacuoles (c). The small organisms which serve as food strike the pseudopodia, pass down to ek.t FIG. rt.-- Actinophrys sol a HELIO- h fa d d are lfed ZOON. An individual with a large gastric J > vacuole (g), contractile vacuole (c), and larger organisms (g) are drawn axial filaments (a) in the raylike pseudo- . , c PV prfll neio-hboHno- podia. (From Calkins, after Grenacher.) pseudopodia acting together. Order 3. Radiolaria. - - Marine RHIZOPODA with raylike pseudopodia, a central perfor- ated capsule of chitin (Fig. 19, sk. ji), and usually a larger en- closing skeleton of silica (sk. i, sk.2). Examples: Actinomma (Fig. 19), Thalassicolla, Heli- osph(Era. The shells of the radio- larians, upon sinking to the sea bottom, form radiolarian ooze; this becomes hardened, producing rock strata as much r - 1 i rpii FIG. io. Actinomma asteracanlhion, as 1000 feet thick. These a RADIOLARIAN . T he shell is broken rocks may take the form of away so as to show the outer (sk. i), , ., a - middle (sk. 2), and inner (sk. 3) spheres. quartzites, flint, or chert con- (From WeyssC( after Haeckel and CretionS. Hertwig.) SK.2 PHYLUM PROTOZOA Order 4. Foraminifera. RHIZOPODA, mostly marine, with fine, branching pseudopodia which fuse forming a protoplasmic net- work. Examples: Allogromia (Fig. 20), Globigerina, Discorbina. Allogromia (Fig. 20) lives in fresh water and has a chitinous shell (sh.}. The shells of many FORAMINIFERA consist of numer- ous chambers connected by open- ings (foramina), and are com- posed of calcium carbonate. When these shells sink to the sea- bottom, they become Globigerina ooze, which solidifies, forming gray chalk (Fig. 21). FIG. 20. Allogromia (order FOR- AMINIFERA). a, aperture of shell; sh, shell. (From the Cambridge Natural History.) FIG. 21. FORAMINIFERA. Shells as they exist in gray chalk. (From Scott, after a photograph by the Geological Survey of Iowa.) 2. CLASS II. MASTIGOPHORA a. Euglena viridis Euglena viridis (Fig. 22) is a small greenish PROTOZOON which will serve to point out the characteristics of the MASTIGOPHORA. It lives in small bodies of fresh water, and may appear in ameba- cultures (p. 28). & FIG. 22. Euglena viridis. A, view of free-swimming specimen showing details of structure; B, another animal showing change of shape and striations; C and D, outlines showing stages of contraction; E, reproduction by longi- tudinal fission; F and G, division within a cyst; am, pyrenoids with sheaths of paramylum; chr, chromatophores; c.v, contractile vacuoles; e, stigma or eye-spot; m, mouth; n, nucleus; r, reservoir. (A-D, from Bourne; E-G from Bourne, after Stein.) PHYLUM PROTOZOA 43 Anatomy. - - Euglena (Fig. 22) is a simple elongated cell, and, although somewhat elastic, maintains a more or less constant shape. It possesses, in addition to ectosarc and endosarc, a thin outer membrane, the cuticle, which is striated, as shown in Figure 22, B. Near the center of the anterior end is a long slender whiplike process, iheflagellum, which extends out from an open- ing called the mouth (Fig. 22, A, m). From the mouth a tubular " gullet" leads to a permanent vesicle, the reservoir (A, r); into this reservoir several contractile vacuoles (A, cv) discharge their contents. Close to the reservoir is a protoplasmic mass con- taining granules of a red coloring matter, hamatochrome ; this is called the stigma or eye-spot (A, e) because it is supposed to be especially sensitive to light. Near the center of the body is a nucleus (A, n}, and scattered about in the protoplasm are many oval bodies, greenish in color, called chromatophores (A, ckr). Physiology. - - NUTRITION. - - Euglena probably does not ingest solid particles by means of the mouth and gullet, but manufactures its own food by the aid of the chlorophyll contained in the chromatophores. As in plants, this chlorophyll is able, in the presence of light, to break down the carbon dioxide (C0 2 ), thus setting free the oxygen, and to unite the carbon with water, forming a substance allied to starch, called paramylum (Fig. 22, A and B, am}. This mode of nutrition is known as holophytic. Some organic substances are probably absorbed through the surface of the body, that is, saprophytic nutrition supplements the holophytic. Euglena differs from most animals in its method of nutrition, since the majority of them ingest solid particles and are said to be holozoic. Behaviour. - - LOCOMOTION. - - Euglena because of its elastic- ity is able to squirm through small openings, but its chief method of locomotion is swimming. The flagellum, consisting of four contractile fibrils which are wound together spirally, bends to and fro, drawing the animal along. REACTIONS TO STIMULI. - - Euglena is very sensitive to light, and is a favorable object for the study of phototropism. It 44 COLLEGE ZOOLOGY swims toward an ordinary light such as that from a window, and if a culture containing Euglena is examined, most of the ani- mals will be found on the brightest side. This is of distinct advantage to the animal, since light is necessary for the assimi- lation of carbon dioxide by means of its chlorophyll. If a drop of water containing Euglence is placed in the direct sunlight and then one half of it is shaded, the animals will avoid the shady part and also the direct sunlight, both of which are injurious to them, and will remain in a small band between the two "* ' in the light best suited for them, that is, their optimum (Fig. 23). By shading various ^. portions of the body of a Euglena it has been found that the region in front of FIG. 23. Phototropism of Euglena. ,1 , ... Diagram showing the reaction of Euglena the e ye-SpOt IS more Sensitive to light. The light comes from the direc- than any other part. It tions indicated by the arrows, while the u u i~ j ^i i opposite side of the vessel is shaded, as should be noted that when indicated by the dots. The Euglena Euglence are Swimming gather in the intermediate region across ,v i ,1 , ,1 the middle. (From Jennings.) through the Water it IS this anterior end which first reaches an injurious environment; the animals give the avoiding reaction at once, and are thus carried out of danger. Reproduction. - - Reproduction in Euglena takes place by binary longitudinal division (Fig. 22, E). The nucleus divides by a primitive sort of mitosis. The body begins to divide at the anterior end. The old flagellum is retained by one half, while a new flagellum is developed by the other. Frequently Euglena become spherical and secrete a gelatinous covering, called a cyst. Periods of drought are successfully passed while in the encysted condition, the animals becoming active when water is again encountered. Sometimes division takes place during encystment (Fig. 22, F, G). One cyst usually produces two Euglence, although these may divide while still within the old PHYLUM PROTOZOA 45 cyst wall, making four in all. Recent observers have recorded as many as thirty-two young flagellated Euglena which escaped from a single cyst. b. Mastigophora in General The MASTIGOPHORA may easily be distinguished from other PROTOZOA by the presence of one or more flagella. Four orders are usually recognized: (i) FLAGELLATA, (2) CHOANOFLAGEL- LATA, (3) DlNOFLAGELLATA, (4) CYSTOFLAGELLATA. Order i. Flagellata. -- MASTIGOPHORA with one or more flagella at the anterior end of the body. Examples: Euglena (Fig. 22), Mastigameba (Fig. 24), Chilomonas (Fig. 25), Uroglena (Fig. 26), Volwx (Fig. 27). Mastigameba (Fig. 24) is of special interest, since it -P FIG. 24. Mas- tigameba re plans, a FLAGELLATE. --nu FIG. 25. - - Chilo- monas, a FLAGELLATE. c.v, contractile vacu- ole; ft, flagella; g, gul- let ; nu, nucleus ; .v, dorsal or upper lip ; y, ventral or lower lip. (From Jennings.) FIG. 26. Uroglena amcri- cana, a large colonial FLAGEL- LATE. (From Bergen and Davis, adapted after Moore.) appears to combine the distinguishing characteristics of both the RHIZOPODA and MASTIGOPHORA, that is, it possesses pseudo- podia and also a distinct flageilum. It is therefore able to creep about on a solid object or swim directly through the water. Chilomonas (Fig. 25) is a very common FLAGELLATE in labo- ratory cultures. Uroglena (Fig. 26) forms spheroidal colonies 46 COLLEGE ZOOLOGY consisting of a great number of individuals held together by a gelatinous matrix. This form is often responsible for the " oily odor " of drinking water caused by the escape of small droplets of an oil-like substance from the cells. Volwx (Fig. 27) is a colonial FLAGELLATE found in fresh- water ponds. It may consist of as many as twelve thousand FIG. 27. - Vohox globular, a large colonial FLAGELLATE. A, a sexually ripe colony, showing microgametes, $ , and macrogametes, 9 . i n various stages of development. B, a portion of the edge of the colony highly magnified, show- ing three flagellate cells united by protoplasmic threads, and a single repro- ductive cell, rp; si, stigma; cv, contractile vacuole. (From Bourne, after Kolliker.) cells. Protoplasmic strands connect each cell with those that surround it (Fig. 27 B); physiological continuity is thus estab- PHYLUM PROTOZOA 47 lished. All of the cells are not alike, since some of them, the germ cells (Fig. 27, after Jennings.) at intervals of about ten to twenty seconds. Their fluid contents are discharged to the outside (Fig. 35). As in Ameba, they act as organs of excretion and respiration. PHYLUM PROTOZOA 55 Metabolism. -- The food of Paramecium consists principally of BACTERIA and minute PROTOZOA. The cilia in the oral groove (Fig. 33, o.g.) create a current of water toward the mouth (m.). Food particles are forced down the gullet (g.) by a row of cilia which have fused side by side, forming an undulating membrane. At the end of the gullet a. food vacuole (f.v.) is produced ; this when fully formed separates from the gullet and is swept away by the rotary stream- ing movement of the endoplasm, known as cydosis. This carries the food vacuole around a definite course, as shown by the arrows in Figure 33. Digestion occurs within the food vacuole. Undigested par- ticles are cast out at a definite anal spot (Fig. 33, an.), which can only be seen when the faces are voided. The processes of diges- tion, absorption, assimilation, ex- cretion, and respiration are similar to those described for Ameba. Behavior. - - LOCOMOTION. - - If confined in close quarters, Para- mecium exhibits elasticity, and can squirm through small openings; but when in a free field it swims by means of its cilia. These are inclined backward and obliquely, so that the body is rotated in its long axis over to the left as well as propelled forward (Fig. 36). 5 6 COLLEGE ZOOLOGY " The cilia in the oral groove beat more effectively than those elsewhere. The result is to turn the anterior end continually away from the oral side, just as happens in a boat that is rowed on one side more strongly than on the other. As a result the animal would swim in circles, turning continually toward the aboral side, but for the fact that it rotates on its long axis. Through the rotation the forward movement and the swerving to one side are combined to produce a spiral course. The swerv- ing when the oral side is to the left, is to the right; when the oral side is above, the body swerves downward; when the oral side is to the right, the body swerves to the left, etc. Hence the swerving in any given direction is compensated by an equal swerving in the opposite direction ; the resultant is a spiral path having a straight axis " (Fig. 36). Rotation is thus effective in enabling an unsymmetrical animal to swim in a straight course through a medium which allows deviations to right or left, and up or down. REACTIONS TO STIMULI. - - Paramecium responds to stimuli either negatively or positively. The negative response is known .- FIG. 37. Diagram of the avoiding reaction of Paramecium. A is a solid object or other source of stimulation. 1-6, successive positions occupied by the animal. (The rotation on the long axis is not shown.) (From Jennings.) as the " avoiding reaction " (Fig. 37) ; it takes place in the follow- ing manner. When a Paramecium receives an injurious stimulus PHYLUM PROTOZOA 57 at its anterior end, it reverses its cilia and swims backward for a short distance out of the region of stimulation; then its rota- tion decreases in rapidity and it swerves toward the aboral side more strongly than under normal conditions. Its posterior end then becomes a sort of pivot upon which the animal swings about in a circle (Fig. 37, 3-5). During this revolution samples of the surrounding medium are brought into the oral groove. When a sample no longer contains the stimulus, the cilia resume their normal beating, and the animal moves forward again. If this once more brings it into the region of the stimulus, the avoiding reaction is re- peated; this goes on as long as the animal receives the stimulus. The repetition of the avoiding reaction is very well shown when Paramccium enters a drop of ^ per cent acetic acid. In attempting to get out of the drop the grounding water is en- , J'^f "ing!" countered; to this the avoiding reaction is ramcdum in a drop given and a new direction is taken within ol . aci j- (From Jen ' III 1 1 -, ^ . j the acid, which of course leads to the water and another negative reaction. The accompanying Figure 38 shows part of the pathway made by a single Paramecium under these conditions. Paramccium responds positively under certain conditions. Often it comes to rest against an object, positive thigmotropism. When subjected to chemical substances or heat, it swims about in all directions, giving the avoiding reaction until it succeeds in getting into a suitable environment. This is the method of trial and error, that is, the animal tries all directions until the one is discovered which allows it to escape from the region of un- favorable stimulation. " For each chemical there is a certain optimum concentration in which the Parameda are not caused to react." There is also an optimum temperature, which lies, under ordinary conditions, between 24 and 28 C. Gravity stimulates Paramecium in some unknown way to 58 COLLEGE ZOOLOGY orient itself with the forward end pointing upward, so that if a number are equally distributed in a test tube of water, they will gradually find their way to the top. In running water, Para- mccia swim upstream, probably because the current would inter- fere with the beating of the cilia if any other direction were taken. The electric current also affects the beating of the cilia and causes certain definite movements. Frequently Paramecium may be stimulated in more than one way at the same time. For example, a specimen which is in contact with a solid is acted upon by gravity, and may be acted upon by chemicals, heat, currents of water, and other stimuli. It has been found that gravity always gives way to other stimuli, and that if more than one other factor is at work the one first in the field exerts the greater influence. Both the spontaneous activities, such as swimming, and re- actions due to external stimuli, are due to changes in the internal condition of the animal. The physiological condition of Parame- cium, therefore, determines the character of its response. This physiological state is a dynamic condition, changing continually with the processes of metabolism going on within the living substance of the animal. Thus one physiological state resolves itself into another; this " becomes easier and more rapid after it has taken place a number of times," giving us grounds for the belief that stimuli and reactions have a distinct effect upon succeeding responses. " We may sum up the external factors that produce or deter- mine reactions as follows: (i) The organism may react to a change, even though neither beneficial nor injurious. (2) Any- thing that tends to interfere with the normal current of life activities produces reactions of a certain sort (' negative '). (3) Any change that tends to restore or favor the normal life processes may produce reactions of a different sort (' positive ') (4) Changes that in themselves neither interfere with nor assist the normal stream of life processes may produce negative or positive reactions, according as they are usually followed by PHYLUM PROTOZOA 59 changes that are injurious or beneficial. (5) Whether a given change shall produce reaction or not often depends on the com- pleteness or incompleteness of the performance of the metabolic processes of the organism under the existing conditions. This makes the behavior fundamentally regulatory." Reproduction. - - Paramecium reproduces only by simple lunar \ division. This process is interrupted occasionally by a temporary union (conjugation] of two indi- viduals and a subsequent mutual fertilization. BINARY FISSION. - - In binary fission the animal divides transversely (Fig. 39). Both the macronucleus (Fig. 39, N) and micro- nucleus (ri) divide, forming daughter nuclei, oj, A new gullet (V) is budded off from the old gullet (0), and two new contractile vacuoles arise. The animal is then divided into two n ' by a constriction. The entire process occupies ' from about half an hour to two hours. The daughter Paramecia grow rapidly and divide again at the end of twenty-four hours or even sooner, depending on the temperature, food, and other external conditions. It has been estimated that one Paramecium may be re- '"'' dividing by binary hssion. N, Sponsible for the production of 268,OOO,OOO jy 1 , "macronucleus; offspring in one month. n > n \' mfcronucleus ; ... o, o l , mouth. The . CONJUGATION. - - The conditions that initi- paramcdum figured ate conjugation are not yet known, but the has two mkronudei. J (From Sedgwick, after complicated stages have been quite fully Hertwig.) worked out. When two Paramecia, which are ready to conjugate, come together, they remain attached to each other because of the adhesive state of the external proto- plasm. The ventral surfaces of the two animals are opposed, and a protoplasmic bridge is constructed between them. As soon as this union is effected, the nuclei pass through a series of stages which have been likened to the maturation processes FIG. 39. - - Para- 6o COLLEGE ZOOLOGY of metazoan eggs (Chap. Ill, p. 81). Reference to Figure 40 will help to make clear the following description. The micro- nucleus moves from its normal position in a concavity of the - FIG. 40. Paramecia conjugating, a-q, stages in the nuclei during con- jugation and the subsequent divisions of the conjugants during the period of nuclear reconstruction. The original macronuclei have been omitted except in stage a. (After Calkins and Cull.) PHYLUM PROTOZOA 6l macronucleus (Fig. 33, mi.), grows larger, then lengthens, forming a spindle (Fig. 40, a), and subsequently divides into two (b). These immediately divide again without the inter- vention of a resting stage. The resultant four nuclei (c) have been compared to the four sper- matozoa produced by a primary spermatocyte or to an egg with its polar bodies, and the divi- sions are considered as the first and second maturation mitoses (see p. 81). Three of the four nuclei degenerate (d) , the fourth divides again. During this divi- sion the granules of chromatin contained in the nuclei separate into two groups, one smaller (Fig. 41, A, m.n.) than the other (Fig. 41, A, f.n.). The smaller nucleus might be con- sidered comparable to the male nucleus, the other to the female. The male nucleus migrates across nuclei Curing the conjugation of the protoplasmic bridge between P^amccium. A, the spindle formed r _ . during the division of the micronucleus the two animals (Fig. 40, /) and which results in the production of a unites with the female nucleus of lar ^, female nucleus (/.) and a smaller male nucleus (m.n). D, the the Other Conjugant (Fig. 40, g; fusion of the male nucleus (m.n) of Fig. 4 I, 5), forming a fusion one conjugant with the female nucleus (/.) of the other conjugant. (trom nucleus (Fig. 40, h). Thus is Calkins and Cull in Archiv f. Prolist.) fertilization effected. The conjugants separate soon after fertilization (Fig. 40, g). The macronucleus, which up to this time has remained at rest, now assumes a vermiform shape, breaks up into small segments, and then dissolves. Shortly after separation the fusion nucleus of each conjugant divides by mitosis into two (/), these two into four (j), and these four into eight nuclei equal in size (k). Four , > . : . ' ... - FIG. 41. Two views of the micro- 62 COLLEGE ZOOLOGY of these increase in size and develop into macronuclei (I); the other four remain micronuclei. The whole animal then divides by binary fission (m, n), each daughter cell securing two of the macronuclei and two micronuclei (o). Another binary division (p) results in four cells each with one macronucleus and one micronucleus (q). An indefinite number of generations are produced by the transverse division of the four daughter cells resulting from each conjugant. The significance of conjugation cannot be definitely stated. Some investigators believe that Paramecium passes through a life cycle containing three distinct stages. The period, of (i) youth is characterized by rapid cell multiplication and growth; (2) maturity by less frequent cell division, sexual maturity, and the cessation of growth; and (3) old age by degeneration and natural death. Death is avoided by conjugation, which rejuve- nates the senescent animals. Jennings has shown that some Paramecia conjugate more often than others, and Woodruff has succeeded in carrying a cul- ture through a period of over five and one half years. During this time there were over three thousand and five hundred generations. These facts " weaken the theory that conjugation is to be considered the result of senile degeneration at the end of the life cycle," and show that this Protozoon "has unlimited power of reproduction without conjugation or artificial stimula- tion " if given a favorable environment. b. Infusoria in General t The INFUSORIA are PROTOZOA with cilia which serve as loco- motor organs and for procuring food. Paramecium is a typical member of the class. There are two subclasses, (i) CiLiATAand (2) SUCTORIA. SUBCLASS i. CILIATA. -- INFUSORIA with cilia in the adult stage, a mouth, and usually undulating membranes or cirri. Many ciliates are confined to fresh water, others occur either in fresh or salt water, and still others are parasitic in METAZOA. PHYLUM PROTOZOA There are four orders : (i) HOLOTRICHA, (2) HETEROTRICHA, (3) HYPOTRICHA, (4) PERITRICHA. Order i. Holotricha (Figs. 33 and 42). -- CILIATA with cilia all over the body and of approximately equal length and thick- ness. Examples: Paramecium (Fig. 33), Colcps (Fig. 42, A), Lo.vophvllum (Fig. 42, B), Colpoda (Fig. 42, C), Opalina (Fig. 42, D\ The HOLOTRICHA are probably the most primitive INFUSORIA. Paramecium caudatum is the best known species. Members of FIG. 42. INFUSORIA of the order HOLOTRICHA. A, Colcps hirlus. B, Loxo- phyllum roslratum. C, Colpoda cucullulus. D, Opalina ranarum; a, macro- nuclei. (A, B, C, from Conn; D from Lankester, after Zeller.) the following genera are frequently found in fresh- water cultures: Coleps (Fig. 42, A), Loxophyllum (Fig. 42, B), and Colpoda (Fig. 42, C). Opalina ranarum (Fig. 42, D) is a large multi- nucleate species living in the intestine of the frog. It has no mouth, but absorbs digested foods through the surface. Order 2. Heterotricha (Fig. 43, .1). -- CILIATA whose cilia cover the entire body, but are larger and stronger about the mouth opening than elsewhere. This adoral ciliated spiral con- sists of rows of cilia fused into membranelles and leads into the mouth. Examples: Spirostomum, Bursar ia, and Stcntor (Fig. 43, A). COLLEGE ZOOLOGY Stentor (Fig. 43, A) may be either fixed or free swimming. It is trumpet-shaped when attached and pear-shaped when swimming. The cuticle is striated and just beneath it are FIG. 43. INFUSORIA. A, Stentor polymorphus of the order HETEROTRICHA. B, Stylonychia mytilns of the order HY.POTRICHA. C, Vorticella of the order PERITRICHA. D, Podophyra of the subclass SUCTORIA. c.vac, contractile vacuole ; mg.nu, macronucleus ; mi.nu, micronucleus ; /, disc; 2, mouth; 3, peristomial groove; 4, vibratile membrane in mouth; 5, ectoplasm; 6, endo- plasm ; 7, food vacuoles ; S, pharynx showing formation of food vacuoles ; Q, contractile vacuoles; 10, permanent receptacle into which contractile vacuole opens; //, micronucleus; 12, nucleus; 13, contractile fibrils running into muscle in stalk; 14, stalk contracted (the axial fiber should touch the cuticle in places). (A and B, from Weysse, after Kent; C, from Shipley and MacBride; D, from Parker and Haswell.) muscle fibers (myonemes). The nucleus is ellipsoidal, or like a row of beads. Order 3. Hypotricha (Fig. 43, B). -- CILIATA with a flattened body and dorsal and ventral surfaces. The dorsal surface is free PHYLUM PROTOZOA 65 from cilia, but spines may be present. The ventral surface is provided with longitudinal rows of cilia and also spines and hooked cirri, which are used as locomotor organs in creeping about. The cilia around the oral groove aid in swimming as well as in food taking. There is a macronucleus, often divided, and two or four micronuclei. Examples: Oxytricha, Stylo- nychia. A side view of a creeping Stylonychia is shown in Figure 43, B. Order 4. Peritricha (Fig. 43, C). --CiLiATA with an adoral ciliated spiral, the rest of the body is without cilia, except in a few species where a circlet of cilia occurs near the aboral end. Examples: Vorticella (Fig. 43, C), Carchesium, Zoothamnium. The common members of this order are bell-shaped and at- tached by a contractile stalk. Certain species are solitary (Vorticella, Fig. 43, C), others form tree-like colonies (Car- chesium), and still others are colonial but with an enveloping mass of jelly (Zoothamnium). The anatomy of Vorticella is shown in Figure 43, C. The stalk contains a winding fiber com- posed of myoneme fibrils; this fiber, on contracting, draws the stalk into a shape like a coil spring. SUBCLASS 2. SUCTORIA. INFUSORIA without cilia in the adult stage. No locomotor organs are present and the animals are attached either directly or by a stalk. No oral groove nor mouth occurs, but a number of tubelike tentacles extend out through the cuticle. Examples: Podophyra (Fig. 43, D), Sphczrophyra. Ciliates are captured by these tentacles and their substance is sucked by them into the body. Both fresh-water and marine species are known. Podophyra (Fig. 43, D) is a well-known fresh-water form. Sphcerophyra is parasitic in other INFUSORIA. 5. PROTOZOA IN GENERAL PROTOZOA may be defined as unicellular animals which in many cases form colonies. An examination of the types dis- cussed in the preceding pages will show that the PROTOZOA differ 66 COLLEGE ZOOLOGY one from another in structure, physiology, and reproduction. These differences are briefly reviewed in the following para- graphs. Morphology. - - PROTOZOA vary in size from the minute blood parasites, such as Plasmodium which causes malaria, to the huge gregarine, Porospora gigantea, which lives in the alimentary canal of the lobster and may be two-thirds of an inch long. Most of them are invisible to the naked eye, and a few are invisible even with the highest powers of the microscope. For example, the organism which is supposed to cause yellow fever is known only by its effects upon human beings, since it has never been seen. The shapes of PROTOZOA are likewise extremely varied. Ameba has no definite shape; many species are globular with radiating projections (HELIOZOA, Fig. 18; RADIOLARIA, Fig. 19) ; Euglena (Fig. 22) is spindle-shaped; Paramecium (Fig. 33) re- sembles a slipper; Vorticella (Fig. 43, C), a bell; Stentor (Fig. 43, A), a trumpet; some like Stylonychia (Fig. 43, B} have definite dorsal and ventral surfaces; in fact, almost every conceivable shape seems to occur in this group. Most of the PROTOZOA are either faintly colored or entirely without pigment. When coloring-matter is present it often con- sists of chlorophyll, or some allied substance, which is contained in chromatophores, e.g. Euglena (Fig. 22, A, chr.\ Drinking water is often colored red by Euglena sanguinea, or yellow by Uroglena (Fig. 26) ; the surface of the sea is sometimes colored orange by vast numbers of Noctiluca (Fig. 31), or red by a DINOFLAGELLATE, Peridimum (Fig. 30). The simplest kind of locomotor organs are pseudopodia like those of Ameba (Fig. 9, j). The pseudopodia of some species have a firm axial rod (HELIOZOA, Fig. 18), and those of others may branch and fuse with one another (FORAMINIPERA, Fig. 20). Flagella may be likened to very thin pseudopodia that have be- come permanent. They seem to be composed of long fibrils that are spirally wound. Cilia are smaller and more numerous PHYLUM PROTOZOA 67 than flagella; often they are fused together in groups forming large cirri (Stylonychia, Fig. 43, B), or side by side, forming mcmbrancUcs as in the gullet of Paramecium. An external covering may be absent from the body of PRO- TOZOA (Ameba) or may be present as a distinct cuticle (Para- mecium}. Shells may also occur; these consist of material se- creted by the animal, e.g. chitin by Arcella (Fig. 16), calcium carbonate by FORAMINIFERA (Fig. 21), and silica by RADIO- LARIA (Fig. 19), or are made up of foreign particles such as grains of sand (Difflugia, Fig. 17). The cytoplasm of PROTOZOA is probably alveolar in structure. It can usually be separated into a firm, clear, outer layer, the ectosarc, and a more fluid, granular, inner mass, the endosarc. Within the cytoplasm are embedded one or more nuclei, vacuoles of several kinds, and frequently plastids. A nucleus is always present, although in some cases its essen- tial substance, chromatin, is scattered throughout the cells, form- ing a " distributed nucleus." Some PROTOZOA have two kinds of nuclei, a macronudeus (Paramecium, Fig. 33, ma.), which is supposed to have charge of the metabolic processes, and a micro- nucleus (Fig. 33, mi.), which functions only in reproduction. During binary division the chromatin of the nucleus may form distinct chromosomes, but in many cases chromosomes have not been observed. Vacuoles are of several kinds: (i) permanent globules of liquid (Actinophrys, Fig. 18), (2) contractile vacuoles (Ameba, Fig. 9, 2), and (3) food vacuoles (Paramecium, Fig. 33,7.1'.). Many PROTOZOA possess plastids; these are usually bodies of starchy food material, or colored bodies called chromatopkores, such as occur in Euglena. Besides these, many other substances may be. present, such as food material, indigestible matter, oil drops, grains of sand, etc. Physiology. - - METABOLISM. - - The food of PROTOZOA con- sists of organic matter both vegetable and animal. BACTERIA, diatoms, and other PROTOZOA form a large part of the bill of fare. 68 COLLEGE ZOOLOGY Such species as Euglena do not ingest solid food, but manufacture it by means of chlorophyll. Usually some structure is present which aids in the ingestion of food, but in the RHIZOPODA, like Ameba, there is no mouth, and food is engulfed at any point on the surface. The flagella of many flagellates and the cilia of ciliates draw or drive food par- ticles toward the mouth and down into the gullet at the end of which a food vacuole is formed (Paramecium, Fig. 33, /. v.). The SUCTORIA (Fig. 43, D) capture their prey with their tentacles and suck the contents into the body. Parasitic PROTOZOA take food directly through the surface of the body. Digestion takes place in the food vacuoles, which are really temporary stomachs. The surrounding protoplasm secretes fer- ments which enter the vacuoles and dissolve certain food sub- stances. Undigested matter is cast out at any point (Ameba), or at a particular spot (Paramecium), or through a definite anal opening (Stentor). Digested food passes out into the cytoplasm and is assimilated, i.e. is transformed into protoplasm. Figure 6 indicates that oxygen is necessary before life activities can be carried on, and carbon dioxide is given off. This is respiration. The oxygen is taken in through the body- wall. It combines with protoplasm, i.e. oxidation takes place. Free energy is a result of this oxidation, and carbon dioxide and other waste matter in solution are by-products. These by-products pass out through the body-wall, and probably by way of the contractile vacuole. The contractile vacuole may therefore be called a primitive excretory organ. From the above discussion it may be concluded that the PRO- TOZOA carry on many of the activities characteristic of the higher organisms without the aid of the systems of organs we usually associate with these functions. Behavior. - - LOCOMOTION. - - Protozoa move from place to place either by creeping over the surface of objects (Ameba, Fig. 9; Stylonychia, Fig. 43, B), or by free swimming. The loco- motor organs are pseudopodia, flagella, and cilia. In some PRO- PHYLUM PROTOZOA 69 TOZOA muscle fibrils (myonemes) are present just beneath the cuticle (Stcntor, Fig. 43, .1; Vorticclla, Fig. 43, C); these are capable of contraction and can change the shape of the animal. In the stalk of Vorticclla the muscle fibrils are agents for moving the bell from place to place. REACTIONS TO STIMULI. - - Brief accounts have been given of the reactions of Ameba (p. 35), Euglena (p. 43), and Paramecium (p. 56) to stimuli. It has been shown that these minute organ- isms are capable of spontaneous activities and respond to a num- ber of different external stimuli, which are changes in their en- vironment. These responses are carried on without the help of a nervous system. The study of the behavior of the lower organisms has become quite prominent within the past decade and has led a prominent investigator in this field to the follow- ing conclusion. " All together, there is no evidence of the exist- ence of differences of fundamental character between the be- havior of the Protozoa and that of the lower Metazoa. The study of behavior lends no support to the view that the life ac- tivities are of an essentially different character in the Protozoa and the Metazoa. The behavior of the Protozoa appears to be no more and no less machine-like than that of the Metazoa; similar principles govern both." (Jennings, Behavior of the Lower Organisms, p. 263.) Reproduction. - - The usual method of reproduction in the PROTOZOA is that of binary division. This occurs in most of the types discussed in the preceding pages (Ameba, Euglena, Para- mecium, etc.). During binary division the body of the PRO- TOZOON divides into two approximately equal parts, the daughter-cells. Binary division is frequently interrupted by conjugation as in Paramecium (p. 59). When the division of the PROTOZOON is unequal, the process is spoken of as budding or gemmation. The parasitic RHIZOPOD, Entameba histolytica (p. 70), reproduces in this way. A third method of reproduc- tion is by the formation of spores (Ameba, p. 33; Monocystis, P- 49; Fi g- 3 2 )- 70 COLLEGE ZOOLOGY 6. PATHOGENIC PROTOZOA The PROTOZOA that cause diseases are said to be pathogenic. One of the best known of these is the malarial fever parasite, Plasmodium. This species belongs, with many other important parasites, to the class SPOROZOA, but all protozoan parasites do not belong to this class. There are many injurious parasites in each of the other classes, and these affect both man and other animals. The importance of pathogenic PROTOZOA has but re- cently been recognized, and, although a vast amount of work has been done in this field, still comparatively little is known about them. A few examples of those affecting man are described in the following paragraphs. Rhizopoda. - - Minute ameba-like organisms, named Enta- meba histolytica, are the cause of amebic dysentery, and are always found in the alimentary canal of patients suffering from this disease. They cause ulcers and other lesions producing enteritis. Other ameboid organisms, which are probably referable to the RHIZOPODA, accompany hydrophobia and may destroy the nerve cells of the brain. In smallpox similar ameboid organisms attack and destroy the epithelial cells of the skin. Whether or not these structures are the direct cause of the disease mentioned or are merely accessories is not known, but they are to be looked upon as dangerous until they are proved to be harmless. FIG. 44. Trypanosoma gam- Mastigophora. - - The Trypano- biense the parasitic FLAGELLATE SQma j s aj . thg present t i me t h e which causes sleeping sickness. > / (From Calkins.) most widely studied of all parasitic MASTIGOPHORA that affect man. In certain parts of tropical Africa they cause the disease called trypanosomiasis, commonly known as sleeping sickness. Try- panosomes are also parasitic in rats and other animals. The species affecting man is named Trypanosoma gambiense (Fig. 44) . PHYLUM PROTOZOA It is carried from one person to another by a certain species of tsetse- fly, Gloss ina palpalis (Fig. 45). The parasite, after gain- ing access to the blood of a human being, multiplies with re- markable rapidity. The nervous system of the patient is af- fected either directly or by a poison secreted by the parasites. The disease may last several months or even years. Irregular FIG. 45. Glossina palpalis, the tsetse fly, which carries the germs of sleeping sickness. (From Calkins.) fever soon follows infection, and later general debility sets in. The victim exhibits an increasing tendency to sleep, gradually wastes away, and finally dies. Sporozoa. --Of the SPOROZOA which affect man, the malarial fever parasite is the most important (pp. 50-52). Infusoria. - - Two species of parasitic CILIATES which are found in the intestine of human beings are thought by some investi- gators to be important in catarrhal inflammation of the intestine. They are Balantidium coli and B. minutum. These parasites 72 COLLEGE ZOOLOGY are sometimes found within the mucous lining and sometimes inside of the muscular layer of the alimentary canal, and, al- though they have not been proved to be the cause of any disease, they are so constantly present in dysentery patients as to be looked upon as dangerous. CHAPTER III AN INTRODUCTION TO THE METAZOA THE METAZOA (Gr. meta, beyond; zoon, animal) are animals consisting of many cells. These cells are not all alike, as in the colonial PROTOZOA, but are separated into groups according to their structure and functions. Although every METAZOON be- gins its existence as a single cell, in the adult stage there are many cells, and one kind of cell cannot exist without the presence of the other kinds of cells; that is, the cells are not independent as in the PROTOZOA, but are dependent upon one another. This is the result of the division of labor among the cells. There is no sharp line between the METAZOA and the PROTOZOA. The colonial PROTOZOA are many-celled animals, and, as we have seen (p. 46), Volwx (Fig. 27) consists of cells which are made interdependent by protoplasmic connections. There are a con- siderable number of animals which are intermediate between the PROTOZOA and the METAZOA, but, on the whole, the two groups are fairly well defined. i. GERM-CELLS AND SOMATIC CELLS There are two chief kinds of cells in all the METAZOA, germ- cells (Fig. 46, A, B} and somatic cells (Fig. 46, C-G). The germ- cells, like those in Volwx (Fig. 27, a simple sponge . OSCj sidered an individual sponge. div > sidc branches. (From Lankester's -.-. . . Treatise on Zoology.) It a branch is examined under a microscope, it will be found to contain a large number of three-pronged (triradiate) spicules, which are embedded in the soft tissue of the body-wall (Fig. 53) ; these serve to strengthen the body and hold it upright. The application of acid results in the dissolution of these spicules and the production of an effervescence, thus proving them to be composed of cal- FIG. 53. Le ucosolema, a simple sponge. View of c i um Carbonate, a branch showing the sieve-like membrane (i) which The body- wall is stretches across the osculum. The lower part shows n- t i^ t 'f spicules only. (From Shipley and MacBride, after Minchin.) difficult to study 94 COLLEGE ZOOLOGY even under the best conditions. It is made up of two layers of cells: an outer layer, the dermal epithelium, and an inner layer, the gastral epithelium. These layers, as will be shown later (p. 104), are not comparable to the ectoderm and entoderm of the CCELENTERATA and other METAZOA. Between these two layers is a jelly-like substance similar to the mesoglea of Hydra (p. 109) in which are many ameba-like wandering cells. The gastral epithelium is peculiar, since it consists of a single layer of collar cells, the \.~n choanocytes (Fig. 54), which resemble the similar cells of the choanoflagellate PROTOZOA (Fig. 29). The flagella of these collar cells FIG. 54. - - A beat constantly, creating a current of water, single collar cell jf a Y\\.\\Q coloring matter is placed in the water. of Leucosolenia. , " H, nucleus. (From it will be drawn into the animal through minute the Cambridge i ncurren l p ores the OStlO, (Fig. CO, A, p) , ill the Natural History, after Bidder.) body-wall and will pass out through the openings in a sieve-like membrane stretched across the osculum (Fig. 53, /). The osculum is therefore the cxhalant opening, and not the mouth, as a casual examination might lead one to believe. The course of the current of water in such a sponge is shown by arrows in Figure 59, A. The presence of the incurrent pores suggested the name PORIFERA for members of this phylum. 2. ANATOMY AND PHYSIOLOGY OF GRANTIA Grantia (Fig. 55) is also known as a simple sponge, though it is more complex than Leucosolenia. It lives in the salt water along the sea-coast and is permanently attached to the rocks and piles just below the low-tide mark. It is shaped like a vase that bulges in the middle, and is about three-fourths of an inch long. Frequently buds occur near the base, and a small colony is formed. PHYLUM PORIFERA 95 Structure. -- A longitudinal section of Grantia (Fig. 56) shows that the body possesses a single cavity as in Leucosolenia, but the body wall is much thicker. This condition has been brought about by the folding of the wall of a larval stage which resembles Leucosolenia, resulting in the production of a series of parallel canals. Part of these are incurrent canals and open to the outside (Fig. 59, B, inc) ; the rest open into the gastral cavity (G.C.), are lined with choanocytes (Fig. 54), and are called flagellated chambers or radial canals (Fig. 59, B,/.c). The area covered by collar cells is enormously increased in this way (compare the black layers in Fig. 59, A and B). Water enters the body of Grantia as shown by arrows in Figure 59, B, by way of the incurrent canals (inc.) ; from these it passes through pores, called prosopyles (pr.p), into the radial canals (fl.c), then through the apopyles (ap.p) into the gastral cavity (G.C.), and finally out of the osculum (osc.~). As in Leucosolenia, Grantia possesses an outer dermal layer of cells, an inner gastral epithelium made up of collar cells which line the radial canals, and a middle jelly-like substance in which are a number of wandering ameboid cells. The last- named cells are considered by some authorities equivalent to the mesoderm of higher animals, but this is probably not the case. The skeleton of Grantia consists of calcareous spicules, of which there are four varieties: (i) long, straight mona.wn rods guarding the osculum, (2) short, straight monaxon rods surround- ing the incurrent pores, (3) triradiate spicules always found em- bedded in the body-wall, and (4) T-shaped spicules lining the gastral cavity ; four- and five- rayed spicules may also be found. FIG. 55. A simple sponge. (After Minchin.) COLLEGE ZOOLOGY Spicules are built up within cells called scleroblasls, which form part of the inner stratum of the dermal layer. Physiology. -- Grantia lives upon the minute organisms and small particles of organic matter that are drawn into the incur- rent canals by the current of water produced by the beating of the collar-cell flagella. The majority of 1 the 1 food particles are en- gulfed by the collar cells. Digestion, as in the PROTOZOA, is infra-' cellular, food vacuoles being formed. The dis- tribution of the nutri- ment is accomplished by the passage of digested food from cell to cell, aided by the ameboid wandering cells of the middle layer. Excretory matter is discharged through the general body surface, assisted probably by the ameboid wandering cells, and possibly by the collar cells, also. Respiration likewise takes place, in the ab- sence of special organs, through the cells of the body- wall. Reproduction. - - Reproduction in Grantia takes place by both sexual and asexual methods. In the latter case, a bud arises near the point of attachment, finally becomes free, and takes up a separate existence. The sexual reproductive cells lie in the jelly-like layer of the FIG. 56. A simple sponge, Sycon. The right-hand member of the colony is shown in longitudinal section. ip, incurrent pores; o, osculum. (From Parker and Haswell.) PHYLUM PORIFERA 97 body-wall. Both eggs and sperms occur in a single individual; i.e. Grantia is monoecious or hermaphroditic. The development of the fertilized egg has been observed in Sycon (Fig. 57) and is probably similar to what occurs in Grantia. The egg (a) seg- FIG. 57. Development of a simple sponge, Sycon. a, ovum ; b, c, ovum segmented; d, blastula; e, amphiblastula; f, commencement of invagination; g, gastrula attached; h, i, young sponge. (From Parker and Haswell, after Schulze.) 98 COLLEGE ZOOLOGY ments by three vertical divisions into a pyramidal plate of eight cells (b, c). A horizontal division now cuts off a small cell from the top of each of the eight, the result being a layer of eight large cells crowned by a layer of eight small cells. The cells now be- come arranged about a central cavity, producing a blastula-like sphere (d) . The small cells multiply rapidly and develop flagelia, while the large cells become granular. The small cells are now partially grown over by the others, forming a structure called the amphiblastula (e). The mass of cells then becomes disc-shaped by the pushing in of the flagellated , cells (f). Two layers are thus formed between which the jelly-like middle layer arises. The invaginated side soon becomes attached (g) , and the embryo lengthens into a cylinder, at the distal end of which an opening, the osculum, appears (h). In the meantime, spicules arise in the body -wall. 3. THE FRESH- WATER SPONGE SPONGILLA The fresh-water sponge lives in ponds and streams and may be found attached to the under surface of rocks, dead leaves, or . sticks. It forms incrustations a fraction of an inch thick or compact masses, and is gray or green in color. The structure of Spongilla is shown in Figure 59, C. The canal system is more complicated than that of either Leucosolenia or Grantia. The choanocytes are restricted to flagellated chambers (C). This is the FIG. 58. Spongilla. A single gemmule, seen in rkagoH type, and there are three distinct section, showing the thick ^ ^ th j g g stem: (l ) the water pasges wall with its opening, J and the central mass of through the dermal ostia (DP}, and, by germinal cells (From f incurrent canals (/#) reaches ( 2 ) Weysse, after a Leuckart- J Nitsche wall-chart.) a number of small chambers (C) lined with choanocytes, thence it is carried through (3) an excurrent canal (Ex) to the gastral cavity (PG), and finally out of the osculum (0). PHYLUM POR1FERA 99 Spongilla and several marine sponges have a peculiar method of reproduction by the formation of gem mutes. A number of germinal cells in the middle layer of the body-wall gather into a ball and become surrounded by protecting spicules. These gemmules (Fig. 58) are formed in the autumn just before the death of the adult sponge. In the spring they develop into new sponges. They are of value in carrying the race through a period of adverse conditions, such as the winter season. 4. SPONGES IN GENERAL (i) Morphology. - - EXTERNAL FEATURES. - Leucosolenia, Grantia, and Spongilla'ka.ve served as types of the Phylum PORI- FERA, but other sponges vary markedly from these both in form and in structure. In many cases the character of the object to which sponges are attached causes them to assume exceedingly irregular shapes, the rocks being frequently incrusted by in- definite masses of spongy tissue. The habit of growth of many sponges is responsible for their shape. Some are branched like trees, or form a network; others are fan-shaped, cup-shaped, or dome-shaped. Some sponges are no larger than a pinhead; others are over five feet high. Most calcareous sponges are white or gray, but others may be brilliantly colored and even iridescent, exhibiting all the hues of the rainbow. CANAL SYSTEMS. - - There are three principal types of canal systems exhibited by sponges: (i) ascon, (2) sycon, and (3) rJiagon. That of Leucosolenia (p. 94, and Fig. 59, A) is of the ascon type, and that of Grantia (page 95, and Fig. 59, B) is of the sycon type. Some sponges, like Span gill a, have a very compli- cated canal system; this, the rhagon type, is diagrammatically shown in Figure 59, C, and described on page 98. SKELETAL SYSTEMS. - - The skeletons of sponges are composed of spicules of carbonate of lime or silicon, or of fibers of spoil gin. A few small species have no skeletons. Some of the more com- mon types of spicules are shown in Figure 60; they are (i) monaxon (a, b), (2) tetraxon (c, d), (3) triaxon (e), and (4) poly- IOO COLLEGE ZOOLOGY axon (f). Spicules with three rays like most of those in Leuco- solenia and Grantia are called triradiate. The skeletons of the > i. ",****.. B DP In FIG. 5g. - - Types of canal systems of sponges. A, Ascon type. B, Sycon type. C, Rhagon type (Spongilla). The arrows indicate the direction of the current of water. The thick black line in A and B represents the gastral layer ; the dotted portion, the dermal layer, ap.p, apopyle; fl.c, flagellated chamber; GC, gastral cavity (cloaca); in.c, incurrent canal; osc, osculum ; pr.p, pro- sopyle. C, flagellated chambers ; DP, dermal pores ; Ex, excurrent canals ; GO, openings of excurrent canals; In, incurrent canals; O, osculum; PG, gastral cavity; SD, subdermal cavity. (A and B, from Minchin in Lankester's Treatise; C, from Parker and Haswell, after a Leuckart-Nitsche wall-chart.) horny sponges, of which the common bath sponge is an example, are made up largely of fibers of spongin (Fig. 61). This sub- stance, which is chemically allied to silk, is secreted by cells of the dermal layer called spongoblasts. PHYLUM PORIFERA 101 HISTOLOGY. -- The sponges are among the simplest of the ETAZOA with regard to the differentiation of their cells, but they seem quite complex when compared with the PROTOZOA. a FIG. 60. Types of sponge spicules. a, b, monaxon; c, d, tetraxon; e, triaxon; f, polyaxon. (From the Cambridge Natural History.) FIG. 61. Piece of net- work of horny fibers from the bath sponge, Eitspongia. (From Sedgwick.) The cells of sponges may be separated into three groups: (i) those of the dermal layer, (2) those of the gastral layer, and (3) the ameboid cells in the jelly between the dermal and gastral layers. The classes of cells and the layers to which they belong are shown in Table III. TABLE III CLASSES OF CELLS FOUND IN SPONGES A. Dermal Layer B. Gastral Layer C. Middle Re- gion I. Epithelial stratum II. Porocytes III. Skeletogenous stratum IV. Gastral epithelium V. Wandering cells VI. Reproductive cells 1. Epithelial cells 2. Contractile cells 3. Gland cells 4. Spongoblasts 5. Pore cells 6. Scleroblasts 7. Fiber cells 8. Choanocytes 9. Ingestive cells 10. Nutritive cells 1 1 . Storage cells 12. Gemmule cells 13. Sexual cells I0 2 COLLEGE ZOOLOGY (2) Physiology. -- METABOLISM. -- The metabolic processes in all sponges are essentially similar to those of Grantia (p. The current created by the beating of the flagella of the choano- cytes brings organic food particles and fresh water into the canals. Most of the food particles are engulfed by the choanocytes and digested within the cells, as in PROTOZOA. The processes of ex- cretion and respiration are carried on by the cells of the body- wall. There is, on the whole, not much difference between the metabolic activities of sponges and those of PROTOZOA. BEHAVIOR. - - Very little is known about the behavior of sponges. The larvae, as stated before, are ciliated and swim through the water, but the adults are all attached to the sea- bottom, to rocks, or to piles, etc. Parker has shown that Stylo- tdla heliophila, of the order MONAXONIDA, responds in a prim- itive way to certain stimuli. Among the reacting elements are fiber-like cells, myocytes, arranged about the osculum, and con- tractile cells lining certain internal cavities. The choanocytes are able to extend and contract their collars and to beat the water with their flagella. No nervous elements have been discovered. The reactions of Stylotella may be briefly stated as follows: - The oscula close in quiet sea-water, on exposure to air, on in- jury to neighboring parts, and in weak solutions of ether and cocaine; they open in currents of sea- water, in fresh water, and in weak solutions of atropine. The ostia close on injury to neighboring parts and in weak solutions of ether and cocaine; they open in dilute sea- water, and in weak solutions of atropine. The choanocyte currents cease in dilute sea- water, at high temperatures, and in weak solu- tions of ether and chloroform. There is very little, if any, trans- mission of stimuli, and the reactive organs respond only to direct stimulation. Investigators look to the lowly organized, many-celled animals for the key to the origin of the nervous system, and the condition in sponges seems to show that muscles, " as represented by the sphincters of sponges, were the first of the neuromuscular organs PHYLUM PORIFERA 103 FIG. 62. Venus' flower-basket. The skeleton of a sponge, Eupleclella. (From Weysse.) to appear." Sense cells are supposed to have developed next as we find them in ccelenterates (p. 112), and finally a central organ was added, completing the neuromuscular mechanism as it exists in higher METAZOA. (3) Reproduction. - - Reproduction is either asexual or sexual. By the asexual method there are produced buds and gemmules. Buds may be set free to take up a separate existence, or may remain attached to the parent sponge, aiding in the formation of a complex assemblage of individuals. Gemmules are formed as de- scribed in Spongilla (p. 99). In sexual reproduction the eggs and spermatozoa are m FIG. 63. The bath sponge, Euspongta derived as in SyCOn (p. 96) offirinalis. (From Lankester, after Schulze.) 104 COLLEGE ZOOLOGY from ameboid wandering cells in the middle layer. A ciliated 'arva is produced from a holoblastic egg. This larva swims about for a while, thus effecting the dispersal of the species, then becomes fixed and passes through many changes, finally developing ostia and an osculum which are necessary for the nutritive processes and growth. One very important peculiarity in sponge embryology is this (Fig. 64): the flagellated cells of the larva do not become the outer Section (dermal) epithelium as do the flagellated cells of the larva of a of the larval ccelenterate (planula, Fig. 73, C, but produce the gastral layer of terior granular cells, choanocytes; and the inner cells do not be- come the inner (gastral) epithelium, as do the similarly situated cells in the ccelen- terate planula, but produce the dermal layer. This is shown in Table IV. TABLE IV THE DEVELOPMENT OF A SPONGE (CLATHRINA) Flagellated cells . . . Gastral layer Ameboid inner cells . . Dermal layer Ovum-Blastomeres Posterior granular cells j Wandering cells (Fig. 64, p.g.c.) \ Sexual cells It therefore seems impossible to homologize the ectoderm and entoderm of ccelenterates and other METAZOA with the layers in the sponge larva, since the outer layer (ectoderm?) of the latter becomes the inner layer (entoderm?) of the adult sponge. The outer layer is consequently termed " dermal epithelium " instead of " ectoderm," and the inner, the " gastral epithelium " instead of " entoderm." (4) Classification. - - PORIFERA. - - SPONGES. - - Diploblastic, radially symmetrical animals; number of antimeres variable; body- wall permeated by many pores, and usually supported by a skeleton of spicules or spongin. PHYLUM PORIFERA 105 CLASS I. CALCAREA. Marine species, mostly white or gray, living in shallow water; spicules of carbonate of lime, either monaxon (Fig. 60, a, b) or tetraxon (Fig. 60, c, d.); flagellated chambers large. Order i. Homocoela. Gastral layer continuous. Example: Lcucosolenia (Fig. 52, Fig. 59, A). Order 2. Heteroccela. Gastral layer discontinuous and re- stricted to flagellated chambers. Example: Grantia (Fig. 55, Fig. 59, B). CLASS II. HEXACTINELLIDA. Deep-sea sponges ; spicules triaxon (Fig. 60, e) , of silicon ; canal system with thimble-shaped chambers. Example: Euplectella aspergillum, Venus' flower- basket (Fig. 62). CLASS III. DEMOSPONGLE. Skeleton of silicious spicules, not triaxon, or with spongin, or with both spicules and spongin, canal system derived from rhagon type (Fig. 59, C) ; most highly organized of phylum ; majority of existing sponges. Order i. Tetraxonida. Typically with tetraxon spicules, Example: Geodia. Order 2. Monaxonida. With monaxon (Fig. 60, a, b), but no tetraxon spicules (c, d). Example: Spongilla (Fig. 59, C). Order 3. Keratosa. Main skeleton of spongin. Example: Euspongia, the bath sponge (Fig. 63). (5) The Position of Sponges in the Animal Kingdom. - - As stated at the beginning of this chapter, sponges are considered many-celled animals. They were formerly, and are even now, placed by some authors in a phylum with the ccelenterates (Chapter V). They differ from the ccelenterates and other METAZOA so widely in certain important characteristics that most zoologists are inclined to separate them from the METAZOA and call them PARAZOA (see diagram, p. 25). Sponges differ from ccelenterates in the presence of choano- cytes, ostia, and oscula, in their unique method of feeding, in the germ-layers, which are apparently reversed in position (p. 104), and in the absence of a mouth and nematocysts (Fig. 66). The 106 COLLEGE ZOOLOGY choanocytes of sponges recall the choanoflagellate PROTOZOA (p. 47), and it is not improbable that they may have evolved from this group. Certain colonial choano flagellates, e.g. Protero- spongia (Fig. 29) resemble what we might imagine to have been the ancestor of the sponges. (6) The Relations of Sponges to Other Organisms and to Man. - Sponges are used as food by very few animals, since they are pro- tected by spicules and by excretions of poisonous ferments mak- ing them distasteful. Nudibranch mollusks (Chap. XII) feed on them to a certain extent. The cavities of sponges offer shel- ter to many animals, especially CRUSTACEA and ccelenterates; this may lead to a sort of partnership called commensalism. For example, certain hermit crabs protect themselves from attack by surrounding their shells with obnoxious sponges. Oysters and other bivalves are often starved by sponges which cover their shells and take away their food supply, and oyster cultur- ists often prevent this by growing the bivalves in frames which are pulled up during a rain, thus killing the sponges with fresh water. The origin of flint is in part due to the activities of sponges. It has been estimated that to extract one ounce of silicious spicules at least a ton of sea water must pass through the canal system of the sponge. The spicules aid in the formation of flint, this substance being always associated with the remains of sponges, RADIOLARIA (p. 40), and other organisms having silicious skele- tons. Of the commercial sponges may be mentioned the beautiful skeleton of Venus' flower-basket, Euplectclla (Fig. 62), which is obtained chiefly in the Philippine Islands, and the common bath sponge, Euspongia (Fig. 63), and others, which are especially grown for market in some localities. The best bath sponges come from the Mediterranean coast, Australia, the Bahamas, Florida, and the north coast of Cuba. They are gathered by means of long hooks, by divers, or by dredging. They are al- lowed to decay, are washed, dried, and then sent to market. PHYLUM PORIFEKA I O y The depletion of the sponge supply by unwise fishing has re- sulted in an attempt to regulate the industry by governmental control. Sponge culture is now carried on successfully in Italy and Florida. Perfect specimens are cut into pieces about one inch square, and " planted " on stakes on clean, rocky bottoms free from cold currents. These grow into marketable size in five or six years. CHAPTER V PHYLUM CCELENTERATA THE Phylum CCELENTERATA (Gr. koilos, hollow; enter on, intestine) includes a great number of aquatic animals, mostly marine, very few of which ever come to the notice of persons who do not visit the sea-shore or are not especially interested in natural history. As in the case of the sponges, many species of ccelenterates, the corals, are known because of the beautiful skeletons they construct. The three classes of ccelenterates are as follows : - CLASS I. HYDROZOA (Gr. hudra, a water serpent; zo'on, an animal), fresh- water polyps, hydroid zoophytes, many of the small medusae or jelly fishes, and a few stony corals; CLASS II. SCYPHOZOA (Gr. skuphos, cup; zo'on, animal), most of the large jelly fishes; and CLASS III. ANTHOZOA (Gr. anthos, a flower; zo'on, animal), (Actinozoa), sea-anemones, most stony corals, sea-fans, sea-pens, and precious corals. A simple member of the CCELENTERATA and one that is com- mon in fresh water is the polyp known as Hydra. A study of this little animal will serve to illustrate ccelenterate charac- teristics and will enable one to understand the more complex species belonging to this phylum. i. THE FRESH-WATER POLYP HYDRA Hydra fusca is abundant in ponds and streams, where it may be found attached by one end to aquatic vegetation. Hydras are easily seen with the naked eye, being from 2 to 20 mm. in \ 108 PHYLUM CCELENTERATA 109 length. They may be likened to a short, thick thread unraveled at the unattached, distal end. Morphology. - - EXTERNAL FEATURES. - - The body of Hydra is really a tube usually attached by a basal disk at one end, and with a mouth opening at the distal or free end. Around the mouth are arranged from six to ten smaller tubes, closed at their outer end, called tentacles (Fig. 65, /). Both the body and ten- tacles vary at different times in length and thickness. One or more buds (Fig. 65, b) are often found extending out from the body, and' in September and October reproductive organs may also appear. The male organs (testes, Fig. 65, y.t, m.t) are con- ical elevations on the distal third of the body; the female organs (ovaries, Fig. 65, y.e, m.e) are knoblike projections near the basal disc. STRUCTURE (Fig. 65).-- Hydra is a diploblastic animal con- sisting of two cellular layers, an outer thin, colorless layer, the ectoderm (ec.) and an inner layer, the entoderm (en.}, twice as thick as the outer, and containing the brown bodies which give Hydra fusca its characteristic color. Both layers are composed of epithelial cells. A thin space containing a non-cellular jelly- like substance, the mesoglea (mes.}, separates ectoderm from entoderm. Not only the body-wall, but also the tentacles, pos- sess these three definite regions. The body, with the exception of the basal disc, is covered by a thin, transparent cuticle. Both body and tentacles are hollow, the single central space being known as the gastrovascular cavity (gv.c.). The ectoderm is primarily protective and sensory, and is made up of two principal kinds of cells: (i) epit/ieliomuscular, and (2) interstitial. The former are shaped like inverted cones, and pos- sess long (up to .38 mm.), unstriped contractile fibrils at their inner ends; these enable the animal to expand and contract. The interstitial cells lie among the bases of the epitheliomuscular cells; they give rise to three kinds of nematocysts or stinging cells (Fig. 65, n; Fig. 66). Nematocysts are present on all parts of the body except the basal disc, being most numerous on the no COLLEGE ZOOLOGY tentacles. The interstitial cell in which the nematocyst develops is called a cnidoblast (Fig. 66); it contains a nucleus (mi) and develops a trigger-like process, the cnidocil (cnc), at its outer end, g b.d. FIG. 65. Diagram of a longitudinal section of Hydra, b, bud; b.d, basal disc; M, blastula; cc, ectoderm; en, entoderm; K, gastrula; gv.c, gastro- vascular cavity; hy, hypostome; m, mouth; m.c, mature egg; m.t, mature testis; n, nematocysts; p. b, polar bodies; /, tentacle; y.c, young egg; y.t, young testis. All the structures shown do not occur on a single animal at one time. but is almost completely filled by the pear-shaped nematocyst (ncm). Within this structure is an inverted coiled thread-like tube with barbs at the base. When the nematocyst explodes, PHYLUM CCELENTERATA III this tube turns rapidly inside out and is able to penetrate the tissues of other animals (Fig. 67, B; Fig. 68, A). The explosion is probably due to internal pressure produced by osmosis, and may be brought about by various methods such as the application of a little acetic acid or methyl green. Many animals when " shot " by nematocysts are immediately paralyzed and some- times killed by a poison called hypno- toxin which is injected into it by the tube. Two kinds of nematocysts smaller than that just described are also found in the ectoderm of Hydra. One of these is cylindrical and contains a thread without barbs at its base; the other is spherical and contains a barb- less thread which, when discharged, aids in the capture of prey by coiling around the spines or other structures that may be present (Fig. 68, B). Certain ectoderm cells of the basal disk of Hydra are glandular and secrete a sticky substance for the attachment of the animal. The enloderm, the inner layer of cells, is primarily digestive, absorptive, and secretory. The digestive cells are large, with muscle fibrils at their base, and flagella or pseudopodia at the end which projects into the gastrovascular cavity. The flagella create currents in the gastrovascular fluid, and the pseudopodia capture solid food particles. The glandular cells are small and without muscle fibrils. Interstitial cells are found lying at the base of the other entoderm cells. The mesoglea is an extremely thin layer of jelly-like substance situated between the other two layers. FIG. 66. Nematocysts of Hydra before and after dis- charge, cnc, cnidocil ; nem, nematocyst; nu, nucleus of cnidoblast; t, thread-like tube. (From Dahlgren and Kepner, after Schneider.) 112 COLLEGE ZOOLOGY From recent investigations it seems well established that Hydra possesses a nervous system, though complicated staining methods are necessary to make it visible. In the ectoderm there is a sort of plexus of nerve-cells connected by nerve- fibers with centers in the region of the mouth and foot. Sensory cells in the surface layer of cells serve as external organs of stimulation, and are in direct continuity with fibers from the nerve cells. Some of the nerve-cells send processes to the muscle fibers of FIG. 67. Nematocysts of Hydra and their action. A, portion of a ten- tacle showing the batteries of nemato- cysts ; cl, cnidocils. B, insect larva covered with nematocysts as a result of capture by Hydra. (From Jennings.) FIG. 68. -- The action of nematocysts. A, a nematocyst piercing the chitinous covering of an insect. B, nematocysts holding a small animal by coil- ing about its spines. (After Toppe in Zool. Anz.) the epitheliomuscular cells, and are therefore motor in function. No processes from the nerve-cells to the nematocysts have yet been discovered, though they probably occur. The entoderm of the body also contains nerve-cells, but not so many as are present in the ectoderm. Physiology. - - NUTRITION. - - Hydra lives on minute aquatic animals which come within reach of its tentacles. The nemato- cysts, and probably a secretion from the tentacles, paralyze the prey, while the viscid surface of the tentacle prevents it PHYLUM OELENTERATA 113 from escaping. Food is carried to the mouth by the bending over of the tentacle which captured it; other tentacles also assist. The mouth opens and slowly moves around the food, which is then forced down to the basal end of the gastrovascular cavity by the contraction of the body-wall behind it. Hydras will not capture prey or respond to food stimuli when they have recently been fed. Moderately hungry specimens will exhibit the characteristic food-taking reactions if both chemical and physical stimuli are applied at the same time, e.g., a piece of filter paper soaked in beef juice. A hungry animal will respond by making swallowing movements when a chemical stimulus alone is applied. Digestion takes place in the gastrovascular cavity and probably also within the entoderm cells. The gland cells of the entoderm secrete a fluid into the gastrovascular cavity ; this fluid dissolves the food. Digestion is aided by the currents set up by the flagella of the entoderm cells and by the churning resulting from the expansion and contraction of the body. Part of the food is evidently engulfed by the pseudopodia of the entoderm cells and undergoes intracellular digestion. The dissolved food is absorbed by the entoderm cells ; part of it, especially the oil glob- ules, is passed over to the ectoderm, where it is stored until needed. BEHAVIOR. - - Hydras are usually found attached to the bot- tom or sides of the aquarium, or to aquatic plants, or are sus- pended from the surface film of the water. The position of rest, with the body stretched out and the tentacles widely spread, allows the animal to obtain food from a considerable area. At intervals of several minutes an undisturbed Hydra, especially if hungry, will contract rapidly and then slowly expand in a new direction, as shown in Fig. 69. This brings it into a new part of its surroundings, where more food may be present. Finally, these spontaneous movements cease, and the animal moves to another place. Locomotion is known to be effected in three ways. Usually I 114 COLLEGE ZOOLOGY the animal bends over (Fig. 70, /) and attaches itself to the sub- stratum by its tentacles (2) ; the basal disc is then released and the animal contracts (j); the body then expands (4), bends over in some other direction and becomes attached (5) ; finally the tentacles are released and an upright position is regained (6). FIG. 6g. Spontaneous changes of positions in an undisturbed Hydra. Side view. The extended animal (i), contracts (2), bends to a new position (3), and then extends (4). (From Jennings.) This method of locomotion has been compared to that of the measuring-worm. At other times the animal uses its tentacles as legs, or glides along on its basal disc. Hydras react to mechanical stimulation, to light, temperature, and electricity. If a watch-glass containing a specimen is jarred, or the surface of the water agitated, a part or all of the body and tentacles contract ; this is the result of a non-localized mechanical stimulus. If the body or a tentacle is touched with a glass rod, the body or tentacles contract, depending on the strength of the stimulus. Changes in the intensity of the light cause Hydras to move PHYLUM CCELENTERATA about until they reach a region where the light is most favorable; this may be called their optimum. They find this optimum by the method of " trial and error," i.e. their movements are in- definite, all directions being tried until the proper conditions are encountered. In a well-lighted area they are most likely to secure the small animals that serve , as food, since these are also attracted by light. When subjected to heat, the trial and error method is likewise em- ployed; the animals escape if they chance to move into a cooler area, but perish if they remain in a heated region too long. The reactions of a hungry Hydra to food indicate that the physio- logical condition of the animal de- termines to a large extent the kind of reactions produced, not only spontaneously, but also by external stimuli. ' ' It decides whether Hydra shall creep upward to the surface FIG- 70. Hydra moving like ,. , , ,, . , a measuring worm. (From Jen- and toward the light, or shall sink ningS) after Wagner.) to the bottom; how it shall react to chemicals and to solid objects; whether it shall remain quiet in a certain position, or shall reverse this position and undertake a laborious tour of exploration." Reproduction. Hydra reproduces asexual! y by budding and by fission, and sexually by the production of eggs and spermatozoa. Budding (Fig. 65, 6) is quite common, and may easily be ob- served in the laboratory. The bud appears first as a slight bulge 'n the body-wall. This pushes out rapidly into a stalk, which soon develops a circlet of blunt tentacles about its distal end. The cavities of both stalk and tentacles are at all times directly connected with that of the parent. When full grown, the bud Il6 COLLEGE ZOOLOGY becomes detached and leads a separate existence. Sometimes the bud may begin to form other buds before it becomes de- tached from the parent animal. In this way a sort of hydroid colony is produced resembling that of certain marine ccelenterates like Obelia (Fig. 73). Fission is less common. The distal end of the animal divides first; then the body slowly splits down the center, the halves finally separating when the basal disc is sev- ered (Fig. 71). Hydras have also been found which bore buds reproducing in this manner. This method of multiplication must, however, be rare, since it is so seldom seen. Transverse fission has also been reported. The processes concerned in sexual reproduction are the pro- duction of spermatozoa and eggs, the fertilization of the egg, the development and hatching of the embryo, and the growth of the young larva. The sper- - I V I Hydm /A? rod i; " d r g by matozoa arise in the testis from longitudinal nssion. (After Koehtz in Zooi. Anz.) ectodermal interstitial cells (Fig. 65, y.t.}; they develop in long cysts (Fig. 65, m.t.) through the end of which they escape into the surrounding water. The eggs arise in the ovary from ectodermal interstitial cells (Fig. 65, y.e.). Usually only one egg develops in a single ovary. When a certain period of growth is reached, two polar bodies (Fig. 65, p.b.) are given off by the egg, which is then said to be mature (Fig. 65, m.e.). Fer- tilization occurs usually within two hours after the polar bodies have been formed. The cleavage of the egg is total and almost equal, a blastula (Fig. 65, bl) being formed with a distinct cavity, the blastoccel. A solid gastrula-like structure (Fig. 65, g) is produced by the filling up of the blastoccel with cells budded off from the blas- tula wall. The outer cells may be called ectoderm and the inner PHYLUM CCELENTERATA TI 7 cells entoderm. The ectoderm now secretes a thick chitinous shell covered with sharp projections. The embryo then separates from the parent and falls to the bottom, where it remains un- changed for several weeks. Then interstitial cells make their appearance. A subsequent resting period is followed by the breaking away of the outer chitinous envelope and the elongation of the escaped embryo. Mesoglea is now secreted by the ectoderm and entoderm cells; a circlet of tentacles arises at one end, and a mouth appears in their midst. The young Hydra thus formed soon grows into the adult condition. Regeneration. - An account of the phe- nomenon of regenera- tion is appropriate at FIG. 72. Regeneration and grafting in this place since the Hydra- A, seven-headed Hydra made by split- ting distal ends lengthwise. B, a piece of Hydra power OI animals to regenerating an entire animal. C, part of one restore lost parts was Hydra grafted upon another. (From Morgan, A, after Trembley ; B, after Morgan; C, after first discovered in Hydra King.) by Trembley in 1744. This investigator found that if Hydras were cut into two, three, or four pieces, each part would grow into an entire animal. Other experimental results obtained by Trembley are that the hypostome, together with the tentacles, if cut off, may produce a new individual ; that each piece of a Hydra split longi- tudinally into two or four parts, becomes a perfect polyp, and that when the head end is split in two and the parts separated slightly, a two-headed animal results (Fig. 72, A). Regeneration may be defined as the replacing of an entire organism by a part of the same. It takes place not only in COLLEGE ZOOLOGY Hydra, but in many other coelenterates, and in some of the rep- resentatives of almost every phylum of the animal kingdom. Hydra, however, is a species that has been quite widely used for experimentation. Pieces of Hydra that measure \ mm. or more in diameter are capable of becoming entire animals (Fig. 72, B). The tissues in some cases restore the lost p^arts by a mul- tiplication of their cells; in other cases, they are worked over directly into a new but smaller individual. Parts of one Hydra may easily be grafted upon another (Fig. 72, C). In this way many bizarre effects have been produced. Space will not permit a detailed account of the many interesting questions involved in the phenomenon of regeneration, but enough has been given to indicate the nature of the process. The benefit to the animal of the ability to regenerate lost parts is obvious. Such an animal, in many cases, will succeed in the struggle for existence under adverse conditions, since it is able to regain its normal condition even after severe injuries. Physiological re- generation takes place continually in all animals; for example, new cells are produced in the epidermis of man to take the place of those that are no longer able to perform their proper functions. Both internal and external factors have an influence upon the rate of regeneration and upon the character of the new part. Temperature, food, light, gravity, and contact are some of the external factors. In man, various tissues are capable of regen- eration; for example, the skin, muscles, nerves, blood-vessels, and bones. Lost parts are not restored in man because the growing tissues do not coordinate properly. Many theories have been advanced to explain regenerative processes, but none has gained sufficient acceptance to warrant its inclusion here. 2. CLASS I. HYDROZOA Hydra is the HYDROZOON which is most easily obtained for study, and by means of Hydra the principal characteristics of the ccelenterates have been illustrated. There are, however, a vast number of related animals that differ widely in form, structure, PHYLUM CCELENTERATA IIQ and habits. The two chief shapes assumed by the HYDROZOA are the hydroid, or polyp, like Hydra and Obelia (Fig. 73), and the jellyfish, or medusa, like Gonionemus (Fig. 74). There are many variations of each of these, and frequently one species may ex- hibit both conditions at different periods in its life-history. a. A Colonial Hydrozoon -- Obelia l Obelia (Fig. 73) is a colonial ccelenterate which lives in the sea, where it is usually attached to rocks, to wharves, or to Lami- naria, Rhodymenia, and other algae. It may be found in low water and to a depth of forty fathoms along the coast of northern Europe and from Long Island Sound to Labrador. Anatomy and Physiology. - - An Obelia colony consists of a basal stem, the hydrorhiza, which is attached to the substratum; this gives off at intervals upright branches, known as hydrocaidi. At every bend in the zigzag hydrocaulus a side branch arises. The stem of this side branch is ringed and is expanded at the end into a hydra-like structure, the hydra nth (Fig. 73, A). A single polyp consists of a hydranth and the part of the stalk be- tween the hydranth and the point of origin of the preceding branch. Full-grown colonies usually bear reproductive members (gonangid) in the angles where the hydranths arise from the hy- drocaulus (Fig. 73, A, 8, Q, id). The Obelia colony as just described and as shown in Fig. 73, A, resembles the structure that would be built up by a budding Hydra if the buds were to remain attached to the parent and in turn produce fixed buds. All of the soft parts of the Obelia colony are protected by a chitinous covering called the perisarc (Fig. 73, A, (5); this is ringed at various places and is expanded into cup-shaped hydro- theccR (Fig. 73, A, 7) to accommodate the hydranths, and into gonotheccB (Fig. 73, A, 10) to inclose the reproductive members. A shelf which extends across the base of the hydrotheca serves to support the hydranth. The soft parts of the hydrocaulus 1 Campanularia is similar to Obelia in most respects. 12O COLLEGE ZOOLOGY and of the stalks of the hydranths constitute the cvnosarc (Fig 73, A, 5), and are attached to the perisarc by minute projections The ccenosarcal cavities of the hydrocaulus open into those of medusa of Obelia. i mouth- , i onotheca B, free-swimming the branches and thence into the hydranths, producing in this way a common gastrovascular cavitv. A longitudinal section of a hydranth and its stalk (Fig. 73 A 3 7) shows the ccenosarc to consist of two layers of cells PHYLUM CCELEXTERATA 121 an outer layer, the ectoderm, and an inner layer, the entoderm. These layers are continued into the hydranth (Fig. 73, A, / and 2). The mouth (j) is situated in the center of the large knob- like hypostome, and the tentacles, about thirty in number, are arranged around the base of the hypostome in a single circle. Each tentacle is solid, consisting of an outer layer of ectoderm cells (/) and a single axial row of entoderm cells; at the extrem- ity are a large number of nematocysts. The hydranth captures, ingests, and digests food as in Hydra. The reproductive members arise, as do the hydranths, as buds from the hydrocaulus, and represent modified hydranths (Fig. 73, 8, 9, 10} . The central axis of each is called a blastostyle (8), and together with 'the gonothecal covering is known as the gonangium. The blastostyle gives rise to medusa-buds (Fig. 73, Q] which soon become detached (Fig. 73, B) and pass out of the gonotheca through the opening in the distal end. Some of the medusa of Obella (Fig. 73, B) produce eggs, and others produce spermatozoa. The fertilized eggs develop into colonies like that which gave rise to the medusas. The medusae provide for the dispersal of the species, since they swim about in the water and establish colonies in new habitats. The structure of a medusa (Gonioncmiis) will be described in sec- tion c of this chapter. The medusa of Obelia is shown in Figure 73, B; it is shaped like an umbrella with a fringe of tentacles (2) and a number of organs of equilibrium (5) on the edge. Hanging down from the center is the manubrium (/) with the mouth at the end. The gastrovascular cavity extends out from the cavity of the manubrium into four radial canals (4) on which are situated the reproductive organs (j). The germ-cells of the medusae of Obelia arise in the ectoderm of the manubrium, and then migrate along the radial canals to the reproductive organs. When mature, they break out into the water. The eggs are fertilized by spermatozoa which have escaped from other medusae. Cleavage is similar to that of Hydra, and a hollow blastnhi and solid gastmla-like structure are 122 COLLEGE ZOOLOGY formed. The gastrula-like structure soon becomes ciliated and elongates into a free-swimming larva called a planula (Fig. 73, C). This soon acquires a central cavity, becomes fixed to some object, and proceeds to found a new colony. b. Metagenesis Metagenesis is the alternation of a generation which repro- duces only asexually by division or budding with a generation which reproduces only sexually by means of eggs and spermato- zoa. This phenomenon occurs in other groups of the animal kingdom, but finds its best examples among the ccelenterates. Obelia is an excellent illustration of a metagenetic animal. The asexual generation, the colony of polyps (Fig. 73, A), forms buds of two kinds, the hydranths and the gonangia. The medusae (Fig. 73, B), or sexual generation, reproduce the colony by means of eggs and spermatozoa. The polyp and medusa stages are not equally important in all HYDROZOA; for example, Hydra has no medusa stage and Geryonia no polyp or hydroid stage. Various conditions may be illustrated by different HYDROZOA. In the following list, O represents the fertilized ovum, H, a polyp, M a medusa, m an inconspicuous or degenerate medusa, and h an inconspicuous or degenerate polyp. 1. H H O (Hydra). 2. H - - m O - - H - - m (Sertularia). 3. O H - - M O H - - M O (Obelia). 4. O~h--M--0~h--M~O (Liriope). 5. M--0 M--0 (Geryonia}. c. A Jellyfish or Medusa Gonionemus The structure of a hydrozoan jellyfish or medusa may be illus- trated by Gonionemus (Fig. 74). This jellyfish is common along the eastern coast of the United States. It measures about half an inch in diameter, without including the fringe of tentacles around the margin. In general form it is similar to the medusa of Obelia (Fig. 73, B). The convex or aboral surface is called PHYLUM CCELENTERATA 123 the exumbrella; the concave, or oral surface, the subumbrella. The subumbrella is partly closed by a perforated membrane called the velum. Water is taken into the subumbrellar cavity and is then forced out through the central opening. in the velum by the contraction of the body; this propels the animal in the opposite direction, thus enabling it to swim about. The tentacles, which vary in number from sixteen to more than eighty, are capable of considerable contraction. Near their tips are adhesive or suctorial pads at a point where the tentacle bends at a sharp angle. Hanging down into the subumbrellar cavity is the manubrium with the mouth at the end sur- rounded by four frilled oral lobes. The mouth opens into a gastrovascular cavity which consists of a central " stomach " and four radial canals. The radial canals enter a circumferential canal which lies near the margin of the umbrella. The cellular layers in Gonionemus are similar to those in Hydra, but the mesoglea is extremely thick and gives the animal a jelly- like consistency. Scattered about beneath the ectoderm are many nerve cells, and about the velum is a nerve ring. Sensory cells with a tactile function are abundant on the tentacles. The margin of the umbrella is supplied with two kinds of sense organs : (i) at the base of the tentacles are round bodies which contain pigmented entoderm cells and communicate with the circumfer- ential canal ; (2) between the bases of the tentacles are small out- growths which are probably organs of equilibrium and, therefore, statocysts. Muscle fibers, both exumbrella and subumbrella, are present, giving the animal the power of locomotion. Suspended beneath the radial canals are the sinuously folded reproductive organs or gonads. Gonionemus is dioecious, each FIG. 74. Goinonemus, a hydrozoan jelly- fish. (From Washburn, after Hargitt.) 124 COLLEGE ZOOLOGY individual producing either eggs or spermatozoa. These repro- ductive cells break out directly into the water, where fertilization takes place. A ciliated planula develops from the egg as in Obelia (Fig. 73, C). This soon becomes fixed to some object, and a mouth appears at the unattached end. Then four tentacles grow out around the mouth and the Hydra-like larva is able to feed (Fig. 75). Other similar Hvdra-likc larvae bud from its V walls. How the medusae arise from these larvae is not known, but it seems probable that a direct change from the hydroid form to the medusa occurs. /' FIG. 75. Hydralike stage in the development of Gonio- nemus. One of the tentacles is carrying a worm (\v) to the mouth. Tentacles in contracted state. (From the Cambridge Natural History, after Perkins.) d. Hydroid and Medusa Compared Although the medusae upon superficial examination appear to be very different from the polyps or hydroids, they are con- fmf rod cn:c FIG. 76. Diagrams showing the similarities of a polyp (A) and a medusa (B). circ, circular canal; eel, ectoderm; end, entoderm; ent. cav, gastrovascu- lar cavity; hyp, hypostome; mnb, manubrium; msgl. mesoglea; mth, mouth; nv, nerve rings; rad, radial canal; v, velum. (From Parker and Haswell.) PHYLUM CCELENTERA I'A 125 structed on the same general plan as the latter. Figure 76 illus- trates in a diagramatic fashion the resemblance between the polyp (A) and the medusa (B) by means of longitudinal sections. If the medusa were grasped at the center of the aboral surface and elongated, a hydra-like form would result. Both have sim- ilar parts, the most noticeable difference being the enormous quantity of mesoglea (tnsgl) present in the medusa. FIG. 77. Physdlia or Por- tuguese man-of-war, a colonial HYDROZOON. (After Agassiz.) FIG. 78. Diagram showing possible modifications of medu- soids and hydroids of a hydro- zoan colony of the order SIPHO- NOPHORA. e, gastrozooid with branched, grappling tentacle, /; , dactylozooid with attached tentacle, //; /, generative mcdu- soid; k, nectophores (swimming bells); /, hydrophyllium (cover- ing piece) ; m, stem or corm; n. pneumatophore. The thick black line represents entoderm, the thinner line ectoderm. (From Lankester's Treatise, after All- man.) 126 COLLEGE ZOOLOGY e. Polymorphism The division of labor among the cells of a METAZOON has al- ready been noted (p. 74). When division of labor occurs among the members of a colony, the form of the individual is suited to the function it performs. A colony containing two kinds of members is said to be dimorphic; one containing more than two kinds, polymorphic. Some of the most remarkable cases of polymorphism occur among the HYDROZOA. The " Portuguese man-of-war " (Fig. 77), for example, consists of a float with a sail-like crest from which a number of polyps hang down into the water. Some of these polyps are nutritive, others are tactile; some contain batteries of nematocysts, others are male repro- ductive zooids, and still others give rise to egg-producing me- dusae. Tables V and VI present briefly the various modifications that may occur among the members of colonial HYDROZOA. TABLE V POLYMORPHIC MODIFICATIONS OF THE MEDUSOIDS OF THE HYDROZOA NAME STRUCTURE FUNCTION Sexual medusoid Nectophore Hydrophyllium Pneumatophore Aurophore Like typical medusa of An- thomedusse (p. 128) or modified because of ar- rested development (Fig. 78, Without tentacles, manu- brium, and mouth (Fig. 78, A-) Shield shaped (Fig. 78, /) Air sac (Fig. 78, n) Ovoid Production of ova or spermatozoa Locomotion Protective Hydrostatic Unknown PHYLUM CCELENTERATA 127 TABLE VI POLYMORPHIC MODIFICATIONS OF THE HYDROIDS OF THE HYDROZOA NAME STRUCTURE FUNCTION Gastrozooid Dactylozooid Blastostylc \Vilh large mouth, nemato- cysls, and tentacle bear- ing nematocysts (Fig. 78, e, /) Without ' mouth ; with many .nematocysts and tentacle (Fig. 78, g, h) Without mouth or tentacles Ingestion of food Offense and defense Produces sexual me- dusoids by budding /. Reproduction in the Hydrozoa The methods of reproduction differ so widely among the HY- DROZOA that only a brief general account can be given here. Reference should be made to the descriptions for Hydra (p. 115), Obelia (p. 121), and Gonionemus (p. 123). Asexual reproduction is characteristic of some HYDROZOA and rare or absent in others. The most common method is by bud- ding (Hydra, p. 115, Fig. 65). The wall of the hydroid sends out a hollow protrusion which may become either a new hydroid or a medusa. Certain medusae also produce medusae by bud- ding. Fission is rare in hydroids (Hydra, p. 116, Fig. 71) and very rare in medusae. Sexual Reproduction. - - Both male and female germ-cells are rarely developed by a single individual as in Hydra (Fig. 65). Usually a colony produces either ova or spermatozoa, or these originate in different individuals of a single colony. Sometimes one blastostyle may give rise to both kinds of germ-cells. The development of the fertilized egg has already been described in Hydra (p. 116), Obelia (p. 121), and Gonionemus (p. 124). 128 COLLEGE ZOOLOGY g. Classification of the Hydrozoa The HYDROZOA may be distinguished from the SCYPHOZOA and ANTHOZOA by the absence of a stomodasum and mesen- teries (Fig. 84), and by the fact that their sexual cells are dis- charged directly to the exterior. In classifying the HYDRPZOA, both the hydroids and medusae are considered. The arrange- ment adopted in this book is from Fowler in Lankester's Treatise on Zoology. Order i. Anthomedusae. HYDROZOA usually with two forms of individuals, (i) non-sexual fixed hydroids, and (2) fixed or free-swimming sexual medusae. The perisarc (absent in Hydra) does not form hydrothecae around the polyp nor gono- thecae around the reproductive zooids. The reproductive or- gans are in the wall of the manubrium. The hydroids are usually colonial, with solid tentacles in one or more whorls. Examples: Hydra, Hydractinia, Eudendrium, Tubular ia. Order 2. Leptomedusae. - - HYDROZOA -with an alternation of non-sexual fixed hydroids and free or fixed sexual medusas. The hydrothecae and gonothecae are specialized portions of the perisarc. The sexual organs are on the radial canals. The medusae possess eye-spots (ocelli) and statocysts containing statoliths of ectodermal origin. Examples: Obelia (Fig. 73), Campanularia, Plumularia, Sertularia, Clytia. Order 3. Trachymedusae. HYDROZOA without alternation of generations, the medusa developing more or less directly from the egg. The sexual organs are on the radial canals. The medusae possess sensory organs called tentaculocysts, contain- ing entodermal statoliths which are usually enclosed in vesicles. Examples: Trachynema, Persa, and Liriope. Order 4. Narcomedusae. - - HYDROZOA without alternation of generations. The sexual organs are on the subumbral floor of the gastric cavity or gastric pouches. The tentaculocysts contain entodermal statoliths which are not enclosed in vesicles. Examples: Cunocantha, Cunina. PHYLUM CCELENTERATA I2Q Order 5. Hydrocorallinae. --Colonial HYDROZOA with alter- nation of generations and a massive or branching calcareous skeleton into which the nutritive polyps (gastrozooids) and protective polyps (dactylozooids) may be drawn. These HYDRO- CORALLINE are often called corals and are found on coral reefs, but they differ in structure from the true corals (Figs. 86-91). Example: Millepora. The staghorn coral (Millepora alcicornis} occurs in Florida. Order 6. Siphonophora. -- Colonial free-swimming HYDRO- ZOA with alternation of generations and highly modified (poly- morphic) hydroid and medusoid members. Example: Physalia (Portuguese man-of-war, Fig. 77). The hydroids and medu- soids of the SIPHONOPHORA may be modified as shown in Tables V and VI. 3. CLASS II. SCYPHOZOA Most of the larger jelly fishes belong to the SCYPHOZOA. They can be distinguished easily from the hydrozoan medusae by the presence of notches, usually eight in number, in the margin of the umbrella. They are called acraspedote (without velum or craspedon) medusae in contrast to the craspedote (with velum or craspedon) medusas of the HYDROZOA. The SCYPHOZOA range from an inch to three or four feet in diameter. They are usually found floating near the surface of the sea, though some of them are attached to rocks and weeds. There is an alterna- tion of generations in their life-history, but the asexual stage (the scyphistoma, Fig. Si, B) is subordinate. a. A Scyphozoan Jellyfish-- Amelia Aurelia (Fig. 79) is one of the commonest of the scyphozoan jellyfishes. The species A. flavidula ranges from the coast of Maine to Florida. Members of the genus may be recognized by the eight shallow lobes of the umbrella margin, and the fringe of many small tentacles. In structure Aurelia differs from Gonionemus and other COLLEGE ZOOLOGY hydrozoan medusae in the absence of a velum, the characteristics of the canal system, the position of the gonads, and the arrange- ment and morphology of the sense-organs. FIG. 79. Aurclia, ventral view with two of the oral arms (or. a) removed a.r.c, adradial canal; gon, gonads; i.r.c, interradial canal; mg.lp, marginal lappet; mth, mouth; or. a, oral arm; p.r.c, perradial canal; s.g..p, sub* genital pit; /, tentacles. (From Parker and Haswell.) The oral lobes or lips of Aurelia (Fig. 79, or. a) which hang down from the square mouth (;;;///) are long and narrow with folded margins. The mouth opens into a short gullet, which leads to the sqmewhat rectangular "stomach." A gastric pouch extends laterally from each side of the stomach. Within PHYLUM CCELENTERATA each gastric pouch is a gonad (Fig. 79, gon) and a row of small gastric filaments bearing ncmatocysts. Numerous radial canals (Fig. 79, a.r.c,i.r.c, p.r. c), some of .which branch several times, lead from the stomach to a circumferential canal at the margin. The gonads (gon) are frill-like organs lying in the floor of the gastric pouches. They have a pinkish hue in the living animal. The eggs or spermatozoa pass through the stomach and out of the mouth. The eight sense-organs of Aurelia lie between the marginal lappets (Fig. 79, mg. Ip) and are known as tentaculocysts. They fnd. Enb Can FIG. 80. Marginal sense-organ (tentaculo- cyst) of Aurelia in longitudinal section. A, superior or aboral olfactory pit ; B, in- ferior or adoral olfac- tory pit ; con, ento- dermal concretion (equilibrium); End,ei\- toderm; Enl, entoder- mal canal continued into the tentaculocyst; H, bridge between the two marginal lappets; oc, ectodermal pigment (ocellus); T, tentaculo- cyst. (From Lankes- ter's Treatise, after Eimer.) FIG. 81. Stages in development of Aurelia. A, hydra-tuba on stolon which is forming new buds at i and 2. B, later stage, or strobila, with strobilization beginning. C, strobilization more advanced. D, free-swimming Ephyra stage. E, same as D seen in profile. (From Shipley and MacBride, after Sars.) are considered to be organs of equilibrium. As shown in Figure 80, each tentaculocyst (T) is a hollow projection connected with the entodermal canal (Ent). It contains a number of calcareous concretions (Con) formed by the entoderm (End); and bears an ectodermal pigment spot, the ocellus (oc), which is sensitive to light. The tentaculocyst is protected by an aboral hood and by lateral lappets. Olfactory pits (A and B) are situated near by. 132 COLLEGE ZOOLOGY An alternation of generations occurs in Aurelia, but the hydroid stage is subordinate. The eggs develop into free-swimming planulae which become attached to some object and produce hydra-like structures, each of which is called a hydra-tuba (Fig. 81, A). This buds like Hydra during most of the year, but finally a peculiar process called stabilization takes place. The hydra-tuba divides into discs which cause it to resemble a pile of saucers (B); at this stage it is known as a strobila. Each disc develops tentacles (C), and, separating from those below it, swims away as a minute medusa called an ephyra (D, E). The ephyra gradually develops into an adult jellyfish. b. Classification of the Scyphozoa Four orders of SCYPHOZOA are usually recognized. The most obvious ordinal characteristics are the presence or absence of stomodreum and mesenteries, and the position of the tentacles and tentaculocysts. The stomodcenm or gullet is a passageway between the mouth and the gastrovascular cavity or " stomach"; it is often held in place by membranes called mesenteries. The position of the tentacles and tentaculocysts is described with regard to their relation to the four radial canals. Those at the ends of the radial canals are said to be perradial (Fig. 79, p.r.c) ; those halfway between two perradii are called interradial (i.r.c) ; and those halfway between a perradius and an interradius are termed adradial (a.r.c). Order i. Stauromedusae. -- SCYPHOZOA without tentacu- locysts; tentacles perradial and interradial; umbrella goblet- shaped; sometimes attached by the aboral pole; a stomodaeum is present, suspended by four mesenteries; no alternation of generations. Examples: Tessera (Fig. 82, A), Lucernaria. Order 2. Peromedusae. -- SCYPHOZOA with four interradial tentaculocysts; tentacles perradial and adradial; umbrella conical, with transverse constriction; a stomodasum is present suspended by four mesenteries; no alternation of generations. Example: Periphylla (Fig. 82, B). PHYLUM CCELENTERATA 133 Order 3. Cubomedusae. -- SCYPHOZOA with four perraclkil tentaculocysts; tentacles interradial; umbrella four-sided, cup- Gf FIG. 82. SCYPHOZOA. A, Tessera prince j>s, order STAUROMEDUS.E. B, Peri- phylla hyacinthina, order PEROMEDUS.E. C, Charybdca marsupialis, order CUBO- MEDUS.. G, gonads; Gf, gastral filaments; Ov, gonads; Rf, annular groove; Rk, marginal bodies; Rm, circular muscle; T, tentacles. (From Sedgwick, after Haeckel.) shaped; no alternation of generations. Example: Charybdea (Fig. 82, C). Order 4. Discomedusae. -- SCYPHOZOA with four or more perradial and four or more interradial tentaculocysts; umbrella disc-shaped; alternation of generations. Examples: Aurelia (Fig. 79), Pelagia, Cassia pea. 4. CLASS III. ANTHOZOA (ACTTNOZOA) There are no medusae among the ANTHOZOA. The polyps may be distinguished from those of the HYDROZOA by the pres- ence of a well-developed stomodaeum or gullet, which is fastened to the body-wall by a number of radially arranged membranes called ^mesenteries. Many of the polyps are solitary, but the majority produce colonies by budding. Most of the ANTHOZOA 134 COLLEGE ZOOLOGY s&jj$ij&L$ffiifisfa secrete a calcareous skeleton, known as coral. Two types are described in the following pages: (i) the sea-anemone, and (2) the coral polyp. a. A Sea-Anemone Metridium Metridium marginatum (Fig. 83) is a sea-anemone which fastens itself to the piles of wharves and to solid objects in tide- pools along the North Atlantic coast. It is a cylindrical ani- mal with a crown of hollow tentacles arranged in a number of circlets about the slit-like mouth. The tentacles as well as the body can be ex- panded and contracted, and the animal's position may be changed by a sort of creeping movement of its basal disc. The skin is soft but tough and contains no skeletal struc- tures. The tentacles capture small organisms by means of nematocysts, and carry the food thus obtained into the mouth. The beating of the ci/'a which cover the tentacles and part of the mouth and guild is necessary to force the food into the gastrovascular cavity. At each end of the gullet, or stomodaum (Fig. 84, 4), is a ciliated groove called the sipho- noglyphe (Fig. 84, 3). Usually only one or two siphonoglyphes are present, but sometimes three occur in a single specimen. A continual stream of water is carried into the body cavity through these siphonoglyphes, thus maintaining a constant supply of oxygenated water. If a sea-anemone is dissected as shown in Figure 84, the central or gastrovascular (ccdenteric) cavity will be found to consist of six radial chambers; these lie between the gullet or FIG. 83. A sea-anemone. (From Weysse, after Emerton.) PHYLUM CCELENTERATA 135 stomodaeum and the body-wall, and open into a common basal cavity. The six pairs of thin, double partitions between these chambers are called primary septa or mesenteries (Fig. 84, 10; FIG. 84. Mftriditim marginatum, a sea-anemone, partly cut away so as to show its structure. /, intermediate zone; 2, lip; j, siphonoglyphe; 4, gullet ; 5, inner end of gullet; 6, edge of mesentery; 7, cavity of a tentacle; 8, inner ostium; Q, outer ostium; 10, primary mesentery; n, muscle-band on primary mesentery; 12, abnormal tertiary mesentery; 13, secondary mesentery; 14, tertiary mesentery; 15, quaternary mesentery; 16, reproductive gland; 17, mesenterial filament; 18, opening for mesenterial filament. (Redrawn from Linville and Kelly.) Fig. 85, p.m). Water passes from one chamber to another through pores (ostia, Fig. 84, Q, 8) in these mesenteries. Smaller mesenteries project out from the body-wall into the chambers, 136 COLLEGE ZOOLOGY but do not reach the stomodaeum; these are secondary mesen- teries (Fig. 84, 73; Fig. 85, s.m). Tertiary mesenteries (Fig, 84, 14; Fig. 85, t.m) and quaternary mesenteries (Fig. 84, 75) lie between the primaries and secondaries. There is considerable variation in the number, position, and size of the mesenteries (Fig. 84, 12). Each mesentery possesses a longitudinal retractor muscle band (Fig. 84, u). The bands of the pairs of mesenteries face I each other except those of the pri- /\ maries opposite the siphonoglyphes. These primaries, which are called directives (Fig. 85, d), have the muscle bands on their outer surfaces. The edges of the mesenteries below the stomodaeum are provided with mesen- teric filaments having a secretory func- tion. Near the base these filaments FIG. 85. Cross-section of a bear long, delicate threads called sea-anemone showing the ar- . ,_,. . rangement of the mesenteries, OCOntia (tig. 84, If). Ihe aCOntia d. directives; p.m, primary are armed with gland cells and mesentery ; s, siphonoglyphe; s.m, secondary mesentery; nematocysts, and can be protruded from the mouth or through minute pores (cinclides) in the body-wall (Fig. 84, 18). They probably serve as organs of offense and defense. Near the edge of the mesenteries lying parallel to the mesen- teric filaments are the gonads (Fig. 84, 16). The animals are dioecious, and the eggs or spermatozoa are shed into the gastro- vascular cavity and pass out through the mouth. The fertilized egg probably develops as in other sea-anemones, forming first a free-swimming planula and then, after attaching itself to some object, assuming the shape and structure of the adult. Asexual reproduction is of common occurrence, new anemones being formed by budding or fragmentation at the edge of the basal disc. Longitudinal fission has also been reported. t.m, tertiary mesentery. (From Weysse.) PHYLUM (TELFATEK \ I \ 137 b. A C'tnal Polyp Astrangia Astrangia dance (Fig. 86) is a coral polyp inhabiting the waters of our North Atlantic coast. A number of individuals live to- -11 FIG. 86. Astrangia dance, a cluster of our Northern coral-polyps, resting on limy bases of their own secretion. (From Davenport, after Sonrel.) gether in colonies attached to rocks near the shore. Each polyp looks like a small sea-anemone, being cylindrical in shape and possessing a crown of tentacles. The most noticeable difference is the presence of a basal cup of calcium carbonate termed the theca (Fig. 87 9). This structure of calcium carbonate is what we commonly call coral. It is produced by the ectoderm of the coral polyp and increases gradually during the life of the animal. The calcareous cup is divided into chambers ^by a number of FIG g; _ Sern ;. diagrarnmatic view radial Septa (Fig. 87, //) which of half a simple coral. /, tentacle; i_ -i, i , i 2, mouth ; ?, gullet ; 4, mesentery ; are built up between the pairs ^ edge o ' f J mes g cnter ; . \ ectoderm! of mesenteries (4) of the polyp. 7, entoderm; 8, basal plate; Q, theca; mi r <-i 10, columella ; //, septum. (From The center of the cup is occu- shipley and MacBride| partly after pied by a columella (10} formed Bourne.) COLLEGE ZOOLOGY in part by the fusion of the inner ends of septa, and in part by projections from the base of the polyp. Although Astrangia builds a cup less than half an inch in height, it produces enormous masses of coral in the course of centuries. c. Coral Reefs and Atolls Coral polyps build fringing reefs, barrier reefs, and atolls. These occur where conditions are favorable, principally in tropi- cal seas, the best known being among the Maldive Islands of the Indian Ocean, the Fiji Islands of the South Pacific Ocean, FIG. 88. A small atoll, being a sketch of Whitsunday Island in the South Pacific. (From Sedgwick, after Darwin.) the Great Barrier Reef of Australia, and in the Bahama Island region. A fringing or shore reef is a ridge of coral built up from the sea bottom so near the land that no navigable channel exists between it and the shore. Frequently breaks occur in the reef, and irregular channels and pools are created which are often inhabited by many different kinds of animals, some of them brilliantly colored. A barrier reef is separated from the shore by a wide, deep channel. The Great Barrier Reef of Australia is over noo miles long and encloses a channel from 10-25 fathoms deep and in some places 30 miles wide. Often a barrier reef entirely surrounds an island. PHYLUM CCELENTERATA 139 An nloV (Fig. SS) is a more or less circular reef enclosing a lagoon. Several theories have been advanced to account for the production of atolls. Charles Darwin, who made extensive studies of coral reefs and islands, is responsible for the subsidence theory. According to Darwin, the reef was originally built up around an oceanic island which slowly sank beneath the ocean, leaving the coral reef enclosing a lagoon. John Murray be- lieves that the 'sland enclosed by the reef does not necessarily sink, but may be worn down by erosion. Besides producing islands and reefs, corals play an important role in protecting the shore from being worn down by the waves. They have also built up thick strata of the earth's crust. d. Classification of the A nthozoa The ANTHOZOA may be divided into two subclasses and ten orders. SUBCLASS I. ALCYONARIA. - - ANTHOZOA with eight hollow, pinnate tentacles, and eight complete mesenteries; with one siphonoglyphe, ventral in position ; and with the retractor muscles of the mesenteries all on the side toward the siphonoglyphe. Order i. Stolonif era. --ALCYONARIA colonial in habit; with stolon attached to a stone or other foreign object; polyps free except at base or joined together by horizontal bars; skeleton either horny or of calcareous spicules. Example: Tubipora (Fig. 89, A). The organ-pipe coral, Tubipora (Fig. 89, A), is common on coral reefs. It has bright green tentacles and a skeleton of a dull red color, and adds considerably to the beauty of the coral reef. Order 2. Alcyonacea. Colonial ALCYONARIA; zooids united into a compact mass by fusion of body-walls ; skeleton of calcareous spicules which do not form a solid axial support. Example: Alcyonium (Fig. 89, B). Order 3. Gorgonacea. -- Colonial ALCYONARIA; skeletal axis branched and not perforated by gastrovascular cavities of the zooids. Example: Corallium (Fig. 89, C). I/p COLLEGE ZOOLOGY This order includes the sea-fans which are to be found in almost every museum, and the precious red coral (Corallium, Fig. 89, C), which occurs in the Mediterranean and is widely used in the manufacture of jewelry. Order 4. Pennatulacea. - - ALCYONARIA forming bilaterally symmetrical colonies; zooids usually borne on branches of an FIG. 89. Coral. A, Tubipora musica, organ-pipe coral, a young colony. lip, connecting horizontal platforms; p, skeletal tubes of the zooids; Si, the basal stolon. B, Alcyonium digit at urn, with some zooids expanded. C., Corallium, a branch of precious coral. P, polyp. D, Pennatula sulcata, a sea- feather. (A and B, from Cambridge Natural History; C, from Sedgwick, after Lacaze Duthiers; D, from Sedgwick, after Kolliker.) axial stem, which is supported by a calcareous or horny skeleton. Examples: Pennatula (Fig. 89, D), Renilla. The sea-pens (Fig. 89, D) live with their stalks embedded in muddy or sandy sea-bottoms. Many of them are phosphorescent. PHYLUM CCELENTERATA 141 SUBCLASS II. ZOANTHARIA. -- ANTHOZOA with usually many simple hollow tentacles, arranged generally in multiples of five or six; two siphonoglyphes as a rule; mesenteries vary in num- ber, the retractor muscles never arranged as in the ALCYONARIA; skeleton absent or present ; simple or colonial ; dimorphism rare. Order i. Edwardsiidea. -- A few shallow water ZOANTHARIA, with eight complete mesenteries and from fourteen to twenty or more tentacles. Order 2. Actiniaria. -- ZOANTHARIA usually solitary; many complete mesenteries; no skeleton. Examples: Metridium (Fig. 84), Halcampa, Bunodes. These are the sea-anemones. Some of them are parasitic; Bicidinm is parasitic on the jellyfish Cyanea. Many sea- anemones are beautifully colored; in the large Stoichactis of the Great Barrier Reef of Australia, " the spheroidal bead-like tentacles occur in irregularly mixed patches of gray, white, lilac, and emerald green, the disk being shaded with tints of gray, while the oral orifice is bordered with bright yellow." (Kent.) Order 3. Madreporaria. ZOANTHARIA usually colonial; many complete mesenteries; calcareous skeleton formed by FIG. go. Oculina speciosa, a branch of madreporarian coral. (From Sedgwick, after Ed. H.) FIG. gi. Mcandrina, a rose-coral of the order MADREPORARIA. (From Weysse.) 142 COLLEGE ZOOLOGY ectoderm cells. Examples: Astrangia (Fig. 86), Oculina (Fig. 90), and Madrepora. Most of the stony corals belong to this order. Astrangia has already been described (p. 137, Fig. 86). Oculina (Fig. go) and Madrepora are branching corals. Meandrina (Fig. 91) is a more compact " brain " coral. Many of the coral polyps are tinted with pink, lilac, yellow, green, violet, red, etc., and give the coral reefs the wonderful color effects for which they are famous. Order 4. Zoanthidea. ZOANTHARIA usually colonial; only one siphonoglyphe ; mesenteries differ from those of ACTINIARIA; no skeleton, but often incrusted by sand. Certain ZOANTHIDEA are the black corals of the Mediterranean ; others live symbiotically with hermit crabs or sponges. Order 5. Antipathidea. Colonial ZOANTHARIA with a horny, usually branching axial skeleton, but no calcareous spicules. The corals belonging to this order are found in all the large seas, usually at a depth of from fifty to five hundred fathoms. Order 6. Cerianthidea. -- Solitary ZOANTHARIA without a skeleton ; one siphonoglyphe ; no bands of retractor muscles on mesenteries. Example: Cerianthus. This order contains a single genus, Cerianthus. One species C. americanus, occurs on the eastern coast of North America; other species occur in widely separated localities. 5. CCELENTERATES IN GENERAL Definition. Phylum CCELENTERATA. POLYPS, JELLY- FISHES, CORALS. - - Diploblastic, radially symmetrical animals, with four or six antimeres; a single gastro vascular cavity; no anus; body- wall contains peculiar structures known as nemato- cysts or stinging cells. Morphology. - - The foregoing account has shown that ccelen- terates all possess a body-wall composed of two layers of cells, an outer ectoderm and an inner entoderm. They are therefore diploblastic, although many ANTHOZOA have a fairly well de- PHYLUM CCELENTERATA 143 veloped mesoderm. Between these layers is a jelly-like non- cellular substance, the mesoglea. The body-wall encloses a single cavity, the ccelenteron or gastrovascular cavity, in which both digestion and circulation take place. In some of the cce- lenterates, like Hydra (Fig. 65), this cavity is simple, but in others, like Aurelia (Fig. 79), it is modified so as to include numerous pouches and branching canals. The two principal types of ccelenterates are the polyp or li yd raid, and the jellyfish or medusa. These are fundamentally similar in structure (Fig. 76), but are variously modified (Tables V and VI). Both polyps and medusae are radially symmetrical. So far as is known, all ccelenterates possess stinging cells called nematocysts ; these are organs of offense and defense. Muscle fibrils are present in a more or less concentrated con- dition. Nerve-fibers and sensory organs are characteristic structures; they may be few in number and scattered as in Hydra (p. 112), or numerous and concentrated as in Aurelia (p. 131, Fig. 80). Physiology. - - The food of ccelenterates consists principally of small, free-swimming animals, which are usually captured by means of nematocysts and carried into the mouth by tentacles and cilia. Digestion is mainly extracellular, enzymes being dis- charged into the gastrovascular cavities for this purpose. The digested food is transported to various parts of the body by currents in the gastrovascular cavity, and is then taken up by the entoderm cells and passed over to the ectoderm cells. Both respiration and excretion are performed by the general surface of the ectoderm and entoderm. Motion is made possible by muscle fibrils, and many species have also the power of loco- motion. There is no true skeleton, although the stony masses built up by coral polyps support the soft tissues to a certain ex- tent. The nervous tissue and sensory organs provide for the perception of various kinds of stimuli and the conduction of im- pulses from one part of the body to another. Ccelenterates are generally sensitive to light intensities, to changes in the 144 COLLEGE ZOOLOGY temperature, to mechanical stimuli, to chemical stimuli, and to gravity. Reproduction is both asexual, by budding and fission, and sexual, by means of eggs and spermatozoa. Economic Importance. - - Ccelenterates as a whole are of very little economic importance. The coral built up by coral polyps form reefs and islands and thick strata of the earth's crust. Some corals are used as ornaments and for the manufacture of jewelry (Fig. 89, C). Ccelenterates are probably very seldom used as food by man but are eagerly devoured by fishes. CHAPTER VI PHYLUM CTENOPHORA THE Phylum CTENOPHORA (Gr. ktenos, of a comb; phoreo, I bear) includes a small group of free-swimming marine animals which are even more nearly transparent than the ccelenterate jellyfishes. They have been placed by many authors under the Phylum CCELENTERATA, but the present tendency is to separate them from that group and rank them as a distinct phylum (p. 25). They are widely distributed, being especially abundant in warm seas. Ctenophores are commonly called sea walnuts because of their shape (Fig. 92), or comb jellies on account of their jelly-like consistency and the comb-like locomotor organs arranged in eight rows on the sides of the body (Fig. 93, A, 5; Fig. 93, B, ctr). A few species have a slender ribbon-like (From Weysse, after shape and may, like Venus' girdle (Fig. 94), A 8 assiz ^ . excretory . & . pore; b, paragastnc reach a length of from six inches to four aan al ; c, circular fggt canal ; d-h, ciliated bands. (From Weysse, The general structure of a ctenophore is after Agassiz.) shown in Figure 93. It is said to possess biradial symmetry, since the parts, though in general radially disposed, lie half on one side and half on the other side of a median longitudinal plane. An end view, as in Figure 93, B, illustrates this fact. The mouth (Fig. 93, A, i) is situated at one end (oral) and a sense-organ (Fig. 93, A, 2) at the opposite or aboral end. Extending from near the oral surface to near L 145 FIG. 92. A cteno- phore, Idyia roseola. 146 COLLEGE ZOOLOGY .4 the aboral end are eight meridional ciliated bands (Fig. 93, A, 5; Fig. 93, B, ctr); these are the locomotor organs. Each band has the cilia arranged upon it in transverse rows and fused at the base; each row thus resembles a comb. These are raised and lowered alternately, starting at the aboral end, and cause an appearance like a series of waves travel- ing from this point toward the mouth. The animal is propelled through the water with the oral end forward. Light is refracted from these moving rows of cilia, and brilliant, changing colors are thus produced. Some species are phosphorescent. Most cteno- phores possess two solid, contrac- tile tentacles (Fig. 93, A, 8) which Pf- - ' "%~-J " \ .,&/ emerge from blind J ^S^-^S^ S5 't'-Hr pouches (Fig. 93, A, 7), one on either side (Fig. 93, B). With one I c.ss. FIG. 03. CTENOPHORA. A, Hormiphora plumosa. Side view. /, mouth ; 2, aboral pole with sense organ; 3, funnel ; 4, paragastric canal ; 5, a ciliated band ; 6, canal; 7, tentacular pouch; S, tentacle; Q, gelatin- exception, the ten- ous substance. B, Pleurobrachia pileus, view of aboral . aspect, showing central statocyst, polar fields (Pf), tades are not pro- and eight ciliated bands (c.ss, c.tr). (A, from Shipley and MacBride, after Chun ; B, from Lankester's Treatise.) vided with nerna- tocysts as are those of the CCELENTERATA, but are supplied with adhesiye or glue cells called colloblasis (Fig. 95). The colloblasts produce a secretion of use in capturing small animals which serve as food. The spiral filament (sf) in each colloblast is contractile, and acts as a spring, often preventing the struggling prey from tearing the cell away. PHYLUM CTENOPHORA 147 THE DIGESTIVE SYSTEM. - - The mouth (Fig. 93, A, /) opens into a flattened stomodceum, where most of the food is digested; FIG. 54. Cestus veneris, Venus' girdle, m, mouth; c 1 -^, ciliated bands; st, st*, x l , x 2 , canals. (From Lankester's Treatise.) this leads to the " infundibulum " or funnel (Fig. 93, A, j) which is flattened at right angles to the stomodaeum. Six canals arise from the infundibulum. Two of these, called excretory canals, open to the exterior near an aboral sense-organ; undigested food probably does not pass through them, but is ejected through the mouth. The two paragastric canals (Fig. 93, A, 4) lie parallel to the stomodaeum, ending blindly near the mouth. The two tentacular canals pass out toward the pouches of the tentacles, then each gives rise to four branches (Fig. 93, A, 6) ; these lead into meridional canals lying just beneath the ciliated bands (Fig. 93, A, 5). The aboral sense-organ (Fig. 96) is a statocyst or organ of equilibrium. It consists of a vesicle of fused cilia (cu) enclosing a ball of calcareous granules, the statolith (of), which is supported (From Lankester's by four tufts of fused cilia. It is probable Jj^^"' after that when the body is at an angle, the cal- careous ball presses more heavily on the inclined side, and thus stimulates the ciliated bands on that side to greater activity. FIG. 05. -- Two adhesive cells from gi, glandular por- ti , on; . "; nudeus : sf, spiral filament. 148 COLLEGE ZOOLOGY cu. FIG. 96. Sense organ Just beneath the statocyst is a ciliated area supposed to be sensory in function, and on either side is a ciliated prolongation called the polar field (Fig. 93, B, Pf). Ctenophores are hermaphroditic. The ova are formed on one side and the spermatozoa on the other side of each meridional canal just beneath the ciliated bands (Fig. 93, A, 5). The germ-cells pass into the infundibulum and thence to the out- -ot. side through the mouth. The fertilized eggs develop directly into the adult without the intervention of an asexual generation as in many ccelenterates. The cellular layers of ctenophores con- "titute a very small part of the body, cu, cupule formed of fused most of it being composed of the trans- (Fr^La^SCat P. arent ^^ &*' The thin ise.) ciliated ectoderm covers the exterior and lines the stomodaeum; and the entoderm, also ciliated, lines the infundibulum and the canals to which it gives rise. The muscle fibers which lie just beneath the ectoderm and entoderm are derived from the mesoderm cells of the embryo. Ctenophores are therefore triploblastic animals, and represent a higher grade of development than that of the ccelenterates. Definition. -- Phylum CTENOPHORA. SEA WALNUTS or COMB JELLIES. -- Triploblastic animals; radial combined with bilateral symmetry ; eight radially arranged rows of paddle plates. The CTENOPHORA differ from the ccelenterates in several important respects besides the presence of a distinct mesoderm. With one probable exception, ctenophores do not possess nematocysts, and the adhesive cells (Fig. 95) which take their place are not homologous to nematocysts. Their ciliated bands, aboral sense-organs, and pronounced biradial symmetry are peculiarities which warrant placing ctenophores in a phylum PHYLUM CTENOPHORA 149 by themselves. They probably evolved from coelenterate-like ancestors, but can no longer be combined with that phylum. A discussion of the resemblances between ctenophores and the flatworms (PLATYHELMINTHES) is reserved for the next chapter (p. 166). CHAPTER VII PHYLUM PLATYHELMINTHES THE Phylum PLATYHELMINTHES (Gr. platus, broad; helmins, an intestinal worm) includes the planarians, liver-flukes, tape- worms, and many other " flatworms." Some of these are free living in fresh water, salt water, or less frequently on land, whereas others are parasitic. Many of the parasites pass through a number of complex stages, and live in the bodies of several species of animals during their life-history. The parasitic flat- worms frequently are responsible for serious diseases of man and other animals. The three classes of the PLATYHELMINTHES are as follows :- CLASS I. TURBELLARIA (Lat. turbo, I disturb), with ciliated ectoderm; free-living habit (Planaria, Fig. 97); CLASS II. TREMATODA (Gr. trema, a pore; eidos, resemblance), with non-ciliated ectoderm; suckers; parasitic habit (Fasciola, Fig. 105); and CLASS III. CESTODA (Gr. kestos, a girdle; eidos, resemblance), with body of segments; without mouth or alimentary -canal; parasitic (Tcenia, Fig. 107). i. A FRESH- WATER FLATWORM -- PLANARIA Planaria (Fig. 97, and Fig. 98, 2) is a flatworm found only in fresh water, usually clinging to the underside of logs or stones. Its body is bilaterally symmetrical and dor so-ventr ally flattened. The anterior end is rather blunt, the posterior end, more pointed. It may reach half an inch in length. Planaria maculata, the common American species, is difficult to study because of the 150 PHYLUM PLATYHELMINTIIES great amount of coloring matter in its body (Fig. 98, 2), but an allied rlatworm, Dendroceelum lacteiim (Fig. 98, /), is cream- colored, and its anatomy is more easily made out. FIG. 97. Planaria polychroa, a fresh-water flatworm. i, eye; 2, side of head; j, proboscis; 4, pharynx sheath; 5, genital pore. (From Shipley and MacBride.) Anatomy and Physiology. - - EXTERNAL FEATURES. - - Figure 97 shows the principal external features of a planarian. A pair of eye-spots (/) are present on the dorsal surface near the anterior end. The mouth is in a peculiar position near the middle of the ventral sur- face. From it the muscular pro- boscis (j) may extend. Posterior to the mouth is a smaller opening, the genital pore (5). The surface of the body is covered with cilia which propel the animal through the water. This is not the only method of locomotion, since mus- cular contraction is also effective. INTERNAL ANATOMY AND PHYSI- OLOGY. A study of the structure of the adult and of the early em- bryonic stages shows Planaria to be a triploblastic animal possessing three germ-layers, ectoderm, meso- fresh water flatworms." i, Den- derm, and entoderm, from which d ' c l m /a '^'""- ' P^naria maculata. (From Davenport, several systems of organs have been after Woodworth.) 2. 7. FIG. 98. -- Two species of 152 COLLEGE ZOOLOGY cn> v derived. There are well-developed muscular, nervous, digestive, excretory, and reproductive systems; these are constructed in such a way as to function without the coordination of a circu- latory system, respiratory system, ccelom, and anus. DIGESTIVE SYSTEM. - - The digestive system (Fig. 99) con- sists of a mouth (m), a pharynx (/>//) lying in a muscular sheath, and an intestine of three main trunks (/, i 2 , is) and a large number of small lateral exten- sions. The muscular pharynx can be extended as a proboscis (Fig. 97, j) ; this facilitates the capture of food. Digestion is both intercellular and intra- cellular, i.e. part of the food is digested in the intestinal trunks by secretions from cells in their walls; whereas other food par- ticles are engulfed by pseudo- podia thrust out by cells lining the intestine, and are digested inside of the cells in vacuoles. The digested food is absorbed by the walls of the intestinal trunks, and, since branches from these penetrate all parts of the body, no circulatory system is necessary to carry nutriment from one place to another. As in Hydra, no anus is present, the faeces being ejected through the mouth. FIG. gg. Anatomy of a flatworm. en, brain ; e, eye ; g, ovary ; i t , ,, i 3 , branches of intestine; In, lateral nerve; m, mouth ; od, oviduct ; ph, pharynx ; t, testis ; u, uterus; 11, yolk glands; vd, vas deferens; $ , penis; 9 , vagina; $ $ , common genital pore. (From Lankester's Treatise, after v. Graff.) PHYLUM PLATYHELMINTHES 153 EXCRETORY SYSTEM. - - The excretory system comprises a pair of longitudinal, much-coiled tubes, one on each side of the body; these are connected near the anterior end by a transverse tube, and open to the exterior by two small pores on the dorsal surface. The longitudinal and transverse trunks give off numerous finer tubes which ramify through all parts of the body, usually ending in a ilame-cell. The flame- cell (Fig. 100) is large and hollow, with a bunch of flickering cilia (c) extending into the central cavity (e). Since it communi- cates only with the excretory tubules, it is considered excretory in function, though it may also carry on respiratory activities. MUSCULAR SYSTEM. - - The power of changing the shape of its body, which may be observed when Planaria moves from place to place, lies principally in three sets of muscles: a circular layer just beneath the ectoderm, external and internal layers of longitudinal muscle fibers, and a set of oblique fibers lying in the mesoderm. NERVOUS SYSTEM. - - Planaria possesses a well-developed nervous system consisting of a bilobed mass of tissue just be- neath the eye-spots called the brain (Fig. 99, en), and two lat- eral longitudinal nerve-cords (In) connected by transverse nerves. From the brain, nerves pass to various parts of the anterior end of the body, imparting to this region a highly sensitive nature. REPRODUCTIVE SYSTEM. - - Reproduction is by fission or by the sexual method. Each individual possesses both male and female organs, i.e. is hermaphroditic. The male organs may be located easily in Figure 99; they consist of numerous spherical testes (t) connected by small tubes called vasa deferentia (vd); the vas deferens from each side of the body joins the cirrus or FIG. ioo. Flame-cell of Planaria. c, cilia ; r, opening into excre- tory tubule. (From Lankester's Treatise.) COLLEGE ZOOLOGY penis ($ ), a muscular organ which enters the genital cloaca. A seminal vesicle lies at the base of the penis, also a number of uni- cellular, prostate glands. Spermatozoa originate in the testes, and pass, by way of the vasa deferentia, into the seminal vesicle, where they remain until needed for fertilization. FIG. 101. Development of Planaria lactea. i, egg (0) surrounded by yolk (v). 2, four blastomeres (bl) from segmented egg. 3, later stage; blas- tomeres (bl) more numerous. 4, much later stage; blastomeres differentiated into ectoderm (ep), entoderm (hy), a provisional pharynx (ph), and wandering cells (w). 5, cellular differentiation more advanced; ep, ectoderm; ent, primitive gut; hy, entoderm; ph, pharynx. 6, embryo changes shape to a flattened ovoid; ent, primitive gut; in, mouth; ph, pharynx. (From Lan- kester's Treatise, after Hallez.) The female reproductive organs comprise two ovaries (g), two long oviducts (od) with many yolk-glands (v) entering them, a vagina ( $ ) which opens into the genital cloaca, and the uterus which is also connected with this cavity. The eggs originate in the ovary, pass down the oviduct, collecting yolk from the yolk- glands on the way, and finally reach the uterus. Here fertiliza- PHYLUM PLATYHELMINTHES 155 f B :<*<*: 1 -:o" '1 lion occurs, and cocoons arc formed, each containing from four to more than twenty eggs, surrounded by several hundred yolk cells. The development of the egg is illustrated and explained in Figure 101. Regeneration. - - Planarians show remarkable powers of re- generation. If an individual is cut in two (Fig. 102, A), the an- terior end will re- generate a new tail (B, B 1 ), while the posterior part de- velops a new head (C, C 1 )- A cross- piece (D) will re- generate both a head at the anterior end, and a new tail at the posterior end (D l -D*). The head alone of a planarian will grow into an entire animal (E- FlG IQ2 _ Regeneration of Planaria maculata. E 3 ). Pieces CUt A, normal worm. B, B 1 , regeneration of anterior from various mrts half " C ' C '' re g eneration of Posterior half. D, cross- piece of worm. D 1 , D 2 , D 3 , D*, regeneration of same. of the body will E, old head. E 1 , E 2 , E 3 , regeneration of same. o]* r^rrpn^mt^ F, F 1 , regeneration of new head on posterior end of old head. (From Morgan.) completely. No difficulty is experienced in grafting pieces from one animal upon another, and many curious monsters have been produced in this way. 2. CLASS I. TURBELLARIA The TURBELLARIA (the class to which Planaria belongs) are free-living PLATYHELMINTHES with ciliated epidermis. Special ectodermal cells secrete mucus or produce rod-like bodies called " rhabdites." 156 COLLEGE ZOOLOGY Order i. Rhabdocoelida (Fig. 103). Small TURBELLARIA, often microscopic, with simple unbranched intestine. Examples: Microstoma, in fresh water; Monoscelis and Monops, marine. Order 2. Tricladida (Fig. 99). TURBELLARIA with intestine of three main branches one median anterior branch ( 1 ) and tv;o FIG. 103. Plan of structure of a Rhabdoccelous Turbellarian. be, bursa copulatrix ; en, brain ; e, eye; g, germarium; i, intestine; In, ventral nerve cord ; m, mouth ; ph. pharynx; rs, seminal recep- tacle ; s, salivary gland ; /, testis ; it, uterus containing an egg ; v, shell gland; vs, seminal vesicle; $ , penis ; $ $ , genital pore. (From Lankester's Treatise, after v. Graff.) IK&, FIG. 104. Plan of structure of a Polyclad Turbellarian. D, branches of intestine; G, brain; M.Go e , male genital pore ; 0, mouth ; Od, oviduct ; Ov, ova; T, vas deferens; V, va- gina ; W.Go e , female genital pore. (From Sedgwick, after Quatrefages ) lateral posterior branches (i 2 , i s ) ; many lateral caeca arise from the main branches. Examples: Planar ia (Fig. 98), Polyscelis, and Dendrocoelum (Fig. 98, /) in fresh water; Bipalium in the tropics living in moist earth, and accidentally introduced into hothouses all over the world; Bdettoura, Gunda, and Poly- chcerus in the sea. PHYLUM PLATYHELMINTHES 157 Order 3. Poly cladida (Fig. 104). Marine TURBELLARIA with a central digestive chamber which gives off many lateral branches (D). Examples: Stylochus and Leptoplana. 3. CLASS II. TREMATODA a. The Liver-fluke Fasciola hepatica The liver-fluke is a flatworm which lives as an adult in the bile ducts of the liver of sheep, cows, pigs, etc., and is occasionally found in man. Figure 105 shows the shape and most of the ana- tomical features of a mature worm. The mouth (0) is situated at the anterior end and lies in the middle of a muscular disc, the anterior sucker. A short distance back of the mouth is the ventral sucker (S) ; it serves as an organ of attachment. Between the mouth and the ventral sucker is the genital opening through which the eggs pass to the exterior. The excretory pore lies at the extreme posterior end of the body, and another pore, the opening of Laurer's canal, is situated in the mid-dorsal line about one third the length of the body from the anterior end. The digestive system is simple. The mouth (Fig. 105, O) opens into a short globular pharynx which leads into another short tube, the oesophagus. The intestine consists of two branches, one extending from near the anterior to the posterior end on each side of the body. Many small branches (Fig. 105, D) are given off from the intestine as in Planar ia (Fig. 99, i), and no circulatory system is therefore necessary for the transportation of food material. The excretory system is similar to that of Planaria (p. 153), but only one main tube and one exterior opening are present. The nervous system also resembles that of Planaria (Fig. 99, en, In). The suckers are provided with special sets of muscles enabling them to fasten the animal to its host. Three layers of muscles lie just beneath the ectoderm: (i) an outer circular layer, (2) a middle longitudinal layer, and (3) an inner diagonal layer. The body of the liver-fluke is triploblastic. The ectoderm is a 153 COLLEGE ZOOLOGY Dr thin, hard covering often called the cuticle; it protects the under- lying tissues from the juices of the host. The ectoderm contains chitinous scales and unicellular glands. The entoderm lines the alimentary tract. The mesoderm is represented by the muscles, the excretory organs, the repro- ductive ducts, and the paren- chyma. The parenchyma is a loose tissue lying between the body-wall and the alimentary canal ; within it are embedded the various internal organs de- scribed above, as well as the reproductive system. Both male and female reproduc- tive organs are present in every adult ; they are extremely well developed, and, as in Planaria, quite complex. Those of the male are as follows: (i) a pair of branched testes (Fig. 105, T) in which the spermatozoa arise ; (2) two ducts, the vasa deferentia, which carry the spermatozoa from the testes to (3) a pear-shaped ^ sac, the seminal vesicle; (4) a con- FIG. 105. The liver fluke, Fas- ciola hepatica. D, anterior part of voluted tube, the ejaculatory duct, intestine (posterior part not shown); w j,: r i, ] P ^A^ t n tVip pnrl nf M q Do, yolk-glands; Dr, ovary; WnlCn 1CadS 1 (5) a 0, mouth; Ov, uterus; s, sucker; muscular copulatory organ, the testes. Sommer.) (From Sedgwick, after The female organs are (i) a single-branched ovary (Fig. 105, Dr) in which the eggs are produced; (2) a convoluted oviduct (Fig. 105, Ov) which trans- ports the eggs from the ovary to (3) the shell gland^ at which PHYLUM PLATYHELMINTHES 159 place (4) the mtelline duct brings in and surrounds the eggs with yolk globules derived from (5) the mtelline glands (Fig. 105, Do); the shell gland then furnishes a chitinous shell, and the eggs pass on. into (6) a tube called the uterus, which leads to the genital pore. One liver-fluke may produce as many as five hundred thou- sand eggs, and, since the liver of a single sheep may contain more K- FIG. 106. Stages in the life-history of the liver fluke, Fasciola hcpatica. a, miracidium (ciliated embryo), b, sporocyst containing rediae (R). c, a redia; C, cercaria; D, gut; A", germ-cells; R, redia. d, cercaria. (From Sedgwick; b, after Leuckart; c and d, after Thomas.) than two hundred adult flukes, there may be one hundred million eggs formed in one animal. The eggs segment in the uterus of the fluke, then pass through the bile ducts of the sheep into its in- testine, and finally are carried out of the sheep's body with the faeces. Those eggs that encounter water and are kept at a tem- perature of about 75 F. continue to develop, producing a ciliated larva (Fig. 106, a) which escapes through one end of the egg-shell and swims about. This larva, called a miracidium, possesses a 160 COLLEGE ZOOLOGY double eye-spot on the dorsal surface near the anterior end, a pair of excretory organs, the nephridia, and a number of centrally placed germ-cells. It swims about until it encounters a certain fresh- water snail, Lymncea truncatula of Europe, or probably Lymnaa humilis in this country. If no snail is found within eight hours, the larva dies. When a snail is reached, the larva forces its anterior papilla (Fig. 1 06, a) into its tissue, and by a whirling motion bores its way into the soft parts of the body. Here in about two weeks it changes into a sac-like sporocyst (Fig. 106, b). Each germ-cell within the sporocyst, after passing through blastula and gastrula stages, develops into a second kind of larva, called a redia (Fig. 1 06, b R; c).. The redise soon break through the wall of the sporocyst and enter the tissue of the snail. Here, by means of germ-cells (Fig. 106, c, A') within their bodies, they usually give rise to one or more generations of daughter redia (Fig. 106, c, R}, after which they produce a third kind of larva known as a cer- can'a (Fig. 106, c, C). The cercariae (Fig. 106, d) leave the body of the snail, swim about in the water for a time, and then encyst on a leaf or blade of grass. If the leaf or grass is eaten by a sheep, the cercariae escape from their cyst wall and make their way from the sheep's alimentary canal to the bile ducts, where they develop into mature flukes in about six weeks. It will be seen from the above description that the life-history of the liver-fluke is complicated by the interpolation of several generations which develop from unfertilized germ-cells; (1) The fertilized egg produces a ciliated larva, the miracidium (Fig. 106, a); (2) The miracidium changes to a sporocyst within which rediae are developed from unfertilized germ-cells (Fig. 106, b); (3) The rediae produce other rediae from unfertilized germ- cells (Fig. 106, c); (4) The rediae finally give rise to cercariae from unfertilized germ-cells (Fig. 106, d) ; and (5) The cercariae develop into mature flukes (Fig. 105). PHYLUM PLATYHELMINTHES 161 The great number of ejj^s ])roduced by a single fluke is neces- sary, because the majority of the larva- do not find the particular kind of snail, and the cercariae to which the successful larvae give rise have little chance of being devoured by a sheep. The generations within the snail of course increase the number of larvae which may develop from a single egg. This complicated life-history should also be looked upon as enabling the fluke to gain access to new hosts. The liver-fluke is not so prevalent in the sheep of this country as in those of Europe. b. Trematoda in General The TREMATODA are parasitic Platyhelminthes without cilia but with a hardened ectoderm in the adult stage. The body is usually flattened and leaf-shaped. One or more ventral suckers are present at or near the posterior end and in the mouth region. Trematodes may be ectoparasitic, i.e. living on the body of another animal, like Gyrodactylus which clings to the gills of the carp, or ento parasitic, i.e. living in the body of another animal, like the liver-fluke. Some of the modifications due to parasitic habits are the absence of eye-spots in most species, the poorly developed brain and sense-organs, and the highly specialized sexual organs. The two orders of TREMATODA differ principally in their method of development. Order i. Monogenea. Trematodes which develop directly from the egg; they possess a large posterior, ventral, terminal sucker, and usually one or two suckers near the mouth. Most of the MONOGENEA are ectoparasitic on aquatic animals, e.g. SpJiyra ultra on the skin of the salamander (Necturus), Polystomum on the gills of the tadpole and later in the urinary bladder of the adult frog, and Epibdella on the body of the halibut. Order 2. Digenea. Entoparasitic TREMATODA which pass through several different forms in their life-history; they pos- sess an anterior and often a ventral sucker. M COLLEGE ZOOLOGY The best-known member of this order is the liver-fluke, which has a fairly representative life-history. Usually the DIGENEA occupy two, but sometimes three, hosts during their development ; one host is generally a vertebrate, one a snail, and the third an insect or other animal. Clonorchis sinensis and Paragonimus ringeri attack human beings in China. A few TREMATODA and their hosts are given in Table VII. (From the Cambridge Natural History.) TABLE VII THE LIFE -HISTORIES OF A FEW DIGENETIC TREMATODES SPECIES FINAL HOST HOST LARVA ENTERS AND CERCARI.E FORMED HOST CERCARI.I ENTER ; EATEN BY FINAL HOST i. Distomum atriventre Frogs and toads of North America Physa hetero- strophia, a snail Not known. 2. D. retusum The frog, Rana The snail, Lym- ncsa stagnalis The snail, Lym- naa stagnalis, and larvae of caddice flies. 3. Gasterosto- mum fim- briatum Perch and pike, Perca and Esox Fresh water clams, Unio and Anodonta Leuciscus ery- throphthalmiis, a small fish. 4. Monosto- mum flavum Anas, a duck A snail, Planor- bis corneus Omitted. 5. Diplodiscus subclava- tus Frogs, toads, and salamanders, Rana, Bufo, and Triton Snails, Planorbis and Cyclas Insect larvae, frogs (Rana) and Toads (Bufo). Often omitted. PHYLUM PLATYHELMINTHES 4. CLASS III. CESTODA a. The Tapeworm - - Tania The tapeworm, Tcsnia soli-urn, is a common parasite which lives as an adult in the alimentary canal of man. A nearly related species, T. saginata, is also a parasite of man. Tcenia, as shown in Figure 107, is a long flatworm consisting of a knob-like head, the scolex (Fig. 107, B), and a great number of similar parts, the proglottides, arranged in a linear series. The animal clings to the wall of the alimentary canal by means of hooks (Fig. 107, B, 2) and suckers (j) on the scolex. Behind the scolex is a short neck (4) followed by a string of proglottides which gradually increase in size from the anterior to the posterior end. The worm may reach a length of ten feet and contain eight or nine hundred proglottides. Since the proglottides are budded off from the neck (Fig. 107, B, 4), those at the posterior end are the oldest. The production of proglottides may be compared to the forma- FIG. 107. - The tapeworm. A, Tasnia tion of enhvraj bv the sa Kinata. The approximate lengths of the portions omitted in the drawing are given, hydra-tuba of Amelia At * the branched uterus and longitudinal (Fig Si) and is Called an< ^ transverse excretory vessels are shown. . . . B, head or scoiex of Tania solium. i, rostellum; Strobilization. 2, hooks; j, suckers; 4, neck; 5, commence- The anatomv of the ent of strobUization. (A from the Cam- bridge Natural History; B, from Shipley and tapeworm is adapted to MacBride.) 164 COLLEGE ZOOLOGY ne.ru. 1 the liver-fluke, but not so well <***** its parasitic habits. There is no alimentary canal, the di- gested food of the host be- ing absorbed through the body-wall. The nervous system is FIG. 108.-- A proglottis of the tapeworm, Tauiia solium, similar to that with mature reproductive apparatus, can.excret, longi- r pj n ,, nr : n anr J tudinal excretory canals with transverse connecting vessels; gl.vit, vitelline or yolk-glands; nrrv.l, longi- tudinal nerves; ov, ov, ovaries; par. gen, genital pore; schld, shell-glands; uler, uterus; vag, vagina; vas.def, vas deferens. The numerous, small, round bodies are the developed (Fig. lobes of the testes. (From Parker and Haswell, after T0 o n Leuckart.) 100, HC)l. L). Longitudinal ex- cretory tubes, with branches ending in flame-cells, open at the posterior end and carry waste matter out of the body (Fig. 108, can. excret.). A mature proglottid is almost completely filled with reproduc- tive organs ; these are shown in Figure .108. Sper- matozoa originate in the spherical testes, which are scattered about through the pro- glottis; they are collected by fine tubes and carried to the genital pore rl FIG. 109. Stages in the development of the tape- worm, T&nia solium, to the cysticercus stage, a, egg with embryo, b, free embryo, c, rudiment of trie head as a hollow papilla on wall of vesicle, d, bladder- (por.gen ) bv way worm ( c y st i cercus ) with retracted head, e, the same y with protruded head. (From Sedgwick, partly after of the vas deferens Leuckart.) PHYLUM PLATYHELMINTHES .--*" se (vas.def.). Eggs arise in the bilobed ovary (ov) and pass into a tube, the inn/ml. Yolk from the yolk-gland (gl.vit) enters the oviduct and surrounds the eggs. A chitinous shell is then provided by the shell gland (schld) and the eggs pass into the uterus (uter). The eggs have in the meantime been fertilized by spermatozoa, which probably come from the same proglottis, and move down the vagina (vag). As the proglottides grow older the uterus becomes distended with eggs and sends off branches (Fig. 107,*), while the rest of the reproductive organs are absorbed. The ripe proglottides break off and pass out of the host with the faeces. The eggs of Tcenia solium develop into six-hooked embryos (Fig. 109, a) while still within the pro- glottis. If they are then eaten by a pig, they escape from their envelopes (Fig. 109, b) and bore their way through the walls of the alimentary canal into the voluntary muscles, where they form cysts (Fig. 109, c). A head is developed from the cyst wall (Fig. 109, d) and then becomes everted (e). The larva is known as a bladder-worm or cysticercus at this stage. If insufficiently cooked pork con- taining cysticerci is eaten by man, the bladder is thrown off, the head becomes fastened to the wall of the intestine, and a series of proglottides is developed. FIG. no. A uniseg- mentalcestod, Archigetes sieboldii, from the coelom of a worm, Tubifex , persist- b. Cestoda in General The CESTODA are all entoparasitic flat- ent larval appendage; worms, called tapeworms ; they inhabit go, genital pore; kk, per- the alimentary canal of vertebrates in the slstent larval ho ? ks; J 0i', ovary ; sc, sucker ; adult stage. The body consists of a head te, testes ; yg, yolk- or " scolex " followed by a chain of similar 8 lan . d 1- Jf r m . e J Cambridge Natural IIis- joints or " proglottides " which are budded tory, after Leuckart.) i66 COLLEGE ZOOLOC.Y off from the "neck." Archigetes (Fig. no) differs from other tapeworms both in structure and habit; it has only one proglot- tis, and lives in the ccelom of an annelid, Tubifex. A few Cestodes and their hosts are given in Table VIII (from the Cambridge Natural History). TABLE VIII THE LIFE-HISTORIES OF A FEW CESTODES NAME FINAL HOST INTERMEDIATE HOST 1. Taenia saginata 2. T. serrata 3. Dipylidium cani- num 4. Hymenolepis di- minuta 5. Drepanidotaenia setigera 6. Bothriocephalus latus Man Dog Man, dog, cat Man, mouse, rat Goose Man, dog Ox, giraffe (in muscles). Rabbit, hare, mice (liver and peritoneum). Flea of dog (body-cavity). Meal-moth, Asopia farinalis; also certain Orthoptera and Coleoptera. Water-flea, Cyclops brevicau- datus. Pike, perch, trout, etc. 5. FLATWORMS IN GENERAL Definition. - - Phylum PLATYHELMINTHES. - - FLATWORMS. - Triploblastic animals; bilaterally symmetrical; single gastro- vascular cavity; no anus; presence of coelom doubtful. The flatworms are more highly organized than the CCELEN- TERATA or CTENOPHORA and are distinctly triploblastic. The middle germ-layer, the mesoderm, which is well developed in flat- worms, is connected with several important systems of organs, since it is from this layer that the muscles, the excretory system, and the reproductive ducts originate. The development of these PHYLUM PLATYHELMINTHES 167 systems of organs is correlated with the thickness of the body- wall. The excretory system is necessary, since it is no longer possible for the animal to get rid of the waste products of metabo- lism through the general surface of the body. Likewise a system of ducts is required to transport the germ-cells to the exterior. No circulatory system appears in the flatworms, but in most cases the food is transported directly to the tissues through the much- branched digestive tract, which serves, as in the CCELENTERATA and CTENOPHORA, as a gastro vascular cavity. Definite bilateral symmetry is exhibited by flatworms and should be considered an advance in morphological development, since the most successful animals have their bodies constructed on this plan. With bilateral symmetry is probably correlated the concentration of nervous tissue, the brain, in the head; the end of the body directed forward in moving would receive sen- sations first, and nerve-cells would be developed in the region of greatest stimulation. It is believed by some authorities that the body-cavity in the larval stages (sporocyst and redia) of liver-flukes represents the ccelom (p. 89) and that the reproduc- tive ducts of the adults should be considered true ccelomic cavities. Our present knowledge of the flatworms seems to indicate that they, as well as the CTENOPHORA, have evolved from ccelenterate stock. Forms like the simplest TURBELLARIA, the RHADOCCE- LIDA, have probably given rise to the more complex members of that class. From these also were probably derived the TREMATODA, no doubt in response to the changed conditions of life resulting from a parasitic habit. Many of the adult CES- TODA appear so closely related to certain TREMATODA that these two classes may have arisen together, or else the former have become separated from the complex TREMATODA (Digenea) as a distinct group. Some authorities believe that the two curious animals Cteno- plana and Cceloplana are connecting links between the CTENO- PHORA and PLATYHELMINTHES. Ctenoplana has been recorded I 68 COLLEGE ZOOLOGY once from the Indian Ocean and once from New Britain. Ccdo- plana inhabits the Red Sea. Economic Importance of Flatworms. - - The TURBELLARIA are of practically no economic importance. Trematodes are para- sitic in a great many vertebrates, but for the most part do not cause serious injuries. The liver-fluke of the sheep, and the trematode Schistosoma htzmatobium which infests the blood- vessels of the urinary bladder and alimentary tract of man, in Africa, are the most important species. The adult tapeworms found in the alimentary canal of man and other animals interfere seriously with the digestion and absorption of food, but the larvae are more dangerous. For example, the tapeworm, Tcenia echinococcus, which lives as an adult in the dog, gives rise to a larva called Echinococcus poly- morphus. These larvae may form large vesicles in man, known to physicians as hydatides, which may break with -serious or even fatal results. The organism which causes " gid " or " staggers " in sheep is the larva, called Ccenmus cerebralis, of the dog tape- worm, Tcenia ccenurus. It becomes lodged in the brain or spinal cord. Goats, cattle, and deer are also attacked by the same species. CHAPTER VIII PHYLUM NEMATHELMINTHES THE NEMATHELMINTHES (Gr. nema, thread; Jielmins, an in- testinal worm) are called round or thread worms. They are usually long and slender, and more or less cylindrical. They may be distinguished from the segmented worms (Phylum AN- NELIDA, Chap. XI) by the entire absence of internal and external segmentation. The microscopic animal which lives in vinegar and is known as the vinegar-eel is a nemathelminth. Other roundworms live as parasites in the alimentary canal of man, and other animals, or, like Trichinella (Fig. 113), live for a time embedded in the tissues of the body. i. A PARASITIC ROUNDWORM ASCARIS LUMBRICOIDES External Features. Ascaris (Fig. in) is a genus of round- worms parasitic in the intestines of pigs, horses, and man. The sexes are separate. The female, being the larger, measures from five to eleven inches in length and about one fourth of an inch in diameter. The body is light brown in color; it has a dorsal and a ventral white narrow stripe running its entire length, and a broader lateral line is present on either side. The anterior end possesses a mouth opening, surrounded by one dorsal and two ventral lips (Fig. 112 a, b, f). Near the posterior end is the anal opening from which, in the male, extend penial seta (Fig. 112 a, a, Sp.) for use during copulation. The male can be distin- guished from the female by the presence of a bend in the pos- terior part of the body (Fig. 112 a, a) . 169 COLLEGE ZOOLOGY / 2 ....7 ' Internal Anatomy. - - If an animal is cut open along the dorsal line (Fig. in), it will be found to contain a straight ali- mentary canal, and certain other organs, lying in a central cavity, the coelom. The alimentary canal (2) is very simple, since the food is taken from material already digested by the host whose in- testine the worm inhabits. It opens at the posterior end through the anus, which is not present in the members of the phyla already discussed. A muscular pharynx (j) draws the fluids into the long non-muscular in- testine (2), through the walls of which the nutriment is absorbed. Just before the anal opening is reached, the intestine gradually becomes smaller; this portion is known as the rectum. The excretory system consists of two longitudinal canals (Fig. 111,7) one in each lateral line ; these open to the outside by a single pore (8} situated near the anterior end in the ventral body-wall (Fig. 112 a, c,P). A ring of nervous tissue surrounds the pharynx and gives off two large nerve-cords, one dorsal, the other ventral, and a number of other smaller strands and connections. PHYLUM NEMATHELMINTHES The male reproductive organs are a single, coiled thread-like lest is, from which a vas dejercns leads to a wider tube, the seminal vesicle; this is followed by the short muscular ejaculalory duct which opens into the rectum. In the female lies a Y-shaped reproductive system. Each branch of the Y consists of a coiled thread-like ovary (Fig. in, j) which is continuous with a larger canal, the uterus (4). The uteri of the two branches unite into a short muscular tube, the vagina (5), which opens to the outside through the genital aperture (6). Fertilization takes place in the uterus. The egg is then surrounded by a shell of chit in, and a FIG. 112 a. Parts of Ascaris lumbricoides. a, hind end of male with the two penial setae (Sp). b, anterior end from the dorsal side, showing the dorsal lip with its two papillae, c, the same from the ventral side with the two lateral ventral lips and the excretory pore (P). d, egg with external membrane of small clear spherules. (From Sedgwick, after I^euckart.) passes out through the genital pore. The chitinous egg-shell prevents the digestion of the egg within the intestine of the host. The relations of the various organs to one another, as well as the structure of the body-wall, and the character o*f the ccelom, are shown in Figure 1 1 2 b, which is a transverse section of a female specimen of Ascaris lumbricoides. The body of the worm should be considered as consisting of two tubes, one the intestine (////.), lying within the other, the body-wall; while between them is a cavity, the ccelom, in which lie the reproductive organs (ovy. and ut). The body-wall is composed of several layers, an outer chitinous cuticle (cu), a thin layer of ectoderm (der.epthm) just beneath it, 172 COLLEGE ZOOLOGY and a thick stratum of longitudinal muscle fibers (w), mesodermat in origin, lining the coelom. Thickenings of the ectoderm form the dorsal (d.l), ventral (v.i<), and lateral (lat.l) lines. In each of the last-named lies one of the longitudinal excretory tubes (ex.v). The nerve-cords are also embedded in the body-wall. The intestine consists of a single layer of columnar cells, the entoderm, coated both within and without by a thin cuticle. loll cx.f- FIG. iizb. Transverse section of Ascaris lumbricoid.es. cu, cuticle; dl, dorsal line; der.epthm, epidermis; ex.v, excretory tube; int, intestine; lat.l, lateral line; m, muscular layer; ovy, ovary; ut, uterus; v.v, ventral line. (From Parker and Haswell, after Vogt and Yung.) The ccelom (see p. 89) of Ascaris differs from that of the higher animals in several respects. Typically the ccelom is a cavity in the mesoderm lined by an epithelium ; into it the ex- cretory organs open, and from its walls the reproductive cells originate. In Ascaris the so-called ccelom is lined only by the mesoderm of the body- wall, there being no mesoderm surround- ing the intestine. Furthermore, the excretory organs open to the exterior through the excretory pore, and the reproductive PHYLUM NEMATHELMINTHES 173 cells are not derived from the coelomic epithelium. The body- cavity of Ascaris, therefore, differs structurally and functionally from that of a true ccelom, but nevertheless is similar in many respects. 2. NEMATHELMINTHES IN GENERAL Definition. - - Phylum NEMATHELMINTHES. ROUNDWORMS. - Bilaterally symmetrical, triploblastic animals with an elon- gated cylindrical body; alimentary canal has a mouth opening at the anterior end and an anal opening on the ventral surface near the posterior end, and lies in a body-cavity, which is prob- ably a ccelom; no cilia present in any part of the body; both free-living and parasitic; sexes separate. It has been customary to place the NEMATOMORPHA (see p. 179) and ACANTHOCEPHALA (see p. 180) in the Phylum NEMAT- HELMINTHES, but the relationships of these animals are so ob- scure that it is considered best to treat them separately. The phylum, therefore, contains only one class, the NEMATODA, whose members have all of the characteristics cited above. Ascaris lumbricoides is but one of the interesting and important nematodes. It belongs with a number of other similar forms to the family ASCARID.E. The family STRONGYLID^E contains several dangerous para- sites. Ancylostoma duodenalis, the European hookworm, is frequently very injurious and sometimes fatal. Nematodes of this species are taken into the alimentary canal with drinking water, or enter the body through the skin, and thousands are sometimes present. Anaemia is caused by their biting into the intestinal wall and destroying the capillaries. Syngamus is the parasite that causes the disease known as gapes in poultry and game birds. The birds swallow the young syngamids, which soon become mature in the trachea and bronchi. To the family TRICHINELLID^E belongs Trichinella spiralis (Fig. 113) which causes the disease of human beings, pigs, and rats called trichinosis. The parasites enter the human body 174 COLLEGE ZOOLOGY FIG. 113. Trichinella spiralis encysted among muscle fibers. (From Shipley and MacBride, after Leuckart.) when inadequately cooked meat from an infected pig is eaten. The larvae soon become mature in the human intestine, and each mature worm deposits probably about 10,000 young. These young are either placed directly into the lymphatics by the female worms or burrow through the intestinal wall; they encyst in muscular tissue in various parts of the body. As many as 15,000 encysted parasites have been counted in a single gram of muscle. Pigs acquire the disease by eating offal or infested rats. In a few countries pork is inspected for this and other parasites by government agents. The family FILARIID^E is also important because of the human diseases caused by certain of its members. The most injurious species is Filaria bancrofti, a parasite in the blood of man. The larvae of this species are about yg-Q inch long. During the day- time they live in the lungs and larger arteries, but at night they migrate to the blood-vessels in the skin. Mosquitoes, which are active at night, suck up these larvae with the blood of the in- fected person. The larvae develop in the mosquito's body, be- coming about one twentieth of an inch long; make their way into the mouth parts of the insect; and enter the blood of the mosquito's next victim. From the blood they enter the lym- phatics and may cause serious disturbances, probably by ob- structing the lymph passages. This results in a disease called elephantiasis. The limbs or other regions of the body swell up to an enormous size, but there is very little pain. No successful treatment has yet been discovered, and the results are often fatal. It is said that from 30 per cent to 40 per cent of the natives of certain South Sea Islands are more or less seriously afflicted. One of the most recent discoveries with regard to parasitic PHYLUM NEMATHELMINTHES 175 round worms is that the shiftlessness of the " poor whites " of the South is to a certain degree the result of the attack of the hookworm, Necator americanus. The larvae of the hookworm develop in moist earth and usually find their way into the bodies of human beings by boring through the skin of the foot. In the localities where the hookworm is prevalent, many of the people go barefoot. The larval hookworms enter the veins and pass to the heart; from the heart they reach the lungs, where they make their way through the air passages into the windpipe, and thence into the intestine. To the walls of the intestine the adults at- tach themselves and feed upon the blood of their host. When the intestinal wall is punctured, a small amount of poison is poured into the wound by the worm. This poison prevents the blood from coagulating, and therefore results in a considerable loss of blood, even after the worm has left the wound. The vic- tims of the hookworm are anaemic, and also subject to tuber- culosis because of the injury to the lungs. It is estimated that 2,000,000 persons are afflicted by this parasite. The hook- worm disease can be cured by thymol (which causes the worm to loosen its hold) followed by Epsom salts. The most important preventive measure is the disposing of human fasces in rural districts, mines, brickyards, etc., in such a manner as to avoid pollution of the soil, thus giving the eggs of the parasites contained in the faeces of infested human beings no opportunity to hatch and develop to the infectious larval stage. CHAPTER IX INVERTEBRATES OF MORE OR LESS UNCERTAIN SYSTEMATIC POSITION THERE are a number of groups of animals whose relationships are so difficult to determine that authorities do not agree as regards their position in the animal series. Most of these groups contain only a few marine species which are of very little economic importance. A few groups like the ROTIFERA and BRYOZOA include fresh-water species which are quite common. i. MESOZOA The term MESOZOA (Gr. mesos, middle; soon, animal) has been employed by a number of zoologists to include three families of parasites of obscure systematic position, (l) theDlCYEMID^E, (2) the ORTHONEC- TID,E, and (3) the HETEROCYEMID.E. They have been regarded as inter- mediate between the PROTOZOA and METAZOA, hence the name MESOZOA. It is probable, how- ever, that they are A MESO- degenerate META- FIG. 114. A MESO- ZOON, Dicyema para- doxum. (From Parker and Haswell, after Kol- liker.) ZOON, Rhopalura giardii, { j m d t male. (From Sedgwick, > after v. Beneden.) 176 the flatworms. INVERTEBRATES OF UNCERTAIN POSITION 177 The DICYEMID^; (Fig. 114) and HETEROCYEMID.E are para- sites in the kidneys of CEPHALOPODA (cuttlefishes and octopods). The ORTHONECTID^: (Fig. 115) are parasites in TURBELLARIA (Chap. VII), NEMERTINEA, ANNELIDA (Chap. XI), and brittle- stars (OPHIUROIDEA, p. 199). 2. NEMERTINEA The NEMERTINEA (Gr. nemertes, true) (Figs. 116, 117) have a superficial resemblance to flatworms and are by some authorities placed in the Phylum PLATYHELMINTHES either as a distinct class or as a supplementary group. Some of them are very long, reaching a length of ninety feet. A few species live in moist earth and fresh water, but most of them are marine. Cerebratulus FIG. 116. Micrura verrilli, one of the NEMERTINEA found on the Paci&c coast. (From Weysse, after Coe.) (Fig. 117) and Micrura (Fig. 116) are marine; Geonemertes and some species of Tetrastemma are terrestrial; and Malacobdella is a parasite in certain mollusks. The most important anatomical features of the NEMERTINEA are the presence of: (i) a long proboscis (Fig. 117,2, 10), which lies in a proboscis sheath just above the digestive tract, and may be everted and used as a tactile, protective, and defensive organ; (2) a blood vascular system consisting usually of a median dorsal and two lateral trunks (Fig. 117, Q)\ and (3) an alimentary canal with both mouth (Fig. 117, 7) and anal openings. The blood vascular system is here encountered for the first time. NEMER- TINEA possess a mesoderm and nervous and excretory systems which do not differ markedly from those of the flatworms. The pro- boscis sheath may represent the ccelom, but this is not certain. N COLLEGE ZOOLOGV 2. Nemertines feed on other animals, both dead and alive. They live, as a rule, coiled up in burrows in the mud or sand, or under stones, but some of them frequent patches of seaweed. Loco- motion is effected by the cilia which cover the surface of the body, by contractions of the body muscles, or by the attachment of the pro- boscis and subsequent drawing forward of the body. Cerebratulus (Fig. 117) swims actively like a leech (Chap. XI). The power of regenerating lost parts is well developed. During development a peculiar larval stage called the PiUdium (Fig. 1 1 8), is usually passed through. This resembles a helmet with cilia on the surface and a FIG. 117. Cerebratulus fus- cus, a NEMERTINE. /, cephalic slits ; 2, opening leading into retracted proboscis; 3, dorsal commissure of nervous system; 4, ventral commissure; 5, brain; 6, posterior lobe of brain; 7, mouth; 8, proboscis; Q, lateral vessel; 10, proboscis; //, pouches of alimentary canal; /.?, stomach. (From Shipley and MacBride, after Burger.) FIG. 118. Pilidium larva of a NEMER- TINE. D, alimentary canal; E, E', the two pairs of ectodermal invaginations. (From Sedgwick, after Metschnikoff.) INVERTEBRATES OF UNCERTAIN POSITION 179 long tuft of cilia at the apex. The adult develops from this larva by the formation of ectodermal imaginations (Fig. 118, E, ') which surround the alimentary canal (D). This in- vaginated portion escapes from the PUidium and grows into the adult nemertine. 3. NEMATOMORPHA This group (Gr. ncwa, thread; morplie, form) contains a single family, the GORDIID.E, and two genera, Gordius, which lives in fresh water, and Nectonema in the sea. They are long, slender thread-like animals (Fig. 119) often found in ditches and commonly called horsehair snakes. Some authors consider them an order of NEMATODA; whereas others rank them as a class under the Phylum NEMAT- HELMINTHES. It seems best to include them with the other invertebrates of more FIG. 119. Gordius (of the group or less uncertain systematic NEMATOMORPHA) twining around a water-plant and laying eggs, a, a, clump position. and string of eggs. (From the Cam- Their resemblance to the ^idge Natural History, after von Linstow.) NEMATODA, indicated by the term NEMATOMORPHA, does not hold for the internal anatomy. A distinct epithelium lines the body-cavity ; no lateral lines are present; there is a pharyngeal nerve-ring and a single ventral nerve-cord ; and the ovaries, which are segmentally arranged, discharge the eggs into the body-cavity. The larvae of Gordius usually migrate into the immature stages of aquatic insects; these are then devoured by other animals in whose intestines the young live and develop until they finally escape into the water. i8o COLLEGE ZOOLOGY 4. ACANTHOCEPHALA The ACANTHOCEPHALA (Gr. akantha, a spine; kephale, the head) are parasitic worms which are also considered by many a class in the Phylum NEMATHELMINTHES. They are spineheaded worms which fasten themselves to the intestinal wall of verte- brates by means of a protrusible proboscis covered with hooks (Fig. 120, R). The presence of this proboscis, and of a com- plex reproductive system, and the absence of an alimentary canal, distinguish the ACANTHOCEPHALA from the NEMATODA and NEMATOMORPHA. The adults are most common in fishes, but all vertebrates, including man, are parasitized by them. There is an alterna- tion of hosts during development. For example, the larva of Echinorhynchus gigas lives in the June bug, the adult in the pig. FIG. ^.-Echino- CH^TOGNATHA (Gr. chaite, horse- CEPHALA), male. B, re- hair ; gnathos, the cheek) are marine tracted bursa: De, ejacu- i 1-1 latory duct; G. gang- ammals which swim about near the sur- lion; Li, ligament; face of the sea. The best-known genus P, penis; Pr, prostatic o '/< 4.1. T sacs; R. proboscis; lb ^agttta, the arrow-worm, figure 121 Rs, sheath of proboscis; shows most of the anatomical features of T, testes; Vd, vasa defer- c 'u i rm entia. (From Sedgwick, * a S ltta hexaptera. There is a distinct after Leuckart.) coelom, an alimentary canal with mouth (a), intestine (b), and anus (c), a well-developed nervous system, two eyes, and other sensory organs. The mouth has a lobe on either side provided with bristles (e) which are used in capturing the minute animals and plants that serve as INVERTEBRATES OF UNCERTAIN POSITION' iSi food. The members of the group are hermaphroditic, possessing both male and female reproductive organs. The CILETOGNATHA are included under the NEMATHELMINTHES by some authori- ties and are placed in a separate phylum by others. -6 -d, 6. ROTIFERA (ROTATORIA) The ROTIFERA (Lat. rota, a wheel ; fero, I carry) (Fig. 122), commonly known as wheel animalcules, are extremely small METAZOA. They were at one time con- sidered INFUSORIA. Most of them are inhabitants of fresh water, but some are marine and a few parasitic. The anatomy of a ROTIFER is shown in Figure 123. The head is provided with cilia (c l , c 2 ) which aid in locomotion and draw food into the mouth (mth). The tail or foot is bifurcated and adheres to objects by means of a secretion from a cement gland (c.gl). The body is usually cylindrical and is covered by a shell-like cuticle (cu). The PROTOZOA and other minute organisms used as food are swept by the cilia through the mouth (mth) into the pharynx (ph), also called the mastax or FIG. 121. The arrow- chewing stomach. Here chitinous jaws, ^/g P *( which are constantly at work, break up NATHA), ventral view. the food. The movements of these jaws *; - ^ v ^ s ^- easily distinguish a living rotifer from lion; e, movable bristles other organisms. The food is digakd in ^SwfTo the glandular stomach (st). Undigested duct; i, vas deferens; particles pass through the intestine (int) {S^lS ^ Mat into the cloaca (cl) and out of the anus (a). Bride, after Hertwig.) j 1&2 COLLEGE ZOOLOGY ^ Two coiled tubes (nph), which give off a number of ciliated lobules (fl.c), and enter a bladder (c.v), constitute the ex- cretory system. The bladder con- tracts at intervals, forcing the contents out of the anus. Since the amount of fluid expelled by the bladder is very large, it is probable that respiration is also a function of this organ, the oxygen being taken into the animal with the water which diffuses through the body-wall, FIG. 122. TWO species of RO- an <3 the carbonic acid beine cast [FERA. A. Phi'lnH,-nP R U..J., .,, "^ with the excretory fluid. The body-cavity is not a true ccelom. The sexes of rotifers are separate. The female possesses an ovary (Fig. I23> O vy) in which the eggs arise, a yolk-gland (vt) ch supplies the eggs with yolk, and an oviduct (ovd) which ** /l.c after Hudson and Gosse.) br nph ~- ^ oi> ovd m FIG. 123. -Diagram showing the anatomy of a ROTIFER .V!^ f r 'i T 5 , C ''P reora1 ' and ^ Pastoral circlet of cilia ^ eeler ^ ev" ^ fl Ioaca; /^/ dermic epithelium; d.f, dorsai nth nenhridal'tnh' flame - Cel ' S ; l < intestine; m, muscles; mth , mouth; npn , nephndial tube; ov, ovum; ovd, oviduct; ovy, germarium- bh st, stomach; vl , vitellarium. (From Parker and HaswelT) INVERTEBRATES OF UNCERTAIN POSITION 183 carries the eggs (ov) into the cloaca (d). From here the eggs reach the exterior through the anus. The males are usually smaller than the females, and often degenerate. They possess a testis in which the spermatozoa arise, and a penis for trans- ferring the spermatozoa to the female. Two kinds of eggs are produced by rotifers: (i) summer eggs, and (2) winter eggs. The summer eggs, which develop parthenogenetically, are thin-shelled, and of two sizes ; the larger produce females and the smaller males. The winter eggs, which are fertilized, have thick shells, and develop females. One peculiarity of the rotifers worth mentioning is their power to resist desiccation. Certain species, if dried slowly, secrete gelatinous envelopes which prevent further drying; in this condition they live through seasons of drought, and may be subjected to extremes of temperature without perishing. The resemblances between rotifers and the trojchophore larvae of certain mollusks, annelids, and other animals to be described later, is quite striking. The larva of the NEMERTINEA (Pilidium, Fig. 118) is likewise similar in some respects to an adult rotifer. This has led to the theory that the rotifers are animals somewhat closely connected with the ancestors of the mollusks, annelids, and certain other groups. 7. BRYOZOA (POLYZOA) TheBRYOZOA (Gr. 6r0,moss; zob'n, an animal), PHORONIDEA, and BRACHIOPODA are sometimes placed together under one phylum, the MOLLUSCOIDEA, because they are mollusk-like in form. It seems probable, however, that they not only repre- sent distinct, but widely divergent groups, and should therefore be discussed separately. The BRYOZOA, or moss-animals, are mostly colonial. They resemble hydroids, like Obelia (Fig. 73), in form, but differ from them markedly in structure. The majority of them live in the sea, but a few inhabit fresh water. Bugula (Fig. 124) is 1 84 COLLEGE ZOOLOGY a common marine genus which shows the principal characteristics of the group. The soft parts constituting the polypide lie within the true ccelomic cavity bounded by the body^waH'oj- zoacmm. The mouth lies in the midst of a crown of ciliated tentacles (Fig. 124) called the lophophore, which serve to draw food particles into the body. The U-shaped alimentary canal con- sists of a ciliated oesophagus (Oes), a stomach (D), and' an intestine which opens by means of an anus lying just outside the lophophore. One retractor muscle (R) serves to draw the polypide into the zocecium. The funiculus (F) is a strand of meso- dermal tissue attached to the base of the stomach. There are no circu- latory nor excretory organs. Both an ovary and a testis are present in each individual ; they may be found attached to the fu- niculus or the body-wall. The eggs are P robabl y fertilized in the ccelom and then develop ill a modified Portion of the zocecium called the OOBCium (Fig. 124, Ovz). The lame of some BRYOZOA resemble a trocho- phore (see p. 183). Certain members of Bugula colonies are modified into struc- tures called avicularia (Fig. 124, Av). These have jaws which probably protect the colony from the attacks of small organisms and prevent the larvae of other animals from settling upon it. The BRYOZOA may be separated into two distinct groups, the ECTOPROCTA and ENTOPROCTA. In the former the anus opens outside of the lophophore, as in Bugula, and a ccelom is present. muscle; Te, tentacular crown, (From Sedgwick, after v. Nord- mann.) INVERTEBRATES OF UNCERTAIN POSITION Plumatella and Pectinatella are fresh-water ECTOPROCTA. The ENTOPROCTA have the anal opening within the lophophore, and the space between the intestine and body- wall is filled with mesoderm cells. Pedicel- Una and Urnatella belong to this group. 8. PHORONIDEA This group consists of a single genus, Phoronis (Gr. Phoronis, name of a king, Fig. 125), containing worm-like animals which live in the sand, enclosed in mem- branous tubes. Their systematic position is still more or less uncertain, but their structure indicates a probable relationship to the ECTOPROCTA. 9. BRACHIOPODA FIG. 125. Phoronis buskii (of the group PHORONIDEA) removed from its. tube and seen from behind. (From , Sedgwick, after M'ln- The BRACHIOPODA (Gr. brachwn, the tosn .) arm; pous, a foot) are marine animals living within a calcareous bivalve shell (Fig. 126). They are usually attached to some object by a peduncle (Fig. 127, 10). B FIG. 126. Magellania flavescens (of the group BRACHIOPODA). A, dorsal aspect of shell. B, shell as seen from the left side. b, beak; d.v., dorsal valve; /, foramen; v.v., ventral valve. (From Weysse, after Davidson.) I 86 COLLEGE ZOOLOGY Because of their shell they were for a long time regarded as mollusks. The valves of the shell, however, are dorsal (Fig. 126, d.v.) and ventral (.?.) instead of lateral as in the bivalve mollusks (Fig. 173). Within the shell (Fig. 127) is a conspicuous structure called the lophophore (2), which consists of two coiled ridges, called arms; thesTbear ciliated tentacles FIG. 127. Anatomy of a BRACHIOPOD, Waldheimia australis. i, mouth; 2, lophophore; j, stomach; 4, liver tubes; 5, median ridge on shell; 6, heart; 7, intestine; 8, muscle from dorsal valve of shell to stalk; g, opening of nephrid- ium; 10, stalk; //, body-wall; 12, tentacles; 13, coil of lip; 14, terminal tentacles. (From Shipley and MacBride.) (12). Food is drawn into the mouth (i) by the lophophore. A true ccelom is present, within which lie the stomach (j), digestive gland (4), and the heart (6). The group BRACHIOPODA is extremely old, and, although found in all seas to-day, brachiopods were formerly more numerous in species and of much greater variety in form than at present. Some of them, for example Lingula, are apparently the same to-day as they were in the Silurian period estimated at about twenty- five million years ago. 10. GEPHYREA The GEPHYREA (Gr. gephura, a mound) are worm-like animals that have been classed by many zoologists with the Phylum ANNELIDA (Chap. XI), Their relations to this phylum are, INVERTEBRATES OF UNCERTAIN POSITION I8 7 however, uncertain, and the affinities of the GEPHYREA to one another are even doubtful. Consequently they have been separated provisionally from the ANNELIDA and divided into tfiree groups as follows : - (i) The Echiuroidea (Fig. 128) have traces of segmentation in the adult, a proboscis (a), a pair of ventral hooked seta (b), FIG. 128. FIG. 129 FIG. 130. FIG. 128. Echiurus pallasii (of the group GEPHYREA). a, mouth at the end of the grooved proboscis; b, ventral hooks; c, anus. (From the Cam- bridge Natural History.) FIG. 129. Sipunculus nudus (of the group GEPHYREA) laid open from the side. A, anus; BD, brown tubes (nephridia); D, intestine; G, brain; Te, tentacles; VG, ventral nerve-cord. (From Sedgwick, after Keferstein.) FIG. 130. Priapuhts caudatus (of the group GEPHYREA). a, mouth surrounded by spines. (From the Cambridge Natural History.) and a terminal anus (c). They usually live in crevices in rocks, using their proboscis for locomotion, for capturing prey, and as an organ of s?nse. There is a trochophore stage (p. 183) in development. (2) The Sipunculoidea (Fig. 129) are unsegmented, with only one pair of nephridia (BD), a large coelom, and an anus (A] on 1 88 COLLEGE ZOOLOGY the dorsal surface near the anterior end. They live in the sand or bore into coral reck, and are capable of slow, creeping loco- motion. The anterior part of the body can be drawn into the larger posterior portion, and is therefore called the introvert. Tentacles (Te) are usually present at the anterior end. (3) The Priapuloidea (Fig. 130) are unsegmented, with an anterior month (a) surrounded by chitinous teeth, and a posterior anus. They live in the mud or sand with the anterior end projecting from the surface. CHAPTER X PHYLUM ECHINODERMATA 1 THE ECHINODERMATA (Gr. echinos, a sea-hedgehog; derma, skin) are " spiny-skinned " animals that live in the sea. They represent the most complex of all radially symmetrical animals. For a long time they were placed with the CCELENTERATA in a group called RADIATA, but when tlu-i; structure and life-history had been thoroughly made out, they were found to have closer affinities with the higher METAZOA. Five classes of echinoderms are recognized by most zoologists. Besides these there are several groups of fossil forms. Phylum ECHINODERMATA. STARFISHES, BRITTLE-STARS, SEA- URCHINS, SEA-CUCUMBERS, SEA-LILIES. Triploblastic, radially symmetrical animals ; usually five antimeres, ccelom well developed; anus usually present; locomotion in many species accomplished by characteristic organs known as tube-feet ; a spiny skeleton of calcareous plates generally covers the body. Class I. ASTEROIDEA (Gr. aster, a star; eidos, resemblance) (Fig. 131). Typically pentamerous; arms usually not sharply marked off from the disc; ambulacral groove present. Ex- amples: Asterias, Astropecten, Culcita. -- Starfishes. Class II. OPHIUROIDEA (Gr. ophis, a snake; oura, a tail; eidos, form) (Fig. 138). Typically pentamerous; arms sharply marked off from the disc; no ambulacral groove. Examples: Ophiura, Amphiura, Astrophyton. -- Brittle-stars. Class III. ECHINOIDEA (Gr. echinos, hedgehog; eidos, form) (Fig, 141). Pentamerous, without arms or free rays; test of 1 The echinoderms form a very complex, aberrant coelomate group, and their Study may be deferred until later if desirable. 189 190 COLLEGE ZOOLOGY calcareous plates bearing movable spines. Examples: Cidaris, Arbacia, Toxopneustes, Strongylocentrotus. Sea-urchins; Echin- arachnius. Sand-dollar; Spatangus. Heart-urchin. Class IV. HOLOTHURIOIDEA (Gr. holos, whole; thourios, rushing) (Fig. 146). Long ovoid; muscular body-wall; tentacles around mouth. Examples: Holothuria, Thyone, Caudina.- Sea-cucumbers. Class V. CRINOIDEA (Gr. krinon, a lily; eidos, form) (Fig. 148). Arms generally branched and with pinnules; aboral pole sometimes with cirri but usually with stalk, for temporary or permanent attachment. Examples: Antedon. Feather- star ; Pentacrinus. - - Sea-lily. i. ANATOMY AND PHYSIOLOGY OF THE STARFISH -- ASTERIAS External Features. - -The starfishes are common along many sea-coasts, where they may be found usually upon the rocks with the mouth down. The upper surface is therefore aboral or abactinal. On the aboral surface (Fig. 131) are (i) many spines (Fig. 133, 8) of various sizes, (2) pedicel- lanes (Fig. 133, 10) at the base of the spines, (3) a madre- porite (Fig. 131, mad], which is the entrance to the water-vascular system, and (4) FIG. 131. The starfish, Asterias rubens, seen from ^ ana j ODenme the aboral surface, mad, madreporite. (From the Cambridge Natural History.) (anus). A glance PHYLUM ECHINODERMATA at the oral surface (Fig. 132) reveals a mouth centrally situated in the membranous peristome, and five grooves (a mbulacral) , one in each arm, from which two or four rows of tube-feet extend (Fig. 133, /;). The Skeleton. - - The skeleton is made up of calcareous plates or ossicles bound together by fibers of connective tissue (Fig. 133, 9, n, 12). The ossicles are regularly arranged about the ,-Mim .fjtjm ^^^M^^m^^^- *-*-**- sucker. =3 muse. B FIG. 132. A, the starfish, Asterias rubens, seen from the oral surface. B, an adambulacral spine, showing three straight pedicellaria?. C, a tube- foot expanded and contracted. (From the Cambridge Natural History.) mouth and in the ambulacral grooves and often along the sides of the arms, but are more or less scattered elsewhere. The am- bulacral and adambulacral ossicles (Fig. 133, //, 12) have muscu- lar attachments and are so situated that w 7 hen the animal is disturbed they are able to close the groove and thus protect the tube-feet. The spines of the starfish (Fig. 131; Fig. 133,' ) are 192 COLLEGE ZOOLOGY short and blunt and covered with ectoderm (Fig. 133, i). Around their bases are many whitish modified spines called pedicellarioK (Fig. 133, 10). These are little jaws which when irritated may_be opened and closed by several sets of muscles. Their function is to protect the dermal bronchia (Fig. 133, 5), to prevent debris and small organisms from collecting on the ....5 10 FIG. 133. Diagram of a transverse section of the arm of a starfish. i, ectoderm; 2, jelly; 3, peribranchial space in the skin; 4, peritoneal lining of the body-cavity; 5, a branchia; 6, pyloric caecum; 7, mesentery support- ing a caecum; 8, spine; g, ossicle in skin; 10, pedicellaria; //, ambulacral ossicle; 12, adambulacral ossicle; 13, radial trunk of water-vascular system; 14, radial septum separating the two perihaemal spaces; /j, radial nerve-cord; 16, ampulla of tube-foot; 17, tube-foot; 18, perihaemal space; 19, coelom. (From Shipley and MacBride.) surface, and to capture food. The skeleton serves to give the animal definite shape, to strengthen the body- wall, and as a protection from the action of waves and from other organisms. The Muscular System. - - The arms of the starfish are not rigid, but may be flexed slowly by a few muscle fibers in the body-wall. The tube-feet are also supplied with muscle fibers. Ccelom. - - The true body-cavity of the starfish is very large and may be separated into several distinct divisions. The PHYLUM ECHINODERMATA 193 perhisceral part of the ccelom (Fig. 133, 19) surrounds the ali- mentary canal and extends into the arms. It is lined with peritoneum (Fig. 133, 4) and filled with sea- water containing some albuminous matter. Oxygen is taken into the ccelomic fluid and carbon dioxide given off through outpushings of the body- wall known as papula; or dermal branchm (Fig. 133, 5). The ccelom also has an ex- cretory function, since cells from the peritoneum are budded off into the ccelomic fluid, where they move about as amcebocytes gathering waste matters. These cells make their way into the der- mal branchiae, through the walls of which they pass to the outside, where they dis- integrate. The Water-vascular Sys- tem. - - The water- vascular system (Fig. 134) is a divi- sion of the ccelom peculiar to echinoderms. Beginning with the madreporite (m) the fol- FlG I34 ._^ ate r-vascular system of lowing Structures are encoun- a starfish. a, ampulla:; ap, Polian 7 / /\ vesicles: r, circular canal; m, madre- tered: the stone-canal (m) porite . ;< madreporic canal . A tube-feet; running downwards enters r, radial canals ; r', branches to am- 7 / ^ 1-1 pullae. (From Parker and Haswell, after the ring-canal (c), which G egenbaur .) encircles the mouth ; from this canal five radial canals (Fig. 134, r; Fig. 133, ij), one in each arm, pass outward just above the ambulacral grooves. The radial canals give off side branches from which arise the tube-feet (Fig. 134, t; Fig. 133, 17} and ampulla (Fig. 134, a; Fig. 133, 16.) The ampullae are bulb-like sacs extending into the ccelom ; they are connected directly with the tube-feet, which pass through tiny o i 9 4 COLLEGE ZOOLOGY pores between the ambulacral ossicles (Fig. 133, n}. Sea-water is forced into this system of canals by cilia which occur in grooves on the outer surface of the madreporite and in the canals which penetrate it. Arising from the ring-canal near the ampullae of the first tube-feet are nine vesicles called, after the name of their discoverer, " Tiedemann's bodies." These structures pro- duce amcebocytes which pass into the fluid of the water- vascular system. Polian vesicles (Fig. 134, ap) are present in some starfishes, but not in Aster ias. The most interesting structures of the water- vascular system are the tube-feel. They are primarily locomotory and function as follows: "When the tube-foot is to be stretched out, the ampulla contracts and drives the fluid downwards. The con- traction of the ampulla is brought about by muscles running circularly around it. The tube-foot is thus distended and its broad flattened end is brought in contact with the surface of the stone over which it is moving and is pressed close against it. The muscles of the tube-foot itself, which are arranged longi- tudinally, now commence to act, and the pressure of the water preventing the tearing away of the sucker from the object to which it adheres, the starfish is slowly drawn forward, whilst the fluid in the tube-foot flows back into the ampulla." Tube- feet are also sensory (p. 197). A number of other spaces and canals have been considered as parts of the ccelom and at one time were supposed to be a " blood"- vascular system. These are the axial sinus lying along the stone-canal and opening to the outside through the madreporite, the inner circumoral perih&mal canal, the outer perihamal canal beneath the ring-canal, the aboral sinus, and the peribranchial spaces. The functions of these various cavities are not clear. Digestion. - - The alimentary canal of the starfish (Fig. 135) is short and greatly modified. The mouth opens into an oesoph- agus which leads into a thin-walled sac, the stomach. Follow- ing this is the pyloric sac. From the pyloric sac a tube passes PHYLUM ECH1NODERMATA into each arm, then divides into two branches, each of which possesses a large number of lateral pouches; these branches are called pyloric or hepatic cceca (Fig. 135, py). They are green in color. Above the pyloric sac is the slender rectum (rect.), which may open to the outside through the anus. Two branched pouches, brown in color, arise from the rectum and are known as rectal cceca (rect.cac.}. The food of the starfish consists of fish, oysters, mussels, barnacles, clams, snails, worms, Crustacea, etc. When a mussel rect. mp br. rect caec. ..-py OSS '. ax! \..' perih. \ peristome Tierv.circ w. v r. perih. miisc.tr. 00- FIG. 135. Diagrammatic longitudinal section of a starfish, ab., aboral sinus; ax, axial sinus; ax.', inner perihasmal ring-canal; br., branchia or gill; g.r, genital rachis; mp., madreporite; musc.tr., muscle uniting ambulacral ossicles; nerv.circ, nerve-ring; n.r., radial nerve-cord; or., eye-pit; oss., ossicles in skin; p.br., peribranchial sinus; p.c., pore canal; perih., (right) perihsemal radial canal, (left) outer perihaemal ring-canal; py, pyloric caecum; red., rectum; rect.ceec., rectal caeca; sp., spines; st.c., stone-canal; I, tentacle terminating radial canal ; w.v.r., water-vascular radial canal. (From the Cambridge Natural History.) is to be eaten, the animal seizes it with the tube-feet " and places it directly under its mouth, folding its arms down over it in um- brella fashion (Fig. 136). The muscles which run around the arms and disc in the body-wall contract, and the pressure thus brought to bear on the incompressible fluid contained in the ccelom, forces out the thin membranous peristome and partially turns the stomach inside out. The everted edge of the stomach is wrapped round the prey. Soon the bivalve is forced to relax 196 COLLEGE ZOOLOGY its muscles and allow the valves to gape. The edge of the stomach is then inserted between the valves and applied directly to the soft parts of the prey, which is thus completely digested. When the starfish moves away, nothing but the cleaned shell is left behind. If the bivalve is small, it may be completely taken into the stomach, and the empty shell later rejected through the mouth." (MacBride.) Schiemenz has shown " (i) that whilst a bivalve may be able to resist a sudden pull of 4000 grammes it will yield to a pull of 900 grammes long continued; (2) that a starfish can exert a pull of 1350 grammes; (3) that a starfish is unable to open a bivalve unless it be allowed to raise itself into a hump (Fig. 136) so that the pull of the central tube-feet is at right angles to the prey. A starfish confined between two glass plates walked about all day carrying with it a bivalve which it was unable to open." (Mac- Bride.) FIG. 136. View of starfish (Echinaster) The lining of the Stomach devouring a mussel. i madreporite. secre tes niUCUS; that of the (From the Cambridge Natural History.) pyloric sac and caeca secretes ferments; these change proteids into diffusible peptones, starch into maltose, and fats into fatty acids and glycerine. Thus is digestion accomplished. Undigested matter is ejected through the mouth, and very little, if any, matter passes out of the anus. The rectal caeca secrete a brownish material of unknown function, probably excretory. Circulation. - - The fluid in the ccelom is kept in motion by cilia and carries the absorbed food to all parts of the body. Excretion. - - This is accomplished by the amcebocytes (neph- rocytes) in the coelomic fluid (p. 193), probably aided by the rectal caeca. PHYLUM ECHINODERMATA 197 Respiration. - The dermal branchiae (Fig. 133, 5) function as respiratory organs (p. 193). The Nervous System. - - Besides many nerve-cells which lie among the ectoderm cells, there are ridges of nervous tissue, the radial nerve-cords (Fig. 135, n.r. ; Fig. 133, 75), running along the ambulacral grooves, and uniting with a nerve-ring (Fig. 135, nerv.circ) encircling the mouth. The apical nervous system consists of a trunk in each arm which meets the other trunks at the center of the disc; these trunks innervate the dorsal muscles of the arms. Sense-organs. - - The tube-feet are the principal sense-organs. They receive nerve- fibers from the radial nerve-cords. At the end of each radial canal (Fig. 135, /) the radial nerve-cord ends in a pigmental mass (oc.} ; this is called the eye, since it is a light- perceiving organ. The dermal branchiae are probably sensory, also. Reproduction. - - The sexes of starfishes are distinct. The reproductive organs are dendritic structures, two in the base of each arm; they discharge the eggs or sperms out into the water through pores in the aboral surface at the interspace between two adjacent arms. The eggs of many starfishes are fertilized in the water; they are holoblastic (p. 87), undergo equal cleavage, and form a blastula and gastrula similar to those shown in Figure 51, K, M. The opening (blastopore] of the gastrula be- comes the anus, and a new opening, the mouth, breaks through. Ciliated projections develop on either side of the body, and a larva, called a Bipinnaria (Fig. 150, B), results. This changes (metamorphosis) into the starfish. Behavior. - - The starfish moves from place to place by means of its tube-feet (p. 194). During the day it usually remains quiet in a crevice, but at night it is most active. The responses of the starfish to stimuli are too complex to be stated definitely. When a starfish is placed on its aboral surface it performs the " righting reaction," i.e. it turns a sort of handspring by means of its arms. Professor Jennings 198 COLLEGE ZOOLOGY taught individuals to use a certain arm in turning over. One animal was trained in eighteen days (180 lessons), and after an interval of seven days apparently " remembered ' which arm to use. Old individuals could not be trained as readily as young specimens. Regeneration. - - The starfish has remarkable powers of re- generation. A single arm with part of the disc will regenerate an entire body. If an arm is injured, it is usually cast off near the base at the fourth or fifth ambulacral ossicle. This is autotomy (see also pp. 117 and 155). Economic Importance. Oyster beds are seriously affected by starfishes. One starfish which was placed in a dish contain- ing clams devoured over fifty of them in six days. Formerly starfishes were taken, cut in two, and thrown back; this of course only increased the number, since each piece regenerated an entire animal. They are now often captured in a mop-like tangle, to the threads of which the pedicellariae cling. They are then thrown out on the shore above high-water mark and left to die in the sun, or killed in hot water. 2. CLASS I. ASTEROIDEA STARFISHES Little need be said of the Asteroidea beyond what has been stated above concerning one of the common species of the wide- spread genus Asterias. The number of arms ranges from five to more than forty, but aside from this diversity the chief dif- ferences in shape among the starfishes are brought about by the variations in the length and breadth of the arms and by their lateral fusion. In some cases this adhesion has gone so far as to result in a pentagonal form (Fig. 137). The skeleton differs in structure in different species and is of importance in classification. The distinctive characteristics of the Asteroidea are as fol- lows: Typically pentamerous; body commonly more or less flattened; arms long or short, usually not sharply marked off PHYLUM ECHtNODERMATA I QO fl FIG. 137. Pentaccros reticiilaris, oral aspect. A large starfish common on the coast of Florida. (From Weysse.) from disc; viscera extend into arms; ambulacral groove on ven- tral surface of arms; anus and madreporite dorsal. 3. CLASS II. OPHIUROIDEA BRITTLE-STARS Distinctive Characteristics. -- Body flattened; arms distinct from disc; no caeca nor gonads in arms; no ambulacral grooves nor anus; madreporite on oral surface. Structural Peculiarities. - -The arms of the brittle-stars (Fig. 138) and basket-fish (Fig. 139) are noticeably different from those of the starfish. They are slender and exceedingly flexible. The ambulacral groove is absent, being covered over by skeletal plates and converted into the epineural canal. Each arm is covered by four rows of plates, one aboral, one oral, and two lateral. Spines are restricted to the lateral plates. Within the arm are plates which have fused together and are known as vertebra. The muscular system of the arm is well developed. 2OO COLLEGE ZOOLOGY The water-vascular system differs in several respects from that of the starfish. The madreporite is on the oral surface. The tube-feet have lost their locomotor function and serve as tactile organs ; the ampullce have consequently disap- peared. Nutrition. - - The food of the brittle-stars consists of minute organisms and decaying organic matter lying on the mud of the sea bottom. It is scooped into the mouth by special tube-feet, FlG. 138. Aboral view of phiogly plia bullata, a brittle-star. (From Shipley and MacBridc, after Thompson.) two pairs to each arm, called the oral tube-feet. The rows of spines which extend out over the mouth opening serve as strainers (Fig. 140). The stomach is a simple sac without caeca; it can- not be pushed out of the mouth. There is no anus. Behavior. - - The locomotion of brittle-stars is comparatively rapid. The arms are bent laterally, and enable animals belonging to certain species to ' run," or climb, and probably to swim. Apparently they cannot be taught like starfishes. PHYLUM ECHINODERMATA 201 FIG. 139. Aboral view of a basket-fish, Astrophyton linckii. (From the Cambridge Natural History, after Thompson.) Regeneration. - - The term brittle-star is derived from the fact that these animals break off their arms if they be- come injured. This auto- tomy often allows the in- dividual to escape from its enemies, and is of no serious consequence, since new arms are speedily regenerated. In a num- ber of species the aboral covering of the disc is normally cast off, prob- ably for reproductive pur- poses. FIG. 140. Oral view of Ophioglypha bitllatii, n brittle-star. (From the Cam- bridge Natural History, after Thompson.) 202 COLLEGE ZOOLOGY 4. CLASS III. ECHINOIDEA. SEA-URCHINS Distinctive Characteristics. - - Pentamerous, without arms or free rays; skeleton usually of twenty columns of firmly united plates, five pairs of ambulacral rows, and five pairs of inter- ambulacral rows. Structural Peculiarities. - - The starfish type may be changed to that of the sea-urchin quite easily. The latter (Figs. 141- FIG. 141. Aboral surface of a sea-urchin, Strongylocentrotus drobachiensis . /.ex- panded tube-feet; 2, spines. (From Shipley and MacBride, after Agassiz.) 142) resembles a starfish whose aboral surface has become exceedingly reduced, being represented by a small area, the periproct (Fig. 142, 2), and the tips of whose arms have at the same time been bent upward and united near the center of the aboral surface. The skeleton of the sea-urchin is known as a shell or test, and is shown in detail in Figure 142. The apical system of plates contains the madreporite (j), four other genital plates (4), with genital pores, and five ocular plates (5), each with a mass of pig- mental cells. There are five pairs of columns of ambulacral PHYLUM ECHINODERMATA 203 plates (7), so called because they are penetrated by tube-feet (8) and five pairs of columns of interambulacral plates (6). On the inside of the test around the peristome in many sea-urchins are five arches, often incomplete, called auricles. Most of the plates bear spines which are attached by muscles and move freely on little knob-like elevations called tubercles (g). The pedicellarice are more specialized than those of the starfish; they commonly i -4 --5 FIG. 142. Dried test of a sea-urchin, Echinus esculentus. I, anus; 2, peri- proct; 3, madreporite; 4, a genital plate; i, an ocular plate; 6, an interambu- lacral plate ; 7, an ambulacral plate ; S, pores for protrusion of tube-feet ; 0, tubercles of primary spines. (From the Cambridge Natural History.) have three jaws. The mouth is provided with five white teeth; these are part of a complicated structure known as " Aristotle's Lantern " (Fig. 143, comp., eph.). Nutrition. - - The food of the sea-urchin consists of marine vegetable and animal matter which is ingested by means of " Aristotle's Lantern." The intestine (Fig. 143, int) is very long; it takes one turn around the inside of the body and then bends upon itself and takes a turn in the opposite direction. A small tube, the siphon (Fig. 143, siph.), accompanies the in- 2O4 COLLEGE ZOOLOGY testine part way, opening into it at either end. The anus (fig. 142, i) of the sea-urchin is near the center of the aboral surface. Respiration. - - A large part of the respiration takes place in most echinoids through ten branched pouches situated on the area comp. ret. romp.clv. amp g.rach cpmp. ;' ,arap. gem rot. oe tooth sac. FIG. 143. Internal anatomy of a sea-urchin, Echinus esculentus. amp., am- pullae of tube-feet; aur., auricle; b.v., '' dorsal blood-vessel "; comp., " com- passes" of Aristotle's lantern; comp. elv., elevator muscles; comp. ret., retractor muscles; eph., epiphyses of jaws; gon., gonad; g.rach, genital rachis; int, in- testine; oe, oesophagus; prol., protractor of Aristotle's lantern; reel., rectum; ret., retractor muscle; siph., siphon; st., stomach; stone c, stone-canal. (From the Cambridge Natural History.) surrounding the mouth, one pair in each angle between the ambulacral plates. The tube-feet also are respiratory in function. Locomotion. - - Both tube-feet and spines are used in loco- motion. ' The spines are pressed against the substratum and keep the animal from rolling over under the pull of the tube- feet and also help to push it on." PHYLUM ECHINODERMATA 205 Echinoidea in General. - - The common sea-urchins just de- scribed live principally on rocky shores. The cake-urchins (Fig. 144) live at or near the surface of the sand; a common m.p pod' / * ss^. pod Vic,. 144. Aboral view of a " sand- dolhir," l-'.chi:id'-:i! h;:ins piinna. m.p. madre- porite; pad, small tube-foot ; pod', llattened respiratory tube-foot. (From the Cam- bridge Natural History.) FIG. 145. Aboral view of the test of a heart- urchin, Brissopsis lyrifera. Af, anus. (From Sedg- wick, after Claus.) form on the eastern coast of North America is the sand-dollar, Echinarachnius. The heart-urchins (Fig. 145) bury themselves in the mud to a depth of from a few inches to a foot. 5. CLASS IV. HOLOTHURIOIDEA. -- SEA-CUCUMBERS Distinctive Characteristics. - - Elongated on principal axis; body-wall muscular with small calcareous plates; contractile tentacles around mouth; no external madreporite. Structural Peculiarities. - The most striking external features of the sea-cucumber (Fig. 146) are its muscular body-wall almost devoid of large skeletal plates, its branching tentacles surrounding the mouth, and its lateral position when at rest or moving about on the sea bottom. The water-vascular system (Fig. 147) is homologous to those of the other classes of echinoderms. There is a circular canal around the oesophagus (2), five radial canals (i) which end 206 COLLEGE ZOOLOGY blindly near the anus (jtf), and tube-feet (Fig. 146). The circular canal (2) gives off a polian vesicle (4) and one or more stone- canals ending in internal madreporites (25). From ten to thirty of the tube-feet surrounding the mouth are modified as tentacles for procuring food. The alimentary canal includes a long looped intestine (Fig. 147, 23, 8, 22), the posterior end of which is a muscular enlargement called the cloaca (75). Water flows into the cloaca through the anus (16} and passes into two long branching tubes, the respira- tory trees (n, ip); here part of it probably finds its way through FIG. 146. A sea-cucumber, Thyone briareus, partly buried in mud. (From Pearse in Biol. Bui.) the walls into the body-cavity. Respiration is carried on by the cloaca, respiratory trees, tentacles, tube-feet, and body-wall. The cloaca and respiratory trees also function as excretory organs. Nutrition. - - The food of most sea-cucumbers consists of organic particles extracted from the sand or mud which is taken into the alimentary canal. Some species are said to stretch out their seaweed-like tentacles on which many small organisms come to rest. " When one tentacle has got a sufficient freight it is bent round and pushed into the mouth, which is closed on it. It is then forcibly drawn out through the closed lips so that all the living cargo is swept off." (Shipley and MacBride.) PHYLUM ECHINODERMATA 207 Behavior. The tube-feet, when present, are organs of locomotion. They pull the animal along on its ventral, flattened surface. Waves of muscular con- traction which travel from one end of the body to the other are important in locomo- tion, and the tentacles may also assist. The common sea- cucumbers, Thyonc briarcus, are sensitive to contact with solid objects, and many of them burrow in the sand or mud. They are extremely sensitive to a decrease in the light intensity and will contract the body if an object passes between them and the source of light. They are also negatively phototropic, since they move away from the light. The following has been written concerning this species: " Passing most of its life buried in the mud, Thy one probably a - 3 .-24 18 FIG. 147. Internal anatomy of a sea- cucumber, one of the Aspidochirotce. i, radial vessel; 2, water-vascular ring; j, blood-vascular ring; 4, Polian vesicle; 5, oesophagus; 6, ventral blood-vessel of intestine; 7, connecting blood- vessel; 8, second part of intestine; Q, 10, radial longitudinal muscles; //, left respiratory tree; 12, dorsal-blood vessel of intestine; 13, circular muscles of body-wall; 14, Cuvierian organs; /5, cloaca; 16, anus; 17, radial muscles of cloaca; 18, cut edge of body- wall ; IQ, right respiratory tree; 20, posterior edge of dorsal mesentery; 21, median ventral longitudinal muscles ; 22, third part of intestine ; 2 j, first part of intestine; 24, gonad; 25, internal madre- porites of two stone-canals; 26, dorsal mesen- tery; 2~, genital duct; 28, internulial; 20, radial piece of calcareous ring ; 30, genital opening. (From Sedgwick, after Leuckart.) 208 COLLEGE ZOOLOGY does not often fall a prey to large enemies, but it is protected from them by the withdrawing reaction, by its locomotion away from the light, and by its habit of pulling eel grass and other debris over the body." (Pearse.) Regeneration. -- Sea-cucumbers possess remarkable powers of regeneration. When one is irritated it contracts the muscles of the body- wall, and " since the fluid in the body-cavity is practically incompressible, the effect is to set up a tremendous pressure. As a result of this, the wall of the intestine near the anus tears, and a portion or the whole of the intestine is pushed out. The gill trees are the first to go, and in some species the lower branches of these are covered with a substance which swells up in sea-water into a mass of tough white threads in which the enemies of the animal are entangled. A lobster has been rendered perfectly helpless as a consequence of rashly in- terfering with a sea-cucumber. These special branches are termed Cuvierian organs. " A Holothurioid is only temporarily inconvenienced by the loss of its internal organs. After a period of quiescence it is again furnished with the intestine and its appendages. Some species, which are able to pull in the mouth end of the body with their tentacles, when strongly irritated snap off even this, and yet are able to repair the loss." (Shipley and MacBride.) Economic Importance. - - Among the South Pacific islands and on the coasts of Queensland and in southern China, dried holothurians are known as " beche-de-mer " or " trepang " and are used for food. The trade mounts into hundreds of thou- sands of dollars annually. 6. CLASS V. CRINOIDEA SEA-LILIES OR FEATHER-STARS Distinctive Characteristics. - - Attached by aboral apex of body during early stages of development; arms usually branched and bearing pinnules; tube-feet like tentacles, without ampullae. There are five or six hundred living representatives of this class; fossil remains are very abundant in limestone formations. Most PHY LI' M KCHINODERM ATA 20Q mouth FIG. 148. A crinoid, Pentacrinus madearanus. Arms and portion of stem. (From the Cambridge Natural History, after Thompson.) of the living crinoids are found at moderate depths, a few are deep- sea forms, and some inhabit shallow water. They are often attached by a jointed stalk. Some species break off from the stalk when they become mature, and probably swim about by means of mus- cular contractions of the arms. The arms of crinoids are usually five in num- / ber. The apparently greater number is due to branching near the base FIG. 149. Fossil Echinoderms. A, Theco- cystis scEculus (THECOIDEA). B, Trochocystis bohemicus (CARPOIDEA). C, Echinosphcerites aurantium (CYSTOIDEA). D, Granatocrinus (BLASTOIDEA). (A, B, C, from the Cam- bridge Natural History. A and B, after Jackel; C, after Zittel ; D, from Weysse.) COLLEGE ZOOLOGY (Fig. 148). The branches may be equal, or one large and the other small; in the latter case the smaller branch is called a pinnule. Some authors place the class CRINOIDEA in the subphylum PELMATOZOA along with four classes of fossil echinoderms, the THECOIDEA (Fig. 149, .4), CARPOIDEA (Fig. 149, B), CYSTOIDEA (Fig. 149, C), and BLASTOIDEA (Fig. 149, D). 7. DEVELOPMENT OF ECHINODERMS In most of the echinoderms, the eggs pass through a ciliated blastula stage, a gastrula stage, and a larval stage, which, in the B FIG. 150. Larval Echinoderms. A, a young larval echinoderm. coe, coelom; int, intestine; oes, oesophagus; si, stomach; stom, stomodaeum. B, a larval Asteroid, Bipinnaria elegans. i, frontal area; 2, preoral arm; j, anterior, 4, posterior transverse portion of ciliated band; 5, postoral; 6, postero-lateral; 7, postero-dorsal arm; 8, anal area; Q, oral depression; 10, antero-dorsal; //, ventro-median, 12, dorso-median arm. C, a larval Ophiuroid (Ophio- pluteus). a, anus; d, antero-lateral arm: d', postero-lateral arm; e, postoral arms; g, postero-dorsal arm; m, mouth. (A, from the Cambridge Natural History; B and C, from Sedgwick, B, after Mortensen; C, after Miiller.) course of from two weeks to two months, metamorphoses into an adult. The larvae (Fig. 150, A) of the four principal classes of echinoderms resemble one another, but are nevertheless quite distinct. They are bilaterally symmetrical, and swim about by means of a ciliated band which may be complicated by a number of arm-like processes. The alimentary canal consists of a mouth PHYLUM ECHINODERMATA 211 (Fig. 150, A, slom), oesophagus (oes), stomach (st), intestine (int), and anus. From the digestive tract two ccelomic sacs (coe) are budded off ; these develop into the body-cavity, water-vascular system, and other ccelomic cavities of the adult. The larvae of the different classes have been given names as follows: those of the ASTEROIDEA are called Bipinnaria (Fig. 150,6); OPHIUROIDEA, Ophiopluteus (Fig. 150, C); ECHINOIDEA, --11 FIG. 151. Larval Echinoderms. A, a larval Echinoid (Echinopluteus). /, frontal area; 2, preoral arm; j, post oral arm; ./.anterior; j, posterior trans- verse portion of ciliated band; 6. unpaired posterior arm; 7, anal area; 8, postero-lateral arm; Q, oral area; 10, postero-dorsal arm; n, antero-dorsal arm; 12, antero-lateral arm. B, a larval Holothurioid (Auricularia stelligera). i, frontal area; 2, preoral process; 3, anterior; 4, posterior portion of ciliated band; 5, postoral process; 6, anal area; /, postero-lateral process; 8, postero-dorsal process; Q, oral de- pression; 10, dorso-median process; n, antero-dorsal process. (From Sedg- wick, after J. Miiller.) Echinopluteus (Fig. 151, A); and HOLOTHURIOIDEA, Auricularta (Fig. 151,6). The adults which develop from these larvae are, as we have seen, radially symmetrical, although many of them, notably the HOLOTHURIOIDEA, are more or less bilateral in struc- ture. The bilateral condition of the larvae indicates that the ancestors of the echinoderms were either bilaterally symmetrical or that the larvae have become adapted to an active life in the water. . 212 COLLEGE ZOOLOGY 8. ARTIFICIAL PARTHENOGENESIS The eggs of echinoderms pass through a total and equal cleav- age, and are easily fertilized and reared to the larval stage in the laboratory. For these reasons they have become classical material for embryological studies and for experimental purposes. One of the most interesting phenomena discovered by means of experiments with echinoderm eggs is the development of a larva from an unfertilized egg when subjected to certain environ- mental conditions. This phenomenon is known as artificial parthenogenesis. The eggs of other animals, for example anne- lids, are also capable of developing under certain conditions without fertilization, and those of some species, like plant lice (Chap. XIII) and rotifers (p. 181), are normally parthenogenetic, but echinoderm eggs have been used for experimental purposes more frequently than any others. Loeb reared normal larvae from unfertilized eggs of echino- derms by immersing them in solutions such as chloride of sodium, potassium bromide, cane-sugar, etc. He considered the in- creased osmotic pressure the cause of development, and thought it probable that in ordinary fertilization the spermatozoon brings a solution with a high osmotic pressure into the egg, thereby causing the withdrawal of water. Sea-water concentrated to 70 per cent of its volume has a similar result. A lowering of the temperature of sea-water to the freezing-point causes eggs of Asterias and Arbacia to develop; when combined with a chem- ical reagent, a higher per cent of blastulae results. Eggs ex- posed to a higher temperature (35 to 38 C.) during the early maturation period develop parthenogenetically, and even me- chanical agitation may have a similar effect. Normal mitotic figures appear during the cleavage of these eggs. None of the larvae thus produced was reared to the adult stage. The ease with which echinoderm eggs can be handled has led to some experiments that have an important bearing upon hered- ity. Of these may be mentioned the fertilization of the eggs of PHYLUM ECHIXODKRMATA 213 one species with the spermatozoa of another species, and the fertilization of enucleated fragments of sea-urchins' eggs with spermatozoa of another species. 9. THE POSITION OF ECHINODERMS IN THE ANIMAL KINGDOM Echinoderms and ccelenterates, because of their radial sym- metry, were at one time placed together in a group called RADIATA. The anatomy of the adult and the structure of the larvae, how- ever, show that these phyla really occupy widely separated posi- tions in the animal kingdom. The adult echinoderms cannot Blastoidea t Echinoidea Holothurioidea Cystoidea Crinoidea Ophiuroidea Protechinoidea Carpoidea \ / s< Asteroidea Protopelmatozoa (Thecoidea ?) First Fixed Ancestor t Protoccelomata FIG. 152. Diagram showing the probable relations of the classes of Echinoderms. (After MacBride.) be compared with any other group of animals, and we must look to the larvae for signs of relationship. The bilateral larva is either a modification for a free-swimming life or an indication of the condition of its ancestors. The latter ^ew is accepted by most zoologists. The ancestors of echinoderms were doubt- less bilateral, worm-like animals which became fixed and were then modified into radially symmetrical adults. The probable relations of the classes of echinoderms are shown in Figure 152 (MacBride). 214 COLLEGE ZOOLOGY It is interesting to compare the echinoderm larva with that of a supposed primitive chordate, the Tornaria of Balanoglossus (Chap. XIV, Fig. 334). The remarkable similarity of these larvae suggests that chordates (Chap. XIV) and echinoderms may have had the same or similar ancestors (see also Chap. XXII). CHAPTER XI PHYLUM ANNELIDA THE annelids (Lat. annellus, a little ring) can, in most cases, be distinguished from other worms, like Planaria (Fig. 97) and Ascaris (Fig. in), by the fact that the body is divided into a number of similar parts called segments, metameres, or somites; these are arranged in a linear series and are visible externally because of the grooves which encircle the body. The earth- worms and leeches are well-known examples. Annelids live in fresh water, salt water, and on land; some are parasitic upon other animals. The ANNELIDA form three classes: - (1) CLASS ARCHIANNELIDA (Gr. arche, beginning; Lat. annel- lus, a little ring) (Fig. 162), without setae (Fig. 153, set) or para- podia (Fig. 164, para); (2) CLASS CILETOPODA (Gr. chaite, bristle; pous, foot) (Fig. 163), with seta?; and (3) CLASS HIRUDINEA (Lat. hirudo, a leech), without setae or parapodia, but with suckers (Fig. 169, i, 2). i. THE EARTHWORM -- LUMBRICUS The earthworm has been for many years and is still a favorite type for illustrating the anatomy and physiology of annelids, and for teaching general zoological principles. The common earth- worm, Lumbricus terrestris, lives in the ground where the soil is not too dry or sandy; it comes to the surface only at night or after a rain. In many parts of this country the species Allolobophora (Helodrilus) longa or one of the species of Diplocardia are more abundant in cultivated soil than L. terrestris. 315 COLLEGE ZOOLOGY External Features. - The body of Lumbricus is cylindroid, and varies in length from about six inches to a foot. The seg- ments, of which there are over one hundred, are easily determined externally because of the grooves extending around the body. dors.V typh neph hep FIG. 153. - - Transverse section through the middle region of the body of the earthworm, Lumbricus. circ.mus, circular muscle fibers; coel, axiom; dors.v, dorsal vessel; epid, epidermis; ext.neph, nephridiopore; hep, chloro- gogen cells; long.mus, longitudinal muscles; neph, nephridium; nephrost, nephro- stome; n.co, nerve-cord; set, setae; sub.n.vess, subneural vessel; typh, typhlo- sole; venl.v, ventral vessel. (From Parker and Haswell, after Marshall and Hurst.) At the anterior end a fleshy lobe, the prostomium (Fig. 156, i), projects over the mouth (5); this is not considered a true seg- ment. It is customary to number the segments with roman numerals, beginning at the anterior end, since both external and internal structures bear a constant relation to them. Segments PHYLUM ANNELIDA 217 XXXI or XXXII to XX XVII uiv swollen in matuiv \\orms, forming a saddle-shaped enlargement, the ditdlum, of use during reproduction. Every segment except the first and last bears four pairs of /-shaped chitinous bristles, the seta, situated as indicated in Figure 153, set; these may be moved by retractor and protractor muscles, and are renewed if lost. The setae on somite XXVI are in mature worms modified for reproductive purposes. The body is covered by a thin, transparent cuticle (Fig. 153, cut) secreted by the cells lying just beneath it. The cuticle protects the body from physical and chemical injury; it con- tains numerous pores to allow the secretions from unicellular glands to pass through, and is marked with fine stria, causing the surface to appear iridescent. A number of external openings of various sizes allow the en- trance of food into the body, and the exit of fasces, excretory products, reproductive cells, etc. (i) The mouth is a crescentic opening situated in the ventral half of the first somite (Fig. 156, 5) ; it is overhung by the prostomium (Fig. 156, i). (2) The oval anal aperture lies in the last somite. (3) The openings of the sperm ducts or vasa deferentia are situated one on either side of somite XV. They have swollen lips; a slight ridge extends posteriorly from them to the clitellum. (4) The openings of the oviducts are small, round pores one on either side of somite XIV; eggs pass out of the body through them. (5) The openings of the seminal receptacles appear as two pairs of minute pores con- cealed within the grooves which separate somites IX and X, and X and XI. (6) A pair of nephridiopores (Fig. 153, e.vt. ncph.}, the external apertures of the excretory organs, open on every somite except the first three and the last. They are usually situated immediately anterior to the outer seta of the inner pair. (7) The body-cavity or ccelom (Fig. 153, ccel.) communicates with the exterior by means of dorsal pores. One of these is lo- cated in the mid-dorsal line at the anterior edge of each somite from VIII or IX to the posterior end of the body. 218 COLLEGE ZOOLOGY General Internal Anatomy. - - If a specimen is cut open from the anterior to the pos- terior end by an in- cision passing through the body-wall a trifle to one side of the mid- dorsal line, a general view of the internal structures may be obtained (Fig. 154). As in A scar is (p. 169, Fig. 112 b), the body is essentially a double tube (Fig. 153), the body-wall constitut- ing the outer, the straight alimentary canal, the inner ; be- tween the two is a cav- ity, the ccelom (coel). The external seg- mentation corresponds to an internal division of t 4 he ccelomic cavity into compartments by means of partitions, called septa (Fig. 154), which lie beneath the grooves. These septa are absent in Ascaris. The alimentary canal passes through the center of the body, and is suspended in the ccelom by the parti- PHYLUM ANNELIDA 2TQ tions. Septa are absent between somites I and II, and incom- plete between somites III and IV, and XVII and XVIII. The walls of the ccelom are lined with an epithelium, termed the peritoneum. The coelomic cavity is filled with a colorless fluid which flows from one compartment to another when the body of the worm contracts. In somites IX to XVI are the repro- ductive organs (Fig. 158); running^ along the upper surface of the alimentary canal is the dorsal blood-vessel (Fig. 153, dors, v) ; and just beneath it lie the ventral blood-vessels (vent, v) and nerve-cord (n.co). Detailed Anatomy and Physiology. - - DIGESTION. - The alimentary canal (Fig. 154) consists of (i) a month cavity or buccal pouch in somites I to III, (2) a thick muscular pharynx (ph) lying in somites IV and V, (3) a narrow, straight tube, the (esophagus (oes), which extends through somites VI to XIV, (4) a thin-walled enlargement, the crop or proventriculus (cr), in somites XV and XVI, (5) a thick muscular-walled gizzard (giz} in somites XVII and XVIII, and (6) a thin-walled in- testine (int) extending from somite XLX to the anal aperture. The intestine is not a simple cylindrical tube; but its dorsal wall is infolded, forming an internal longitudinal ridge, the tvphlosole (Fig. 153, typh). This increases the digestive surface. Surrounding the alimentary canal and dorsal blood-vessel is a layer of chlorogogen cells (Fig. 153, hep}. The functions of these cells are not known with certainty, but they probably aid in the elaboration of food and are excretory. Three pairs of cakiferous glands lie at the sides of the oesophagus (Fig. 154, oes. gl) in seg- ments X to XII ; they produce carbonate of lime, which prob- ably neutralizes acid foods. The food of the earthworm consists principally of pieces of leaves and other vegetation, particles of animal matter, and soil. This material is gathered at night. At this time the w r orms are active; they crawl out into the air, and, holding fast to the tops of their burrows with their tails, explore the neighborhood. Food particles are drawn into the buccal cavity by suction pro- 220 COLLEGE ZOOLOGY duced when the pharyngeal cavity is enlarged by the contrac- tion of the muscles which extend from the pharynx to the body- wall. In the pharynx, the food receives a secretion from the pharyn- geal glands; it then passes through the oesophagus to the crop, where it is stored temporarily. .In the meantime the secretion from the calciferous glands in the oesophageal walls is added, neutralizing the acids. The gizzard is a grinding organ; in it the food is broken up into minute fragments by being squeezed and rolled about. Solid particles, such as grains of sand, which are frequently swallowed, probably aid in this grinding process. The food then passes on to the intestine, w r here most of the diges- tion and absorption takes place. Digestion in the eartrrvvorm is very similar to that of higher animals. The digestive fluids act upon proteids, carbohydrates, and fats; in them are special chemical compounds, called fer- ments or enzymes, which break up complex molecules without themselves becoming changed chemically. The three most im- portant enzymes are: (i) trypsin, which dissolves proteid; (2) dias- tase, which breaks up molecules of carbohydrates; and (3) steap- sin, which acts upon fats. These three enzymes are probably present in the digestive fluids of the earthworm. The proteids are changed into peptones, the carbohydrates into a sugar com- pound, and the fats are divided into glycerine and fatty acids. The food is now ready for absorption. This is accomplished through the wall of the intestine by a process known as osmosis, assisted by an ameboid activity of some of the epithelial cells. Osmosis is the passage of a liquid through a membrane. Upon reaching the blood, the absorbed food is carried to various parts of the body. Absorbed food also makes its way into the coelomic cavity and is carried directly to those tissues bathed by the ccelomic fluid. In one-celled animals, and in such METAZOA as Hydra, Planaria, and Ascaris, no circulatory system is neces- sary, since the food either is digested within the cells or comes into direct contact w r ith them; but in large, complex animals a PHYLUM ANNELIDA 221 special system of organs must be provided to enable the proper distribution of nutriment. CIRCULATION. - - The blood of the earthworm is contained in a complicated system of tubes which ramify to all parts of the body. A number of these tubes are large and centrally located; these give off branches which likewise branch, finally ending in exceedingly thin tubules, the capillaries. The functions of this system of tubes are to carry nourishment from the alimentary canal to all parts of the body, to transport waste products, and to convey the blood to a point near the surface of the body where oxygen may be obtained and supplied to the tissues. The blood of the earthworm consists of a plasma in which are suspended a great number of colorless cells, called corpuscles. Its red color is clue to a pigment termed h&moglobin which is dissolved in the plasma. In vertebrates the haemoglobin is located in the blood corpuscles. There are five longitudinal blood-vessels connected with one another and with various organs by branches, more or less regu- larly arranged. These are shown in Figure 155, and are as follows: (i) the dorsal or supra-intestinal vessel (sp), (2) the ventral or subintestinal trunk (sb.) , (3) the subneural trunk (sn), (4) two lateral neural trunks (/), (5) five pairs of hearts (///) in segments VII to XI, (6) two intestino-tegumentary ves- sels (it in A and B) arising in segment X and extending to the oesophagus, integument, and nephridia in segments X to VI, (7) branches from the ventral trunk to the nephridia and body- wall (D), (8) parietal vessels connecting the dorsal and sub- neural trunks in the intestinal region, (9) branches from the dorsal trunk to the intestine, (efi. in C), (10) a typhlosolar ves- sel connected by branches with the intestine and dorsal trunk, and (n) branches from the ventral vessel to the nephridia and body-wall (sb. in D). The dorsal trunk and hearts determine the direction of the blood flow, since they furnish the power by means of their muscular walls. Blood is forced forward by wave-like contrac- 222 COLLEGE ZOOLOGY tions of the dorsal trunk, beginning at the posterior end and traveling quickly anteriorly. These contractions are said to be FIG. 155. Diagrams showing the arrangement of the blood-vessels in the earthworm. A, longitudinal view of the vessels in somites VIII, IX, and X. B, transverse section of same region. C, longitudinal view of the vessels in the intestinal region. D, transverse section through the intestinal region. af.i, afferent intestinal vessel; cv, parietal vessel; ef.i, efferent intestinal vessel; ht, heart; //, intestine; II, intestine- tegumentary; ;//, lateral-neural vessel ; oe, oesophagus ; s, septa ; sb., ventral vessel ; sn., sub-neural vessel ; sp., dorsal vessel ; ty., typhlosolar vessel. (From Bourne, after Benham.) peristaltic, and have been likened to the action of the fingers in the operation of milking. Valves in the walls of the dorsal trunk prevent the return of blood from the anterior end. In somites PHYLUM ANNELIDA 223 VII to XI the blood passes from the dorsal trunk into the hearts, and is forced by them both forward and backward in the ventral trunk. Valves in the heart also prevent the backward flow. From the ventral trunk the blood passes to the body-wall and nephridia. Blood is returned from the body-wall to the lateral- neural trunks. The flow in the subneural trunk is toward the posterior end, then upward through the parietal vessels into the dorsal trunk. The anterior region receives blood from the dorsal and ventral trunks. The blood which is carried to the body- wall and integument receives oxygen through the cuticle, and is then returned to the dorsal trunk by way of the subneural trunk and the intestinal connectives. Because of its proximity to the subneural trunk, the nervous system receives a continu- ous supply of the freshest blood. RESPIRATION. - - The earthworm possesses no respiratory system, but obtains oxygen and gets rid of carbon dioxide through the moist outer membrane. Many capillaries lie just beneath the cuticle, making the exchange of gases easy. The oxygen is combined with the haemoglobin. EXCRETION. - - Most of the excretory matter is carried out- side of the body by a number of coiled tubes, termed nephridia (Fig. 153, neplr), a pair of which are present in every somite except the first three and the last. A nephridium occupies part of two successive somites; in one is a ciliated funnel, the nephro- stome (Fig. 153, nephrosi), which is connected by a thin ciliated tube with the major portion of the structure in the somite posterior to it. Three loops make up the coiled portion of the nephridium. The cilia on the nephrostome and in the nephrid- ium create a current which draws solid waste particles from the ccelomic fluid. Glands in the coiled tube take waste matter from the blood, and the current in the tube carries it out through the nephridiopore (ext.nepJi). NERVOUS SYSTEM. - - The nervous system differs from that of the types studied heretofore in being more concentrated. There is a bilobed mass of nervous tissue, the brain or suprapharyngeal 224 COLLEGE ZOOLOGY ganglion, on the dorsal surface of the pharynx in segment III (Fig. 156, 2). This is connected by two circumpharyngeal connectives (j) with a pair of subpharyngeal ganglia, which lie t just beneath the pharynx (4). From the latter the ventral nerve- cord (Fig. 154, n.c] extends posteriorly near the ventral body- wall (Fig. 153, n.co). The ventral nerve-cord enlarges into a ganglion in each segment and gives off three pairs of nerves in every segment pos- terior to IV. Each ganglion really consists of two ganglia fused to- gether. Near the dorsal surface of every ganglionic mass are three longitudinal cords, the neurochords or " giant fibers '' (Fig. 157, vg.}. The brain and FIG. 156. Diagram of the anterior end of an earth- worm to show the arrangement of the nervous system. /, prostomium ; 2, brain; j, circumpharyngeal connec- tive; 4, subpharyngeal ganglion; 5, mouth; 6, pharynx; 7, setae ; S, tactile nerves to prostomium ; o, dorsal nerves Bride.) 10, ventral nerves. (From Shipley and Mac- nerve-cord con- stitute the central nervous system; the nerves which pass from and to them repre- sent the peripheral nervous system. The nerves of the peripheral nervous system are either efferent or afferent. Efferent nerve- fibers (Fig. 157, mf.) are extensions from cells in the ganglia of the central nervous system. They pass out to the muscles or other organs, and, since impulses sent along them give rise to movements, the cells of which they are a part are said to be motor nerve-cells (me.}. The afferent fibers (sf.) originate from nerve-cells in the epidermis (sc) which are sensory in function, and extend into the ventral nerve-cord. The functions of nervous tissue are perception, conduction, and stimulation. These are usually performed by nerve-cells. PHYLUM ANNELIDA 225 called neurons. The neuron theory " supposes that there is no nerve-fiber independent of nerve-cell and that the cell with all its prolongations is a unit or a neuron ; that these units are not united to one another anatomically, but act together physio- logically by contact; that the entire nervous system consists of superimposed neurons; . . ." (Barker.) The reflex carried out either consciously or unconsciously is considered the physiological unit of nervous activity. The ap- paratus required for a simple reflex in the body of an earthworm "SL FIG. 157. Transverse section of the ventral nerve chain and surrounding structures of an earthworm, cm, circular muscles; ep., epidermis; lm., longi- tudinal muscles; inc., motor cell body; inf.,- motor nerve-fiber; sc, sensory cell body; sf., sensory nerve-fiber; vg., ventral ganglion. (From Parker in Pop. Sci. Monthly, modified after Retzius.) is represented in Figure 157. A primary sensory neuron (sc.}, lying at the surface of the body, sends a fiber (sf.) into the ven- tral nerve-cord, where it branches out; these branches are in physiological continuity with branches from a primary motor neuron (me.) lying in the ganglion of the ventral nerve-cord. The second neuron (me.) sends fibers (mf.} into a reacting organ, which in this case is a muscle. These fibers extending to the re- acting organ are called motor fibers (mf.) ; those leading to the ventral nerve-cord are termed sensory fibers (sf.}. The first neuron, or receptor, receives the stimulus and produces the nerve impulse; the second neuron, the adjiislor, receives, directs, and modifies the impulse; and the muscle or other organ stimulated 226 COLLEGE ZOOLOGY to activity is the effector. Within the ventral nerve-cord are association neurons whose fibers serve to connect structures within one ganglion or two succeeding ganglia. These short neurons overlap one another, and are doubtless responsible for the muscular waves which pass from the anterior to the posterior end of the worm during locomotion. The three giant fibers, which lie in the dorsal part of the ventral nerve-cord throughout almost its entire length, are connected by means of fibrils with nerve-cells in the ganglia, and probably distribute the impulse that causes a worm to contract its entire body when strongly stimulated. SENSE-ORGANS. - - The sensitiveness of Lumbrlcus to light and other stimuli is due to the presence -of a great number of epidermal sense-organs. These are groups of sense-cells con- nected with the central nervous system by means of nerve- fibers and communicating with the outside world through sense- hairs which penetrate the cuticle. More of these sense-organs occur at the anterior and posterior ends than in any other region of the body. REPRODUCTION. - - Both male and female sexual organs occur in a single earthworm. Figure 158 shows diagrammatically the position and shape of the various structures. The female system consists of: (i) a pair of ovaries (o) in segment XIII; (2) a pair of oviducts (pd) which open by a ciliated funnel in seg- ment XIII, enlarge into an egg sac (R) in segment XIV, and then open to the exterior; and (3) two pairs of seminal receptacles or spermatheccB (s), in somites IX and X. The -male organs are (1) two pairs of glove-shaped testes (T) in segments X and XI, (2) two vasa defer entia (vd) which lead from ciliated funnels (SF) to the exterior in segment XV, and (3) three pairs of seminal vesicles in segments IX (A), XI (C), and XII, and two central reservoirs (B). Self-fertilization does not take place, but spermatozoa are transferred from one worm to another during a process called copulation. Two worms come together, as shown in Figure 159, PHYLUM ANNELIDA 227 A ; slime tubes are formed, and then a band-like cocoon is secreted about the clitellar region. Eggs and spermatozoa are deposited FIG. 158. Diagram of the reproductive organs of the earthworm, dorsal view. A, B, C, seminal vesicles; N, nerve-cord; 0, ovary; OD, oviduct; R, egg sac; 5, spermatheca; 5F, seminal funnel; T, testes; VD, vas deferens. (From Marshall and Hurst.) in the cocoon, but fertilization does not occur until the cocoon is slipped over the head (Fig. 159, B). The eggs of the earthworm are holoblastic, but cleavage is unequal. A hollow blastula is formed and a gastrula is produced by invagination. The mesoderm develops from two of the 228 COLLEGE ZOOLOGY blastula cells, called mesomeres. These cells divide, forming two mesoblastic bands which later become the epithelial lining of the ccelom. The embryo escapes from the cocoon as a small worm in about two or three weeks. Behavior. - - EXTERNAL STIMULI. - The external stimuli that have been most frequently employed in studying the behavior of earthworms are those dealing with thig- motropism, chemotropism, and phototropism. THIGMOTROPISM. - - Mechanical stimula- tion, if continuous and not too strong, calls forth a positive reaction ; the worms live A B FIG. ISQ. A, the anterior segments of two copulating earthworms. Slime tubes encircle the pair from the 8th to the 33d segment. B, cocoon, freshly deposited, of an earthworm, surrounded by one-half of a slime tube. (After Foot, in Joiim. Morph.} where their bodies come in contact with solid objects; they apparently like to feel the walls of their burrows against their bodies, or, when outside of their burrows, to lie or crawl upon the ground. Reactions to sounds are not due to the presence of a sense of hearing, but to the contact stimuli produced by vibra- tions. Darwin showed that musical tones produced no response, but that the worms contained in a flower-pot drew back into their burrows immediately when a note was struck, if the pot were placed upon a piano, this result being due to vibrations. CHEMOTROPISM. - - In certain cases chemotropic reactions result in bringing the animal into regions of favorable food con- ditions, or turning it away from unpleasant substances. Mois- ture, which is necessary for respiration, and consequently for the life of the earthworm, causes a positive reaction, provided it PHYLUM ANNELIDA comes in contact with the body, no positive reactions being produced by chemical stimulation from a distance. Negative reactions, on the other hand, such as moving to one side or back into the burrow, are produced even when certain unpleasant chemical agents are still some distance from the body. These reactions are quite similar to those caused by contact stimuli. Darwin explained the preference of the earthworm for certain kinds of food by supposing that the discrimination between edible and inedible substance was possible when in contact with the body. This would resemble the sense of taste as present in the higher animals. PHOTOTROPISM. - - No definite visual organs have been dis- covered in earthworms, but nevertheless these animals are very sensitive to light, as is proved by the fact that a sudden illumina- tion at night will often cause them to " dash like a rabbit " into their burrows. One investigator claims to have found cells in the ectoderm, especially in the prostomium and posterior end, which act as visual organs. The entire surface of the body, however, is sensitive to light, although the anterior region is more sensitive than the tail, and the middle less than either of the others. Very slight differences in the intensity of the light are distinguished, since, if a choice of two illuminated regions is given, that more faintly lighted is, in the majority of cases, selected. A positive reaction to faint light has been demon- strated for the manure worm, Allolobophora feet id a. This positive phototropism to faint light may account for the emer- gence of the worms from their burrows at night. PHYSIOLOGICAL STATE. - - From the foregoing account it might be inferred that only external stimuli are factors in the behavior of the earthworm. This, however, is not the case, since the physiological condition, which depends largely upon previous stimulation, determines the character of the response. Different physiological states may be recognized, ranging from a state of rest in which slight stimuli are not effective, to a state of great excitement caused by long-continued and intense 230 COLLEGE ZOOLOGY stimulation, in which condition slight stimuli cause violent responses. Regeneration and Grafting. - Earthworms have considerable powers of regeneration and grafting (p. 117). Some of the results of experiments along this line are shown in Figure 160. A posterior piece may regenerate a head of five segments (A) or in certain cases a tail (B). Such a double- tailed worm slowly starves to death. An anterior piece regenerates a tail (C). Three pieces from several worms may be united so as to make a long worm (D) ; two pieces may fuse, FIG. 1 60. Regeneration and grafting in the earthworm. A, head end of five segments regenerated from the posterior piece of a worm. B, tail re- generated from the posterior piece of a worm. C, tail regenerated from an anterior piece of a worm. D, union of three pieces to make a long worm. E, union of two pieces to make a double-tailed worm. F, anterior and pos- terior pieces united to make a short worm. The dotted portion represents regenerated material. (From Morgan.) forming a worm with two tails (E) ; and an anterior piece may be united with a posterior piece to make a short worm (F). In all these experiments the parts were held together by threads until they became united. Economic Importance. --Charles Darwin in his book on the Formation of Vegetable Mold through the Action of Worms has shown by careful observations extending over a period of forty years how great is the economic importance of earthworms. One acre of ground may contain over fifty thousand earthworms. PHYLUM ANNELIDA 23! The faeces of these worms are the little heaps of black earth, called "castings" which strew the ground, being especially noticeable early in the morning. Darwin estimated that more than eighteen tons of earthy castings may be carried to the surface in a single year on one acre of ground, and in twenty years a layer three inches thick would be transferred from the subsoil to the sur- face. By this means objects are covered up in the course of a few years. Darwin speaks of a stony field which was so changed that " after thirty years (1871) a horse O Could gallop over the COm- FIG. 161. Section through the upper pact turf from one end of the stratum of a field showing the work of \ earthworms. .4 and B, arable soil held to the Other, and not thrown up by earthworms. C, marl Strike a single Stone with its and cinders buried by worm castings. . D, subsoil not disturbed oy the earth- Shoes (tig. l6l). worms. (From Schmeil.) The continuous honeycomb- ing of the soil by earthworms makes the land more porous and insures the better penetration of air and moisture. The thorough working over of the surface layers of earth also helps to make the soil more fertile. 2. CLASSIFICATION OF ANNELIDS Definition. - - Annelids are segmented worms, the body consisting of a linear series of more or less similar parts. Many of the internal organs are segmentally arranged, notably the blood-vessels, excretory organs, and nervous system. A large perivisceral ccelom is usually present, and in some cases a tro- chophore stage (Fig. 162) appears in development. Setae are characteristics of the majority. 232 COLLEGE ZOOLOGY The classes of annelids are as follows: - (1) Class Archiannelida. -- Marine worms without setae or parapodia. There is only one family, including two genera. Example: Polygordius (Fig. 162). (2) Class Chaetopoda. -- Marine, fresh-water, or terrestrial worms with setae and a perivisceral coelom ; often divided by septa. Examples: Lumbricus (Fig. 154), Nereis (Fig. 163). (3) Class Hirudinea. - - Marine, fresh- water, or terrestrial worms without setae or parapodia. Anterior and posterior suckers are present. Examples: Hirudo (Fig. 169), Clepsine (Fig. 171). 3. CLASS I. ARCHIANNELIDA A single family, POLYGORDIID^E, belongs to this class; it includes two genera, Polygordius (Fig. 162, A) and Protodrilus. -e \ l-cc. pnp. FIG. 162. Polygordius appendicidatus. A, dorsal view. an, anus; ct., cephalic tentacles; /z, head. B, trochosphere larva, an, anus; e, eye-spot; m., mouth. C and D, stages in development of trochosphere into the worm. pnp, pronephridium. (From Bourne, after Fraipont.) PHYLUM ANNELIDA 233 4. CLASS II. CH.ETOPODA The CILETOPODA are annelids which possess conspicuous setae. Two subclasses are recog- nized: (i) the POLYCH^TA, like Nereis (Fig. 163), with many setae situated on paired fleshy outgrowths, the parapodia (Fig. 164, para), and Polygordius is a marine worm living in the sand. It is about an inch and one half long, and only indistinctly segmented externally. The prostomium (Fig. 162, h) bears a pair of ten- tacles (ct.}. The mouth opening is in the ventral part of the first segment, and the anal opening (an] in the last segment. A pair of ciliated pits, one on either side of the prostomium, probably serve as sense-organs. Internally Polygordius resembles the earthworm, but in some respects is more primitive. The ccelom is divided into compartments by septa. The internal organs are repeated so that almost every segment possesses ccelomic cavities, longitudinal muscles, a pair of nephridia, a pair of gonads, a section of the alimentary canal, and part of the ventral nerve-cord. The development of Polygordius includes a trochophore stage. As shown in Figure 162, B, the trochophore larva at first resembles a top with cilia around the edge, an eye-spot (e}, and a digestive tract with both mouth (m} and anal (an} openings. This larva resembles the Pilidium larva of the NEMERTINEA (Fig. 118) and certain adult rotifers (Figs. 122-123). The adult develops from the larva by the growth and elongation of the anal end as shown in Figure 162, B, C. This elongation becomes segmented (D) and by continued growth transforms into the adult (A). C/2 ? O e < <*> o 234 COLLEGE ZOOLOGY FIG. -164. Anatomy of Nereis, dors, isess, dor- sal vessel; gl, cesophageal glands; int, intestine; ne.co, nerve-cord; ni'ph, nephridia; ass, oesoph- agus; palp, palp; para, parapodia; perist, peri- stome ; pcrisl.tcal, peristomial tentacle ; p/i, pharynx with its jaws; pra-est, prostomium ; lent, pro'stomial tentacles ; vcnl.vess, ventral vessels. (From Parker and Haswell.) , the sexes usually separ- ate; and (2) the OLIGO- CILETA, like the earth- worm, with a lesser number of sessile setae projecting out from the body-wall ; hermaphro- ditic. Subclass i. Polych&ta Nereis. Nereis (Fig. 163), the sand or clam worm, is a common annelid living in burrows in the sand or mud of the sea-shore at tide level. The burrows are some- times two feet deep and are kept from collapsing by a lining of mucus which holds together the grains of sand. By day the sandworm rests in its burrow, but at night it extends its body in search of food, or may leave the burrow en- tirely. A comparison of the figures of Nereis (Figs. 163-165) with those of the earthworm (Figs. 153-154) shows that these two animals have much in common, but PHYLUM ANNELIDA 235 nevertheless many differences. Both are segmented externally and internally, but Xcrcis possesses parapodia (Fig. 104, para), a pair of chitinous jaws, a pair of tentacles (tent), and two pairs of eyes on. the prostomium (praest), a pair of palpi (palp), and four pairs of tentacles on the peristome (perist.tent) . The parapodia (Fig. 165) are primarily used as loco- motor organs, but the lobes (DP and VP) are supplied with numerous blood- vessels and serve also as respiratory organs or gills. Each parapodium bears jointed locomotor setce, and is moved by muscles at- DP Ae FIG. 165. Parapodium of Nereis Ac, aciculum; Be, ven- tral cirrus; DP, notopodium ; Re, dorsal cirrus; V P, neuro- podium, with bundles of setae. (From Sedgwick. after Quatre- fages.) FIG. 1 66. APoly- chae t, .1 utolytus, which reproduces by buds, bud, head of the budded indi- vidual. (From D a v e n p o r t , after Agassiz.) FIG. 167. Am- phitrite johnstani. g, gills ; t, prosto- mial tentacles. (From Sedgwick. after Cunningham and Ramage.) tached to a sort of internal skeleton consisting of two buried bristles called acicula (Ac). The sense organs of Nereis are more highly developed than those of the earthworm. The tentacles (Fig. 164, perist.tent} are organs of touch, the palpi (palp) are probably organs of taste, and the eyes, organs of sight. 236 COLLEGE ZOOLOGY The two principal groups of the POLYCILETA are the PHANE- ROCEPHALA and CRYPTOCEPHALA. Order i. Phanerocephala. POLYCH^TA with most of the segments similar, a distinct head (prostomium) and a protrusible pharynx usually provided with chitinous jaws. Examples: Nereis (Fig. 163), Aphrodite, Autolytus (Fig. 166). Order 2. Cryptocephala. - - Polychaeta with head (prosto- mium) usually small and indistinct; segments differentiated, forming two or more regions, the thorax and abdomen, and palpi often divided into a crown of gills. Examples: Ampki- trite (Fig. 167), Spirorbis, Terebella, Sabella. Subclass 2. Oligochceta The earthworm illustrates the chief characteristics of this subclass. There are usually only a few setae, and no parapodia nor tentacles. The sexes are united, i.e. hermaphroditic. Most of the OLIGOCILETA are either terrestrial or live in fresh water. Two orders are recognized: (i) the MICRODRILI, and (2) the MACRODRILI. Order i. Microdrili (Limicola). - These are mostly small fresh- water animals. Examples: Tubifcx, Dero, Nais (Fig. 168). Many of them reproduce by transverse fission ^ weU ag sexually _ Order 2. Macrodrili. (Terricola). - This order contains the terrestrial OLIGOCHCETA. Examples: Lumbricus (Fig. 154), Allolobophora, Diplocardia. 5. CLASS III. HIRUDINEA The animals included in this class are commonly called leeches (Fig. 169). They are usually flattened dorso-ventrally, but FIG. X68.--M. a, mouth; o, anus; c, intestine. (trom Davenport, after Leunis.) PHYLUM ANNELIDA 237 differ externally from the flatworms (PLATYHELMINTHES, Chap. VII) in being distinctly segmented. The external segmenta- tion, however, does not correspond exactly to the internal seg- mentation, since there are a variable number of external grooves (from two to fourteen) to every real segment, e.g. usually five in the me- dicinal leech, Hirudo (Fig. 169), and its allies, and three in Clepsine. Anatomical features which distinguish the HIRUDINEA from the ARCHIAN- NELIDA and CH^TOPODA are (i) the presence of a definite number of seg- ments (thirty-three), (2) two suckers (Fig. 169, i, 2), one formed around the mouth and the other at the pos- terior end, and (3) the absence of seta? (except in one genus). They are hermaphrodites. Hirudo medicinalis, the medicinal leech (Fig. 169), is usually selected as an example of the class. It is about four inches long, but is capable of great contractions and elongation. The suckers are used as organs of attachment, and during locomotion are alternately fastened to and re- leased from the substratum, the animal FIG. 169. - - A leech, Hirudo medicinahs. i, mouth; 2, pos- looping along like a measuring- worm, terior sucker; 3, sensory papil- Leeches are also able to swim through !* ^ rom shi P ley and Mac ' Bnde.) the water by undulating movements. The alimentary tract (Fig. 170, 1-7) is fitted for the digestion of the blood of vertebrates, which forms the principal food of some leeches. The month lies in the anterior sucker (Fig. 169, /) and is provided with three jaws armed with chitinous teeth for biting. The blood flow caused by the bite of a leech is difficult 238 COLLEGE ZOOLOGY 3 17 -/ to stop, since a secretion from glands opening near the jaws tends to prevent coagulation. Blood is sucked up by the dilation of the mus- cular pharynx (Fig. 170, 2). The short oesophagus leads from the pharynx into the crop, which has eleven pairs of lateral branches (j, 4). Here the blood is stored until digested in the small globular stomach (5). A leech is able to ingest three times its own IZ weight in blood, and, since it may take as long as nine months to digest this amount, meals are few and far between. The intestine (6) leads directly to the anus (7). The absorbed food passes into the blood-vessels (Fig. 170, //) and the ccdomic cavities, and is carried to all parts of the body. The ccelom is usually small because of the develop- ment of a peculiar kind of connective tissue known as botryoidal tissue. The spaces in the body which are not filled up by this tissue are called sinuses, and in many species contain a fluid very much like true blood. Respiration is carried on at the surface of the body, oxygen being taken into and carbon dioxide given 7 jQk Zf& off by many blood capillaries in the FIG. 170. View of the internal organs of the leech, Birudo medicinalis. I, head with eye-spots; 2, muscular pharynx; 3, ist diverticulum of crop; 4, nth diverticulum of crop; 5, stomach; 6, rectum; 7, anus; 8, cerebral ganglia; Q, ventral nerve-cord; 10, nephridium; n, lateral blood-vessel; 12, testis; 13, vas deferens; 14, prostate gland; 15, penis; 16, ovary; 17, uterus. (From Shipley and MacBride.) 4 -A---V- PHYLUM ANNELIDA 2 39 skin. Waste products are extracted from the blood and coelomic fluid by seventeen pairs of nephridia (Fig. 170, 10) which re- semble those of the earthworm (Fig. 153, nepli), but frequently lack the internal opening. Leeches are hermaphroditic, but the eggs of one animal are fertilized by spermatozoa from another leech. The spermatozoa arise in the nine pairs of segmentally arranged testes (Fig. 170, 12); they pass into the vas defer ens (/j), then into a convoluted tube called the cpididymus (14), where they are fastened into bundles called spermatophores, and are finally de- posited within the body of another leech by means of the muscular penis. The eggs arise in the ovaries of which there is a single pair (16} ; they pass into the oviducts, then into the uterus (17), and finally out through the genital pore ventrally situated in segment XI. Copulation and the formation of a cocoon are similar to FIG. 171. Two leeches. these processes in the earthworm A, Poniobdella. B, ckpsine. (From Parker and Haswell. B -79^ A, after Bourne; Many leeches have jaws resembling Cuvier.) B, after those of Hirudo, for example Hcemopis and Macrobdella, but others have a slender protrusible proboscis in place of jaws. Clepsine (Fig. 171) belongs to the latter type; it feeds chiefly on fish and snails. Ickkhyobddla and Pontobdella (Fig. 171) are marine jawless leeches which are parasitic on fish. 240 COLLEGE ZOOLOGY 6. ANNELIDS IN GENERAL Three morphological characteristics of the ANNELIDA are espe- cially worthy of notice: (i) metamerism, (2) the ccelom, and (3) the trochophore stage in development. Metamerism. - -The segmentation of the body as exhibited in annelids is called metamerism, and is here encountered for the first time. This type of structure is of considerable interest, since the most successful groups in the animal kingdom, the ARTHRO- PODA and VERTEBRATA, have their parts metamerically arranged. How this condition has been brought about is still doubtful, but many theories have been proposed to account for it. According to one view the body of a metameric animal has evolved from that of a non-segmented animal by transverse fission. The in- dividuals thus produced remained united end to end and gradu- ally became integrated both morphologically and physiologi- cally so that their individualities were united into one complex individuality. Some zoologists maintain that the segmental arrangement of organs such as nephridia, blood-vessels, and re- productive organs has been caused by the division of a single ancestral organ, and not by the formation of new organs as the fission theory demands. True metamerism, as exhibited by annelids, should not be confused with the pseudometamerism of the tapeworms (p. 163, Fig. 107). The proglottides of the tapeworms are individuals budded off from the posterior end and differing from one another only in the degree of development. The tapeworm may be considered a row of incomplete individuals. The Coelom. The coelom has already been defined (p. 89) as a cavity in the mesoderm lined by an epithelium; into it the excretory organs open, and from its walls the reproductive cells originate. The development of the ccelom is described on page 89. The importance of the ccelom should be clearly understood, since it has played a prominent role in the progressive develop- PHYLUM ANNELIDA 24! ment of complexity of structure. The appearance of this cavity between the digestive tract and body-wall brought about great physiological changes and is correlated with the origin of ne- phridia for transporting waste products out of the body, and of genital ducts for the exit of eggs and spermatozoa. The ccelom also affected the distribution of nutritive substances within the body, since it contains a fluid which takes up material absorbed by the alimentary canal and carries it to the tissues. Excretory matter finds its way into the ccelomic fluid and thence out of the body through the nephridia. So important is the ccelom considered by most zoologists that the METAZOA are frequently separated into two groups: (i) the ACCELOMATA without a ccelom, and (2) the CCELOMATA with a ccelom. The PORIFERA, CCELENTERATA, and CTENOPHORA are undoubtedly ACCELOMATA. Likewise the ANNELIDA, ECHINODERMATA, ARTHROPODA, MOLLUSCA, and CHORDATA are certainly CCELOMATA. But whether the PLATYHELMINTHES, NEMATHELMINTHES, and a number of other groups possess a ccelom is still uncertain (see p. 25). The Trochophore. - - The term trochophore has been applied to the larval stages of a number of marine animals. The de- scription and figures of the development of Polygordius (p. 233, Fig. 162) are sufficient to indicate the peculiarities of this larva. Many other marine annelids pass through a trochophore stage during their life-history; those that do not are supposed to have lost this step during the course of evolution. Since a trochophore also appears in the development of ani- mals belonging to other phyla, for example, MOLLUSCA and BRYOZOA, and resembles very closely certain ROTIFERA, the con- clusion has been reached by some embryologists that these groups of animals are all descended from a common hypo- thetical ancestor, the trochozoon. Strong arguments have been advanced both for and against this theory. CHAPTER XII II i PHYLUM MOLLUSCA THE Phylum MOLLUSCA (Lat. mollis, soft) includes the snails, slugs, clams, oysters, octopods, and nautili. They are primitively bilaterally symmetrical, but unsegmented, and many of them possess a shell of cal- cium carbonate. Mussels (Fig. 1 73), clams, snails (Fig. 1 80), and squids (Fig. 191) do not appear at first sight to have much in common, p but a closer examination '-3 reveals several structures possessed by all. One of these is an organ called the foot, which in the snail (Fig. 172, I, 4) is usually used for creeping over surfaces, in the clam (II, 4) gener- ally for plowing through the FIG. 172. - Diagrams of three types of m ud,and in the squid (III, 4} mollusks, I, a Prosobranch Gastropod, for seizing prey. In each II, a Lamellibranch, and III, a Cephalo- ,1 pod, to show the form of the foot and there 1S a S P aCe called the its regions and the relations of the vis- mantle Cdvitv (Fig. 172 ?) ceral hump to the antero-posterior and u . , , dorso-ventral axes. A, anterior surface; between the mam body and D, dorsal surface; P, posterior surface; an enclosing envelope, the V, ventral surface; /, mouth; 2, anus; ,, m, 3, mantle cavity ; 4, foot. (From Shipley mant ^- NlC (WHS (2) Opens and MacBride, after Lankester.) into the mantle cavity. 242 III '.--3 PHYLUM MOLLUSCA 243 The mollusks are divided into five classes according to their symmetry and the characters of the foot, shell, mantle, gills, and nervous system. Definition. - - Phylum MOLLUSCA. CLAMS, SNAILS, SQUIDS, OCTOPI. Triploblastic, bilaterally symmetrical animals; anus and ccelom present; no segmentation; shell usually present; the characteristic organ is a ventral muscular foot. CLASS I. AMPHINEURA (Gr. amphi, on both sides; neuron, a nerve), the chitones (Fig. 179), with bilateral symmetry, often a shell of eight transverse calcareous plates, and many pairs of gill filaments; CLASS II. GASTROPODA (Gr. gaster, the belly; pous, a foot), the snails (Fig. 180), slugs (Fig. 184), whelks, etc., with a symmetry and usually a spirally coiled shell; CLASS III. SCAPHOPODA (Gr. skaphe, a boot; pous, a foot), the elephants'-tusk shells (Fig. 188), with tubular shell and mantle; CLASS IV. PELECYPODA (Gr. pelekos, hatchet; pous, a foot), the clams, mussels (Fig. 174), oysters, and scallops, usually with bilateral symmetry, a shell of two valves, and a mantle of two lobes; CLASS V. CEPHALOPODA (Gr. kephale, head; pous, a foot), the squids (Fig. 191), cuttlefishes, octopods (Fig. 196), and nautili (Fig. 194), with bilateral symmetry, a foot divided into arms provided with suckers, and a well-developed nervous system concentrated in the head. i. THE PEARLY FRESH-WATER MUSSEL ANODONTA AND THE UNIONES The fresh-water mussel is a mollusk belonging, together with the oyster, the long-neck clam, the scallop, and other similar animals, to the class PELECYPODA. Mussels inhabit the lakes and streams of this country wherever the water contains car- bonate of lime and does not entirely evaporate during any part of the year. Anodonta and the Uniones are similar except for minor details. 244 COLLEGE ZOOLOGY 4. External Features. - - Mussels usually lie almost entirely buried in the muddy or sandy bottom of lakes or streams. They burrow and move from place to place by means of the foot (Fig. *73> 9\ which can be extended from the anterior end of the shell. Water loaded with oxygen and food material is drawn in through a slit-like opening at the posterior end, called the ventral sip/ion (8), and excretory sub- stances and faeces along with deoxy- genated water are carried out through a smaller dorsal siphon (7). THE SHELL. The shell consists of two parts, called valves (Fig. 173), which are fastened together at the dorsal surface by an elastic ligamen- tous hinge. In Unio the valves articulate with each other by means of projections called teeth, but these are almost entirely atrophied in Anodonta. A number of concentric ridges appear on the outside of each valve; these are called lines of growth (Fig. 173, 10), and, as the name implies, rep- resent the intervals of rest between successive periods of growth. The small area situated dorsally toward the anterior end is called the umbo (6) ; this is the part of the shell with which the animal was provided at the beginning of its adult stage. The umbo is usually eroded by the carbonic acid in the water. The structure of the shell is easily determined. There are three FIG. 173. External features of a clam, Anodonta mutabilis. Behind is the inner face of an empty shell. /, points of insertion of anterior protractor (above) and retractor muscles (below) of the shell; 2, of anterior adductor muscle; j, of posterior pro- tractor of the shell; 4, of posterior adductor muscle; 5, lines formed by successive attachment of mantle; 6, umbo; 7, dorsal siphon; 8, ventral siphon; Q, foot protruded; 10, lines of growth. (From Shipley and MacBride.) PHYLUM MOLLUSCA 245 layers: (i) an outer thin, horny layer, the periostracum, which is secreted by the edge of the mantle, it serves to protect the underlying layers from the carbonic acid in the water, and gives the exterior of the shell most of its color; (2) a middle portion of crystals of carbonate of lime, called the prismatic layer, which is also secreted by the edge of the mantle; and (3) an inner na- creous layer (mother-of-pearl), which is made up of many thin lamellae secreted by the entire surface of the mantle, and pro- duces in the light an iridescent sheen. Anatomy and Physiology. - - GENERAL ACCOUNT. - - The valves of the shell are held together by two large transverse 15 FIG. 174. Right side of Anodonta mutabilis with mantle cut away and right gills folded back. /, mouth ; 2, anus ; j, cerebro-pleural ganglion ; 4, anterior adductor muscle; 5, anterior protractor muscle of shell; 6, re- tractor muscle; 7, dorsal siphon; 8, inner labial palp; g, foot; 10, external opening of nephridium; n, opening of genital duct; 12, outer right gill- plate; 13, inner right gill-plate ; 14, ventral siphon; 75, epibranchial chamber; 16, posterior protractor muscle. (From Shipley and MacBride, after Hatschek and Cori.) muscles which must be cut in order to gain access to the internal organs. These muscles are situated one close to either end near the dorsal surface; they are called anterior adductors (Fig. 174, 4; Fig. 175, a.ad) and posterior adductors (Fig. 175, p. ad). As the shell grows, they migrate outward from a position near the umbo, as indicated by the faint lines in Figure 173. When these muscles are cut, or when the animal dies, the shell gapes 246 COLLEGE ZOOLOGY open, the valves being forced apart by the elasticity of the ligamentous dorsal hinge, which is compressed when the shell is closed. The two folds of the dorsal wall of the mussel which line the valves are called the mantle or pallium (Fig. 175, m). The mantle flaps are attached to the inner surface of the shell along aline shown at 5 in Figure 173. The space be- tween the mantle-flaps containing the two pairs of gill plates (Fig. 174, 12, 13), the foot (9), and the visceral mass, is called the mantle cavity. DIGESTION. - - The food of the mussel consists of organic material carried into the mantle cavity with the water which flows through the ventral siphon (Fig. 173, 8; Fig. 174, 14). The mouth (Fig. 174, /; Fig. 175, mth) lies between two pairs of triangular flaps, called labial palps (Fig. 174, 8). The cilia on these palps drive the food particles into the mouth. A short oesophagus (Fig. 175, gul) leads from the mouth to the stomach. On either side of the stomach is a lobe of a glandular mass called the digestive gland or liver (d.gl) ; a digestive fluid is secreted by the liver and is carried into the stomach by ducts, one for each lobe. The food is mostly digested and partly absorbed in the stomach; it then passes into the intestine (Fig. 175, inf), by whose walls it is chiefly absorbed. The intestine coils about in the basal portion of the foot, then passes through the pericardium (pc), runs over the posterior adductor muscle (p.ad), and ends in an anal- papilla (a). The faeces pass out of the anus and are carried away by the current of water flowing through the dorsal siphon (Fig. 173, 7). CIRCULATION. - - The circulatory system comprises a heart, blood-vessels, and spaces called sinuses. The heart (Fig. 175, r.au., v) lies in the pericardium (pc). It consists of a ventricle (v) which surrounds part of the intestine (ret), and a pair of auricles (r.au). The ventricle by its contractions drives the blood forward through the anterior aorta (a.ao) and backward PHYLUM MOLLUSCA 247 through the posterior aorta (p.ao). Part of the blood passes into tin- mantle, where it is oxygenated, and then returns directly to the heart. The rest of the blood circulates through numerous spaces in the body and is finally collected by a vessel called 6t ct pa. i.lj int vyn yon- w.t FIG. 175. Internal anatomy of Anodonta cygnea, dissection from the left side, a, the anus ; a. ad, anterior adductor ; a.ao, anterior aorta ; a.v.ap, auriculo-ventricular aperture ; bl, urinary bladder ; c.pl.gn, cerebro-pleural ganglion; d.d, duct of digestive gland; d.gl\ digestive gland; d.p.a, dorsal pallial aperture; ex.sph, exhalent siphon; ft, foot; g.ap, genital aperture; gon, gonad; gul, gullet; i.l.j, interlamellar junction; in.sph, inhalent siphon; 'int, intestine ; kd, kidney ; m, mantle ; mth, mouth ; p.ao, posterior aorta; p. ad, posterior adductor; pc, pericardium; pd.gn, pedal ganglion; r.ap, renal aperture; r.au, right auricle; ret, rectum; r.p.a, reno-pericardial aperture; st, stomach; ty, typhlosole; ?, ventricle; v.gn, visceral ganglion; it-.t, water- tubes. (From Parker and Haswell.) the vena cava, which lies just beneath the pericardium. From here the blood passes into the kidneys, then into the gills, and finally through the auricles and into the ventricle. Nutriment and oxygen are carried by the blood to all parts of the body, and carbon dioxide and other waste products of metabolism are transported to the gills and kidneys. 248 COLLEGE ZOOLOGY .3 9-' RESPIRATION. - - The respiratory organs of the mussel are the gills or branchicR or ctenidia. A pair of these hang down into the mantle cavity on either side of the foot (Fig. 176). Each gill is made up of two plates or lamellae (Fig. 177, //) which lie side by side and are united at the edges except dorsally (Fig. 176). The cavity between the lamellae is divided into vertical water tubes by partitions called interlamellar junctions (Fig. 177, ilj}. Each lamella consists of a large number of gill filaments (if), each supported by two chitinous rods (black spots in Fig. 177, if), and covered with cilia. FIG. 176. Diagrammatic Openings, called ostia, lie between the section through Anodonta ,, r, , / \ near posterior edge of foot. S lU filaments, and blood-vessels (v) are i, right auricle; 2, epibran- present in the interlamellar junctions chial chamber; ?, ventricle; , rl 4, vena cava ; 5, non- and filaments - glandular part of kidney ,- Water is drawn through the ostia into 6, glandular part of kidney; ,, ,, ... , . , 7, intestine in foot ; 8, peri- the water-tubes by the cilia which cover cardium; Q, shell; 10, liga- the gill filaments; it flows dorsally into ment of shell. (From Shiplev jt , ., 7-77 /- /- \ and MacBride, after Howes.") the epibranchial chamber (Fig. 176, 2); from here it enters the dorsal mantle cavity and passes out through the dorsal siphon (Fig. 175, ex. spli). The blood which circulates through the gills discharges carbon dioxide into the water and takes oxygen from it. Respiration also takes place through the surface of the mantle. EXCRETION. - - The organs of excretion are two U-shaped kidneys or nephridia lying just beneath the pericardium, one on either side of the vena cava (Fig. 175, kd). Each kidney con- sists of a ventral glandular portion (kd) into which the pericar- dium opens (r.p.a) by a ciliated slit and a dorsal thin-walled bladder (bf) which opens to the exterior through the renal aperture (r.ap). Some excretory matter is probably driven into the kidney PHYLUM MOLLUSCA 249 ilHfr -liJxM ? ::^.. ?w from the pericardium by cilia, and other excretory matter is taken from the blood by the glandular portion (kd). These waste products of metabolism are carried out of the body through the dorsal siphon (e.v.sp/i). NERVOUS SYSTEM. - - There are only a few ganglia in the body of the mussel. On each side of the oesophagus is a so-called cerebropleural ganglion (Fig. 175, c.pl.gn), connected with its fellow by a nerve called the cerebral commis- sure which passes above the oesophagus. From each cerebropleural ganglion a nerve-cord passes ventrally, ending in a pedal ganglion (pd.gti) in the foot. The two pedal ganglia are closely joined together. Each cere- bropleural ganglion also gives off a cerebrovisceral connective (dotted in Fig. 175) which may be enclosed by the kidneys and leads to a visceral ganglion (v.gn}. SENSORY ORGANS. - - Fresh-water mussels are not well pro- vided with sensory organs. A small vesicle, the statocyst, con- taining a calcareous concretion, the statolith, lies a short way behind the pedal ganglia. It is an organ of equilibrium. A thick patch of yellow epithelial cells covers each visceral ganglion and is known as an osphradium. The functions of the osphradia are not certain. They probably test the water which enters the mantle cavity. The edges of the mantle are provided with sensory cells ; these are especially abundant on the ventral siphon (Fig. 175, in.sph), and are probably sensitive to contact and light. REPRODUCTION. - - Mussels are usually either male or female; a few are hermaphroditic. The reproductive organs are situated FIG. 177. Transverse section of por- tion of an outer gill-plate of Anodonta. il, inner lamella; //', outer lamella; ilj, interlamellar junctions; v, large ver- tical vessels. (From the Cambridge Natural History, after Peck.) 250 COLLEGE ZOOLOGY in the foot (Fig. 175, gon}. They are paired bunches of tubes and open (g.ap) just in front of the renal aperture (r.ap) on each side. The spermatozoa are carried out through the dorsal siphon of the male and in through the ventral siphon of the female. The eggs pass out of the genital aperture and come to lie in various parts of the gills according to the species. The spermatozoa enter the gill of the female with the water and fertilize the eggs. That por- tion of the gill in which the eggs develop is termed the marsupium. The eggs undergo complete but unequal segmentation. Blastula and gastrula stages are passed through, and then a peculiar larva known as a FIG. 178. The glochidium stage , /.,. /T -,. in the development of Anadonla. glOC/lldlUm IS produced ad, anterior adductor muscle ; by, bys- sus ; 5, setae ; sh, shell. (From Lan- kester, after Balfour.) 178). The glochidium has a shell (sfy consisting of two valves which are hooked in some species; these may be closed by a muscle (ad) when a proper stimulus is applied. A long, sticky thread called the byssus (by) extends out from the center of the larva, and bunches of seta (s) are also present. In Anodonta the eggs are fertilized usually in August, and the glochidia which develop from them remain in the gills of the mother all winter. In the following spring they are discharged, and, if they chance to come in contact w r ith the external parts of a fish, this contact stimulus causes them to seize hold of it by closing the valves of their shell. The glochidium probably chemically stimulates the skin of the fish to grow around it, forming the well-known " worms" or "blackheads." While thus embedded the glochidium receives nourishment from the fish and undergoes a stage of development (metamorphosis) , during which the foot ; muscles ; and other parts of the adult are formed. PHYLUM MOLLUSCA 251 After a parasitic life within the tissues of the fish of from three to twelve weeks the young mussel is liberated and takes up a free existence. i In i'nio the eggs arc fertilized during the late spring and summer, and the glochidia are discharged before the middle of September. The glochidium of Unio is smaller than that of Aiwdonta and is usually hookless. It does not as a rule be- come permanently attached to the fins, operculum, or mouth as in Anodonta, but usually lodges on the gill filaments of the fish. One result of the parasitic habit of larval mussels is the dis- persal of the species through the migrations of the fish. Only in this way can we account for the rapid colonization of certain streams by mussels, since the adult plows its way through the muddy bottom very slowly. Economic Importance. - - Fresh-water mussels are of con- siderable importance in certain parts of this country, especially in Iowa and Illinois, because their shells are used extensively in the manufacture of pearl buttons. Often, also, pearls of con- siderable value are found in fresh-water bivalves. The de- crease in the number of mussels in the Mississippi River and its tributaries has led the United States Bureau of Fisheries to investigate the possibility of artificially propagating them so as to restock the depleted waters. It seems probable that this can be done successfully. Mussels are instrumental in purifying the water in which they live by using as food the organic particles contained in it. 2. CLASS I. AMPHINEURA The Amphineura are marine mollusks of wide distribu- tion. Two rather distinct groups of animals belong to this class. Order i. Polyplacophora. - -These are the chitons (Fig. 179, A, B). They are characterized by a broad, flat foot (B,/), a shell of eight transverse calcareous pieces (A), and a row of gills COLLEGE ZOOLOC,Y (B, g) between the mantle (pa) and the foot (/). The mouth (m) is at one end and the anus (a) at the other. Examples: Ami- cula, Trachydcnnon, Chiton. The chitons are slow-moving mollusks which live near the sea- shore in shallow water. They are usually herbivorous. Order 2. Aplacophora. - These are worm-like mollusks (Fig. 179, C) without a shell, but with many calcined spicules over FIG. 170. CHITONES. A, upper surface of Onithochiton. B, under sur- face of Lepido pic urns, a, anus; /.foot; g, gills ; in, mouth; pa, mantle; te, pallial tentacles. C, ventral view of Paramenia. b, mouth; si, foot groove. (A from Tryon; B and C, from Lankester's Treatise.) the surface. The mantle surrounds the entire body, and the foot lies in a groove (si). Example: Chcstoderma. The APLACOPHORA live on coral polyps and hydroids. They are most abundant at a depth of about fifty fathoms. 3. CLASS II. GASTROPODA The snails, slugs, limpets, and other similar mollusks belong- ing to this class possess a foot, a mantle, and a mantle cavity comparable with those of the mussel (Fig. 172, I-II), but they differ considerably in the form and structure of their bodies as well as in their life-histories. Three peculiarities are characteris- tic of most GASTROPODA: (i) asymmetry, (2) a well-developed head, and (3) frequently a spirally coiled shell formed of one piece. PHYLUM MOLLUSCA 253 a. A Land-snail External Features. - - The body of a snail consists of a head (Fig. i So, Ko.), neck, foot (F), and visceral hump. The head bears two pairs of tentacles (Fii.): (i) a short anterior pair containing the olfactory nerves, and (2) a longer pair containing the eyes. The mouth (I/.) is in front and below the tentacles, and just beneath the mouth is the opening of the pedal mucous gland. The foot is broad and flat (F) ; it is a muscular organ of locomo- tion with a mucous- secreting integu- ment. Both the foot and head may be withdrawn into the shell. The spiral shell encloses the visceral hump, consisting of parts of the diges- tive, Circulatory, trance to ma ntle cavity indicated by arrow; D., in- respiratory, excre- testine; F, foot; Fit., tentacles; Ko., head; M., mouth: and FIG. 180. Diaprram showing the structure of a snail. .4, anus; At, respiratory aperture, the en- Mh, mantle cavity; Ml., mantle; R.Ml., free edge of mantle; Sch., shell. (From Schmeil.) tory, and repro- ductive systems. The mantle (Fig. 180, 1/7.) lines the shell, and is thin except where it joins the foot; here it forms a thick collar which secretes most of the shell. An opening beneath this collar is the respiratory aperture (At) leading into the mantle cavity. The arms (A) opens just back of this aperture. The genital pore is on the side of the head. Anatomy and Physiology. - - DIGESTION. - - The general anat- omy of a snail is shown in Figure 181. The digestive organs include a buccal mass, (esophagus (2), salivary glands (j), crop, stomach (4), digestive glands (5), intestine, rectum (6), and amis (7). The food is chiefly, if not entirely, vegetation, such as lettuce. This is scraped up by a horny jaw or mandible and devoured after 254 COLLEGE ZOOLOGY 13 12 21 --28 25 23 FIG. 181. Diagram showing the anatomy of a snail, Helix pomatia. /, pharynx; 2, oesophagus; 3, salivary glands; j, stomach; 5, liver; 6, rectum; 7, anus; 8, kidney; Q, ureter; 10, opening of ureter; n, ventricle; 12, auricle; 13, pulmonary vein; 14, opening of nephridium into pericardium; 75, ovo- testis; 16, common duct of ovotestis; 17, albumen gland; iS, female duct; IQ, male duct; 20, spermatheca; 21, flagellum; 22, accessory glands; 23, penis; 24, dart sac; 25, vagina; 26, eye tentacle retracted; 27, anterior tentacle retracted; 28, muscle which retracts head, pharynx, tentacle, etc. (From Shipley and MacBride, after Hatschek and Cori.) PHYLUM MOLLUSCA 255 being rasped into fine particles by a band of teeth termed the radula (Fig. 182). The radula and the cartilages and muscles that move it backward and forward constitute the buccal mass. The salivary glands (Fig. 181, j) which lie one on either side of the crop pour their secretion by means of the salivary ducts into the buccal cavity, where it is mixed with the food. The oesophagus (2) leads to the crop, and from here the food enters the stomach (4). The two digestive glands (5) occupy a large part of the visceral hump. They secrete a diastatic ferment which converts starchy matters into glucose, and are comparable to the pan- creas in vertebrate ani- mals. This secretion enters the stomach and aids in digestion. Ab- sorption takes place chiefly in the intestine, and the fasces pass out through the anus (Fig. "^ l82 ._ Part of the radula of Ph y Sa iSo, A ', Fig. l8l, 7). fonlinalis, with central tooth and two marginal r teeth highly magnified. (From the Cambridge Natural History.) RESPIRATION. - The blood of the snail consists of a colorless plasma containing corpuscles, and serves to transport nutriment, oxygen, and waste products from one part of the body to another. The heart lies in the pericardial cavity (Fig. 181, 14). The muscular ventricle (11) forces the blood through the blood-vessels by rhythmical pulsations. One large aorta arises at the apex of the ventricle; this gives rise at once to a posterior branch, which supplies chiefly the digestive gland, stomach, and ovotestis, and an anterior branch which carries blood to the head and foot. The blood passes from the arterial capillaries into venous capil- 256 COLLEGE ZOOLOGY I lanes and flows through these into sinuses. Veins lead from these sinuses to the walls of the mantle cavity, where the blood, after taking in oxygen and giving off carbon dioxide, enters the pulmonary vein (Fig. 181, ij) and is carried to the single auricle (12} and finally into the ventricle (17) again. EXCRETION. -The glandular kidney (Fig. 181, 8) lies near the heart. Its duct, the ureter or renal duct (p), runs along beside the rectum and opens (id) near the anus (7). NERVOUS SYSTEM. - - Most of the nervous tissue of the snail is concen- trated just back of the buccal mass and forms a ring about the oesoph- agus (Fig. 181, in black; Fig. 183). There are five sets of ganglia and four ganglionic swellings. The supra- cesophageal or cerebral ganglia (Fig. 183, 4) are paired and lie above the oesophagus. Nerves extend anteri- orly from them, ending in the two buccal ganglia (/), the two eyes, the two ocular ganglionic swellings (j), the FIG. 183. -Central portion two olfactory ganglionic swellings, and of the nervous system of Helix , pomatia. i, buccal ganglion; the mouth. Nerves called commis- 2, optic nerve with thickened sures connect the supra-cesophageal root (j) arising from the cere- bral ganglion (7) ; ,-, pedal, g an gua with the ganglia which lie 6, pleural 7, parietal, s, vis- beneath the oesophagus. Here are ceral ganglion. (From Lang, . < after Bohmig and Leuckart.) i ur pairs of ganglia lying close to- gether --the pedal (5), pleural (6), parietal (7), and visceral (8). Nerves pass from them to the visceral hump and the basal parts of the body. SENSE-ORGANS. - - Both the foot and the tentacles are sensitive to contact, and are liberally supplied with nerves. Each long tentacle (Fig. 180, Fit.} bears an eye. These eyes are probably not organs of sight, but only sensitive to light of certain intensities. PHYLUM MOLLUSCA 257 Many snails feed mostly at night, and their eyes may be adapted to dim light. Snails possess a sense of smell, since some of them are able to locate food, which is hidden from sight, at a distance of eighteen inches. We are not certain where the sense of smell is located, but investigators are inclined to believe that the small tentacles (Fig. 1 80) are the olfactory organs. A sense of taste is doubtful. There are two organs of equilibrium (statocysts) , one on either side of the supra-cesophageal ganglia. They are minute vesicles containing a fluid in which are suspended small calcareous bodies (statoliths) . Nerves connect them with the supra-cesophageal ganglia. LOCOMOTION. - - The snail moves from place to place with a gliding motion. The slime gland which opens just beneath the mouth deposits a film of slime, and on this the animal moves by means of wave-like contractions of the longitudinal muscular fibers of the foot. Snails have been observed to travel two inches per minute (Baker). REPRODUCTION. --Some gastropods are dioecious; others are monoecious. Helix is hermaphroditic, but the union of two animals is necessary for the fertilization of the eggs, since the spermatozoa of an individual do not unite with the eggs of the same animal. The spermatozoa arise in the ovotestis (Fig. 181, 15); they pass through the coiled hermaphroditic duct (16) and into the sperm duct; they then enter the vas deferens (ip) and are transferred to the vagina (25) of another animal by means of a cylindrical penis (23) which is protruded from the genital pore. The eggs also arise in the ovotestis and are carried through the hermaphroditic duct; they receive material from the albumen gland (//) and then pass into the uterine canal ; they move from here down the oviduct (18) into the vagina (25), where they are fertilized by spermatozoa which were transferred to the seminal receptacle (20) by another snail. In almost all other land pul- monates impregnation is mutual, each animal acting during copulation as both male and female, s 258 COLLEGE ZOOLOGY b. Gastropoda in General Classification. - - There is considerable diversity among gas- tropods both in form and structure. The chief characteristics used in dividing them into groups are the structure of the nervous system, the method of respiration and structure of the respiratory organs, and the condition of the sexual organs. There are two subclasses, each containing two orders. SUBCLASS I. STREPTONEURA. --Dioecious GASTROPODA with visceral connectives usually twisted into a figure 8 ; the heart is usually posterior to the gills. Order i. Aspidobranchia. STREPTONEURA with usually two gills, two auricles, and two nephridia. Examples: Acmcea (limpet), Haliotis (ear- shell), Margarita.' Order 2. Pectinibranchia. STREPTONEURA with one kidney, one auricle, and one gill. Examples: Littorina, Sycotypus (Fig. 1 86, A), Crepidula (Fig. 186, B), Urosalpinx. SUBCLASS II. EUTHYNEURA. Monoecious GASTROPODA with visceral connectives not twisted (Fig. 183); the gill when present is posterior to the heart. Order i. Opisthobranchia. Marine EUTHYNEURA usually with a gill and mantle. Examples: Bulla, Clione, Doris. Order 2. Pulmonata. Land and fresh- water EUTHYNEURA which breathe air; gill usually aborted and mantle cavity con- verted into a lung. Examples: Helix, Polygyra (Fig. 185, C), Lymn&a (Fig. 185, G), Limax (Fig. 184), Physa (Fig. 185, D), Planorbis (Fig. 185, B). Air-breathing Gastropods. - - The air-breathing gastropods belong chiefly to the order PULMONATA, and inhabit fresh water or live on land. The slugs also live on land, but are without a well-developed shell. Limax maximus (Fig. 184) is a large slug. It was introduced from Europe and is now more or less of a pest in greenhouses because of its fondness for green leaves. The shell of Limax is a thin plate embedded in the mantle. Three common fresh- water snails with shells are Phvsa, Lvm- S t * PHYLUM MOLLUSCA 259 ncea, and Planorbis. Physa (Fig. 185, D) lives in ponds and brooks and feeds on vegetable matter. It is a sinistral snail, since if the shell is held so that the opening faces the observer and the spire points upward, the aper- ture will be on the left. Lymncea (Fig. 185, G) is the common pond-snail. Its shell is coiled in an opposite direction from that of Physa and is called dextral. Both Physa and Lymncea usu- ally come to the surface to breathe. In dry weather many snails have the power of se- creting a mucous epiphragm over the mouth of the shell so as to FIG. 184. Limax maximus. PO, pul- monary orifice. (From the Cambridge Natural History.) B FIG. 185. The shells of certain GASTROPODA. A, Helicodiscus parallelus. B, Planorbis trivohis. C, Polygyra albolabris. D, Physa gyrina. E, Pleuro- cera elcvatum, F, Goniobasis liviscens. G, Lymncea palustris, (From various authors.) 260 COLLEGE ZOOLOGY prevent the evaporation of moisture from their bodies. Plan- orbis (Fig. 185, B) differs from Physa and Lynmcea in having a shell coiled in one plane like a watchspring. Marine Gastropods. - The majority of the marine gastropods have shells, but many of them do not ; some of the latter are called nudi- branchs. Littorina lit- torea, the periwinkle, is a very common shelled snail on the North At- lantic sea-shore. It was FIG. 1 86. - - Two marine GASTROPODS, introduced from Europe, A, bycotypus camculatus. B, Crepidula. (A, from Davenport; B, from Weysse.) where in many localities it is used as an article of food by the natives. In Crepidula (Fig. 186, B) the spiral has almost disappeared, and the shell is boatlike. Acmaa, the limpet, is a sea-snail modified so as to cling closely to rocks. Its shell is conical. In Europe limpets are used as food. Sycotypus (Fig. 186, A) is a very large marine gastro- pod that lives in shallow water and feeds on other mollusks. Urosalpinx, the oyster drill, and several other marine snails, make a practice of boring through the thick shells of oysters and other bivalves with their radulas and taking out the soft body of the victims through the hole. The term nudibranch is applied to certain shell-less marine gastropods. The nudi- branchs resemble the terrestrial slugs ; they do not breathe air, however, but take oxygen from the water by means of naked Davenport.) PHYLUM MOLLUSCA 261 gills, or through the mantle. Eolis (Fig. 187) and Dendronotus are common genera. The shelled marine GASTROPODA usually breathe by means of gills. In Sycoty-pus, for example, there is a trough-like extension of the collar, the siphon, which leads a current of water into the mantle cavity where the gill is situated. The direction of this current of water prevents contamination by the faeces and excretory products. 4. CLASS III. SCAPHOPODA This class contains only a few aberrant marine mollusks called tooth shells. The mantle forms a tube around the body and secretes a crescent-shaped tubular calcareous shell larger at one end than at the other. Both ends of the shell are open. The foot (Fig. 1 88, /), which is used for boring in the sand, can be protruded from the larger anterior aperture. The head is rudimentary, but a radula is present. Eyes and a heart are absent. The sexes are separate. Ex- ample: Dental mm (Fig. iSS). 5. CLASS IV. PELECYPODA * FIG. 1 88. AScA- PHOPOD, Dcntalium. a, anterior aperture of mantle ; /, foot ; g, genital gland ; k, kidney ; /, liver. (From the C a m- The PELECYPODA or LAMELLIBRANCHIATA, bridge Natural as they are often called, are the mussels, rj u thiers ) clams, oysters, and other bivalves. They are simple in structure and therefore favorite mollusks for lab- oratory dissection (pp. 243 to 251), but are probably less prim- itive than the GASTROPODA. They do not possess a head or radula. The mantle is bilobed and secretes a bivalve shell. The gills are usually lamellate. The PELECYPODA are all aquatic and mostly marine. They 262 COLLEGE ZOOLOGY feed on minute organisms. Most of them burrow into the sand or mud; a few bore cavities for themselves in calcareous rocks; and still others are sessile, like the oyster. Some PELECYPODA live commensally or parasitically on or in the bodies of ascidians, sponges, and echinoderms. Classification. - - The PELECYPODA are divided into four orders according to the structure of the gills. Order i. Protobranchia (Fig. 189, A). PELECYPODA with plate-like gill filaments (e, /) which are not reflected; mantle FIG. 189. Morphology of the gills of PELECYPODA, seen diagrammatically in section. A, PROTOBRANCHIA. B, FILIBRANCHIA. C, EULAMELLIBRANCHIA. D, SEPTIBRANCHIA. e, e, external row of filaments; I, i, internal row of fila- ments; e', external row or plate folded back; i', internal row folded back; /, foot; m, mantle; s, septum; v, visceral mass. (From the Cambridge Natural History, after Lang.) cavity not divided into two parts. Examples: Nucula, Leda, Yoldia. Order 2. Filibranchia (Fig. 189, B). PELECYPODA with gill filaments reflected and united by ciliary junctions. Examples: Area, Mytilus, Modiola, Pecten. Order 3. Eulamellibranchia (Fig. 189, C). PELECYPODA with gill filaments forming plates or lamellae. Examples: Ostrca, Cyclas, Unio, Anodonta, Mactra, Venus, My a, Teredo (Fig. 190), Solen. Order 4. Septibranchia (Fig. 189, D). PELECYPODA with gills transformed into a muscular septum (s) and not functioning as respiratory organs. Examples: Silenia, Cuspidaria. PHYLUM MOLLUSCA 263 Economic Importance. Several of the PKLKCYPODA are of considerable importance as food for man. The most valuable are the oyster and the long-neck or soft-shell clam. Razor-shells, hen-clams, mus- sels, scallops, and a number of other bivalves are also eaten. The oyster, Ostrea virginiana, in- habits the shallow water along the Atlantic coast from Massachusetts to Florida. It is attached to rocks and other objects by its left valve, and does not move about in the adult stage. The Chesapeake Bay oyster- beds are large and important. The value of the oyster industry along the Atlantic seaboard is from twenty to thirty million dollars annually. Oysters lay an enormous number of eggs. Professor Brooks placed the number for a single female in one season at nine million or more. Those eggs which are fertilized and not eaten by fishes and other animals develop into free-swimming larvae which soon become fixed to some object and grow into the adults. The larvae are preyed upon by many animals, especially crabs (Chap. XIII). Those that reach the adult stage may be attacked by starfishes FIG. i go. A ship -worm," (p. 196), boring snails (p. 260), T . ere * nav alis ' ,! n a pi c e " of timber. P, pallets; 55, si- sponges (p. 106), and parasites. phons; T, tube; u, valves The value of the pearl-button in- f .. she "; (F ?"L the c * m - bndge Natural History, after dustry has already been mentioned Mobius.) 264 COLLEGE ZOOLOGY (p. 251). Pearl-fishing should also be noted. Pearls are pro- duced by secretions of the mantle around a foreign substance, such as a grain of sand or a parasitic worm. The PELECYPODA of the Persian Gulf yield the finest pearls. One bivalve, the ship worm, Teredo navalis (Fig. 190), is in- jurious to ships and piles. It burrows into the wood with its shell, sometimes to a depth of two feet. 6. CLASS V. CEPHALOPODA The Cephalopoda are the squids, octopods, and nautili. They are constructed on the same fundamental plan as other mollusks (Fig. 172, III), but are very different in form and habits. a. The Common Squid - - Loligo Loligo pealii (Fig. 191) is one of the common squids found along the eastern coast of North America from Maine to South Carolina. It probably lives in deep water during the winter, but about May i it enters shallow water in large schools to lay its eggs. Squids are of some economic importance, since they are used as food by Chinese and Italians, and as bait for line and trawl fishing. They feed on small fish, Crustacea, and other squids, and in turn furnish food for cod and other large fish. Anatomy and Physiology. - - The body of Loligo is spindle- shaped. When swimming through the water the morphological ventral surface is usually anterior (Fig. 191, V); the dorsal sur- face is posterior (D); the anterior surface is dorsal (.4); and the posterior surface is ventral (P). The skin may change color rapidly; sometimes it is bluish white, at others, mottled red or brown. The/oo/ consists of ten lobes (Fig. 191, 5, 6, 7) and a funnel (j). Eight of the lobes are arms (5, f) and two are long tentacles (6). The inner surfaces of both arms and tentacles are provided with suckers. The arms are pressed together and used for steering when the squid swims, but when capturing prey the tentacles are PHYLUM MOLLUSCA 265 Oo. Pn_. extended, seize the victim with their suckers, and draw it back to the arms, which hold it firmly to the mouth. The funnel (j) is a muscular tube extending out be- yond the edge of the mantle collar (2, Q) beneath the head (4). Water is ex- pelled from the mantle cavity (Fig. 1 9 2, M. C) through it. The funnel is the principal steer- ing organ; if it is directed forward, the jet of water passed through it propels the animal backward ; if di- rected backward, the animal is pro- pelled forward. A thick muscular mantle encloses the visceral mass and mantle cavity. It terminates ven- Al FIG. 191. The squid, trally in a collar Loligo pealiit side view . A, anterior; D, dorsal; P, posterior; V, ventral. i, fin; 2, edge of mantle; 3, siphon ; 4, head ; 5, arm; 6, long arm with suckers; 7, arm; 8, eye; (Fig. 191, 2, 9) which articulates with the visceral mass and funnel by three pairs of 9, edge of mantle. (From Williams.) FIG. 192. Diagram showing the structure of the squid, Loligo pealii. A 1 , arm; A*, long arm with suckers; An, anus; Ca, czecum ; E, eye ; Gi, gill ; Go, gonad ; IS, ink-sac; LV, liver; M.C, mantle cavity; Nc, nephridium; Ph, phar- ynx; -Pn, pen; Si, siphon; Si, stomach; SiV, valve of siphon. (From Wil- liams.) interlocking sur- faces. Water is drawn into the mantle cavity at the edge of the collar by the expansion of the mantle and forced out through the funnel by the contraction of the mantle. On each side of the animal is a triangular fin-like projection of the mantle 266 COLLEGE ZOOLOGY (Fig. 191, /); these fins may propel the squid slowly forward or backward by their undulatory movements, or may change the direction of the squid's progress by strong upward or downward strokes. The shell or pen of Loligo (Fig. 192, Pri) is a feather-shaped plate concealed beneath the skin of the back (anterior surface) . The true head is the short region between the arms and the mantle collar; it contains two large eyes (E). The digestive system includes a pharynx or buccal mass (Fig. 192, Pit), (esophagus, salivary glands, stomach (Sf), cacum (Co), intestine, rectum, inksac (IS), liver, and pancreas. There are two powerful chitinous jaws in the pharynx ; they resemble a par- rot's beak inverted, and are moved by strong muscles. A rad- ula is also present. Two salivary glands lie on the dorsal surface of the pharynx, and one is embedded in the ventral end of the liver; they all pour their secretions into the mouth. The oesoph- agus leads from the pharynx through the liver and into the stom- ach. Closely connected with the muscular stomach is the large, thin-walled caecum. Food is probably partially digested in the stomach by fluids brought in from the pancreas and liver; it then passes into the caecum, where digestion is completed and absorption takes place. Bones and other indigestible material are forced from the stomach into the intestine and out through the anus (An). The blood of the squid is contained in a double, closed vascular system. Arterial blood is forced by a muscular systemic heart to all parts of the body by three aorta: (i) anterior, (2) posterior, and (3) genital. It passes from arterial capillaries into venous capillaries, and thence into the large veins. From these it enters the right and left branchial hearts, and is then forced into the gills through the branchial arteries. In the gills the blood is aerated, and is finally carried by the branchial veins back to the systemic heart. There are two gills in the squid (Fig. 192, Gi). The water PHYLUM MOLLUSCA 267 I... TV' Jia.c opy which enters the mantle cavity flows over them, supplying oxy- gen to the blood and carrying away carbon dioxide. The two nephridia or kidneys (Fig. 192, Ne) are white trian- gular bodies extending forward from the region of the branchial hearts and opening on either side of the intestine at the ends of small papillae. The nervous system consists of a number of ganglia mostly in the head. The principal ones are the supra-cesophageal, in- fra- cesophageal, suprabuccal, infrabuccal, stellate, and optic ganglia. The sensory organs are two very highly developed eyes, two sl-atocysis, and prob- ably an olfactory organ. The statocysls are two vesicles lying side by side in the head ; each contains a concretion, the statolith, and is probably an organ of equilibrium. The eyes (Fig. 192, E ; Fig. 193) are large and somewhat similar FIQ I03 ._ Diagram of superficially to those of vertebrates (com- the eye of a squid, Loliw, -r^. -,, -i^- T 4- u i i a. o.c, anterior optic chain- pare Fig. 193 with Fig. 351). Just behind ber; - ^ cornea < .,. iris . the eye is a fold which projects back- J, lens; Z', external portion ward under the collar, and is probably .*'> '/^ p c 8t X olfactory. optic chamber; r, retina. . , .,, r Squids are either male or female. reproductive organs (Fig. 192, Go] of the Grenadier.) male are the testis, a vas Jcfcrcns, a spermatopl/oric sac, which contains sperms bound together into bundles called spermatophores, and a copulatory organ, the penis. The female organs are an ovary, oviduct, omducal gland, and nidamental gland. b. Cephalopoda in General Classification. - - The CEPHALOPODA may be divided into two orders according to the number of gills, kidneys, and auricles, and the character of the shell. rpi (From the CambrM: . The Natural History> aftcr 2 68 COLLEGE ZOOLOGY Order i. Tetrabranchia. CEPHALOPODA with four gills, four kidneys, and four auricles; with a large, external shell; no suckers; and very short arms. Example: Nautilus (Fig. 194). --8 7-' FIG. 194. The chambered nautilus, Nautilus pompilius. i, last com- pleted chamber of shell; 2, hood part of foot; j, shell muscle; 4, mantle cut away to expose, 5, the pinhole eye; 6, outer wall of shell, partly cut away to show chambers; 7, siphon; 8, lobes of foot; Q, funnel. (From Shipley and MacBride, after Kerr.) Order 2. Dibranchia. CEPHALOPODA with two gills, two kidneys, and two auricles; with shell enveloped by the mantle; and long arms provided with suckers. Suborder i. Decapoda. DIBRANCHIA with ten arms - two long and eight short. Examples: Loligo (Fig. 191), Om mast replies , Rossia . Suborder 2. Octopoda. DIBRANCHIA with eight arms of equal length. Examples: Octopus (Fig. igf)), Alloposus. FIG. 195. --The paper nautilus, Argo- f livinir nauta argo (female), swimming. (From a Sedgwick.) Nautili. - There are only few living species belong- ing to the genus Nautilus in 1'HVLUM MOLLUSCA 269 the order TETRABRANCHIA. The chambered or pearly nautilus, \autihis pompilius (Fig. 194), lives on the bottom of the sea near certain islands 'of the South Pacific. The shell is spirally coiled in one plane and is composed of compartments (i) of different sizes, which were occupied by the animal in successive stages in its growth. The compartments are filled with gas and are connected by a calcareous tube in which is a cylindrical growth of the animal called the siphuncle (Fig. 194, 7). The gas in the compart- ments counterbal- ances the weight of the shell. Octopods. The OCTOPODA differ from the decapods, like Loligo, in the absence of the two long tentacular arms (Fig. 191, 6}. The paper nautilus, Argonauta argo (Fig. 195), is an octopod, the female of which secretes a delicate, slightly coiled shell. The octopus or devil-fish, Octopus vulgar is (Fig. 196), lives in the Mediterranean Sea and West Indies. It may reach a length of over ten feet and a weight of seventy- five pounds. Devil- fishes have been accused of serious attacks on man, but are prob- ably not so bad as generally supposed. 7. MOLLUSCA IN GENERAL Morphology. - The MOLLUSCA are unsegmented, triplo- blastic animals with bilateral symmetry (except in most of the FIG. 196. The octopus, Octopus vulgaris. A, at rest; B, in motion. /, funnel; the arrow shows direc- tion of propelling current of water. (From the Cambridge Natural History, after Merculiano.) 2 ;o COLLEGE ZOOLOGY GASTROPODA and certain PELECYPODA). There is usually a ventral muscular foot, a mantle fold, a radula, and a coelom. The shell, if present, is usually univalve, bivalve, eight-parted, or pen-shaped. The bodies of mollusks are soft (Lat. mollis = soft) and gen- erally covered by a slimy integument. They are therefore fitted for life in the water or in moist places. In most cases the body is supported and protected by a shell. As shown in Figure 172, the foot is present in all mollusks, but is variously modified; it enables the mussel to plow its way through the sand, the snail to glide along, and the squid to swim through the water and cap- ture its prey. The mantle is a fold of the body- wall which secretes the shell. If there are two lobes, a bivalve shell is produced, as in the mussel. If only one lobe is present, a univalve shell is formed, as in snails. The shape of the animal does not depend upon the shell so much as upon the mantle which secretes it. The MOLLUSCA possess a distinct coelom which is usually recognizable in the adult as (i) the pericardial cavity, and (2) the cavities of the reproductive organs. Metabolism. - - Mollusks eat both vegetable and animal food. Jaws are present in many of them, especially the gastropods and cephalopods. A rasping organ, the radula (Fig. 182), exists in the buccal cavity of many mollusks; it consists of rows of chi- tinous teeth which tear up the food by being drawn across it. In the stomach the food is acted upon by secretions from the liver, which is physiologically a hepato-pancreas, and may also excrete waste products into the alimentary canal. The cavities which contain the blood represent the h&moccel. The blood is forced through these cavities by the muscular con- tractions of the heart. Oxygen, absorbed food, and excretory sub- stances are transported by it. Respiration takes place either in the gills or in the mantle. Most of the fresh-water and land- snails (pulmonate gastropods) take air into the mantle cavity, which thus serves the purpose of a lung. The PELECYPODA, PHYLUM MOLLUSCA 271 CEPHALOPODA, and marine gastropods breathe mainly by means of gills. Reproduction. - - No cases of asexual reproduction have been reported in mollusks. The sexes are usually separate, though the members of one entire subclass of GASTROPODA (EUTHY- NEURA) are hermaphroditic. The number of eggs laid, by some mollusks is very great ; for example, 9,000,000 in the oyster. In all such cases the eggs are subjected to the dangers of the ocean rn. th-- FiG. 197. Stages in the development of a mollusk, Patella. A, trocho- phore stage. /, foot; fi, flagellum; m, mouth; pac, postanal cilia; tr, velum. B, veliger stage, 130 hours old. /, rudimentary foot; op, operculum; sh, shell; v, i; velum. (A, from Lankester's Treatise, after Patten; B, from the Cam- bridge Natural History, after Patten.) waves and to numerous enemies, and also pass through a meta- morphosis after hatching. Other mollusks lay very few eggs, for example, Lymncsa, twenty to one hundred ; Helix, forty to one hundred ; and Paludina, about fifteen. These are terrestrial or fresh-water species whose eggs produce young in the adult form, or, as in Paludina, the eggs hatch within the body of the parent. The development of the eggs of most mollusks includes a tro- chophore stage (Fig. 197, A) which becomes a veliger larva (Fig. 197, B), so called because of the presence of a band of cilia, the velum (v), in front of the mouth. The velum is an organ of loco- 272 COLLEGE ZOOLOGY motion and is largely responsible for the dispersion of the species, since with its help the larvae may travel long distances. The primary germ-layers (ectoderm and entoderm) arise either by the imagination of a blastula (Fig. 198, B) or by the growing over of certain cells (epibole, Fig. 198, C). The mesoderm originates in two primitive mesoderm cells derived from one of the larger FIG. 198. Stages in the development of mollusks' eggs. A, cleavage of the egg of Crepidula, showing the origin of the first mesodermic cell (mes). ma, macromeres; mi, micromeres. B, frontal section of an embryo of Paludina, showing gastrulation by the invagination of a blastula (embolic). mes., meso- derm bands; ud., archenteron; ., velum. C, an embryo of Crepidula, showing epibolic gastrulation. bl. blastopore; ec, ectoderm; en, entoderm. (A and C, from Lankester's Treatise, after Conklin ; B, from Korschelt and Heider, after Tonniges.) cells (macromeres) of the cleavage stage (Fig. 198, A, mes). Two mesoderm bands (Fig. 198, B, mes) are produced by the mul- tiplication of the primitive mesoderm cells. The Position of the Mollusks in the Animal Kingdom. - - We are not at all certain as to the relations of the Phylum MOLLUSCA to other phyla. Some investigators have sought to derive the mollusks from turbellarian-like ancestors. Considerable im- portance is attached to the presence of a trochophore in the de- PHYLUM MOLLUSCA 273 velopmental history of certain mollusks, and many embryolo- gists are inclined to consider this stage an indication of the ances- tral condition. According to this view, the mollusks, annelids, and other animals which pass through a trochophore stage in their ontogeny were all derived from a similar ancestral form. CHAPTER XIII PHYLUM ARTHROPODA i. INTRODUCTION THE ARTHROPODA (Gr. arthron, a joint; pans, a foot) are the crayfishes, water-fleas, barnacles, centipedes, millipedes, scor- pions, spiders, mites, and insects. All of these animals have a common plan of construction, as shown in Figure 199. The body consists of a series of segments some or all of which bear jointed 'ft. FIG. 199. Diagrammatic representation of the structure of an Arthropod. A, eye; Z>, intestine; F, antenna; G, jointed limbs; H, heart; If, mouth parts; N, nervous system; 5, gullet; Sk, chitinous exoskeleton; iiS, oS, supra- and infra-cesophageal ganglia. (From Schmeil.) appendages (G). The body is covered by a chitinous exoskele- ton (sk) secreted by the cells just beneath it. Within the body is a central tube, the alimentary canal (D), with an anterior mouth opening (at M) and a posterior anal opening. Dorsal to the alimentary canal is a blood-vessel called the heart (H), and ventral to the alimentary canal is the nerve-cord (N). There is a ganglionic mass, the brain (05), dorsally situated in the head. The Phylum ARTHROPODA includes a greater number of species than all of the other phyla of the animal kingdom combined. PHYLUM ARTHROPOD A 275 This number is estimated at from one million up, although only about four hundred thousand species have been described. Economically certain members of this phylum are of great im- portance. We need only mention the lobster as an article of food, the honey-bee as a producer of honey and beeswax, the silk- worm as the source of silk, the gypsy-moth caterpillar as a de- stroyer of trees, and the mosquito and housefly as carriers of disease germs. The ARTHROPODA may be grouped for convenience in the fol- lowing manner : - Phylum Arthropoda. CRAYFISH, CRABS, CENTIPEDES, IN- SECTS, SPIDERS, SCORPIONS, TICKS. Triploblastic, bilaterally symmetrical animals; anus present; ccelom poorly developed; segmented, somites usually more or less dissimilar; paired, jointed appendages present on all or a part of the somites; chitinous exoskeleton. SECTION A. BRANCHIATA. Mostly aquatic ARTHROPODA usually breathing by means of gills. Class I. Crustacea. Examples: crayfish (Fig. 202), water- flea (Fig. 21 1), barnacle (Fig. 214), sow-bug (Fig. 220). SECTION B. TRACHEATA. Air-breathing ARTHROPODA with tracheae (Fig. 243). Division i. Protracheata. Primitive tracheates which pos- sess nephridia and other annelid characteristics, and tracheae and other insect characteristics. Class II. Onychophora. Example: Peripaius (Fig. 228). Division 2. Antennata. Tracheates with one pair of an- tennae (Fig. 250). Class III. Myriapoda. Antennata with many similar legs. Examples: centipedes (Fig. 233), millipedes (Fig. 232). Class IV. Insecta. Antennata with three pairs of legs, and usually wings. Examples: grasshopper (Fig. 249), honey-bee (Fig. 236). Division j. Arachnid a. Tracheates without antennae, and with tracheae, book lungs, or book gills. 276 COLLEGE ZOOLOGY Class V. Arachnida. Examples: scorpion (Fig. 318), spider (Fig- 3 J 3)> mite (Fig. 322), king-crab (Fig. 327). 2. CLASS I. CRUSTACEA a. The Crayfish-- Cambarus The crayfish is abundant both in this country and in Europe. In the eastern United States Cambarus affinis is common. Cambarus virilis is plentiful in the Middle states. The European crayfish is Astacus (Potomobius) flumatiUs. The anatomy and physiology of these three species as well as of the lobster agree except in minor de- tails, and the fol- lowing account may be used as a de- scription of any of them. Crayfishes usu- ally hide by day un- der rocks or logs at the bottom of ponds and streams. They maybe captured by hand, with a net, or with a string baited FIG. 200. Transverse section through the ab- . , . ,. domen of the crayfish. DA, dorsal abdominal With a piece of meat, artery ; EM, extensor muscles of the abdomen ; They thrive in an EP, enimeron ; FM, flexor muscles of abdomen ; _ , , M, muscles of appendage; N, endopodite; NG, nerve aquarium, ar ganglion; P, protopodite ; PL, pleuron, PR, intes- entire life-history tine; S, sternum; T, tergum; V, ventral abdominal , , i artery; X, exopodite. (From Marshall and Hurst.) ma y in the laboratory. The yearly decrease in the number of lobsters available for food, and the steadily increasing demand for crayfishes, will undoubtedly soon make it worth while to raise the latter for market. PHYLUM ARTIIROPODA 277 ://'-- ex. Anatomy and Physiology. EXTERNAL FEATURES. The cray- fish is a segmented animal, but the joints have been obliterated on the dorsal surface of the ante- rior end. The body shows two distinct regions, an anterior rigid portion, the ccphalothorax, and a posterior flexible abdomen. A chitinous exoskeleton, impregnated with lime salts, supports and pro- tects the soft parts of the body. A typical segment (Fig. 200) consists of a tergum (T),a, sternum (S), two pleura (PL), and two epimera (EP). The cephalo- thorax includes segments I-XIII; a cervical groove separates the cephalic or head region from the thoracic region. The dorsal shield of the cephalothorax is called the carapace; its anterior pointed extension is known as the rostrum, and the heavy flap on either side protecting the gills, , ,. . ,, FIG. 201. Types of crayfish as a branckwstegite. There are appendages. A, foliaceous type, six segments and a terminal exten- second maxilla. 1-4, basipodite ; , 5, endopodite; 6, scaphognathite ; sion, the telson, in the abdomen. ~ ep ^ ep ipodite. B, biramous type, APPENDAGES. -- Each segment swimmeret. r.v, bs., protopodite; ,. . . ex., exopodite ; en., endopodite. bears a pair of jointed appendages c , uniramous type, second walk- which in most cases differ from im ? le s- />, f>p, protopodite; . ip, mp, cp, pp, dp, segments of the other pairs in structure and endopodite; e p., epipodite. (A and function, but all are probably c -. from the Cambridge Natural History ; B, from Lankester's variations of a biramous type Treatise.) (Fig. 200) consisting of a basal protopodite (P), an inner branch, the endopodite (N), and an outer branch, the exopodite (X). Three types of appendages can COLLEGE ZOOLOGY be distinguished in an adult crayfish : (i) foliaceous (second maxilla, Fig. 201, A), (2) biramous (swimmerets, Fig. 201, B), and (3) uniramous (walking legs, Fig. 201, C). Figure 202 shows the position and shape of most of the appendages, and IMIVLI'M AKTIIKOI'ODA 279 a 1 j_, tn U 2 "3 r^ "o cr X3 ^ 'rt "cd "o S & O H O IU ^ C I !3 1| a i^ w M W 83 o3 u of i ^ o o 04 o W u _g 'o " 1 it .g ft S-g -4- ^J ^3 , c bc'C -g >, p ^ w C C c3 (]j P tn 1 c " ^^'s, PQ d ,9* C C *O a t> c bo ? cu thin lamellae extend- ing inward bilobed lamellae thin segments extend- ing inward ; a broad plate, the epipodite extending outward CO 01 N 0. M 0. 1 o U _rt R) 1 1 1 rJU 3 1 'S3 cj 03 4-J 1 1 s tn H d (N tn H H-5 HH K- 1 hH h- 1 h- 1 > ^ 2 So COLLEGE ZOOLOGY tn jb 'rt to (3 03 "vn ' tn bC m JJ ~ r^ .S ^ fe d -2 4^ ** G ^ t^H pj ~J H O HH HH -S be a -S-a ^^ ^^ r __i ^ p^ t ^^ C o O O C 15 ..a O ^-t *"* "*~* 13 60 'Jj ** bC bD ^ S3 }-H in . 4) j-i _G .S C 1 .1 |.s ^1 1 ^ G3 O rt 'O co c/5 ^ CO P ^ ^11.2 42 SM o in O H oj"" , HH ^.S <3 o ? H r* Tj ,^^ ^^ ill G L P^ '^ HH P "+J G C/3 WT o 43 o a *^-*H '2^ "a X tt3 HH HH X g "G o -5 "*"* "S *- X o 4J 3 w S^6 rt tjO S rt I G 05 >H rt"S M ofi c^ Q .G D en O P g 4n in C ft 1 S '&. 1 10 C/5 to ^ CO c/5 CO t-H O KH ^_ O ^^ t^| ft *^^ J^^ o 3 O w (H _ ( _ ) 4J ^_> ^ ^ [ 1 j 03 C3 a c a |3| g ^ 4> Si 4) CO 4> en ,2 Q 42 r ^o 42 42 CO CO "* "*! *! < < rt " *-> O 4) 6 6 c i tn tn bO;3 On.'ri OH^H X O Qj o3 a H 42 -So g'g o3 4) 'in o O '^ X O 004) U 4^ 4) Q 42 o3 ^O rt p^, 4) hH bo .s S 13 o CO 1 4-J bO 13 43 IO . bC HH HH 1^^ g ^Ji, ^ fe HH X X^ X PHYLUM ARTHROPODA 281 .g^2 o ^ g> *~ fe o HHj O *-> - - -rt o2 c T3 g S^ s cj O D C .a|l "c * 5 2j p C -- S o > HH > "3 S^_ U K^ ^* > (U bO rN r * o .g.-s C d 4_> -d ^ .-H """ \ hH 3 < < E jj d -a .g |o g ^ _> c X <3 U tn Ll i T3 J-> 1- CJ ri D. g g HH ^^ as o lj d X .2 X _c 3 S * > 2- o-^o c hH 1 < en E d I * OJ g U bC g be 13 ts , t/3 j > hH hH 2 ID ^ p> ^ "rt CD (U kJ A 1 g bO 1, _d 4* O " en d ^j hH CN ^ <^ ^ S i ro E .-o'> >^ ._ C/3 gls ^.S o _^f^ O " 1- HH HH X X X X X 282 COLLEGE ZOOLOGY Table IX gives a brief description of each and the modifications due to differences in function. INTERNAL ORGANS. - - Definite systems of organs are present in the crayfish for the performance of the various functions. The coelom is small, and is restricted to the cavities of the repro- ductive organs and green glands. The cavities around the alimentary canal are blood spaces, and therefore represent a hasmoccel. Some of the organs, like the muscles and nervous ganglia, are segmentally arranged; others like the excretory organs are concentrated in a small space. DIGESTION. Crayfishes live chiefly on living snails, tadpoles, young insects, and the like, but sometimes eat one another, and may also devour decaying organic matter. They feed at night, being most active at dusk and daybreak. The maxilli- pedes and maxillae hold the food while it is being crushed into small pieces by the mandibles. The food particles pass down the (esophagus (Fig. 202, 20) into the anterior, cardiac chamber of the stomach (21), where they are ground up by a number of chitinous ossicles, called the gastric mill. When fine enough, the food passes through a sieve-like strainer of hair-like setae into the pyloric chamber of the stomach (22); here it is mixed with a secretion from the digestive glands brought in by the hepatic ducts. The dissolved food is absorbed by the walls of the in- testine (24). Undigested particles pass on into the posterior end of the intestine, where they are gathered together into faeces, and egested through the anus ((5). CIRCULATION. - - THE BLOOD. - - The blood into which the absorbed food passes is an almost colorless liquid in which are suspended a number of ameboid cells, the blood corpuscles or amebocytes. The principal functions of the blood are the trans- portation of food materials from one part of the body to another, of oxygen from the gills to the various tissues, of carbon dioxide to the gills, and of urea to the excretory organs. BLOOD-VESSELS. - - The principal blood-vessels are a heart, seven arteries, and a number of spaces called sinuses. Blood PHYLUM ARTHROPOD A 283 enters the heart from the surrounding sinus through three pairs of valvular ostia. Rhythmical contractions then force it for- ward, backward, and downward. (i) The ophthalmic artery (Fig. 202, j^) supplies part of the stomach, the oesophagus, and head. (2, 3) The two antennary arteries (35) carry blood to the stomach, antennae, excretory organs, and other cephalic tissues. (4, 5) The two hepatic arteries (36) lead to the digestive glands. (6) The dorsal abdominal artery (ji) supplies the intestine and surrounding tissues. (7) The sternal artery (jo) divides into a ventral thoracic and a ventral abdominal artery which carry blood- to the appendages and other ventral organs. SINUSES. - - The blood passes from the arteries into spaces lying in the midst of the tissues, called sinuses. The heart lies in the pericardial sinus. The thorax contains a large ventral blood space, the sternal sinus, and a number of branchio-cardiac canals extending from the bases of the gills to the pericardial sinus. A perivisceral sinus surrounds the alimentary canal in the cephalothorax. THE BLOOD FLOW. - - The heart, by means of the rhythmical contractions, forces the blood through the arteries to all parts of the body. Valves are present in every artery where it leaves the heart; they prevent the blood from flowing back. The finest branches of these arteries, the capillaries, open into spaces between the tissues, and the blood eventually reaches the sternal sinus. From here it passes into the afferent channels of the gills and into the gill filaments, where the carbonic acid in solution is exchanged for oxygen from the water in the branchial chambers. It then returns by way of the efferent gill channels, passes into the branchio-cardiac sinuses, thence to the pericardial sinus, and finally through the ostia into the heart. The valves of the ostia allow the blood to enter the heart, but prevent it from flowing back into the pericardial sinus. 284 COLLEGE ZOOLOGY RESPIRATION. - - Between the branchiostegites and the body- wall are the branchial chambers containing the respiratory organs, the gills. At the anterior end of the branchial chamber is a channel in which the scaphognathite of the second maxilla (Fig. 201, A, 6} moves back and forth, forcing the water out through the anterior opening. Fresh water flows in through the poste- rior opening of the branchial chamber. GILLS. - - There are two rows of gills; the outer, podobranchice, are fastened to the coxopodites of certain appendages (see Table X) and the inner double row, the arthrobranchia, arise from the membranes at the bases of these appendages. In Astacus there is a third row, the pleurobranchice, attached to the walls of the thorax. The number and arrangement of these gills are shown in Table X. Each gill possesses a number of gill filaments. TABLE X THE NUMBER AND POSITION OF THE GILLS OF THE CRAYFISH (Cambarus) ARTHROBRANCHI^E SEGMENT PODO- BRANCHLE TOTAL NUMBERS Anterior Posterior VI o (ep.) o o (ep.) VII I I O 2 VIII I I I 3 IX I I I 3 X I I I 3 XI I I I 3 XII I I I 3 6 (ep.) 6 S 17 (ep.) EXCRETION. - - The waste products of metabolism are taken from the blood by a pair of rather large bodies, the "green glands " (Fig. 202, 40) situated in the ventral part of the head PHYLUM ARTIIROPODA 285 anterior to the oesophagus. Each green gland consists of a glandular portion, green in color (40), a thin-walled dilata- tion, the bladder (41), and a duct open- ing to the exterior through a pore at the top of the papilla on the basal segment of the antenna (42). NERVOUS SYSTEM. - - The morphology of the nervous system of the crayfish is in many respects similar to that of the earthworm. The central nervous system includes a dorsal ganglionic mass, the brain (Fig. 202, 25), in the head, and two circumcssophageal connectives (26) passing to the ventral nerve-cord (27), which lies near the median ventral sur- face of the body. The brain sends nerves to the eyes, antennules, and an- tennae. Each segment posterior to VII possesses a ganglionic mass, which sends nerves to the surrounding tissues. The large subcesophageal ganglion in segment VII consists of the ganglia of segments III- VII fused together. It sends nerves to the mandibles, maxillae, and first and second maxillipeds. Visceral nerves arise from the brain and extend posteriorly to the viscera. SENSE-ORGANS. EYES. - - The eyes of the crayfish (Fig. 202, 28) are situated at the end of movable stalks, one on either side of the head. Each eye is covered by a modified portion of the chitinous cuticle called the cornea. The cornea is divided into rectangular areas known as FIG. 203. Longitudinal sections of two ommatidia of the crayfish. A, pigment arranged as influenced by light. B, pigment arranged as influenced by darkness. i, cornea ; 2, nucleus of corneagen cells; ?, nucleus of vitrella ; 4, nucleus of pigment cell; 5, crystalline cone; 6, tapetum cell; 7, rhabdom; S, retinal cell; 0, basement membrane ; 10, retinal nerve fiber. (From Sedgwick's Zoology, after Parker.) 286 COLLEGE ZOOLOGY facets, which are the ends of long visual rods, the ommatidia. The average number of ommatidia in a single eye is 2500. The parts of an ommatidium are shown in Figure 203. VISION. - - The eyes of the crayfish are supposed to produce an erect mosaic or "apposition image"; this is illustrated in Figure 204, where the ommatidia are represented by a-e, and the fibers from the optic nerve by a'-e'. The rays of light from any point a, b, or c will all encounter the dark pigment cells surround- ing the ommatidia and be absorbed, except the ray which passes directly through the center of the cornea, as d or e ; this ray will penetrate to the fibers from the optic nerve. One ommatidium thus re- ceives a single impression, and since the ommatidia are directed to different, though adjoining, regions, the sum FIG. 204 --Diagram to explain mosaic of the resu lti ng images may vision (see text). (From Packard, after J Lubbock.) be compared to a mosaic. This method of image forma- tion is especially well adapted for recording motion, since any change in the position of a large object affects the entire 2500 ommatidia. When the pigment surrounds the ommatidia (Fig. 203, A), vision is as described above; but it has been found that in dim light the pigment migrates partly toward the outer and partly toward the basal end of the ommatidia (Fig. 203, B). When this occurs, the ommatidia no longer act separately, but a com- bined image is thrown on the retinular layer. STATOCYSTS. - - The statocysts of Cambarus are chitinous- lined sacs situated one in the basal segment of each antennule. In the statocyst are a number of sensory hairs, among which are a few grains of sand, called statoliths, placed there by the cray- fish. The contact of the statoliths with the hairs determines PHYLUM ARTHROPODA 287 the orientation of the body while swimming. Statocysts are, therefore, organs of equilibration. When the crayfish changes its exoskeleton in the process of molting, the statocyst is also shed. Individuals that have just molted, or have had their stato- cysts removed, lose much of their powers of orientation. Per- haps the most convincing proof of the function of equilibration is that furnished by the experiments of Kreidl. This investi- gator placed shrimps, which had just molted and were therefore without statoliths, in filtered water. When supplied with iron filings, the animals filled their statocysts with them. A strong electromag- net was then held near the stato- cyst, and the shrimp took up a position corresponding to the re- sultant of the two pulls, that of gravity and of the magnet. MUSCULAR SYSTEM. - - The prin- cipal muscles in the body of the crayfish are situated in the ab- domen, and are used to bend that part of the animal forward upon FIG. 205. -Female reproductive organs of the crayfish. /, right the ventral Surface of the thorax, oviduct; 2, right lobe of ovary; thus producing backward locomo- 3 - l lobe opened to show central . cavity ; 4, external opening of tion 111 Swimming. Other muscles oviduct; 5, base of third walking extend the abdomen in the prepara- g - < From shi P le y a "d Mac- Bride.) tion for another stroke. The ap- pendages are all supplied with muscles which give them the power of motion. It is of interest to note that the muscles are internal, and attached to the inner surface of the skeleton. In man, on the contrary, the skeleton is internal and the muscles external. REPRODUCTION. - - The sexes of crayfishes are normally sep- arate (dioecious). In the male the spermatozoa arise in the bilobed testis (Pig. 202, j/), pass through the paired vasa defer- 288 COLLEGE ZOOLOGY entia (j#) and out of the genital apertures (8}, one in the base of each fifth walking leg. In the female the eggs arise in the bilobed ovary (Fig. 205, 2, 3), pass through the paired oviducts (/), and out of the genital apertures (4), one in the base of each third walking leg. The spermatozoa are transferred from the male to the seminal receptacle of the female during copulation, which usually takes place in the autumn. The seminal receptacle is a cavity in a fold of cuticle between the fourth and fifth pairs of walking legs. The eggs are laid in April and are probably fertilized by the spermatozoa at this time. They are fastened with a sort of glue FIG. 206. Female crayfish aerating eggs by raising and straightening abdomen and waving swimmerets back and forth. (From Andrews in Am. Nat.) to the swimmerets, and are aerated by being moved back and forth through the water (Fig. 206). The cleavage of the egg is superficial (Fig. 207, A), and the em- bryo appears first as a thickening on one side (Fig. 207, B). The eggs hatch in from five to eight weeks, and the larvae cling to the egg-shell. In about two days they shed their cuticular covering, a process known as molting or ecdysis. This casting off of the covering of the body is not peculiar to the young, but occurs in adult crayfishes as well as in young, and adults of many other animals. In the larval crayfish the cuticle of the first stage becomes loosened and drops off. In the meantime, the hypo- dermal cells have secreted a new covering. Ecdysis is necessary before growth can proceed, since the chitin of which the exo- skeleton is composed does not allow expansion. In adults it is PHYLUM ARTHROPODA also a means of getting rid of an old worn-out coat and acquiring a new one. The young stay with the mother for about one month, B FIG. 207. Stages in the development of the egg of the crayfish. A, super- ficial cleavage of the egg. B, embryo in the Nauplius stage. A, anus; a 1 , antennule; a' 2 , antenna; e, rudiment of eye; /, upper lip; m, mandible; ta, thoraco-abdominal plate. (From Korschelt and Heider, after Reichenbach.) and then shift for themselves. They molt at least seven times during the first summer. The life of a crayfish usually extends over a period of three or four years. Regeneration. - - The crayfish and many ^ other crustaceans have fj_ the power of regenerat- \jL ing lost parts, but to a much more limited ex- tent than such animals as Hydra and the earth- worm. Experiments have been performed Upon almost every one FIG. 208. Diagram showing antenna-like Of the appendages as organ regenerated in place of an eye of Pa/ . (From Morgan, after Herbst.) well as the eye. The growth of regenerated tissue is more frequent and rapid in young specimens than in adults. The new structure is not u 2QO COLLEGE ZOOLOGY always like that of the one removed. For example, Figure 208 shows an antenna which regenerated in place of an eye in a marine crustacean, Palcemon. Autotomy. - - Perhaps the most interesting morphological structure connected with the regenerative process in Cambarus is the definite breaking point near the bases of the walking legs. If the chelae are injured, they are broken off by the crayfish at the breaking point. The other walking legs, if injured, may be thrown off at the free joint between the second and third segments. A new leg, as large as the one lost, develops from the end of the stump remaining. This breaking off of the legs at a definite point is known as autotomy, a phenomenon that also occurs in a number of other animals. The leg is separated along the break- ing point by several successive muscular contractions. It has been shown " that autotomy is not due to a weakness at the breaking point, but to a reflex action, and that it may be brought about by a stimulation of the thoracic ganglion as well as by a stimulation of the nerve of the leg itself." (Reed.) The power of autotomy is of advantage to the crayfish, since the wound closes more quickly if the leg is lost at the breaking point. No one has yet offered an adequate theory to account for autotomy. It is probably " a process that the animal has acquired in connection with the condition under which it lives, or, in other words, an adaptive response of the organism to its condition of life." (Morgan.) Behavior. - - When at rest, the crayfish usually faces the en- trance to its place of concealment, and extends its antennas. It is thus in a position to learn the nature of an approaching object without being detected. Activity at this time is reduced to the movements of a few of the appendages and the gills; the scaphognathites of the second maxilla? move back and forth, baling water out of the forward end of the gill chambers; the swimmerets are in constant motion creating a current of water; the maxillipeds are likewise kept moving; and the antennae and eye-stalks bend from place to place. PHYLUM ARTHROPOD A 29 1 LOCOMOTION. --Locomotion is effected in two ways, walking and swimming. Crayfishes are able to walk in any direction, forward usually, but also sidewise, obliquely, or backward. Sii'imming is not resorted to under ordinary conditions, but only when the animal is frightened or shocked. In such a case the crayfish extends the abdomen, spreads out the uropod and tel- son, and, by sudden contractions of the bundles of flexor abdom- inal muscles, bends the abdomen and darts backward. The swimming reaction apparently is not voluntary, but is almost entirely reflex. If turned over on its back, the crayfish either raises itself on one side and topples over, or else gives a quick backward flop. REACTIONS TO STIMULI. - - THIGMOTROPISM. - - The crayfish "is sensitive to touch over the whole surface of the body, but es- pecially on the chelae and chelipedes, the mouth parts, the ven- tral surface of the abdomen, and the edge of the telson." (Bell.) Positive thigmotropism is exhibited by crayfishes to a marked degree, the animals seeking to place their bodies in contact with a solid object, if possible. The normal position of the crayfish when at rest under a stone is such as- to bring its sides or dorsal surface in contact with the walls of its hiding place. Thigmot- ropism, no doubt, is of distinct advantage, since it forces the animal into a place of safety. CHEMOTROPISM. - - The reactions of the crayfish to food are due in part to a chemical sense, and, since " the animals react to chemical stimulation on any part of the body . . . we must assume that there are chemical sense-organs all over the body." (Bell.) The anterior appendages, however, are the most sensi- tive, especially the outer ramus of the antennule. Positive re- actions result from the application of food substances. For example, if meat juice is placed in the water near an animal, the antennae move slightly, and the mouth parts perform vigorous chewing movements. Acids, salts, sugar, and other chemicals produce a sort of negative reaction indicated by scratching the carapace, rubbing the chelae, or pulling at the part stimulated. 292 COLLEGE ZOOLOGY HABIT FORMATION. - - It has been shown by certain simple experiments that crayfishes are able to learn habits and to modify them. They learn by experience and modify their behavior slowly or quickly, depending upon their familiarity with the situation. One investigator has trained them to come to him for food. (Holmes.) b. Crustacea in General (1) Distinguishing Features. - - The CRUSTACEA (Lat. crusta, skin) are arthropods most of which live in the water and breathe by means of gills. The body is divided into head, thorax, and abdomen, or the head and thorax may be fused, forming a cephalo- thorax. The head usually consists of five segments fused to- gether; it bears two pairs of antennae (feelers), one pair of mandibles (jaws), and two pairs of maxillae. The thorax bears a variable number of appendages, some of which are usually locomotory. The abdominal segments are generally narrow and more mobile than those of the head and thorax; they bear appendages which are often reduced in size. (2) Classification of the Crustacea. 1 - - The CRUSTACEA belong- ing to Subclasses I-IV are often placed in one group and called ENTOMOSTRACA. They are of small size, with a variable num- ber of body segments, and usually no gastric mill in the stomach. They are apparently more primitively organized than the mem- bers of Subclass V, the MALACOSTRACA. Certain fossil animals, called TRILOBITES (Fig. 209), are by many authorities included with the CRUSTACEA. They have one pair of antenna?, and nu- merous body segments, all of which bear biramous appendages. SUBCLASS I. BRANCHIOPODA. -- CRUSTACEA with an elongated body, usually a carapace or shell, and many pairs of lobed, foliaceous swimming feet. Order i. Phyllopoda. -- BRANCHIOPODA with from ten to thirty pairs of leaf-like, swimming feet. Examples: Branchipus, (Fig. 210, A), Artemia (Fig. 210, B). 1 Somewhat simplified from Caiman in Lankester's Treatise on Zoology. PHYLUM ARTHROPODA 293 FIG. 209. FIG. 210. FIG. 209. Dorsal surface of a Trilobite, Triarthrus becki. (From Sedg- wick's Zoology, after Beecher.) FIG. 210. Order PHYLLOPODA. A, Branchipus stagnalis; B, Artemia salina. (From Verworn, after Semper.) .anl.Z, dyl 9 FIG. 211. V X FIG. 212. FIG. 211. Order CLADOCERA. Daphnia, a water-flea. ant.i, antennule ; ant. 2, antenna ; br, brain; br.p, brood-pouch; E, eye; d.gl, digestive gland; /, swimming feet ; hi, heart ; sh.^l, shell-gland. (From Parki-r and Haswell, after Claus.) FIG. 212. Subclass OSTRACODA. Cypris candid't. i, antennules; -', anten- nae; 3, mandibles; 4, ist maxilleC ; 5, 2d maxilla;; 6, ist pair of legs; 7, 2d pair of legs ; to market annually, and unless their capture is regulated, they will soon be exterminated. Shrimps and prawns are also used as food for man. Pal&monetes (Fig. 224) is a common shrimp 302 COLLEGE ZOOLOGY living among seaweeds; it is almost transparent. The hermit- crab, Eupagurm, lives in an empty snail-shell which protects it from many enemies. Some hermit-crabs place sea-anemones or hydroid colonies upon their shells; these furnish additional protection. The edible or blue crab, Callinectes, lives along the Atlantic and Gulf coasts and is captured in large numbers for market. It is called the soft-shelled crab just after molting. The fid- dler-crabs, Uca pugilator, are common along our eastern coast, where they dig holes in the mud and sand. The spider-crab, Libinia, has long slender legs, which enable it to run over uneven surfaces with ease. The Japanese spider-crab is very large, sometimes measuring twenty feet across from tip to tip of the first pair of legs. (5) The Biogenetic Law. - - Early in the past century it was noticed that animals could be arranged in a series beginning with the PROTOZOA and passing through the simpler diploblastic forms, and that the stages in this series correspond to the early stages in the embryology of the METAZOA. This led to the formulation of the biogenetic law, i.e. that the development of the individual recapitulates the stages in the evolution of the race, or ontogenv recapitulates phylogeny. These stages contrasted appear as follows : - PHYLOGENETIC STAGE ONTOGENETIC STAGE (1) Single-celled, animal Egg cell (2) Ball of cells Blastula (3) Two-layered sac Gastrula (4) Triploblastic animal Three-layered embryo Zoologists soon became interested in the recapitulation theory, and enlarged upon it. Of these, Fritz Miiller and Ernst Haeckel are especially worthy of mention. The latter expressed the facts as he saw them in his " fundamental law of biogenesis." The ancestor of the many-celled animals was conceived by him as PHYLUM ARTHROPOD A 33 a two-layered sac something like a gastrula, which he called a Gastrcea. The ccelenterates were considered to be gastrasa slightly modified. Fritz M tiller de- FIG. 225. Larva of lobster in My sis stage. (From Sedgwick, after Sars.) rived strong arguments in favor of biogenesis from a study of certain CRUSTACEA belonging to the MALACOSTRACA. Many members of this group do not emerge from the egg so nearly like the adult as does the crayfish. The lobster, for example, upon hatching (Fig. 225) re- sembles a less specialized A / I B ' FIG. 226. Two stages in the development of the shrimp, Peiueus. A, Naupliiis stage. B, Protozoan stage. (From Sedgwick's Zoology, after Fritz Miiller.) 34 COLLEGE ZOOLOGY prawnlike crustacean called My sis (Fig. 217), and is said to be in the My sis stage. The shrimp, Penceus, passes through a number of interesting stages before the adult condition is attained. It hatches as a B FIG. 227. Two later stages in the development of Penceus. A, Zocea stage. B, Mysis stage. (From Korschelt and Heider, after Claus.) larva, termed a Nauplius (Fig. 226, A), possessing a frontal eye and three pairs of appendages (A', A", Mdf.); this Nauplius molts and grows into a Protozo&a stage (Fig. 226, B), which bears three more pairs of appendages and the rudiments of segments III-VIII. The Protozocea stage grows into the Zoaa stage PHYLUM ARTHROPODA 305 (Fig. 227, A). The cephalothorax and abdomen are distinct at this time; eight pairs of appendages are present (I-VIII) and six more are developing (ai-ae). The Zocea grows and molts and becomes a My sis (Fig. 227, B) with thirteen pairs of appendages (I-VIII) on the cephalothorax. Finally, the My sis passes into the adult shrimp, which possesses the characteristic number of appendages (I- XIX), each modified to perform its particular function. The Xaiiplius of Pen (BUS resembles the larvae of many simple crustaceans; the Zo&a is somewhat similar to the condition of an adult Cyclops (Fig. 213); the Mysis is like the adult Mysis (Fig. 217); and finally the adult Penceus is more specialized than any of its larval stages, and belongs among the higher CRUSTACEA. The above facts have convinced some zoologists that Penceus recapitulates in its larval development the progress of the race; that the lobster has lost many of these stages, retaining only the Mysis; and that the crayfish hatches in practically the adult condition. The Nauplius stage of the latter is supposed to be represented by a certain embryonic phase (Fig. 207, B). The law of biogenesis has been criticized severely by many prominent zoologists, but it has furnished an hypothesis, which has concentrated the attention of scientists upon fundamental embryological processes, and has, therefore, had a great influence upon zoological progress. 3. CLASS II. ONYCHOPHORA This class (Gr. onux, a claw; phoreo, I bear) contains about fifty species of a peculiar arthropod, usually placed in a single genus, Peripatus (Fig. 228), but probably belonging to a number of genera. Peripatus has been reported from isolated regions in Africa, Australia, New Zealand, Tasmania, New Britain, Mexico, South America, West Indies, and Malaya, and is, there- fore, an excellent example of an animal with a discontinuous distribution. It lives in crevices of rock, under bark and stones, and in other dark places. As the animal moves slowly from x 306 COLLEGE ZOOLOGY place to place by means of its legs, the two extremely sensitive antennae test the ground over which it is to travel, while the eyes, one at the base of each antenna, enable it to avoid the light. FIG. 228. Peripatus capciisis, drawn from life. (From Sedgwick.) When irritated, Peripatus often ejects slime, sometimes to the distance of almost a foot, from a pair of glands which open on the oral papillae. This slime sticks to everything but the body of the animal itself; it is used principally to capture flies, wood-lice, termites, and other small animals, and in addition is probably a weapon of defense. A pair of modified ap- pendages serve as jaws and tear the food to pieces. Most species of Peripatus are viviparous, and a single large female may produce thirty or forty young in a year. These young resemble the adults when born, differing chiefly in size and color. The external appearance of Peri- patus capensis is shown in Figures 228 and 229. Figure 230 shows the principal internal organs of a male specimen. The head bears three pairs of append- ages: (i) the antenna (Fig. 229, ant.), (2) the oral papilla (or.p}, and (3) the jaws, a pair of simple eyes, and a ventrally placed FIG. 229. Peripatus ca- pensis, ventral view of head. ant, antenna; F.I, first leg; or.p, oral papillae; T, tongue. (From Sedgwick.) PHYLUM ARTHROPOD A 307 mouth. The fleshy frg.s number from seventeen pairs to over forty pairs in different species; each (Fig. 229, F.I) bears two claws. The anus is at the posterior end; the genital pore is situated between the last pair of legs; and a ne- phridiopore lies at the base of each leg. The skin is covered with papilla, each bearing a spine; these pa- pillce are especi- ally numerous on the antennte, lips, and oral papillae, and are probably tactile (Fig. 229). The digestive system (Fig. 230, 8) is very simple, consisting of a muscular phar- ynx, a short oesophagus, a long, saccular stomach, and a short intes- tine. The pair of salivary glands (n), which open into the mouth cavity, are modified nephridia. The heart is the only blood-vessel; it is a dorsal tube with paired ostia connecting it with the pericardial cavity in which it lies. The body-cavity is a blood space, i.e. a hgemoccel. The breathing OJ ->- T *-> o .^ rt g m 60 .-a "'rt - ^ .- tj r|S *"& -J= to ^^ s.-^ g ft, ^0 - '^ -"S ^ j g N *i V - I Ul' MO o i; a; IT. u. ft, O > in B) has been applied to .these structures, since they are used to remove the wax plates from the abdomen of the worker. The wings are membranes supported by hollow ribs called nerves or veins. The pair of wings on one side of the body may be joined together by a row of booklets on the anterior margin of FIG. 230. - - Foot of the honey-bee, an, claw; fh, tactile hairs; pv, pul- villus; t, tarsal segments (From Packard, after Cheshire.) PHYLUM ARTHROPOD A 3*7 the hind wing, which are inserted into a trough-like fold in the posterior margin of the fore wing. When flying, the wings act as inclined planes, and locomotion for- ward is attained by both up and down strokes, the tips of the wings moving in a curve shaped like a figure S. Motion backward, or a sud- den stop, may be accomplished by changing the inclina- tion of the plane of oscillation. The abdomen is made up of a series of six visible seg- ments; thin, chitin- ous membranes con- nect the segments and make the move- ment and expansion of the abdomen pos- sible. Each of the last four visible seg- ments of the worker FIG. 240. Sting of worker honey-bee, b, barbs bears a pair of Wax on darts; /. k, I, levers to move darts; n, nerves; elands At the end of p ' stin ^- fep| >r : #S, poison gland; ps, poison sac; sh, sheath; jth g, fifth abdominal ganglion. (From the abdomen of the Packard, after Cheshire.) worker and queen is the sting, and the slit-like openings of the sexual organs and anus. There is no sting in the drone, but a copnhitory organ is present. The sting is a very complicated structure (Fig. 240). Before COLLEGE ZOOLOGY the bee stings, a suitable place is selected with the help of the sting feelers (p) ; then the two barbed darts (b) are thrust forward. The sheath (sh) serves to guide the darts, to open up the wound, and to aid in conducting the poison. The poison is secreted in a pair of glands (pg), one acid, the other alkaline, and is stored in a reservoir (ps). Generally the sting, poison glands, and part of the in- testine are pulled out when a bee stings, so that death ensues after several hours, but if only the sting is lost, the bee is not fatally in- jured. The queen seldom uses her sting except in combat with other queens. The Anatomy and Physiology of the Internal Organs. - DIGESTION (Fig. 241). --The mouth opens into a narrow oesophagus (a?) , FIG. 241. Internal organs of honey-bee, bl, mal- , yn j cn leads to pighian tubules; c.s, true stomach; dv, dorsal vessel; e, eye; g, ganglia of nerve chain; hs, honey sac; the honey SttC (/), li, rectum; Ip, labial palpus; mesa.t, mesothorax ; situated near the mela.l, metathorax; mx, maxilla; n, nerves; No. I, No. 2, No. 3, salivary glands; ce, oesophagus; p, stomach anterior end of mouth; pro.t, prothorax ; si, small intestine (ileum); |y. p abdomen v, ventricles of dorsal vessel. (From Packard, after Cheshire.) The Stomach PHYLUM ARTHROPODA 319 TraSc mouth (/>), with its four triangular lips, regulates the passage of the pollen or honey taken in as food into the true stomach (c.s). The digestive juices se- creted by the walls of the true stomach change the food into chyme. Part of the chyme is absorbed ; the rest of the food ma- terial is forced by mus- cular contractions into the small intestine (si), where digestion and ab- sorption are completed. Undigested particles pass into the rectum (If) and out of the anus. One pair of salivary glands (No. 2) lie in the head, a second pair (No. 3) in the thorax; they pour alka- line secretions upon the food as it is taken into the oesophagus. CIRCULATION. - The blood is a plasma contain- ing ameboid corpuscles, but differs from that Of most animals since it FlG - 242. -- Respiratory system of worker carries very little, if any, oxygen. The dorsal ves- sel or heart (Fig. 241, dv) is the principal organ of circulation. Blood en- ters it through five pairs of lateral ostia, and is forced forward by rhythmical contractions. From the head region the blood finds HtTraSc VDSp honey-bee as seen from above, one anterior pair of abdominal sacs removed and transverse ventral commissures of abdomen not shown. / sf>, III sp, VII sp, spiracles; HtTraSc, Tra Sc, i, 2, 4, 7, 8, 10, tracheal sacs; Tra, tracheae. (From Snodgrass, Tech. Series 18, Bur. Ent., U. S. Dep't of Agric.) 320 COLLEGE ZOOLOGY its way through spaces (haemoccel) to the ventral part of the body, and thence to the pericardial sinus just beneath the heart. The muscular diaphragm of the pericardial sinus forces the blood through the ostia into the heart. RESPIRATION (Fig. 242). --The honey-bee breathes through seven pairs of lateral openings called spiracles, one pair in the pro thorax (1 Sp), one in the metathorax (7 Sp), and five in the abdomen (/// Sp, VII Sp). The spiracles open into tubes called trachea (Tra) which branch and carry air to all parts of the body. Cer- tain tracheae are dilated to form air sacs ( TraSc) , which are supposed to be of value during flight, since they can be enlarged at will and the specific gravity of the insect correspondingly decreased. Figure 243 shows the trachea to consist of a tube of a single layer of cells (a) lined with chitin which is thickened so as to form a spiral thread. This chitinous lining keeps the trachea open. Each spiracle is provided with a valve which helps prevent the entrance of dust. Oxygen is carried directly a, cellular wall ; to the tissues by the tracheae and does not need to be transported by the blood. EXCRETION. - - The excretory organs are long, thread-like tubes called malpighian tubules (Fig. 241, bt). They pour their excretions into the intestine at the point where it joins the stomach. NERVOUS SYSTEM. - - There is a complicated bilobed ganglionic mass, the brain, in the dorsal part of the head. Nerves connect the brain with the compound eyes, ocelli, antennas and labrum. The brain is connected by nerve-cords with the subcesophageal ganglion which lies beneath the oesophagus in the head. This FIG 243. Portion of a trachea. b, nuclei. (From Packard, after Leydig.) PHYLUM ARTHROPODA 321 ganglion innervates the mandibles, labium, and other mouth parts. From the suboesophageal ganglion a ventral chain of ganglia (Fig. 241, g) extends posteriorly through the thorax and into the abdomen. Small slomato-gastric ganglia are connected with the organs of digestion, circulation, and respiration, and a delicate, sympathetic nervous system is also present. SENSE ORGANS. - - The compound eyes are constructed on a plan similar to those of the crayfish (p. 285, Fig. 203) and are especially adapted for seeing moving objects. The ocelli are less complex than the compound eyes, and are probably of use n FIG. 244. Longitudinal section through part of an antenna of a worker honey-bee, c, conoid hairs; /, tactile hairs; ho, auditory pits; n, nerves; s, smell hollows. (From Cheshire.) only to distinguish light from darkness, although they may per- ceive form at very short distances. The principal organs of smell are situated on the antennae. They are hollows in the cuticle (Fig. 244, s), connected with a cell supplied with nerve- fibers (it). The queen possesses about. 1600 smell hollows on each antenna, the worker 2400, and the drone 37,800. The sense of smell is considered of great impor- tance in the life activities of bees. Pits near the mouth of the bee have been identified as taste organs. Taste setae are present near the end of the ligula (Fig. 237, b). Certain pits on the antennae are supposed to be end organs of hearing (Fig. 244, ho). Sounds are produced by the vibra- 322 COLLEGE ZOOLOGY tions of the wings and by the vibrations of a membrane which lies within each spiracular opening of the respiratory system. Sense-organs of touch are hair-like structures on various parts of the body, but especially numerous on the antennae. Two kinds are shown in Fig. 244, (i) small hairs (/), and (2) large " conoid " hairs (c). REPRODUCTION. - - The sexes are separate except in abnormal cases. The spermatozoa arise in the two testes (Fig. 245, Tes), and pass through the vasa deferentia (VDef) into the seminal vesicles ( Ves) , where they are stored. The sem- inal vesicles open into large mucous glands (AcGl) which unite at a point where the ejaculatoryduct begins (/ D). During mating the sperma- tozoa pass through the FIG. 24S .- Reproductive organs of drone ejaculatory duct and are bee, dorsal view, natural position. AcGl, ac- transferred to the seminal cessory gland; B, bulb of penis; EjD,eja.c- rprpntar l p n f t ], p f prna l p ulatory duct; Pen, penis; Tes, testis; f? 1 vDef, vas deferens; Ves, seminal vesicle; (Fig. 246, Spm) by the II, uu, yy, zz, parts of penis. (From Snod- . /T- N grass, Tech. Series, 18, Bur. Ent., U.S. "**' 2 45> \ Dep't of Agric.) The reproductive organs of the workers are undevel- oped ovaries. The abdomen of the queen is almost completely filled by the two ovaries (Fig. 246, Ov). Each ovary consists of a number of ovarian tubules (ov) in which are eggs in various stages of development. When ready for deposition, the eggs pass through the oviducts (OvD) into the vagina ( Vag). They are fertilized by spermatozoa from the seminal receptacle (Spm) or spennatheca. The queen seems to be able to lay fertilized or unfertilized eggs according to the size of the cell in which they are to develop. Fertilized eggs are laid either in small worker cells (Fig. 248) or in large irregular queen cells, and develop into PH YLU ,N I ARTHROPOD A 3^3 queens or workers. Unfertilized eggs are usually laid in drone cells, and those that develop become drones. How fertilization is controlled is still unknown. The egg undergoes superficial cleavage l/jm. H /MJ r. , A w$ml Ov p fill! Ov BCI- BCpx- (p. 86, Fig. 50, D) as in the crayfish (p. 289). A blastoderm of a single layer of cells is formed at the surface; this &!* soon thickens on the ventral side, forming a germ band. The germ band segments, sends out protrusions which become append- ages, and grows until it completely surrounds the egg. In three days the larva emerges from the egg-shell. The changes that take place in an insect i . ,T FIG. 246. -- Reproductive organs, sting, and during its growth con- poison gland of quecn honcy . bee . AGl> acid StitutC its metamor- gland; AGIO, duct of acid gland; BGl, alkaline hhnw\ The lifp ViiQ gland; Ov > ovary; 1 '' ovarian tubules; OvD, "" ' oviduct; PsnSc, poison sac; Spm, spermatheca ; tory of an individual Stn, sting; StnPlp, sting feeler; Vag, vagina, i. i- i j (From Snodgrass, Tech. Series 18, Bur. Ent., bee may be divided LT s Dept Agric } into four periods (Fig. 247): (i) egg, (2) larva (FL, SL), (3) pupa (A T ), (4) adult or imago (Fig. 236). When the larva hatches, it lies at the base of the cell (Fig. 247, FL), floating in the food prepared by the workers and known as chyle or " bee milk." Chyle is com- posed of digested honey and pollen, probably mixed with a StnPIp Sm-- 3 2 4 COLLEGE ZOOLOGY glandular secretion, and is given to all of the larvae by the nurse bees during the first three days. Then the larva; that will become workers are given honey and digested pollen in gradually increasing amounts; the drone larvte, after the fourth day, also receive honey and undigested pollen; but the queen larvae are fed lavishly on the rich albuminous bee milk, the " royal jelly," until they change to pupae. Growth during the larval period is accompanied by several molts of the chitinous larval envelope. At the end of the larval period the cells containing the young brood are covered over an e FIG. 247. Larvae and pupa of honey-bee in their cells. SL, larva spin- ning cocoon; N, pupa; FL, young larva, an, antenna; ce, eye; co, cocoon; m, mandible; sp, spiracles; /, tongue; w, wing. (From Packard, after Cheshire.) with wax, feeding ceases, and the larvae proceed to spin a cocoon of silk from their spinning glands (Fig. 247, SL). These spin- ning glands become the salivary glands of the adult. It takes the worker thirty-six hours to spin its cocoon, then it slowly changes into a pupa, or chrysalis (Fig. 247, N). Prac- tically the entire body is made over at this time; the three re- gions, head, thorax, and abdomen, become distinct; externally the wings (w.), legs, mouth parts (/, m), sting, antennae (an), and eyes are visible; and the internal changes are even more striking, the larval organs developing into those of the adult, and new organs appearing. After a period of rest the pupa casts off its exoskeleton, and emerges as an adult. PHYLUM ARTHROPODA 325 The Activities of the Workers. - - All of the duties necessary for maintaining a successful colony arc performed by the workers, except mating with the queen, which is accomplished by the drones, and laying the eggs, which is done by the queen. BUILDING HONEYCOMB. - - The wax which is used to build honeycomb is secreted in thin scales by the wax glands. The wax is removed by the wax (Fig. 238, pinchers B, icp) Drone cells Transition cells A Worker cells and transferred to the mouth, where it is mixed with saliva and kneaded by the mandibles. If new comb is to be built, the wax is plastered to the roof, and in some mysterious way each bee puts its contribution almost exactly where it is to remain. The cells which are built up are hexagonal in shape and of various sizes. Six kinds may be recognized (Fig. 248), (i) worker cells in which workers are reared, (2) drone cells in which drones develop, (3) queen cells which are large and irregular, (4) transition cells between worker and drone cells, (5) attachment cells which fasten the comb to the top or sides of the hive, and (6) honey cells in which honey is stored. Honey may be stored also in drone, worker, and transi- tion cells. Careful measurements have shown that the cells are FIG! 248. Honeycomb showing various kinds of cells. A, diagram showing comparative size of drone cells and worker cells. B, photograph of a piece of honeycomb showing circular cells and attachment cells. (From Root.) 326 COLLEGE ZOOLCXiN seldom perfectly symmetrical, although in many cases they appear so to our eyes. The honey cells are built with entrances slightly above their bases, so that the honey stored in them will not flow out before it becomes " ripe." THE COLLECTION OF PROPOLIS. -- " Bee glue," as propolis is sometimes called, is a resinous material collected from buds and crevices of trees. It is transported in the pollen baskets, and is used, as soon as collected, to paint the inside of the hive, to fill up cracks, and to strengthen any loose parts. GATHERING POLLEN. - - Pollen grains are very small, of various shapes and colors, and are formed within a part of the flower known as the anther. To the bee, pollen is invaluable as a food, and is also used in preparing the cells containing pupae. The peculiar structures on the legs and other parts of the bee's body used in collecting pollen have already been described (p. 316). Upon reaching the hive the pellets of pollen are pried out of the pollen basket by the spur at the termination of the tibia of the middle leg (Fig. 238, D, s), and deposited usually in worker cells. Pollen is the principal food of the larvae. It is very rich in nitrogenous material, a food element not found in honey, and without which the young would starve. The gathering of pollen by bees has a great influence upon the flowers visited, since many species depend upon bees for transporting pollen from one to another. CARRYING WATER. - - During warm weather water is sucked up into the honey sac from dew, or brooks and pools, and carried to the larvae in the hive. THE MANUFACTURE OF HONEY. - Bees do not collect honey from flowers, but gather nectar, which is later transformed into honey. The nectar is lapped up by the tongue (Fig. 237, /), and transferred to the honey sac (Fig. 241, hs), where it is stored while the bee is in the field. Nectar is placed in open cells in the well- ventilated hive until all but 1 8 to 20 per cent of the water contained in it has evaporated. When a cell is finally filled with " ripe " honey it is sealed with a cap of wax. The flavor PHYLUM ARTHROrODA 327 of honey depends upon the kind of flowers from which the nectar is collected. The amount of honey produced in one hive in a fair season ranges from an average of about thirty pounds of comb honey to possibly fifty pounds of extracted honey. This will net the bee keeper from ten to fifteen cents per pound. CLEANING THE HIVE. - - The health of the swarm depends upon the cleanliness of their domicile, since perfect sanitary conditions are necessary where so many individuals live in such close quarters. Dead bees, pieces of old comb, the excreta of the queen, drones, and others that remain in the hive, and any other waste materials, are immediately removed. VENTILATING THE HIVE. - - Fresh air for the hive is obtained by the exertions of certain of the workers. Many bees near the entrance, and at other places in the hive, are busily engaged in vibrating their wings, and creating a current of -air, which keeps the hive fresh, and aids in ripening the nectar. The loud buzzing which accompanies this activity is often heard at night after a large amount of nectar has been collected. GUARDING THE HIVE. - - The hive is guarded against the in- trusions of yellow-jackets, bee-moths, and other bees by workers, who wander back and forth near the entrance, and examine every creature that visits the colony. If the swarm is strong, the guards succeed, with the aid of the bee-keeper, in warding off all honey-loving enemies. SWARMING. - - The number of bees in a hive increases very rapidly, since the queen usually lays from 950 to 1200 eggs per day. When the colony is in a prosperous condition, and there is danger of overcrowding, queen cells are built by the workers, usually around the fertilized eggs, and new queens are reared. Two queens do not live amicably in one hive, and, if such a con- dition arises, either there is a battle between the two, resulting in the death of one of them, or the workers kill one, or else the old queen collects from two to twenty thousand workers about her and flies away with them to found a new colony. This is 328 COLLEGE ZOOLOGY known as swarming. The old hive is not broken up, but continues its existence as before. Swarming occurs in May, June, or July, according to latitude, and a second swarming period may be inaugurated if weather conditions result in a midsummer flow of honey. Before issuing from the hive, the honey sacs are filled with honey to serve until a new home is found. The swarm, after flying a short distance, comes to rest upon the limb of a tree or other object, where it remains sometimes for several hours. A site for the new colony is sometimes chosen by scouting bees several days before the swarm leaves the parent hive. These scouts may also partially prepare the place by cleaning out loose dirt, bark, etc. The usual choice is a hollow tree, such as the wild ancestors of the honey-bee inhabited, and henceforth is called a " bee tree." One of the duties of the bee-keeper is to hive the swarms before they succeed in escaping to the woods. Swarms may also be formed artificially. THE ENEMIES AND DISEASES OF BEES. - - The bee-moth, Galleria mellionella, bee-louse, Braula cceca, kingbird, toad, lizard, spider, rat, skunk, bear, and other bees are all enemies of the honey-bee. Weak or neglected hives are especially liable to attack, and the bee-keeper is often obliged to help his bees com- bat the foe. The principal diseases of bees are foul brood, which is an infectious disease due to bacteria, and dysentery, which is usually caused by improper food or long confinement in the hive. b. The Anatomy and Physiology of Insects in General There are a larger number of species of insects known than of all other animals combined. Over three hundred thousand have been described and the number still unknown can only be imagined. The number of individuals of many species is also enormous. Insects range in size from -f-^ mm. long (certain parasites) to over 155 mm. in length (Dynastes hercules, the Venezuelan beetle). PHYLUM AKTHROPODA 3 2 9 Anatomy and Physiology. The honey-bee is a highly specialized insect and ex- hibits adaptive structures to a re- markable extent. It does not, how- ever, illustrate general anatom- ical features as well as some other species, e.g. the grasshopper (Fig. 249). An insect's body consists of three principal parts, (i) head, (2) thorax, (3) ab- domen. The head bears a compound eye on either side, three simple eyes (ocelli) and a pair of antennse in front, a frontal piece called the clypeus, and four pairs of append- ages constituting the mouth-parts. The thorax con- tains three seg- ments, - - protho- 33 COLLEGE ZOOLOGY rax, mesothorax, and metathorax. The mesothorax and meta- thorax bear each a pair of wings in most insects. Certain simple species (Aptera, p. 337, Fig. 259) do not possess wings; others (lice and fleas, pp. 341 and 359, Figs. 266 and 296) have no wings, but this is because they are degenerate. The flies (Diptera, p. 356, Fig. 292) have a pair of clubbed threads, called balancers or halters, in place of the meta- thoracic wings. Attached to each thoracic segment is a pair of legs. The parts of a thoracic segment are well shown in the grasshopper. The dorsal part, the tergum, is composed of- four pieces, termed sdcrites, which are especially marked on the prothoracic seg- ment. They are named the prce- scutum, scutum, scutdlum, andpost- scutellum. The side of a thoracic FIG. 250. Different forms of se g m ent is called the pleurum; it antennae of insects, a, bristle-like . antenna of a grasshopper, Locusla; Consists of three SClentCS, the b, filiform, O f a beetle, Carabus ; episternum, epimeron, and parap- c, momliform, of a beetle, Tenebrlo; ' r d, dentate, of a beetle, Elater ; t&TOn. The Underside of each ^pectinate, of Ctenicera; j Brooked, thoracic segment is called the of honey-bee, Apis ; g, club-shaped, of beetle, Silpha: h, knobbed, of sternum. beetle, Necrophorus ; i, lamented The abdomen is made up Q f of beetle, Melolonlha; k, with bristle, from fly, Sargus. . (From eleven segments. The posterior end in the female is usually modi- fied by egg-laying structures (ovi- positors), and in the male by a copulatory apparatus (genitalid). The abdomen is usually punctured by seven pairs of breathing pores (spiracles) and the thorax generally by two pairs. The antennas, mouth-parts, legs, and wings are among the most interesting external features of insects. The antenna are Sedgwick's Zoology, meister.) after Bur- PHYLUM ARTHROPODA 33 1 usually tactile, olfactory, or auditory in function. They differ widely in form and structure, as shown in Figure 250. Often the antennae of the male differ from those of the female. The mouth-parts of insects are in most cases fitted either for biting (mandibulatc) or sucking (suctorial). The cockroach pos- sesses typical mandibulate mouth- parts (Fig. 251) consisting of an upper lip, the labrum, a lower lip, the labium (B), a pair of jaws, the mandibles (C), and a pair of auxil- I/.in FIG. 251. Mouth parts of a cockroach, Periplaneta. A, ist maxilla. C, cardo ; L.ex, galea; L.in, lacinia; Mxt, maxillary palpus; St, stipes. B, labium or lower lip; lettering as above. C, mandible (Md). (From Sedgwick's Zoology, after Savigny.) FIG. 252. Mouth parts of a mosquito, Culex memo- rosus. H, hypopharynx for piercing; Lb, lower lip or proboscis; Lbr, upper lip; Lt, labial palp; Md, mandi- bles; MX, maxillae. (From Sedgwick's Zoology, after Becher.) iary jaws, the maxillae (-4). The labium and maxillae bear jointed feelers or palps (Mxt) which function as sense-organs. The labrum and labium hold the food while it is being mas- ticated by the mandibles and maxillae. The mandibles of insects that live on vegetation are adapted for crushing; those of carnivorous species are usually sharp and pointed, being fitted for biting and piercing. Suctorial mouth-parts are adapted for 33 2 COLLEGE ZOOLOGY piercing the tissues of plants or animals and sucking juices. The mouth-parts of the honey-bee (Fig. 237) are suctorial, but highly modified. In the female mosquito (Fig. 252) the labrum and epipharynx combined (Lbr) form a sucking tube; the mandibles (Md) and maxillae (Mx) are piercing organs ; the hypopharynx (H) carries saliva; and the labium (Lb) con- stitutes a sheath in which the other mouth-parts lie when not FIG. 253. Mouth parts of a moth, Noctua. A, an- tenna ; Lr, upper lip ; Lt, where labial palp has been cut away; MX, maxilla ; Mxt, maxillary palp: Oc, eye. (From Sedgwick's Zoology, after Savigny.) FIG. 254. Different forms of legs of insects. a, predatory leg of praying-mantis, Mantis; b, running leg of a beetle, Carabus; c, leaping leg of a grasshopper, Acridium ; d, digging leg of mole-cricket, Gryllotalpa ; e, swimming leg of Dytiscus. (From Sedgwick's Zoology, after regne animal.) in use (Dimmock). The proboscis of the butterflies and moths (Fig. 253, MX) is a sucking tube formed by the maxilla;. The mouth-parts of insects are of considerable importance from an economic standpoint, since insects that eat solid food can be destroyed by spraying the food with poisonous mixtures, whereas those that suck juices must be smothered with gases or have their spiracles closed with emulsion. The legs of insects are used for various purposes and are highly PHYLUM ARTHROPODA 333 modified for special functions. Those of the honey-bee have already been described (pp. 314 and 316, Fig. 238). A typical leg consists of five parts, coxa (Fig. 238, B, c), trochanter (tr), femur (/), tibia (//), and tarsus (/). The tarsus (Fig. 239) is usually composed of five segments and bears at the end a pair of claws (an) , between which is a fleshy lobule, the pulvillus (pv) , Figure 254 shows a number of legs adapted for different uses. Running insects possess long, slender legs (b) ; the mantis (a) has its fore legs fitted for grasping; the hind legs of the grass- hopper (c) are used in leaping; the fore legs of the mole cricket FIG. 255. The right wing of a male mosquito, Anopheles maculipennis. A, anal area; ist A, anal nervure; C, costa; Cu, cubitus; H, humeral cross- nervure; 7, cross-nervure between R* and /?4+s; /, cross-nervure between radial and medial systems; A', cross-nervure between medial and cubital sys- tems; M, media; 0, cross-nervure between 7?i and Ri; R, radius; Sc, sub- costa. (From Sedgwick's Zoology, after Nuttall and Shipley.) (d) are modified for digging; and the hind legs of the water beetle (e) are fitted for swimming. Many other types could be mentioned. The wings of insects enable their owners to fly rapidly from place to place and thus to escape from enemies and to find a bountiful food supply. The success of insects in the struggle for existence is in part attributed to the presence of wings. Wings are outgrowths of the skin strengthened by a framework of chitinous tubes, called veins or nervures, which divide the wing into cells. The veins vary in distribution in different species, but are quite constant in individuals of any given species; they are consequently used to a considerable extent for purposes of classification. The principal longitudinal veins, as shown in Figure 255, are the costa (C), subcosta (Sc), radius (R), media 334 COLLEGE ZOOLOGY (M), cubitus (Cw), and anal (A}. Cross veins (7, /, K) frequently occur. Modifications come about by reduction or by addition. In the beetles (COLEOPTERA) the fore -wings are sheath-like, and are called elytra. The fore-wings of ORTHOPTERA (grasshoppers, etc.) are leathery and are known as tegmina. Of the internal organs of insects the alimentary canal and res- piratory systems are of particular interest. The alimentary canal is modified according to the character of the food. An insect with mandibulate mouth-parts (Fig. 256) usually pos- sesses (i) an (Esophagus (Oe) which is dilated to form a crop (Jn) in which food is stored, (2) a muscular gizzard or proventriculus (Pv) which strains the food and may aid in crushing it, (3) a stomach or ventriculus (Chd) into which a number of glandular tubes (gastric cceca) pour digestive fluids, and (4) an intestine (K) with urinary or malpighian tubules (Mg) at the anterior end. Suctorial insects, like the butterflies and moths (Fig. 257), are provided with a muscular pharynx which acts as a pumping organ and a sac ( V) for the storage of juices. The respiratory system of insects is in general like that of the honey-bee (p. 320, Figs. 242 and 243), but modifications occur in many species, especially in the larvae of those that live in water. Aquatic larvae, in many cases, do not have spiracles, but get oxygen by means of thread-like or leaf-like cuticular outgrowths at the sides or posterior end of the body, termed tracheal gills (Fig. 261, A). Damsel-fly larvae possess caudal tracheal gills, and the larvae of the dragon- flies take water into the rectum which is lined with papillae abundantly supplied with tracheae. The economic importance of a tracheal respiratory system has already been pointed out (p. 332). GROWTH AND METAMORPHOSIS. - - Three types of insects may be distinguished with respect to the method of their develop- ment, (i) ametabola, (2) heterometabola, and (3) holometabola. The ametabolous insects are essentially like the 'adult, except in size, when they hatch from the egg; they develop to maturity PHYLUM ARTHROPODA 335 without a metamorphosis. The APTERA (p. 337, Fig. 259) are ametabolous. The heterometabolous insects hatch from the egg and develop into adults without passing through a true pupal period. In the grasshopper, for example (Fig. 258), the young resembles the Chef FIG. 256. Alimentary canal and glandular ap- pendages of a beetle, Cara- bus. Ad, anal glands with vesicle; Chd, chylific ven- tricle; Jn, crop; Me,, mal- pighian tubule; Oe, oesoph- agus ; Pv, proventriculus ; R, rectum. (From Sedg- wick's Zoology, after Du- four.) FIG. 257. Longitudinal sec- tion through the body of a moth, Sphinx ligitstri, showing the ali- mentary canal of a sucking insect. A, anus; At, antenna; E, rectum; G, testis; Gi, subcesophageal ganglion; Gs, brain; H, heart; M, mesenteron ; MX, maxillae forming proboscis; .V, thoracic and abdominal ganglia; /, palp; V, oesophagus; I" 1 , suctorial stomach; Vm, malpighian tubules. (From Sedgwiek's Zoology, after Newport.) 33 6 COLLEGE ZOOLOGY adult except for the absence of wings and mature reproductive organs. Such a stage is usually spoken of as a nymph. Orders II to XI of Table XII contain heterometabolous insects. Many of the species belonging to these orders change considerably during their growth period, but they are all more or less active FIG. 258. Partial metamorphosis of a grasshopper, Melanoplus fcmur- rubrum, showing the five nymph stages, and the gradual growth of the wings. (From Packard, after Emerton.) throughout their development and are said to undergo direct or incomplete metamorphosis. Holometabolous insects, such as the honey-bee (Fig. 247), pass through both a larval and a pupal stage in their development. The majority of insects belong to this type (Table XII, orders XII to XIX). c. General Survey of the Orders of Insects Classification. - - Insect classification is based principally on the following characteristics: (i) the presence or absence of wings, and their structure when present, (2) the structure of the mouth-parts, and (3) the character of the metamorphosis. Au- thorities differ with regard to the number of orders that should be recognized, and two rather definite classifications have re- PHYLUM ARTTIROPODA 337 suited; these are known as (i) the condensed classification, and (2) the extended classification, and arc correlated in Table XII. Because of the large number of orders space will permit only a few words about each. Illustrations have been provided to show the principal characteristics. TABLE XII CONDENSED CLASSIFICATION EXTENDED CLASSIFICATION ORDER ORDER I. Aptera II. Pseudoneuroptera III. Orthoptera . IV. Hemiptera . V. Neuroptera . VI. Lepidoptera . VII. Diptera . . VIII. Coleoptera . IX. Hymenoptera I Aptera . . . II Ephemerida . III Odonata . . IV Plecoptera V Isoptera . . VI Corrodentia . VII Mallophaga . VIII Thysanoptera IX Euplexoptera X Orthoptera . . XI Hemiptera XII Neuroptera . XIII Mecoptera XIV Trichoptera . . XV Lepidoptera . f XVI Diptera . 'I XVII Siphonaptera . XVIII Coleoptera . XIX Hymenoptera COMMON NAMES Springtails, fish-moths. May-flies. Dragon-flies. Stone-flies. Termites or white ants. Book-lice, bark-lice. Biting bird-lice. Thrips. Earwigs. Grasshoppers, crickets, cockroaches. Lice, bugs, plant-lice. Ant-lions, hellgramite flies. Scorpion flies. Caddice-flies. Moths, skippers, but- terflies. Flies, sheep-ticks. Fleas. Beetles. Ants, wasps, bees, saw- flies, ichneumon-flies. Order i. Aptera. -- SPRINGTAILS AND FISHMOTHS (Figs. 259, 260). -- Insects without wings, probably descended from wingless ancestors; biting mouth-parts retracted within the cavity of the head; no metamorphosis. The very primitive living insect, Campodea staphylinus (Fig. 259), belongs to this order. The most common species is the fishmoth, Lepisma saccharina (Fig. 260), which lives on dry starchy food such as book bindings and starched clothing. An- 33$ COLLEGE ZOOLOGY FIG. 250. Order APTERA. Campodca staphylinus. (From Sedgwick's Zoology, after Lubbock.) other interesting species is the snow-flea, Achorutes nivicola, which is some- times a pest in maple sugar camps, since large numbers collect in the sap. Order 2. Ephemerida. - MAY-FLIES (Fig. 261). -Insects possessing deli- cate membranous wings, with many cross veins ; the fore-wings large, the FIG. 260. Order , . APTERA. Lepisma nmd Wings Small or want- saccharina, the fish- m g. mouth-parts poorly moth. (From Sedg- wick's Zoology.) developed; metamorpho- sis incomplete. The young (nymph) may- fly (Fig. 261, A) lives in the water and breathes by means of tracheal gills. After from one to three years, depending upon the species, the nymph emerges from the water and becomes a winged adult (Fig. 261, B). This adult is said to be in the subimago stage, since it moults after acquir- ing wings. No other insect is known to do this. The paired con- - A FIG. 261. Order EPHEMERIDA. A, nymph of the May-fly, k, tracheal gills; t, principal trunk of tracheal system. B, adult May-fly. Af, anal filaments. (From Sedgwick's Zoology.) PHYLUM ARTHROPOD A 339 dition of the egg ducts of the female is also unique. Adult may- flies probably take no food; they mate, lay their eggs, and, after a few hours, die. Order 3. Odonata. - DRAGON-FLIES AND DAMSEL-FLIES (Fig. 262). -- Insects possessing four membranous wings, with many cross veins; hind \\ings as large as or larger than fore- wings; each wing with joint, the nodus, on front margin; bking mouth-parts; metamorphosis incomplete. The dragon- flies are also called darning-needles and snake doctors. When at rest they hold their wings horizontally, differ- ing in this respect from the damsel- flies, which hold their wings FIG. 262. Order ODONATA. A dragon-fly, Libettula depressa. (From Miall, after Charpentier.) vertically over their backs. The adult dragon- flies devour large numbers of mosquitoes, but unfortunately feed only by day, whereas some of the mosquitoes are most active after dark. The young live in the water; they breathe by drawing in and expelling water from the rectum, which is lined with tracheal gills. The damsel- flies are more delicate than the dragon- flies. Their young possess leaf -like tracheal gills at the posterior end of the body. The compound eyes of the ODONATA are made up of an enormous number of elements (ommatidia) ; more than 30,000 facets have been counted in the eye of one species. 340 COLLEGE ZOOLOGY Order 4. Plecoptera. - - STONE-FLIES (Fig. 263). Insects with four membranous wings; hind wings large and folded like a fan; biting mouth-parts; metamorphosis incomplete. The stone- fly nymphs live in brooks on the underside of stones, and breathe by means of filamentous tracheal gills which extend out from just behind the legs. They serve as food for fishes. Order 5. Isoptera. TERMITES or WHITE ANTS (Fig. 264). - - Insects with four similar wings, leathery in structure and lying flat on the back, or wingless (workers); biting mouth-parts; metamorphosis incomplete. FIG. 263. -- Order , ' v . . PLECOPTERA. Stone- ^ ne termites are social insects and live fly, Peria maxima. i n colonies. Each colony contains a queen (From Sedgwick's ,,-,. _ N . Zoology, after Pictet.) v.* ^ 26 4, &) that lays all of the eggs, a winged male (A) that fertilizes the queen, a number of wingless workers (C) that build the nest, procure C D FIG. 264. Order ISOPTERA. Termites. A, male or king of Termes. B, female or queen of Termes. C, worker of Termes. D, soldier of Termes. (From the Cambridge .Natural History; C aad D, after Grassi.) PHYLUM ARTHROPODA 341 food, and raise the young, and wingless soldiers (D) whose duty it is to protect the colony. The food of termites consists prin- cipally of dead wood, and in the tropics of Africa and South America, where white ants abound, a good deal of damage is done to houses, furniture, etc. Even in North America injuries to the timbers in buildings and to books in libraries have been reported. The termites work only in the dark, and build tunnels for this purpose. Their nests are often inhabited by other species of insects; these are called termitophiles. Over one hundred species of termi- tophiles have been recorded. _ _ FIG. 265. Order CORRODENTIA. A Order 6. Corrodentia. bark-louse, Psocus. (From Brehm.) BOOK-LICE AND BARK-LICE (Fig. 265). -- Insects without wings or with four membranous wings, with few cross veins; fore -wings larger than hind wings; wings held roof-like over body; biting mouth- parts; metamorphosis incomplete. Book-lice are wingless insects often found in old books, the paper and bindings of which they devour. Bark-lice (Fig. 265) have wings. They live out of doors on tree trunks and feed on lichens. Order 7. Mallophaga. -- BITING BIRD- LICE (Fig. 266). -- Parasitic insects without wings; biting mouth-parts; metamorphosis incomplete. Bird-lice live among the feathers of birds or hair of mammals. They eat hair, feathers, inhabiting and epidermal scales, but are not injurious (From SedgwfSX on this account - The irritation caused by Zoology, after Piaget.) their sharp claws makes their hosts restless \ FIG. 266. Order MALLOPHAGA. Biting bird-louse, Menopon pallid um, 34? COLLEGE ZOOLOGY and consequently weak and thin. Chickens take dust baths to rid them- selves of Menopon pal- lidum (Fig. 266), the most common species. Order 8. Thysanop- tera. THRIPS (Fig. 267). -Insects with four narrow', membranous wings fringed with long hairs; mouth -parts inter- mediate ; the metamor- phosis transitional, not lie. 267. Order THYSANOPTERA. Pear thrips, Euthrips pyri. (From Moulton, Bui. Complete, but a quiescent 80, Bur. Ent., U. S. Dept. Agric.) stage OCCUrs The feet of these insects are without claws, their place being taken by bladders adapted for clinging to leaves or flowers. The males are not com- mon, since parthenogenesis is the usual method of reproduction. Several species are distinct pests; these are the onion- thrips (Thrips tabaci), the w r heat-thrips (Euthrips tritici), the grass- thrips (Anaphothrips stri- atus), and the fruit thrips (Euthrips pyri) (Fig. 267). Order 9. Euplexoptera. EARWIGS (Fig. 268). --Insects usually with four wings; fore -wings leathery, small, and veinless; biting mouth-parts; posterior end of ab- domen bears pair of forceps; metamorphosis incomplete. This order contains the family FORFI- CULID.E. The earwigs are not common in lima. (From Daven- North America. They feed at night on fruit port.) FIG. 268. -- Order EUPLEXOPTERA. Ear- PHYLUM ARTHROPOD A 343 and flowers, but are not of any economic importance in this country. Order 10. Orthoptera. COCKROACHES, WALKING-STICKS, MANTIDS, GRASSHOPPERS, LOCUSTS, KATYDIDS, AND CRICKETS (Figs. 269-274). --Insects with four wings ; the fore- wings leathery ; the hind wings folded like a fan; biting mouth-parts ; metamorphosis incom- plete. The principal families of ORTHOP- TERA are as follows : (1) BLATTID.E (COCKROACHES, Fig. 269). These insects have legs fitted for running. The common American species are the " croton-bug " (Ectobia germanica) which was introduced from Germany, and the " black-beetle " (Periplaneta oriental-is, Fig. 269) from Asia. (2) MANTIDS (PRAYING-MANTIS, Fig. 270). The fore legs of these insects are fitted for grasping. Their food consists largely of other insects. (3) PHASMID^: (WALKING-STICKS, Fig. 271). The legs of the phasmides are adapted for walking. Walking-sticks feed on foliage and are difficult to distinguish from twigs, hence their name. FIG. z6g. Order ORTHOP- TERA. Cockroach, Periplaneta orientalis. (From Sedgwick's Zoology.) FIG. 270. Order ORTHOPTERA. Praying-mantis, Phasmomantis Carolina. (From Davenport, after Packard.) 344 COLLEGE ZOOLOGY FIG. 272. Order ORTHOPTERA. Rocky Moun- tain grasshopper or locust, Melanoplus sprelus. a, a, a, females in different positions, laying eggs; b, egg-pod taken from ground, with end broken open; c, eggs lying loose on ground; d, e, earth partly removed to show egg mass in place (e) and one being' placed (d); f, where egg mass has been covered up. (After Riley, from Yearbook Dept. Agric., 1908.) FIG. 271. Order OR- THOPTERA. The north- ern " walking-stick," Diapheromera femorala. (From Davenport.) FIG. 274. Order ORTHOPTERA. House-cricket, Gryl- lus domestic us. (From the Cam- bridge Natural His- tory.) FIG. 273. Order ORTHOPTERA. Katydid, Microcentrum retinerve. (From Sedgwick's Zoology, after Riley.) PHYLUM ARTHROPODA 345 (4) ACRIDIID.E (Locusxs OR SHORT-HORNED GRASSHOPPERS, Fig. 272). The locusts have leaping legs and short antenna?. They feed on vegetation and often do considerable damage. The most famous species is Mela no plus spirt us, the Rocky Mountain locust (Fig. 272), which is occasionally migratory and devours everything in its path. The red-legged locust, Mel a no plus femur -rubrum, and the Carolina locust, Dissosteira Carolina, are common species. (5) LOCUSTID^: (LONG-HORNED GRASSHOPPERS, Fig. 273). The members of this family have slender antennae longer than the body. The meadow grasshoppers and katydids belong here. (6) GRYLLID.E (CRICKETS, Fig. 274). The mole crickets burrow in the ground; the true crickets are those that make themselves known by their chirping about houses; the tree crickets inhabit trees. Order ii. Hemiptera. BUGS, LICE, APHIDS, SCALE INSECTS (Fig. 275-279). -- Insects without wings or with four wings; one suborder with fore-wings thickened at base; sucking mouth -parts; meta- morphosis incomplete. HEMIPTERA may be separated con- veniently into three suborders. (i) PARASITICA (LICE, Fig. 275). This suborder is represented in North America by a single family, the PEDI- CULID^E. These are wingless and para- sitic on the bodies of man and other mammals. They have claws fitted for clinging to hairs, and an unjointed beak for penetrating the skin and suck- FlG - *" ,T Ord " TERA. Head-louse, Pediculus ing juices. The species infesting man capiiis. (From the Cam- are Pediculus capitis, the head-louse bridge Natural History, after (Fig. 275), P. vestimenti, the body-louse, and Phthirius inguinalis, the crab-louse. Domestic animals are infested by members of the genus Hcematopinus. H. piliferus COLLEGE ZOOLOGY is the dog-louse, //. urius, the hog-louse, and //. spinulosus, the rat-louse. (2) HOMOPTERA (PLANT-LICE, SCALE INSECTS, CICADAS, TREE HOPPERS, SPITTLE INSECTS, Figs. 276-278). The HOMOPTERA have wings, when present, similar in thickness, and a jointed beak which arises from the posterior. ric. 276. Order HEMIPTERA. Grape-louse, Phylloxera vastalrix. ventral part of the head. a, wingless form, b same, ventral The plant-lice oraphids (Family surface. c, winged form. (From J Sedgwick's Zoology.) APHIDHD.E, Fig. 276) are of con- siderable biological and economic importance. They are very small (less than \ inch), but ex- tremely prolific. In summer certain females, called the stem mothers, bring forth living young which have developed within their bodies from unfertilized eggs. In the au- tumn fertilized eggs are laid, which serve to carry the race through the winter. Many aphids are very de- structive to, vegetation. The grape-phylloxera, Phylloxera vastatrix (Fig. 276), is the most notorious; it punctures the roots of grape-vines, causing decay or " cancer " and the formation of tuber- cles. The woolly apple- aphis attacks the roots and FIG. 277. Order HEMIPTERA. San twigs of apple trees; the Jos6 sca A 't' As P^ iot s pernidosus, on pear. Above, single scale enlarged. green fly' injures wheat, (After Howard.) PHYLUM ARTHROPODA 347 cats, and other grains. A host of other plants are also infested. The scale insects (Family Coccnxa:) are of the greatest im- portance to fruit growers. They are small but numerous. The San Jose scale, Aspidiotus perniciosus (Fig. 277), was imported from its native home in Japan or China to California. It has increased and spread over a large part of this country and has been the cause of considerable legis- lation in an effort to control its dep- redations. The cottony cushion scale, Icerya pur- chasi, which came near ruining the orange groves of California, was successfully con- trolled by a lady beetle, Novius car- dinal is (Fig. 302), \ o O / 3 introduced from Australia. This beetle is the natural enemy of the cottony cushion scale, which is also a native of Australia. In two or three years these beetles checked the inroads of this species of scale insect. The cicadas (Family CICADID^E, Fig. 278) are especially inter- esting, since one of them, the seventeen-year cicada or "locust" (Cicada sept end ecim, Fig. 278), lives underground as a nymph for over sixteen years. The eggs (F) are laid in slits made by the female in living twigs (E). The young (A) hatch in about six weeks, drop to the ground, and burrow beneath the surface (B). Here they feed on juices from roots and on humus until the summer of the se\enteenth year, when they emerge from t 2 ^' Order HEMIPTERA. Seventeen-year locust, Cicada septendecim. A, larva. B, nymph. C, nymph skin after emergence of adult. D, adult. ^' sect i n f tree showing how eggs are laid. F, two eggs enlarged. (From Sedgwick's Zoology, after Riiey.) 348 COLLEGE ZOOLOGY the ground (C) and transform into adults (D). Twenty dif- ferent broods are known in this country, and it is possible to foretell approximately when and where each swarm will appear. The common cicada is the green dog-day harvest- fly, Cicada tibicen. The males are provided with sound-making organs, and, since these are lacking in the female, the philosopher Xen- archos remarked, " Happy is the cicada, since its wife has no voice." (3) HETEROPTERA (THE TRUE BUGS, Fig. 279). The first pair of wings of the HETEROPTERA, when present, are thickened at the base. The jointed beak arises from the front part of the head. About twenty-six families are recog- nized in this suborder. They in- clude aquatic forms such as water- boatmen (CORISID^;), back-swimmers (NOTONECTID^E), giant water-bugs (BELOSTOMATID^E) , water-striders (Hy- DROBATID^E), and marsh-treaders (LiM- NOBATID.E), and land-bugs such as the assassin bugs (REDUVHD.E) , bedbugs FIG. 270. Order HEMIP- (ACANTHIID^), chinch-bugS (LYG,EID,E, TERA. Chinch-bug, Blissus -r-.- , i /,-, \ leucopterus. (After Webster.) Fl g' 2 79), Squash-bugS (COREID^), and stink-bugs (PENTATOMID.E). The aquatic members of this suborder show remarkable adaptations for life in the water. In many the legs are modified for swim- ming, the colors of the body are such as to conceal them, and the methods of obtaining oxygen while under water are extremely interesting. Certain of the terrestrial species are of great economic importance. The assassin bugs usually prey upon obnoxious insects, including the bedbug, and are therefore beneficial to man; the chinch-bug (Fig. 279) is noted for the enormous damage it has done to the grain fields in the Mississippi Valley ; and the squash-bugs infest squash and pumpkin vines. PHYLUM ARTHROPOD A 349 Order 12. Neuroptera. APHIS-LIONS, DOBSON-FLIES, AND ANT-LIONS (Fig. 280). --Insects possessing four membranous wings with many veins; biting mouth-parts ; com- plete metamorphosis. Only a few families have been left in the old Linnean order NEUROP- TERA ; the rest have been taken out and grouped to- gether as distinct orders. The dobson-fly, Corv- FlG - 28 - Order NEUROPTERA. Lace- 7 ,. . wing fly, Chrysopd, with eggs and larva. daks cornuta, is a well- (From Packard .) known representative. Its larva has many local names and is used extensively as fish bait. The larvae of Hemerobius and of the lace- wing fly, Chrysopa (Fig. 280), are called aphis-lions since they destroy countless numbers of aphids by piercing them with their sharp jaw r s and drinking their blood. The / Myfl e ^ s ^ Ch r y s P a are fastened to the ul/nJ7\ jA t O p o f upright threads which are attached to a twig or leaf; they are thus protected from predaceous insects, including the young aphis-lions them- selves. The larvae of many ant-lions live at the bottom of pits in the sand, where they capture and drink the blood of any ants that chance to slip down into the trap. Order 13. Mecoptera. SCORPION FLIES AND OTHERS (Fig. 281). In- sects possessing four membranous wings with numerous veins; head prolonged into a beak; biting mouth-parts; metamorphosis complete. The common name of these insects is due to the fact that in FIG. 281. Order MECOP- TERA. Scorpion fly, Panorpa communis, male. (From Sedgwick's Zoclogy, after Sharp.) 35 COLLEGE ZOOLOGY E W* some species the abdomen of the male terminates in a structure resembling the sting of a scorpion. Little is known about the habits of the MECOPTERA. Order 14. Trichoptera. -- CADDICE -FLIES (Fig. 282). In- sects possessing four membranous wings with many longitudinal veins and covered with hairs ; rudi- mentary mouth- parts; metamorpho- sis complete. The term caddice- fly is derived from the case (Fig. 2 8 2, A) which its aquatic larva builds of leaves, grass stems, or grains of sand as a means of protec- tion. The larva (B) can extend the fore part of the body and drag its case from place to place or can retreat into its house for safety. Thread-like trachea! gills are present on the abdomen. Each species builds a certain kind of case which can be distinguished from those built by other species. Order 15. Lepidoptera. BUTTERFLIES, SKIPPERS, AND MOTHS (Figs. 283-290). --Insects with four membranous wings covered with scales; usually sucking mouth-parts; meta- morphosis complete. The members of this order are famous for their varied and brilliant colors; these are produced by the scales. The mouth- parts form a sucking tube (Fig. 253) which may be five or six' inches long and is coiled under the head when not in use. This sucking proboscis is used to obtain nectar from flowers. The FIG. 282. Order TRICHOPTERA. Stages in the development of a caddice-fly, Enoicyla. A, case of full-grown larva. B, larva and case enlarged. C, larva removed from case. D, wingless adult female. E, male. (From the Cambridge Natural History, after Ritsema.) PHYLUM ARTHROPODA 351 larvae of the LEPIDOPTERA are called caterpillars, and are in many cases extremely injurious to vegetation. Over seven thousand species of LEPIDOPTERA have been described as inhabitants of this country. These may be sepa- rated for convenience into two suborders, (i) the RHOPALOCERA or butterflies and skippers, and (2) the HETEROCERA or moths. SUBORDER i. RHOPALOCERA (BUTTERFLIES AND SKIPPERS). -The butterflies and skippers may be distinguished from the FIG. 283. Order LEPIDOPTERA. Monarch butterfly, Anosia plexippus. (After Riley.) moths by the knoblike swelling near the end' of the antennas. The skippers usually possess in addition to this knob a ter- minal recurved point. Moths do not possess knobbed antennae. The members of the two suborders differ also in habits, since the butterflies are active during the day, whereas the moths usually fly at night or twilight.- Most of the skippers belong to the family HESPERID.E. They are generally small and comparatively dull-colored RHO- PALOCERA that " skip " about close to the ground from one plant to another, like a wounded butterfly. The beautiful swallowtail butterflies belong to the family PAPILIONID^;. They are characterized by one to three " tails " projecting backward from their hind wings. The tiger swallow- 352 COLLEGE ZOOLOGY tail, Papilio turnus, is a well-known species. Its larvae feed principally on the wild cherry. A "negro" variety of the tiger swallowtail called glaucus occurs in some localities. The family NYMPHALID.E, or brush-footed butterflies, con- tains many common and interesting species. The mourning- cloak, Envanessa antiopa, is one of the first to appear in the spring. Its larvae are injurious to willows and poplars, the leaves of which they devour. The milkweed or monarch butterfly, Anosia plcxippus (Fig. 283), is abundant about milkweed. It is distasteful to birds, and is therefore immune to attack. FIG. 284. Order LEPIDOPTERA. Cabbage butterfly, Pieris rapa. a, caterpillar, b, chrysalis. (From Osborn, after Riley.) The viceroy, Basilarchia ar chip pus, which is edible, apparently mimics the monarch so as to profit by the immunity of the latter. The cabbage-butterfly, Pieris rapa (Fig. 284), is a member of the family PIERID.^E. It is a serious pest because of the de- struction to cabbages caused by its green caterpillars. This species was accidentally introduced from Europe. It was first discovered at Quebec in 1860. From there it rapidly spread over a large part of North America. SUBORDER 2. HETEROCERA (MOTHS). - -The moths are of great importance to man because of the damage done by some of them and the benefits derived from others. The hawk-moths, or humming-bird moths (SPHINGID.E) , have a thick body and narrow, pointed wings, and, when hovering before a petunia or PHYLUM ARTHROPODA 353 primrose, resemble a humming-bird. The larvae live on the leaves of tomato and tobacco plants, Virginia creeper, and many others; they are usually very large. The family ARCTIID.E contains the fall-webworm, Hyphantria cunea, the larva? of which live together in a web and eat the leaves of many kinds of trees and shrubs. The white-spotted tussock- FIG. 285. Order LEPIDOPTERA. Gypsy-moth, Porthetria dispar. A, female. B, larva. C, pupa. (From Osborn, after Howard.) moth, whose larva? feed on the leaves of trees and are often very troublesome, belongs to the family LYMANTRIDJ*:. Another important member of this family is the gypsy-moth, Porthetria dispar (Fig. 285). The gypsy-moth w r as imported from Europe. FIG. 286. Order LEPIDOPTERA. Silkworm, Bombyx mart. A, caterpillar. B, cocoon. C, adult female moth. (From Shipley and MacBride.) Its caterpillars devour leaves and have killed many of the finest shade trees in certain parts of Massachusetts. A number of large common moths are placed in the family BOMBYCID^E ; for example, the cecropia, Platysanria cecropia, the giant silkworm moth, Tclca polyphcmus, the luna moth, 2 A 354 COLLEGE ZOOLOGY Tropaa -luna, the " tent-caterpillar," Clisiocampa amcricana, and the silkworm moth, Bombyx niori. The silkworm moth (Fig. 286, C) is thoroughly domesticated and, so far as is known, does not occur in a wild state. The silk industry originated in China many centuries B.C. It did not become very important in this country until the nineteenth century. There are now about a hundred million dollars invested in the silk industries of the United States. The moths lay their eggs on cloth or paper provided for them. The larva? (Fig. 286, A) are fed principally on mulberry leaves, and when about forty days old spin a cocoon (B) of a single continuous thread averaging over a thousand feet long. In the cocoon the larva pupates. Silk is obtained by killing the pupa with heat or boiling water, then clearing away the loose out- side floss, and unwinding the thread. Among the important moths of the family NOCTUID.E are the army- worm, Heliophila uni- puncta, the cotton-worm, Aletia argillacea, and the boll-worm, Heliothis armiger. The army- Spring worms (Fig. 287) are striped FIG. 287. Order LEPIDOPTEEA. Army- worm, Heliophila unipuncla. a, adult, b, larva, with eggs of a parasitic fly (tachinid) on back, c, pupa or chrysalis. (From Webster, Yearbook Dep't Agric., 1908.) _ Qrder LEPIDOPTERA . canker-worm. a, male. <' ndari caterpillars that feed on growing Circ. 9, Bur. Ent., U. S. Dep't Agric.) PHYLUM ARTIIROPODA 355 wheat, oats, corn, timothy., blue grass, and other plants. They mi- grate from one field to another in large numbers, hence their name. The tachina flies parasitize many of them and fungus diseases attack others, so that they are partially held in check by their natural ene- mies. The cotton- worm eats the leaves of the cot- ton plant. The boll -worm is - FIG. 289. Order LEPIDOPTERA. Codlin-moth, Carpocapsa pomonella. a, adult, b, larva in an apple, c, pupa or chrysalis. (From Farmer's Bui. 283, U. S. Dep't Agric.) widely distributed and feeds not only upon the cotton boll but also upon corn, tomatoes, tobacco, and other plants. The larvae of the GEOMETRID^: are called measuring worms because of their looping method of locomotion. One of the most important species is the spring canker-worm, Paleacrita i-cniata (Fig. 288), the larvae of which eat the foliage of fruit trees in various parts of the country. The codlin-moth, or apple- worm (Fig. 289), Carpocapsa pomonella (Family TORTRICID.E) , is the foremost apple pest in this country. The annual loss due to this moth is estimated at $11,400,000 (Simpson). The eggs are laid upon the young fruit, and the larvae eat their way into the core. The family TINEID.E FIG. 290. Order LEPIDOPTERA. Clothes- Contains a large lium- moth, Tincii f>rlliiiii?ll>i 1 .iM 1 ;2i^-..-viT.'nv\V-c.->%\ : FIG. 2gi. Order DIPTERA. Mosquito, C-ulex pungens. a, adult female. b, egg mass on surface of water, c, young hanging from surface of water. (From Howard, Bui. 25, Bur. Ent., U. S. Dep't Agric.) many lay eggs in plant tissue whose larvae when hatched cause an abnormal growth called a gall, e.g. the pine-cone willowgall. One gall-gnat, the Hessian fly, Cecidomyia destructor (Fig. 292), causes a loss of about $10,000,000 annually to the wheat crop in this country. Several species of this family are paedogenetic (seep. 80). The midges (CHIRONOMID^E) are harmless little insects resembling mosquitoes. The larvae of some of them are the blood-red little worms found in water. The black flies (SIMULIID^E) are notorious blood-sucking pests and the special torment of hunters, fishermen, and campers. Their larvae live in swift FIG. 2Q2. Order DIPTERA. Streams Clinging to the Surfaces of Hessian fly, Cecidomyia destructor. rocks, and the adults are therefore a ' la f rva f ; b ' pup f" J F m D ?\- port, after Standard Natural His- found in the vicinity of water. tory.) 358 COLLEGE ZOOLOGY The BRACHYCERA include the horse-flies, bee-flies, house- flies, bot-flies, and flower-flies. The horse-flies (TABANID^;) are well-known pests of cattle and horses and often man. The female sucks blood, but the male lives on nectar. The larvae live in the water or in the earth, where they feed on small ani- mals. The bee-flies (BOMBYLIID.E) look somewhat like true bees. They feed on nectar as adults, but the larvae are car- nivorous, living on the young of bees, wasps, and grasshoppers. The house-flies belong to a family (MUSCID.E) which contains about a third of all the known DIPTERA. The house-fly, Musca FIG. 293. Order DIPTERA. House-fly, Musca domestica. (From Howard, Circ. 71, Bur. Ent., U. S. Dep't Agric.) FIG. 294. Order' DIPTERA. Horse bot-fly, Gastrophilus eqai. a, larva. b, adult. (From Sedgwick's Zoology, after Brauer.) domestica (Fig. 293), is dangerous, since it carries disease germs, such as typhoid and tuberculosis, from place to place. Its eggs are laid principally in horse manure and the larvae are called maggots. The adults can be controlled by keeping the horse manure and other filth under cover. The flesh-flies deposit living young in meat or in open wounds. The blow-fly lays its eggs on meat, which is then said to be " blown." The tachina- flies are beneficial, since their larvae are parasitic upon cater- pillars (Fig. 287), often exterminating vast hordes of army- PHYLUM ARTHROPODA 359 worms and other pests. The fruit-flies are abundant ilies and easily reared. The bot-flies (GEsxRiD^) are responsible for large losses every year because of their attacks on domestic animals. The horse bot-fly, Gastrophilus equi (Fig. 294), fastens her eggs to the hair on the legs or shoulders of horses. The larvae, which are licked off and swallowed, attach themselves to the lining of the stomach, where they live until ready to pupate. They then pass out of the alimen- tary canal. Other common members of this family are the ox-u'arble, the larvae of which FlG - 2 s- -- Order . DIPTERA. Sheep-tick, rum the hides of cattle by boring through u e i pkagus ovinus. the skin, the sheep bot-fly, which lives in (From Sedgwk-k's the nostrils of sheep, and the rabbit bot-fly. The flower-flies (SYRPHID^E) live on nectar and pollen and are therefore found near flowers. The larvae feed on other in- sects or on vegetable matter. The drone-fly, Eristalis tcna.\\ resembles a drone honey-bee. The suborder PUPIPARA contains parasitic insects, in- cluding bird, sheep, and horse ticks, and bee-lice. The sheep-tick, Melophagus ovinus (Fig. 295), and the horse-tick, Hippobosca equina, are com- mon species. Order 17. Siphonaptera. -FLEAS (Fig. 296). Degen- erate insects without wings; sucking mouth-parts; meta- morphosis complete. The fleas live among the hairs or feathers of domestic and wild mammals and birds. Their bodies are laterally compressed, FIG. 296. Order SIPHONAPTERA. Cat and dog flea, Ctenocephalus canis. a, egg. b, larva in cocoon, c, pupa, d, adult. (From Howard, Circ. 108, Bur. Ent., U. S. Dep't Agric.) 360 COLLEGE ZOOLOGY their heads are very small, and their legs are fitted for leaping. The larvae feed on decaying animal and vegetable matter. The cat and dog flea, Ctenocephalus canis (Fig. 296), is the most common species. It does not restrict its attacks to the dog, however, but also visits man. The human flea, Pulex irritans, is found all over the world. The rat flea, Lcemopsylla chcopus, is of considerable importance, since it seems to be able to trans- mit the bubonic plague from rats to man. The jigger or chigoe flea, Sarcopsylla penetrans, burrows into the skin of man and often causes considerable trouble. Order 18. Coleoptera. -- BEETLES (Figs. 297-304). -- In- sects with four wings, the fore- wings sheath-like (elytra) and covering the membranous hind wings; biting mouth-parts; metamorphosis complete. This order contains a great number of species; there are nearly twelve thousand known in North America, north of Mexico. For convenience they have been grouped into eight suborders. SUBORDER i. ADEPHAGA. (CARNIVOROUS BEETLES, Fig. 297.) - - The four principal families of carnivorous beetles are the tiger-beetles (CiciN- DELID.E, Fig. 297), pre- daceous ground beetles (CARABID.E), predaceous diving-beetles (DYTIS- CID.E), and whirligig- beetles (GYRINHXE). The FIG. 297. Order COLEOPTERA. Tiger- nrs t two families are ter- beetles, CICINDELID.E. (From Davenport, after Packard.) restrial; they remain on the ground most of the time, where they are busily engaged in capturing other insects for food. The whirligig- and diving-beetles are aquatic and are . modified for life in the water. In general it may be said that the carnivorous beetles and other carnivorous insects are bene- ficial, since they usually destroy insects harmful to man. PHYLUM ARTHKOPODA 361 SUBORDER 2. CLAVICORNIA. (CLUB-HORNED BEETLES, Fig. 298.) - - The club-horned beetles have clubbed antennae. They have little in common ; some are aquatic, others terrestrial ; some are pre- daceous, and therefore beneficial; others herbivorous, and consequently harmful; and a few feed on decaying organic matter. Some of the commoner species are known as water-scavenger beetles (HYDROPHILID. the latter diur - nal and predaceous ; and the checkered beetles (CLERID.E), some of which devour the larvae of wood-boring insects. SUBORDER 4. LAMELLICORNIA. (BLADE-HORNED BEETLES, Fig. 300.) The blade-horned beetles have antennae whose terminal segments form flat teeth or lamellae. The stag- beetles (LUCANID^E) have received their name because of the peculiar antler-like processes of the males of certain species. The leaf chafers and scavenger-beetles (SCARAB^EID^E) have very different habits, although they belong to one family. The 362 COLLEGE ZOOLOGY scavenger-beetles eat or bury decaying matter and are therefore beneficial. The tumble-bugs make balls of dung in which an egg is laid; the larva feeds on the ball. To this group belongs the Sacred Scara- beus of the Egyptians (Fig. 300). The leaf chafers are injurious. The adults feed on leaves, pollen, and flower-petals. The common June-bug, Lachnosterna fusca, the obnoxious rose-chafer, Macro- dactylus subspinosus, and the rhinoceros- beetles, Dynastes, belong to this group. One of the latter, D. hercules, found in the West Indies, is six inches long. SUBORDER s- PHYTOPHAGA. (PLANT- FIG. 300. Order COLE- OPTERA. Sacred beetle of EATING BEETLES, Fig. 301.) - The the Egyptians, Scarabeua plant-eating beetles include the leaf- sacer. (From Sedgwick's . Zoology, after Sharp.) beetles (CHRYSOMELID^EJ , the pea- and bean-weevils (BRUCHID^E), and the long-horn beetles (CERAMBYCID.E) . The potato-beetle, Lep- tinotarsa lo-lineata (Fig. 301), belongs to the first family. It migrated up from Mexico into Colorado and thence east and west until it became an important pest. The elm leaf beetle, Galeru- cella luteola, is another injurious chrysomelid beetle. It has de- stroyed a great number of valuable elm trees in Massachusetts and neighboring states. The larvae of the pea- and bean- weevils burrow into peas and beans, making them unfit either for food or seed. The larvae of the long-horn beetles burrow in wood and are among the (arsa most destructive enemies of trees. Cambridge Natural History.) FIG. 301. Order COLEOP- PHYLUM ARTHROPODA 363 Some of the worst pests are the locust borer, Cyllcnc robinice, the apple tree borer, Saperda Candida, and the sugar maple borer, Plagionolus speciosus. A common species, Tetraopcs teiraophthal- mus, is found on milk- weed. SUBORDER 6. TRI- MERA. (LADYBIRD BEETLES, Fig. 302.)- FIG. 302. Order COLEOPTERA. Novius cardi- The CorrTiSTFTTTD/F na ^ s > Australian ladybird beetle, feeding on the fluted scale, Icerya purchasi. a, ladybird larvae or ladybird beetles, feeding on adult female and egg sac ; b, pupa ; arp nrpHarprms hntVi c - adult ladybird; d, orange twig, showing scale drc ureudLeous. ijuin , , , ,. , , . /T -, ,, , , , and ladybirds natural size, (rrom Marlatt.) as larvae -and adults, feeding largely on plant-lice and scale-insects. They are conse- quently beneficial since they help control these pests (see p. 347). SUBORDER 7. HETEROMERA. (DARKLING, BLISTER- AND OIL- BEETLES, Fig. 303.) - -The HETEROMERA contains the darkling ground-beetles (TENEBRIONID.E) , one of which, the meal-worm, Tenebrio molitor (Fig. 303), is quite common in mills and grocery stores and is used as food for cage birds. This group also includes the blister- and oil-beetles (MELOID.E) ; some of these when dried and pulverized have a effect when FIG. 303. Order COLEOPTERA. Meal- blistering worm, Tenebrio molitor. A, larva. B, pupa. aDD li e( J to the human C, adult. (From the Cambridge Natural History.) skin. 3 6 4 COLLEGE ZOOLOGY SUBORDER 8. RHYNCHOPHORA. (SNOUT-BEETLES, Fig. 304.) - The RHYNCHOPHORA are the curculios, weevils, bill-bugs, and snout-beetles. The front of the head is prolonged into a beak or snout, with the mouth-parts at the end. Weevils (Fig. 304, A) attack many varieties of fruits, nuts, and grain. The bark-beetles (ScoLY- TID^E) are the most de- structive of all insects to forest trees, their depredations reaching a total of probably $100,000,000 annually. The genera Dendroc- tonus (Fig. 304, B) and Tomicus are the most FIG. 304. Order COLEOPTERA. A, cotton- no torious boll weevil. B, southern pine beetle, Dendroc- tonus frontalis. (A, from Farmer's Bui. 189; B, from Hopkins, Bui. 83, Bur. Ent., U. S. Dep't Agric.) B Order 19. Hymenop- tera. - - SAW -PLIES, GALL-FLIES, ICHNEU- MON-FLIES, ANTS, BEES, WASPS (Figs. 305-312). -- Insects possessing four membranous wings with few veins; first ab- dominal segment fused or partly fused with thorax; mouth-parts both mandibulate and suctorial; female with an ovipositor; metamorphosis complete. There are about seventy-five hundred species of HYMENOP- TERA inhabiting North America. They may be grouped into suborders, superfamilies, families, subfamilies, etc., but because of the limited space that can be devoted to them in this book, only a few of the most important families will be considered; these are the saw-flies (TENTHREDINID.E) , the chalcid- flies (CHALCIDID.E), the gall-flies (CYNIPID.E), the ichneumon-flies (ICHNEUMONID^:), the bees (APID.E), the solitary wasps (Eu- MENID^:), the social wasps (VESPLELE), the digger-wasps (SPHEGID.E), and the ants ( PHYLUM ARTHROPODA 365 The saw-flies (TENTHREDINID.E, Fig. 305) are not generally noticed as adults, but their larva?, which feed on the leaves of FIG. 305. Order HYMENOPTERA. Saw-fly, Nematus venlricosus. a, adult female ; b, larva? (currant worms) ; c, adult male. (From Report State Ento- mologist of Minnesota.) the rose, currant, pear, willow, and larch, are only too well known. The eggs are usually laid in slits made in plant tissue by the saw-like ovipositor of the female. The larvae possess usually from six to eight pairs of abdominal legs and can thus be dis- tinguished from the larvae of LEPIDOPTERA, w r hich have not more than five pairs. Some adult saw- flies lay eggs which develop parthenogenetically. The clmhid-flies (CiiAL- CIDID.E, Fig. 306) are minute parasites which . FIG. 306. -Order HYMENOPTERA. Chal- ... cid-fly, Prospalta murtfeldlii. (From Insect perform a service of in- Life.) estimable value to man, since they attack the eggs, caterpillars, and adults of many injurious insects. The eggs are laid on or in the host and the larvae slowly devour its soft parts. One species, Blasto- 366 COLLEGE ZOOLOGY phaga grosser um, is held responsible for the fertilization of the fig. The gall-flies (CYNIPID.E, Fig. 307) are small, dull-colored insects possessing a long ovipositor with which eggs are laid in plant tissue. In some way the plant is stimulated so that an abnormal growth, called a gall, is produced. The young gall- A FIG. 307. Order HYMENOPTERA. A, gall-fly, Rhodites rosa, female. B, galls produced by a bug. (A, from the Cambridge Natural History; B, from Davenport, after Kerner.) fly is protected by the surrounding tissue. Many species are parthenogenetic, and only females are known. The bees (APID.E) comprise a large family, of which the honey- bee is the best-known example. All grades of social life are exhibited by bees. The leaf-cutter, Megachile acuta, is a solitary species; she lays her eggs in leaf-lined cavities in wood, places pollen and nectar in the cavities for the larvae to feed on, and then flies, away never to return. The carpenter bee, Ceratina dupla, is also a solitary bee, but she watches her young until they mature. Certain mining bees, e.g. Andrena, lay eggs in burrows in the ground (Fig. 309, B). They are solitary bees but often build their tunnels close together, i.e. they have a tendency toward a gregarious habit. The PHYLUM ARTHROPODA 367 females of other mining bees, e.g. Halictus, band together and use a single main burrow from which the individual channels branch off (Fig. 309, A). These bees therefore have a tendency toward com- munity life. The bumble- bees, Bombus, live in colonies during the sum- mer, but these colonies are temporary, since all members but the young queens perish in the . , - ., , FIG. 308. Order HYMENOPTERA. Ich- autumil. And finally the ncumo n-n y , Thalcssa hinator, laying eggs honey-bees, as we have (oviposition). (From Sedgwick's Zoology, after Riley.) seen, are banded together in permanent colonies and have a very complex social life. The solitary wasps (EUMENID.-E) are miners, carpenters, or masons, i.e. they dig tunnels in the earth, excavate cavities in wood, or build mud-nests. Like the solitary bees, the Eu- menidae provision their nests, lay their eggs, and then fly away, leaving their young to shift for themselves. Many of the digger-wasps belong to the family SPHE- GID^E. The mud-daubers are common species. They attach their mud-nests to the ; \j> ceilings of buildings or to the FIG. 309. Diagrams of nest burrows lower surface of stones, and of short-tongued mining bees. A, nest of ision them with spiders . Halictus. B, nest of Andrena. (From Hegner, after Kellogg.) The digger- wasps of the West 3 68 COLLEGE ZOOLOGY (genus Ammophila, Fig. 310) paralyze caterpillars with their sting and place them in their burrows in the ground for the larvae to live on. The burrows are then carefully filled up with earth and the top made level with the surrounding surface. The social wasps (VESPID^E) live in temporary colonies con- taining females, males, and sexu- ally undeveloped females, called workers. They do not leave their FIG. 310 -Order HYMENOPTERA. to liye u food stored Solitary digger-wasp, A mmophila, J putting inchworm into nest burrow, for them, but care for them con- (From Bailey and Coleman, after stan tly. The Commonest genera Peckham.) are Polistes and Vespa. The hor- net, Polistes (Fig. 311), builds a nest of a single layer of cells made out of wood-pulp. This single comb nest is hung by a stalk under the eaves or to the ceiling of an outbuilding, or FlG. 311.- Hornet and nest, Polistes tepidus. (From Shipley and MacBride.) porch. Only the females survive the winter, and new colonies must therefore be established each spring. The yellow- jacket 7 PHYLUM ARTHROPODA 3 6 9 Vespa. builds a more elaborate nest than that of Polities. It consists of a series of combs one above the other, and is sur- rounded by a paper covering with an entrance near the pointed lower end. The ants (FORMICID^E) constitute in many ways the most remarkable group of insects hi the world. Their adaptations for the complex social life that they lead are very wonderful. A colony, as in the social bees and wasps, contains a queen, males, and workers. The workers may be modified as large or small workers, or as soldiers. Ants usually live in tunnels in the ground, FIG. 312. Honey ants and leaf -cutting ants. (From Brehm.) or in wood, or in the hollow stems of plants. Beetles and other insects live in ants' nests. The honey-ant, Myrmecocystus (Fig. 312, 1} is a peculiar form. Some of the workers cling to the roof of the mound-like nests and serve as reservoirs for the storing of a sort of honey until it is needed by the colony. The leaf-cutter ants (Fig. 312, 2} of the genus A tta ((Ecodoma) have a peculiar method of securing food. Certain workers cut out pieces of leaves and carry them to the nest, where the other workers pack them into balls on which they cultivate a fungus, Rozites gongy- lophora. The ants regulate the growth of this fungus in such a way that it produces white masses which serve as food for the colony. 2 B 376 COLLEGE ZOOLOGY d. The Economic Importance of Insects The economic importance of certain insects has been em- phasized during our discussion of the orders of insects. A few species of insects are of considerable value to man. For example, the honey-bee produces enormous quantities of both honey and wax; the silkworm supplies us with delicate silk threads; the bees and many other insects cross-fertilize flowers; the bodies of the scale insect, Coccus cacti, are known as cochineal ; pre- daceous species usually prey upon injurious insects; and many parasitic species attack destructive caterpillars. On the other hand, the injurious insects are numerous and im- portant. Some of them are responsible for the transmission of certain diseases. For example, the house-fly carries the germs of typhoid, tuberculosis, cholera, and many other diseases on its TABLE XIII ANNUAL LOSSES DUE TO INSECT PESTS OF THE UNITED STATES PRODUCT VALUE PERCENTAGE OF Loss AMOUNT OF Loss Cereals .... Hay $2,OOO,OOO,OOO ^ T.O OOO OOO IO IO $2OO,OOO,000 ^,000,000 Cotton .... Tobacco .... Truck crops . . . Sugar Fruits J^J ' 600,000,000 53,000,000 265,000,000 50,000,000 1 3;, ooo, ooo 10 IO 20 IO 20 60,000,000 5,300,000 53,000,000 5,000,000 27,000,000 Farm forests . . Miscellaneous crops Animal products \J *s * 110,000,000 58,000,000 1,750,000,000 IO IO IO 11,000,000 5,800,000 175,000,000 Total . . . Natural forests and forest products . Products in storage 5,551,000,000 595,100,000 100,000,000 100,000,000 Grand total 795,100,000 PHYLUM ARTHROPODA 371 legs, proboscis, and body; the anopheles mosquito transmits the malaria germ; the stegomyia mosquito transmits the yellow fever germ ; the rat flea carries plague germs ; the body-louse transmits relapsing fever; and the tsetse- fly is responsible for sleeping-sickness. Millions of dollars are lost every year because of the attacks of insects upon domestic animals. Among these insects are the blood-sucking gnats, buffalo-gnats, horse-flies, gadflies, bot-flies, horn-flies, flesh-flies, ticks, fleas, sucking lice, and bird-lice. Even more enormous are the losses due to insects that eat the leaves of plants, bore into their sterns, suck their juices, or de- stroy their fruits. Table XIII presents a conservative estimate of these losses. (Marlatt.) 6. CLASS V. ARACHNIDA The class ARACHNIDA (Gr. arachne, a spider) includes the spiders, ticks, mites, scorpions, and king-crabs. These animals differ markedly from one another, but agree in several important respects: (i) they have no antennae; (2) there are no true jaws; (3) the first pair of appendages are nippers, termed chelicerae; and (4) the body can usually be divided into an anterior part, the cephalothorax, and a posterior part, the abdomen. Twelve orders of arachnids are recognized in this book. The first four orders ARANEIDA, SCORPIONIDEA, PHALANGIDEA, and ACARINA contain most of the living species ; the last order, EURYPTERIDA, is known only from fossils. a. The Spiders Order i. Araneida. -- SPIDERS. -- Since the spiders are the most common of all arachnids, they are used here to illustrate the anatomical and physiological characteristics of the class. External Features. -- Figure 313 shows the principal external features of a spider. The body consists of a cephalothorax which is undivided, and an abdomen which is usually soft, rounded, and unsegmented. 372 COLLEGE ZOOLOGY There are six pairs of appendages attached to the cephalo- thorax. Antennae are absent; their sensory functions are in part performed by the walking legs. The first pair of appendages are called chelicera (Fig. 314, ip). They are in many species com- posed of two parts, a basal "mandible" (Fig. 313, B), and a terminal claw. Poison-glands (Fig. 314, 20) are situated in the chelicerae. The poison they secrete passes through a duct and out of the end of the chelicera (Fig. 314, ip); it is strong enough to kill insects and to injure larger animals. The second pair of appendages are the pedipalpi (Fig. 313, palpus and maxilla) ; their bases, called " maxillae," are used as jaws to press or chew the food. The pedipalpi of the male are used as copulatory organs. Following the pedipalpi are four pairs of walking legs. This number easily distinguishes FIG. 313. External features of a _* . spider. A, under surface; all but one spiders from insects, since the leg removed. B, front of head show- latter possess only t h ree pairs, ing eyes and mandibles. (rrom * Emerton.) Each leg consists of seven joints, - - (i) coxa, (2) tro- chanter, (3) femur, (4) patella, (5) tibia, (6) metatarsus, (7) tarsus, and is terminated by two toothed claws (Fig. 315) and often a pad of hairs (s) which enables the spider to run on ceilings and walls. The bases of certain of the legs some- times serve as jaws. The sternum lies between the legs, and a " labium " is situated between the " maxillae." The eyes, usually eight in number, are on the front of the head (Fig. 313, B). The mouth (Fig. 314, j) is a minute opening between the bases of the pedipalpi (max- PHYLUM ARTHROPODA 373 illae) ; it serves for the ingestion of juices only, since spiders do not eat solid food. The abdomen is connected by a slender waist with the cephalo- thorax. Near the anterior end of the abdomen on the ventral FIG. 314. Diagram of a spider, Epeira diademata, showing the arrange- ment of the internal organs. /, mouth; 2, sucking stomach; 3, ducts of liver; 4, so-called malpighian tubules; 5, stercoral pocket; 6, anus; 7, dorsal muscle of sucking stomach; 8, caecal prolongation ot stomach; Q, cerebral ganglion giving off nerves to eyes; 10, subcesophageal ganglionic mass; n, heart with three lateral openings or ostia; 12, lung sac; 13, ovary; 14, acinate and pyri- form silk glands; 75, tubuliform silk glands; 16, ampulliform silk gland; i/, dendriform silk glands; 18, spinnerets; IQ, distal joint of chelicera; 20, poison gland; 21; eye; 22, pericardium; 23,' vessel bringing blood from lung sac to pericardium; 24, artery. (From the Cambridge Natural History.) surface is the genital opening, protected by a pair of appendages which have fused together to form a plate called the cpigynum (Fig. 313). On either side of the epigy- num is the slit-like opening of the respir- atory organs or lung books (Fig. 313; Fig. 314, 12). Some spiders also possess trachea which open to the outside near the posterior end on the ventral surface (Fig. 313). Just back of the tracheal opening are three pairs of tubercles or SpinilCretS (Fig. 313; Fig. 314, l8] , Used and pencil consisting of for spinning threads. The anus (Fig. 314, 6} lies posterior to the spinnerets. Hermann.) FIG. 315. End of foot 374 COLLEGE ZOOLOGY Internal Anatomy and Physiology (Fig. 314). - -The food of the spider consists of juices sucked from the bodies of other ani- mals, principally insects. Suction is produced by the enlarge- ment of the sucking stomach (Fig. 314, 2], due to the contraction of muscles attached to its dorsal surface and to the chitinous covering of the cephalothorax (7). The true stomach, which follows the sucking stomach, gives off five pairs of caca or blind tubes (8) in the cephalothorax. The intestine passes almost straight through the abdomen; it is enlarged at a point (j) where ducts bring into it a digestive fluid from the " liver," and again near the posterior end, where it forms a sac, the " stercoral pocket " (5). Tubes, called Malpighian tubes (4), enter the intestine near the posterior end. The alimentary canal is surrounded in the abdomen by a large digestive gland or " liver." This gland se- cretes a fluid resembling pancreatic juice and pours it into the intestine through ducts (3). The circulatory system consists of a heart, arteries, veins, and a number of spaces or sinuses. The heart (Fig. 314, u) is situ- ated in the abdomen and is surrounded by the digestive glands. It is a muscular, contractile tube lying in a sheath, the peri- cardium (22), into which it opens by three pairs of ostia. It gives off posteriorly a caudal artery, anteriorly an aorta which branches and supplies the tissues in the cephalothorax, and three pairs of abdominal arteries (24). The blood, which is colorless and contains mostly ameboid corpuscles, passes from the ar- teries into sinuses and is carried to the book lungs (12) where it is aerated; it then passes to the pericardium by way of the pulmonary veins (25), and finally enters the heart through the ostia. Respiration is carried on by tracheae and book lungs ; the latter are peculiar to arachnids. The book lungs (Fig. 314, 12], of which there are usually two, are sacs, each containing generally from fifteen to twenty leaf-like horizontal shelves through which the blood circulates. Air entering through the external openings is thus brought into close relationship with the blood. Tracheae PHYLUM ARTHROPODA 375 are also usually present, but do not ramify to all parts of the body as in the insects (p. 320, Fig. 242). The excretory organs are the Mai pig/nan tubules (Fig. 314, 4), which open into the intestine, and two coxal glands in the cepha- lothorax. The coxal glands are sometimes degenerate, and their FIG. 316. Orb web of a spider, Epeira. a, first spiral line; b, second spiral line; c, line to nest. (From Davenport, after Emerton.) openings are difficult to find ; they are homologous with the green glands of the crayfish (p. 284, Fig. 202, 40-42). The nervous system consists of a bilobed ganglion above the oesophagus (Fig. 314, p), a subcesophageal ganglionic mass (10), and the nerves which arise from them. There are sensory hairs on the pedipalps and probably on the walking legs, but the prin- cipal sense-organs are the eyes. There are usually eight eyes (Fig. 313, B; Fig. 314, 21), and these differ in size and arrange- COLLEGE ZOOLOGY ment in different species. Spiders apparently can see objects distinctly only at. a distance of four or five inches. The sexes are separate, and the testes or ovaries (Fig. 314, ij) form a network of tubes in the abdomen. The spermatozoa are FIG. 317. A, crab-spider, Thomisus. B, jumping-spider, Attus. C, young spider, Lycosa, preparing for an aerial voyage. D, house-spider, Theridium epidariorum. (A, B, C, from Davenport, after Emerton ; D, from Emerton.) transferred by the pedipalps of the male to the female, and fer- tilize the eggs within her body. The eggs are laid in a silk co- coon, which is attached to the web or to a plant, or carried about by the female. The young leave the cocoon as soon after hatch- ing as they can run about. The spinning organs of spiders are three pairs of appendages called spinnerets (Fig. 313; Fig. 314, 18} . The spinneret* are pierced by hundreds of microscopic tubes through which a fluid PHYLUM ARTHROPODA 377 secreted by a number of abdominal silk glands (Fig. 314, 14-17], passes to the outside and hardens in the air, forming a thread. These threads are used to build nests, form cocoons, spin webs, and for many other purposes. An orb web, such as is shown in Figure 3 16, is spun in the following manner. A thread is stretched across the space selected for the web; then from a point on this thread other threads are drawn out and attached in radiating lines. These threads all become dry and smooth. On this foundation a spiral is spun of sticky thread. The spider stands in the center of the web or retires to a nest at one side and waits for an insect to become entangled in the sticky thread; it then rushes out and spins threads about its prey until all struggles cease. Many spiders do not spin webs, but wander about capturing insects, or lie in wait for them in some place of concealment. In this group belong the crab-spiders (THOMISID^E, Fig. 317, A), jumping- spiders (AxxiD^;, Fig. 317, B), ground-spiders (DRAS- SID^E), and running spiders (LYCOSID.E, Fig. 317, C). The cob- web spiders spin various kinds of nets for capturing insects. The tube-weavers (AGELENID,E) build platforms on the grass and hide in a tube at one side; the line weavers (LINYPHIAD^E) spin flat webs with irregular meshes; the round-web spiders (EPEIRI- build webs like that shown in Figure 316; and theTHERi- (Fig. 317, D) build irregular webs in corners and on plants. b. Other Arachnida Order 2. Scorpionidea. -- SCORPIONS. - -The scorpions are rapacious arachnids measuring from half an inch to eight inches in length. They live in tropical and subtropical regions, hiding in crevices or in pits in the sand during the daytime, but running about actively at night. They capture insects and spiders with their pedipalpi (Fig. 318), tear them apart with their chelicerae, and devour the pieces. Larger animals are paralyzed by the sting on the end of the tail. This sting does not serve as a weapon of defense unless the scorpion is hard pressed; and is not used, as 378 COLLEGE ZOOLOGY is often stated, to sting itself to death, since its poison has no effect upon its own body. The scorpion's body (Fig. 318) is more obviously segmented than that of most of- the other arachnids. There is a cephalo- thorax (prosoma), and an abdomen of two parts a thick an- terior portion (mesosoma) , and a slender tail (metasoma) which hand . Peclipalp Lateral eyes .-' .Median eyes Prosoma Afesosoma B tfelasom* acuteus. FIG. 318. Scorpion, Bulhus occitanus. A, dorsal view. B, ventral view. (From the Cambridge Natural History, after Kraepelin.) is held over the back when the animal walks. The dorsal shield of the cephalothorax bears a pair of median eyes and three lateral eyes on each side. The sense of sight is, however, poorly de- veloped. On the ventral surface of the second abdominal seg- ment are two comb-like appendages called pectines (Fig. 318, B) ; these are probably special tactile organs. Tactile hairs are dis- PHYLUM ARTHROPODA 379 tributed over the body, and the sense of touch is quite delicate. There are four pairs of lung books opening by means of stigmata (Fig. 318, B) on the under surface of ab- dominal segments III-VI. The mating activi- ties of scorpions are very curious, and include a sort of promenade (Fig. FIG. 319. The "promenade a deux" of the *,Tf\\ Q/-,-.iT~,irM-.c OT-O scorpion, Buthus occitanus. (From the Cambridge Natural History, after Fabre.) viviparous. The young ride about upon the back of the female for about a week, and then shift for themselves. They reach maturity in about five years. Order 3. Phalangidea. - - HARVESTMEN OR DADDY-LONG- LEGS. - - The harvestmen may be distinguished from spiders by FIG. 320. -Order PHALANGIDEA. Harvestman, (From Sedgwick's Zoology.) opilio, male. their extremely long legs (Fig. 320), the absence of a waist, and their segmented abdomen. They are able to run rapidly over leaves and grass. Their food consists of small living insects. Order 4. Acarina. - - MITES AND TICKS. - - These are minute arachnids without any external signs of segmentation. Many of them are parasitic and often cause serious diseases. COLLEGE ZOOLOGY The family TROMBIDIID^: includes the harvest mites or " chiggers " (Fig. 321). These little creatures are transferred by contact from plants to the bodies of man and other animals. They burrow into the skin, with painful results. Treatment with a one or two per cent solution of carbolic acid is the proper remedy. The poultry tick, Dermanyssus gall i nee (Fig. 322, A) belongs to the family GAMASID^:. It sucks the blood of chickens, and is a pest on poultry j FIG. 321. Order ACARINA. Harvest- mites or " chiggers." Leptus irritans on the right; L. americana on the left. (From Osborn, after Riley.) farms. The family IXODID.*: contains a number of injurious species. The cattle tick, Boophilus (Margaropus) annulatus (Fig. 322, B), is perhaps the most important. These ticks cling to the skin of cattle with their strong mouth-parts, and suck the blood of their host. When full grown the females drop to the ground and lay from 2000 to 4000 eggs; these soon hatch, and the young crawl upon a blade of grass and wait for cattle to come past to which they can fasten themselves. The principal injury done by the FIG. 322. Order ACARINA. A, poultry tick, Dermanyssus gallina, young. B, cattle tick, Boophilus annulatus. PHYLUM ARTHROPODA 381 E FIG. 322, continued. Order ACARINA. C, follicle mite, Demodex folliculorum. D, itch-mite, Sarcoptcs scabiei. E, sheep-scab mite, I'soraptcs commitnis var. oms (A, B, E, from Osborn ; B, after Packard; C. D, from Scd^wick's Zoology ; C, after Megnin, D, after Gudden.) ticks is the transference of a sporozoan parasite, Piroplasma bigeminum, from the blood of one animal to that of another. This parasite produces Texas fever, a disease that causes an annual loss of about $100,000,000 in the United States. Other members of the order ACARINA that should be men- tioned are: (i) the follicle mites, Demodex folliculorum (Fig. 322, C), that lives in the sweat-glands and hair follicles of man and some domestic animals, causing what are known as "black- heads " ; (2) the itch-mite, Sarcoptes scabiei (Fig. 322, D) which burrows beneath the epidermis of man and causes intense itching; and (3) the scab parasite, Psoroptes coin- munis (Fig. 322, E), which feeds on the skin of sheep, cattle, and horses, producing scabs. FIG. 323. Order PEDIPALPI. A /-\ T-> i i - /!-< South American specie?, Adtnetus Order ^ Pedioaloi (ri' ) In front of the ventral fin the lower surface of the body is flattened, and on each side is an expansion of the integument called the metaplenral fold (Fig. 342, mp). The body-wall is divided into a number (62) of V-shaped muscle segments, the myotomes (Fig. 341, w 1 , w 36 , tw 62 ), these are sepa- rated from one another by septa of connective tissue. The myo- tomes on one side of the body alternate with those on the other side. The muscle fibers contained in them are longitudinal, and, PHYLUM CHORDATA 395 since they are attached to the connective tissue partitions, are able to produce the lateral movements of the body used in swimming. The mouth opening is at the bottom of a funnel-shaped cavity in the ventral surface near the anterior end, called the vestibule \ nph deo C^s .), and similar structures (Fig. 343, sk) that support the cirri (cir) of the oral hood (or.fhd). DIGESTIVE SYSTEM (Fig. 343). - - The food of Amphioxus con- sists of minute organisms which are carried into the mouth with the current of water produced by cilia on the gills (compare with mussel, p. 246). The mouth (mth) is an opening in a membrane, the velum (vl) , and may be closed by circular muscle fibers which surround it. Twelve sensory-oral or velar tentacles (vl.t) pro- tect the mouth, and, when folded across it, act as a strainer, thus preventing the entrance of coarse, solid objects. The funnel- shaped vestibule is the cavity of the oral hood (or.fhd). The twenty-two ciliated cirri (cir} which project from the edge of the oral hood are provided with sensory cells. The inner wall of the oral hood bears a number of ciliated lobes and is known as the wheel organ because its cilia appear to produce a rotatory movement. Water is forced into the mouth by the cilia. The mouth opens into a large, laterally compressed pharynx (Fig. 343, ph; Fig. 342). A ciliated dorsal indentation in the pharynx is called the hyperbranchial groove (Fig. 342, hy.). A ventral groove, the endostyle (en], is also present. The endo- style consists of a median ciliated region with a glandular portion on either side. The glands secrete strings of mucus (compare tunicate, p. 391) in which food particles are entangled. The cilia then drive this mucus forward by way of two peri- pharyngeal grooves into the hyperbranchial groove. From here it is carried by the hyperpharyngeal cilia into the intestine (Fig. 343, int). A ventral finger-shaped diverticulum of the intestine is known as the liver (Ir), or hepatic cacum, since it is supposed PHYLUM CHORDATA 397 to secrete a digestive fluid similar to that produced by the liver in the vertebrates. The intestine leads directly to the anus (an). ccnl.c FIG. 343. -- Diagram of the anatomy of Amphioxus. A, anterior, B, posterior part, an, anus ; atr, atrium ; atr 1 , its posterior prolongation ; atrp, atriopore ; br, brain ; br.d, branchial clefts ; brf, brown funnel ; br.srp.i, br.sep.2, branchial lamellae; br.r.i, br.r.2, branchial rods; caud.f, caudal fin; cent.c, central canal; cir, cirri; coel, ccelom; dors.f, dorsal fin; dors.f.r, dorsal fin-ray; en coe, cerebral vesicle; e.sp, eye spot; gon, gonad; int, intestine ; h, liver ; mth, mouth ; myom, myotomes ; nch, notochord ; nph, nephridia ; olj.p, olfactory pit ; or.f.hd, oral hood ; fh, pharynx ; sk, skeleton of oral hood and cirri (dotted); sp.cd, spinal cord; vent.f, ventral fin; vent.f. r, ventral fin-ray; vl, velum; vl.t, velar tentacles. (From the Cambridge Natural History, after Parker and Haswell.) RESPIRATORY SYSTEM. --The pharynx (Fig. 343, ph ; Fig. 342) is attached dorsally and hangs down into a cavity called the atrium (Figs. 342-343, air.). The atrium is not the ccelom 39* COLLEGE ZOOLOGY but is lined with an ectodermal epithelium and is really external to the body, as has been proved by the study of its development. Water which is carried into the pharynx by way of the mouth passes through the gill-slits into the atrium and out of the atrio- pore (Fig. 341, atp ; Fig. 343, atrp). The gill-slits, sometimes as many as one hundred and eighty, are separated by gill-bars (Fig. 342, p.b.) ; these are ciliated and supported by chitinous rods. Respiration takes place as the water, driven by the cilia, flows through the gill-slits. CIRCULATION. - - Amphioxus does not possess a heart. The position of the principal blood-vessels and the direction of the \h,e.p>porl is FIG. 344. Diagram of the vascular system of Amphioxus. af.br. a, afferent branchial arteries ; cp. intestinal capillaries ; d.ao, paired dorsal aortae ; d.ao, 1 median dorsal aorta; ej.br. a, efferent branchial arteries; hep.port.v., hepatic portal vein; hcp.v, hepatic vein; /;//, intestine; Ir, liver; ph, pharynx; s.int.i), subintestinal vein. (From Parker and Haswell.) blood flow are shown in Figure 344. The subintestinal vein (s.int.v) collects blood loaded with nutriment from the intes- tine (int} and carries it forward into the hepatic portal vein (hep. port.v), and thence to the liver (//). The hepatic vein (hep.v) leads from the liver to the ventral aorta (v.ao). Blood is forced by the rhythmical contractions of the ventral aorta into the af- ferent branchial arteries (af.br. a), which are situated in the gill- bars, and then through the efferent branchial arteries (ef.br. a) into the paired dorsal aortae (d.ao). It passes back into the median dorsal aorta (d.ao 1 } and finally byway of intestinal capil- laries (cp} into the subintestinal vein (s.int.v). The blood is PHYLUM CHORD ATA 399 oxygenated during its passage through the branchial arteries. The direction of the blood flow, backward in the dorsal and for- ward in the ventral vessel, is like that of the vertebrates (p. 407), but just the reverse of that in annelids and arthropods (see pp. 221 and 283). THE CCELOM. - - The ccelom arises from five embryonic pouches of the primitive digestive tract as in Balanoglossus (p. 388), but is difficult to make out in the adult. The position of the ccelomic cavities is shown in Fig. 343, coel, and Fig. 342, d.co. EXCRETORY SYSTEM. - - The excretory organs are ciliated nephridia (Figs. 342-343, nph) situated near the dorsal region of the pharynx. The nephridia connect the dorsal ccelom (Fig. 342, d.co) with the atrial cavity. A pair of brown funnels (Fig. 343, br.f), one on either side and dorsal to the intestine in the region of myotome twenty-seven, may also be excretory organs. NERVOUS SYSTEM. Amphioxus possesses a central ncnc-cord (Fig. 343, sp.cd ; Fig. 342, nt) lying entirely above the alimen- tary canal (compare annelids, p. 216, and arthropods, p. 285). It rests on the notochord and is almost as long. A minute canal (Fig. 343 cent.c) traverses its entire length and enlarges at the anterior end into a cerebral vesicle (en.coe) which is the only trace of a brain present. An olfactory pit (olf.p) opens into this vesicle in young specimens. At the anterior end of the nerve- cord is a mass of pigmented cells forming an eye-spot (e.sp). Two pairs of sensory nerves arise from the cerebral vesicle, and supply the anterior region of the body. The rest of the nerve- cord gives off nerves on opposite sides, but alternating with one another. These nerves are of two kinds : (i) dorsal nerves with a sensory function which pass to the skin, and (2) ventral nerves with a motor function which enter the myotomes. The sense- organs include the olfactory pit, eye-spot, and sensory cells in the ectoderm, on the cirri, and on the velar tentacles. REPRODUCTION. - - In Amphioxus the sexes are separate. The twenty-six pairs of gonads (Fig. 341, g l , g 26 ; Fig. 342, go) project into the atrium. The germ-cells are discharged into the 400 COLLEGE ZOOLOGY atrial cavity and reach the exterior through the atriopore. Fer- tilization takes place in the water. The early development of the egg of Amphioxus was described in Chapter III (pp. 87 to 89), and is illustrated in Figure 51. For a detailed description of the embryology of Amphioxus, the student is referred to Willey's Amphioxus and the Ancestry of the Vertebrates and to advanced text-books of zoology. 4. SUBPHYLUM IV. VERTEBRATA: INTRODUCTION The VERTEBRATA are animals with an axial notochord at some period in their existence. This notochord persists in some of the lower vertebrates, but is modified by an investment of carti- lage which becomes segmented and constitutes the vertebral col- umn. In the higher vertebrates the vertebral column is made up of a series of bodies called vertebrae, and the notochord disappears before the adult stage is reached. The vertebrates are the lam- preys, hags, sharks, rays, chimasras, fishes, frogs, toads, sala- manders, lizards, snakes, crocodiles, turtles, birds, hairy quadru- peds, whales, seals, bats, monkeys, and man. Seven classes of vertebrates are recognized. Class I. CYCLOSTOMATA (Gr. kyklos, circle; stoma, mouth). LAMPREYS and HAGS (Figs. 352-356). -- Cold-blooded, fish-like vertebrates without jaws and lateral fins. Class II. ELASMOBRANCHII (Gr. elasmos, metal plate; bran- chia, gills). -- SHARKS, RAYS, and CHIMERAS (Figs. 358-367).- Cold-blooded, fish-like vertebrates with jaws, a cartilaginous skeleton, a persistent notochord, and placoid scales. Class III. PISCES (Lat. piscis, fish). -- FISHES (Figs. 368- 408). -- Cold-blooded vertebrates with jaws, and usually with lateral fins supported by fin-rays. They breathe chiefly by gills. Class IV. AMPHIBIA (Gr. am phi, both; bios, life). -- FROGS, TOADS, and SALAMANDERS (Figs. 409-438). Cold-blooded, naked vertebrates mostly with pentadactyle (five-fingered) limbs. The young are usually aquatic and breathe by gills; the adults usually lose the gills, and breathe by means of lungs. PHYLUM CHORDATA 401 Class V. REPTILIA (Lat. repcre, to crawl). -- SPHENODON, CHAMELEONS, LIZARDS, SNAKES, CROC A ODILES, and TURTLES (Figs. 439-469). -- Cold-blooded vertebrates breathing by means of lungs and usually having a scaly skin. Class VI. AVES (Lat. avis, bird). - - BIRDS (Figs. 470-509). Warm-blooded vertebrates with the fore limbs modified into wings and the body covered with feathers. Class VII. MAMMALIA (Lat. mamma, breast). HAIRY QUAD- RUPEDS, WHALES, SEALS, BATS, MONKEYS, and MAN (Figs. 510- 550). -- W T arm-blooded vertebrates with a hairy covering at some stage in their existence; the young nourished after birth by the secretion of the mammary glands of the mother. Plan of Structure. - - The vertebrates resemble the other chordates in their metamerism and bilateral symmetry and in the SPINAL CANAL) NEURAL TUBE SPINAL CORD BRAIN NOTOCHORD VISCERALTUBE(C0CMV mTygvrq - /XUIN^ -J^SSS* 1 "" tf *Si .^^^^T < ab^^efe&3>Xr^M > / ORAL CAVITY J STERNAL GILL SLITS HEART LIVEK AlIiNZ NARY DUrr 3ENITALDUCT SPLEEN CLOACA ' URINARY BLADDER BILE DUCT PANCREAS FIG. 345. Diagrammatic longitudinal section of a vertebrate (female). (From Wiedersheim.) possession of a ccelom, a notochord, and gill-slits -at some stage in their existence, and a dorsal nerve tube. They differ from other chordates and resemble one another in the possession of carti- laginous or bony vertebra, usually two pairs of jointed appendages containing a central skeleton, a venlrally situated heart with at least two chambers, and red corpuscles in the blood. 2 D 4O2 COLLEGE ZOOLOGY cL-.a-o The body of a vertebrate may be divided into a head, neck (usually), and trunk. In many species there is a posterior ex- tension, the tail. Two pairs of lateral appendages are generally present, the thoracic (pectoral fins, forelegs, wings, or arms) and the pelvic (pelvic fins, hind legs). The limbs support the body, are locomotory, and usually have other special functions. A general account of the plan of struc- ture of an ideal ver-. tebrate can be given most clearly with the aid of diagrams showing longitudi- nal and cross sec- tions' through the body (Figs. 345- 346). As in Am- phioxus. the nerve FIG. 346. Transverse section through the trunk cor( j (sp.c) IS dorsal of a vertebrate, en, centrum of vertebra; cod, ccelom; . crd.v, cardinal vein; d.ao, dorsal aorta; d.f, dorsal but extends in tront fin; d.m, dorsal muscles; f.r, fin-ray; gon, gonad; Q f ^e enc j o f ^ e int, intestine ', l.i\ lateral vein ; mes, mesentery; ms.n.d, mesonephric duct ; ms.nph,. mesonephros; notochord and en- na, neural arch; p.n.d, pronephric duct; pr, peri- largCS into a brain. toneum, parietal layer; pr', visceral layer; r, sub- peritoneal rib; r', intermuscular rib; sp.c, spinal Ihe nowcliora DC- cord; t.p, transverse process; v.m, ventral muscles. comes invested by (From Parker and Haswell.) .,. the verteorae (Fig. 346, en). The ccdom (coel) is large. The alimentary canal forms a more or less convoluted tube (int) which lies in the bod> cavity. The liver, pancreas, and spleen are situated near the alimentary canal. In the anterior trunk region are the lungs and heart. The kidneys (ms.nph) and gonads (gon) lie above the alimentary canal. Integument (Fig. 347). --The outer covering of the verte- brates is the skin, consisting of an outer ectodermal layer, the epidermis (Sc, SM), and an inner mesodermal layer, the dermis PHYLUM CHORDATA 403 (Co). The skin is chiefly protective and sensory, but may also carry on respiration and excretion. Excretion takes place by means of glands, which may be simple, as the mucous glands of fishes, or complex, as the sweat, oil, and mammary glands. The skin often produces numerous outgrowths such as hair, feathers, nails, hoofs, claws, scales, teeth, and bony plates. Skeleton. - - The outgrowths "of the integument noted above constitute the exoskeleton. The internal supporting framework of the body is the endoskcleton. This consists of (i) an axial- portion comprising the skull and vertebral column, and (2) an FIG. ^547. Section through human appcildlCllUu- portion Which SVLp- skin . Co, dermis; F, subcutaneous ports the appendages. f at ;GP, vascular papillae ;#, hair with sebaceous glands (D); N, G, nerves; I he bones of the endoskeleton are typically formed in and around cartilage. The animal part of the bone is the cartilage ; this can be obtained by dissolving out the mineral part, the bone- ash, in hydrochloric acid. The bone-ash consists principally of carbonate and phosphate of lime, and is the residue when a bone is burned. The mineral constituents give the bone rigidity; the cartilage furnishes pliancy and elasticity. Bones support the soft parts, furnish points of attachment for the muscles, and protect certain delicate organs, such as the brain, spinal cord, and eyes. The axial skeleton consists typically of the skull, the vertebrae, and the ribs which may be attached to a ventral bone, the sternum. The skull includes a brain case or cranium, which protects the brain, and a visceral skeleton, which supports the respiratory apparatus and includes the facial bones. NP, sensory papillae ; Sc, stratum conu'iim ; SD, sweat-glands with their ducts (SD'); SM, stratum mal- pighi. (From Wiedersheim.) 404 COLLEGE ZOOLOGY The vertebral column serves as a supporting axis for the body, Its structure, however, is such as to allow movement, since it is composed of a number of movable parts, the vertebra. The vertebrae develop from cartilaginous tissue which forms a sheath around the notochord. A typical vertebra consists of SCP mils. 5 JIT ' FIG. 348. Diagrams of A, fore limb and girdle, and B, hind limb and girdle of a vertebrate. I-V, digits; actb, acetabulum; C L, clavicle ; cn.i, CH.J, cen- tralia; COR, coracoid ; dst. 1-5, distalia; F E, femur; FI, fibula; fi, fibulare; gl, glenoid cavity; HU, humerus; I L, ilium; int, intermedium; IS, ischium; mtcp.i-5, metacarpals ; mtts.is, metatarsals; p. cor, procoracoid ; ph, pha- langes ; P U, pubis; RA, radius; ra, radiale ; SCP, scapula; TI, tibia; ti, tibiale; U L, ulna; ul, ulnare. (From Parker and Haswell.) a supporting basal portion, the centrum (Fig. 346, en), a dorsal or neural arch (no), which protects the spinal cord (sp.c), a neural spine, which extends dorsally from the center of the neural arch and serves for the attachment of muscles, and a transverse process (t.p) on each side of the centrum to which a rib (r) may be joined. PHYLUM CHORDATA 405 Four types of vertebra are recognized; (i) cervical vertebra in the neck, (2) dorsal or thoracic 'ccrlrbrce which bear ribs, (3) sacral vertebra with which the skeleton of the hind limbs are united, and (4) caudal vertebra posterior to the sacrum. The ribs support the walls of the trunk and may be united with a plate-like breast-bone, the sternum. Ribs that are not attached to the sternum are called false ribs. The appendicular skeleton serves to support the appendages and fasten them to the axial skeleton. The anterior appendages are joined to the pectoral girdle; the posterior appendages to the pelvic girdle. The bones of these girdles and of the appendages are shown in Figure 348. The appendicular skeleton of fishes is usually more simple than that of the higher vertebrates. Muscular System. 1 -- The "flesh" of the vertebrates con- sists largely of muscle. Muscular tissue is capable of con . ^-tion and is responsible for all the movements of an animal, rhe muscles are attached to the bones by tendons. The body muscles are called axial, those of the appendages, appendicular. The muscles of the internal organs are involuntary, i.e. they do not depend upon the will of the animal (see p. 74). Digestive System. The organs of digestion vary considerably among the vertebrates. The mouth opens into a buccal cavitv which is usually provided with jaws generally bearing teeth. The teeth are used to hold the food and often to masticate it. In many cases a fluid from salivary glands enters the buccal cavity and is there mixed with the food, making it easier to swallow and digest. Following the buccal cavity is the pharvnx. In lower vertebrates and in the embryos of higher forms the pharynx opens to the outside by gill-slits. The (esophagus leads from the pharynx to the stomach. It is usually a narrow tube, but may be en- larged as in birds, to form a crop for storing and softening food. The stomach varies in shape and structure according to the kind of food to be digested in it. Its walls contain glands which 1 A general account of the systems of organs and their functions will be found on pages 76 to 79. 406 COLLEGE ZOOLOGY secrete digestive ferments or enzymes (p. 220) and hydro- chloric acid; these help dissolve the food so that it can he absorbed. A circular muscle, called the pyloric sphincter, regu- lates the passage of food into the small intestine. Connected with the small intestine by a bile duct is the liver. This organ secretes an alkaline fluid called bile which is poured into the intestine, where it divides fatty food into particles fine enough to penetrate the walls of the intestine. Often an en- largement, the gall-bladder, is present, in which the bile is stored. The liver also changes sugar into a substance called glycogen, which is stored up as a reserve for the future needs of the animal. Another large gland, the pancreas, secretes a digestive fluid, the pancreatic juice, which enters the intestine through the pancreatic duct. This fluid contains three important ferments; (i) amylopsin, which forms soluble sugar from starch, (2) trypsin, which converts proteid into peptones, and (3) steapsin, which changes fat into soluble fatty acids and glycerin. The intestine is usually longer than the body and therefore coiled within the abdomen. Through its walls most of the di- gested food is absorbed into lymphatic tubes and blood capil- laries. The absorbent surface is often increased by folds and small prominences called mlli. Undigested particles are formed into fceces in the posterior part of the intestine and ejected through the anus. In many vertebrates the intestine opens into a terminal sac, the cloaca, into which the excretory and reproductive ducts also open. Circulatory System. - - The blood into which the digested food passes from the alimentary canal consists of a colorless plasma containing .passive red corpuscles and active, ameboid, colorless corpuscles. The color of the red corpuscles is due to the presence of a substance called htzmoglobin. The heart of vertebrates lies in a part of the ccelom termed the pericardium. It consists of at least two chambers: (i) an auricle into which the blood is brought by the veins, and (2) a ventricle which forces the blood through the arteries. PHYLUM CHORDATA 407 The smallest blood vessels are called capillaries. The ex- change of substances between the blood and tissues takes place through the walls of the capillaries. Certain capillaries unite to form veins, which carry blood from all parts of the body to the heart. Arterial blood leaves the heart chiefly through the aorta. The aorta gives off branches which in turn branch until they end in minute arterial capillaries. The functions of the circulatory system are like those of this system in invertebrates, i.e. the transportation of nutriment, oxygen, and waste products from one part of the body to another. In close connection with the circulatory system are a number of spaces and channels com- prising the lymphatic system. Lymph is a clear fluid containing ameboid cells like the colorless blood corpuscles. Respiratory System. - - Two kinds of respiration may be recognized, (i) external respiration, during which oxygen passes into the blood from the air or water and carbon dioxide passes out of the blood, and (2) internal respiration, during which the blood supplies oxygen to and takes carbon dioxide from the cells of the body. External respiration is carried on by gills in most aquatic vertebrates and by lungs in terrestrial vertebrates. Respiration also takes place to some extent through the skin. Oxygen unites readily with the haemoglobin in the red corpuscles. The haemoglobin is then transported by the blood from the respiratory organs to the capillaries, where it breaks up, the oxygen being absorbed by the tissues. Carbon dioxide from the tissues becomes chemically combined with the sodium in the blood, is carried to the respiratory organs, and discharged to the outside. Excretory System. - - The substances resulting from the oxi- dation of protoplasm are eliminated by the kidneys, respiratory organs, and skin. These waste products are carried by the blood. Carbon dioxide is eliminated by the respiratory organs. Ni- trogenous waste products are excreted by the kidneys in the form of urea or uric acid. Ducts, called ureters, lead from the kidneys either directly to the outside or empty the excretion into a storage vesicle, the urinary bladder. 408 ZOOLOGY Nervous System. -- The nervous system of vertebrates is more complex than that of any other animals. It comprises a central nervous system consisting of the brain and spinal cord, a peripheral nervous system consisting of the cerebral and spinal nerves, and a sympathetic system. The brain is made/up of three primary vesicles, a fore-brain, mid-brain, and hind-brain. The fore-brain is thought to correspond to the cerebral vesicle of clr e.eorl FIG. 349. Diagram of the spinal cord showing the paths taken by nervous impulses. The direction of the impulses is indicated by arrows, c.c, central canal; col, collateral fibers; c.cort, cell in the cerebral cortex; c.g, smaller cerebral cell; d.c, cells in dorsal horn of gray matter; d.r, dorsal root; g, gan- glion of dorsal root; g.c, ganglion cell in dorsal ganglion; g.m, gray matter; M, muscle; m.c, cell in medulla oblongata; m.f, motor fiber; S, skin; s.f, sen- sory fiber ; sp.c, spinal cord ; v.c, cells in ventral horn of gray matter ; v.r, ventral root; w.m, white matter. (From Holmes, after Parker.) Amphioxus (Fig. 343, br). The fore-brain usually gives rise to a pair of cerebral hemispheres, the mid-brain to a pair of optic lobes, and the hind-brain to the cerebellum and medulla oblongata. The spinal cord is a thick tube directly connected with the brain ; it passes through the neural arches of the vertebral column. The peripheral nervous system consists of ten to twelve pairs of cranial nerves and a number of pairs of spinal nerves. The origin, distribution, and function of the cranial nerves are indicated in Table XIV. The spinal nerves arise from the spinal cord in pairs, one on PHYLUM C1IOKDATA 409 TABLE XIV THE NUMBER, NAMES, ORIGIN, DISTRIBUTION, AND FUNCTIONS OF THE CRANIAL NERVES OF VERTEBRATES NUMBER NAME ORIGIN DISTRIBUTION FUNCTION I Olfactory Olfactory Lining of nose Sensory lobe of fore-brain II Optic Second vesi- Retina of eye Sensory cle of fore- brain III Oculomotor Ventral re- Muscles of eye Motor gion of mid-brain IV Trochlearis Dorsal re- Superior oblique Motor (patheticus) gion of the muscle of eye mid-brain V Trigeminal Side of me- Skin of face, mouth, Largely (trifacial) dulla and tongue, and sensory (hind- muscles of jaws brain) VI Abducens Ventral re- External rectus Motor gion of muscle of eye medulla VII Facial Side of me- Chiefly to muscles of Largely dulla face motor VIII Auditory Side of me- Inner ear Sensory dulla IX Glossopharyn- Side of me- Muscles and mem- Sensory geal dulla branes of pharynx, and and tongue motor X Vagus (pneu- Side of me- Posterior visceral Sensory mogastric) dulla arches, lungs, heart, and stomach and intes- motor tines XI Spinal acces- Side of me- Chiefly muscles of Sensory sory (not dulla shoulder and present in motor all verte- brates) XII Hypoglossal Ventral re- Muscles of tongue Motor (not present gion of and neck in all verte- medulla brates) 410 COLLEGE ZOOLOGY either side in each body segment, and pass out between the ver- tebras. Each nerve has two roots (Fig. 349), a dorsal root (d.r) and a ventral root (v.r). The dorsal root possesses a ganglion (g) containing nerve cells (g.c). Its fibers carry impulses tow- ard the spinal cord from various parts of the body and are therefore sensory. The fibers of the ventral root carry impulses from the spinal cord to the tissues and are therefore motor. The constitution of the nerve cells (neurons) is similar to that of the earthworm (p. 225). The direction of the nervous impulses is indicated by arrows in Figure 349. On each side of the spinal cord is a chain of ganglia which is connected at various places with the central nervous system. This is known as the sympathetic nervous system. These ganglia send nerves chiefly to the alimentary tract, circulatory system, and glandular organs. Sense-Organs. - - Vertebrates possess a number of highly developed sense-organs nose, eyes, and ears. In addition to these there are many species with sense-cells, single or in groups, scattered over the body. In some of the lower vertebrates these take the form of lateral line organs (p. 427) of doubtful function. Usually sense-organs of taste occur as pits over the tongue and soft palate. The sense-organs of smell are located in the nose. The nose consists of a pair of cavities at the anterior end of the body. These cavities are lined with folds of mucous epithelium covered with olfactory sense-cells. The two ears of vertebrates arise as cavities of the skin at the sides of the midbrain. They are rather complicated in structure, as indicated in Figure 350. They function as organs of hearing and equilibrium. The internal ear is called the membranous labyrinth and is enclosed by cartilage or bone. Within the labyrinth is a fluid called endolympk; and between the labyrinth and the sur- rounding cartilage or bone is a fluid called perilymph. The labyrinth is usually constricted into two chambers, (i) a dorsal PHYLUM CHORDATA ca nss Htricnlus (Fig. 350, u) which gives rise to three semicircular canals (ca, ce, cp), and (2) a ventral sacculns (,v) bearing an out- growth called the cochlea (I). The bases of the semicircular canals are enlarged into ampulla (aa, ae, ap) containing cells with long sense hairs which record change of position in any direction and are therefore organs of equilibrium. The cochlea of the sac- culus in higher vertebrates is well developed, contains the auditory sense- cells, and is the true organ of hearing. Sound waves are brought to the cochlea in the ears of higher vertebrates by means of the middle ear. This con- sists of a vibrating membrane, the tympanum, which transmits vibrations to the inner ear with the aid of a chain of three bones. In many vertebrates a funnel-shaped fold of skin, which is supported by cartilage, and called the pinna or ex- ternal ear, aids in catching sound waves. In aquatic animals this collecting ap- paratus is not necessary, since the water carries the sound waves to the tissues which transmit them directly to the inner ear. The eyes are the most complex of the sense-organs of vertebrates. They arise in part from the sides of the fore- brain and in part from the skin and connective tissue. The principal elements of structure and the method of action may be pointed out by means of a diagram of the human eye (Fig. 351). The eye is nearly spherical. It consists of three concentric coats enclosing transparent substances. The outer or sclerotic coat (Set) is the white of the eye. It is composed of connective tissue and FIG. 350. Semidiagram- matic figure of the left membranous labyrinth of a vertebrate, aa, ae, ap, am- pullje of semicircular canals; ass, apex of sinus utriculi superior; ca, ce, cp, anterior, external, and posterior semi- circular canals; cus, utriculo- saccular canal; de,se, ductus and saccus endolymphaticus; /, recessus sacculi; rec, re- cessus utriculi; 5, sacculus; sp, sinus utriculi posterior; ss, sinus utriculi superior ; u, utriculus. (From Wieders- heim.) 412 COLLEGE ZOOLOGY ec; Civ serves as a protective covering. In front of the lens (L) the sclerotic coat forms a transparent area called the cornea (c). Beneath the sclerotic coat is the middle coat or choroid (Ch) ; this is supplied with blood vessels and contains a great deal of black pigment ( P. E) which prevents light from entering except through the cornea. The choroid coat is separated from the sclerotic coat and perfo- rated just in front of the lens; the opening is the pupil, and a part of the choroid surrounding the pupil is the iris (/). The inner coat, the retina (R), is the most important, since it is the sensitive layer, being an expansion of the optic FIG. 351. Diagrammatic horizontal Section [ of the eye of MAN. c, cornea; Ch, choroid nerve (O.N}. It lines (dotted); C. P., ciliary processes; e.c, epithelium ^ e cav jty back of the of cornea; e.cj, conjunctiva; f.o, yellow spot; /, iris; L, lens; O.N, optic nerve; os, ora lens. The lens (L) is serrata; o-x, optic axis; p.c.R anterior non- biconvex and trans- visual portion of retina; P.E, pigmented epithelium (black); R, retina; sp.l, suspen- parent. It IS attached sory ligament; Scl sclerotic; F.ff., vitreous to thfi choroid coat by chamber. (Prom Parker and Haswell, after Foster and Shore.) a suspensory ligament (sp. /) , and separates the small anterior cavity, filled with a fluid called aqueous humor, from the large posterior cavity, filled with a jelly-like substance called vitreous humor ( V.H.). The eye is like a camera in certain respects. With the aid of the lens an image is formed on the sensitive retina of the objects in front of the cornea. The eye is accommodated for PHYLUM CHORDATA 413 recording images of distant and near objects by changes in the convexity of the lens caused by its own elasticity, and the pull exerted upon it by the elastic choroid coat and the ciliary muscles (C.P.). In viewing near objects the ciliary muscle counteracts the pull of the choroid coat and allows the lens to assume a more convex shape, whereas distant objects are made distinct by the flattening of the lens. The eye is moved by six muscles; four straight (rectus) and two oblique. Folds of skin, the eyelids, protect the eye in higher vertebrates. There may be three eyelids : an upper and a lower lid which act vertically, and a lateral lid (nictitating membrane) which moves outward from the inner angle of the eye. In some reptiles the eyelids are transparent and fused over the eye. Terrestrial vertebrates have lacry-mal glands in connection with the eye, the secretion from which keeps the surface of the eye- ball moist and washes away foreign particles. Reproductive System. - - The sexes of vertebrates, with few exceptions, are separate. The reproductive organs arise in close connection with the excretory organs, and the excretory ducts may serve to carry germ-cells to the exterior. Fertiliza- tion takes place in some AMPHIBIA and most fishes after the eggs are extruded. In other vertebrates fertilization is internal. Most vertebrates lay eggs, i.e. are oviparous, but many of them, especially mammals, bring forth their young alive, i.e. are viviparous. CHAPTER XV SUBPHYLUM VERTEBRATA: CLASS I. CYCLOSTOMATA THE CYCLOSTOMATA (Fig. 352) are vertebrates that have a superficial resemblance to eels, but differ from them as well as from all other vertebrates in many important respects. They are without functional jaws and lateral appendages, and have FIG. 352. CYCLOSTOMES. A, Bdellostoma dombeyi. Light apertures along side are mucous pits; dark apertures are branchial openings. B, Myxiitr tfutinosa. Left common branchial aperture is at *. C, Petromyzon m-ariim* (From Dean.) only one olfactory pit. Cyclostomes are commonly known as hags and lampreys. There are two subclasses, the MYXINOIDEA or hagfishes, and the PETROMYZONTIA or lampreys; the former are all marine; the latter are found both in salt water and fresh water. They usually feed on the mucus, blood, and even the internal organs of fishes, which they attack with their rasping mouth, 414 CLASS CYCLOSTOMATA 415 i. THE LAMPREY - - PETROMYZON Petromyzon marinus, the sea lamprey (Fig. 352, C), inhabits the waters along the Atlantic coast of North America, the coasts of Europe, and the west coast of Africa. It swims about near the bottom by undulations of its body, or, when in a strong cur- rent, progresses by darting suddenly forward and attaching itself to a rock by means of its suctorial mouth. In the spring the lamprey ascends the rivers to spawn. External Features. - - The lamprey reaches a length of about three feet. Its body is nearly cylindrical, except at the posterior end, where it is laterally compressed. There is no exoskeleton. The skin is soft and is made slimy by secretions from epi- dermal glands. It is mottled greenish brown in color. A row of segmental sense pits, the lateral line, lies on each side of the body and on the head. The mouth (Fig. 353, mth) lies at the bottom of a suctorial disc, the buccal of the he A ad f Pet ""*y*" '"- ' nn us. hue. I, buccal funnel; funnel (buc.f), and is held open by a ////, mouth ; />, papilla; ; ring of cartilage (Fig. 354, 2). Around '; '; ' 3 - teet . h f buccal f "" nel; /". teeth of tongue. (From the mouth are a number of papilla Parker.) (Fig. 353, p) and horny teeth (/'-/ 3 ). Just beneath the mouth is a piston-like tongue which also bears teeth (/ 4 ). On each side of the head is an eye, and, posterior to the eye, seven gill-slits (Fig. 352, C). Between the eyes on the dorsal surface is a single opening, the nasal aperture (Fig. 355, na"). The anus opens on the ventral surface near the posterior end; just behind it is the urino genital aperture in the end of a small papilla. There are two dorsal fins and one caudal fin (Fig. 352, C), FIG. 353. Ventral view 416 COLLEGE ZOOLOGY The Skeleton (Fig. 354). --The notochord of Petromyzon persists as a well-developed structure in the adult (Fig. 355, nc\ Fig. 354, 12). In the trunk region the notochord is supple- mented by small cartilaginous neural arches (Fig. 354, jj). Cartilaginous rays hold the fins upright. The organs in the head are supported by a cartilaginous skull and a cartilaginous bran- chial basket (10). The skull is very simple. Its principal parts, as shown in Figure 354, are an annular cartilage (2) which holds the mouth FIG. 354. Lateral view of skull of Petromyzon mariniis. i, horny teeth; 2, annular cartilage; 3, anterior labial cartilage; 4, posterior labial cartilage; 5, nasal capsule; 6, auditory capsule; 7, dorsal portion of trabeculse; 8, lateral distal labial cartilage; Q, lingual cartilage; 10, branchial basket; n, cartilag- inous cup supporting pericardium ; 12, sheath of notochord ; 13, anterior neural arches fused together. (From Shipley and MacBride, after Parker.) open, two labial cartilages (3, 4) which form a roof-like support for the buccal funnel, a lingual cartilage (p) supporting the tongue, an olfactory capsule (5), two auditory capsules (6), and a cranial roof (7). The branchial basket is a cartilaginous frame- work (zo) which supports the gill-sacs and the walls of the peri- cardium (n). The Muscular System. - - The muscles of the body-wall are zigzag myotomes (Fig. 355, d.m, v.m.). The tongue (/, f 1 ) is moved by large muscles (p.m.t, r.m.tJ), and the buccal funnel is supplied with a number of radiating muscles. The Digestive System. - - Petromyzon lives on the blood of other animals. The expansion of the buccal funnel (Fig. 355, o.f.) causes the mouth to act like a sucker and enables the ani- mal to cling to stones or to fasten itself to fishes such as shad, 2 E 4 l8 COLLEGE ZOOLOGY sturgeon, cod, and mackerel. With its rasp-like tongue a hole is made in the flesh of the victim and the blood sucked out. The mouth opens into a buccal cavity (Fig. 355, m). Two tubes lead posteriorly from the latter, a dorsal (esophagus (a?s) and a ventral respiratory tube (/./), guarded by a fold called the velum (vl). There is no distinct stomach. The oesophagus is separated from the intestine (int) only by a valve. A fold in the intestine called the typhlosole (see also p. 219) forms a sort of spiral valve. A liver (Ir) is present, but there is usually no bile duct (b.d.) in the adult. The Circulatory System. - - Petromyzon possesses a heart, a number of veins and arteries, and many lymphatic sinuses (Fig. 355, s, s'). The heart lies in the pericardium (pc), and consists of a ventricle (v) which forces the blood into the arteries and an auricle (au) which receives the blood from the veins. A renal portal system is absent. The Respiratory System. - - Respiration is carried on by means of seven pairs of gill pouches (Fig. 355, br.$), which open to the outside by the gill-slits (e.a) and internally to the respiratory tube (r.t). Each gill pouch contains numerous gill lamella (br.$). Water is taken into the gill-sacs through the gill-slits, and discharged by the same openings. The Nervous System. - - The brain (Fig. 355, br.} of the adult lamprey is very primitive and in many respects similar to that of the embryos of higher vertebrates. It is remarkable because of its thin membranous roof and the small band-like cerebellum. The spinal cord is flat, and lies on the floor of the neural canal (n.ca.). The Sensory Organs. --Organs of taste, smell, hearing, and sight are present in the lamprey. The end organs of taste are situated between the gill pouches on the pharyngeal wall. The organ of 5 mell is an olfactory sac (Fig. 355, no) which lies in the nasal capsule (Fig. 354, 5) and opens by a nasal aperture (Fig. 355, na") on the dorsal surface between the eyes. The olfactory CLASS CYCLOSTOMATA 419 sac gives off ventrally a tube of unknown function, called the hypophysis or pituitary body (Fig. 355, na'). The auditory organs of Petromyzon, which lie in the auditory capsule (Fig. 354, 6), have only two semicircular canals instead of the usual number, three (Fig. 350). The hagfish has only one. The eyes of the lamprey are poorly developed. The Urinogenital System. - - The excretory and reproductive systems are so closely united in the lamprey that it is custo- mary to treat them together as the urinogenital system. The kidneys lie along the dorsal wall of the body-cavity, and each pours its secretions by means of a duct, called the ureter, into the urinogenital sinus, and thence to the outside through the urinogenital aperture. The sexes are separate, but eggs are some- times present in the testis of the male. The single gonad (Fig. 355, ov) fills most of the abdominal cavity. The germ-cells break out into the ccelom, make their way through two genital pores into the urinogenital sinus, and then pass out through the urinogenital aperture into the water, where fertilization occurs. Development. - - The eggs produce larvae known as Ammo- ccetes. The larva differs in many respects from the adult, and apparently represents a stage of development intermediate between Amphioxus and a primitive vertebrate. As in Amphi- oxus, food particles are drawn into the mouth by means of a current of water produced by cilia. An endostyle, which repre- sents the thyroid gland of the adult, secretes mucus which en- tangles the food and carries it into the alimentary canal. The Ammoccetes lies buried in mud and sand, and probably keeps its skin free from bacteria, fungi, and other parasitic growths by means of an integumentary secretion. In the winter of the third or fourth year the larval lamprey undergoes a meta- morphosis during which the structure and habits of the adult are acquired. Relationships. - - The hagfishes and lampreys are the lowest vertebrates. Many of their structures, such as the cranium and vertebral column, are very primitive, but others are appar- COLLEGE ZOOLOGY ently highly specialized. The absence of jaws and of limbs may be due to degeneration. Economic Importance. - - The flesh of the lamprey is used as food both in Europe and America. The number of lampreys, however, has decreased so much within recent years that their value as food is now almost negligible. Fishermen charge the lamprey with destroying numbers of food fishes, which are attacked just beneath the pectoral fins. The flesh is torn with their rasping teeth and the blood sucked out of the body. 2. CYCLOSTOMATA IN GENERAL SUBCLASS I. MYXINOIDEA. THE HAGFISHES. One family, the MYXINID.E, belongs to this subclass. The MYXINID*: are all marine, and are represented by three genera: (i) Bdcllostoma (Fig. 352, A) and (2) Paramy\inc in the Pacific, and (3) Myxine (Fig. 352, B) in the Pacific, Atlantic, and North Sea. These hagfishes differ from the lampreys in a number of characters: (i) the nasal aperture is terminal; (2) the pituitary body opens into the pharynx; (3) there are four tentacles on either side of the mouth; (4) the oral sucker is absent, and there is only a single large tooth; (5) there are no neural arches in the trunk, and the branchial basket is poorly developed; and (6) the gills may open by a single common pore on each side (Myxine). The hagfishes live in the mud of the sea bottom down to a depth of nearly three hundred and fifty fathoms. They are very destructive to fishes, especially those caught on lines or in nets, boring their way into the body and eating out the soft parts. Cod and flounders are the fish usually attacked. SUBCLASS II. PETROMYZONTIA. - - THE LAMPREYS. - - The lampreys all resemble Petromyzon in general structure. There is a single family, PETROMYZONTID.E, and a number of genera. Petromyzon inhabits the rivers and seas of America, Europe, and Asia; Lampetra and Ichthyomyzon live in North American streams and lakes; Mordacia and Geotria in South America and Tasmania. CLASS CYCLOSTOMATA 421 Lampetra wilder}, the l>n>ok lamprey of North America, breeds in the spring. Stones are moved by means of the buccal funnel until a space is cleared on the bottom where a number of individuals congregate (Fig. 356). A male clings to the head of a female for a moment, winds his tail about her body, and discharges spermatozoa over the eggs when they are extruded. The adults die soon after spawning; they probably take no food, and are there- fore not injurious to fishes. FIG. 356. Lampetra wilder!, in the act of spawning. (From Shipley and MacBride, after Dean and Sumner.) FIG. 357. Palaospon- dylus gunni, a Devonian Cyclostome. (From Dean, after Traquair.) A fossil vertebrate, Palaospondylus gunni (Fig. 357), was probably closely allied to the cyclostomes. It was found in the Devonian rocks of Scotland and is about an inch long. CHAPTER XVI SUBPHYLUM VERTEBRATA: CLASS II. ELASMO- BRANCHII THE elasmobranchs are the sharks, dogfish sharks, and rays or skates. They resemble the true fishes (PISCES, Chapter XVII) in external form, but differ from them so widely in struc- ture that they are placed in a class by themselves. 1 The elasmobranchs exhibit a number of structural advances over the cyclostomes; there are paired fins, a lower jaw, gill arches, and placoid scales. Among the peculiarities which separate the elasmobranchs from the true fishes (PISCES) are the absence of membrane bones, of an air bladder, and of true scales, and the presence of skeletal characteristics which are not found in true fishes. Two subclasses of living elasmobranchs are recog- nized: the SELACHII or sharks and rays, and the HOLOCEPHALI or chimaeras. i. THE DOGFISH SHARK SQUALUS ACANTHIAS The common dogfish shark (Fig. 358) is abundant in the waters off the coast of New England and northern Europe. FIG. 358. The dogfish shark, Squalus acanthias. (From Dean, after Goode.) 1 See Jordan, Guide to (he Study of Fishes, Vol. I. pp. 506-511. 422 CLASS ELASMOBRANCHII 423 CO . - , tfc 55 cd tn -^ is ^ ^3 ^ C 5 .- . >- ' kj C 8*1; 3 rt tn '/] C aTg -4 _rt ^ -*-) S s r ] *- O P. &U X C. S ." O 3 C3 QJ B) --^7 rt <=q Srf~ ^a"r..g .X O O ^ B) 3 6 ^'' is *" cd u ^ rt rt S O -C O c< o 1 S S d ^ 4J O C 3 e ca i; o|S s 0) 2* *- o> "S rf co' a ^ & cd 3 4J CJ * u. -3 -*- 1> ~ U ft IS 3 cj > -a 3 ? I5"| CO 3 >:5 -MI., C3 >. y S a3 O cd a. > - o ju O ni *-J - - C rt c p r-< C ^ Ij "" 1J rt ~ F^H o j /i 3 : J .9 flfe; .. o JS 5 -r; .. cs g OJ ni n." ft <-> ^< 424 COLLEGE ZOOLOGY It is widely used for laboratory study, and detailed accounts of its anatomy may be found in several laboratory manuals. It will suffice here to point out certain of its more prominent characteristics. External Features. 1 - - The body is fusiform and about two and one half feet long. There are two dorsal fins (Fig. 359, D) each with a spine (not shown in Fig. 359) at the anterior end, two pectoral fins, and two ventral fins (VF). The ventral fins in the male possess cartilaginous appendages, known as daspers (CL'}. The tail is heterocercal (see Chap. XVII). The mouth is a trans- verse slit on the ventral surface of the head. On either side above the mouth is an eye, and in front an olfactory organ (Fig. 359, N}. Anterior to each pectoral fin are six gill-slits (GS), the first of which is situated just back of the eye of %ranTand and modified as a spiracle (SP). Between shark viewed from the ventral fins is the cloacal opening (CL). side and top. (From r^i f j . .-, . , . , Dean ^ I he surface is covered with placoia scales or dermal denticles (Fig. 360) which form shagreen. They represent a primitive exoskeletal structure and have been the starting-point for the development of the scales and bony plates of the true fishes. Over the jaws they are modified as teeth with their points directed backward, and are used for holding and tearing prey. A placoid scale consists of a bony basal plate with a spine in the center composed of dentine and covered with enamel. The Skeleton. - - The skeleton is cartilaginous. The axial skeleton consists of the vertebral column, skull, and visceral arches. The vertebra (Fig. 359, C') are hour-glass-shaped (amphiccelous), and the notochord persists in the lenticular spaces between them. The skull is much more highly developed than that of the cyclostomes. It is composed principally of the cranium or brain case (CC), two large anterior nasal capsules, 1 Figure 350 shows the anatomy of a shark which differs slightly from that of the dogfish shark. CLASS ELASMOBRANCHII 425 and two posterior auditory capsules. The visceral skeleton com- prises the jaws, the hyoid arch, and five branchial arches. The appendicular skeleton consists of the skeletons of the fins (B, R) and those of the pectoral and pelvic girdles which support them. The Digestive System. The alimentary canal is longer than the body. Following the mouth (Fig. 359, M} is a large pharynx into which open the spiracles and gill-clefts. The pharynx leads into the short, wide oesophagus which opens into the U-shaped stomach (S}. The hinder end of the stomach is provided with a sphincter, or circular muscle marking it off from the intestine. The latter is provided interiorly with a spiral fold of mucous membrane, called the spiral valve (/), which furnishes a large surface for absorption and prevents the too rapid passage of food. The liver (L) is large, and consists of two long lobes; its secretion, the bile, is stored up in a gall-bladder and emptied through the bile-duct into the intestine. A pancreas and spleen are also present. The Circulatory System (Fig. 361). --As in the cyclostomes and most of the true fishes, the heart (Fig. 361, s.v, an, v, c.arf) contains venous blood only. This is pumped through the ventral aorta (v.ao) and thence into the afferent branchial arteries (a.br.a), becoming oxygenated in the capillaries of the gills. It then passes into the efferent branchial arteries (e.br.a), which carry it to the dorsal aorta (d.ao). The dorsal aorta supplies the various parts of the body as shown in Figure 361. Veins carry the blood back to the heart, opening into the sinus venosus (s.v). Other veins, called the hepatic portal system (h.p.v), transport the blood from the alimentary canal, pancreas, and spleen to the liver. A third system, the renal portal system (r.p.v), conveys the blood from the hinder portion of the body to the kidneys. The Respiratory System. - - Respiration is carried on by means of gills. These are folds of mucous membrane well supplied with blood-vessels and borne by the hyoid arch and first four branchial arches. They are supported both by these arches and CLASS ELASMOBRANCHII 427 by gill-rays. Water entering the mouth passes between the branchial arches and out through the gill-slits (Fig. 359, GS), thus bathing the gills and supply- ing oxygen to the branchial blood- vessels. The Nervous System. - - The brain (Fig. 362) is more highly developed than that of the cyclo- stomes. It possesses two remark- ably large olfactory lobes (j), a cerebrum of two hemispheres (4), a pair of optic lobes (7), and a cerebellum (g) which projects backward over the medulla oblon- gata (10). There are ten pairs of cranial nerves (Fig. 362 and Table XIV). The spinal cord is a dorso- ventrally flattened tube with a narrow central canal; it is pro- tected by the vertebral column. Spinal nerves arise from its sides in pairs. The Sense-organs. tory sac (Fig. 362) is characteristi- cally large in elasmobranchs. The ears (Fig. 350) are membranous V VII VIII FIG. 362. Brain of a dogfish The OJfaC- shark, .SYv///Mz i al it! us, dorsal view. 2, pineal stalk; 3, olfactory lobe ; 4, cerebral hemisphere ; 5, thalamencephalon ; 7, optic Q, cerebellum; 10, roof of _-brain; //, 12, ij, 14, muscles SaCS each with three Semicircular that move the eyeball; 15, ninth 16, i6a, branches of vagus 17, main trunk of vagus II-X, roots of the cranial (From Shipley and Mac- canals; they lie within the auditory nerve J nerve Capsules. The eves (Fig. 362) are nerve; well developed. ' Along each side of the head and body is a longi- tudinal groove, called the lateral line (Fig. 359, LL), and on the head are also mucous canals which open on the dorsal and ventral surfaces and end in ampullae at the anterior end of the snout. These structures are supposed to be sensory in function. 428 COLLEGE ZOOLOGY The Urinogenital System. - The dogfish shark possesses two ribbcn-like kidneys (Fig. 359, A'), one on either side of the dorsal aorta. Their secretion is carried by small ducts into a larger duct, the ureter ( UD), which empties into a urinogenital sinus ; it then passes out of the body through the cloaca! aperture (C L}. A series of yellowish gland-like bodies, called suprarenals, are associated with the kidneys. The spermatozoa of the male arise in two testes and are car- ried by the vasa deferentia into the urinogenital sinus. During copulation they are transferred to the oviducts of the female with the aid of the daspers. The eggs of the female arise in the single ovary (Fig. 359, OF), which is attached to the dorsal wall of the abdominal cavity. They break out into this cavity and enter the funnel-like open- ings of the oviducts (OVD). When they reach an expanded portion, called the oviducal gland, they receive a horny covering which protects them from injury after they are laid. 2. ELASMOBRANCHS IN GENERAL The chief characteristics of the elasmobranchs are the presence of a cartilaginous skeleton, a persistent notochord, placoid scales, a spiral valve in the intestine, and claspers in the male ; and the absence of a gill-cover or operculum, pyloric caeca, and an air- bladder. The mouth is a transverse aperture on the ventral side of the head. SUBCLASS I. SELACHII. - - There are two distinct types of elasmobranchs belonging to this subclass: (i) sharks, which are slender and cylindrical and have the gill-slits on the side; and (2) rays, which are flattened dorso-ventrally and have the gill- slits underneath. Order i. Squall. -- SHARKS AND DOGFISH SHARKS. -- The sharks and dogfish sharks resemble in general the common horned dogfish shark (Fig. 358). Most sharks are under eight feet in length, and although carnivorous and voracious, very seldom attack man. They feed principally on small fish, squids, and CLASS ELASMOBRANCHII 429 CRUSTACEA. The great white shark, Carcharodon carcharias, occurs in all warm seas. It reaches a length of over thirty feet and has earned the name of man-eater by occasionally devouring a human being. One of the most peculiar sharks is the hammer- FIG. 363. Hammerhead shark, Sphyrna tudes. af., anal fin; c.f, caudal fin; cl, clasper; e, eye. (From Lankester's Treatise, after Day.) head, Sphyrna tudes (Fig. 363), which is also found in warm seas. Its head is shaped like the head of a mallet, with an eye (e) at either end. Order 2. Raji. - - RAYS or SKATES. - - The rays or skates are flattened dorso-ventrally and adapted for living on the bottom. FIG. 364. Sawfish, Pristis pectinatus. A, side view. B, ventral view. (From Dean; A, after Goode.) Some of them are only slightly flattened, whereas others are broader than long. The sawfish, Pristis pectinatus (Fig. 364), lives in tropical seas and is abundant in the Gulf of Mexico. It reaches a length of from ten to twenty feet. The saw of a large specimen is about five feet long; it is used as a 43 COLLEGE ZOOLOGY FIG. 365. Sting-ray, Dasyatis sabina, dorsal view. Evermann.) (From Jordan and weapon of defense, and dangerous sidewise strokes can be made with it. The sting-ray, Dasyatis sabina (Fig. 365), lives half buried in the sand along the coast of Florida. There is a barbed spine on its whip- like tail which makes a painful wound if driven into the hand or naked foot. The torpedo (Family TORPEDINID^E, Fig. 366) is inter- esting because of the presence of modified bundles of muscles (Fig. 366, EO] lying on either side of the head which are capable of storing up electrical energy and discharg- ing it. The discharge of these elec- tric organs is sufficient to paralyze large animals ; they thus may serve as weapons of offense and defense. FIG. 366. Torpedo with electric organ, EO, and brain exposed, dorsal view. Br, branchial sacs; GR, sensory canal tubes of the skin; Le, electric lobe of brain; O, eye^; Tr, trigeminal nerve; V, vagus nerve. (From Sedg- wick's Zoology, after Gegenbaur.) CLASS ELASMOBRANCHII 431 SUBCLASS II. HOLOCEPHALI. - -The members of this subclass differ from the SELACHII in a number of minor structural char- acters. There is a single family, the CHIM^RID^;, containing 77V FIG. 367. Chimczra monstrosa, male, m, mouth; n.p, frontal clasper: op, operculum. (From the Cambridge Natural History.) three genera. The species shown in Figure 367 is the sea-cat of the North Atlantic. 3. THE ECONOMIC IMPORTANCE OF ELASMOBRANCHS Many destructive species belong to the elasmobranchs. The smooth dogfish shark, Mitstclus canis, is an important enemy of the lobster. It is estimated that the minimum number of lob- sters destroyed by these dogfish sharks in Buzzards Bay during one year is about 640,000. The sand-shark, Carcharias Uttoralis, devours large numbers of valuable fishes, including menhaden, flounders, and scup. The horned dogfish shark, S qualm acan- thias (Fig. 358), is the most serious destructive agency with which fishermen have to contend. It devours valuable food fishes, drives away or destroys schools of squid used by the fishermen for bait, and robs and injures nets and other fishing gear. Experts estimate the damage from dogfish sharks to marketable fish and fishing gear owned in Massachusetts at not less than $400,000 per year. They suggest that dogfish sharks be converted into oil and fertilizer so as to make it profitable for fishermen to capture them and thus bring about a decrease in their numbers. CHAPTER XVII SUBPHYLUM VERTEBRATA: CLASS III. PISCES THE PISCES are the true fishes. The class includes the com- mon fishes and the lung-fishes. They are aquatic animals and are, therefore, adapted to life in the water. The respiratory organs of fishes are gills. Usually a dermal exoskeleton of scales or bony plates furnishes a protective covering for the body. Living fishes are grouped into two subclasses. Subclass I. TELEOSTOMI. - - Fishes with a skeleton consist- ing wholly or partially of bone, usually wjth scales (never placoid scales), and a well-developed operculum covering the gills. Subclass II. DIPNOI. - - Fishes with a skeleton of cartilage and bone, a single or double lung, and an operculum covering the gills. i. A BONY FISH- -THE PERCH External Features. - - The yellow perch, Perca flavescens (Fig. 368), inhabits the fresh-water streams and lakes of the north- FIG. 368. Perch, Perca fiavescens. (From Dean, after Goode.) 432 CLASS PISCES 433 eastern United States, and ranges west to the Mississippi Valley. Its body is about a foot long and is divisible into head, trunk, and tail. There are two dorsal fins, a caudal fin, a single median anal fin just posterior to the anus, two lateral ventral fins, and two lateral pectoral fins. On each side of the body is a lateral line. The head bears a mouth with well-developed jaws armed with teeth, a pair of lateral eyes, a pair of nasal apertures in front of each eye, and gill-covers or opercula beneath which are the gills. The skin is provided with a number of dermal scales which are arranged like the shingles on the roof of a house, and protect the fish from mechanical injury. Locomotor Organs. - - The body of the perch, and of most other fishes, is spindle- shaped and offers little resistance to the FIG. 369. -- Front view of a fish (Spanish mackerel). (From Dean.) water through which the animal swims (Fig. 369). It is kept at the same weight as the amount of water it displaces by means of an air-bladder. The fish is thus able to remain stationary without muscular exertion. The principal locomotor organ is the tail. By alternating contractions of the muscular bands on the sides of the trunk and tail, the tail with its caudal fin is lashed from one side to the other, moving in a curve shaped like a figure 8 as shown in Figure 370. Similar movements are em- ployed in sculling a boat, and the method of progress is analogous to the action of the screw of a steamer. During the flexions and extensions of the tail, the trunk is curved in such a w.ay as to bring about the most effective extension or forward stroke and a weak flexion or non-effective stroke. The fins are integumentary expansions supported by bony or cartilaginous rays. The paired lateral fins (pectoral and ven- tral) are used as oars in swimming, but only when the fish is moving slowly. They also aid the caudal fin in steering the 434 COLLEGE ZOOLOCxY animal, for, although the course is altered largely by the pointing of the head and tail in the desired direction, the lateral fins assist in swerving the body to one side or the other, either by executing more powerful strokes on one side, or by the expansion of one fin and the folding back of the other. These methods are like those used in steering a rowboat with oars. Movement up or down results from holding the lateral fins in certain positions obliquely backwards with the anterior edge higher for the ascent, and obliquely forwards for the descent. Fishes must maintain their equilibrium. in some way, since the back is the heaviest part of the body and tends to turn them over. The dorsal, anal, and caudal fins increase the vertical surface of the body (Fig. 369) and, like the keel of a boat, assist the animal in maintaining an upright position. The paired lateral fins are also organs of equilibration, acting as balancers; if both pectoral fins are removed, the an- terior end of the fish sinks downward; if a pectoral or both pectoral and ventral fins are removed from one side, the fish turns toward that side; and if all four lateral fins are cut off, the fish turns completely over with the ventral surface upward. The Skeleton. - - The e.voskeleton of the perch includes scales and fin-rays. The scales develop in pouches in the dermis. They are arranged in oblique rows and overlap like the shingles on the roof of a house, thus forming an efficient protective covering. The posterior edge of each scale which extends out from under the preceding scale is toothed, and therefore rough to the touch. Scales of this kind are called ctenoid scales (Fig. 371, A). The FIG. 370. Diagram to illustrate the mode in which the tail of an or- dinary fish is used in swimming. (From the Cambridge Natural His- tory, after Pettigrew.) CLASS PISCES 435 fin-rays support the fins. Those of the first dorsal fin (Fig. 372, Ri.}, and at the anterior edge of the anal (.4) and ventral fins (B), are unjointed and unbranched spines. The caudal (S) and pectoral fins ( Br) and most of the anal and ven- tral fins are supplied with jointed, and usually branched, soft Jin-rays. The cndoskckton (Fig. 372) consists principally of bones, and includes the skull, vertebral column, ribs, pectoral girdle, and B FIG. 371. Scales. A, ctenoid. B, ganoid. C, cycloid. (From the Cambridge Natural History; A, B, after Giinther; C, after Parker and Haswell.) the interspinal bones or pterygiophores (Fr) which aid in sup- porting the unpaired fins. The body of the fish is to a consid- erable extent supported by the surrounding water; consequently, the bones do not need to be so strong as those of land animals, like birds and mammals, which must support the entire weight of the body. The vertebra (Fig. 372, w) are simple and comparatively uni- form in structure. They are called amphicceloits vertebrae because the centrum has concave anterior and posterior faces. A typical vertebra has a cylindrical supporting centrum, a neural arch through which the spinal cord extends, a neural spine (oD) for the attachment of muscles, and short ventral projections, the parapophyses, to which the ribs are attached. The centrum of one vertebra is connected with those of the preceding and following vertebrae by ligaments. The spaces between the centra contain the remains of the notochord. 436 COLLEGE ZOOLOGY Ribs (Fig. 372, R) are attached by ligaments to the centra or parapophyses of the abdominal vertebrae and serve as a pro- tecting framework for the body-cavity and its contents. There is no sternum. I ntermuscular bones (G) are also attached to some of the vertebra?. In the caudal region hcemal arches and hcsmal spines (uD) extend down from the centrum, and the caudal artery and caudal vein pass through these arches. The $i *-~.v-.-- ,A^t"-*v>->* FIG. 372. Skeleton of perch. A., anal fin; An., orbit; B., ventral fin; Be, pelvic bones; Br, pectoral fin; Fr, interspinous bones; Kd, parts of operculum ; o, maxilla; oD, neural spines; R, ribs; Ri., ist dorsal fin; R2., second dorsal fin; S, caudal fin; Sch, bones of shoulder girdle; u, man- dible; uD, haemal spines; z, premaxilla. (From Schmeil.) extreme posterior portion of the vertebral column is modified so as to furnish a support for the caudal fin (S) . The skull of the perch (Fig. 372) consists of a large number of parts, some of bone, others of cartilage. As in Petromyzon, these parts may be grouped into the cranium and the visceral skeleton. The cranium is originally of cartilage, but becomes strengthened by the addition of membrane bones, which are dermal ossifications. The cranium protects and supports the brain, auditory organs, and olfactory sacs, and furnishes orbits (Au) for the eyes. CLASS PISCES 437 The visceral skeleton, which is represented in Fctromvzon by the branchial basket (Fig. 354, /o), is, in the perch, composed of seven arches more or less modified. The first or mandibiilar arch, forms the jaws. The upper jaw consists principally of two pairs of bones, the premaxilla (Fig. 372, z) and the maxilla, (o). The premaxillae bear teeth. The lower jaw or mandible (u} also bears teeth. The second or hyoid arch is modified as a support for the gill-covers. Arches three to seven support the gills and are known as gill-arches. The first four of these bear spine-like ossifications, the gill-rakers, which act as a sieve to intercept solid particles, and keep them away from the gills. The appendicular skeleton is represented in the perch by a pec- toral girdle only (Fig. 372, Sch}. This consists of a number of bones which lie just behind the head on either side and furnish a firm foundation for the attachment of the muscles that move the pectoral fins. The fin-rays of the pectoral fin articulate with the girdle by means of four rod-like bones, the pterygiophores or radials, and a number of small cartilages. There is no pelvic girdle. The ventral fins articulate with a flat bone, the basepterygium (Fig. 372, Be}, which is probably formed by the fusion of interspinal bones (pterygiophores). The Muscular System. - - The principal muscles are those used in locomotion, in respiration, and in obtaining food. The movements of the body employed in swimming are produced by four longitudinal bands of muscles, one heavy band on either side along the back and a thinner band on either side of both trunk and tail. These are arranged in zigzag myotomes. Weaker muscles move the gill-arches, operculum, hyoid, and jaw r s. The Digestive System. - - The aquatic insects, mollusks, and small fishes that constitute a large part of the food of the perch are captured by the jaws and held by the many conical teeth. Teeth are borne on the mandibles and premaxillae, and on the roof of the mouth. They are not used to masticate the food. A rudimentary tongue projects from the floor of the mouth 438 COLLEGE ZOOLOGY cavity; it is not capable of independent movement, but func- tions as a tactile organ. The mouth cavity is followed by the pharynx, on either side of which are four gill-slits. Food passes directly to the stomach through a short oesophagus. Digestion is begun in the stomach by the fluids secreted by its walls. The partially digested food then passes through the pyloric valve into the intestine. Three short tubes, called pyloric C(Bca, open into the intestine and increase its secreting surface. The liver lies in the anterior part of the body-cavity; its secretion, the bile, is stored in the gall-bladder and then passed into the intestine through the bile-duct. About the intestine, which curves slightly in the body-cavity, is a mass of fat. Undigested substances pass out through the anus. A large red gland, the spleen, is situated near the anterior end of the intestine; it has no duct. The Circulatory System. - - The blood of the perch contains oval nucleated red corpuscles and ameboid white corpuscles. The h*e*rt lies in a portion of the ccelom, the pericardium, beneath the pharynx. Circulation in the perch is similar to that in the dog- fish shark (Fig. 361). Blood is carried into the thin- walled auricle (au) from the veins through the sinus venosus (s.v). It passes into the muscular -ventricle (v) and is forced by rhyth- mical contractions into the ventral aorta (v.ao) and thence by afferent branchial arteries (a.br.a) into the gills. The aerated blood is collected by the efferent branchial arteries (e.br.a) and conveyed to the dorsal aorta (d.ao). Various parts of the body are supplied by branches from the dorsal aorta. Oxygen is sup- plied to the tissues by the arterial capillaries, and waste sub- stances are taken up by the venous capillaries and transported to the excretory organs. Veins carry the blood back to the heart. Circulation is much slower in fishes than it is in the higher vertebrates. The Respiratory System. - - The perch breathes with four pairs of gills supported by the first four gill-arches. Each gill bears a double row of branchial filaments (Fig. 373) which are CLASS PISCES 439 abundantly supplied with capillaries. The afferent branchial artery (Fig. 373, A; Fig. 361, a.br.d) brings the blood from the heart to the gill- filaments; here an exchange of gases takes place. The carbonic acid gas with which the blood is loaded passes out of the gill, and a supply of oxygen is taken in from the continuous stream of water which enters the pharynx through the mouth and bathes the gills on its way out through the gill-slits. The oxygenated blood is collected into the efferent branchial artery (Fig. 373, j; Fig. 361, e.br.a) and carried about the body. The gills are protected from external injury by the gill covering or operculum (Fig. 372, Kd) and from solid particles which enter the mouth by the gill-rakers (p. 437). Because oxygen is taken up by the capillaries of the gill- filaments, a constant supply of fresh water is necessary for the life of the fish. If deprived of water entirely, respiration is prevented, and the fish dies of suffocation. The air-bladder is a comparatively large, thin-walled sac lying in the dorsal part of the with two gill fila- body-cavity. It is filled with gas and is a hydrostatic organ or " float " ; in fishes it may also aid in respiration. The gas contained in it is a mixture of oxygen and nitrogen, and is derived from the blood-vessels in its walls. The air-bladder decreases the specific gravity, making the body of the fish equal in weight to the amount of water it displaces. The fish, therefore, is able to maintain a stationary position without muscular effort. The amount of gas within the air- bladder depends upon the pressure of the surrounding water, and in some way is regulated by the fish according to the depth. If a fish is brought to the surface from a great depth, the air- bladder, which was under considerable pressure, is suddenly FIG. 373. Trans- Certain 2, efferent chial vessel. Schmeil.) bran- (From 440 COLLEGE ZOOLOGY relieved, and therefore expands, often forcing the gullet out of the mouth. The Excretory System. - - The kidneys lie just beneath the backbone in the abdominal cavity. They extract urea and other waste products from the blood. Two thin tubes, the ure- ters, carry the excretory matter into a urinary bladder, where it is stored for a time and then expelled through the urinogenital opening just posterior to the anus. The Nervous System. - - The brain of the perch is more highly developed than that of Petromyzon or Squalus. The four chief divisions are well marked, - - the cerebrum, optic lobes, cere- bellum, and medulla oblongata. The brain gives off cranial nerves to the sense-organs and other parts of the anterior portion of the body. The spinal cord lies above the centra of the verte- bral column and passes through the neural arches of the vertebrae. Spinal nerves arise from the sides of the spinal cord. Sense-organs. - - The principal organs of sense are the eyes, ears, and olfactory sacs. The mucous membrane of the mouth is the seat of the sense of taste, but this sense is not well developed. The integument, especially that of the lips, serves as an organ of touch. Lateral line organs are also present, but their function is not certain. The two olfactory sacs lie in the anterior part of the skull and open by a pair of apertures in front of each eye. They are not connected with the mouth cavity, and take no part in respiration. The inner surface is thrown up into folds which are covered with sense-cells. Water flows in and out through the external open- ings. The ear consists of the membranous labyrinth only. As in Petromyzon and Squalus, the sound waves are transmitted by the bones of the skull to the fluid within the labyrinth. Three semi- circular canals (Fig. 350, ca, ce, cp) are present, and the sac- culus (s) contains concretions of carbonate of lime, called ear- stones or statoliths. The ear is both an organ of hearing and an organ of equilibrium. CLASS PISCES 441 The eye of the perch differs in several respects from that of terrestrial vertebrates. The eyelids are usually absent in fishes, since the water keeps the eyeball moist and free from foreign objects. The cornea is flattened and of about the same refractive power as the water. The lens is almost spherical. The pupil is usually larger than that of other vertebrates and allows the entrance of more light rays ; this is necessary, since semi-darkness prevails at moderate depths. When at rest the eye focuses at about fifteen inches. To focus on distant objects the lens is moved back. Fishes cannot see in air. The Reproductive System. - - The sexes are separate. The ovaries or testes lie in the body-cavity. The germ-cells pass through the reproductive ducts and out of the urinogenital opening. Perch migrate in the spring from the deep waters of lakes and ponds, where they spend the winter, to the shallow waters near shore. The female lays about a hundred thousand eggs in a long ribbon-like mass. The male fertilize:, the eggs by depositing spermatozoa (milt) over them. Very few of the eggs develop because of the numerous animals, such as other fishes and aquatic birds, which feed upon them. Development. - - The young perch hatches from the egg in from two to four weeks, depending upon the temperature of the water. The egg passes through stages similar to those shown in Figure 374. A large part of the egg consists of yolk. A pro- toplasmic accumulation which forms a slight projection at one end is called the germinal disc. The fusion nucleus, resulting from the union of the egg nucleus and the nucleus brought into the egg by the spermatozoon, soon divides, and two cells are formed. Cleavage of the germinal disc continues (Fig. 374, A , B) and the blastoderm (bt) produced gradually grows around the yolk (C-G). The embryo (E, emb} appears as a thickening of the edge of the blastoderm. This grows in size (F, emb, G) at the expense of the yolk. After a time the head and tail be- 442 COLLEGE ZOOLOGY cmb come free from the yolk, and the young fish breaks out of the egg membranes (/) . The young fish lives at first upon the yolk in the yolk-sac (7, y.s), but is soon able to obtain food from the water. This consists of small crustaceans; insects are added after a time, and still later larger crustaceans, mollusks, and small fishes. Economic Impor- tance. - - The perch is perhaps the best pan- fish among American fresh-water fishes. In many localities it is taken largely for mar- ket. It is not a good game-fish, but has one advantage it is easy to catch. The perch has been introduced successfully into sev- eral small lakes in Washington, Oregon, and California. It can be artificially propa- gated, but other fishes, such as whitefish, lake trout, and pike-perch are of commercial im- portance and are, therefore, preferred for propagative purposes to the yellow perch. y.s FIG. 374. Nine stages in the development of a fish (Salmo fario). A-H, before hatching; I, shortly after hatching. bl, blastoderm ; emb, embryo; r, thickened edge of blastoderm; y.s, yolk-sac. (From Parker and Haswell ; A-G, after Henneguy.) CLASS PISCES 443 2. AN ABRIDGED CLASSIFICATION OF LIVING FISHES The classification of fishes is attended with many difficulties, since it is as yet impossible to determine the relationships of many of the groups. That adopted in this book is a simplified arrangement of the classifications used in some of the recent publications. Synonyms are placed in parentheses after some of the names. There are about twelve thousand species of fishes known from the entire world. Of these Jordan and Evermann in their large four-volume work on the Fishes of North and Middle America have described . one hundred and ninety-eight families and thirty-three hundred species from the waters of North America north of the Isthmus of Panama. Besides the living fishes there are a great many species known only as fossils; in fact, a number of orders, suborders, and fam- ilies contain nothing but fossil forms. These will be considered later (p. 474). SUBCLASS I. TELEOSTOMI. THE TRUE FISHES. Order i. Crossopterygii. The Polypteridse. Order 2. Chondrostei. The Paddle-fishes and Sturgeons. Family POLYODONTID^E. The Paddle-fishes. Family ACIPENSERID.E. The Sturgeons. Order 3. Holostei. The Garpikes and Bowfins. Family AMIID^E. The Bowfins. Family LEPISOSTEID^E. The Garpikes. Order 4. Teleostei. The Bony Fishes. Suborder i. CYPRINIFORMES (OSTARIOPHYSI). The Carp, Minnows, Suckers, and Catfishes. Family CYPRINID^:. The Carp, Minnows, and Suckers. Subfamily CATOSTOMIN.E. The Suckers. Subfamily CYPRININ.E. The Carp and Minnows. Family SILURID^:. The Catfishes. Suborder 2. CLUPEIFORMES (ISOSPONDYLI, MALACOP- TERYGII). The Herrings, Trouts, Salmons, etc. 444 COLLEGE ZOOLOGY Family ELOPID,E. The Tarpons. Family CLUPEID^:. The Herrings. Family SALMONID.E. The Whitefishes, Trouts, and Salm- ons. Suborder 3. ESOCIFORMES (HAPLOMI). The Pikes, Cave- fishes, and Flying-fishes. Family ESOCID.E. The Pikes. Family AMBLYOPSID^. The Cave-fishes. Family EXOCCETID.E. The Flying-fishes. Suborder 4. ANGUILLIFORMES (APODES) . The Eels. Family ANGUILLID^. The True Eels. Family LEPTOCEPHALID^E. The Conger Eels. Suborder 5. SYMBRANCHIFORMES (SYMBRANCHII). The SYMBRANCHID.E and AMPHIPNOID^E. Suborder 6. GASTEROSTEIFORMES (CATOSTEOMI, HEMI- BRANCHII, LOPHOBRANCHII). The Sticklebacks, Pipe- fishes, and Sea-horses. Family GASTEROSTEID^:. The Sticklebacks. Family SYNGNATHID.E. The Pipe-fishes and Sea- horses. Suborder 7. NOTACANTHIFORMES (HETEROMI). Mostly Deep-sea Fishes. Suborder 8. MUGILIFORMES (PERCESOCES). The Silver- sides and Mullets. Suborder 9. ACANTHOPTERYGII. The Spiny-rayed Fishes. Family SERRANID.E. The Sea-basses. Family DIODONTID.E. The Porcupine Fishes. Family PERCID_. The Perches. Family CENTRARCHID^E. The Sunfishes and Basses. Family ECHENEIDID^:. The Remoras. Family LOPHIID^:. The Anglers. Family SCOMBRID^E. The Mackerels. Family XIPHIID^:. The Swordfishes. Family PLEURONECTID^:. The Flounders. Family GADID.E. The Codfishes. CLASS PISCES 445 SUBCLASS II. DIPNOI. THE LUNG-FISHES. Family CERATODONTID^E. The Australian Lung-fishes. Family LEPIDOSIRENID.E. The South American and African Lung-fishes. 3. THE ANATOMY AND PHYSIOLOGY or FISHES IN GENERAL External Features. - - FORM or THE BODY. - - The body of the majority of fishes is spindle-shaped and laterally com- pressed, as in the perch --a form that offers slight resistance to progress through the water (Fig. 369). Variations in form are correlated with the habits of the fish. For example, the flat- fishes, or flounders, have thin bodies and are adapted for life on the sea bottom; they are laterally compressed and swim on one side or the other; the eels have a long cylindrical body which enables them to enter holes and crevices; and the globe-fishes when disturbed inflate themselves with air, becoming almost spherical, in which condition they float in the water. The shape of the head differs considerably among the fishes ; in the angler- fish it is enormous ; in the garpike it is long and pointed; and that of the paddle-fish extends forwards as a thin paddle-like structure. Many fishes, like the sea-horse (Fig. 398) and some deep-sea species, are so curiously shaped as to show little resem- blance to our common fishes. FINS AND TAIL. - - Fins arise in the embryo as median and lateral folds of the integument (Fig. 375, A) which are at first continuous. Later, parts of the folds disappear and the isolated dorsal, caudal, anal, ventral, and pectoral fins persist (Fig. 375, B). There is a theory that the paired fins arise from gill-arches, but this method of origin seems less probable than that just described. The ventral fins of fishes vary considerably in position, prob- ably because their skeletal parts are held only by muscles. In the perch (Fig. 368) they are situated beneath the pectoral fins and are said to be ventral; in the fresh-water dogfish (Fig. 384) they are just in front of the anus and are called abdominal ; and COLLEGE ZOOLOGY in certain other species they are in the throat region and are said to be jugular in position. In most fishes the fins are sup- ErF FIG. 375. Diagram showing A, the undifferentiated condition of the paired and unpaired fins in the embryo, and B, the manner in which the permanent fins are formed from the continuous folds. AF, anal fin; An, anus; BF, pelvic fin; BrF, pectoral fin; D, dorsal fin-fold; FF, dorsal fin; RF, dorsal fin; SF, tail-fin; S, S, lateral folds which unite at 5' to form ventral fold. (From Wiedersheim.) ported, as in the perch, by cartilaginous rods and bony spines; this type of appendage is called an ichthyopterygium. In a few fishes (e.g. Polypterus, Fig. 380) the pectoral fins have a median axis, which may be jointed, and bears rays about the edge ; this is termed an archipterygium (Fig. 376). The fingered appendage (cheiropterygium) of higher vertebrates may have arisen from the latter type. The shape of the caudal fin and the terminal por- FIG. 376. Archipterygial pectoral fin tion of the tail differs in of a lung-fish, Neoceratodus. B, basal; ., grouDS Q f fi s hes D, dermal; R, radial. (From Dean, after ~ b > Howes.) and is therefore of im- CLASS PISCES 447 portance in classification. The most primitive condition is exhibited by very few if any living fishes, except in the embryo or early larval stages. It is termed protocercal or diphycercal, and is symmetrical both externally and in internal structure (Fig. 377, A). The second type, or heterocercal tail, is not symmetrical, and the vertebral column extends into the dorsal lobe; this condition exists in the sturgeons (Fig. 382) and many others. The stroke of the asymmetrical heterocercal tail forces the anterior part of the body downward. This type is therefore of advantage to and characteristic of those fishes that have a R*N RfN B A ^*3? FIG. 377. Two types of caudal fins. A, diphycercal (Polypterus). B, homocercal. D, dermal fin supports ; N, notochord ; R, radials ; R+N, neural spines. (From Dean; A, after Agassiz ; B, after Ryder.) ventrally situated mouth and feed on the bottom. The third type, or homocercal tail, is externally symmetrical but internally unsymmetrical (Fig. 377, B}. The stroke of the homocercal tail forces the fish straight forward. It is characteristic of fishes with a terminal mouth and is the type possessed by most bony fishes. Fins are normally used in locomotion through the water, but may be modified for other purposes. For example, the pectoral fins of the flying fishes (Fig. 394) are used somewhat like the wings of an aeroplane to sustain the fish in the air during its leap from the water; the pectoral fins of the African goby serve the purpose of feet, enabling the fish to move about on the ground 448 COLLEGE ZOOLOGY in search of food; and the first dorsal fin of the sucker- fish, Remora (Fig. 400), forms a sucker for the attachment of its possessor to a shark or turtle. SCALES. - - The scales of fishes form a protecting exoskeleton. They are of three principal types: (i) ganoid, (2) cycloid, and (3) ctenoid. Ganoid scales are usually rhombic in shape (Fig. 371, B). They have a superficial covering of dentine called ganoin. Ganoid scales occur in most of the CHONDROSTEI and HOLOSTEI, and these are often called ganoid fishes. Cycloid and ctenoid scales are arranged in overlapping rows as described for the perch (p. 434). Cycloid scales (Fig. 371, C) are nearly circular with concentric rings about a central point. Ctenoid scales (Fig. 371, A) are similar to cycloid scales, but the part which extends out from under the neighboring scales bears small spines. In many fishes ^ 3 -^^%W^ &&W r> 5(s^ fc *3?ik&b*9!53ff* the scales develop into large protective spines, or may fuse to form bony plates. COLOR. - - The general impression is that fishes are not brightly colored, but many of them, espe- cially in tropical waters, are exceedingly brilliant. FIG. 378. Chromatophores in skin of The Colors are due to upper side of a freshly killed flounder, Plcitro- pi g ments within S p ec ial nectes flesus. Black bodies represent black Chromatophores; gray bodies, yellow; small dermal Cells, Called chro- Kjay plates, iridocytes. (From the Cambridge mato phores, Or to refleC- Natural History, after Cunningham and Mac- ' Munn.) tion and iridescence re- sulting from the physical structure* of the scales which contain crystals of guanin (irido- cytes, Fig. 378). The pigments are red, orange, yellow, or black, but other colors may be produced by a combination of Chromatophores; for example, yellow and black when blended CLASS PISCES 449 give brown. Usually the colors are arranged in a definite pattern consisting of transverse or longitudinal stripes, and spots of various sizes. Coral-reef fishes have long been famous for their brilliant colors, and many fresh-water fishes of the temperate zone exhibit bright hues distributed so as to form striking and intricate patterns (e.g. the rainbow darter). The contraction and expansion of the chromatophores of certain fishes result in changes in coloration. These changes " are due to incident light reflected from surrounding surfaces, acting through the visual organs and the nervous system on the differently colored chromatophores." (Bridge.) The changes are therefore dependent upon the color of the fish's environment, and are often such as to conceal the animal, being consequently protective. The change is slow in many fishes, but may be quite rapid, as in the flounder. Male fishes are often more brightly colored than the females, especially during spawning activities. The Skeleton. - - The skeleton differs among the fishes chiefly in the relative amount of bone and cartilage. Both the TELEO- STOMI and DIPNOI possess skeletons which consist to a greater or less extent of bones preformed in cartilage, and membrane bones which are developed as dermal ossifications. The ver- tebra are usually amphiccelous, as in the perch, and bear neural arches; some of them in the trunk region bear ribs; others in the tail bear haemal arches. There is no sternum. The cranium is independent of the visceral arches. It is complicated in the teleosts by the addition of numerous mem- brane bones. The visceral skeleton consists of seven arches ; five of them are usually gill-arches. The lower jaw articulates with the upper jaw and not directly with the cranium. The bones contained in the gill-cover or operculum develop from the hyoid arch. The Digestive System. - - The food of our common fishes consists of vegetation, insect larvae, crustaceans, mollusks, and other smaller fishes. Some fishes are voraciously carnivorous, 2G 450 COLLEGE ZOOLOGY and, like the sharks, attack animals larger than themselves; others are herbivorous to a considerable extent, feeding on seaweeds and other vegetation ; and still others act as scavengers or swallow mud from which both living and dead organisms are obtained. Fishes are ultimately dependent upon microscopic organisms, as is illustrated by the following example : - " On the morning of July 23 there was taken a large specimen (squeteague) whose stomach contained an adult herring. In the stomach of the herring were found two young scup (besides many small Crustacea), and in the stomach of one of these scup were found copepods, while in the alimentary tract of these last, one could identify one or two of the diatoms (unicellular plants) and an infusorian test among the mass of triturated material which formed its food." (Peck.) Most fishes possess teeth on the jaws, roof of the mouth, or gill-arches. These are used principally for holding food, but in some cases for mastication. The most primitive type of tooth is a simple pointed cone. Some fishes have front teeth for capturing prey and back teeth for crushing; and in others the teeth are all modified for crushing. Teeth that are lost or worn away are generally replaced. The alimentary canal is usually similar to that of the perch. Gastric glands in the walls of the stomach secrete digestive juices. The intestine often possesses blind pouches, the pyloric caeca, which increase the secretory surface. The Circulatory System. - - Circulation in fishes is essentially like that already described (Fig. 361). Lymph spaces and lymph capillaries are situated in various parts of the body ; they collect blood plasma from the tissues and transport it to the veins. The body of the fish contains several ductless glands which may be considered under the circulatory system. The functions of these glands are not well known. The extirpation of them results in serious disturbances, and, in some cases, death. They secrete substances (internal secretions) directly into the blood CLASS PISCES 451 or lymph. The thyroid is homologous to the endostyle of tuni- cates (p. 391) and Amphioxus (p 396). It lies in .the branchial region and is paired. The thymus is situated dorsally in the branchial region. The spleen is a large gland usually lying near the stomach , colorless blood corpuscles are formed in it, and old red corpuscles are destroyed by it. The suprarenal bodies are situated close to the kidneys. The Respiratory System. - - Respiration takes place in the gills, and, in the DIPNOI and some teleosts, also to some extent FIG 37Q Diagram illustrating the mechanism of respiration in A, phase of inspiration B, phase of expiration (From Wtcdc-rshL-im. alter Dahlgren.) in the air-bladder During respiration in teleosts the walls of the mouth act like a pump (Fig 379) In inspiration (A) the oral cavity (cavoris) is enlarged by the raising of the opercular apparatus, and water is therefore drawn into it through the mouth. Folds of mucous membrane (branchiostegal mem- 45 2 COLLEGE ZOOLOGY branes) prevent water from entering through the opercular aperture. Expiration (E) results from the contraction of the opercular apparatus; the branchiostegal membrane is opened and water passes out through the gill-slits. The exit of water by way of the mouth is prevented by valves of mucous mem- brane (maxillary and mandibular valves). 4. GENERAL ACCOUNT or SOME OF THE PRINCIPAL GROUPS OF FISHES SUBCLASS I. TELEOSTOMI. - - To the TELEOSTOMI belong the majority of fishes. The four orders of living forms are unequal in number of species, most of which belong to the TELEOSTEI. Order i. Crossopterygii. - - Most of the CROSSOPTERYGII are extinct, and the order contains only one family and two FIG. 380. Polyptents senegalus. (From the Cambridge Natural History.) genera of living forms. One species, Polypterus senegalus (Fig. 380), lives in the Nile. It is of special interest to morphologists because it presents many structural features characteristic of ancient crossopterygians. Order 2. Chondrostei. - -This order contains the sturgeons and paddle-fishes. These have a skeleton largely of cartilage, a heterocercal tail, ganoid scales (Fig. 371, B), and abdominal pelvic fins. The family POLYODONTID^E contains two species of paddle- fishes, Polyodon spat-hula (Fig. 381) of the Mississippi Valley, and Psephurus gladius of the Yang-tse-Kiang in China. Poly- odon reaches a length of six feet and a weight of one hundred and sixty pounds, but the specimens usually taken weigh no more than fifty pounds. Its large, paddle-shaped snout is re- garded as a sense-organ, and its use is still unknown. The CLASS PISCES 453 food of Polyodon consists largely of niinulc plants and ani- mals, of which enormous numbers are devoured. The paddle- FIG. 381. The spoonbill sturgeon or paddle- fish, Polyodon spathula, ventral and side view. (From Dean, after Goode.) fish is good to eat, but its roe, from which caviar is made, is more valuable than its flesh. The family ACIPENSERID^E contains two genera of sturgeons, Acipenser and Scaphirhynchus. They inhabit the seas, lakes, and rivers of Europe, Asia, and America. Sturgeons possess a cephalic prolongation or rostrum which bears on its ventral surface a number of tactile filaments called barbels. The scales form five longitudinal rows of bony scutes between which are smaller ossifications. The mouth lacks teeth. The common FIG. 382. The common sturgeon, Acipenser stiirio. (From Dean, after Goode.) sturgeon, Acipenser sturio (Fig. 382), lives along the Atlantic coast and ascends the rivers of northern Europe and the United States. Acipenser rubiciuidus is the sturgeon of the rivers and lakes of the middle west. It feeds on the bottom, using its snout 454 COLLEGE ZOOLOGY for stirring up the mud and its barbels for locating snails, cray- fishes, and insect larvae. Sturgeon flesh is a valued article of food, the eggs are made into caviar, and the air-bladders furnish isinglass. Orders. Holostei. - - Most of the HOLOSTEI are extinct; only two of the eight families have living representatives, namely the LEPISOSTEID^E or garpikes, and the AMUD^E or bow- fins. These fishes are called bony ganoids, since the skeleton is bony and the scales are often ganoid. In some the scales are cycloid (Fig. 371). The tail is diphycercal or homocercal, with a tendency toward the heterocercal type, and the ventral fins FIG. 383. The alligator-gar, Lepisosteus tristaschus. (From Jordan and Evermann.) are abdominal. The living species of garpikes and bowfins are known only from America. The garpikes belong to the genus Lepisosteus. There are three common species, the long-nosed garpike, .the short-nosed gar, and the alligator gar (Fig. 383). The long-nosed gar, Lepi- sosteus osseus, is common in the lakes and rivers of the United States. It is about four feet long. The body is slender with an extended beak, at the end of which are the nostrils. Its heavy ganoid scales effectively protect it from every other living crea- ture in the water. Garpikes are voracious, devouring minnows, young fish, and other aquatic animals, and where they occur in large numbers are very harmful to the fishing industry. Amia (Amiatus) calva, the mudfish, fresh- water dogfish, or bowfin (Fig. 384), is the only existing representative of the family AMIID^E. It inhabits the sluggish waters of the Great Lakes region CLASS PISCES 455 and the Mississippi Valley. The body is about a foot and one half long, is dark olive in eolor, and bears, in the male, a black sp< >t at the base of the caudal fin. It is very voracious, feeding on fish, crayfishes, mollusks, and other aquatic animals. The breeding season is in April, May, or June, according to the latitude. The male clears a space in the vegetation of a quiet inlet in which the eggs are laid, and then guards the nest (Fig. 384) during FIG. 384. The fresh-water dogfish or bowfin, Amia (Amiatus) calva, and its nest. (From the Cambridge Natural History, after Dean.) the hatching period of from eight to ten days, and while the young remain in the nest - - about nine days more. The male accompanies the young when they leave the nest, and con- tinues to guard them until they reach a length of about four inches. Order 4. Teleostei. - - This order contains the majority of living species, the bony fishes. The skeleton is extensively ossified; the tail is usually homocercal (Fig. 377, B); and the scales are cycloid or ctenoid (Fig. 371). Space will allow a few notes on only about one eighth of the families of fishes included in the order. 45 6 COLLEGE ZOOLOGY Family i . C YPRINID.-E. - - The Carp, Minnows, and Suckers. Subfamily CATOSTOMIN.E. - - The Suckers. Most of the suckers are inhabitants of the fresh waters of North America; two of the seventy or more species occur in Asia. Their mouths are usually very protractile and possess fleshy lips. They feed on the bottom, eating vegetation, worms, insect larvae, and other soft-bodied animals. In the spring suckers swim upstream to spawn. The sucker is barely edible, but is nevertheless an important commercial fish. The common or white sucker, Jr* ' ^"lir ^H^^ ' FIG. 385. The common sucker, Catostomus commersoni. (From Jordan and Evermann.) Catostomus commersoni (Fig. "385), is very widely distributed. This subfamily includes, besides the suckers, the red-horses, buffaloes, quillbacks, and fresh-water mullets. Subfamily CYPRININ^E. - - There are about two hundred genera and a thousand species of fishes belonging to this sub- family. About two hundred and twenty- five species occur in the United States. They are mostly small, but should not be mis- taken for" young fish on that account. The chubs, hornyheads, fall- fish, and squaw fish are common in various parts of the country. The German carp (Fig. 386) was introduced into North America in 1872, and is now firmly established in our waters. It will live in muddy ponds and streams, is prolific, grows rapidly, and is edible, although not very good. Since its introduction it has been accused of driving away other fishes, of CLASS PISCES 45 making clear lakes muddy, of eating wild celery and grasses on which ducks feed, and of devouring the eggs of other fishes. FIG. 386. The carp, Cyprinus carpio. (From Lankester's Treatise, after Seeley.) Family 2. SILURID.E. - - The Catfishes. These are mostly fresh- water fish, about thirty species of which are known from the United States. The body of the catfish is naked ; the head bears eight barbels; and there is a short, fatty, adipose fin back of the FIG. 387. The bullhead or catfish, Ameiurus mclas. (From Dean, after Goode.) dorsal fin. The bullhead or horned pout, Ameiurus nebulostis, is a common fish in the ponds and streams of the North and East. The black bullhead, Ameiurus melas (Fig. 387), is found 458 COLLEGE ZOOLOGY chiefly west of the Mississippi River. The bullhead is tenacious of life and can live out of water for some time. The blue or Mississippi catfish, Ictalurus furcatus, is a valuable food-fish. It inhabits the sluggish waters of the streams of the Mississippi Valley and Gulf States, and is the largest member of the family, sometimes reaching a length of five feet and attaining a weight of over one hundred pounds. Another large species is the chan- nel or spotted catfish, Ictalurus punctatus. It occurs in the Great Lakes region and Mississippi Valley, and prefers clear, flowing water. Family ELOPID^E. - - The Tarpons. There are four or five species of tarpons inhabiting the tropical seas. The common FIG. 388. The tarpon, Tarpon atlanticus. (From the Cambridge Natural History, after Goode.) tarpon, Tarpon atlanticus (Fig. 388), is a famous game-fish on the coast of Florida, and is called the " silver king." Family CLUPEID.^. - - The Herrings. The members of this family are mostly salt-water forms. They are not game-fishes, FIG. 389. The herring, Clupea harengus. (From Jordan and Evermann.) CLASS PISCES 459 but about ten species are of commercial value. The common herring, Clupea harengus (Fig. 389), is " the most important of the food-fishes in the Atlantic." (Jordan and Evermann.) Herring swim about the North Atlantic in immense shoals, often covering half a dozen square miles and containing as many as three billion individuals. On the New England coast herring are smoked, salted, pickled, packed as sardines, or serve as bait for cod- fishing. Family SALMONID.E. - - The Whitefishes, Salmons, and Trouts. Many of our most important food and game fishes belong to this FIG. 390. The whitefish, Coregonus clupeiformis. (From Jordan and Evermann.) family, such as the mountain trout, rainbow-trout, and steel- head trout of the West, the lake-trout and common whitefish of the Great Lakes, the brook trout of the East, the Atlantic salmon of Europe and North America, and the quinnat or chinook salmon, the blueback or sockeye salmon, and the silver or coho salmon of the Pacific. These fishes are easily reared, and millions of their eggs or young are distributed each year by the United States Bureau of Fisheries (see Table XV). The common whitefish, Coregonus clupeiformis (Fig. 390), occurs throughout the Great Lakes region. During the winter it prefers deep water, but in the spring it migrates to the shallow water to secure insect larvae which become abundant at that 460 COLLEGE ZOOLOGY time. It migrates to shallow water again in the autumn to spawn. The mouth is on the under side, and the crustaceans, mollusks, and other animals used as food are picked up from the bottom. The eggs are laid over honeycomb rock, and, since many of them are covered by sediment or fall prey to mud- puppies, yellow perch, crayfishes, and other enemies, very few reach the adult stage. Because of this fact the government each year gathers, rears, and distributes millions of whitefish eggs. Whitefishes are captured in deep water by means of gill-nets which hold the fish just behind the gill-covers. The average weight is about four pounds, but they may become as heavy as twenty pounds. The lake-trout, Cristivomer namaycush, is another important food-fish of the Great Lakes region. It is the largest of our trouts, averaging about eighteen pounds, but occasionally attain- ing a weight of over one hundred pounds. Lake-trout are cap- tured usually in gill-nets. They are omnivorous, but show special preference for lake herring. The spawning season ranges from September to November, according to the latitude. Mil- lions of eggs are cared for and distributed by the government each year. The brook or speckled trout, Salvelinus fontinalis, is one of Dur most beautiful and well-known game-fishes. It prefers clear, cool streams with a swift current and a gravelly bottom. The mountain or cut-throat trout, Salmo clarkii, is a large species inhabiting the streams and lakes of the Rocky Mountain region. The rainbow-trout, Salmo irideus, is also a Western species. It is a good game-fish and takes the fly readily. In weight it averages about two or three pounds. The steelhead or salmon trout, Salmo gairdneri, is found in the streams along the Pacific coast. Like the salmon it migrates upstream to spawn. Its average weight is about eight pounds. Thousands of steelhead trout are taken each year for canning purposes, especially in the Columbia River. They are also considered excellent game-fish. CLASS PISCES 461 The chinook or quinnat salmon, Oncorhynchus tschawytscha (Fig. 391), is the most important commercial fish of the family. It lives in the sea along the Pacific coast " from Monterey Bay, California, and China, north to Bering Straits." It enters the fresh-water streams to spawn, especially the Sacramento, Columbia, and Yukon rivers. The ascent takes place in the spring and summer, beginning in February or March in the Columbia River. The salmon do not feed during this migra- tion, but swim at first slowly and then more rapidly until they reach the small, clear, mountain streams often more than a thousand miles from the sea. Spawning occurs from July to FIG. 3gi. Quinnat salmon (female). Oncorhynchus tschawytscha. (From Jordan and Evermann.) December, according to the temperature of the water, which apparently must be below 54 Fahr. The eggs are deposited upon the gravelly bottoms of the streams, after which both males and females die ; consequently an individual spawns only once during its lifetime. The eggs hatch in about seven weeks, and the young remain on the spawning ground for six weeks. They then float slowly downstream and may be four or five inches long when they reach the sea. The adults are captured by gill-nets and other devices as they ascend the rivers, and are considered the most important of all commercial fishes. The government is artificially propagating the chinook salmon, otherwise its numbers would soon be materially decreased. 462 COLLEGE ZOOLOGY Family ESOCID/E. - - The Pikes. There is one genus with seven species of pikes; all of them occur in North America. The FIG. 392. The pike, Esox Indus. (From Jordan and Evermann.) common pike or pickerel, Esox Indus (Fig. 392), inhabits "all suitable fresh waters of northern North America, Europe, and Asia." It is extremely voracious, feeding on other fishes, frogs, aquatic birds, and many other aquatic animals. The pike is an excellent game-fish, but its flesh is not very good. The muskal- lunge, Esox masquinongy, resembles the pike in form and habits. It is found in the Great Lakes region and is a king among fresh- water game-fishes, reaching a length of over seven feet and a weight of almost a hundred pounds. Family AMBLYOPSID.E. - - The Cave-fishes. There are six species of cave- fishes known from the subterranean streams of the FIG. 393. A cave-fish, Amblyopsis spelceus. (From Lankester's Treatise, after Jordan and Evermann.) cave region of Indiana, Kentucky, and Missouri. They are small fish, but are of special interest because the eyes of some of CLASS PISCES 463 them are rudimentary and covered with a thick skin. Amblyop- sis spclaus (Fig. 393) is common in the river Styx of the Mam- moth Cave. Family EXOCCETID.E. - -The Flying-fishes (Fig. 394). There are about sixty- five species in this family, inhabiting warm FIG. 394. A flying fish, Exoccetus calloplcrus. (From Lankester's Treatise, after Giinther.) seas. Some of them are able to leave the water, and, rising in the air a few feet, " fly " a distance of from a few rods to more than an eighth of a mile. It seems probable that the pectoral fins do not force the fish forward, but simply sustain the body in the air. Family ANGUILLID.E. - - The Eels. The true eels should not be confused with the lamprey eels of the class CYCLOSTOMATA FIG. 395. The common uel. An^uilla rostrata. (From Jordan and Evermann.) (p. 414). The single species of eel, AnguiUa rostrata (Fig. 395), in North America occurs in the streams of the Atlantic coast. 464 COLLEGE ZOOLOGY It is long and slender, and its scales are inconspicuous. The dorsal, caudal, and anal fins are continuous. The eels enter the sea in the autumn to spawn, after which they die. The eggs are deposited on mud-banks usually near the mouths of rivers. The young develop in the sea and then migrate up the rivers. Eels are considered by many a good article of food, and are therefore of commercial value. Family GASTEROSTEID.E. - - The Sticklebacks. These are small fishes famous for their nest-building habits. The common FIG. 306. The two-spined stickleback, Gasterosteus bispinosus. Above, nest with eggs, and male entering. Below, male depositing its milt on the eggs. (From Davenport.) Eastern stickleback, Gasterosteus bispinosus (Fig. 396), has two large spines preceding the dorsal fin. The nest is built of sticks CLASS PISCES 465 fastened together with threads secreted by a gland in the male. The female lays eggs in the nest; the male then enters and fertilizes them, after which he guards them from intruders. --I.C FIG. 397. The pipe-fish, Syngnathus acus. (From Lankester's Treatise, after Giinther.) Family SYNGNATHID.E. - - The Pipe-fishes and Sea-horses. The pipe-fishes (Fig. 397) are extremely thin, with a tubular snout, abbreviated fins, and a covering of bony armor. Their food is captured by in- serting the snout into the cavities in sponges and corals, and by picking off minute ani- mals from the branches of seaweeds. The sea-horses (Fig. 398) are small species that do not look much like fish, the head remind- ing one of the head of a horse. They swim by means of the dorsal fin, hold- ing themselves in a vertical position as in Figure 398. They cling to objects with their prehensile tail. The eggs are carried in a brood pouch (mp) of the male until they hatch. Family SERRANID.E. - - The Sea-basses. This is a large family containing over four hundred species, mostly marine. The white lake bass, Roccus chrysops, is a fresh-water species of the Great Lakes region. The FIG. 398. Thesea- !' n e, Hippocampus Kill I nlalus, male. a, anus; b.a, branchial aperture; m.p, brood- pouch. (From the Cambridge Natural History.) 2 H 4 66 COLLEGE ZOOLOGY striped bass, Roccus lincalus, is a fine game-fish occurring along the coast of eastern North America. It has also been success- fully introduced along the coast of California. The jewfish or black sea-bass, Stereolepis gigos, is the giant game-fish of the California coast. It can be taken with a sixteen-ounce rod, and there are many records of specimens captured by this method weighing over three hundred pounds. Family DIODONTID^E. - - The Porcupine-fishes. These in- habitants of tropical seas are covered with movable spines, FIG. 399. The porcupine fish, Diodon maculalus. A. normal; B, inflated. (From Lankester's Treatise, after Giinther.) hence their name. They live on the bottom among seaweeds and corals, and when disturbed inflate their bodies by swallow- ing air (Fig. 399). They then float belly upward, in which con- dition they are not easily injured by their enemies. CLASS PISCES 467 Family PERCID.E. --The Perches. The perch family contains a large number of small fresh- water fishes, most of which are of little economic importance. The yellow perch, Percaflavescens, was chosen as a type of the class (pp. 432-442). The wall-eyed pike or pike-perch, Slizostedion litrcum, is another well-known and valuable species. It is common in the Great Lakes region and is ex- tensively propagated by the Bureau of Fisheries (see Table XV). Family CENTRARCHID^E. - - The Basses, Crappies, and Sun- fishes. These fishes inhabit the fresh waters of North America. There are about thirty species, most of which are good game- fishes and also excellent for the table. Some of the most com- mon species are the crappie, Porno. vis annularis, the rock-bass, Ambloplites rupestris, the bluegill, Lcpomis pallid us, the com- mon sunfish or pumpkin-seed, Eupomolis gibbosus, the small- mouthed black bass, Micropterus- dolomieu, and the large- mouthed black bass, Micro'ptems salmoides. The small-mouthed black bass is considered " inch for inch and pound for pound, the gamest fish that swims." (Henshall.) The male bass in May or June makes a nest by clearing away a place near shore where there are good-sized stones. Eggs are then laid and fer- tilized, and the male guards them during the hatching period of five or six days. The male continues to protect the young until they reach a length of an inch and a quarter. Black bass are successfully propagated in artificial ponds by the Bureau of Fisheries (see Table XV). Family ECHENEIDID.E. - - The Remoras (Fig. 400). This family contains about a dozen species of peculiar fishes that live FIG. 400. A sucking fish, Remora brachyplera. (From the Cambridge Natural History, after Goode.) COLU-XIK ZOOLOGY in tropical, warm seas. The first dorsal fin is modified to form a sucker by means of which the fish attaches itself to sharks, turtles, whales, other large aquatic animals, and floating objects such as boats. They are able to swim, but prefer to be carried about by other animals. Their food consists of other fish and probably of the scraps obtained when the shark, or other animal to which the individual is attached, has a meal. Family LOPHIID.E. - - The Anglers. Living on the bottom of the Atlantic, Indian, and Pacific oceans are about a dozen FlG. 401. The fishing-frog or angler, Lophius piscatori'us. (From Sedgwick's Zoology, after Cuvier.) species of extremely large-mouthed fishes known as anglers. Lophius piscatorius, the fishing-frog or goose-fish .(Fig. 401), occurs on the coast of North America. It is said to lie on the bottom with its mouth open and to use its long first dorsal ray, which is inserted on the snout, as a bait to attract other fishes into its mouth cavity. It reaches a length of over three feet and has a mouth more than a foot wide. Family SCOMBRID.E. - - The Mackerels. There are about sixty species of food-fishes belonging to this family, fifteen of which inhabit the salt waters of North America. The common mackerel. Scomber scombrus (Fig. 402), occurs in the North CLASS PISCES 469 Atlantic, swimming about in enormous schools. It feeds on small aquatic animals, such as CRUSTACEA, and furnishes food for other fishes. It is also a valuable food- fish for man. The Spanish mackerel, Scomberomorus nnn'nlalns, is also a common food-fish of the North Atlantic. The tuna, Thunnus thynnus, is called the tunny or horse-mackerel on our eastern coast, but is the tuna of California. They are eagerly sought with hook FIG. 402. The mackerel, Scomber scombrus. (From Jordan and Evermann.) and line, and many have been landed by this means that weighed over one hundred pounds. Family XIPHIID.E. - - The Swordfishes. The single species, Xiphias gladius, belonging to this family is widely distributed in salt waters. It reaches a maximum weight of about six hun- dred pounds, and its prolonged upper jaw makes it a formidable foe. Sometimes fishing boats are pierced and sunk by the sword of large individuals. The food of the swordfish consists of squids, mackerel, menhaden, and other fish, and it in turn is a valuable article of food for man. Family PLEURONECTID.E. - - The Flounders. These are flat- fishes known as flounders, halibuts, soles, plaice, and turbots. They are flattened from side to side, and thus adapted for life on the sea bottom. Frequently they are colored on the upper surface so as to resemble the sand or other material surrounding them. The young flatfish resembles an ordinary fish when it hatches, but it soon begins to broaden laterally and swim on its side, while the eye on the lower side moves around to the upper 470 COLLEGE ZOOLOGY side. The common halibut, Hippoglossus kippoglossus, and the winter flounder, Pseudopleuronectes americanus (Fig. 403), are important American food- fishes. > " , ;-'--- ; ^,^ v,//;/j '-'.'/?;// FIG. 403. The flounder, Pseudopleuronectes americanus. (From Dean, after Goode.) Family GADID.E. - - The Codfishes. Many of our most im- portant food-fishes, the pollacks, codfishes, haddocks, and hakes, belong to this family. The common codfish is Gadus callarias (Fig. 404). " From the earliest settlement of America the cod jj vig FIG. 404. The cod, Gadus callarias. (From the Cambridge Natural History, after Goode.) has been the most valuable of our Atlantic coast fishes. In- deed, the codfish of the Banks of Newfoundland was one of the CLASS PISCES 471 principal inducements which led England to establish colonies in America." (Jordan and Evermann.) The total weight of the codfishes landed at Boston and Gloucester in 1908 was 41,615,- 277 pounds, valued at $1,042,683. The Bureau of Fisheries distributes millions of fry every year (see Table XV). SUBCLASS II. DIPNOI. THE LUNG-FISHES. - -The lung-fishes, of which there are only three living genera, are said to be inter- mediate between the fishes and amphibians. They possess certain structural features not found in other fishes, but char- acteristic of AMPHIBIA. On the other hand, they are in many respects like the HOLOCEPHALI and CROSSOPTERYGII. Among their important characters are their acutely lobate, paired fins (Fig. 405), an opening between the nasal sac and the mouth cavity, a persistent, unconstricted notochord, and an air-bladder which opens into the pharynx and functions as a lung. Family CERATODONTID.E. --The Australian lung-fish, Neocera- todus foster i (Fig. 405), is the only living species belonging to this FIG. 405. The Australian lung-fish, Neoceratodus fosleri. (From Sedg- wick's Zoology, after Giinther.) family. It lies on the bottom of stagnant pools and feeds on worms, mollusks, crustaceans, and other small animals that it gathers from the vegetation. Occasionally it comes to the sur- face in order to change the air in its single lung. Because of this lung it can exist in water unfit for fishes that breathe entirely with gills. Such an environment may have led to the evolution of lung-breathing AMPHIBIA from gill-breathing fishes. Family LEPIDOSIRENID^E. - - This family contains two genera of living fish. The three species of the genus Protopterus (Fig. 472 COLLEGE ZOOLOGY 406) are found in the marshes of Central Africa. They feed on crustaceans, worms, insects, and frogs, and breathe with a pair of lungs. During the dry summer season they burrow about FIG. 406. The African lung-fish, Protoplerus annectens. (From Sedgwick's Zoology, after Claus.) eighteen inches into the mud, where a cocoon of slime is secreted, and the fish remains inactive, breathing with its lungs, and living on fat stored in the kidneys and gonads, until the rainy season comes again. The second genus of this family, Lepidosiren, has but a single species, Lepidosiren paradoxa (Fig. 407), confined to the marshes and swamps of South America. It feeds on algae, mollusks, FIG. 407. The South American lung-fish, Lepidosiren paradoxa. (From Shipley and MacBride, after Kerr.) and other plants and animals, and comes to the surface to change the air in its lungs. Like the African lung- fish, it hibernates in the mud during the dry season. 5. DEEP-SEA FISHES Many families of fishes contain deep-sea species, and about thirty families of teleosts are known only from specimens taken in the sea at depths of over a thousand fathoms. At this depth conditions are quite different from those near the surface. There is probably no sunlight below two hundred fathoms; the CLASS PISCES 473 temperature is always a few degrees above the freezing-point; the pressure is a ton or more to the square inch, whereas it is only about fifteen pounds at the surface; and there is no vege- tation, so that the inhabitants of the depths must be carnivorous or live on organisms that sink toward the bottom. Fishes meet these conditions in various ways and are often curiously modified. Some have very large eyes so as to catch FIG. 408. A deep-sea fish, Stomias boa. The white dots are the luminous organs. (From Parker and Haswell, after Filhol.) as many rays of light as possible; these eyes probably serve in connection with phosphorescent organs. Others have small or rudimentary eyes and are blind; they depend upon tactile organs instead of eyes. Many have large mouths with long, sharp teeth, and enormous stomachs. The phosphorescent organs are vari- ously distributed over the body (small circular areas in Fig. 408). Some of them consist of a cup of secretory cells covered by a cellular lens. The secretion is luminous, and in certain cases acts as a lure; in others it probably enables the fish to see in the dark abyss of the ocean. 474 COLLEGE ZOOLOGY 6. FOSSIL FISHES A large number of species of fish are known only from their fossil remains. The earliest fish remains consist of spines and scales from the lower Silurian or Ordovician strata of the earth's crust, which were laid down probably twenty-five million years ago (see Table XVII). The slightly younger Devonian age is called the " Age of Fishes " because of the predominance of fishes over the other animals that lived at that time. A con- siderable portion of the TELEOSTOMI are fossils; four of the five families of the CROSSOPTERYGII; five of the seven families of the CHONDROSTEI; six of the eight families of the HOLOSTEI; and about fifteen families of the TELEOSTEI are fossil forms. In the DIPNOI there are two families of fossil and two of living species. The study of fossil fishes is very important because of the light these prehistoric forms shed upon the affinities of modern species. 7. THE ECONOMIC IMPORTANCE OF FISHES Fishes furnish an important article of food for man, and many of them provide a means of recreation because of the difficulty of hooking them and the desperate struggles they make before they can be captured. Most game-fishes are also useful as food, but this is not always the case; for example, the tarpon which occurs on our Atlantic coast is the greatest of game-fishes, but is not ordinarily eaten by man. A few species are injurious be- cause of the number of food-fishes and other valuable animals they destroy. The value of the fishing industry may be judged from sta- tistics obtained at Boston and Gloucester, where about seven eighths of all the fish captured offshore along the Atlantic coast are brought by the fishermen. During the calendar year 1908, 181,465,000 pounds of fish, worth to the fishermen $4,629,000, were landed at these two cities. The most important species CLASS PISCES 475 were the cod, haddock, hake, pollock, halibut, and mackerel. The salmon fisheries of Alaska are even more valuable. The total quantity taken in 1908 was 198,952,814 pounds, valued at $10,683,051. Fifty canneries and forty salting establish- ments were operated, and 12,183 persons were employed to catch, prepare, and transport the canned, pickled, fresh, and frozen fish. Of the fresh-water fishes the whitefish, lake-trout, rainbow- trout, brook trout, catfishes, sturgeon, suckers, black bass, pike, and perch are some of the more important species. In many places the fishes have been captured in such great numbers that laws regulating the fishing industry have been passed. The federal and state governments have also for many years operated fish hatcheries where the eggs of important fishes are kept during their development. In nature very few eggs are allowed to develop because of the attacks of fungi, and of animals such as other fishes, crayfishes, and wild fowls. A large percentage of the eggs collected and cared for in fish hatcheries develop. They are distributed either as well-de- veloped eggs or as young fish, and are planted in the waters from which the adult fishes were taken, and also in waters where the fishes are not native. In 1909 the Bureau of Fisheries operated 35 hatcheries and 84 subhatcheries, auxiliaries, and egg-collecting stations; these were located in 32 states and territories. " The regular hatcheries may be classified as follows with reference to the fishes propa- gated: Marine species, 3; river fishes of the eastern seaboard, 5; fishes of the Pacific coast, 5 ; fishes of the Great Lakes, 7 ; fishes of the interior regions, 15." (Bowers.) The total output of fish and eggs in 1909 was 3,107,131,911. "During the year applications were received for fish for planting in 10,111 dif- ferent bodies of water." A summary of distributions is given in Table XV. 476 COLLEGE ZOOLOGY TABLE XV SOME OF THE FISH AND EGGS DISTRIBUTED BY U.S. BUREAU OP FISHERIES FROM JUNE 30, 1 908, TO JUNE 30, 1909 SPECIES EGGS FRY 1 FlNGERLINGS 2 TOTAL i. Flatfish 786,626,000 786,626,000 2. Pike-perch 457,850,000 l87,O5O,OOO 644,900,000 3. Whitefish 142,220,000 277,445,000 419,665,000 4. White perch 24,500,000 318,760,000 2,650 343,262,650 5. Yellow perch IO,OOO,OOO 213,610,410 50,873 223,661,283 6. Cod 153,536,000 153,536,000 7. Blueback salmon IOO,OOO 93,409,49 6 93,509,496 8. Lake-trout 22,806,000 27,188,177, 1,345,100 51,339,277 9. Brook trout 905,000 5,821,322 3,723,489 10,449,811 10. Rainbow- trout 286,150 292,408 2,026,463 2,605,021 ii. Large- mouth black bass 32,500 540,962 573,462 12. Small-mouth black bass 262,674 111,924 374,598 Besides this, 568,150 eggs were shipped to Argentina, France, and Germany. The destructive fishes are injurious principally because they devour other valuable fish, lobsters, etc. Of the fresh-water fishes belonging in this category may be mentioned the bow fin, Amia caha (Fig. 384), which bites voraciously and breaks tackle; the garpike, Lepisosteus osseus (Fig. 383), which is very de- structive to young fish; the German carp, Cyprinus carpio (Fig. 386), which stirs up mud and keeps out superior fish; and the muskallunge, Esox masquinongy, which does considerable damage by devouring the young of whitefish and other food- fishes. 1 Fry = fish up to the time the yolk sac is absorbed and feeding begins. " Fingerlings = fish between the length of one inch and the yearling stage. CHAPTER XVIII SUBPHYLUM VERTEBRATA: CLASS IV. AMPHIBIA THE common amphibians are the frogs, toads, and salamanders. They spend part or all of their existence in the water or in damp places. Most of them lay their eggs in the water, and the larvae, which breathe with gills, are known as tadpoles or pollywogs. Some amphibians are often confused with reptiles (especially with the lizards) because of their similarity of form, but almost all reptiles possess scales, whereas amphibians have usually a smooth, slimy skin without scales except in a few rare species. There are two orders of extinct amphibia and three orders of living forms. The latter are as follows: - Order i. APODA. --The APODA or CCECILIANS are legless, worm-like amphibians inhabiting tropical and subtropical regions. Order 2. CAUDATA. --These are amphibians with tails. They include the mud-puppies, sirens, and salamanders. Order 3. SALIENTIA. - - The tailless AMPHIBIA, frogs and toads, belong to this order. i. THE FROG The leopard frog, Rana pipiens, lives in or near fresh-water lakes, ponds, and streams, and is distributed over the North American continent except on the Pacific slope. The frog leaps on land and swims in the water. The hind legs are large and powerful. When the frog is on land they are folded up, and a sudden extension propels the body through the air. Like- wise in swimming the hind legs are alternately folded up and 477 478 COLLEGE ZOOLOGY extended, and during their backward stroke the toes are spread apart so as to offer more resistance to the water. Frequently frogs float on the surface with just the tip of the nose exposed and with the hind legs hanging down. When disturbed in this position, the hind legs are flexed, a movement which withdraws the body, the fore legs direct the frog downward, and then the hind legs are extended, completing the dive. Frogs croak mostly during the breeding season, but also at other times of the year, especially in the evening or when the atmosphere becomes damp. Croaking may take place either in air or under water. In the latter case the air is forced from the lungs, past the vocal cords, into the mouth cavity, and back again. The principal enemies of frogs are snakes, turtles, cranes, herons, other AMPHIBIA, and man. The excellence of frogs' legs for the table has resulted in widespread destruction, and this has been augmented by the capture of great numbers for use in scientific investigations. Tadpoles fall a prey to aquatic insects, fishes, and water-fowl, and very few of them reach maturity. External Features. - - The body of the frog may be divided into the head and trunk. The eyes usually protrude from the head, but are drawn into their orbits when the frog closes its eye- lids. Behind each eye is a tympanic membrane covering the ear- drum. A pair of nostrils or external nares are situated on the dorsal surface near the end of the snout. Just in front of the eyes in some specimens is a light area, called the brow spot, which, in the embryo, was connected with the brain. The mouth of the frog extends from one side of the head to the other. The anus is situated at the posterior end of the body. The fore legs are short and serve to hold up the anterior part of the body. The hands possess four digits and the rudiment of a fifth, the thumb. In the male the inner digit is thicker than the corresponding digit of the female, especially during the breed- ing season. The hind legs are folded together when the frog is CLASS AMPHIBIA 479 at rest. They are long and powerful. The five toes are con- nected by a web, making the foot an efficient swimming organ. The skin is smooth and loose ; it contains large black pigment spots and a lesser amount of green and golden pigments. The skin consists, as in other vertebrates (Fig. 347), of two layers, an outer epidermis and an inner derm-is. It is furnished with a large number of mucus glands which secrete the fluid that makes the surface of the body slimy, and a smaller number of poison glands, which secrete a whitish fluid of use probably for defen- sive purposes. General Internal Anatomy. The body of the frog is supported by a bony skeleton, is moved by muscles, and contains a well-de- veloped nervous FIG. 409. Diagrammatic transverse section of the body of a female frog, to show relation of peri- toneum (broken line) to viscera. Ao, aorta; Ds, dorsal subcutaneous lymph space; G, intestine; IV C, inferior vena cava; A" : kidney; LS, lateral , -re ,1 i i .1 K C, interior vena cava; yv. Kiuiiey; L,J, laieia system. the body- suhcutaneous lymph space . NC , spinal cord, wall IS slit open in n,n, nerves; Od, oviduct; Of, ovary; S, great dorsal the ventral middle lymph space; line from the terior end of subcutaneous lymph space; i, 2, 3, mesenteries sus- pending the intestine, ovaries, and oviducts. The skin is represented by a thick black line. (From Bourne.) pos- the body to the angle of the jaw, the organs in the body-cavity or coelom will be exposed. The heart lies within the sac-like pericardium ; it is partially surrounded by the three lobes of the reddish brown liver. The two lungs lie one on either side near the anterior end of the ab- dominal cavity. Coiled about within the body-cavity are the stomach and intestine. The kidneys are flat reddish bodies 480 COLLEGE ZOOLOGY attached to the dorsal body-wall. The two testes of the male are small ovoid organs suspended by membranes and lying at the sides of the alimentary canal. The ovaries and oviducts of the female occupy a large part of the body-cavity during the breeding season. The ccelom is lined with a mesodermal mem- brane, the peritoneum (Fig. 409). The reproductive organs and alimentary canal are suspended by double layers of peritoneum called mesen- teries (Fig. 409, i, 2, j). The ' Digestive System. - - The food of the frog consists principally of living worms and insects. These are usually captured by the extensile tongue, which can be thrown forward as shown in Figure 410. The object adheres to the tongue, which is covered with a sticky secretion, and is then drawn into the mouth. No attention is paid to objects that are not moving. Large insects are pushed into the mouth with the forefeet. If the object swallowed is undesirable, it can ^g ejected through the mouth. . . , . ~. The mouth cavity is large (Fig. 411). I he f on a ue (T) \{ es O n the floor of the cavity with its anterior end attacned to the jaw and its forked posterior end lying free. When a lymph space beneath the tongue is filled, the tongue is thrown forward for capturing insects (Fig. 410). The teeth are conical in shape and are borne by the upper jaw and by two bones of the roof of the mouth called vomers (Fig. 411, V). They are used only for holding food and not for masticating it. New teeth replace those that become worn out. The oesophagus opens into the mouth cavity by a horizontal slit (Fig. 411, O); it is a short distensible tube leading directly to the stomach. The stomach is crescent-shaped and lies mostly on the left side of the body; it is large at the anterior or cardiac FIG. 410. - Three stages of the movement of the tongue of a frog, Rana csculenta. (From the Cambridge Natural History.) CLASS AMPHTRfA 481 tr- end, but constricted at the posterior or pyloric end where it joins the small intestine. The walls of the stomach are thick, con- sisting of four layers : (i) the outer thin peritoneum; (2) a tough muscular layer; (3) a spongy layer, the submucosa; and (4) an inner folded mucous layer, the mucosa. The mucosa is made up of glands lying in connective tissue. Near the cardiac end the glands are longer than at the pyloric end. The anterior portion of the small in- testine is known as the duodenum; this leads to the much-coiled ileum, which widens into the large intestine. The ali- mentary canal, as well as the urinary bladder and reproductive ducts, open into a sac-like cavity called the cloaca. The inner layer of the intestine, the mucosa, is much folded ; it consists of ordinary absorptive cells and goblet cells. The digestive glands are the pancreas The pancreas lies between G, glottis; /, lower jaw; L, lateral subrostral fossa; M, median subrostral fossa: N, posterior nares; 0, oesophagus; P, pulvinar rostrale ; S, opening of empties it into the common bile-duct, vocal sac; T, tongue; v, r^, ; , ,, i t. j j j i_ vomer ; tp, tuberculum pre- The liver is a large three-lobed reddish linguale (From Ho lmes.) gland which secretes an alkaline diges- tive fluid called bile. This fluid is carried by bile capillaries into the gall-bladder, where it is stored until food enters the in- testine, when it passes into the duodenum through the common bile-duct. Digestion begins in the stomach. The alkaline fluid secreted by the mucosa layer of the oesophagus and the acid gastric juice secreted by the glandular walls of the stomach digest out the proteid portion of the food by means of & ferment, called pepsin, 2 I and liver. the duodenum and the stomach. It is a much-branched tubular gland which secretes an alkaline digestive fluid and T-- FIG. 411. Mouth of the frog widely opened. E, Eustachian tubes; 482 COLLEGE ZOOLOGY which changes proteids into soluble peptones. The food then passes through the pyloric constriction into the intestine. Here it is attacked by the pancreatic juice and the bile. The pan- creatic juice contains three ferments: (i) irypsin, which converts proteids into peptones; (2) amylopsin, which converts starch into sugar; and (3) steapsin, which splits up fats into fatty acid and glycerin. The bile emulsifies fats and converts starch into sugar. The intestinal wall produces a secretion which probably aids in converting starch into sugar. Absorption begins in the stomach, but takes place principally in the intestine. The food substances which have been dis- solved by the digestive juices are taken up by the mucosa layer, passed into the blood and lymph, and are then transported to various parts of the body. The undigested particles of food pass out of the intestine into the cloaca and are then discharged through the anus as faeces. The absorbed food is used by the frog to build up new pro- toplasm to take the place of that consumed in the various life activities, and to increase the size of the body. Food is stored up in the liver as glycogen, a carbohydrate similar to starch and often called " animal starch." When needed by the body, this glycogen is changed into dextrose by enzymes produced by the liver, and slowly passed into the blood. During the winter the hibernating frog lives largely on the glycogen stored up in the liver in the autumn. The Respiratory System. - - Respiration takes place to a con- siderable extent through the skin both in water and in air, but is carried on principally by the lungs. As shown in Figure 412, air passes through the nostrils or external nares (Fig. 412, A, e.n) into the olfactory chamber (olf.s), and then through the internal or posterior nares (Fig. 412, /./?; Fig. 411, N) into the mouth cavity. The external nares are then closed (Fig. 412, B, e.n), the floor of the mouth is raised, and the air is forced through the glottis (Fig. 412, B, gl; Fig. 411, G) into a short tube, the larynx, and thence into the lungs (Ing). Air is expelled from the lungs CLASS AMPHIBIA 483 into the mouth cavity by the contraction of the muscles of the body-wall. The air in the mouth cavity is changed by throat movements. The glottis remains closed, while the floor of the mouth is alter- prn e.n i.'t FIG. 412. Diagram to illustrate the respiratory movements of the frog. In A the floor of the mouth is depressed, the nares are open, and air rushes through them into the buccal cavity. In B, the floor of the mouth is raised, the nares are closed, and air is forced from the buccal cavity into the lungs. e.n, external nares ; gl, glottis ; gul, gullet ; i.n, internal nares ; Ing, lung ; olf.s, olfactory chamber ; pmx, premaxillary bone ; tng, tongue. (From Holmes, after Parker.) nately raised and lowered. Air is thus drawn in and expelled through the nares. The lungs are pear-shaped sacs with thin, elastic walls. The area of their inner surface is increased by folds which form minute chambers called alveoli. Blood capillaries are numerous in the walls of these alveoli. The larynx is strengthened by five cartilages. Across it are stretched two elastic bands, the vocal cords. The croaking of the frog is produced by the vibrations of the free edges of the 484 COLLEGE ZOOLOGY vocal cords due to the expulsion of air from the lungs. The laryngeal muscles regulate the tension of the cords, and hence the pitch of the sound. Many male frogs have a pair of vocal sacs which open into the mouth cavity (Fig. 411, 5"); they serve as resonators to increase the volume of sound. The Circulatory System. - - The circulatory system of the frog consists of a heart, arteries, veins, and lymph spaces. The blood is a plasma containing three kinds of corpuscles, - - red corpuscles, white corpuscles, and spindle cells. The blood plasma carries food and waste matter in solution. It coagu- lates under certain conditions, forming a dot of fibrin and cor- puscles, and a liquid called serum. The power of coagulation is of decided benefit, since the clot soon closes a wound and thus prevents loss of blood. c -^sssss^ The red corpuscles FIG. 413 a. -- Blood corpuscles of the frog, (erythrocytes, Fig. a, red; b, white; c, spindle cells. (From Holmes, \ pllmtiril after Dekhuyzen.) 4I 3 a > a ) ar lcal > flattened cells con- taining a substance called hamoglobin. Haemoglobin combines with oxygen in the capillaries of the respiratory organs and gives it out to the tissues of the body. The white corpuscles (leucocytes, Fig. 413 a, b] are ameboid in shape, vary in size, and are capable of independent movement. They are of great value to the animal, since they engulf small bodies, such as bacteria, thereby frequently preventing the multiplication of pathogenic organisms and consequently helping to overcome germ diseases. White corpuscles also aid in the removal of broken-down tissue. The spindle cells (Fig. 413 a, c] are usually spindle-shaped. In the springtime they develop into red cor- puscles. Blood corpuscles arise principally in the marrow of the bones. They also increase in numbers by division while in the blood-vessels. Some white corpuscles are probably formed CLASS AMPHIBIA 485 in the spleen, a gland in which worn-out red corpuscles are destroyed. The heart (Fig. 413 b, Fig. 414) is the central pumping station of the circulatory system. It is composed of a conical, muscular ventricle (Fig. 413 b, /), two thin- walled auricles, one on the right (2), the other on the left (j), a thick- walled tube, the truncus arteriosus (4) , which arises from the base of the ventricle, and a FIG. 413 b. Heart of the frog. A, ventral view. B, dorsal view. C, ven- tral wall removed. /, ventricle; .', right auricle; 3, left auricle; 4, truncus arteriosus; 5, carotid arch; 6, lingual artery; 7, carotid gland; 8, carotid artery; g, systemic arch; 10, pulmocutaneous arch; //, innominate vein; /.?, subclavian vein; 13, vena cava inferior; 14, vena cava superior; ij, opening of sinus venosus into right auricle; 16, pulmonary vein; 17, aperture of entry of pulmonary vein; 18, semi-lunar valves; ig, longitudinal valve; 20, point of origin of pulmocutaneous arch. (From Shipley and MacBride, after Howes.) thin-walled, triangular sac, the sinus venosus (Fig. 413 b, B), on the dorsal side. The arteries (Fig. 414) carry blood away from the heart. The truncus arteriosus (Fig. 413 b, 4; Fig. 414, tr.a) divides as shown in Figure 413, A, and each branch gives rise to three arteries. (i) The common carotid (Fig. 413 b, A, 5; Fig. 414, c.c) divides into the lingual or external carotid (Fig. 414, /), which supplies the tongue and neighboring parts, and the internal carotid, which gives off the palatine artery to the roof of the mouth, the cerebral 4 86 COLLEGE ZOOLOGY carotid to the brain, and the ophthalmic artery to the eye. Where the common carotid branches is a swelling called the carotid gland (Fig. 413 b, A, 7); this body impedes the blood flow in the internal carotid artery. (2) The pulmocutaneous artery (Fig. 413 b, A, /o ; Fig. 414, p.cu) branches, forming the pulmonary artery, which passes to the lungs, and the cutane- ous artery. The latter gives off the auricularis, which is distributed to the lower jaw and neigh- boring parts, the dorsalis, which supplies the skin "^ , of the back, and the -/7c ~ V7t lateralis, which supplies -y * =- , M~~ u the skin of the sides. \ f f I ^*n' Most of these branches carry blood to the re- spiratory organs lungs, skin, and mouth. (3) The third branches 3C . /T-" ~ TV . , or systemic arches (rig. FIG. 414. Diagram of the arterial system of the frog, ventral view, ao", aortic arch; 413 b, A, 9; Fig. 414, ao") au', right auricle; aw", left auricle; br, brachial artery ; c.c, carotid ; c.gl, carotid gland ; c.tt, common iliac ; cce, coeliaco-mesenteric ; CCE', cceliac; cu, cutaneous; d.ao, dorsal aorta; fm, femoral ; g, gastric ; h, hcemorrhoidal ; hp, hepatic; hy, epigastrico-vesical; k, kidney; /, lingual; Ig", left lung; m, anterior mesen- teric; m.i, posterior mesenteric; oc, occipital; pc', pancreatic ; p.cu, pulmocutaneous ; put, pulmonary; re, renal; sc, sciatic; sp, splenic; tr.a, truncus arteriosus; ts, testis; v, vertebral. (From Holmes, after Howes.) after passing outward and around the aliment- ary canal unite to form the dorsal aorta (d.ao). As shown in Figure 414, each systemic arch gives off an occipito-vertebral artery, which divides, one CLASS AMPHIBIA 487 branch, the occipital (oc), supplying the jaws and nose, the other, the vertebral (v), supplying the vertebral column, and a subclavian artery (br), which is distributed to the shoulder, body- wall, and arm. The dorsal aorta (d.ao) gives off the cceli- aco-mesenteric artery (cos); this divides, forming the cceliac (coe 1 ), which supplies the stomach, pancreas, and liver, and the anterior mesenteric (m), which is distributed to the intestine, spleen, and cloaca. Posterior to the origin of the cceliaco- mesenteric, the dorsal aorta gives off four to six urinogenital arteries (re) which supply the kidneys (k), reproductive organs (ts), and fat bodies. A small posterior mesenteric artery (m.i) arises near the posterior end of the dorsal aorta and passes to the rectum, and in the female to the uterus. The dorsal aorta finally divides into two common iliac arteries (c.il), which are distributed to the ventral body- wall, the rectum, bladder, the anterior part of the thigh (femoral artery, fm), and other parts of the hind limbs (sciatic artery, sc). The veins (Fig. 415) return blood to the heart. The blood from the lungs is collected in the pulmonary veins (put) and poured into the left auricle (/. au). The rest of the venous blood is carried to the sinus venosus (s.v) by three large trunks, the two anterior venae cavae (pr. cv) and the posterior vena cava. The anterior venae cavae receive blood from the external jugulars (ext. ju) which collect blood from the tongue, thyroid, and neighboring parts, the innominates which collect blood from the head by means of the internal jugulars (int. ju} and from the shoulder by means of the subscapulars, and the subclavians which collect blood from the fore limbs by means of the brachial (br) and from the side of the body and head by means of the musculocutaneous veins (ms. cu). The posterior vena cava receives blood from the liver (for) by means of two hepatic veins (/;/>), from the kidneys (kd) by means of four to six pairs of renal veins (rn), and from the reproductive organs (ts) by means of spermatic or ovarian veins. The veins which carry blood to the kidneys constitute the 488 COLLEGE ZOOLOGY npl FIG. 415. Diagram of the venous system of the frog, dorsal aspect. abd, abdominal vein; br, brachial vein; cd, cardiac vein; ds.lmb, dorso-lumbar vein; du, duodenal; ext.ju, external jugular; fm, femoral; gs, gastric; hp, hepatic; hp.pt, hepatic portal; int, intestinal; int.ju, internal jugular vein; kd, kidney; l.au, left auricle; Ing, lung; hr, liver; ms.cu, musculocu- taneous vein; pr.cv, precaval; pt.cv, postcaval; pul, pulmonary; pv, pelvic; r.au, right auricle; rn, renal; rn.pt, renal portal; sc, sciatic; spl, splenic; spm, spermatic; s.v, sinus venosus; ts, testis; ves, vesical veins. (From Parker and Haswell.) CLASS AMPHIBIA" 489 renal portal system. The renal portal vein (Fig. 415, rn.pt] receives the blood from the hind legs by means of the sciatic (sc) and femoral (fm) veins, and blood from the body-wall by means of the dorso-lumbar vein (ds.lmb). The liver receives blood from the hepatic portal system. The femoral veins (fm] from the hind limbs divide, and their branches unite to form the abdominal vein (abd]. The abdominal vein also collects blood from the bladder, ventral body-wall, and heart. The portal vein carries blood into the liver from the stomach, intestine, spleen, and pancreas. Circulation takes place in the following manner: The sinus venosus contracts first, forcing the impure venous blood into the right auricle (Fig. 413 b, C, 75). Then both auricles contract, and the oxygenated blood brought into the left auricle by the pulmonary veins is forced into the left part of the ventricle, and the impure blood from the right auricle is forced into the right side of the ventricle. The ventricle then contracts and the impure blood is forced out first, passing principally into the pulmocutaneous arteries and thence to thje lungs and skin, and the oxygenated blood is forced out later through the carotid and systemic arteries to the other parts of the body. The blood is prevented from flowing back, and the oxygenated blood and impure blood are distributed as stated above, by means of valves (Fig. 413 b, C, 18, 19]. The blood that is thus forced through the arteries makes its way into tubular blood-vessels that become smaller and smaller until the extremely narrow capillaries are reached. Here food and oxygen are delivered to the tissues, and waste products are taken up from the tissues. The renal portal system carries blood to the kidneys, where urea and similar impurities are taken out. The hepatic portal system carries blood to the liver, where bile and glycogen are formed. The blood brought to the lungs and skin is oxygenated and then carried back to the heart. The passage of blood through the capillaries can easily be observed in the web of the frog's foot or in the tail of the tadpole. 4QO COLLEGE ZOOLOGY The lymph spaces in the frog's body are very large. They communicate with one another and with the veins. Four lymph hearts, two near the third vertebra and two near the end of the vertebral column, force the lymph by pulsations into the internal jugular and transverse iliac veins. The lymph is colorless and contains colorless corpuscles. The Excretory System (Fig. 416). -- A certain amount of sub- stance resulting from the breaking down of living matter is --12 A B FIG. 416. --Urinogenital organs of the frog. A, male. /, fat body; 2, mesentery; j, efferent ducts of testis; 4, ducts of seminal vesicle; 5, seminal vesicle; 6, archinephric duct; 7, cloaca; 8, orifice of ureter; Q, proctodeum ; 10, allantoic bladder; //, rectum; 12, kidney; 13, testis; 14, adrenal body. B, female. /, oesophagus; 2, mouth of oviduct; j, left lung; 4, fat body; 5, left ovary; 6, archinephric duct; 7, oviduct; 8, allantoic bladder; Q, cloaca; 10, aperture of oviduct; //, aperture of archinephric duct; 12, proctodeum; 13, mesentery; 14, kidney. (From Shipley and MacBride, after Howes.) excreted by the skin, liver, and intestinal walls, but most of it is taken from the blood in the kidneys (Fig. 416, A, 12), passes through the ureters (6), and then by way of the cloaca (7) into CLASS AMPHIBIA 491 the bladder (10), where it is stored until expelled from the body through the anus. The kidney is composed of connective tissue containing a large number of uriniferous tubules (Fig. 417, 7"), each of which begins in a Mai pig/nan body U/), consisting of a coiled mass of blood-vessels, the glomerulus, and an enclosing membrane called Bosnian's capsule. The excretions are carried by the uriniferous tubules to a collecting tubule (C) and thence into the ureter (U). Ciliated funnels, called nephrostomes (N), occur in the ventral portion; these are in the young frog con- nected with the renal tubules, but open into branches of the T U FIG. 417. Diagram of a cross-section of the kidney of the frog. B, Bidder's canal; C, collecting tubule; D, dorsal surface of kidney; L, lateral edge of kidney; M, Malpighian body; N, nephrostome; T, uriniferous tubules; U, ureter; V, renal portal vein. (From Holmes.) renal vein in the adult. Renal arteries (Fig. 414, re) and the renal portal vein (Fig. 415, rn.pt; Fig. 417, V] bring blood into the kidney. Blood leaves the kidney by way of the renal veins (Fig. 415, ni). The Reproductive System. - - The sexes are separate. The male can be distinguished from the female by the greater thick- ness of the inner digit of his fore legs. The spermatozoa of the male arise in the testes, pass through the vasa ejffcrentia (Fig. 416, A, j) into the kidneys, then by way of Bidder's canal (Fig. 417, B} to the ureter (Fig. 416, A, 6); and thence out through the anus. The eggs arise in the ovaries of the female (Fig. 416, B, 5), break out into the body-cavity, make their way into the coiled 492 COLLEGE ZOOLOGY oviduct (7) through a small opening (2), and pass down into the thin-walled, distensible uterus. The glandular wall of the ovi- duct secretes the gelatinous coats of the eggs. The fertilization and development of the eggs will be described later (pp. 506- Just in front of each reproductive organ is a yellowish, glove- shaped fat-body (Fig. 416, A, /; B, 4) which serves to store up nutriment. Glands. - - Besides the liver and pancreas, there are a number of glands in the body of the frog that are of great importance because of their secretions. These glands have no ducts, but empty their products directly into the body; they are therefore called ductless glands, and their products are called internal secretions. Internal secretions are also produced by other organs, e.g. the liver forms sugar and urea. The spleen is a reddish body situated above the anterior end of the cloaca. In it old blood corpuscles are destroyed and new colorless corpuscles are probably formed. The two thyroid glands are situated one on either side of the hyoid. Their secretions contain a large amount of iodin. The function of the thyroid is not certain in the frog. In man its atrophy causes a disease called cretinism. The two thymus glands lie one behind each tympanum, be- neath the depressor mandibulae muscle. Their function is not certain. The adrenal bodies are long, thin glands lying on the ventral surface of the kidneys. They secrete adrenalin, a substance . necessary for the life of the animal.. When adrenalin is ex- tracted and then injected into the blood of a mammal, it causes a contraction of the blood-vessels and therefore raises the blood pressure. The Skeleton. - - The skeleton of the frog consists principally of bone. The axial portion comprises the skull and vertebral column. The appendicular portion consists of the pectoral and pelvic girdles and the bones of the limbs which they support. CLASS AMPHIBIA 493 FIG. 418. Skeleton of the frog. A, skull and vertebral column, dorsal surface. B, skull and vertebral column, ventral surface. C, side view of urostyle; bristle passes through opening of loth spinal nerve. D, visceral arches, ar, neural arch; av, atlas; c, centrum; ex, exoccipital; fm, foramen magnum; H, basilingual plate; Ha, hyoid arch; H p, thyrohyal; mx, maxilla; na, nasal; O, orbital fossa; pal, palatine; par, parasphenoid; pf, parieto- frontal; pinx, premaxilla; pro, prootic; pig, pterygoid; qj, quadratojugal; sp. el, sphenethmoid; sq, squamosal; trv, transverse process; ur, urostyle; vo, vomer; zyg, zygopophysis (From Bourne, after Ecker.) 494 COLLEGE ZOOLOGY The cartilage and bones of the skull may be grouped into two main divisions: (i) the brain case and auditory and olfactory capsules, which constitute the cranium; and (2) the jaws and hyoid arch, which constitute the visceral skeleton. CRANIUM. - - A large part of the cranium consists of cartilage (dotted in Fig. 418). The bones are either ossifications of the cartilage (the exoccipitals (ex), prootics (pro), and ethmoid), or are developed from membranes and invest the cartilage and cartilage bones. The spinal cord passes through a large open- .ing, the foramen magnum (Fig. 418, fm), in the posterior end of the cranium. On either side of this opening is a convexity of the exoccipital bones (ex), called the occipital condyle, which articulates in life in a concavity of the first vertebra (av), and enables the frog to move its head. The cranial bones of the dorsal side are the prootics (Fig. 418, pro) which inclose the inner ears, the frontoparictals (/>/) which form most of the roof of the cranium, the sphenethmoid (sp. et) which forms the posterior wall of the nasal cavity, and the nasals (no) which lie above the nasal capsules. The ventral surface of the cranium discloses the central, dagger-shaped parasphenoid (par) and the vomers (vo) which bear the vomerine teeth. THE VISCERAL SKELETON. - - The jaws and hyoid, which con- stitute the visceral skeleton, are also preformed in cartilage and then strengthened by ossifications. The upper jaw or maxillary arch consists of a pair of premaxilla (Fig. 418, pmx), a pair of maxilla (mx), and a pair of quadratojugals (qj). The maxillae and premaxillae bear teeth. The lower jaw or mandibular arch consists of a pair of cartilaginous rods (Meckel's cartilages) invested by a pair of dentary bones, and a pair of angulo-splenials. The jaws are attached to the cranium by a suspensory apparatus consisting of the squamosals (Fig. 418, sq), the ptery golds (ptg), and the palatines (pal). The visceral arches are represented in the adult by the hyoid and its processes (Fig. 418, D). The cartilaginous basilingual plate lies in the floor of the mouth cavity. The hyoid arches CLASS AMPHIBIA 495 (Fig. 418, D, Ha) curve upward and join the prootics on either side. Two ossified posterior processes, the thyrohyals (Hp) help support the larynx. THE VERTEBRAL COLUMN (Fig. 418). - - The vertebral column consists of nine vertebra and a blade-like posterior extension, the urostyle. The vertebrae consist of a basal centrum, which is concave in front and convex behind (proccelous type), and a neural arch (Fig. 418, ar) through which the spinal cord passes. The neural arch possesses a short, dorsal spine, a transverse process (trv) on each side (except on the first vertebra, av), and a pair of articulating processes, called zygapophyses (zyg), at each end. The vertebras are held together by ligaments, and move on one another by means of the centra and zygapophyses. The vertebral column thus serves as a firm axial support which also allows bending of the body. THE APPENDICULAR SKELETON. - - The pectoral girdle and sternum (Fig. 419, A) support the fore limbs, serve as attach- ments for the muscles that move the fore limbs, and protect the organs lying within the anterior portion of the trunk. They are composed partly of bone and partly of cartilage. The supra- scapulae lie above the vertebral column, and the rest of the girdle passes downwards on either side and unites with the sternum in the ventral, middle line. The principal parts are the supra- scapula (Fig. 419, A, s. sc), the scapula (sc), the clavicles (cl), the coracoids (cor}, the epicoracoids (ep.c), the ommosternum (os), episternum (ep), mesosternum (mes), and xiphisternum (.v/). The end of the long bone of the fore limb (humerus) lies in a concavity in the scapula and coracoid called the glenoid fossa (gl). The pelvic girdle (Fig. 419, B) supports the hind limbs. It consists of two sets of three parts each, the ilium (II), the ischium (Isch), and the pubis (Pu). The pubis is cartilaginous. The anterior end of each ilium is attached to one of the trans- verse processes of the ninth vertebra. Where the parts of each half of the pectoral girdle unite, there is a concavity, called 49 6 COLLEGE ZOOLOGY the acetabulum (Ac}, in which the head of the long leg bone (femur) lies. The fore limbs (Fig. 420, A) consist of a humerus which articu- lates with the glenoid fossa of the pectoral girdle at its proximal FIG. 419. Skeleton of the frog. A, pectoral girdle, cl, clavicle; cor, cora- coid; ep, episternum; ep.c, epicoracoid; gl, glenoid cavity; mes, mesosternum; os, ommosternum; sc, scapula; s.sc, suprascapula; xi, xiphisternum. B, pelvic girdle, side view. Ac, acetabulum; //, ilium; Isch, ischium ; Pu, pubis. (From Bourne, after Ecker.) end and with the radio-ulna (ru) at its distal end. The bone of the forearm (radio-ulna) consists of the radius and ulna fused. The wrist contains six bones: the ulnare (u) f radiale (r), inter- CLASS AMPHIBIA 497 medium (/?;?), and three car pah (a, b, c). The hand is supported by five proximal metacarpal bones, followed in digits II and III by two phalanges, and in digits IV and V by three phalanges. The hind limbs (Fig. 420, B) consist of (i) & femur or thigh bone, (2) a tibio-fibula (the tibia and fibula fused) or leg bone, (3) four tar sal bones, the astragalus (tibiale, a), the calcaneum B FIG. 420. -Skeleton of the limbs of the frog. A, fore limb, a, b, c, carpals; im, intermedium ; r, radiale ; rn, radis-ulna ; I-V, digits. B, hind limb. a, ostragalus ; c, calcaneum; I-V, digits ; X,. accessory digit. (From Bourne, after Ecker.) (fibulare, b}, and two smaller bones, (4) the four metatarsals of the foot, (5) the phalanges of the digits, and (6) the prehalhix (X) of the accessory digit. The Muscular System (Fig. 421). -- Muscles are usually attached by one or both ends to bones either directly or by means of a tendon, which is an inelastic band of connective tissue. The two ends of a muscle are designated by different terms : the origin is the end attached to a relatively immovable part; the insertion is the movable end. A muscle which bends one part upon 2 K acifi fiul olfactory nerve; Op, optic nerve ; Spni, ist spinal medulla and ends in the Uro- nerve; Sgi-io, ten ganglia of sympa- style. It is surrounded by ^ etic sy , stem; f Vg ' 8 asseria ganglion: J Xg, ganglion of vagus. (From Sedg- two membranes, an outer wick's Zoology, after Ecker.) 504 COLLEGE ZOOLOC.Y dura mater and an inner pia mater. The cord is composed of a central mass of gray matter (Fig. 349, gni) consisting mainly of nerve-cells, and an outer mass of white matter made up chiefly of nerve-fibers. A median fissure occurs both in the dorsal and in the ventral side of the cord, and a central canal (c.c) lies in the gray matter and communicates anteriorly with the cavities of the brain. THE SPINAL NERVES. - - The relation of the spinal nerves to the spinal cord and the paths taken by nervous impulses are indicated in Figure 349. There are ten pairs of spinal nerves in the frog (Fig. 423, Spni, Br, Js). Each arises by a dorsal (Fig. 349, d.r) and a ventral (v.r) root (see p. 408) which spring from the horns of the gray matter of the cord. The two roots unite to form a trunk, which passes out between the arches of adjacent vertebras. The largest nerves are the brachial (Fig. 423, Br), which are composed of the second and branches from the first and third pairs of spinal nerves, and are dis- tributed to the fore limbs and shoulder, and the sciatics (Js), which arise from plexuses composed of the seventh, eighth, and ninth spinal nerves, and are distributed to the hind limbs. THE SYMPATHETIC SYSTEM (Fig. 423, Sgi-id). - -This system consists of two principal trunks, which begin in the prootic ganglion and extend posteriorly, one on either side of the vertebral column. Each trunk is provided with ten ganglionic enlargements (Sgi-io) at the points where branches from the spinal nerves unite with it. The nerves of the sympathetic system are distributed to the internal organs which are thus intimately connected. Sense-organs. - - The principal sense-organs are the eyes, ears, and olfactory organs. There are many smaller structures on the surface of the tongue, and on the floor and roof of the mouth, which probably function as organs of taste. Pn the skin are also many sensory nerve endings which receive contact, chemical, temperature, and light stimuli. CI-\SS \\IIMHI5IA 505 THE OLFACTORY ORGANS. The olfactory nerves (Fig. 423, 01) extend from the olfactory lobe of the brain (Fig. 422) to the nasal cavities (Fig. 412, olf.s), where they are distributed to the epithelial lining. The importance of the sense of smell in the life of the frog is not known. THE EAR. - - The inner car of the frog lies within the audilorv capsule and is protected by the prootic (Fig. 418, pro) and ex- occipital (ex) bones. It is similar in structure to that shown in Figure 350, page 411, and is supplied by branches of the auditory nerve. There is no external ear in the frog. The middle car is a cavity which communicates with the mouth cavity through the Eustachian tube (Fig. 411, E), and is closed externally by the tympanic membrane. A rod, the colitmclla, extends across the cavity of the middle ear from the tympanic membrane to the inner ear. The vi- brations of the tympanic membrane produced by sound waves are transmitted to the inner ear through the columella. The sensory end organs of the auditory nerve are stimulated by the vibrations, and the impulses carried to the brain give rise to the sensation of sound. The inner ears serve also as organs of equilibration. Frogs from which they are removed cannot main- tain ar upright position. THE EYE. - - The eyes of the frog resemble those of man in general structure and function (Fig. 351, pp. 411-413), but differ in certain details. The eyeballs lie in cavities (orbits, Fig. 418, 0) in the sides of the head. They may be rotated by six muscles and also pulled into the orbit. The upper evelid does not move independently. The lower eyelid consists of the lower eyelid proper fused with the third eyelid or nictitating membrane. The lens is large and almost spherical. It cannot be changed in form nor in position, and is therefore fitted for viewing distinctly objects at a certain definite distance. Movements are noted much oftener than form. The amount of light that enters the eye can be regulated by the contraction of the pupil. The retina of the eye is stimulated l>v tin rays of light which pass 506 COLLEGE ZOOLOGY through the pupil, and the impulses which are carried through the optic nerve to the brain give rise to sensations of sight. Behavior. - - The activities of the frog are such as to enable it to exist within the confines of its habitat. The ordinary movements are those employed in leaping, diving, crawling, burrowing, and maintaining an upright position. These and most of its other activities may be resolved into a series of reflex acts, although they are commonly said to be instinctive. In- stinct is " the faculty of acting in such a way as to produce cer- tain ends, without foresight of the ends, and without previous education in the performance." (James.) Some of the movements of the frog are due to internal causes, but many of them are the responses to external stimuli. Frogs are sensitive to light, and experiments have shown that both the eyes and skin are stimulated by it. The reaction to light causes the animal to orient its body so that it faces the source and is in line with the direction of the rays. Nevertheless, frogs tend to congregate in shady places. Frogs also seem to be stimulated by contact (thigmotropism, p. 36), as shown by their tendency to crawl under stones and into crevices. The desire for shade may, however, have some influence upon this reaction. The temperature modifies the responses both to light and to contact. Investigators who have studied the behavior of frogs have come to the conclusion that they are very stupid animals. It is possible to teach them certain things, and habits once formed are not easily changed. For example, Yerkes found that a frog could learn to follow a path in a labyrinth after about one hun- dred trials. If we consider the power to learn by individual experience as evidence of the presence of mind, then we must attribute a primitive sort of mind to the frog. Development. - - Frogs lay their eggs in water in the early spring. The male clasps the female firmly with his fore legs just behind her fore legs. After the male has been carried about by the female for several days, the eggs pass from the uterus out of the cloaca and are fertilized by the spermatozoa of the male, CLASS AMPHIBIA 507 which the latter discharges over them as they are extruded. The male then loses the clasping instinct and leaves the female. The jelly which surrounds and protects the eggs soon swells up through the absorption of water. Cleavage takes place as indicated in Figure 424. Some of the cells, called macromcrcs (Fig. 425, A, mg), are large because of a bountiful supply of yolk ; others, the micromeres (mi), are smaller. A blastula (Fig. 425, A) is formed by the appearance of a cavity, the blastocoel (bl. r/), near the center of the egg. Gastrulation is modified in the frog's egg because of the amount of yolk present. The dark FIG. 424. Segmentation of the frog's egg. after Ecker.) (From Sedgwick's Zoology, side of the egg gradually grows over the lighter portion until only a circular area of the latter, called the yolk plug (Fig. 425, yk.pl), is visible. This gastrula contains two germ-layers, an outer ectoderm (C, ect) and an inner entoderm (C, end). A third layer, the mesoderm (C, mes), soon appears between the other two, and splits into two, an inner splanchnic layer, which forms the supporting tissue and musculature of the alimentary canal, and an outer somatic or parietal layer, which forms the connective tissue, muscle, and peritoneum of the body-wall. The cavity between these two mesodermal layers is the ccdom. Soon after gastrulation a groove called the primitive or medullary groove (Fig. 425, B, md.gr) appears, on either side of which is a medullary fold (md.f). The medullary folds grow together at the top, forming a tube which later develops into the brain and spinal cord of the embryo. The medullary groove lies 508 COLLEGE ZOOLOGY along the median dorsal line, and the embryo now lengthens in this direction. The region where the yolk plug was situated lies at the posterior end. On either side near the anterior end two gill-arches appear (Fig. 425, D, br.cl), and in front of each of these a depression arises which unites with its fellow and ec ent FIG. 425. Development of the embryo of the frog. A, section of blastula. bl.casl, blastoccel; mi, micromeres; mg, macromeres. B, formation of medul- lary groove, ind.gr, and medullary fold, md.f; yk.pl, yolk-plug. C, section of egg in stage B to show germ-layers, bl.ccel, blastoccel ; blp, blastopore; ect, ectoderm; end, entoderm; ent, enteron; mes, mesoderm; nch, notochord; yk.pl, yolk-plug. D, older embryo, br.cl, branchial arches; stdm, stomo- daeum; /, tail. E, newly hatched tadpole, br.i, br.2, gills; e, eye; pcdm, procto- daeum; sk, sucker; stdm, stomodseum; t, tail. (From Parker and Haswell: A, D, after Ziegler's models; B, C, E, after Marshall.) moves to the ventral surface, becoming the ventral sucker (Fig. 425, E, sk). An invagination soon appears just above the ventral sucker; this is the stomodceum (stdm) which develops into the mouth. The invagination (proctod&um, Fig. 425, E, pcdm) which becomes the anus appears beneath the tail (/) at the posterior end. On either side above the mouth a thickening of the CLASS AMPHlllIA 509 ectoderm represents the beginning of the eye, and just above the gills (E, br.i, br.2.) appear the invaginations which form the vesicles of the inner ears. The markings of the muscle segments show through the skin along the sides of the body and tail. FIG. 426. Tadpoles in different stages of development, from those just hatched (i) till the adult form is attained (8). (From Mivart.) The embryo moves about within the egg by means of cilia, but these soon disappear after hatching. The tadpole, after breaking out of the egg membranes, lives for a few days on the yolk in the alimentary canal, and then feeds on algae and other vegetable matter. The external gills gr.>w out into long, branch- ing tufts (Fig. 426, 2, 2 a). Four pairs of internal ^ilh are formed 5io COLLEGE ZOOLOGY later, and, when the external gills disappear, these function in their stead, the water entering the mouth, passing through the gill-slits, and out of an opening on the left side of the body, called the spiracle. The hind limbs appear first (Fig. 426, 5). Later the fore limbs break out (6). The tail decreases in size as the end of the larval period approaches and is gradually resorbed (7). The gills are likewise resorbed, and the lungs develop to take their place as respiratory organs. Finally the form resembling that of the adult frog (8) is acquired. 2. A BRIEF CLASSIFICATION OF LIVING AMPHIBIA 1 There are about one thousand different species of AMPHIBIA - a number very much smaller than that of the other principal classes of vertebrates. Approximately forty of these belong to the order APODA, one hundred to the CAUDATA, and nine hun- dred to the SALIENTIA. Order i. Apoda (GYMNOPHIONA, Fig. 427). -- CCECILIANS. - Worm-like AMPHIBIA without limbs or limb-girdles; usually with small scales embedded in the skin; tail short or absent. Family CCECILIID^:. - - With the characters of the order. Examples: Dermophis, Coecilia, Gymnopis, Siphonops, Ichthyophis (Fig. 427). Order 2. Caudata (URODELA, Figs. 428-433). - Tailed AM- PHIBIA. AMPHIBIA with a tail ; without scales; usually two pairs of limbs; the adults with or without external gills and gill slits. Suborder i. PROTEIDA (Fam. PROTEID.E, Fig. 428). -- MUD- PUPPIES. --Tailed AMPHIBIA with two pairs of limbs; three pairs of external gills and two pairs of gill-open- ings persistent; no eyelids. 1 1 am indebted to Dr. Alexander G. Ruthven for the main divisions of this classification. CLASS A.MI'IHHTA 511 Family PROTEID.E. - With characters of the suborder. Examples: Xeclurus, Proteus, Typhlomolge. Suborder 2. MEANTES (Fam..SiRENiDAE, Fig. 429). SIRENS. -Tailed AMPHIBIA without hind limbs; three pairs of external gills and three pairs of gill-openings persistent; no eyelids. Family SIRENID.E. - - With the characters of the suborder. Examples: Siren, Pseudobranchus. Suborder 3. MUTABILIA (Fam. SALAMANDRID.E, Figs. 430- 433). SALAMANDERS. --Tailed AMPHIBIA with two pairs of limbs; without gills and generally without gill-openings in adult ; usually with movable eye- lids. Superfamily i. AMPHIUMOIDE^E. - - MUTABILIA with two pairs of small limbs; sometimes one pair of gill-open- ings; vertebrae amphiccelous ; without eyelids. Family CRYPTOBRANCHIP.E. - - With the characters of the superfamily. Examples: Cryptobranchus (Fig. 430), Superfamily 2. SALAMANDROIDE^E. - - MUTABILIA with- out gills or gill-openings in the adult; with movable eyelids; vertebrae usually opisthoccelous. The families are distinguished from one another principally by the position of the teeth and the number of toes. Family i. SALAMANDRID.E. -- Examples: Salamandra, Triton (Fig. 431), Diemyctylus. Family 2. AMBYSTOMID.E. - - Examples: Ambystoma (Fig. 432), Chondrotus. Family 3. PLETHODONTID.E. -- Examples : Plethodon, Spe- lerpes, Desmognathus (Fig. 433). Order 3. Salientia (ANURA, Figs. 434-436). - -TAILLESS AM- PHIBIA. AMPHIBIA without a tail ; without scales ; two pairs of limbs; without external gills or gill-openings in adult. Suborder i. AGLOSSA. -- SALIENTIA without a tongue; 512 COLLEGE ZOOLOGY Eustachian tubes open by single aperture; no distinct tympanic membrane; vertebrae opisthoccelous. Family AGLOSSID^E. - - With the characters of the sub- order. Examples: Pi pa (Fig. 434), Xcnopus. Suborder 2. LINGUATA (PHANEROGLOSSA). -- FROGS and TOADS. SALIENTIA with a tongue; Eustachian tubes open by two apertures. Family i. PELOBATID^E. -- Spade-foot toads. Examples: Pelobatcs, Scaphiopus. Family 2. BUFONHLE. -- TOADS. Examples: Bufo, Rhi- nophrynus. Family 3. HYLID^E. -- TREE-FROGS. Examples: Acris, Chorophilus, Hyla, Nototrema (Fig. 435). Family 4. CYSTIGNATHID.E. Examples: Hemiphractus, Hylodes, Paludicola. Family 5. ENGYSTOMATID.E. Examples: Engystoma, Phryniscus, Hypopachus. Family 6. RANID.E. - - TRUE FROGS. Examples: Rana, Phyllobatcs, Oxyglossus. Suborder 3. COSTATA (DISCOGLOSSID^:). -- SALIENTIA with a tongue; Eustachian tubes open by two apertures; with short ribs. Family DISCOGLOSSID^:. - - With the characters of the suborder. Examples: Discoglossus, Alytes, Bom- binator. 3. REVIEW OF THE ORDERS AND FAMILIES OF LIVING AMPHIBIA Order i. Apoda. - - The single family, CCECILIHXE, of this order includes about forty species of worm-like or snake-like leg- less AMPHIBIA. They inhabit the tropical regions of America, Africa, India, Burma, and northern Australasia, but none occurs in the United States. They burrow in moist ground with their strong heads, and, as a result of living in darkness, their eyes are CLASS AMPHIBIA 513 small and concealed under the skin or maxillary bones. A sensory tentacle which can be protruded from between the eyes and the nose aids the animal in crawling about. They feed on small invertebrates. Most of the ccecilians lay eggs, but some are viviparous. Ickthyophis glutinosa (Fig. 427), which lives in India, Ceylon, and the Malay Islands, and is about one foot long, has- been more carefully studied than any other species. Order 2. Caudata. - - The tailed . ,.,.,. . , , , FIG. 427. A legless am- AMPHIBIA differ so widely from one p h;hian, Ickthyophis glutinosa, another that it has been found female guarding her eggs. (From the Cambridge Natural History, necessary to recognize three sub- a f te r Sarasin.) orders. Suborder i. PROTEIDA. - - This suborder contains a single family, PROTEIDA, the mud-puppies, and three genera, Necturus, Typhlomolge, and Proteus, with one species each. Necturus maculosus (Fig. 428) is confined to the rivers and lakes of the northern and eastern part of the United States, west of the Alle- ghanies. It breathes by means of bushy red gills which extend out from in front of the fore legs. The food of Necturus consists chiefly of crustaceans, frogs, worms, insects, and small fishes. During the day the mud-puppy lies concealed in a dark place, zmfy FIG. 428. The " mud-puppy," Necturus maciilosus. (From Mivart.) but at night it swims or crawls about with wavy movements of the body. Proteus anguinus is a protean about one foot long, which has / T 2 L COLLEGE ZOOLOGY been found only in the caves of Austria. It is white, but if exposed to the light may become dark and ultimately black. It has rudimentary eyes. Typhlomolge rathbuni is a blind protean that came up with the water of an artesian well one hundred and eighty-eight feet deep, in Texas. It probably feeds on the crustaceans in under- ground streams, since four species of these, all new to science, came up along with the amphibians. Suborder 2. ME ANTES. - - This suborder also contains a single family, SIRENID^E, the sirens, and two genera, Siren and Pseudo- bronchus, with one species each. Siren lacertina (Fig. 429), the " mud-eel," bur- rows in the mud of ditches and ponds, FIG. 429. - The " mud-eel," Siren lacertina. and swims b y un ~ (From the Cambridge Natural History.) dulations of the body. It has three pairs of gill-slits and four toes, and reaches a length of two and one half feet. It inhabits the ponds and rivers from Texas to North Carolina. Pseudobranchus striatus has but one pair of gill-slits and only three toes. It has been found in Georgia and Florida. Suborder 3. MUTABILIA. - - Family CRYPTOBRANCHID^:. - There are three genera, Cryptobranchus, Megalobatrachus, and Amphiuma. Cryptobranchus alleghaniensis, the hellbender (Fig. 430), occurs only in the streams of the eastern United States. It reaches a length of from eighteen to twenty inches. Its food consists of worms and small fish. Megalobatraclms maximus is the giant salamander of Japan, the largest of all the AMPHIBIA. It feeds on fishes, amphibians, worms, and insects, and may reach a length of over five feet. Amphiuma means, the Congo " snake," is long and eel-shaped, and possesses two widely separated pairs of small legs. It occurs in the marshes and CLASS A.MI'HIUIA 515 muddy streams of the southeastern United States, and feeds on crayfishes, mollusks, and small fish. FIG. 430. The " hellbender,'' Cryptobranchus. (From Davenport, after the Standard Natural History.) Family SALAMANDRID^:. - - This family contains the true salamanders and the newts or tritons. " Of the twenty-five species, only two are American, four are eastern Asiatic, and of the remaining nineteen, two are Algerian, while the rest live in Europe or in Asia Minor." (Gadow.) The two American species are Diemyctylus viridescens and Triton torosus. Dlemyctylus viridescens, the crimson-spotted newt, is common in the ponds of the northern and eastern portions of the United States. It is about three and one half inches long and has a row of crimson spots on either side. Its food consists principally of insect larvae, worms, and small mollusks. The eggs are laid in April, May, or June, and a sort of " nest " of aquatic vegetation is constructed for each egg. The young live for a time on land under stones and logs, but return to the water after several years, becoming aquatic adults. COLLEGE ZOOLOGY FIG. 431. Triton cristata. i, female; 2, male as he appears during the breeding season. (From Shipley and MacBride, after Gadow.) Triton torosus, the newt of western North America, is a large species reaching a length of six inches. It feeds on earthworms. The common fire salamander of Europe is Sala- mandra maculosa, a species about six inches long. It is black, with bright yellow spots, and the glands of the skin secrete a poisonous sub- stance. The enemies of salamanders are supposed to be " warned " by the conspicuous colors and will not attack this poisonous species. Pronounced sexual dimorphism, i.e. differences between the male and female of the same species, is exhibited by Triton cristatus (Fig. 431), the European crested newt. The male is conspicuously colored and develops a high serrated crest during the breeding season. Family AMBYSTOMID^:. - A common member of this family is Ambystoma tlgr'i- num (Fig. 432). This species occurs from New York to California and south to cen- tral Mexico, and reaches a length of from six to nine inches. It is dark colored and marked with yellow spots. The larval form, called axolotl, was for a long time considered a separate species because the external gills persisted in the adult. Later it was discovered (1865) that if forced to breathe air the axolotls would shed their gills and FIG. 4.32. The axolotl stage of the tiger salamander, Ambystoma tigrinum. (From the Cambridge Natural History.) CLASS AMPHIBIA 5 1 ? become air-breathing salamanders of the species Ambystoma tigrinum. Family PLETHODONTID^:. - - All except one species of the eight genera belonging to this family are confined to America. Desmognathus fusca (Fig. 433), the dusky salamander, is a species four or five inches long that lives under stone-s and in other dark, moist places. The eggs of this species are laid in two long strings which the female takes care of in some place of conceal- ment by winding them about her body. Typhlotriton spel&us is a blind species found in a cave in Missouri. The slimy salamander, Plethodon gluti- nosus, is common from Ohio to the Gulf of Mexico. It gives off a great quantity of slime when irritated. Autodax lugubris is an inhabitant of the western United States. Flr " 433--- A lungless salamander, . , , Desmognathus fuscus ; female with eggs It lays its eggs in holes in the in a hole under ground. (From the branches of Cambridge Wilder.) Natural History, after live-oak trees. Spelerpes biUneatus occurs in the Atlantic states. The only European species of the family PLETHODONTID^: is Spele/pes fuscus. Order 3. Salientia. - - Most of the AMPHIBIA, about nine hundred species of frogs and toads, belong to this order. They resemble one another very closely and are classified according to the characteristics of certain internal structures. In North America there are seven families and about fifty-six species. Some of them (toads and tree-frogs) live on land, but others (water frogs) spend a large part of their time in the water. The terrestrial species possess only slightly webbed hind feet or no webs at all. They crawl or hop on land, burrow in the earth, or climb trees. Dark, moist hiding places are usually required, and most of them take to water only during the breeding season. 5'* COLLEGE ZOOLOGY Suborder i. AGLOSSA. - -There are only a few toads in this suborder; all of them are tongueless and belong to the family AGLOSSID^E. Pipa americana inhabits the northern portion of South America; Hymenochirus bcettgeri and Xenopus Icevis are confined to Africa. The Surinam toad, Pipa americana (Fig. 434), has a peculiar method of carrying its eggs. They are placed on the back of the female during copulation, are held there by a sticky secre- tion, and are gradually enveloped by the skin. Within the FIG. 434. The Surinam toad, Pipa americana. (From Mivart.) epidermal pouches thus formed the eggs develop and the tadpole stage is passed; then the young toad escapes as an air-breathing terrestrial animal. Suborder 2. LINGU ATA. -- Most of the frogs and toads are included in the six families of this suborder. Family i. PELOBATID.E. - -There are about twenty species, called spade-foot toads, in this family. One genus, Scaphiopus, with four species, occurs in North America. The spade-foot toads are burrowing AMPHIBIA, and usually have thick hind feet provided with a sharp spur for digging. The spade-foots of CLASS AMPHIBIA 519 eastern North America belong to the species Scaphiopus hol- brookii. They are seldom seen or heard except during the breed- ing season, when they come out of their burrows in great numbers and seek ponds in which to deposit their eggs. Family 2. BUFONID^:. - - This family includes over one hundred species of toads, most of which belong to the genus Bufo. About fifteen species of this genus have been reported from North America. Bufo americanus, the common toad of the northeastern United States, possesses a rough, warty skin, but does not cause the appearance of warts upon the hands of those who handle it, as is often supposed. Toads secrete a milky, poisonous fluid by means of glands in the skin, which protects them from many animals that would otherwise be important enemies. During the day they remain concealed in some dark, damp place, but at night they sally forth and hop about, feeding upon worms, snails, and especially insects, which they capture with their sticky tongue, as in the case of the frog (p. 480, Fig. 410). The value of toads as destroyers of insects injurious to vegetation is con- siderable. Kirkland has estimated that one toad is worth $19.44 in a single season because of the cutworms it devours. During the winter toads hibernate in some sheltered nook, but as soon as conditions are favorable in the spring (about May i) they emerge from their winter's home and proceed to water to deposit their eggs. At this time the males utter their sweet, tremulous calls. The eggs are laid in long strings. They develop very much like those of the frog (pp. 506-510). Family 3. HYLID.E. - - The tree-frogs are arboreal amphib- ians with adhesive discs on their toes and fingers which usually enable them to climb trees. They are provided with large vocal sacs and have a correspondingly loud voice. Of the more than one hundred and eighty species belonging to the family, fifteen occur in North America, and about one hundred and thirty in Central and South America. The North American species belong to the genera Hyla, Acris, Chorophilis, and Smilisca. 520 COLLEGE ZOOLOGY Hyla verslcolor is the common tree-frog. It is about two inches long and has the power of slowly changing its color from white to stone-gray or brown and from white to green. These changes usually produce such a perfect harmony between the frog and its surroundings that the animal becomes practically invisible. The eggs are laid in May. They are attached in groups to plants at the surface of the water. Hyla pickeringii, the spring peeper, has the discs on the fingers and toes so small that they are scarcely discernible. FIG. 435. Brooding tree-frog, Nototrema, female, from Venezuela. In posterior part of trunk is opening of brood-pouch. (From Davenport's Zoology.) Acris gryllus is called the cricket-frog. Chorophilus nigritus, the swamp tree-frog, has fingers and toes with minute discs. The brooding tree-frog, Nototrema (Fig. 435), of Venezuela, has a pouch with an opening in the hinder part of the trunk in which the eggs are placed and the young are reared. Family 4. CYSTIGNATHID^E. - - This family contains almost as many species (over one hundred and fifty) as the family HYLID^:, but only three species occur in North America. Litliodvtes latrans and Syrrophus marnockii have been recorded CLASS A.Mi'IIIHIA 521 from Texas, and Lithodytcs ricordli from Florida. Most of the CystignathidcB occur in Mexico and Central and South America. They form a comparatively heterogeneous group and are not easily defined. Family 5. ENGYSTOMATID^:. - - The narrow- mouthed toads as a rule inhabit the tropics. Only three of the seventy or more species are found in the United States. Engystoma carolinense ranges from South Carolina to Florida and west to Texas. Like other members of the family, its head is narrow and pointed and is thus adapted for the capture of ants and other small insects. Family 6. RANID.E. - - The true frogs occur in all parts of the globe except Australia, New Zealand, and southern South America. Only one genus, Rana, and about seventeen species are found in North America. Of these Rana pipiens (pp. 477- 510) is the most common. Rana catesbiana, the bullfrog, is found all over the United States east of the Rocky Mountains. It is the largest of the family in this country, often reaching a length of six or eight inches. Bullfrogs usually remain in or near water. They possess a deep, bass voice like that of a bull, and when a number are engaged in a nocturnal serenade they can be heard for a con- siderable distance. Their food consists of worms, insects, mollusks, other frogs, young water-fowl, etc. The eggs are de- posited in ponds from the last of May until July. The tadpoles do not become frogs the first year as do those of the leopard- frog, but transform during the second or even the third year. Bullfrogs are worth from one to four dollars per dozen in the market, because of the demand for frogs' legs. Rana dam i tans, the green frog, is common in the ponds of eastern North America. It is little more than half as long as the bullfrog, from which it may be distinguished by the presence of two glandular folds of skin along the sides of the back. Rana syhatica, the eastern wood-frog, is not restricted to the vicinity of water, but usually lives in damp woods. It is found throughout the northeastern United States. 522 COLLEGE ZOOLOGY Rana palustris, the pickerel frog, inhabits the brooks and ponds of eastern North America, and is often found also in fields and meadows. It reaches a length of three inches. Suborder 3. COSTATA. --The five genera and eight species of SALIENTIA included in this suborder all belong to the single family DiscoGLOSsm^E. Only one species occurs in North America ; this is the American discoglossoid toad, Ascaphus truci, of which only a single specimen from Humptulips, Washington, is known. An interesting European species is the obstetrical toad, Alytes obstetricans (Fig. 436). The male of this toad carries the FIG. 436. The ob- egg strings with him wound about his stetrical frog, Alytes ob- stetricans ; male, with hind limbs, and when the tadpoles are string of eggs. (From rea d y to emerge, takes to the water and Sedgwick's Zoology, after Claus.) allows them to escape. 4. GENERAL REMARKS ON AMPHIBIA Color and Color Change. - - The pigments in the skin of AMPHIBIA are diffuse or granular. The latter are usually brown, black, yellow, or red and are contained in cells called chromat- ophores. The power of changing its colors is possessed by most AMPHIBIA, but especially by the frogs. These are supplied with black pigment cells, interference cells, golden pigment cells, and sometimes red pigment cells. The black chromatophores are branching cells which may spread out or contract, as shown in Figure 437. When ex- panded the pigment covers a larger area and consequently gives the skin a darker color. The yellow pigment is contained in spherical golden cells. The green color results from the re- flection of light from granules of guanin in the skin through the golden cells. Most of the color changes are due to changes in the concentration of the black and yellow pigments. CLASS AMPHIBIA 523 Color changes are brought about by direct stimulation of the pigment cells or indirectly through the central nervous system. Light is an important stimulus; it acts both directly and through the central nervous system. In a bright light the skin of the frog becomes light in color, whereas in the dark it changes to a darker hue. Temperature is another important factor. The pigment becomes more concentrated if the temperature is raised, and the skin changes to a lighter color. An expansion FIG. 437. Pigment cells from the frog, in different states of extension. (From Holmes, after Verworn.) of the pigment and a darker color result from subjection to cold. Changes in the circulation, in the moisture of the frog's habitat, and in the chemical composition of the animal's environment affect the chromatophores and consequently produce changes in color. In many cases the color changes are such as to cause the frog to resemble more closely its surroundings, and hence to conceal it. Regeneration. - - The power of regenerating lost parts is remarkably well developed in many AMPHIBIA. For example, the hand of a two-year-old axolotl was cut off, and in twelve weeks 524 COLLEGE ZOOLOGY a complete hand was regenerated in its place (Barfurth). Triton has been observed to regenerate both limbs and tail. The SALIENTIA are apparently unable to regenerate lost parts to any considerable extent, except in the early stages. As a general rule, the younger tadpoles regenerate limbs or tail more readily than older specimens. There is a distinct advantage in the possession of the power of regeneration, since amphibians no doubt often escape from their enemies with mutilated limbs or tail, but are not seriously inconvenienced by the loss, as new parts rapidly grow out. Breeding Habits. - - Most AMPHIBIA are oviparous, and their eggs, as in the leopard-frog, are fertilized by the male after ex- trusion. In some of the CAUDATA and in the APODA, however, the eggs are fertilized before they are laid. A few species of CAUDATA bring forth their young alive; for example, the fire salamander, Salamandra macuhsa, of Europe. Several curious brooding habits have already been referred to; for example, the obstetrical toad (p. 522), the Surinam toad (p. 518), and the dusky salamander (p. 517). The " marsupial " frogs of the genus Nototrema should also be mentioned. They have a permanent pouch on the back in which the eggs develop. These frogs belong to the family HylidcB and inhabit the tropical forest region of South America. Hibernation. - - Many AMPHIBIA bury themselves in the mud at the bottom of ponds in the autumn, and remain there in a dormant condition until the following spring. During this period of hibernation the vital processes are reduced; no air is taken into the lungs, since all necessary respiration occurs through the skin ; no food is eaten, but the physiological activities are carried on by the use of nutriment stored in the body; and the temperature decreases until only slightly above that of the surrounding medium. The temperature of all cold-blooded vertebrates cyclostomes, elasmobranchs, fish, amphibians, and reptiles --varies with the surrounding medium. Frogs cannot, however, be entirely frozen, as is often stated, since death CLASS AMIMIIIUA 525 ensues if the heart is frozen. In warm countries many AMPHIBIA seek a moist place of concealment in which to pass the hotter part of the year. They are said to aestivate. Poisonous Amphibia. - - The poison-glands of the leopard- frog (p. 479) and of the common toad (p. 519) have already been mentioned. Certain salamanders and newts are also provided with poison-glands. The poison acts upon the heart and the central nervous system. It has no effect upon the skin of in- dividuals of the same species, but if inoculated into the blood it poisons even the individual that produces it. As a means of defense the poison is very effective, since an animal that has once felt the effects of an encounter with a poisonous amphibian will not soon repeat the experiment. Some of the most poison- ous species, for ex- ample, Salaniandra maculosa, are said to be warningly colored. Prehistoric Am- phibia. --Two orders of amphib- ians, the STEGO- CEPHALIA and Mi- CROSAURIA are known only from fossils. The STEGO- CEPHALIA are sala- mander-like extinct animals (Fig. 438) that lived in the Carboniferous, Per- mian, and Triassic periods. They were probably fresh-water or terrestrial creatures. They possessed large, bony dermal V jo FIG. 438. STEGOCEPHALIA. Branchiosaitrus am- blystomus. A, skeleton of adult. B, restoration of larva with branchial arches. (From Sedgwick's Zoology, after Credner.) 526 COLLEGE ZOOLOGY plates on the dorsal surface of the skull and often on other parts of the body. Some of the STEGOCEPHALIA are called LABYRINTHODONTS because the dentine of their teeth is much folded. MICROSAURIA are small extinct animals probably belonging to the AMPHIBIA, though they are often placed with the reptiles. The Economic Importance of the Amphibia. - - The AMPHIBIA are practically all beneficial to man. Many of them are so rare as to be of little value, but the frogs and toads are of consider- able importance. Frogs have been and are now used extensively for laboratory dissections and for physiological experiments and investigations. They seem in fact to have been " especially designed as a subject for biological research." Frogs' legs are eagerly sought as an article of food. New York, Maryland, Virginia, Indiana, Ohio, Missouri, and Cali- fornia furnish the largest number for market. Frog hunters obtain an annual price of about $50,000 for their catch. " Frog farms " are now carried on profitably in Wisconsin, California, and several other states. Small frogs are often used as fish bait. Frogs and toads are widely recognized as enemies of injurious insects. The toads are of special value, since they are accustomed to live in gardens where insects are most injurious (see p. 519). In France the gardeners even buy toads to aid them in keeping obnoxious insects under control. CHAPTER XIX SUBPHYLUM VERTEBRATA: CLASS V. REPTILIA THE reptiles constitute one of the most interesting, but gener- ally least known, classes of the VERTEBRATA. They are cold- blooded; usually covered with scales and frequently with bony plates ; and breathe with lungs. The popular notion that reptiles are slimy is erroneous. Contrary also to general belief, very few reptiles, at least in the United States, are dangerous to man, but the majority of them are harmless and many even beneficial. The reptiles that are living to-day are but a remnant of vast hordes that inhabited the earth's surface in prehistoric times. In fact, of the twenty orders of reptiles now recognized by her- petologists, only four possess living representatives, and one of these includes only one nearly exterminated species con- fined to New Zealand. The four orders of. living reptiles are as follows: ORDER i. TESTUDINATA (CHELONIA) .-- Turtles and Tor- toises. . ORDER 2. RHYNCHOCEPHALIA. One lizard-like reptile con- fined to New Zealand. ORDER 3. CROCODILINI. -- Crocodiles, Alligators, Gavials, and Caimans. ORDER 4. SQUAMATA. -- Chameleons, Lizards, and Snakes. i. THE TURTLE The turtle has been selected as a type of the REPTILIA. It will not be discussed in detail, as was the frog, but only the more important points regarding its external and internal anatomy and physiology will be mentioned. 527 528 COLLEGE ZOOLOGY External Features. - - The shell of the turtle is broad and flattened, and protects the internal organs. Even the head, limbs, and tail can be more or less completely withdrawn into the shell. The neck is long and very flexible. The head is flattened dorso-ventrally and triangular in shape. The mouth is large, but, instead of teeth, horny plates form the margin of the jaws. The nostrils, or external nares, are placed close to- gether near the anterior end of the snout. The eyes, situated one on each side of the head, are each guarded by three eyelids: (i) a short, thick, opaque upper lid; (2) a longer, thin lower lid; and (3) a transparent nictitating membrane, which moves over the eyeball from the anterior corner of the eye. Just behind the angle of the jaw on either side is a thin tympanic membrane. The limbs usually possess five digits each ; most of the digits are armed with large claws, and connected one with another by a more or less complete web. The skin is thin and smooth on the head, but thick, tough, scaly, and much wrinkled over the exposed parts of the body. Internal Anatomy and Physiology. - - THE SKELETON. - Since the life of the turtle is influenced so strongly by the skeleton, this system will be described first. The exoskeleton (Fig. 439) consists of a convex dorsal portion, the carapace (c), and a flattened ventral portion, the plastron (Hyp, Hpp, Xp) ; these are usually bound together on each side by a bony bridge (at M) . Both carapace and plastron are usually covered by a number of symmetrically arranged epidermal plates forming a shield; the plates do not correspond either in number or arrangement to the bony plates beneath them. The number and shape of the plates vary according to the species, but are usually constant in individuals of the same species. The horny shields of the " Hawk's-bill Turtle " (Fig. 447) furnish the tortoise- shell of commerce. Beneath the shields are a number of bony plates formed by the dermis and closely united by sutures (Fig. 439). The endoskeleton may, as in other vertebrates, be divided into an axial portion and an appendicular portion. The skull CLASS REPTILIA 529 (Fig. 440) is very firm. It is devoid of teeth. The pre- maxillse (pinx), maxillae (w.v), and dentary bones possess sharp edges which are covered with horn, and form a beak. The quadrate bone (q) is stationary; no transverse bone is present FIG. 43Q. Skeleton of a turtle, Cistudo lutaria, ventral aspect; plastron removed to one side, c, costal plates; co, coracoid; e, entoplastron; ep, epi- plastron; /, fibula; fe, femur; h, humerus; hpp, hypoplastron; hyp, hyoplas- tron; jl, ilium; js, ischium; m, marginals; nu, nuchal; pb, pubis; psc, precora- coid; py, suprapygal; r, radius; sc, scapula; /.tibia; u, ulna; xp, xiphiplastron. (From Zittel.) as in other reptiles; there is one occipital condyle, and only one sphenoidal bone, the basisphenoid (BSph}. The supraoccipital (so) has a prominent crest. There are comparatively few vertebras (Fig. 439) - - usually eight cervical, ten thoracic, two sacral, and a variable number of caudal. The vertebrae of the neck move very freely upon one 2 M 53 COLLEGE ZOOLOGY another by cup and ball joints. The thoracic or trunk vertebrae bear ribs which are closely united with the carapace. They lack transverse and articulating processes. The pectoral and pelvic girdles (Fig. 439) are peculiarly situated within instead of outside of the ribs. They serve, in fact, as 8 i\i ' C* I/ 1 ' 1 "' Fa '- '- \* , . j.|a| Pa f}-^*' s,- FIG. 440. Skull of a turtle, Trionyx gangeticus. A, dorsal; B, ventral aspect. bo, basioccipital ; bsph, basisphenoid ; ch, internal nares; exo, exoccipital ; fr, frontal; j, jugal; tn.v, maxilla; n, external nostril; op, opisthotic; pa, parietal; pi, palatine; pmx, premaxilla; prf, prefrontal +- nasal; pro, prootic; ptj, post- frontal; q, quadrate; quj, quadratojugal; s, supratemporal fossa; so, supra- occipital; sq, squamosal; vo, vomer. (From Zittel.) braces to keep the plastron and carapace apart. The limbs are almost typically pentadactyl. The Digestive System. - - Turtles feed on both plants and animals; some are entirely vegetarian. The animals preyed upon are water-fowl, small mammals, and many kinds of in- vertebrates. The flexible neck enables the turtle to rest on the bottom and reach out in all directions for food. The jaws of the snapping-turtle, Chelydra serpentina, are powerful enough to amputate a finger, or even, in large specimens, a hand. CLASS REPTILIA 531 The digestive organs are simple. The broad, soft tongue is attached to the floor of the mouth cavity; it is not protrusible. The two posterior nares are situated in the anterior part of the roof of the mouth. At the base of the tongue is a longitudinal slit, the glottis, and a short distance back of the angle of the jaw are the openings of the Eustachian tubes. The pharynx is thin-walled and very distensible; it leads into the more slender and thicker- walled (Esophagus. The stomach opens by a pyloric valve into the small intes- tine; this is separated from the large intestine by the ileoccecal valve. The terminal portion of the alimentary canal is the rectum ; it opens into the cloaca. There is no intestinal caecum. The liver discharges bile into the in- testine through the bile-duct. Several pancreatic ducts lead from the pan- creas to the intestine. The Circulatory System. - The heart (Fig. 441) consists of two auricles (d, s), and a single ventricle which is divided into two septum. body is carried by the postcaval vein d ' right auricle; d.ao dorsal aorta; pd, right; ps, left pul- and the two precaval veins into the mbnary artery; s, left auricle; sinus venosus and thence into the d.ao FIG. 441. Heart and ar- by a perforated teries of a turtle > 1 - ad, right; as, left aortic arch; The venOUS blood from the f , carotid; c', cceliac artery; sj < rl ^> . left subclavian artery. (From bedgwick s right auricle (a). From here it passes Zoology, after Gegenbaur.) into the right side of the ventricle, and, when the latter contracts, is forced out through- the pul- monary artery, which sends a branch (pd, ps) to each lung, and through the left aorta (as} which conveys blood to. the viscera (c 1 ) and into the dorsal aorta (d.ao). The blood which is purified in the lungs is returned by the pulmonary veins to the left auricle (5) and thence into the left 53 2 COLLEGE ZOOLOGY side of the ventricle. This blood is pumped out through the right aortic arch (ad), which merges into the dorsal aorta (d.ao). Because the septum dividing the ventricle into two parts is perforated, the blood that enters the right aortic arch is a mixture of purified blood from the left auricle and venous blood from the right auricle. There is no renal portal system in the turtle, but the hepatic portal system shows an advance in development over the condition as described in the frog (p. 489). The Respiratory System. - Turtles breathe by means of lungs. Air enters the mouth cavity by way of the nasal passages. The glottis opens into the larynx, through which the air passes into the trachea or windpipe. The larynx is supported by the hyoid ap- FIG. 442. Cloaca and urinogenital p a ratus. The trachea divides, organs of a turtle, Chelydra serpentina. ' ,. , 7 c, c', blind sacs of cloaca; d, cloaca; Sending One bronchus to each e, epididymis and vas deferens; p, penis, lung. The lungs are more r, kidneys; re, rectum; 5, groove on ,. r A penis; /, testis; , ureter; ug, cloacal Complicated than those of AM- opening of bladder; v, bladder. (From pHIBIA. The bronchi branch Sedgwick's Zoology, after Gegenbaur.) . . , , a number of times, and the lung cavity is broken up into many spaces, thus increasing the respiratory surface. The shell of the turtle prevents the expansion and contraction of the lungs by means of abdominal or thoracic muscles. Air is therefore drawn in and expelled partly by the hyoid apparatus and partly by alternately extending and drawing in the neck CLASS REPTILIA 533 and appendages. The air is thus pumped into the lungs or else swallowed. Many aquatic turtles possess a pair of thin-walled sacs (Fig. 442, cc'}, one on either side of the cloaca (cl), which are alternately filled with water and emptied through the anus. They have walls plentifully supplied with blood-vessels, and act as auxiliary breathing organs (compare sea-cucumber, p. 206, and nymph of dragon-fly, p. 339). The Urinogenital Organs (Fig. 442). - - Excretion is carried on by the two kidneys (r). Their secretions pass through the ureters (u) into the cloaca (cl), are stored in the urinary bladder (v), and then make their exit (ug) through the anus. The sexes are separate. The male organs are a pair of testes (t) and a pair of vasa deferentia (e) through which the spermat- ozoa pass to the grooved copulatory organ, or penis (p), at- tached to the front wall of the cloaca (cl). The female organs are a pair of ovaries and a pair of oviducts ; the latter open into the cloaca. Turtles are oviparous. The eggs, which are white, round or oval, and covered by a more or less hardened shell, are laid in the ground /, olfactory nerve ; //, optic nerve ; H, hypo- r ,1 physis; HH, cerebellum; Inf, infundibulum; Lol, olfactory lobe; MH, optic lobe; NH, me- dulla; R, spinal cord; VH, cerebral hemi- spheres. (From Davenport, after Wieders- heim.) FlG 5. - Side view of brain of a turtle. a few inches surface. The Nervous System. - The brain (Fig. 443) is more highly developed than in the AMPHIBIA. The cerebral hemispheres (VH) are larger, and a distinction can be made between the superficial gray layer and the central white medulla. The cerebellum (HH) is also larger, indicating an increase in the power of correlating movements. Sense-organs. - - The eye is small. It has a round pupil and an iris which is usually dark in terrestrial forms, but often 534 COLLEGE ZOOLOGY colored in aquatic turtles. The sense of hearing is fairly well developed, and turtles are easily frightened by noises. The sense of smell enables the turtle to distinguish between various kinds of food both in and o\it of the water. The skin over many parts of the body is very sensitive to touch, 2. A BRIEF CLASSIFICATION OF LIVING REPTiLiA 1 The four thousand or more species of living reptiles may be grouped into four orders: (i) the TESTUDINATA, containing about two hundred and twenty-five species of turtles and tor- toises; (2) the RHYNCHOCEPHALIA, represented by a single New Zealand species; (3) the CROCODILINI, containing about twenty- three species of crocodiles, ga vials, and alligators; and (4) the SQUAMATA, containing about three thousand seven hundred species of lizards, chameleons, and snakes. In most cases the orders, families, and subfamilies of reptiles are indicated by means of structural characters, such as the position of the teeth, the shape and arrangement of the bones of the skull, and the form of the vertebrae. Since these cannot be determined by the beginning student, they are mostly omitted from the following paragraphs. Order i. Testudinata (CHELONIA). TURTLES and TORTOISES. -Reptiles with the body incased in a bony capsule; jaws without teeth; quadrate bone immovable ; usually pentadactyl appendages. Superfamily i . CRYPTODIRA. - - TESTUDINATA with the carapace covered with horny shields; neck bends in S-shaped curve in a vertical plane; pelvis not fused with the carapace. Family i. CHELYDRID.E. - - SNAPPING-TURTLES. - - CRYP- TODIRA with small plastron; tail long; limbs, neck, and head large and cannot be withdrawn into shell; 1 1 am indebted to Dr. Alexander G. Ruthven for the main divisions of this classification. CLASS REPTILTA 535 snout with hooked beak. 'Examples: CJiclydra, Macrochelys (Fig. 444). Family 2. KINOSTERNID.E. MUSK- and MUD-TURTLES. -CRYPTODIRA possessing a nuchal plate with costi- form processes underlying the marginals ; eight bones in the plastron. Examples : Kinosternon, Aromochdys. Family 3. DERMATEMYDID.E. - - FRESH-WATER TURTLES of Southern Mexico and Central America. CRYPTO- DIRA with nuchal plate as in KINOSTERNID^:; nine bones in plastron. Examples: Dermatemys, Stauroty- pus, Claudius. Family 4. PLATYSTERNID^;. CRYPTODIRA without costi- form processes on nuchal plate. Examples: Platy- sternum (a single species, P. megacephalum, in Burma, Siam, and China). Family 5. TESTUDINID.E. --TORTOISES and most TURTLES. CRYPTODIRA without costiform processes on nuchal plate; lateral temporal arch usually present; no parieto-squamosal arch. Examples: Testudo (Fig. 446), Chrysemys (Fig. 445), Emys. Superfamily 2. CHELONIIDEA (CHELONKME -f- ATHECA).- SEA-TURTLES. --MARINE TESTUDINATA with paddle- shaped limbs. Family i. CHELONIID^E. - - Four species inhabiting tropical and semitropical seas (Fig. 447). Family 2. DERMOCHELYID.E. - - The leathery turtle of tropical and semitropical seas (Fig. 448). Superfamily 3. PLEURODIRA. - -TESTUDINATA with neck bending laterally; pelvis fused with the shell. Family i. PELOMEDUSID.E. -- FRESH-WATER TURTLES. PLEURODIRA with neck completely retractile within the shell; carapace without nuchal shield; plastron ot eleven bones. Examples: Pelomedusa, Podocmmis, Sternothcerus. 536 COLLEGE ZOOLOGY Family 2. CHELYDID.E. - - FRESH- WATER TURTLES. PLEURODIRA with neck not completely retractile within the shell; plastron of nine bones. Examples: Hydras- pis, Emydura. Superfamily 4. TRIONYCHOIDE A. - - TESTUDINATA with soft, leathery skin, without horny shields. Family i. CARETTOCHELYDID.E. - - TRIONYCHOIDEA with paddle-shaped limbs; neck not retractile. Example: Carettochelys (one species C. insculpta from New Guinea.) Family 2. TRIONYCHID.E. SOFT-SHELLED TURTLES. TRI- ONYCHOIDEA with digits broadly webbed; head and neck retractile, bending in vertical plane. Examples: Trionyx (Fig. 449), Emyda. Order 2. Rhynchocephalia. One genus of New Zealand lizard- like reptiles. Vertebras biconcave, often containing remains of the notochord; immovable quadrate bone; parietal organ present. Example: Sphenodon (Fig. 45) Orders. Crocodilini. -- CROCODILES, ALLIGATORS, GA VIALS, and CAIMANS. Reptiles with proccelous vertebras; nostril single, at end of snout; anterior appendages with five digits, posterior with four and traces of a fifth; anal opening a longitudinal slit. Family i. GAVIALID.E. -- GA VIALS. CROCODILINI with long, slender snout. Example: Gavialis (Fig. 451). Family 2. CROCODILID^:. CROCODILES, ALLIGATORS, and CAIMANS. CROCODILINI with broad, rounded snout. Examples: Crocodilus, Alligator, Caiman (Fig. 451). Order 4. Squamata. CHAMELEONS, LIZARDS, and SNAKES. - Reptiles usually with horny epidermal scales; vertebra usually proccelous; quadrate bones movable. Suborder i. RHIPTOGLOSSI. - - CHAMELEONS. - - SQUAMATA with body laterally compressed; tail prehensile; tongue vermiform, projectile; well-developed limbs; CLASS REPTILIA 537 digits in groups of two and three, tor grasping (see Fig. 45 2 )- Family i. CHAM^LEONTID.^:. - - CHAMELEONS. - With characters of the suborder. Examples: Chamcdcon (Fig. 452), Brookes ia, Rliampholeon. Suborder 2. SAURIA (LACERTILIA). LIZARDS. SQUAMATA with transverse anal opening; paired copulatory organs; at least a vestige of a pectoral arch; usually well- developed limbs; rami of lower jaw united. (Only ten of the twenty families are listed below.) Family i . GECKONID.E. GECKO. SAURIA with four legs ; eyes usually without movable lids; tongue protrusible ;* many with adhesive digits for climbing. Examples: Gecko (Fig. 453), Gymnodactylus, Sphcerodactylus. Family 2. AGAMID^E. -- OLD-WORLD LIZARDS. SAURIA with well-developed limbs; eyes with complete lids; tongue broad and short; teeth usually differentiated into incisors, canines, and molars (heterodont), and always situated on the edge of the jaw (acrodont). Examples: Draco (Fig. 454), Gonyccphalus, Calotcs. Family 3. IGUANHXE. -- NEW-WORLD LIZARDS. SAURIA resembling AGAMID^E, but usually with teeth similar (homodont) and fastened in a groove (pleurodont). Examples: Anolis, Scdoporus, Phrynosoma (Fig. 457), Iguana (Fig. 456). Family 4. ANGUID.E. OLD and NEW-WORLD LIZARDS. SAURIA with teeth in a groove ; anterior part of tongue thin, and retractile into posterior part; limbs present or absent; body protected by bony plates. Family 5. HELODERMATID.E. - - BEADED LIZARDS. SAURIA with grooved teeth ; poisonous; tongue bifid, protractile; limbs short but strong. Examples: Heloderma(Fig.4$g). Family 6. VARANID.E. MONITORS. SAURIA with tongue long, smooth, deeply bifid and retractile; tail long; limbs well developed. Example: Varanus. 538 COLLEGE ZOOLOGY Family 7. TEIID^:. NEW-WORLD LIZARDS. SAURIA with tongue long and bifid, with scale-like papillae; limbs normal or reduced. Examples: Ameiva, Cnemido- plwrus. Family 8. AMPHISB^ENID^E. -- WORM LIZARDS. Vermi- form SAURIA with short tail; limbs absent (except in Chirotes); girdles reduced; eyes and ears concealed; skin divided into regular rings. Examples: Amplris- bana, Monopeltis, Lepidosternon. Family 9. LACERTID.E. - - TYPICAL OLD-WORLD LIZARDS. - SAURIA with well-developed, pentadactyl limbs, with sharp claws; tail long, brittle; tongue long, bifid, with papillae or folds. Examples: Lacerta, Acanilio- dactylus, Eremias. Family 10. SCINCID.E. SKINKS. SAURIA with tongue scaly, and only slightly nicked ; limbs may be reduced or absent; strongly developed bony plates on head and body. Examples: Mabuia, Lygosoma, Eumeces. Suborder 3. SERPENTES (OPHIDIA). SNAKES. --Elongated SQUAMATA without limbs; anal opening transverse; copulatory organs paired; without movable eyelids, tympanic cavity, urinary bladder and pectoral arch; rami of lower jaw connected by ligament. (Four of the nine families and several of the subfamilies are not included in the following list.) Family i. TYPHLOPID.E. -- BURROWING SNAKES. SER- PENTES with reduced eyes covered by scales; without teeth in lower jaw; pelvis represented by vestiges. Examples: TypMops, Helminthophis. Family 2. GLAUCONIID^E. --BURROWING SNAKES. SER- PENTES resembling the TYPHLOPID^: ; lower jaw toothed ; vestiges of pelvis and hind limbs. Examples: Glau- conia , A nomalepis. Family 3. BOID.E. PYTHONS and BOAS. SERPENTES usually large, with vestiges of pelvis and hind limbs; CLASS REPTILIA 539 Ventral scales transversely enlarged; eyes functional and free. Subfamily i. PYTHONIN.E. PYTHONS. Examples: Lox- ocemus, Liasis, Python (Fig. 460). Subfamily 2 . BOIN.E. BOAS. Examples : Epicrates, Boa, Ungalia. Family 4. COLUBRID.E. - - HARMLESS and POISONOUS SNAKES. SERPENTES with facial bones movable; both jaws toothed. Series A. AGLYPHA. -- COLUBRHXE with solid teeth, not grooved or tubular. Non-venomous. Subfamily i. COLUBRIN.E. - TYPICAL HARMLESS SNAKES. - Examples: Thamnophis (Fig. 461), Zamc- nis, Elaphe. Series B. OPISTHOGLYPHA. COLUBRID.E with grooved fangs in the rear of the upper jaw. Venomous. Subfamily 2. HOMALOPSIN.E. -- RIVER SNAKES. Ex- amples: Hypsirhina, Homalopsis. Subfamily 3. DIPSADOMORPHIN.-E. Examples: Taniilla, Philodryas, Oxyrhopus. Series C. PROTEROGLYPHA. - - COLUBRID.E w T ith fangs in the front of the upper jaw. Venomous. Subfamily 4. HYDRIN.E. - - SEA-SNAKES. - - Examples : Hydrophis, Distira, Platurus. Subfamily 5. ELAPIN^E. COBRAS and CORAL-SNAKES. Examples: Naja (Fig. 462), Elaps, Denisonia. Family 5. VIPERID.E. - -THICK-BODIED POISONOUS SNAKES. - Poisonous SERPENTES with a pair of large perforated fangs. Subfamily i. VIPERIN^:. - - TRUE VIPERS. Examples: Viper a, Atractaspis. Subfamily 2. CROTALIN^:. - - PIT- VIPERS. - - Examples: Crotalus (Fig. 466), Agkistrodon (Figs. 463 and 464),, Lachesis. 540 COLLEGE ZOOLOGY 3. REVIEW or THE ORDERS AND FAMILIES or LIVING REPTILES Order i. Testudinata. -- TURTLES and TORTOISES. -- The TESTUDINATA are reptiles with a short, stout body provided with a shell --a structural feature that distinguishes them from other animals as effectively as wings and feathers do the birds. They are without teeth; the neck is very flexible; and the limbs are fitted for creeping, running, or swimming. The position of the pectoral and pelvic girdles within instead of outside of the ribs is peculiar. They all deposit eggs in sand or earth, where they are left to develop. Some turtles are carnivorous; others are herbivorous. America is the richest of all countries in TESTUDINATA. Three of the eleven families - - DERMATEMYDID.E, KINOSTERNID.E, and CHELYDRID.E are now restricted to North and Central America. Most of the land and fresh-water turtles hibernate in the earth during the winter, but in warmer countries they sleep during the hotter months (activate). Family CHELY- DRID.E. SNAPPING- TURTLES. - Only three species belong to this family. Chelydra serpen- lina, the common snapping-turtle, in- habits fresh-water FIG. 444. The alligator turtle, Macrochelys lacertina. (From Gadow.) ponds and streams of North America east of the Rocky Moun- tains and southward to Ecuador. It is a voracious, carnivorous animal feeding on fish, frogs, water-fowl, etc., and does not hesitate to attack man with its formidable beak, often inflicting CLASS RKPTILIA 541 severe wounds. The plastron is very small and offers little protection for the body. Chelydra rossignonii is a native of Mexico and Guatemala, differing only slightly from C. serpentina. The alligator snapping-turtle, Macrochelys lacertina (Fig. 444), lives in the streams of the southeastern United States. It is the largest North American turtle, attaining a weight of one hundred and forty pounds and a length of shell of tw-enty-eight inches. It has " a head as large as that of a bull- terrier and jaws that can chop up an ordinary broom handle," and a bad temper as well. The flesh of the snapping-turtle is a regular article of food in certain localities. Family KINOSTERNID^:. MUSK- and MUD-TURTLES. - -These are all confined to America. There are three species of musk- turtles belonging to the genus Aromochelys, and eleven species of mud-turtles of the genus Kinosternon. The common musk-turtle, Aromochelys odoratus, is an inhabit- ant of the muddy streams of the eastern United States. It has a carapace three or four inches long, a large head, and broadly webbed feet. It is voracious and carnivorous. The disagree- able odor it emits when captured has given it its name. The common mud-turtle, Kinosternon pennsykanicum, shares the habitat of the musk-turtle, and resembles the latter in size and in habits. Family TESTUDINID^:. - - TURTLES, TERRAPINS, and TOR- TOISES. - - There are twenty-two genera and about one hundred and ten species in this family. Space will permit a brief dis- cussion of only six or eight of these. The painted terrapin, Chryscmys picta (Fig. 445), inhabits the ponds and sluggish rivers of eastern North America. It loves to sun itself upon a log or protruding rock, from which it slides off into the water when disturbed. It feeds on aquatic insects, tadpoles, fishes, and water-plants. The shells of the painted terrapin are beautifully colored and are often carefully cleaned and then varnished, in which condition they make very pretty ornaments. 542 COLLEGE ZOOLOGY The diamond-back terrapin, Malacoclemmys palustris, is famous as an article of food. It lives in the salt marshes of the Atlantic coast. Persistent persecution by market hunters has caused a great decrease in the number of these animals and a corresponding increase in their value. The price has risen from twenty- five cents for a large specimen to seventy dollars per dozen for small ones (Horna- day). The spotted or pond turtle, Clemmys guttatus, is abundant in the ponds, marshes^ and streams of the eastern United States. Like the painted terra- pin, they may often be seen in groups sunning themselves on floating logs. They feed on dead fish, insect larvae, and probably water-plants. The western pond turtle, Clemmys marmorata, is the only common fresh-water turtle along the Pacific coast. Blanding's turtle, Emys blandingii, is a fresh-water form common in the Middle States. Its carapace measures about eight inches in length and its plastron is hinged so that it can be partially closed. This species is not as aquatic as the TESTU- DINHLE already described, but is often found wandering about on wet ground. Unlike the more aquatic turtles, it can eat out of water. Emys orbicularis is the European pond turtle. Terrapene Carolina is the common box turtle. The plastron of this species, and of the five other species belonging to the genus Terrapene, is hinged transversely near the center so that the shell can be closed completely when the animal is in danger. Terrapene Carolina has a highly arched carapace about five inches in length. It occurs in the Northeastern states and is terrestrial in habits, living in dry woods and feeding on berries, tender shoots, earth- worms, and insects. FIG. 445. The painted terrapin, Chrysemys picta. (From Gadow.) CLASS REPTILIA 543 The gopher tortoise, Gopherus polyphemus, lives in burrows in dry, sandy areas of the southeastern United States. It is a slow- moving, herbivorous, terrestrial animal. The common Greek tortoise of southern Europe belongs to the genus Testudo. The giant tortoises (Fig. 446) are interesting not only because of their great size, but also because they are living representatives of the fauna of past ages. Six species inhabit the Galapagos Islands off the west coast of South America; four species occur in the Aldabra Islands of the Indian Ocean, and four species inhabit the Mauritius-Rodri- guez Group of islands. Some of those captured on the Galap- agos Islands weigh over three hundred pounds and are prob- ably over four hundred years old. These giant tortoises live on cacti, leaves, berries, and coarse grass. They have been persecuted for food and for scientific purposes so per- sistently that extermination in a wild state seems certain within a few years. Family CHELONIID^E. SEA-TURTLES. - -These are the giant water turtles. They inhabit tropical and semitropical seas and come to land only to lay their eggs on sandy beaches. Their limbs are modified as paddles for swimming. The two species of loggerhead turtles belong to the genus Thalassochelys. Some individuals have a carapace four feet in length and weigh five hundred pounds. The green turtle, Chelonia- niydas, so called because of the green color of its fat, is almost as large as the loggerhead. It is famous as an article of food, and is common in the markets of the large cities of the eastern United States. It feeds largely on aquatic vegetation and probably eats fish, and other animals also. FIG. 446. A giant tortoise, Testudo abingdoni. (From Gadow.) 544 COLLEGE ZOOLOGY The hawk's-bill or tortoise-shell turtle, Chelonia imbricata (Fig. 447), has the shields of its carapace arranged like the shingles on a roof. These which shields, of a large speci- G. 447. The hawk's-bill turtle, L'kdonia imbricata, young. (From Gadow.) men yields about eight pounds, are the " tor- toise " shell of com- merce. The shields are detached either after the turtles have been killed and im- mersed in boiling water or after the living animals have been suspended over a fire. In the latter case the animals are liberated and allowed to regenerate a new covering of shields. The re- generated shields, however, are not, as supposed, of commercial value. Hawk's-bill turtles are smaller than the logger-head and green turtles, reaching a weight of about thirty pounds and a carapace length of thirty inches. They are carnivorous, feeding largely on fish and mollusks. Family DERMOCHELYID^E. LEATH- ERY TURTLE. - - The single species of this family, Sphargis coriacea (Fig. 448) , is the largest of all living turtles, some- times attaining a weight of a thousand pounds. It has a leathery covering over the shell instead of horny shields. It inhabits tropical and semitropical Fl ^ 448. - The leathery turtle, Sphargis coriacea seas and goes to land only to deposit young. (From Gadow.) CLASS REPTILIA 545 its eggs. The limbs are modified as flippers for swimming. The flesh is not used for food. Family CHELYDID^E. - - This is one of the families of turtles, the members of which bend the neck laterally. They are all fresh-water, semiaquatic species and are found in South America, Australia, and New Guinea. Family TRIONYCHID.E. -- SOFT-SHELLED TURTLES. - -The six genera and about twenty-four species belonging to this family inhabit fresh-water ponds and streams in various parts of North America, Africa, Asia, and the East Indies. The four species occurring in North America are members of the genus Triony.v. They are thoroughly aquatic and have large, strongly webbed feet. The body is flat; the neck is long and very flexible; the nose terminates in a small proboscis ; and the shell is leathery without shields, and with only a few scattered bones. Trionyx ferox (Fig. 449) is the southern soft-shelled turtle of North America, occurring in muddy-bottomed streams and FIG. 449. The soft-shelled turtle, Trionyx ferox. (From Gadow.) ponds of Georgia, Florida, and Louisiana. In the Central United States the common species is the spiny soft-shelled turtle, Triony.v spinifer. These turtles are voracious and carnivorous, 2 N 546 COLLEGE ZOOLOGY fording on fish, frogs, young water-fowl, and mollusks. When attacked they are very vicious. The shell as well as other parts of the animals are used as food and are regularly sold in the markets. Order 2. Rhynchocephalia. - - There is only a single living representative of this order -- Sphenodon punctatum (Fig. 450). This reptile, which formerly inhabited all of the main islands of New Zealand, is now restricted to some small islets in the Bay FIG. 450. Sphenodon punctatum. (From Gadow.) of Plenty, and will probably soon be entirely exterminated. It is about two feet long and resembles a lizard in form. It lives in burrows, is nocturnal, and feeds on other live animals. One of its most striking peculiarities is the presence of a well- developed parietal organ or pineal eye in the roof of the cranium, which has all the characters of a simple eye. It is also the only reptile without a copulatory organ. Numerous skeletal char- acteristics are like those possessed by some of the oldest fossil reptiles, and the ancestors of living reptiles were apparently much like this queer relic of past ages. CLASS REPTILIA 547 Order 3. Crocodilini. -- CROCODILES, ALLIGATORS, GA VIALS, and CALMANS (Fig. 451). These reptiles are lizard-like in form, but have the jaws extended into a long snout. The nostrils are at the end of the snout and the eyes protrude from the head so that the crocodilians can float at the surface with only these parts above the water. The skin is -thick and leathery, covered with horny epidermal scales, and with dorsal, and sometimes FIG. 451. CROCODILINI. A long-snouted gavial (Gavialis gaiigelicus) on top of an American crocodile (Crocodilus amcricanus). A Nile crocodile (Crocodilits niloticus) in the foreground. A " mugger " (Crocodilus paluslris) in the right upper corner. Notice peculiar floating attitude of young. (From Gadow.) ventral bony plates somewhat like those in the shell of the turtles. The nostrils and ears are provided with valves and are closed when the animal is under water. The limbs are well developed. There are five digits on the fore limbs and four more or less webbed digits on the hind limbs. The tail is a laterally compressed swimming organ. The anus is a longitudinal slit. Two pairs of musk glands are present, - one on the throat, and one in the cloaca. Some of the peculiarities of the internal structures are as 548 COLLEGE ZOOLOGY follows. The vertebrae are mostly procoelous; all of the cervi- cal and trunk vertebrae and some of the caudal vertebras bear ribs, a number of which are attached by two heads; there is a sternum, but no clavicles; the teeth are conical and are shed at intervals, being replaced by others which grow up beneath them; they are set in sockets (thecodont) on the premaxillae, maxillae, and dentary bones; the tongue is flat and non-pro- trusible, but can be raised and lowered, serving as a valve to prevent water from entering the oesophagus when the mouth is opened under water; palatal folds separate the upper air- passage from the lower food passage; there are no salivary glands, no intestinal caecum, and no bladder; the lungs are partitioned off from the rest of the organs in the body-cavity by a membrane which assists in respiration and is analogous to the diaphragm of mammals; the ventricle of the heart is completely divided into two by a septum, whereas that of other reptiles is only partially divided; the cerebellum is more highly developed than in the other reptiles; the penis resembles that of the turtles (see Fig. 442). Family GAVIALID^I. - - Two of the twenty-one species of living CROCODILINI belong to this family. Gavialis gangdicus, the Indian gavial, lives in northern India, and Tomistoma schle- gcli, the Malayan gavial, lives in Borneo and Sumatra. The Indian gavial (Fig. 451) reaches a length of twenty feet or more, and has a very long, slender snout. It inhabits the Ganges and Brahmaputra rivers and their territories. The food of the gavial consists principally of fish ; man is seldom if ever attacked. Family CROCODILID^. - - This family contains four genera - Crocodilus, Osteolcemus, Caiman, and Alligator. Crocodilus americanus, the American crocodile (Fig. 451), is an inhabitant of Florida, Mexico, and Central and South America. It has a triangular head becoming very narrow toward the snout. It attains a length of fourteen feet. In Florida the crocodile digs burrows in the bank in which to hide; the openings are entirely CLASS REPTILIA 549 or partly under water. The American crocodile is not dangerous to man. The African crocodile, Crocodilus niloticus (Fig. 451), is one of the few man-eating species, and has probably destroyed more human beings than any other kind of wild animal in the dark continent. Formerly it was held sacred by the Egyptians, and many specimens were preserved as mummies. The other nine species of the genus Crocodilus live in various parts of the world - - C. intermedius, the Orinoco crocodile, in Venezuela ; C. r/wmbifer, the Cuban crocodile, in Cuba ; C. moreletti, the Guatemala crocodile, in Guatemala and Honduras; and the others in Africa, Australia, Siam, Java, India, Malaysia, or Madagascar. The salt-water crocodile, C. porosus, which occurs in India and Malaysia, is a man- eating species. The five species of caimans occur in Central and tropical South America. The spectacled caiman, Caiman sclerops, ranges from southern Mexico southward into Argentina. It reaches a length of eight feet. The largest American crocodile is the black caiman, Caiman niger, of the upper Amazon. Some of these animals are said to be twenty feet long. There are two species of the genus Alligator; the American alligator, A. mississippiensis, inhabits the southeastern United States; and the Chinese alligator, A. sinensis, is found only in China. The American alligator has a broad, blunt snout, and is stouter, less active, and less vicious than the crocodiles. It attains a length of sixteen feet, but most of the large specimens have been killed for their hides, so that probably none now exist in the wild state over twelve feet long. The habits of the alli- gator are similar to those of the crocodile. The nest is a mound of earth and rotting vegetation. From twenty to forty eggs are deposited in this nest and left to hatch without any assistance from the parents. The Chinese alligator inhabits the Yangtse-Kiang River of China. It is only six feet long. 550 COLLEGE ZOOLOGY Order 4. Squamata. CHAMELEONS, LIZARDS, and SNAKES. These animals resemble one another rather closely in structure. They are all protected by horny, epidermal scales, and often by dermal plates of bone. The horny layer of the skin is cast off periodically. The anus is a transverse slit and there are two copulatory organs in the male. The legless lizards and snakes have undoubtedly evolved from ancestors with limbs. In all the living Squamata the limbs, when present, are adapted for walking on land. Suborder i. RHIPTOGLOSSI. -- CHAMELEONS. A number of different kinds of SQUAMATA are called Chameleons, but the true Chameleons be- long to the single family CHAM^ELE- ONTID.E of the suborder RHIPTO- GLOSSI. There are fifty species, all of which live in Africa and Madagascar; two of them also occur in Spain, India, and Ceylon. The three genera are Cham ale on (Fig. 452) with species, and Rham- FIG. 452. The chameleon, Chamodeon vulgaris. (From Gadow.) forty- five species, Brookesla with three pholeon with two species. The Chameleons differ from other SQUAMATA both in external features and in internal structure. The body is laterally com- pressed; the tail is prehensile, is not brittle, and cannot be re- generated if lost; the limbs are long and slender, and the digits are grouped so that two are permanently opposed to the other three; the head usually bears a prominent crest; no tympanum and tympanic cavity are present ; the pectoral girdle lacks clavicles CLASS REPTIUA 551 and interclavicles; the eyelids are united into a single fold with a small central opening; the eyes are moved separately, causing the animal to squint. The tongue is club-shaped and covered by a sticky secretion; it can be projected by muscles and by the inflow of blood to a distance of over six inches, and is used like that of the frog (p. 480, Fig. 410) for capturing live insects which constitute its entire food. The skin is covered with granules; it is shed several times a year, coming off in large flakes when the body is rubbed against stones or the limbs of trees. One of the features that has made the chameleons famous is the power of rapidly changing their colors. This is brought about with the aid of chromatophores (see p. 522) and is ap- parently partly under the control of the animal and partly due to external stimuli, such as light and temperature. A few chameleons are viviparous, but most of them deposit their eggs in the ground. In northern Africa the animals be- come fat in the autumn and hibernate in the ground during the winter. The common chameleon of North Africa, Syria, and Asia Minor is Chameleon mdgaris (Fig. 452). It is usually greenish in color and reaches a length of from eight inches to a foot, about half of which consists of the tail. Suborder 2. SAURIA. -- LIZARDS. - -The lizards constitute a very diversified group of reptiles. They usually have an elon- gated body and four well-developed limbs that are used for run- ning, clinging, climbing, or digging. Some have no limbs or only vestiges, but the pectoral and pelvic girdles are always present and there is usually a trace of a sternum. The tail is generally long; it is easily broken off, but a new organ is soon regenerated, which, however, does not possess vertebrae. The eyelids are movable except in some of the degenerate burrowing forms in which the eyes have become concealed beneath the skin. The skin is covered with small scales. Lizards are in most cases oviparous, and the eggs are pro- 552 COLLEGE ZOOLOGY tected by a parchment-like shell. They feed largely on insects, worms, and other small animals, but many are exclusively vegetarian. The more than fifteen hundred and twenty- five species of lizards are placed in two hundred and fifty-seven genera and twenty families. Only eight of these families are reviewed in the following paragraphs. Family GECKONIDJL --GECKOS (Fig. 453). - -This is a large family containing forty-nine genera and about two hundred and seventy species. Geckos inhabit all the warmer parts of the globe, are harm- less, and usually nocturnal. Many of them have la- mellae under the toes (Fig. 453), which enable them to climb over trees, rocks, walls, and ceilings. Three species occur in North America - the reef geckos, Sph&rodactylus no- tatus, of Florida, Cuba, and the Bahamas, the tubercular gecko, Phyllodactylus tuberculosus, of Lower California, and the cape gecko, P. unctus, also of Lower California. The genus Sph&rodactylus contains, besides reef geckos, seventeen species inhabiting Central and South America and the West Indies. The reef gecko is about three inches long. It has been reported from Key West, Florida. Phyllodactylus is another large genus; its twenty- five species occur in tropical South America, Africa, Australia, and islands in the Medi- terranean. FIG. 453. Geckos, Hemidactylus turicus (left); Tarentola mauritanica (right). (From Gadow.) CLASS REPTILIA 553 FIG. Family AGAMID^:. -- OLD WORLD LIZARDS. - -These lizards can be readily distinguished by the position of their teeth, which are set on the edges of the jaw- bones (acrodont dentition) and not in grooves or sockets. There are thirty genera and about two hundred species in the family. The flying- dragon, Draco volans (Fig. 454), is a species whose sides are ex- panded into thin membranes supported by ribs. These mem- branes are employed as a parachute when leaping from tree to tree, and are folded when not in use. It is about ten inches long and inhabits the Malay Penin- sula, Sumatra, Java, and Borneo, Members of the genus Calotes have the power of chang- ing their colors rapidly. Another interesting genus is Chlamydosaurus, which includes the 454. The flying dragon, Draco volans. (From Gadow.) FIG. 455. The frilled lizard, Chlamydosaurus kingi, at bay. (From Gadow.) frilled kingi This lizard, C. (Fig. 455). species in- 554 COLLEGE ZOOLOGY habits Queensland and northern Australia and reaches a length of about three feet. The skin at the sides of the neck is ex- panded into a sort of frill, and when the animal is irritated, this frill is extended by means of rib-like horns of the hyoid apparatus. Family IGUANID^E. - - NEW WORLD LIZARDS. All but three of the forty-eight genera belonging to this family are confined to America. The habits of these lizards vary considerably. Some are arboreal; others terrestrial; and still others semi- aquatic. The anoles, often called chameleons, the iguanas, the swifts, and the horned " toads " are the best- known groups. The genus Anolis contains over one hundred species. These are mostly small, with a long, slender tail. They have the power of changing color rapidly and are popularly called "chameleons." They are enabled to run about on smooth, vertical surfaces by lamellae under the central portion of each toe. Anolis carolinensis, the American " chameleon," is common in the southeastern United States and in Cuba. The iguanas range from the southwestern United States south- ward through tropical South America. The marine iguana, Amblyrhynchus cristatus, lives on the Galapagos Islands. Colonies of these iguanas, many of the individuals being over four feet long, inhabit the sea-coast and feed on seaweed. The common iguana, Iguana tuberculata (Fig. 456), reaches a length FIG. 456. The common iguana, Iguana tuberculata. (From Gadow.) CLASS REPTILIA 555 of six feet. It inhabits tropical America and is a favorite article of food. It loves to bask in the sun, lying stretched out on a stone fence or the limbs of a tree. The food of this iguana con- sists largely of insects, but it will also take small animals, and certain kinds of vegetation. The swifts belong to the. genera Ufa and Sceloporus. They are common in western North America, Mexico, and Central America. Most of them are small, and, as their popular name implies, very active. The sixteen species of small-scaled swifts FIG. 457. The horned " toad," Phrynosoma coronatum. (From Gadow.) are included in the genus Ufa. They live in the arid regions of the Southwestern states and are all terrestrial. The genus Sceloporus contains about thirty-five species of spiny swifts. The scales on the dorsal surface of the body terminate in sharp, spine-like points. The horned " toads " (genus Phrynosoma, Fig. 457) occur in the western United States and in Mexico. They live in hot, dry regions, many of them inhabiting the deserts, where they run about in search of insects for food. They are viviparous. Horned " toads " can be kept very easily in captivity if placed in a warm, dry place and fed on meal worms. Family ANGUID^:. OLD AND NEW WORLD LIZARDS. - -These lizards have a deep fold on each side of the body. Most of them 556 COLLEGE ZOOLOGY have poorly developed limbs or none at all. The glass " snakes," Ophisaurus apus of Europe, and O. ventralis of America, have no limbs and move, as do snakes, by lateral undula- tions. They can be distinguished from true snakes by the presence of mov- ~??..c- -V*KX_ --.-**>- -- able e y elids and - Srt^jL- an ear opening. FIG. 458. A limbless lizard, Anguis fragilis, the Their name is due " slow-worm " or " blind-worm." (From Shipley and f f i, MacBride.) brittleness of the tail. Another species, called the " blind- worm " or " slow- worm," Anguis fragilis (Fig. 458), inhabits Europe, western Asia, and Algeria. It looks like a large, brightly colored worm, but is not blind, since it has well-developed eyes. Family HELO- DERMATID.E. - BEADED LIZARDS. -The two species included in this family are the gila monster, Helo- _ derma suspedum, of Arizona and New Mexico, and the beaded lizard, H. horrid um, of Mexico and Cen- tral America. I-IG. 459. The Gila monster, Heloderma suspecium. (From Gadow.) The gila monster (Fig. 459) is the only poisonous lizard of the United States. It has a stout body and is conspicuously colored with bright CLASS REPTILIA 557 red and black. A large specimen measures a foot and one half in length. Gila monsters possess grooved fangs on the lower jaw, and, when fighting, viciously grasp their prey and throw themselves on their back, thus allowing the poison to flow down into the wound. The bite is fatal to small animals and dan- gerous to man. Family AMPHISB^ENID^:. - - WORM LIZARDS. - - These are limbless, burrowing lizards resembling worms in appearance. There are about ten genera and sixty species known from both the Old and New Worlds. Of these only one, the Florida worm lizard, Rhineura floridana, is found in the United States. This species is restricted to the Florida peninsula. It is about eight inches long. Family LACERTID.E. - - TYPICAL OLD-WORLD LIZARDS. - There are seventeen genera and about ninety-six species of lizards that are included in this family. They all possess well- developed limbs, and a long, fragile tail. The green lizard, Lacerta viridis, is a species common in central and southern Europe. Lacerta vivipara of Europe is viviparous. Family SCINCID^E. -- SKINKS. - -The skinks are found in many parts of the globe. In North America there are two genera and fifteen species. Ettmeces quiiiijuclineatus, the five- lined or blue skink, is the species common in the Eastern and Central states. The young are black with a longitudinal yellow stripe on the back and two on either side, and a blue tail. The females " retain dull stripes through life, but the males become uniform, dull olive-brown on the body and bright red about the head." This color change has been the cause of several specific and common names. The length of this skink is about nine inches. Suborder 3. SERPENTES. -- SNAKES. - -The snakes resemble the lizards and chamejeons in many of their anatomical features. They differ from them in at least four respects: (i) the right and left halves of the lower jaw are not firmly united, but are connected by an elastic band; (2) there is no pectoral girdle; 558 COLLEGE ZOOLOGY (3) the urinary bladder is absent; and (4) the brain case is closed anteriorly. Snakes are covered with scales; those on the head are so regular as to be of importance in classification. On the ventral surface in front of the anus is a single row of broad scales, called abdominal scutes, to which the ends of the ribs are attached. The outer, horny layer of the skin is shed a number of times during the year. Appendages are entirely absent except in a few species, like the python, which possess a pair of short spur-like projections one on either side of the anus, - vestiges of the hind limbs. The eyelids are fused over the eyes, but there is a transparent portion which allows the animal to see. When the skin is being shed, the snake is partially blind. There is no tympanic membrane, and the sense of hearing is very slightly developed. The tongue is a slender, deeply notched protrusible structure that can be thrust out even when the mouth is closed, because of the presence of grooves in the jaws. It is very sensitive to vibrations and probably serves as an organ of hearing. The prevalent idea that the tongue can inflict an injury is erroneous. The teeth are sharp and recurved. They are adapted for forcing the food into the throat. In the venomous snakes certain teeth are grooved or tubular, and serve to conduct poison into any object bitten. The bones of the skull are so arranged that the jaws are ex- tremely mobile. The snake is on this account able to swallow objects four or five times the diameter of its neck. When swallowing, the glottis is pulled forward, thus preventing the snake from choking. The vertebrae are very numerous - there may be over four hundred and a large number of ribs are also present. Movement on land is accompanied by .lateral undulations of the body. The body is drawn forward by pressing the rough posterior edges of the abdominal scutes against the substratum. Snakes cannot move forward on a smooth surface. Most CLASS REPTILIA 559 species are able to swim, and this, of course, is the normal method of locomotion of the aquatic forms. The majority of snakes are oviparous, but some of them bring forth their young alive. The idea that they swallow their young in order to protect them and then spew them out again when the danger has passed is erroneous. The tropics are more plentifully supplied with snakes than are the temperate zones. Snakes are, however, found in many places not inhabited by lizards. Madagascar seems to be the only large country in warm and temperate latitude not inhabited by dangerous snakes. As in the other groups of vertebrates, the serpents are found in almost every kind of habitat ; ' some species live in salt water, others in fresh water; some are arboreal; and many live underground. Only four of the nine families of SERPENTES occur in North America. With a few exceptions those described below are found in the United States. Family GLAUCONIID.-E. -- BLIND SNAKES. --Two species of these small, burrowing reptiles occur in the United States - Glaucoma dulcis, the Texas blind snake, in Texas and New Mexico, and G. hum His, the California blind snake, in Arizona, and southern California. They dig long tunnels in the earth and feed on worms and insect larvae. Family BOID.E. PYTHONS and BOAS. --The members of the family BOID.E are constrictors. They live almost exclusively upon birds and mammals which they squeeze to death in their coils (Fig. 460). None of them is venomous and only a few are large enough to be dangerous to man. The largest species on record is the regal python, Python reticulatus, of Burma, which attains a length of thirty feet. The anaconda or water boa, Eunectes murinus, of South America averages about seventeen feet in length. Not all of the BOID^: are large. Many of them are of moderate size or even small. Four species are found in North America, but they are comparatively rare and confined to the South- COLLEGE ZOOLOGY western states. There is only one " boa-constrictor ' with several varie- ties. It belongs to the genus Boa and its specific name is constrictor. It is a native of tropical South America and reaches a length of eleven feet. Boa- FiG. 460. The python, Python molurus, devouring , , a mammal. (From Gadow.) docile in captivity and therefore preferred by snake " charmers." Family COLUBRID^:. - - This family contains about 90 per cent of all living snakes and is so large that it is usually divided into three series. Series A. AGLYPHA. - - The snakes placed in this series have solid teeth, and no grooved nor perforated fangs. They are all non-venomous and are found in every country inhabited by snakes. Half a dozen of the most common species found in the United States are briefly described below. The common garter-snake or striped snake, Thamnophis sirtalis (Fig. 46 1 ) , is usually provided with three longitudinal yellow stripes, one on the FIG. 461. The garter-snake, Thamnophis sirtalis. (From Gadow.) CLASS REPTILIA 561 back and one on either side. Every portion of North America is inhabited by a species or variety of this genus. The garter- snakes are so difficult to classify that our description must be only a general one. The species T. sirtalis possesses nineteen rows of scales on the body, and certain peculiarities in the scales (shields) on the chin. The garter-snakes are the most abundant of our harmless snakes. They are the first to appear in the spring and the last to hibernate in the autumn. Their food consists largely of frogs, toads, fishes, and earthworms. The young are brought forth alive, usually in August, and become mature in about one year. The common water-snake, Natrix fasciatus variety sipedon, belongs to a genus whose species and varieties are abundant in the United States, Europe, and Asia. They are semiaquatic serpents, living in swampy places or in the vicinity of ponds and streams. The water is usually selected by them as an avenue of escape when disturbed. The variety sipedon of the eastern United States is pale brownish or reddish in color, with wavy cross bands of brown; these break up into blotches on the hinder part of the body. The length of an adult is usually about three feet six inches. Like the garter-snake, the water-snake is vivip- arous and about twenty-five young are produced in August or September. The water-snake is often erroneously called " water-moccasin." The black-snake, Zamenis constrictor, is a slender, long-tailed snake of the eastern United States which reaches a length of six feet. West of the Mississippi it gives way to a color variety Z. constrictor variety flaviirntris, called the " blue ' racer. In the East the black-snake is slaty black except the chin and throat, which are milky white. In Michigan and adjoining states it is bluish green above and immaculate white beneath. Con- trary to popular belief, this reptile does not attack snakes larger than itself, has no power to squeeze its prey to death, and is unable to hypnotize birds and squirrels. Its prey is almost always smaller than itself, and is swallowed while still alive, often 2 O 562 COLLEGE ZOOLOGY being held down by a portion of the body during the process. Black-snakes prefer dry and open situations, especially at the edge of meadows. They are partial to birds' eggs and young, but also devour mice, frogs, and various other small animals. Their eggs to the number of a dozen or more are deposited in June or July, usually under a stone or in soft, moist soil. The king-snakes belong to the genus Opkibolus. They are of various sizes, are constrictors, and have received their common name because they prey on other snakes. Of the seven species occurring in the United States, the milk-snake, O. doliatus variety triangulus, the scarlet king-snake or " coral-snake," O. doliatus variety coccineus, and the common king-snake, 0. getulus, are of special interest. The milk-snake derives its name from its supposed habit of stealing milk from cows. This is not true, since rats and mice are its principal articles of food. The color of this variety is gray above, with brownish saddle-shaped blotches on the back, and smaller blotches on the sides. It averages about three feet in length, and is oviparous. The scarlet king-snake or " coral-snake " is a small variety about a foot long. It is ringed with bright bands of scarlet, yellow, and black, causing it to resemble the venomous coral- snake, Elaps fulvius (see p. 564). The common king-snake or chain-snake is a heavy-bodied constrictor of the eastern United States. Other snakes, both harmless and venomous species, and field mice, are squeezed to death and devoured by it. King-snakes are immune to venom and do not hesitate to attack rattlesnakes, water-moccasins, and copperheads. The length of an average adult is about five feet. The hog-nosed snakes of the genus Heterodon are represented in North America by three species popularly known as " puff- adders," " spreading vipers," or " blow snakes." The common hog-nosed snake, Heterodon plalyr/ilnus, inhabits dry, sandy places over most of the United States east of the Rocky Moun- CLASS REPTILIA 563 tains. The snout is turned up at the end, whence its common name. It is non-venomous and entirely harmless, but when disturbed throws itself 'into a defiant attitude, dilates its neck like a cobra, and makes a hissing sound. If this does not frighten away the enemy, the snake may suddenly open its mouth, and appear to be injured and to lose strength. ' Then a convulsion seemingly seizes the snake, as it contorts its body into irregular undulations, ending in a spasmodic wriggling of the tail, when the reptile turns on its back and lies limp and to all appearances dead. " So cleverly and patiently does the snake feign death that it may be carried about by the tail for half an hour or more, hung over a fence rail where it dangles and sw r ays to a passing breeze, or tied in a knot and thrown in the road, and to all of this treatment there is no sign of life except from one condition. In spite of this remarkable shamming, the snake may be led to betray itself if placed upon the ground on its crawling surface. Then like a flash it turns upon its back again and once more be- comes limp and apparently lifeless. It appears, according to this creature's reasoning, that a snake to look thoroughly dead should be lying upon its back. This idea is persistent, and the experi- ment may be repeated a dozen times or more. " Should the observer retreat some distance away, while the reptile lies thus, or he seek near-by concealment, the craftiness of the animal may be realized. Seeing nothing further to alarm, the serpent raises its head slightly and surveys its surroundings, and if there is no further sign of the enemy, it quickly rolls over upon its abdomen and glides away as fast as its thick body will carry it. But at such a moment a move on the observer's part would send the reptile on its back again, with ludicrous pre- cipitation." (Ditmars.) Series B. OPISTHOGLYPHA. - - The opisthoglyphs are COLU- BRiDjE which possess grooved teeth in the rear of the upper jaw. They are all poisonous, but very few are dangerous to man. The subfamily HOMALOPSIN/E contains about twenty-three 564 COLLEGE ZOOLOGY species of fish-eating, river snakes of the East Indies. The sub- family DIPSADOMORPHIN^E contains about two hundred and seventy-five species of slender, long-tailed snakes of cosmopolitan distribution. They are terrestrial, sub terrestrial, arboreal, or semiaquatic in habits. The opisthoglyphs of the United States are found only in the southern part. They are moderate or small in size, few in number, and not very dangerous. Series C. PROTEROGLYPHA. - - The proteroglyphs are COLU- BRID.E which possess fixed, tubular fangs in the anterior part of the upper jaw. As in the case of the opisthoglypha, they are all venomous. Many of them are the most dangerous of all poisonous reptiles. There are two subfamilies. The HYDRIN.S:, or sea-snakes, are true sea-serpents. They inhabit the Indian Ocean and the western, tropical Pacific, and one species occurs along the western coast of tropical America. They reach a length of from three to eight feet or more, and most of them are very poisonous. The tail, and some- times the body, is laterally compressed -- an adaptation for swimming. The subfamily ELAPIN^E contains twenty-nine genera and about one hundred and fifty species of poisonous snakes. They are most abundant in Australia and New Guinea, but occur also in India, Malaysia, Africa, and America. The single genus Flaps of the New World contains about twenty-eight species of coral-snakes. Two of these are found in the United States, the harlequin or coral snake, Elaps fulvius, and the Sonoran coral-snake, E. euryxanthus. The harlequin snake of the southeastern United States aver- ages about two and a half feet in length. Its body is ringed by broad cross bands of scarlet and blue-black, separated by nar- row bands of yellow. It can easily be distinguished from the harmless scarlet king-snake (p. 562), since in the latter the yellow bands are bordered by the black ones. The harlequin snake burrows in the ground, and feeds chiefly upon lizards and snakes. It is oviparous. Most writers consider this snake dangerous CLASS REPTILIA 565 only to small animals, but its fangs are capable of injecting a venom more virulent than that of the rattlesnake. The cobra-de-capello, Xaja tri pud inns (Fig. 462), of India, China, and the Malay Archipelago, is the most notorious relative of the harlequin snake. The cobra is very vicious; when dis- turbed it raises the anterior part of the body from the ground, spreads its neck (hood) with a hiss, and strikes at once. In India the bare-legged natives are killed in large numbers by cobras; for example, in 1908, 21,880 were killed by snake bites, most of them probably the bites of this species. There are nine other species of cobras seven confined to Africa, one in the Philippine Islands, and one, the king cobra, inhabiting the same countries as the cobra-de- capello. Family VIPERID.E. - -THICK- BODIED POISONOUS SNAKES. --The viperine snakes are often termed solenoglyphs to distinguish them from the three series of the family COLUBRID^E. Their fangs are tubular, firmly attached to the movable maxillary bones, and folded flat against the roof of the mouth when the jaws are closed. The two subfamilies of viperine snakes are the VIPERINE, or true vipers, of the Old World, and the CROTALIN.E, or pit-vipers, of both the New World and Old World. The pit-vipers are easily recognized by the presence of a deep pit on each side of the head between the eye and the nostril. The function of this pit is not known. There are four genera and about seventy species. Those found in the United States are the copperhead, water-moccasin, and fifteen species of rattlesnakes. The water-moccasin, Agkistrodon pisciwrus (Fig. 463), occurs FIG. 462. The cobra, Naja tripudians. (From Gadow.) 5 66 COLLEGE ZOOLOGY hi the swamps of the Atlantic coast south of North Caro- lina, and in the Mississippi Valley from southern Illi- nois and Indiana southward. The length of an aver- age specimen is four feet, but a length of over five feet is sometimes attained. The moccasin is one of the most poison- ous of all snakes. It feeds upon cold-blooded ani- mals such as frogs, I FIG. 463. The water-moccasin, Agkistrodon piscivorus. (From Gadow.) and also upon small birds and mammals. The young are brought forth alive. The copperhead snake, Agkistrodon contortrix (Fig. 464), is another very ven- omous snake. Its range extends from southern Massa- chusetts to north- ern Florida and west to Texas. In the southern part of its range the copperhead prefers to live on the plantations, but in the North it is found in or near thick forests. An average specimen measures about two and a half feet in length. FIG. 464. The copperhead, Agkistrodon contortrix. (From Gadow.) CLASS REPTILTA The rattlesnakes are easily distinguished by the rattle at the end of the tail. This consists of a number of horny, bell-shaped segments loosely held together. Each segment was once the end of the tail; it was shed when the skin was shed, but was held by the newly developed end of the tail. Rattles are therefore added as often as the skin is shed, and, since this happens several times per year, and also since rattles are often detached and lost, it is obvious that the number of rattles is no indication of the age of the snake. Usually before striking, 'the rattle- .D; FIG. 465. Poison apparatus of the rattlesnake. A, A, eye; Gc, poison- duct entering poison-fang at f ! Km, muscles of mastication, cut at * ; Me, Me', constrictor muscle; N, nasal opening; S, fibrous poison-sac; 2, tongue; za, opening of poison-duct; zf, pouch of mucous membrane enclosing poison-fangs. B, position of apparatus when mouth is closed. C, position when mouth is opened widely. Di, digastric muscle: G, groove or pit characteristic of Crotaline snakes: J, poison-fang; M, maxillary; P, palatine; Pe, sphenopterygoid muscle; Pm, premaxillary; Pt, pterygoid; Q, quadrate; Si), squamosal; Ta, insertion of anterior temporal muscle; Tr, ectopterygoid. (A, from Parker and Haswell, after Wiedersheim; B, C, from Gadow.) snake vibrates the end of the tail rapidly, producing a sort of buzzing noise, which, to the wise, serves as a warning. The poison apparatus of the rattlesnake is shown in Figure 465. The poison is secreted by a pair of glands (Fig. 465, A, S) lying above the roof of the mouth. These glands open by poison ducts (Gc) into the poison-fangs (f). The poison-fangs are pierced by a canal, which opens near the end (za), and are en- closed by a pouch of mucous membrane (zf). When the jaws 5 68 COLLEGE ZOOLOGY are closed (Fig. 465, B), the fangs lie back against the roof of the mouth. When the snake bites, the digastric muscle (Fig. 465, C, Di) opens the jaws; the sphenopterygoid muscle (Pe) contracts, pulls the pterygoid bone (Pi) forward and pushes the ectopterygoid bone (7>) against the maxillary bone (M). The maxillary bone is thus rotated, and the poison-fang (/) is erected. The poison-glands are so situated that the opening of the jaws and erection of the fangs squeezes the poison out of them, through the fangs, and' into the object bitten. There are several pairs of small fangs lying just behind the functional ones, which are held in reserve to replace those that are lost in struggles with prey or are normally shed. Rattlesnakes are most abun- dant both as regards the num- ber of species and the number of individuals in the deserts of the southwestern United States, but almost every part FIG. 466. The Texas rattlesnake, o f this country is inhabited by one or more species. The diamond-back rattlesnake, Cro- talus adamanteus , is the most deadly and largest rattlesnake,, measuring sometimes over eight feet in length. It inhabits the pine swamps and hummock lands of the southeastern United States. A nearly allied species is the Texas rattlesnake, Crotalus atrox (Fig. 466). This species inhabits the subarid and desert regions of Texas and the Southwest. These snakes are nocturnal in habit, and prefer the common rabbit as food. Their bite is usually fatal to man within an hour. Other species that should be mentioned are the timber, or Crotalus atrox. (From Shipley and MacBride, after Baird and Girard.) CLASS REPTJLIA 569 banded rattlesnake, Crotalus horridus, of the eastern United States; the horned rattlesnake, Crotalus cerastes, inhabiting the deserts of the southwestern United States; and the massasauga, Sistrurus catena/us, which is a rather common species in the central United States. 4. THE POISONOUS SNAKES OF NORTH AMERICA As the preceding discussion shows, there are only twenty-two species of poisonous snakes in the United States; namely, the harlequin snake, the Sonoran coral-snake, the copperhead, the water-moccasin, seven unimportant opisthoglyphs (p. 563), and fifteen species of rattlesnakes. It is important for any one who spends much time in the country to be able to distinguish be- tween these poisonous snakes and the non-poisonous species. This can easily be done by means of the following key, which was prepared by Professor Alexander G. Ruthven. Key to the Venomous and Non-venomous Snakes of the United States A. Pupil of eye vertical. B. A pit between the eye and nostril. - - Pit-vipers (venomous) C. Tail terminating in a rattle . . . Rattlesnakes. CC. Tail not terminating in a rattle. Moccasin and copperhead. BB. No pit between eye and nostril. --Non-venomous or opisthoglyph and not dangerous to man. AA. Pupil of eye round. B. Body ringed with red, black, and yellow, the black rings bordered by the yellow ones. Coral-snakes (venom- ous). BB. Body not ringed with red, black, and yellow, or if so the yellow rings bordered by the black ones. - - Non- venomous or opisthoglyph and not dangerous to man. 570 COLLEGE ZOOLOGY Notwithstanding the fear of snakes possessed by most people, very few are bitten by poisonous species in this country, and of these probably not more than two per year die. Snake Venom. - - Venom is a highly complex physiological product elaborated by the poison-glands. Among its powers are the dissolution of various body cells and the destruction of the bactericidal property of the blood. Venoms are albuminoid. They are capable of producing in the blood an antidote or neutralizing substance, called an antibody. It is thus possible, as in the case of smallpox, tetanus, etc., to obtain an antibody (an antivenin) which, when injected into the blood, will counter- act the effects of the venom. Unfortunately each kind of venom requires a special sort of antivenin, so that it is impracticable as a rule to carry antivenin into the field. The best method of procedure when bitten by a poisonous snake is to apply a ligature between the wound and the heart so as to prevent the blood from carrying the venom toward the heart. This ligature should not be kept on more than half an hour, since, as stated above, the venom destroys the bactericidal power of the blood, and gangrene will set in rapidly about the wound if fresh blood is not supplied. After the ligature is in place, the wound should be incised deeply in all directions, and a solution of potassium permanganate injected freely into the tissues about the wound. This treatment should serve to destroy most of the venom before it travels far in the system. Sucking the poison from the wound is a common practice, but there is danger of poison finding its way into the blood through slight abrasions of the lips or mouth, and, besides, this procedure is of no value. It also seems certain that the drinking of large quantities of alcohol is not only useless, but of considerable detriment. 5. THE ECONOMIC IMPORTANCE or REPTILES The economic importance of the various kinds of reptiles has been emphasized during the discussion of the orders and families. It will therefore suffice here to give a brief summary of the subject. CLASS REPTILIA 571 The food of reptiles consists of both animals and plants. The animals eaten belong to practically all classes. Many of the snakes live almost entirely upon birds and mammals. Frogs, fish, and other reptiles are favorite articles of food. Most of the smaller species of reptiles feed upon worms and insects. In general it may be stated that reptiles do very little damage be- cause of the animals and plants they destroy for food, but are often of considerable benefit, since they kill large numbers of obnoxious insects and other forms. The turtles and tortoises rank first as food for man. Espe- cially worthy of mention are the green turtle (p. 543) , the diamond- back terrapin (p. 542), and the soft-shelled turtle (p. 545). In some parts of this country it would seem possible to establish turtle farms that would utilize land useless for other purposes, and would be commercially successful. Certain lizards, such as the iguana of tropical America, form a valuable addition to the food supply in various localities. The skins of the crocodilians are used rather extensively for the manufacture of articles that need to combine beauty of surface with durability. The alligators in this country have decreased so rapidly because of the value of their hides that they will be of no great economic importance unless they are consistently protected or grown on farms. Of less value are the skins of certain snakes. Tortoise-shell, especially that procured from the horny covering of the carapace of the hawk's- bill turtle (p. 544, Fig. 447), is widely used for the manufacture of combs and ornaments of various kinds. As previously stated, the poisonous snakes of the United States are of very little danger to man. In tropical countries, espe- cially India (p. 565), venomous snakes cause a larger death-rate than that of any other group of animals. The Gila monster, which is one of the few poisonous lizards, and the only one in- habiting the United States, very seldom attacks man, and prob- ably never inflicts a fatal wound. 572 COLLEGE ZOOLOGY 6. PREHISTORIC REPTILES Sixteen of the twenty orders of reptiles are known only from their fossil remains embedded in the earth's crust. Three of these orders will serve to give a general idea of the nature of the extinct reptiles. FIG. 467. Fossil reptiles. A, Brontosaurus cxcelsus. B, Slegosaurus ungulatus. C, Ceratosauru* naxiconiis. (A, B, from Sedgwick's Zoology, after Marsh; C, from Zittel, after Marsh.) CLASS REPTILIA 573 Order Dinosauria. - - The DINOSAURIA were extremely large reptiles that probably lived in swamps or in the neighborhood of water during Triassic, Jurassic, and Cretaceous times. Re- mains have been found in America, Europe, Asia, Africa, and Australia, and footprints have been discovered in the sandstone of the Connecticut Valley. Some species measured over one hundred feet in length. Both herbivorous and carnivorous forms existed. Brontosaurus (Fig. 467, A) was about sixty feet long; was herbivorous; and had four limbs about equally well developed. Its remains have been found in Wyoming and Colorado. Steg- osaurus (Fig. 467, B) reached a length of about twenty-eight feet and was also herbivorous. It possessed huge triangular plates along the back. Remains have been discovered in Wyo- ming and Colorado. Ccratosaunis (Fig. 467, C) was a carnivorous dinosaur with a comparatively large head. The character of its skeleton indicates that it walked about on its hind limbs and rested on its tail, much like a kangaroo. Remains have been found in Colorado. Order Ichthyosauria. - - The ICIITIIVOSAURS (Fig. 468) were fish-eating, aquatic reptiles. Their bodies were admirably FIG. 468. A fossil reptile, Ichthyosaurus communis. Caudal fin not shown. (From Parker and Haswell, after Owen.) adapted for life in the water, and they have been called the " whales " of the Mesozoic Era. The remains of ICHTHYOSAURS occur in North America, Europe, Asia, Africa, and Australia. Order Pterosauria. - - The PTEROSAURIA were reptiles of the Mesozoic Era which had the fore limbs modified for flight. They resemble birds in certain skeletal characters, but differ from 574 COLLEGE ZOOLOGY them in others. Rhamphorhynclms (Fig. 469) possessed teeth and a long tail. Pteranodon is the largest form known; it had FIG. 469. Restoration of a fossil, flying reptile, Rhamphorhynchus phyllurus. (From Sedgwick's Zoology, after Woodward.) a skull two feet long, and a spread of wing of twenty feet. Teeth are absent, and the tail is short. CHAPTER XX SUBPHYLUM VERTEBRATA: CLASS VI. AVES THE class AVES contains the birds. Birds are easily dis- tinguished from all other animals, since they alone possess feathers. The ten thousand or more species of birds are grouped into two subclasses: (i) ARCH^ORNITHES, which contains the fossil form Archceopteryx ; and (2) NEORNITHES, which contains four orders of extinct forms and seventeen orders with living representatives. i. THE PIGEON The common pigeons have been derived from the blue rock- pigeon, Columba lima (Fig. 470), which ranges from Europe through the Medi- terranean coun- tries to central Asia and China. Since pigeons are easily obtained and of moderate size, they are usually selected as a type of the class AVES for laboratory study. External Fea- tures. The body of the pigeon is spindle-shaped, and therefore adapted for movement through the air. Three regions may be recognized, --head, neck, and 575 ^^jy^asgasigyi-/^ FIG. 470. The blue rock pigeon, Columba lima. (From Brehm.) COLLEGE ZOOLOGY trunk. The head is prolonged in front into a pointed, horny beak, at the base of which is a patch of naked, swollen skin, the cere. Between the beak and the cere are the two oblique, AD MOMP PO 0, >^, P P. M K FIG. 471. Anatomy of the pigeon. .1, nostril; AD, ad-digital primary feather; B, external auditory meatus; BW , bastard wing; C, oesophagus; CA, right carotid artery; D, crop; DA, aorta; E, keel of sternum; F, right auricle; G, right ventricle; HV, hepatic vein; ///, left bile-duct; //_', right bile-duct; /. distal end of stomach; IA, right innominate artery; IV, posterior vena cava; JA, left innominate artery; JV, right jugular vein; A", gizzard; L, liver; M, duodenum; MD, mid-digital primary feathers; MP, metacarpal primaries; Mi, preaxial metacarpal; M2, middle metacarpal; M 3, postaxial metacarpal; N, cloacal aperture; Ni, preaxial digit; 0, bursa FabTicii, Oi, proximal phalanx of middle digit; 02, distal phalanx of middle digit; P, pancreas; PA, right pectoral artery; PD, predigital primary; PV, portal vein; Pi, first pancreatic duct; P2, second pancreatic duct; Pj, third pancre- atic duct; Q, pygostyle; R, rectum; RC, radial carpal bone; RX, rectrices; Ri, ulnar digit; S, ureter; SA, right subclavian artery; 57, right anterior vena cava; T, rectal diverticulum; U, kidney; UC, ulnar carpal bone; V, pelvis; W, lung; X, humerus; Y, radius; Z, ulna. (From Marshall and Hurst.) slit-like nostrils (Fig. 471, A). On either side is an eye which is provided with upper and lower lids, and with a well-developed third eyelid, or nictitating membrane. The third eyelid can be CLASS AVES 577 drawn across the eyeball from the inner angle outward. Below and behind each eye is an external auditory aperture (Fig. 471, B) which leads to the tympanic cavity. The neck is long and flexible. At the posterior end of the trunk is a projection which bears the tail feathers. The two wings can be folded close to the body or ex- tended as organs of flight. The hind limbs are covered with horny epidermal scales, and their digits are each provided with a horny claw. Feathers. Feathers are peculiar to birds. They arise, as do the scales of reptiles, from dermal papilla? with a covering f pnirlprmic; FIG. 472. Feathers of the pigeon. A, proximal por- ' tion of a contour feather. B, filoplume. C, nestling down, cal, calamus; inf.umb, inferior umbilicus; rch, rachis; sup.umb, superior umbilicus. (From Parker and Haswell.) and become en- veloped in a pit, the feather fol- licle. A typical feather (Fig. 472, .4) consists of a stiff axial rod, the scapus or stem; the proximal portion is hollow, and semitrans- parent, and is called the quill or calamus (cal) ; the distal portion is called the vane, and that part of the stem passing through it is the shaft or rachis (;r//). The vane is composed of a series of parallel barbs, and each barb bears a fringe of small processes, 2 P 573 COLLEGE ZOOLOGY B the barbules, along either side. The barbules on one side of the barb bear hooklets which hold together the adjacent barbs. The whole structure is thus a pliable, but nevertheless resistant, organ wonderfully adapted for use in flight. The three principal kinds of feathers are: (i) the contour feathers or pennae like that just described; these possess a stiff shaft and firm vanes, and since they appear on the surface, determine to a large degree the contour of the body. (2) The down feathers or plumulae t f t ^^W ~^%il possess a soft shaft and a vane without barbs; they lie beneath the contour feathers and form a cover- ing for the retention .of heat. The barbs of some down feathers arise directly from the end of the quill, and no shaft is present (Fig. 472, C). (3) The jtfo plumes (B) pos- sess a slender, hair-like shaft and very few or no barbs. Only certain portions of the pigeon's body bear feathers ; these feather tracts are termed pteryla, and the featherless spaces are known as apteria. The feather tracts differ in different species of birds; those of the pigeon are shown in Figure 473. Birds shed their old feathers, i.e. molt, usually in the fall, and acquire a complete new set which are formed within the follicles and from the papilla; of those that are cast off. There may be a partial molt in the spring, when the bird assumes its breeding plumage. At this time the plumage often changes FIG. 473. Feather tracts of the pigeon. A, ventral; B, dorsal, al.pt, alar pteryla or wing tract; c.pt, cephalic pteryla or head- tract; cd.pl, caudal pteryla or tail tract; cr.pt, crural pteryla; cr apt, cervical apte- rium or neck-space; fm.pl, femoral pteryla; hu.pt, humeral pteryla; lat.apt, lateral apterium; sp.pt, spinal pteryla; v.apt, ven- tral apterium; v.pt, ventral pteryla. (From Parker and Haswell, after Nitzsch.) CLASS AVES 579 color; this is caused probably either by an actual chemical change in the pigment, or by the breaking off of the tips of the feathers. The Skeleton. - - The principal differences between the skele- ton of a pigeon and that of a reptile are those that are made necessary by the methods of locomotion of the former. The hind limbs and pelvic girdle are modified for bipedal locomotion ; the fore limbs and pectoral girdle are modified ior flight; the skeleton of the trunk is rigid;' the sternum has a distinct crest for the attachment of the large muscles that move the wings ; short projections, called uncinate processes, which extend back- ward from some of the ribs, make the thoracic framework more firm; and the bones are very light, many of them containing air- cavities. The skeleton of the common fowl (Fig. 474) is larger and more easily studied than that of the pigeon, and is similar to the latter in most respects. The skull (Fig. 474, 7-7) is very light, and most of the bones in it are so fused together that they can be distinguished only in the young bird. The cranium is rounded; the orbits are large ; the facial bones extend forward into a beak ; the quadrate is movable and connects the lower jaw with the squamosal of the cranium; there is but a single occipital condyle for articulation with the first vertebra; and no teeth are present. The cervical vertebras (Fig. 474, 8) are long and move freely upon one another by saddle-shaped articular surfaces, making the neck very flexible. This enables the bird to use its bill for feeding, for nest building, and for many other purposes. The vertebrae of the trunk are almost completely fused together into a rigid skeletal axis which is necessary to supp3rt the body while in flight. There are four or five free caudal vertebras followed by a terminal pygostyle (Fig. 474, 18) consisting of five or six fused vertebrae. The pygostyle (Fig. 471, Q) supports the large tail feathers (rectrices, Fig. 471, RX), and the free caudal ver- tebras allo^v the movements of the tail which enable the bird to 5 8o COLLEGE ZOOLOGY 83 -- j J2 30 ," 18 13 FIG. 474. Skeleton of the common fowl, male. /, pre- maxilla; 2, nasal; 3, lachry- mal; 4, frontal; 5, mandible; 6, lower temporal arcade; 7, tympanic cavity; 8, cer- vical vertebra; g, ulna; 10, humerus ; n, radius; 12, carpo-metacarpus; /.?, first phalanx of second digit; 14, third digit; 75, sec- ond digit; 16, ilium; 17, ilio- ischiatic foramen; 18, pygo- style; IQ, femur; 20, tibio- tarsus; 21, fibula; 22, patella; 23, tarso-metatarsus; 24, first toe; 25, second toe; 26, third toe; 27, fourth toe; 28, spur 2Q, pubis ; jo, ischium 31, clavicle ; 32, coracoid 33, keel of sternum ; 34, xiphoid process. (From Shipley and MacBride.) CLASS AVES 581 use this organ as a rudder while flying and as a balancer while perching. There are two cervical ribs and five thoracic ribs on each side. The second cervical and first four thoracic ribs bear each an uncinate process which arises from the posterior margin and overlaps the succeeding rib, thus making a firmer framework. The thoracic ribs are connected with the sternum or breastbone. The sternum is united in front with the coracoid (Fig. 474, 32) of the pectoral girdle and bears on its ventral surface a large crest or keel (carina, Fig. 474, jj) to which the muscles that move the wings are attached. The pectoral girdle consists of a pair of blade-like scapula, the shoulder-blades, which lie above the ribs one on either side of the vertebral column in the thorax. The coracoids (Fig. 474, 32) connect the sternum with the anterior end of the scapulas at the shoulders. A concavity in these bones at their junction furnishes the articular surface for the long wing bone (humerus), and is called the glenoid cavity. The two clavicles (Fig. 474, ji) connect proximally with the shoulder and are fused together distally, forming a V-shaped furcula or " wishbone." The clavicles are homologous to the collar-bones of man, and serve to brace the shoulders. The fore limb or wing of the pigeon (Fig. 471) is greatly modified. There are but three digits, and only one of these is well developed. The distal row of carpal bones and the three metacarpals are fused together forming a carpo-metacarpus (Fig. 47 1 , Mi-Ms) '> this adds to the rigidity of the wing. The arm contains, as in other vertebrates, a single bone, the humerus (X), with a convex head which lies in the glenoid cavity. The fore arm possesses two bones, the radius (F) and ulna (Z). The wrist contains two carpal bones (UC and RC); the other carpal bones are fused with the three metacarpals (Mi-Mj), forming the carpo-metacarpus, as stated above. Besides the carpo-metacarpus, the hand possesses a preaxial digit with two small bones (Ni), which supports a small tuft of feathers and 5 g 2 COLLEGE ZOOLOGY is known as the bastard wing (BW); a middle digit with three phalanges (0/-02);- and a postaxial digit (Ri) containing a single phalanx. The pelvic girdle consists of the ilia (Fig. 474, 16) , the ischia (30) , and the pubes (29), as in nearly all of the vertebrates above the fishes. These bones are firmly fused together and united with the posterior part of the vertebral column in the trunk which is called the sacrum. At their junction on either side is a con- cavity, the acetabulum, in which the head of the thigh-bone fits. The hind limbs are used for bipedal locomotion. The thigh is concealed beneath the feathers. The femur (Fig. 474, 19) is the short, thick, thigh-bone. In the leg are the slender fibula (21], and the long, stout tibiotarsus (20) which consists of the tibia fused with the proximal row of tarsal bones. The ankle- joint is between the tibiotarsus (26) and the tar so -metatarsus (23) ; the latter represents the distal row of tarsal bones and the second, third, fourth, and fifth metatarsals fused together. The foot possesses, besides the tarso-metatarsus, four digits; the first is directed backwards and is called the hallux (24) ; and the other three (25, 26, 27} are directed forwards. Each digit bears a terminal claw. The tarso-metatarsus of the fowl bears a back- wardly directed spur (28}. The Muscular System. - - The muscles of the neck, tail, wings, and legs are especially well developed. Those that produce the downward stroke of the wings, the pectoral muscles, are the largest ; they weigh about one fifth as much as the entire body; they take their origin from the sternum and its keel, and constitute what is popularly known as the " breast " of the bird. Con- nected with the leg muscles is a mechanism which enables the bird to maintain itself upon a perch even while asleep. If the hind limb is bent, a pull is exerted on a tendon which flexes all of the toes and bends them automatically round the perch. When resting, the mere weight of the body bends the hind limb and con- sequently causes the toes to grasp the perch and hold the bird firmly in place. CLASS AYES 583 The Digestive System. - - Pigeons feed principally upon vegetable food, such as seeds. The month cavity opens into the oesophagus (Fig. 471, ( '), which enlarges into a crop (D) ; here the food is macerated. The stomach consists of two parts, an an- terior proventriculus (I) with thick glandular walls, which secretes the gastric juice, and a thick muscular gizzard (K), which grinds up the food with the aid of small pebbles swallowed by the bird. The intestine forms a U-shaped loop, the duodenum (.17), which leads into the coiled small intestine, or ileum, and finally passes into the rectum (R) at a point where two blind pouches, the cceca (T), are given off. The alimentary canal leads into the cloaca into which the urinary and genital ducts also open. The cloaca opens to the outside by means of the anus (A 7 )- In young birds a thick glandular pouch, the bursa Fabricii (0), lies just above the cloaca. The two bile ducts (Hi, H.2), one from each lobe of the liver (L), discharge the bile fnto the duodenum. There is no gall- bladder. The pancreas (P) pours its secretions into the duo- denum through three ducts (Pi, P2, Pj). There is a spleen, paired thyroids, adrenal bodies, and, in young pigeons, paired tlivmus glands (see p. 492). The Circulatory System (Fig. 475). - -The heart of a bird is comparatively large. It is composed of two entirely separated muscular ventricles (l.vn, r.vn) and two thin-walled auricles (I. an, r.au). The right auricle (r.au) receives impure, venous blood from the right precaval (r.prc), the left precaval (l.prc), and the postcaval veins (ptc). This blood passes from the right auricle into the right ventricle (r.vn), and is then pumped through the pulmonary artery, which divides into right (r.p.a) and left (l.p.a) pulmonary arteries, leading to the right and left lungs respectively. The left auricle (Fig. 475, l.au) receives the blood which returns, after being aerated in the lungs, through four large pulmonary veins. It passes from the left auricle into the left ventricle, and is then pumped through the right aortic arch COLLEGE ZOOLOGY 1.C FIG. 475. --The hean and chief blood-vessels of the pigeon, ventral as- pect, a. ao, aortic arch; a.m.a, anterior mesenteric artery; a.r.v, afferent renal veins; a.r.v', vein bringing blood from pelvis into renal portal system; br.a, brachial artery; br. V, brachial vein; c, cau- dal artery and vein ; c.c, common carotid artery ; c.m.v, coc- cygeo-mesenteric vein ; cos. a, cceliac artery ; d.ao, dorsal aorta; ex, external carotid artery ; epg, epigastric vein; e.r.v, efferent renal vein; f.a, femoral artery; /.?, femoral vein; h.v, he- patic vein; i.c, internal carotid artery; i.il, in- ternal iliac artery and vein; i.m, internal mam- mary artery and vein ; in. a, innominate artery; z.i', iliac vein; ju, jugular vein; ju', anastomosis of jugular veins; l.au, left auricle; l.p.a, left pul- monary artery; l.pre, left precaval vein; l.vn, left ventricle; pc, left pectoral arteries and veins; pc. a, right pectoral ar- tery; PCM, right pectoral vein; p.m. a, posterior mesenteric artery; pic, postcaval vein; ra.i, ra.2, ra.3, renal arteries; r.au, right auricle ; r.p.v, renal portal vein ; r.p.a, right pulmonary artery; r.pr.v, right pre- caval. vein; r.v, renal vein; t.vn, right ven- tricle ; sc.a, sciatic ar- tery ; sc.v, sciatic vein ; scl.a, subclavian artery; vr, vertebral artery and vein. (From Parker and Haswell, after Parker.) CLASS AVES 585 (a.tfo), which gives off the Innominate arteries (in.a) and then continues as the dorsal aorta (d.ao). Contrasting the circulatory system of the pigeon with that of the turtle, it should be noted that the venous blood and arterial 'blood are not allowed to mingle in the heart of the pigeon. The renal portal system of the pigeon has almost completely dis- appeared, the blood being taken from the posterior part of the body directly to the heart, and not through the renal capillaries, as in all knver vertebrates. The jugular veins (Fig. 475, ju) of the pigeon are united just under the head by a cross vein (ju'} ; this enables blood to pass back to the heart from the head when the neck becomes momentarily twisted so that one of the jugular veins is stopped up. The Respiratory System. - - The two lungs in birds are as- sisted by a remarkable system of air-sacs. During inspiration, the relaxation of the thoracic and abdominal muscles allows the elastic expansion of the thorax and abdomen. Air enters the mouth cavity through the nostrils, as in reptiles; it then passes through the glottis into the trachea or windpipe, which divides, sending a branch (bronchus} to each lung. The bronchi communicate with nine large thin-walled air-sacs, which lie principally along the sides and dorsal surface of the body-cavity. During expiration, the muscles of the thorax and abdomen con- tract, forcing the air from the air-sacs, through the lungs and trachea, and out of the nostrils. At each inspiration practically all of the air in the lungs is renewed. The air-sacs enable the bird to breathe easily when in flight, since air is forced into them during the rapid progress through the atmosphere and out of them by the compression of the pectoral muscles, which lower the wings. In man, violent move- ments interfere with the alternate inspiration and expiration of air. The trachea is held open by partially ossified cartilaginous rings. Where the trachea divides into the two bronchi, it en- larges to form the vocal organ, or syrinx, a structure peculiar to 586 COLLEGE ZOOLOGY birds. Extending forward from the angle of bifurcation of the trachea is a flexible valve which is vibrated when air is forcibly expelled from the lungs, thus producing a sound. A number of muscles are able to alter the tension of this valve and conse- quently the number of its vibrations and the pitch of the note produced. The Excretory System. - -The kidneys are a pair of three-lobed bodies situated as shown in Figure 471, U. Each discharges its secretion, the urine, through a duct, the ureter (S), into the cloaca. There is no urinary bladder, but the urine passes directly out of the anus with the faeces. The Reproductive System. - - In the male are a pair of oval testes. From each testis a duct, the vas defer ens, passes back and opens into the cloaca; it dilates at its distal end to form a seminal vesicle. The spermatozoa pass through the vasa def- erentia; are stored in the seminal vesicles; and, when copula- tion takes place, are discharged into the cloaca, and transferred by contact to the cloaca of the female. There is no copulatory organ. The right ovary of the female disappears during development and only the left ovary persists in the adult. The ova break out of the ovary and enter the oviducts. During their, passage through the oviducts the albuminous substance, known as the " white " of the egg, is secreted about them by the walls of the middle portion. The double, parchment-like shell-membrane is then secreted about the egg, and finally the shell is added by the posterior part of the oviduct a short time before deposition. Fertilization takes place about forty-one hours before the eggs are laid. Two eggs are laid by pigeons at a sitting, the first usually between four and six P.M., and the second between one and two P.M., two days later. They are kept at a temper- ature of about 100 F. by the sitting bird for usually fourteen days. At the end of this period of incubation, the young birds have developed to such a stage that they are able to break through the shell, i.e. they hatch. They are at first covered with CLASS AVES 587 fine down, but soon acquire a covering of contour feathers. During their early life as nestlings they are fed upon " pigeon's milk," a secretion from the crop of the adult. The Nervous System. - - The brain of the pigeon (Fig. 476) is very short and broad. The cerebellum (cb) is comparatively large, as are also the optic lobes (o.l), showing that birds have FIG. 476. The brain of the pigeon, side view, cb, cerebellum; c.h, cerebral hemispheres; /, flocculus; m.o, medulla oblongata; o.l, optic lobes; o.t, optic tracts; pn, pineal body; II-XII, cerebral nerves. (From Parker and Haswell.) well-developed powers of coordination and of sight. The ol- factory lobes (olf), on the other hand, are very small, indicating poorly developed olfactory organs. The Sense-organs. - - The bill and tongue serve as tactile organs. Tactile nerves are also present at the base of the feathers, especially those of the wings and tail. Birds are unable to dis- tinguish delicate odors, and on the whole their sense of smell is very poor. The sense of taste is also very poorly developed, but is nevertheless present, as can easily be proved if a bad- tasting morsel of food is presented to a bird. The cochlea of the ear is more complex than that of reptiles. The Eustachian tubes open by a single aperture on the roof of the pharynx. Birds have acute and discriminating powers of hear- ing a power correlated with their singing ability. The eyes of birds are very large, and have a biconvex shape. They are surrounded by bony sclerotic plates, and contain a fan- 588 COLLEGE ZOOLOGY shaped, highly vascular, pigmented structure called the pecten, which is suspended in the vitreous humor. The function of the pecten is uncertain ; it may have some connection with the nutri- tion of the eyeball, or with the process of accommodation. The latter process is remarkably well developed in birds, since their eyes are equally adapted both for far and near vision, and a bird can fly rapidly among the branches of a tree without striking a branch, or can swoop down to the ground from a great height in the air, changing from far-sighted to near-sighted vision in an instant. 2. A BRIEF CLASSIFICATION OF BIRDS The birds form a more homogeneous class of vertebrates than the reptiles and cannot be separated into a few well-defined groups. There are comparatively few fossil birds known to man; in fact, only one subclass, containing a single genus, and four orders, are not represented by living forms. The structural differences that distinguish the orders, families, genera, and species are, for the most part, so slight as to make it impossible to state them in a brief and clear manner. More than twelve thousand species of birds have been de- scribed, and no two authorities agree as to their classification. The following arrangement is adopted from Knowlton's Birds of the World. CLASS AVES. BIRDS. - - Warm-blooded vertebrates with feathers; usually with fore limbs adapted for flight; the adults of existing species without teeth. SUBCLASS I. ARCH^ORNITHES. Ancient, reptile-like, fossil birds. Only three specimens of the single genus Archaopteryx are known. SUBCLASS II. NEORNITHES. - - RECENT BIRDS. - - There are four orders containing only extinct forms, and seventeen orders containing living representatives. Order i. Hesperornithiformes. -- Fossil, toothed-birds from America, with teeth set in a groove. Example: Hesperornis (Fig. 478). CLASS AVES 589 Order 2. Ichthyornithiformes. - - Fossil, toothed-birds from America, with teeth set in separate sockets. Example: Ich- thyornis (Fig. 479). Orders. Struthioniformes. -- OSTRICHES. -- Flightless, ter- restrial birds with naked head, neck, and legs; feet with two toes; without pygostyle; no keel on sternum. Example: Struthio, African Ostrich (Fig. 480). Order 4. Rheiformes. RHEAS. Flightless, terrestrial birds with partially feathered head and neck; feathers without after- shaft; feet with three toes. Example: Rhea, American Ostrich (Fig. 481). Order 5. Casuariiformes. - - CASSOWARIES and EMEUS. - Flightless terrestrial birds with very small wings; feathers with large aftershaft. Examples: Casuarius, Cassowary; Drom&us, Emeu (Fig. 482). Order 6. Crypturiformes. - - TINAMOUS. - - Flying, terrestrial birds, with short tail; no pygostyle. Example: Tinamus (Fig. 483). Order 7. Dinornithiformes. MOAS. Flightless, terrestrial birds, with enormous hind limbs; wing bones absent ; all extinct. Example: Dinornis (Fig. 484). Order 8. -5pyornithiformes. ELEPHANT-BIRDS. Flightless, terrestrial birds, with enormous hind limbs; sternum and wings small ; eggs very large ; all extinct. Example : jEpyornis. Order 9. Apterygiformes. - - KIWIS. - - Flightless terrestrial birds; feathers hair-like and without aftershaft; all small in size. Example: Apteryx (Fig. 485). Order 10. Sphenisciformes. PENGUINS. Flightless marine birds, with small, scale-like feathers ; wings modified as paddles for swimming; one family. Example: Spheniscus (Fig. 486). Order u. Colymbiformes. LOONS and GREBES. Aquatic birds with webbed or lobed toes; feet far back; body carried upright; two suborders and two families. Examples: Gavia, Loon (Fig. 487); Dytes, Grebe, 590 COLLEGE ZOOLOGY Order 1 2 . Procellariif ormes. ALBATROSSES and PETRELS. - Marine birds with webbed toes; powers of flight, great; sheath of bill of several pieces; three families. Examples: Diomedea, Albatross (Fig. 488); Procellaria, Petrel (Fig. 489). Order 13. Ciconiiformes. STORK-LIKE BIRDS. Aquatic or marsh-birds with feet adapted for wading; four suborders, one superfamily, and thirteen families. Examples: PELECANID.E, Pelicans; PHALACROCORACID^E, Cormorants (Fig. 490); AN- HINGID.E, Snake-birds; ARDEID., Herons; IBIDID.E, Ibises; PHCENICOPTERID.E, Flamingos (Fig. 491). Order 14. Anseriformes. -- GOOSE-LIKE BIRDS. --Aquatic birds with beak covered by a soft, sensitive membrane and edged with horny lamellae ; two suborders and two families. Examples : PALAMEDEID.E, Screamers; ANATID^E, Swans, Geese, and Ducks (Fig. 492). Order 15. Falconif ormes. -- FALCON-LIKE BIRDS. Carniv- orous birds with curved beak, hooked at the end; feet adapted for perching and provided with strong, sharp claws; three sub- orders and four families. Examples: CATHARTID.E, American Vultures; GYPOGERANID.E, Secretary-birds; FALCONID.E, Falcons; BUTEONID.E, Eagles, Hawks, Vultures, etc. (Figs. 493-495). Order 16. Galliformes. FOWL-LIKE BIRDS. - -Terrestrial or arboreal birds with feet adapted for perching; four suborders and seven families. Examples: PHASIANID.E, Turkeys, Quails, Pheasant, etc.: OPISTHOCOMID.E, Hoactzin. Order 17. Gruiformes. CRANE-LIKE BIRDS. Mostly marsh birds; seven families. Examples: RALLUXE, Rails; GRUID.E, Cranes. Order 18. Charadriiformes. PLOVER-LIKE BIRDS. Terres- trial, arboreal, or marine birds; four suborders and twelve families. Examples: CHARADRIID.-E, Plovers, Snipes, and Curlews; LARID^, Gulls and Terns (Fig. 497); ALCID.E, Auks (Fig. 498); COLUMBID^:, Pigeons (Fig. 470). Order 19. Cuculiformes. -- CUCKOO-LIKE BIRDS. Arboreal birds with first and fourth toes directed backwards; fourth toe CLASS AVES 591 i may be reversible; two suborders and four families. Examples: CUCULID.E, Cuckoos (Fig. 499); PSITTACID^:, Cockatoos and Parrots. Order 20. Coraciiformes. ROLLER-LIKE BIRDS. Arboreal birds with short legs; seven suborders and eighteen families. Examples: CORACIID^E, Rollers; ALCEDINID^E, Kingfishers (Fig. 500); STRIGID.E, Owls (Fig. 501); CAPRIMULGID^E, goat- suckers; TROCHILID^E, Humming-birds (Fig. 502); MICRO- PODUXE, Swifts; PICID.E, Woodpeckers (Fig. 503). Order 21. Passeriformes. -- SPARROW-LIKE BIRDS. --More than half of all the birds known belong to this order. There are two suborders, four superfamilies, and sixty-four families. The twenty- five North American families are as follows :- FAMILY COMMON NAME 1. TYRANNID^E .... Tyrant Flycatchers (Fig. 504, A) 2. COTTNGID.E .... Cotingas 3. ALAUDID^E Larks 4. MOTACILLID.E . . . Wagtails 5. TURDID.E Thrushes, Bluebirds, etc. 6. MIMID^E Thrashers, Mocking-birds, etc. (Fig, 54, H) 7. CINCLID.E Dippers 8. TROGLODYTTD.E . . Wrens (Fig. 504, G) 9. CHAM^EID^E .... Wren-Tits 10. SYLVIID.E Warblers, Kinglets, and Gnatcatchers 11. HIRUNDINID.*: . . . Swallows (Fig. 504, E) 12. BOMBYCILLID/E . . Waxwings (Fig. 504, F) 13. PTILOGONATID^: . . Silky Flycatchers 14. LANIID.E Shrikes 15. VIREONID.E .... Vireos 1 6. SITTHXE Nuthatches 17. PARID.E Titmice 18. CORVID.E Crows, Jays, etc. (Fig. 504, B) 19. STURNID^E Starlings 592 COLLEGE ZOOLOGY FIG. 477. Archaopteryx llthographlca. c, carpal; c, furcula; co, coracoid; A, humerus; r, radius; 5c, scapula; u, ulna; I-IV, digits. (From Zittel, aftef ^teinmann and Doderlein.) CLASS AVES 593 FAMILY 20. CERTHIID.E . 21. CCEREBID/E . 22. MNIOTILTID^: 23. TANAGRID.E . 2\, ICTERID.E . . 25. FRINGILLID.E COMMON NAME Creepers Honey Creepers Wood Warblers Tanagers Blackbirds, Orioles, etc. (Fig. 504, C) Finches, Sparrows, etc. (Fig. 504, D) 3. A REVIEW or THE ORDERS AND FAMILIES OF BIRDS It is, of course, impossible in the limited space that can be devoted to birds in this book to give anything more than a brief survey of the subject. Most of the families that are considered are represented by living species inhabiting the United States. SUBCLASS I. ARCH.EORNITHES. - The single genus, Archa- oplery.v (Fig. 477), belonging to this subclass is known from a feather and two fairly complete skeletons that were found in the litho- graphic slates of Solenhofen, Bavaria, of the Upper Juras- sic period. Archce- opteryx was about the size of a crow. It possessed teeth embedded in sockets, fore limbs with three clawed digits (Fig. 477, I, II, III) and separate metacarpal bones, and a lizard- like tail with large feathers (rectrices) on either side. The 2Q FIG. 478. IJ-sperornls regalis. (From Zittel, after Marsh.) 594 COLLEGE ZOOLOGY bird-like characteristics predominate over the reptilian features so that this curious creature is placed in the class AVES, although it is a connecting link between the birds and the reptiles. SUBCLASS II. NEORNITHES. - - RECENT BIRDS. Order i . Hesperornithif ormes. - - There are three species of fossil birds in this order. Hesperornis regalis (Fig. 478), the best- known species, was nearly four feet in length. It possessed teeth set in a groove, strong hind limbs with webbed feet, which were used like oars, and a sternum without a keel. The entire anatomy indi- cates that Hesperor- nis was a flightless, swimming and diving bird which lived upon fishes and other aquatic animals. The remains of this and the two other species probably be- longing to this order were found in the Cretaceous deposits of Kansas. Order 2. Ichthyornithif ormes. -- Of the dozen or more species of fossil birds included in this order, Ichthyornis victor (Fig. 479) from the Cretaceous deposits of Kansas, is the best known. This bird had teeth set in sockets, a keeled sternum, and well-developed wings. It was about the size of a pigeon, was a strong flier, and probably fed upon fish. FIG. 479. Ichthyornis victor. after Marsh.) (From Zittel, CLASS AVES 595 , Order 3. Struthioniformes. OSTRICHES. - -The ostriches are the largest living birds, attaining a height of more than eight feet, and a weight of over three hundred pounds. Four species are recognized by some authorities. The ostriches or camel birds of North Africa, Struthio camelus (Fig. 480), live in desert regions and travel about in groups, usually of from four to twenty. They are very suspicious and flee from any signs of danger. They do not stick their heads in the sand and think themselves hidden, as commonly reported. Their speed is remarkable, reach- ing sixty miles an hour, and their single strides may measure more than twenty- five feet. They are omnivorous, feeding upon many kinds of plants and animals. The nest is a hollow in the sand, and several females lay their eggs in a single nest. Each egg weighs from three to four pounds. The males do most of the incubating. The young, which appear in six or seven weeks, run about as soon as they emerge from the shell. Ostrich feathers are now procured almost entirely from domesticated birds. In 1904 there were in South Africa over three hundred and fifty thousand tame ostriches which yielded an annual income of about $18 each. Ostrich farming is now successfully carried on in California, Arizona, Arkansas, North Caro- lina, and Florida. The feathers are clipped without pain to the birds; those from a single adult weigh about one pound. FIG. 480. Ostrich, Struthio camelus. (From Evans.) 596 COLLEGE ZOOLOGY FIG. 481. Rhea, Rhea americana. Evans.) (From Order 4. Rhei- formes. - - RHEAS. - These are the New- world ostriches (Fig. 481). There are three species inhabiting the pampas of South America; They are smaller than the true ostriches, but their habits are quite similar. Order 5. Casuari- iformes. CASSO- WARIES and EMEUS. - The two families in this order contain .ostrich-like birds; the DROM^ID^; or emeus (Fig. 482), which are, next to the ostriches, the largest of living birds, are confined to Australia ; the CASUARIID.E or cassowaries inhabit New Guinea and neighboring islands. The cas- sowaries usually possess a bony, helmet-like knot on the head, and have brightly colored lobes on the head and neck; these are absent in emeus. Order 6. Crypturiformes. TIN- AMOUS. --About forty species of tinamous are known. They re- semble game-birds in appearance and are called partridges by the natives of southern Mexico and Central and South America, where they live. The powers of flight of FIG. 482. Emeu, Dromaus nova- the tinamous are not well devel- hoiiandice. (From Evans.) CLASS AVES 597 oped. In size they range from a length of six inches to that of the rufous or great tinamou, Rhynclwlus rufescens (Fig. 483), of Brazil, which is fourteen inches long. Tinamous are solitary birds, but may band together into coveys. They make a nest by scratching a hollow in the earth and lining it with grasses, leaves, and feathers. The eggs number from five to a dozen or more to a setting; they are incubated by the male. FIG. 483. Great tinamou, Rhyn- chotus rufescens. (From Evans.) FIG. 484. Moa, Palapteryx elephan- topus. (From Zittel, after Owen.) Order 7. Dinornithiformes. MOAS (Fig. 484). --The moas have probably become extinct within the past five hundred years. The remains of these peculiar birds have been found in great numbers in caves and refuse heaps in New Zealand, to which country they appear to have been confined. Twenty or thirty species are known from these remains. They ranged in size from COLLEGE ZOOLOGY that of a turkey to nearly ten feet high. They were flightless, but possessed enormous hind limbs. Order 8. ^Epyornithiformes. - - ELEPHANT-BIRDS. - - These birds have probably become extinct within the past five centuries. They inhabited Madagascar, were flightless, and possessed hind limbs more enormous even than those of the moas. Many of their eggs have been found in the sand near the sea-shore ; they are more than thirteen inches in length and nine inches wide, and have a capacity of over two gallons. Order 9. Apterygiformes. - - KIWIS. - - These wingless birds of New Zealand belong to the single genus Apteryx (Fig. 485) and to five or six species. They are about the size of a common fowl; their wings are aborted, and they lack tail- feathers. In habit, they are nocturnal, feeding upon worms, which they probe FIG. 485. Kiwi, Apteryx aitslralis. (From ^QJ. w j-(-^ their loll ' Evans.) beaks, and also upon vegetable matter. The nest is made in a hole in the ground, and one or two large eggs are laid. Order 10. Sphenisciformes. PENGUINS. The penguins, of which about twenty living species are known, are confined to the rocky and barren islands of the Antarctic region. They are adapted for life in the water; the fore limbs are modified as paddles for swimming; the feet are webbed; the cold water can be shaken entirely from the feathers; and a layer of fat just beneath the skin serves to keep in the bodily heat. They feed on fishes and other marine animals. On shore they stand erect (Fig. 486), side by side. They nest in colonies, laying the one or two eggs either among the rocks or in a burrow. CLASS AVES 599 FIG. 486. Penguins or rock-hoppers, Eudyptes chrysocome. (From Evans, after Thomson.) Order u. Colymbiformes. -- LOONS and GREBES. FAMILY GAVIID^E. -- LOONS or DIVERS (Fig. 487).- -The one genus, Gavia, and five species of loons inhabit the northern half FIG. 487. Loon. (From Evans.) of the northern hemisphere. They are large birds with strong powers of flight, and with an ability to swim and dive that is not surpassed by any other species. Loons are awkward on land. 6oo COLLEGE ZOOLOGY The two eggs are laid in a slight depression in the ground, near water. FAMILY PODICIPEDID.^E. --GREBES. 'The grebes are smaller than the loons, but are excellent swimmers and divers. There are about twenty- five species in the family, distributed through- out the world, chiefly about fresh waters. The six to eight eggs are laid in a nest consisting usually of a mass of floating rushes. Order 12. Procellariiformes. ALBATROSSES and PETRELS. These are marine birds with tubular external nostrils, fully webbed toes, and long, narrow wings. They are strong fliers, gregarious, and come to land rarely except to lay their eggs. There are about fifteen species of albatrosses; six of these have been reported from North America. The wandering al- batross, Diomedea exulans (Fig. 488), is over three and a half feet in length, and has a spread of wing of over ten feet. The petrels, fulmars, and shearwaters, of which there are about seventy species, belong to the family PRO CELL ARIID^E. The fulmars are large gull-like birds. The common fulmar, Fulmarus glacialis, is abundant in the North Atlantic. It lays its single, white egg on crags over the sea. The shearwaters are very restless birds that inhabit all oceans. The common Atlantic shearwater is Puffinus major. The stormy petrels are small birds under ten inches in length. The common stormy petrel, . - FIG. 488. Wandering albatross, Diomedea exulans. (From Evans.) CLASS WES 601 Procclhiyia pclagica (Fig. 489), is known from the Atlantic and Mediterranean coasts of Europe, Africa, and North America. FIG. 489. Stormy Petrel, Procellaria pelagica. (From Evans.) Order 13. Ciconiiformes. STORK-LIKE BIRDS. --This order includes the tropic birds, cormorants, anhingas, pelicans, gan- nets, man-o'-war birds, herons, bitterns, boatbills, shoebills, hammerheads, storks, ibises, spoonbills, and flamingos. Most of these birds have long legs, long, slender necks, elongated bills, and feet fitted for wading or swim- ming. The pelicans (Family PELE- CANID^E) possess r a huge membran- ous pouch between the branches of the lower jaw, with which they scoop up small fish (Fig. 507, g). The cormorants (Family PHALACROCORACID^E) comprise the FIG. 490. Cormorant, Phalacrocorax carbo: ( From Evans.) 602 COLLEGE ZOOLOGY majority of the species in the order. They are almost cosmo- politan and very sociable. In China and a few other countries these birds are trained to catch fish and are of considerable value to their owners. The common cormorant, or shag, Phalacrocorax carbo (Fig. 490), occurs on the Atlantic coast of Europe and North America and breeds on the rocky shores of Labrador and Newfoundland. The herons and bitterns (Family ARDEID.E) possess long legs fitted for wading, broad wings, and short tails. They are found in the warmer regions of the globe and feed chiefly on fishes. The great blue heron, Ardea herodias, is a large species occurring in all parts of North America. It is about four feet long and has an extent of wings of about six feet. Its large flat nest is built of coarse sticks usually in the top of a high tree; four to six greenish blue eggs are laid. The seven species of fla- mingos (Family PHCENICOPTE- Fig. 491) .inhabit the tropics ; one of them occurs in Florida. They are gregarious birds, congregating in thousands on mud flats where they build their conical mud nests. They are rosy vermilion in general color. Order 14. Anseriformes. GOOSE-LIKE BIRDS. - -These birds are either adapted for swimming, with short legs and fully webbed front toes, or for wading, with large feet and a short decurved bill. Their young are entirely covered with down and can swim or run about soon after hatching, i.e. are precocious. . <;\-i. FIG. 491. Flamingo, Phcenicopterus roseus. (From Evans.) CLASS AYKS 603 The screamers (Family PALAMEDEID^E) are all natives of South America. The family ANATID^E contains about two hundred and ten species of duck-like birds which are aquatic or semi- aquatic in habits, and cosmopolitan in distribution. There are five North American subfamilies of the ANATID^E: (i) the swans, CYGNIN.E; (2) the geese, ANSERINE; (3) the river- ducks, ANATIISLE; (4) the sea-ducks, FULIGULIN.^; and (5) the mergansers, MERGING. The most beautiful of all our ducks is the wood duck, .l/.v sponsa (Fig. 492). This bird ranges over the entire United States. Its favor- ite haunts are the smaller streams, lakes, and ponds. The eggs, from six to fifteen in number, are laid in cavities in the trunks or limbs of trees. The wood- duck is one of our game-birds that is decreasing so rapidly in num- bers that it seems FlG . 4Q2 . _ Wood-duck, Aix sponsa. on the verge of extinction, and drastic action must be taken by the federal and state governments if this species is not to vanish entirely. Order 15. Falconiformes. -- FALCON-LIKE BIRDS. -- These diurnal bird^ of prey possess, in most cases, powerful wings, a stout, hooked bill with a cere at the base, and strong toes armed with sharp claws. The order is divided into the CATHARTID^, or American vultures, the GYPOGERANID^E, or secretary-birds, the FALCONID/E, or falcons, and the BUTEONID^:, or eagles, hawks, kites, etc. 604 COLLEGE ZOOLOGY The nine or ten species of American vultures are weaker than the other FALCONIFORMES. They live on carrion and are valu- able in warm countries as scavengers. The species occurring in the United States are the turkey-vulture or turkey-buzzard, Cathartes aura, the black vulture or carrion crow, Catharista urubu, and the California vulture, Gymnogyps calif ornianus. The California vulture and the condor, Sar- c o r h a m p k u s gryphii s (Fig. 493), which lives in the Andes Moun- tains, are two of the largest of flying birds. The secretary-bird, Gypogeranus secre- tarius, of South Africa, is the only represent- ative of the family GYPOGERANID^E. Its common name was suggested by the re- semblance of some plumes on its head to a bunch of quills stuck Secretary-birds feed on frogs, toads. FlG. 493. Condor, Sarcorhamphus gryphus (From Evans.) behind the ear of a clerk, insects, and snakes. The FALCONID^: are the falcons, tropical goshawks, and caracaras. About seventeen species of the genus Falco are found in North America. The white gyrfalcon, F. islandus, inhabits the Arctic regions; the prairie-falcon, F. mexicanus, occurs in the western United States; the duck-hawk, F. per- egrinus ana-turn-, ranges over both North and South America; the pigeon-hawk, F. columbarius columbarius, is a North Ameri- can species; and the sparrow-hawk, F. sparverius sparverius in- habits North America east of the Rocky Mountains. All of CLASS AVES 605 m^w^-^ \\V>W 'V \ ' Afl il tt^^SllgfS ^^w^mM'- fV'%v/,V r //'V' ; mmtffy " WMnriM -^S^ 6: Y". FIG. 494. Swainson's hawk, Buteo swainsoni. (From Fisher, Yearbook U. S. Dep't Agric., 1894.) these birds are of medium size and active. The wings are long and pointed, and the bill has a pronounced notch and tooth. The two species of cara- caras that reach the United States are known as carrion- buzzards. Audubon's cara- cara, Pol\borus cheriway, is found in Florida. It lives largely on carrion, but also captures frogs, lizards, and snakes. The BUTEONID.-E are the kites, buzzards, eagles, hawks, ospreys, Old-world vultures, and harriers. Common North American representatives of these groups are the swallow- tailed kite, Elanoidcs for- ficatus, which occurs in the warm temperate regions ; the osprey, or fish-hawk, Pandion haliaetus caro- lineiisis, inhabiting temper- ate and tropical America; the bald eagle, Haliaetus leucocephalus, generally dis- tributed in North America; the red-shouldered hawk, Buteo lineatns ; Swainson's hawk, Bnteo swainsoni (Fig. 494) ; the marsh- hawk, or harrier, Circus FIG .495-- Cooper's hawk Accipiter i nilhonius ; the red-tailed coopen. (I-rom tishcr, Yearbook I 1 . S. Dep't Agric., 1894.) hawk, or buzzard, Buteo 6o6 COLLEGE ZOOLOGY borealis ; the Cooper's hawk, Accipiter cooperi (Fig. 495); and the goshawk, Astur atricapillus. Order 16. Galliformes. -- FOWL-LIKE BIRDS. --This is a widely distributed group containing seven families, only two of which have North American representatives: (i) the CRA- CID.E or curassows and guans, with one species in Texas ; and (2) the PHASIANID.E, or turkeys, partridges, etc. The PHASIANID^E are the true game-birds, and are known as bob-whites, quail, grouse, partridges, ptarmigan, chickens, hens, and turkeys. Among the best-known species inhabiting the United States are the wild turkey, Mdeagris gallopavo sihestris, which is the largest American game-bird and a native species, but now nearly extinct; the bob- white, or quail, Colinus virginianus; the ruffed grouse, Bonasa umbellus ; the willow ptarmigan, Lagopus lagopus, of the Arctic regions; and the prairie-chicken, Tympanuchus americanus. The game-birds are, as a rule, terrestrial, but many of them roost or feed in trees. Their nests are usually made on the ground in grass or leaves, and generally a large number of eggs, from six to eighteen, are laid. The members of one family often remain together as a " covey," and in some species the coveys unite to form large flocks. Order 17. Gruiformes. -- CRANE-LIKE BIRDS. --The seven families belonging to this order contain mostly wading birds with incompletely webbed front toes. The families RALLID.E and GRUID.E are represented by North American species. The RALLID^E are the rails, gallinules, and coots. The rails are seldom seen, spending most of their time among the reeds and rushes in marshes. The king-rail, Rallus elegans, of eastern North America is a large species, being about eighteen inches in length. The gallinules also inhabit marshes. The Florida gallinule, Gallinula galeata, is a common form. The coots are frequently called mud-hens, and sometimes hell-divers, because of their ability to dive quickly. There is only one common species, Fulica americana. CLASS AYES 607 The GRUID.E are the cranes, courlans, and trumpeters. The cranes are large birds with long legs and neck. They live in grassy plains and marshes. The whooping-crane, Grus amcri- cana, measures about four and a half feet in length, and has a spread of wings of about eight feet. It breeds in central North America, making a nest of grasses and weed stalks on marshy ground. Order 18. Charadriiformes. --PLOVER-LIKE BIRDS. -- Five of the twelve families in this order have North' American repre- FIG. 4g6. Spotted Sandpiper, Aflitis macularia. (From Davenport, after Fuertes.) sentatives : (i) the CHARADRIID.^, plovers, snipes, and curlews; (2) the JACANIDE, jacanas; (3) the LARID.E, gulls, terns, and skimmers; (4) the ALCID.E, auks; and (5) the COLUMBID.T., pigeons. The CIIARADRIID^; are the turnstones, oyster-catchers, lap- wings, true plovers, dotterels, avocets, stilts, phalaropes, sand- pipers, curlews, whimbrels, woodcock, snipe, and dowitchers. 6o8 COLLEGE ZOOLOGY The spotted sandpiper, Actitis macularia (Fig. 496), which may be taken as an example of this enormous family, occurs through- out temperate North America. It lives in the vicinity of water, and feeds upon insects, earthworms, and other small animals. The four eggs are laid in a hollow in the ground, and the young are able to run about as soon as hatched. The JACANID^E are tropical marsh-birds, with very long toes and claws enabling them to walk over lily pads without sinking. The Mexican jacana, Jacana spinosa, reaches Texas. FIG. 497. Common tern, Slcnni Itinindo. (From Davenport, after Fuertes.) The LARID.E are known as gulls, terns, skimmers, kittiwakes, noddies, skuas, and jaegers. The American herring-gulls, Larus argentatus, are about two feet long. They breed along the Atlantic coast and also in the interior from Minnesota north- wards. Their nests are built on the ground of grasses, seaweed, etc., and two or three eggs are laid. The terns, or sea-swallows (Fig. 497), are as a rule smaller and slimmer than the gulls. They frequent the shores of both fresh and salt water, feed upon fish, CLASS AVES 609 and nest in colonies. The black skimmer, Kvnr/wps nigni, is found along our Atlantic coast. It flies along the surface of the water with its lower mandible immersed, and literally skims small aquatic animals from the top. The ALCID^E are the puffins, auklets, murrelets, murres, guillemots, and true auks. They spend a large part of their existence at sea. Most of them are strong fliers, and excellent swimmers and divers, but very awkward on land. They feed on fish, crustaceans, and other small marine animals, and nest in colonies, usually on rocky shores. The puffins, or sea-parrots, are grotesque-looking birds with enormous beaks that are grooved and brightly colored. The murres possess bills which are narrow and without grooves. The true auks are North American birds represented by three species. The great auk, or garefowl, Plautus im- pennis (Fig. 498), became ex- tinct in 1844, when the last one appears to have been FlG - 498. ~Grea.ta.uk, Plautusimpenfiis. , .,, , (From Evans, after Hancock.) killed. 1 hey were destroyed for their feathers, and their eggs were used as food. " All that remains to-day of the Great Auk are about seventy skins, sixty- five eggs, and some twenty- five more or less perfect but com- posite skeletons, that is, skeletons made up from the bones of many different individuals." (Knowlton.) The COLUMBID^E are the pigeons or doves (Fig. 470) of which twelve of the three hundred known species occur in North America. The passenger-pigeon, Ectopistes migratorius, is an- other bird that is practically extinct, although flocks were seen a century ago that contained over two billion birds. The mourn- ing-dove, Zenaidura macroura, is common and often mistaken 2 R 6io COLLEGE ZOOLOGY for the passenger-pigeon. It makes a flimsy nest of a few twigs, and lays two white eggs. The young are naked when born, and are fed by regurgitation. Order 19. Cuculiformes. CUCKOO-LIKE BIRDS. --This order contains the cuckoos, plantain-eaters, lories, nestors, cockatoos, and parrots. The cuckoos (Family CUCULID^:) are mostly tropical birds. The majority of them do not build a nest, but lay their eggs in the nests of other birds. This is not true, however, of the North American species. The black-billed and yellow- billed cuckoos (Fig. 499) of this country are long, slender birds of solitary habits and with the peculiar vocal powers which have given them their common name. The American species of parrots, about one hundred and fifty in number, are included in the family PSITTACID.E. Only one species, the FIG. 499- Yellow-billed cuckoo, Coccyzus Carolina paroquet. Conu- americanus. (From Judd, Bui. 17, Bur. Biol. Survey, u. S, Dep't Agric.) ropsis carolmensis, occurs in the United States. Parrots and paroquets live in forests and feed on fruits and seeds. They have shrill voices, but can, with few exceptions, be taught to talk. The African parrot, Psittacus erythacus, learns to talk most readily. Order 20. Coraciiformes. ROLLER-LIKE BIRDS. The birds placed in this order may be grouped into seven suborders, and about eighteen families. They include the rollers, motmots, kingfishes, bee-eaters, hornbills, hoopoes, oil-birds, frogmouths, goatsuckers, humming-birds, swifts, colies, trogons, puff-birds, jacamars, barbets, honey-guides, toucans, woodpeckers, wry- necks, and owls. There are about two hundred species and subspecies of king- CLASS AYES 611 fishers (ALCEDINID^E), three of which occur in North America. The belted kingfisher, Ceryle alcyon (Fig. 500), breeds from Florida to Labrador. Its five to eight white eggs are laid at the end of a horizontal hole about six feet deep dug by the birds usually in the bank of a stream. The kingfisher captures small FIG. 500. Belted kingfisher, Ceryle alcyon. (From Davenport, after Fuertes.) fish by hovering over a stream and then plunging into the water and securing the unsuspecting prey in its bill. The owls (STRIGID^:) are the nocturnal birds of prey. They possess large, rounded heads, strong legs, feet armed with sharp claws, strong bills with the upper mandible curved downward, large eyes directed forward and surrounded by a radiating disc of feathers, and soft, fluffy plumage which renders them noiseless 6l2 COLLEGE ZOOLOGY during flight. Owls feed upon insects, mice, rats, and other small mammals, birds, and fish. The indigestible parts of the food are cast out of the mouth in the form of pellets. Most species are beneficial to man. The great horned owl, Bubo mrginianus (Fig. 501), is one of the large North American species. It nests in old squirrels' and hawks' nests, in hollow trees, or in crevices in rocky cliffs. Two or three large white eggs are laid. Its food con- sists principally of birds and mammals, especially rabbits, and its harmful and beneficial qualities are about equal. The goatsuckers (CAPRI- MULGID.E) are represented in North America by thir- teen species, of which the whippoorwill and night- hawk are the best known. The whippoorwill, A ntrosto- mus vociferus, inhabits the woods and thickets of east- ern North America. It is most active after sun- down and early in the morning, when it captures its insect food while on the wing. The two eggs are laid on the leaves in the woods. The night-hawk, Chordeiles mrginia- nus, has a range similar to that of the whippoorwill. During the day it perches on a limb, fence post, or on the ground, but in the evening it mounts into the air after its insect prey. The two eggs are laid on the bare ground, usually on a hillside or in an open field; often they are deposited on the gravel roofs of city buildings. The humming-birds (TROCHILID^E), which are confined to the FIG. 501. -Great-horned owl, Bubo r- gmianus. (trom lusher, \earbook U. b. Dep't Agric., 1894.) CLASS AVES 613 New World, have been appropriately called feathered gem?, or, according to Audulxm, "glittering fragments of the rainbow." Only seventeen of the five hundred or more species occur in the United States, and only one, the ruby-throated humming-bird, Trochilus colubris (Fig. 502), is found east of the Mississippi River. This beautiful little bird is only three and three-quarters inches in length. It hovers before flowers, from which it obtains nectar, small insects, and spiders. The nest, which is saddled on the limb of a tree, is made of plant down and so covered with lichens as to resemble its surroundings very closely. Two tiny white eggs are laid. The young are fed by regurgitation. The swifts (MiCRO- PODID.E) resemble the swallows superficially, but their anatomy shows that there is no real resem- blance between the two groups. Of the one hun- dred species and sub- species of swifts, four are inhabitants of North America, and one, the chimney-swift (Chatura pelagica), breeds commonly in eastern North America. This species formerly made its nest in hollow trees, but now usually frequents chimneys. \Yhen in the open air it is always on the wing, catching insects or gathering twigs from the dead branches of trees for its nest. The twigs are glued together with saliva and firmly fastened to the inside of the- chimney, forming a cup-shaped nest. Certain species of swifts inhabiting -China make nests entirely of a secretion from the FIG. 502. Ruby-throated humming-bird, Trochilus colubris. (From Davenport, after Fuertes.) 6 14 COLLEGE ZOOLOGY salivary glands, producing the edible birds'-nests of the Chinese. The woodpeckers (PicnxE), comprising about three hundred and fifty species, are found in wooded regions almost everywhere except in the Australian region and Madagascar. About fifty species occur in North America. The downy, hairy, and red- headed woodpeckers, the nicker, and the yellow-bellied sap- sucker are the best known. Woodpeckers use their chisel-shaped bills for excavating holes in trees, at the bottom of which their eggs are laid, or for digging out grubs from beneath the bark. Most of them are of great benefit because of the insects they destroy, but the yellow-bellied sap- sucker (Fig. 503) is harm- ful, since it eats the cam- bium of trees and sucks sap. Order 21. Passeri- f ormes. - - SPARROW-LIKE Yellow-bellied sapsucker, Sj>*y- rapicus vanus. (From Judd, Bui. 17, Bur. Biol. Survey, U. S. Dep't Agric.) FIG. 503. g ^ 504). --It is necessary, because 01 lack of space, to refer the student to books on birds for a detailed account of the birds included in this order. On page 591 will be found a list of the principal families. Almost half, about seven thousand species and subspecies, of all the birds known belong to this order. They are grouped into sixty-four families ; rep- resentatives belonging to twenty- five of these occur in North America. Passerine birds are usually small or of medium size, but are the most highly organized of the class AVES. Their feet are CLASS AVES FIG. 504. Types of common passerine birds. (From Judd. Bui. 17, Bur Biol. Survey, U. S. Dep't Agric.) A, kingbird, Tyrannus tyraniins (TvR.\x- NID.E). B, blue jay, Cyanocitta cristuta (CORVID.E). C, bobolink, Dolichonyx oryzi-corus (!CTERID.E). D, song-sparrow. Mclospiza mclodia (FRI.VGILLID.E). E, barn-swallow, Hirundo crythrogastra (HiRrxnixiD.*:). F, cedar waxwing, Bombydlla cedrorum (Bombycillidae). G, house wren, Troglodytes a'edon (TROGLODYTID.E). H, mocking-bird. Minuis polyglottus 616 COLLEGE ZOOLOGY four-toed and adapted for grasping. The first toe, or hallux, is directed backward, and is on a level with the other three, which are directed forward. Two superfamilies of the PASSERIFORMES have North Amer- ican representatives, the CLAMATORES and the OSCINES. The CLAMATORES are non-melodious birds, with a syrinx which is in- effective as a musical apparatus. Only two families occur in this country: (i) the COTINGID^: or chatterers, with one species recorded from Arizona; and (2) the TYRANNID.E, or tyrant fly- catchers, with a large number of common species, such as the kingbird, phoebe, and wood-pewee. The OSCINES are the singing birds. Twenty- five of the forty- nine families are known from North America. Many of the " singing-birds " are almost voiceless, but their structure neces- sitates their inclusion in the superfamily. 4. A GENERAL ACCOUNT or THE CLASS AVES a. Form and Function The bodies of birds have become adapted to various environ- ments. This adaptation is best shown by the wings, tails, feet, and bills. Wings. The wings of most birds are used as organs of flight, and the more time spent in the air, the longer and stronger they become. Birds like the swallows, gulls, and albatrosses have long, pointed wings characteristic of aerial birds; whereas ter- restrial birds, such as the bob- white and song-sparrow, possess short, rounded wings which enable them to fly rapidly for short distances. Many species of birds that spend their lives mostly in the water possess wings, but are unable to fly. For example, the wings of the penguins (Fig. 486) are like flippers and covered with scale-like feathers; they are moved alternately and are the sole organs of locomotion in swimming under water, the legs being used simply as a rudder. Other sea-birds, like the auks CLASS AXES 6l 7 and murres (ALCID.E), use their wings effectively in diving be- neath the waves. Among the flightless birds belong a number of terrestrial species, like the ostrich (Fig. 480), rhea (Fig. 481), emeu (Fig. 482), and kiwi (Fig. 485). These birds all possess the remnants of wings, but these are, for the most part, of no use in locomotion, and in some (Fig. 485) are practically concealed beneath the FIG. 505. A, lyre-bird, Menura superba. (From Evans.) B, bird of paradise, Paradisea rubra. (From Brehm.) feathers. Their legs are, on the other hand, very well developed, and quickly carry them out of danger. The primitive use of wings was for climbing. Archaopteryx (Fig. 477) was provided with three strong claws on its fore limbs. Of living birds the young of the hoactzin, a peculiar bird inhabit- ing South America, should be mentioned, since it is able to climb about before it can fly, by the aid of two claws on each fore limb. Wings may also serve as organs of offense and defense, or as musical instruments; for example, the " drumming " of the ruffed grouse. Tails. - - During flight the tail acts as an aerial rudder, and a, long-tailed bird is able to fly in short curves, or follow .in 618 COLLEGE ZOOLOGY erratic course without difficulty. The tail is light, and therefore easy to manage, and the tail-feathers (rectrices, Fig. 471, RX) are firmly supported by the terminal bone of fused vertebrae, the pygostyle (Fig. 471, Q). Movement of the tail is allowed by the freely movable vertebras just preceding the pygostyle. While perching the tail acts as a " balancer." Birds that cling to the sides of trees, like the woodpeckers (Fig. 503), or to the sides of other objects, like the chimney-swift, brace themselves by means of their tails. In many birds the tail of the male differs from that of the female, being more beautiful in the former, and serving as a sexual character. Two of the most famous of these dimorphic species are the lyre-bird (Fig. 505, A) and the birds of paradise (Fig. 505, B). Feet. - - The feet (Fig. 506) are used for locomotion, for ob- taining food, for building nests, and for offensive and defensive purposes. Ground-birds usually have strong feet, fitted for running (Fig. 506, A), or scratching (c); perching birds (see p. 6 1 6) possess feet adapted for grasping a perch (d) ; aerial birds use their feet very little, and these organs are consequently weak (a, e) ; swimming birds (/', /, n) and wading birds (g, k, m) are provided with toes that are more or less completely lobed ; birds of prey possess strong feet with sharp claws (/) for capturing other animals; woodpeckers have feet (b) adapted for clinging to the bark of trees. Bills. - - The bills of birds (Fig. 507) serve as hands, and their most important function is to procure food. Since bills are also used to construct nests, to preen feathers, and to perform other duties, their adaptations are such as to make them serve several purposes. In preening the feathers a drop of oil is pressed from the oil-gland at the base of the tail and spread by means of the bill. Seed-eating birds possess short, strong bills for crushing seeds (Fig. 507, c); birds that eat insects have longer and weaker bills (d, q); birds of prey are provided with strong, curved beaks CLASS AVES 619 fitted for tearing flesh (e); the pelicans (g) and skimmers (/') scoop up fishes and other animals from the water; and the avocet (Ji) uses its long, curved bill like a scythe, swinging it from side y w* !J m FIG. 506. The most important forms of birds' feet, a, clinging foot of a swift, Cypsclus ; b, climbing foot of woodpecker, Picus ; c, scratching foot of pheasant, Phasianus ; d, perching foot of ouzel, Turdus ; e, foot of king- fisher, Alcedo; f, seizing foot of falcon, Falco; .?, wading foot of stork, Myc- teria; h, running foot of ostrich, Struthio; i, swimming foot of duck, Mergus; k, wading foot of avocet, Reeurciroxtrii; 1. diving foot of grebe, Podicepcs; m, wading foot of coot, Fulica; n. swimming foot of tropic-bird, Phaeton (From Sedgwick's Zoology: b, c, d, f, n, from rrmir animal.) 62O COLLEGE ZOOLOGY to side near the bottom in shallow water and securing food it cannot see; the bill of the woodpecker serves as a chisel; and FIG. 507. The most important forms of birds' beaks, a, flamingo, Phae- nicopterus; b, spoonbill, Platalea; c, yellow bunting, Emberiza; d, thrush, Turd us; e, falcon, Falco; f, duck, Mergus; g, pelican, Pelican us; li, avocet, Recurvirostra; i, black skimmer, Rhynchops; k, pigeon, Columba; I, shoebill, Balceniceps; m, stork, Anastomus; n, aracari, Ptcroglossus; o, stork, Mycteria; p, bird of paradise, Faleinellus; q, swift, Cypselus. (From Sedgwick's Zoology: a, b, c, d, k, after Naumann; g, i, m, o, after regne animal; 1, after Brehm.) that of the woodcock as a probe for capturing small animals in the muddy shores of ponds and streams. Many other ex- amples might be cited. CLASS AVES 621 b. The Colors of Birds Birds are among the most beautifully colored of all animals. This color is due to pigments within the feathers (chemical colors) or to structural peculiarities, such as prismatic shapes which break up the rays of light into their component colors (physical colors), or to both causes. Nestling birds possess dis- tinctively colored feathers which later give way to the " imma- ture plumage "; this is worn usually throughout the first winter, and is generally dull in color, often resembling the plumage of the adult female. Males and females frequently differ in color (sexual dimorphism) , especially during the breeding season, when the male acquires a brightly colored coat. The attempt to ex- plain this difference has led to the theory of sexual selection. 1 One important use of color is its protective value to the bird. The colors and color patterns of birds, as well as other animals, are such as to conceal these animals amid their surroundings. 2 c. Bird Songs The songs of birds, as explained on page 585, are produced by the air passing through the syrinx. For one who wishes to study birds, a knowledge of bird songs is indispensable, since one hears a great many more birds than he is able to see. Songs should be distinguished from call-notes. The former are usually heard during the breeding season, and are generally limited to the males. Call-notes, on the other hand, are uttered throughout the year, and correspond in their meaning and effect to our con- versation. By means of call-notes a bird is able to express anxi- ety or fear, and to communicate to a limited extent with other birds. d. Bird Flight One of the most important functions of birds is that of flight. The bodies of flying birds are structurally adapted so as to offer 1 Darwin, The Descent of Man and Selection in Relation to Sex. 2 Thayi-r. CoiKfaliiiK Coloration in tin- Animal Kingdom. 622 COLLEGE ZOOLOGY little resistance to the air; the wings are placed high up on the trunk to prevent the body from turning over; and the bones are hollow and the body contains air-sacs, which decrease the specific gravity. In flying, the tip of the wing describes a figure 8 as it is brought downward and forward and then backward and upward (Fig 508). The wing works on the principle of the inclined plane, and both the down and up strokes propel the bird forward. The body is sustained in the air by the downward strokes, which force it upward. A great many birds are able to glide, and a number are fond of sailing or soaring. Birds are able to glide or skim by spread- ing their wings and then moving forward by means of their ac- FIG. 508. Gull flying. (From Headley, after Marey.) quired velocity. In soaring, birds do not depend upon acquired velocity, but apparently rely upon favorable air currents. The rate of speed at which birds fly varies considerably. The carrier-pigeon in this country maintains an average racing speed of about thirty-five miles per hour. Ninety miles per hour has been recorded for ducks (Forrester), but this rate is not sustained for any great length of time. During long flights the distances 'traveled per day are comparatively short, e.g. an albatross is known to have covered over three thousand miles in twelve days or two hundred and fifty miles per day, and a carrier-pigeon flying from Pensacola, Florida, to Fall River, Massachusetts, a distance of over a thousand miles, attained a daily average of seventy-six miles. e. Bird Migration Formerly birds were supposed to hibernate during the winter in caves, hollow trees, or, in the case of swallows ? in the mud at CLASS AVES 623 the bottom of lakes and ponds. This is now known to be incor- rect, and when birds disappear in the fall they depart to spend the winter in a more congenial southern climate. Migration means moving from one place to another, and the idea of distance is emphasized. Birds are the most famous of all animals from the standpoint of their migrations. As winter approaches in the north temperate zone, they gather together in flocks and move southward, returning on the advent of the following spring. Birds that breed farther north spend the winter in parts of the temperate zone. Not all birds migrate, for example, the great horned owl and bob-white remain with us throughout the winter. Certain other birds move southward only when the weather becomes very severe. One of the most remarkable of all migratory birds is the golden plover. These plovers arrive in the " barren grounds " above the Arctic Circle the first week in June. In August they fly to Labrador, where they feast on the crowberry and become very fat. After a few weeks, they reach the coast of Nova Scotia, and then set out for South America over twenty-four hundred miles of ocean. They may or may not visit the Bermuda Islands and the West Indies. After a rest of three or four weeks in the West Indies or northern South America, the birds depart and are next heard from on their arrival in southern Brazil and Argentine. Here they spend the summer, from September to March, and then disappear. Apparently they fly over northern South America, and Central America, and over the central portion of North America, reaching their breeding grounds in the Arctic Circle the first week in June. The elliptical course they follow is ap- proximately twenty thousand miles in length, and this remark- able journey is undertaken every year for the sake of spending ten weeks in the bleak, treeless, frozen wastes of the Arctic Region. Most birds migrate on clear nights at an altitude sometimes of a mile or more. Each species has a more or less definite time of 624 COLLEGE ZOOLOGY migration, and one can predict with some degree of accuracy the date when it will arrive in a given locality. The speed of migra- tion is, as a rule, rather slow, and a daily rate of twenty-five miles is about the average. During their migrations, birds are often killed in great num- bers by striking against objects, such as the Washington Monu- ment, lighthouses, and telegraph wires. Over fifteen hundred birds were killed in one night by dashing against the Bartholdi Statue in New York Harbor. Birds may also be driven out .to sea or be killed by severe storms. Many theories have been advanced to account for the migra- tion of birds, such as the temperature and condition of the food supply. Other theories attempt to explain how birds find their way during migration. The best of these seems to be the " fol- low- the-leader " theory. According to this, birds that have once been over the course find their way by means of landmarks and the inexperienced birds follow these leaders. /. The Nests, Eggs, and Young of Birds Some birds, like the hawks and owls, mate for life, but the ma- jority of them live together for a single season only. The nesting period varies according to the species. The eggs of the great horned owl are often deposited before the snow has left the ground, but most birds are forced to wait until April or later, when the supply of insects is sufficient to feed their young. The nest site is chosen with considerable care, and is deter- mined upon from the standpoint of protection. As a rule, birds conceal their nests, or else build them in places that are prac- tically inaccessible; for example, the nest of the song sparrow is hidden beneath a tuft of grass, whereas that of the great blue- heron is placed in the top of the tallest tree. Many species, like the auk and certain other sea-birds, and the night-hawk and whippoorwill, make no pretence to build a nest, but lay their one or more eggs directly upon the ground. The killdeer and other plovers deposit their eggs in a small, crudely CLASS AVI.S 625 lined hollow in the ground. The great horned owl lays its eggs in an old hawk's or squirrel's nest. The mourning-dove builds a loose platform of twigs. There are all stages of complexity between this simple attempt and the beautifully woven, hanging nest of the Baltimore oriole. Certain features distinguish the nest of one bird from that of another; thus the nest of the chip- ping sparrow almost invariably contains a lining of horsehair, that of the shrike contains feathers, that of the American gold- finch is lined with thistle-down, and the nests of the ruby- throated humming-bird and the wood pewee are covered exter- nally with lichens. A few birds not only do not build nests, but even refuse to incubate their eggs and take care of their offspring. This is true of the European cuckoo and the American cow-bird. The breeding habits of the latter are very interesting. There are more male cowbirds than females and each female therefore mates with several males, --a condition known as polyandry. The females seek out the nests of other birds, usually those smaller than themselves, in which to lay their eggs. The young cow- birds are carefully reared by their foster parents, and often starve out the rightful owners. The eggs of birds vary in size, color, and number. The small- est eggs are those of certain humming-birds, measuring less than half an inch long; the largest eggs are those of the extinct ele- phant-birds of Madagascar, sEpyornis, which measure over thir- teen inches in length (see p. 598). As a rule, eggs laid in dark places, such as those of the bank- swallow, kingfisher, woodpecker, and owl, are white. Many eggs are colored, some possessing a uniform groundcolor; others, spots of various hues; and still others, both a ground color and spots. These colors usually vary but slightly in the eggs laid by different individuals of the same species, and those of one species are, in most cases, easily distinguished from those of an- other species. The eggs laid at a setting vary in number from one to about 2 s 626 COLLEGE ZOOLOGY twenty. For example, the murre lays one; the mourning dove, two; the red-tailed hawk, two or three; the robin, three or four; the blue jay four or five; the bank swallow, six; the flicker, six to eight; the ruff ed grouse, eight to fourteen ; the bob-white, ten to eighteen. The average period of incubation for passerine birds is about twelve days. The eggs of the ostrich hatch in about forty-five days. In some cases the female alone incubates ; in other cases both male and female assist in incubation; and in a few birds, such as the ostrich, the male performs practically all of this duty. Two general classes of young are recognized: (i) those that are able to run about, like young chickens, soon after hatching, known as precocious birds; and (2) those that remain in the nest for a greater or less period before they are able to take care of themselves. The latter are known as altricial birds. g. The Economic Importance of Birds Commercial Value. - - Without taking into consideration the more than three million dollars annually derived from poultry products in this country, we may say that the principal sources of revenue derived from birds are the flesh of game birds, the eggs of certain colonial sea-birds, the feathers of many species of use for millinery purposes, and the excreta and ejecta of certain species, which have accumulated on tropical islands and are known as guano. Guano contains two important elements of use in fertilizing the soil, phosphoric acid and nitrogen. The Chincha Islands off the coast of Peru have been for centuries the habitation of large numbers of sea-birds, whose excreta and remains have dried and formed a deposit in some places a hundred feet thick. The sup- ply on these islands is now almost exhausted, though in 1853 the Peruvian government estimated the amount at that time at 12,376,100 tons. There are many other deposits in the rainless latitudes of the Pacific, but none as rich as were those of the Chinchas. CLASS AVES 627 Birds are in some localities persecuted to a considerable extent for their eggs, which are used as food. This is true of certain gulls, terns, herons, murres, and ducks. Egging is not carried on now as much as formerly, since many of the colonies have been driven away from their breeding places, or the government has prohibited the practice. In 1854 more than five hundred thousand murres' eggs were collected on the Farallone Islands and sold in the markets of San Francisco in two months. The game-birds have been and still are in certain localities a common article of food. Most of them, however, have been so persistently hunted by sportsmen and market men that they are now of no great commercial importance. Several species, like the wood-duck and heath-hen, have been brought to the verge of extinction. The repeating shotgun, introduction of cold- storage methods, and easy transportation facilities soon depleted the vast flocks of prairie-chickens and other game-birds of the Middle West. One New York dealer in 1864 received twenty tons of these birds in one consignment. The hunting and trans- portation of game-birds is now regulated by law in most localities. The use of birds' skins and feathers as ornaments has been for many years a source of income for many hunters, middlemen, and milliners. Laws and public sentiment are slowly overcoming the barbarous custom of killing birds for their plumes, and it is hoped that the women of the country will soon cease to demand hats trimmed with the remains of birds. The Value of Birds as Destroyers of Injurious Animals. - Within the past two decades detailed investigations have been carried on by the United States Department of Agriculture, state governments, and private parties in order to learn the relations of birds to man with regard to the destruction of injurious ani- mals. The results of these researches may be found in govern- ment publications or in books such as Weed and Dearborn's Birds in their Relation to Man, and Forbush's Useful Birds and their Protection. A very large proportion of the food of birds consists of insects. 628 COLLEGE ZOOLOGY Figure 509 shows diagrammatically the food of nestling and adult house wrens, birds that are very common about gardens. Practically all of the insects devoured by birds are injurious to plants or animals and consequently harmful to man. Another large element in the food of birds consists of small mammals, such as field-mice, ground-squirrels, and rabbits. For many years hawks, owls, and other birds of prey have been killed whenever possible, because they were supposed to be in- jurious on account of the poultry and game-birds they captured. FIG. sog. Diagram showing the kind and comparative quantity of food of the nestling (A) and adult (B) house wren. (From Judd, Bui. 17, Bur. Biol. Survey, U. S. Dep't Agric.) Careful investigations by Dr. A. K. Fisher have shown, however, that at least six species are entirely beneficial; that the majority (over thirty species) are chiefly beneficial; that seven species are as beneficial as they are harmful; and that only the gyrfal- cons, duck-hawk, sharp-shinned hawk, Cooper's hawk (Fig. 495), and goshawk are harmful. As examples of beneficial birds of prey may be mentioned (i) the rough-leg hawk, which feeds almost entirely on meadow mice during its six months' sojourn in the United States, (2) the red-tailed hawk, or " hen hawk," sixty-six per cent of whose food consists of injurious mammals and only seven per cent of CLASS AVES 629 poultry, and (3) the golden eagle, which is highly beneficial in certain localities because of the noxious rodents it destroys. The Cooper's hawk (Fig. 495) is the real " chicken hawk "; its food is made up largely of poultry, pigeons, and wild birds, but also includes the harmful English sparrows. The beneficial qualities of birds are well shown by Dr. S. D. Judd * from a seven years' study of conditions on a small farm near Marshall Hall, Maryland. Modern methods of investiga- tion led Dr. Judd to the following conclusions :- " At Marshall Hall the English sparrow, the sharp-shinned and Cooper hawks, and the great horned owl are, as everywhere, inimical to the farmers' interests and should be killed at every opportunity. The sapsucker punctures orchard trees exten- sively and should be shot. The study of the crow is unfavorable in results so far as these particular farms are concerned, partly because of special conditions. Its work in removing carrion and destroying insects is serviceable, but it does so much damage to game, poultry, fruit, and grain that it more than counter- balances this good and should be reduced in numbers. The crow blackbird appears to be purely beneficial to these farms during the breeding season and feeds extensively on weed seed during migration, but at the latter time it is very injurious to grain. More detailed observations are necessary to determine its proper status at Marshall Hall. " The remaining species probably do more good than harm, and except under unusual conditions should receive encouragement by the owners of the farms. Certain species, such as flycatchers, swallows, and warblers, prey to some extent upon useful para- sitic insects, but, on the whole, the habits of these insectivorous birds are productive of considerable good. Together with the vireos, cuckoos, and woodpeckers (exclusive of the sapsuckers), they are the most valuable conservators of foliage on the farms. The quail, meadow-lark, orchard oriole, mocking-bird, house wren, 1 Bulletin No. 17 of the Division of the Biological Survey of the United States Department of Agriculture. 630 COLLEGE ZOOLOGY grasshopper sparrow, and chipping sparrow feed on insects of the cultivated fields, particularly during the breeding season, when the nestlings of practically all species eat enormous num- bers of caterpillars and grasshoppers. " The most evident service is the wholesale destruction of weed seed. Even if birds were useful in no other way, their preservation would still be desirable, since in destroying large quantities of weed seed they array themselves on the side of the Marshall Hall farmer against invaders that dispute with him, inch by inch, the possession of his fields. The most active weed destroyers are the quail, dove, cow-bird, red-winged blackbird, meadow-lark, and a dozen species of native sparrows. The util- ity of these species in destroying weed seed is probably at least as great wherever the birds may be found as investigation has shown it to be at Marshall Hall." h. Domesticated Birds Birds have for many centuries been under the control of man, and have produced for him hundreds of millions of dollars' worth of food and feathers every year. The common hen was prob- ably derived from the red jungle-fowl, Callus gallus, of northeast- ern and central India. The varieties of chickens that have been derived from this species are almost infinite. The domestic pigeons are descendants of the wild, blue-rock pigeon Columba lima (Fig. 470), which ranges from Europe through the Mediterranean countries to central Asia and China. Breeders have produced over a score of varieties from this ances- tral species, such as the carriers, pouters, fantails, and tumblers. Young pigeons, called squabs, constitute a valuable article of food. Of less importance are the geese, ducks, turkeys, peacocks, swans, and guinea-fowls. The geese are supposed to be derived from the gray-lag goose, Anser anser, which at the present time nests in the northern British Islands. Most of our domestic breeds of ducks have sprung from the mallard, Anashoscas. This CLASS AVES 631 beautiful bird inhabits both North America and temperate Europe and Asia. The common peacock, Paw cristatus, of the Indian peninsula, Ceylon, and Assam, has been in domestication at least from the time of Solomon. It has been distributed by man over most of the world. The swan is, like the peacock, used now chiefly as an ornament. The mute swan, Cygnus olor, of Central Europe and Central Asia, is the common domesticated species. The guinea-fowl, Numida meleagris, is a native of West Africa. Farmers usually keep a few of them to " frighten away the hawks." The turkey is a domesticated bird that has been brought under control within the past four centuries. Our Puritan ancestors found the wild turkey abundant in New England. It was intro- duced into Europe early in the sixteenth century and soon be- came a valuable domestic animal. In its wild state, it is now almost extinct except in some of the remoter localities. Our domestic turkeys are descendants of the Mexican wild turkey. CHAPTER XXI SUBPHYLUM VERTEBRATA: CLASS VII. MAMMALIA THE mammals are popularly known as " animals." The name of the class is derived from the fact that most mammals possess mammary glands which secrete milk for the nourishment of their young. Mammals also possess a covering of hair at some time in their existence and are distinguished by this characteristic as certainly as birds are by their feathers. With few exceptions adult mammals are provided with at least a small number of hairs. The seventy-five hundred or more species of living mammals, and the three thousand or more species of fossil mammals may be grouped into two subclasses, (i) PROTOTHERIA, or egg-laying mammals, and (2) EUTHERIA, or viviparous mammals. The three living genera of the PROTOTHERIA are included in one order which is confined to Australia, Tasmania, and New Guinea. They are the spiny ant-eater and duckbills (Fig. 513). The EUTHERIA may be grouped into two divisions : - I. DIDELPHIA, or marsupials, such as the opossum and kanga- roo, with a pouch in which the young are carried after birth, and without a typical placenta (see p. 641). II. MONODELPHIA, or placentals, with a typical placenta before birth, and more highly developed young. The MONODELPHIA may be subdivided into four sections :- (A) UNGUICULATA, or clawed mammals, such as the moles, bats, dogs, cats, seals, squirrels, mice, ant-eaters, and sloths. (B) PRIMATES, with fingers usually terminating in " nails," such as the lemurs, monkeys, apes, and man. 632 CLASS MAMMALIA 633 (C) UNGULATA, or hoofed animals, such as the pigs, deer, sheep, oxen, horses, and elephants, and (D) CETACEA, or whales, which have probably been derived from the unguiculate division. i. THE RABBIT The rabbit belongs to the order of gnawing mammals the RODENTIA or GLIRES. This order is made up of a number of families, one of which, the LEPORID^E, contains about sixty species of rabbits and hares. Rabbits are generally common in North FIG. 510. Lateral view of skeleton with outline of body of the rabbit. (From Parker and Haswell.) America, both wild and in a state of domestication. They are, therefore, usually easy to obtain. This fact together with their convenient size have made them favorite objects for the intro- duction of students to mammalian anatomy. The following account, however, is not intended as a laboratory guide, but sim- ply as a means of pointing out some of the more obvious mam- malian characteristics with the aid of an animal that can be examined easily in the class room. External Features. -- The rabbit (Fig. 510) is a four- footed animal (quadruped) adapted for leaping. It possesses an external covering of hair, two large external ears, or pinna, 634 COLLEGE ZOOLOGY and separate genital and anal apertures. The mouth is bounded by soft, fleshy lips which aid in seizing and holding food. At the end of the snout are two obvious slits, the nostrils. The large eyes, one on either side of the head, are protected by an upper and a lower eyelid bordered by thin eyelashes, and a white, hairless third eyelid, or nictitating membrane, which may be drawn over the eyeball from the anterior angle. Above and below the eyes and on either side of the snout are long, sensitive hairs, the whiskers or mbrissce. The trunk may be separated into an anterior portion, the tho- rax, which is supported laterally by the ribs, and a posterior portion, the abdomen. The tail is short. Beneath it is the anus, and just in front of this is the urinogenital aperture. On either side of the anus and just anterior to it is a hairless depression, the perinceal pouch into which a strong-smelling secretion is poured by the perinaeal glands. Four or five pairs of small papillae, the teats or mamma, are situated in pairs on the ventral surface of the thorax and abdomen. At the end of the teats open the ducts of the mammary or milk glands. The fore limbs of the rabbit are used, as in the frog, for holding up the anterior part of the body. They possess five clawed digits each. The hind limbs are longer and more powerful than the fore limbs and serve as leaping organs. They are provided with only four digits; the one corresponding to the great toe in man is absent. The rabbit places the sole of its foot upon the ground, and is, therefore, said to be plantigrade (L. planta, the sole of the foot; gradior, walk). The Skeleton. -- An outline of the skeleton is shown in Fig. 510. It consists principally of bone, but a small amount of cartilage is also present. As in the fishes, amphibians, reptiles, and birds, there are cartilage-bones, preformed in cartilage, and membrane-bones, arising by the ossification of dermal portions of the skin. A third type, called sesamoid bones, occurs in the tendons of some of the limb-muscles, the action of which they modify; for example, the knee-cap. CLASS MAMMALIA 635 19 The axial skeleton consists, as in the pigeon, of a skull, ribs, sternum, and vertebral column. The skull (Fig. 511) is formed of both cartilage- and membrane -bones, and only a small amount of cartilage. The individual bones are immovably united to one another, and their boundaries are in many cases obliterated in the adult and can only be made out in the embryo. The follow- ing points are worthy of special mention. The occipital ring is completely ossi- fied and there are two occipital con- dyles (Fig. 511, 1$ 20) ; the cranial and olfactory cavities are sepa- rated by a bony cribriform plate ; 14 20 articulates rectly with (li- the FIG. 511. Side view of skull of the rabbit, /.nasal bone; 2, lachrymal bone; 3, orbito-sphenoid; 4, frontal; 5, optic foramen; 6, orbital groove for trigeminal nerve; the lower jaw (l7) 7, zygomatic process of squamosal; 8, parietal; g, squa- mosal; 10, supra-occipital; //, tympanic bones; 12, ex- ternal auditory meatus; 14, lower incisor; 75, anterior premolar; 16, anterior upper incisor; 17. mandible; 18, maxilla; IQ, premaxilla; 20, occipital condyle. Squamosal (g) ; ( From Shipley and MacBride.) three small but distinct auditory ossicles are present; and there is no distinct parasphenoid on the under surface. The teeth are cutaneous structures, as are the scales and teeth of the dogfish-shark (p. 424), and are developed from the mucous membrane of the mouth. Each tooth possesses an outer, hard covering, called enamel, a central softer substance, called den- tine, and about the base and in the surface folds a bony layer, the cement. The teeth of the rabbit remain open at the base and continue to grow throughout life, thus supplying new material to replace that worn away in grinding its vegetable food. The rabbit lacks canine teeth, and the incisors (Fig. 511, 14, 16} 636 COLLEGE ZOOLOGY are widely separated from the grinding teeth (75). There are two pairs of incisors (16) lodged in sockets (alveoli) in the pre- maxillae of the upper jaw, and one pair (14) projecting forward from the anterior end of the lower jaw. Only the outer, curved surface of the incisors is covered with enamel, and since the inner dentine wears away more rapidly than the enamel, a chisel- shaped form results that is admirably fitted for gnawing. The grinding teeth are called premolars and molars. The premolars develop after a preceding set of " milk " teeth have fallen out; the molars have no deciduous predecessors. The upper jaw contains three pairs of anterior premolars and three pairs of posterior molars. The last molar is smaller than the others. The lower jaw is provided with two pairs of premolars and three pairs of molars; the last molar is small. The vertebral column, as in other vertebrates, supports the body, and protects the spinal cord. The vertebra move upon one another; are separated by intervertebral disks of fibrocartilage, except in the sacrum; and are connected by intervertebral liga- ments. The vertebrae of the neck, or cervical vertebra, are al- most always seven in number; those of the chest, the thoracic vertebra, bear movably articulated ribs; those of the trunk region are called lumbar vertebra; the three or more sacral ver- tebra are fused together and support the pelvis; and the caudal vertebra, about sixteen in number, form the skeletal axis of the tail. The ribs and sternum constitute the framework of the thorax, and not only protect the vital organs in that region, but also play an important role in respiration. There are twelve, or sometimes thirteen, pairs of ribs (Fig. 510). The first seven pairs articulate with the sternum; the others do not reach the sternum. The sternum is a long, laterally compressed structure consisting mostly of bone. It is situated in the ventral wall of the thorax, and is transversely divided into six segments, or sternebrae. The pectoral girdle consists of two scapulas, two imperfect CLASS MAMMALIA 637 clavicles, and two knob-like coracoids. Each half of the pelvic girdle is called an innominate bone, and is made up of the ilium, ischium, and pubis fused together. The concavity in the in- nominate bone in which the head of the femur articulates is called the acetabulum. The ankle-joint of the rabbit lies between the tibia and fibula above, and the tarsal bones below. The fourth and fifth carpal bones and corresponding tarsal bones are fused together, forming, in the fore limb, the unciform bone, and in the hind limb the cuboid bone. One of the sesamoid bones of the hind limb which is situated on the front of the distal end of the femur is called the kneepan, or patella. The tibiale is fused with the inter- medium of the tarsus to form the astragalus ; and the fibulare, which lies along its outer side, is called the calcaneum. Internal Anatomy. - - Unlike other vertebrates, the body- cavity of the rabbit and mammals in general is divided by a transverse muscular partition, called the diaphragm, into two parts, an anterior thoracic portion containing the heart and lungs, and a posterior portion containing the abdominal viscera. THE DIGESTIVE SYSTEM. - - The mouth or buccal cavity bears on the anterior portion of the roof a series of transverse ridges against which the tongue works. That part of the roof which has a bone foundation is known as the hard palate. Posterior to this is a muscular flap, the soft palate, which separates the mouth from the pharynx. At the sides of the posterior part of the soft palate are a pair of small masses of lymphoid tissue containing pits of unknown function, called the tonsils. The tongue is attached to the floor of the mouth. It bears a number of taste papilla on the anterior part and sides. The two orifices of the eustachian tubes and the two apertures of the naso palatine canals, which connect the nasal and buccal cavities, are situated in the roof of the mouth behind and above the soft palate. There are four pairs of salivary glands: (i) the parotids, (2) the infra- orbitals, (3) the submaxillaries, and (4) the sublinguals. They pour their secretions into the mouth cavity. 638 COLLEGE ZOOLOGY The posterior continuation of the mouth cavity is called the pharynx. In the floor of the pharynx is the respiratory opening, the glottis, which is covered by a bilobed cartilaginous flap, the epiglottis, during the act of swallowing. The pharynx leads into the narrow, muscular (esophagus. Following this is the stomach; then comes the U-shaped duodenum, into which the pancreatic duct from the pancreas and the bile duct from the liver open. The small intestine, which is seven or eight feet in length, leads into the colon, which is continued as the rectum. At the an- terior end of the colon a large, thin-walled tube, the ccecum, is given off. This caecum is about an inch in diameter and twenty inches long; it ends in a thick- walled, finger-like process about four inches long, called the "vermiform appendix. A large caecum is characteristic of most herbivorous animals with simple stomachs. The rabbit possesses the following ductless glands : the spleen, the thymus, the thyroid, and the suprarenals. THE CIRCULATORY SYSTEM. - - The blood corpuscles of the rabbit are unlike those of the lower vertebrates, being smaller, round instead of oval, biconcave, and without nuclei. The heart is four chambered, as in the pigeon, but the main blood- vessel, the aorta, arising from the left ventricle, has only the left arch, whereas in birds the right arch persists. The right sys- temic arch of the rabbit is represented by the innominate artery, which is the common trunk of the right carotid and subclavian arteries. An hepatic-portal system is present, but no renal-portal system. The lymphatic system is important in rabbits and other mam- mals. The fluid portion of the blood, which, because of the blood pressure, escapes through the walls of the capillaries into the spaces among the tissues, is collected into lymph vessels. These vessels pass through so-called lymph glands, and finally empty into the large veins in the neck. The lymphatics which collect nutriment from the intestine are called lacteals. CLASS MAMMALIA 639 THE RESPIRATORY SYSTEM. - - The rabbit and all other mammals breathe air by means of lungs. The glottis opens into the larynx, from which a tube called the trachea or windpipe arises. The trachea is held open by incomplete rings of cartilage ; it divides into two bronchi, one bronchus going to each lung. The larynx is supported by a number of cartilages and across its cavity extend two elastic folds called the vocal cords. The lungs are conical in shape, and lie freely in the thoracic cavity sus- pended by the bronchi. Air is drawn into the lungs by the enlargement of the thoracic cavity. This is accomplished both by pulling the ribs forward and thus separating them, as in most reptiles, and by means of the diaphragm. The diaphragm is normally arched forward and when it contracts it flattens, thus enlarging the thoracic cavity. The increased size of this cavity results in the expansion of the lungs, because of the air pressure within them, and the inspiration of air through the nostrils. Air is pumped out of the lungs (expiration) by the contraction of the elastic pulmonary vesicles, and of the thoracic wall and diaphragm. THE EXCRETORY SYSTEM. - - The urine excreted by the two kidneys is carried by two slender tubes, the ureters, into a thin- walled, muscular sac, the urinary bladder. At intervals the walls of the bladder contract, forcing the urine out of the body through the urinogenital aperture. THE NERVOUS SYSTEM. - - The rabbit possesses a brain, cranial nerves, spinal cord, spinal nerves, and a sympathetic nervous system. The brain (Fig. 512), as in other mammals, differs from that of the lower vertebrates in the large size of the cerebral hemi- spheres (f.b) and cerebellum (h.b). The cerebral hemispheres are slightly marked by depressions, or sulci, which divide the surface into lobes or convolutions not present in the pigeon. The olfactory lobes (b.o) are very large and club-shaped. The optic lobes are each divided by a transverse furrow into two. The 640 COLLEGE ZOOLOGY cerebellum is divided into three parts, a central portion (cb f ) and two lateral lobes. THE SENSE ORGANS. - - The eyes of mammals are without a pecten such as is present in birds. The large outer ear, or pinna, serves to collect sound waves; the middle ear transmits the vibrations of the tympanic membrane, or eardrum, by means of three auditory ossicles, which extend across the tympanic cavity, to the inner ear. The cochlea of the inner ear is spirally eV. md. i 'v- ii h.l. P- v - V1 FIG. 512. Side view of brain of the rabbit, b.o, olfactory bulb; cb', supe- rior vermis of cerebellum; f.b, cerebral hemisphere; h. b, cerebellum; h.l, hippo- campal lobe; m.d, medulla oblongata; p.v, pons Varolii; r.f, rhinal fissure; i-xii, cranial nerves. (From Wiedersheim.) coiled, and not simply curved as in the pigeon. The nasal cavities are very large, indicating a highly developed sense of smell. THE REPRODUCTIVE SYSTEM. - - The two testes of the male lie in oval pouches of skin, called scrotal sacs, one on either side of the copulatory organ, or penis. They may be drawn back into the abdominal cavity through the narrow inguinal canals. The spermatozoa pass from the testes into irregular convoluted tubes called the epididymes; they then enter the vasa deferentia which lead into the abdominal cavity and open into a medium sac, the uterus masculinus, attached to the dorsal surface of the urino- genital canal, or urethra. During copulation the spermatozoa pass into the urethra and are transferred to the female by the penis. Surrounding the vasa deferentia is a prostate gland CLASS MAMMALIA 641 which opens by short ducts into the urethra, and just behind are a pair of Cow per' s glands. The secretions from these glands are added to the spermatozoa, making the seminal mass more fluid. The two ovaries of the female are oval bodies exhibiting small, rounded projections on the surface; these are the outlines of the Graafian follicles, each of which contains an ovum. The ovi- ducts consist of an anterior Fallopian tube and a middle uterus ; the uteri unite posteriorly to form the vagina. The anterior end of the Fallopian tube is wide and funnel-shaped; it carries the ova from the ovary to the uterus, where the young are developed. The urinogenital canal, or vestibule, is a wide, median tube. On its ventral wall lies a small rod-like body, the clitoris, corresponding to the penis of the male. The ova undergo holoblastic segmentation in the oviduct; they then pass into the uterus, where they receive nourishment from the blood of the mother through a structure called the placenta, which is formed from the fcetal membranes and united with the mucous membrane of the uterine wall. The interval between fertilization and birth, known as the period of gestation, is thirty days. Eight or ten young may be produced at a birth, and a new litter may be born every month for a large part of the year. Young rabbits breed when three months old. 2. A BRIEF CLASSIFICATION OF LIVING MAMMALS 1 As stated on page 632, there are about seventy- five hundred species of living mammals, and three thousand or more species of fossil forms known to man. The living mammals may be grouped into two subclasses and eighteen orders. Class Mammalia. -- M AMMALS or "ANIMALS." -Warm- blooded vertebrates with a covering of hair at some stage in their existence, and with cutaneous glands in the female, which secrete milk for the nourishment of the young. 1 Modified from Osborn's Age of Mammals, 2 T 642 COLLEGE ZOOLOGY SUBCLASS I. PROTOTHERIA. EGG-LAYING MAMMALS. Order i. Monotremata. MONOTREMES. Examples: Or- nithorhynchus, duckbill (Fig. 513); Echidna, spiny ant- eater. SUBCLASS II. EUTHERIA. VIVIPAROUS MAMMALS. Division I. DLDELPHIA (METATHERIA). MARSUPIALS. Order i. Marsupialia. MARSUPIALS. Mammals which usually carry their young in a marsupium or pouch; allantoic placenta usually absent. Suborder i . POLYPROTODONTIA. CHIEFLY CARNIVO- ROUS MARSUP