a, ••%*, liOLOgY LIBRAIT MANUAL OF ZOOLOGY .FOR THE USE OF STUDENTS WITH A GENERAL INTRODUCTION ON THE PRINCIPLES OF ZOOLOGY BY HENRY ALLEYNE NICHOLSON M.D., D.Sc., M.A., PH.D. (Goxx.), F.R.S.E., F.G.S. PROFESSOR OF NATURAL HISTORY AND BOTANY IN UNIVERSITY COLLEGE, TORONTO FORMERLY LECTURER ON NATURAL HISTORY IN THE MEDICAL SCHOOL OF EDINBURGH ; ETC. ETC. THIRD EDITION REVISED AND ENLARGED WILLIAM BLACKWOOD AND SONS EDINBURGH AND LONDON MDCCCLXXIII The Right of Translation is reserved pic 6 hA PREFACE TO SECOND EDITION. THE call for a new issue of this work within little more than six months after the appearance of the last, is a very gratifying proof that, in spite of its defects, the work supplies a recognised want, and that the Author has to some extent succeeded in the objects aimed at. With regard to the present edition, the Author need only say that the entire work has been carefully revised, and all the more striking discoveries of recent date have been noticed, whilst some errors have been corrected. Considerable additions have also been made, especially in the department of Vertebrate Zoology. The Author, however, would ask his readers to remember that the compass of the work will not admit of the introduction of many details, which must be sought for in other more extensive treatises, and that only the more important facts of Natural History should be looked for in a work of such limited size. Lastly, no change has been made in the plan of classi- fication adopted in the former editions of this work, and based essentially upon the views put forth by Professor Huxley. It is true that this classification is a modern VI PREFACE. one, and that it departs widely from older arrangements. The Author, however, must seek his excuse for its adoption — if such be needed — in his firm belief that of all classifications this approximates most nearly to a natural one, and that though subsequent researches may compel its partial modification, its broad outlines will long endure unaltered. UNIVERSITY COLLEGE, TORONTO, October 2, 1871. PREFACE TO FIRST EDITION OF PART I. IN bringing out the present work, the Author has been mainly guided by the recollection of his own difficulties as a student, and by the belief that he is supplying a distinct want. Many excellent and original works on Natural History are extant, but they mostly labour under disadvantages which more or less disqualify them as text-books for students. So vast, for in- stance, have been the additions to our Zoological knowledge within the last few years, that no work on Natural History, except the most recent ones, represents adequately the present state of the Science. Under this inevitable disqualification all the older Manuals labour. Other works, again, of the most profound research, are unsuitable for ordinary students from their bulk, cost, and, more than all, from their very profundity. The Author's aim, therefore, has simply been to present to the ordinary student those leading facts in Natural History, the knowledge ofi which is essential, but which lie scattered through the pages of other larger and more costly works, inaccessible to those who merely desire to learn the outlines of the Science. In carrying out this object, it is unnecessary for the Author to remark that he does not lay any claim to originality. He trusts, however, that he has succeeded in laying before his PREFACE. vii readers, not a mere mass of undigested facts, but something like an orderly and systematic review of the main points re- quired to be known by the student. The Author is conscious of many imperfections in his plan, and also in the execution of his plan. The subject, however, is so extensive, and so con- stantly changing, that he can reasonably claim some indulgence, if the brief leisure-time of a busy life has not enabled him in every respect to keep abreast of the latest discoveries. Such defects as there may be, are, it is hoped, of such a nature as not to diminish the value of the work for ordinary students. Amongst the sources upon which the Author has mainly drawn, it is, perhaps, invidious to mention one more than another. He feels, however, bound to acknowledge with gratitude the very great assistance which he has derived from the various works of Professor Huxley. EDINBURGH, November 2, 1869. PREFACE TO FIRST COMPLETE EDITION. IN issuing the first part of the present work in a second edition, and in bringing out the second part, the Author has little to add to what he has already said. The chief point upon which it may be desirable to say a few words is, as to the object aimed at in the Introductory portion of the work. The Introduction is intended to exhibit to the student, in as brief a form as possible, the leading principles of Zoological Science. These principles are of the highest importance, and no adequate knowledge of Zoology can be attained without their full comprehension. At the same time, the principles in question depend, in many cases, upon data which are only evolved during the systematic study of the sub- ject. For this reason, it is not to be expected that the student Vlll .PREFACE. should find himself fully able to comprehend the Introductory portion of the work, whilst still standing at the threshold of the subject. Whilst the student, therefore, will do well to glance over the Introduction before commencing the study of the systematic portion of the work, he must be prepared to find many points which he can only fully grasp after he has attained a knowledge of the leading modifications of structure exhibited in the Animal Kingdom. The Author has only to add that the first part of the work (on the Invertebrate Animals) has been carefully revised, and, as far as possible, brought up to the present level of the Science; whilst the illustrations, with very few exceptions, have been drawn upon the wood by himself. EDINBURGH, December i, 1870. CONTENTS. PART I.-INVERTEBRATE ANIMATE. GENERAL INTRODUCTION. PAGE Definition of Biology and Zoology — Differences between organised and unorganised bodies — Nature of life — Vital force — Differ- ences between animals and plants— Morphology and physiology — Differences between different animals — Specialisation of func- tions—Morphological type — Von Baer's law of development — Homology, analogy, and homomorphism — Correlation of growth — Classification — Definition of species — Impossibility of a linear classification — Reproduction — Sexual reproduction — Non-sexual reproduction — Gemmation and fission — Reproduction by internal gemmation — Alternation of generations — Parthenogensis— De- velopment, transformation, and metamorphosis — Spontaneous generation — Origin of species — Distribution, geographical and geological, . ' . 1-47 CHAPTER I. General characters of the Protozoa — Classification of the Protozoa — Gregarinidse — Psorospermiae, ... ... 48-52 CHAPTER II. General characters of the Rhizopoda — Monera — Amcebea, . . 53'58 CHAPTER III. Foraminifera — Classification of the Foraminifera— Bathybius— Cocco- liths, Coccospheres — Affinities of the Foraminifera — Distribution of Foraminifera in space — Distribution of Foraminifera in Time, 58-66 CHAPTER IV. Radiolaria — Acanthometrse — Polycystina— Thalassicollida, . . 67-69 CHAPTER V. Sponges — Nature of Sponges — Classification of Spongida — Distribu- tion of Sponges in space and in time — Affinities of Sponges, 69-76 X CONTENTS. CHAPTER VI. Infusoria — Order Ciliata — Suctoria — Flagellata — Noctiluca — Phos- phorescence of the Sea, ....... 76-84 CHAPTER VII. General characters of the Ccelenterata— Divisions of the Ccelenterata — Hydrozoa — General terminology of the Hydrozoa, . . 85-90 CHAPTER VIII. Divisions of the Hydrozoa — Sub-class Hydroida — Order Hydrida — Order Corynida — Reproduction of Hydroida — Sertularida — Cam- panularida, 90-103 CHAPTER IX. Siphonophora or Oceanic Hydrozoa — Calycophoridse — Divisions of Calycophoridae — Physophoridae — Divisions of Phyeophoridae, 103-110 CHAPTER X. Discophora — Structure of Medusidae — Value of Medusidae as an order of Hydrozoa, . . . 110-113 CHAPTER XI. Lucernarida — Steganophthalmate Medusae — Lucernariadse — Pelagidae — Rhizostomidae — Reproduction in Rhizostomidae — Sub-class Graptolitidae — Definition of the Sub-class — Structure of Grapto- lites, 114-122 CHAPTER XII. Distribution" of Hydrozoa in space — Distribution of Hydrozoa in time — Oldhamia — Corynida — Sertularida — Graptolites, . . 123-124 CHAPTER XIII. General characters of the Actinozoa — Zoantharia Malacodermata — Actinidae — Ilyanthidae — Zoanthidse — Zoantharia Sclerobasica — Sclerobasic and Sclerodermic Corals — Antipathidae — Hyalone- madae — Zoantharia Sclerodermata — Gemmation and fission amongst Corals, . . 124-137 CHAPTER XIV. Alcyonaria— Alcyonidae — Tubiporidae — Pennatulidse — Gorgonidse — , Red Corals, . . . . . . . . . 137-140 CHAPTER XV. Rugosa— Distinctions between the Coralla of the different Orders of Actinozoa, 140-142 CONTENTS. CHAPTER XVI. Ctenophora — General characters — Anatomy of Pleurobrachia — Divi- sions of Ctenophora, ....... 142-146 CHAPTER XVII. Distribution of Actinozoa in space — Coral Reefs, their structure, and mode of origin — Distribution of Actinozoa in time — Tabular view of the divisions of the Zoantharia Sclerodermata and Rugosa, 147-153 CHAPTER XVIII. Annuloida — General characters of the Annuloida — General characters of the Echinodermata — Development of the Echinodermata Divisions of Echinodermata, ...... 154-157 CHAPTER XIX. Echinoidea — General characters — Anatomy of Echinus — Divisions of Echinoidea, 157-163 CHAPTER*XX. Asteroidea and Ophiuroidea — General characters of the Asteroidea — Divisions of the Asteroidea — General characters of the Ophiuroi- dea— Families of the Ophiuroidea, 164-170 CHAPTER XXI. Crinoidea, Cystoidea, and Blastoidea — General characters of Crinoi- dea — Of Cystoidea — Of Blastoidea, 170-177 CHAPTER XXII. Holothuroidea — General characters — Families of Holothuroidea, 177-180 CHAPTER XXIII. Distribution of Echinodermata in space — Distribution of Echinoder- mata in time — Crinoidea — Blastoidea — Cystoidea — Asteroidea — Ophiuroidea — Echinoidea — Holothuroidea, . . . 180-183 CHAPTER XXIV. Scolecida — General characters of the class Scolecida — Entozoa — Platyelmia — Tseniada — Structure and development of the Tape- worm—Hydatids, 183-189 CHAPTER XXV. Trematoda and Turbellaria — General characters of the Trematoda — General characters of the Turbellaria — Planarida — Nemer- tida, 189-193 Xll CONTENTS. CHAPTER XXVI. Nematelmia — Acanthocephala — Gordiacea — Nematoda — Parasitic Nematoids — Free Nematoids, i93-!97 CHAPTER XXVII. Rotifera — General characters of 'the Rotifera — Affinities of the Roti- fera, 198-202 CHAPTER XXVIII. Annulosa — General characters of the Annulosa — General characters of the Anarthropoda — Class Gephyrea — General characters of the class Annelida, 203-207 CHAPTER XXIX. Divisions of the Annelida — Hirudinea — Oligochseta — Tubicola — Errantia — Distribution of the Annelida in time — Tabular view of the Annelida — Class Chsetognatha, 207-217 CHAPTER XXX. Arthropoda — General characters — Divisions of Arthropoda, . 217-218 CHAPTER XXXI. Crustacea — Characters of the class Crustacea — General morphology of Crustacea — Divisions .of Crustacea, 219-226 CHAPTER XXXII. Epizoa — Ichthyophthira — Rhizocephala — Cirripedia — Characters of Cirripedia — Development — Reproduction — Divisions, . 226-233 CHAPTER XXXIII. Entomostraca — Lophyropoda — Ostracoda — Copepoda — Branchio- poda — Cladocera — Phyllopoda — Trilobita — Merostomata — > Xiphosura — Eurypterida, 233-241 CHAPTER XXXIV. Malacostraca — Edriophthalmata — Laemodipoda — Amphipoda — Iso- poda — Podophthalmata — Stomapoda — Decapoda — Macrura — Anomura — Brachyura, 242-251 CHAPTER XXXV. Distribution of the Crustacea in space — Distribution of the Crustacea in time, 251-254 CHAPTER XXXVI. General characters and divisions of the Arachnida, . . . 254-258 CONTENTS. CHAPTER XXXVII. Divisions of the Arachnida — Podosomata — Acarina — Adelarthroso- mata — Pedipalpi — Araneicla, . . 258-264 CHAPTER XXXVIII. Myriapoda — General characters of the class — Chilopada — Chilog- natha — Pauropada — Distribution of Myriapoda in time, . 264-267 CHAPTER XXXIX. General characters of the Insecta — Metamorphoses of Insects Sexes of Insects, 267-276 CHAPTER XL. Divisions of the Insecta — Anoplura — Mallophaga — Thysanura — Hemiptera— Orthoptera — Neuroptera — Aphaniptera — Diptera Lepidoptera — Hymenoptera — Strepsiptera — Coleoptera, . 277-292 CHAPTER XLI. General characters of the Mollusca — Digestive system— Circulatory system — Respiratory system — Nervous system — Reproduction — Shell, f 293-297 CHAPTER XLII. Molluscoida — Polyzoa — Distinctions between the Polyzoa and Hy- drozoa — Polypide of the Polyzoa — Anatomy of the Polyzoa — Reproduction and development — Divisions of the Polyzoa, . 298-306 CHAPTER XLIIL Tunicata — General characters — Development — Types of — Homo- logics — Divisions, . 306-311 CHAPTER XLIV. Brachiopoda — General characters — Shell — Afms — Atrial system- Divisions, 312-317 CHAPTER XLV. Distribution of Molluscoida in space — Distribution of Molluscoida in time, 3l8'3i9 CHAPTER XLVI. General characters and divisions of f the Mollusca Proper— Lamelli- branchiata — General characters and anatomy — Divisions — Fami- lies of the Lamellibranchiata, 32O'329 CHAPTER XLVIL Encephala — Gasteropoda — General characters — Development — Shell of Gasteropoda, 329'334 XIV CONTENTS. CHAPTER XLVIII. Divisions of the Gasteropoda — Prosobranchiata— Opisthobranchiata — Heteropoda — Pulmonate Gasteropoda — Families of the Gastero- poda, 335-341 CHAPTER XLIX. Pteropoda— General characters— Divisions — Families, . 342-343 CHAPTER L. Cephalopoda — General characters — Arms — Respiratory organs — Re- productive process — Shell — Divisions, 344-35° CHAPTER LI. Dibranchiate Cephalopods — General characters— Octopoda — Argon- autidse — Octopodidse — Decapoda — Teuthidse — Sepiadae — Spiru- lidse — Belemnitidse — Tetrabranchiate Cephalopods — Structure of the Pearly Nautilus — Shell of the Tetrabranchiata — Nautilidse — Ammonitidse — Families of the Cephalopoda, . . . 350-358 CHAPTER LII. Distribution of the Mollusca Proper in time, . 358-361 Tabular view of the chief subdivisions of the Invertebrata, . . 361-365 PART II.- VERTEBRATE ANIMALS. CHAPTER LIII. General characters of the Vertebrata — Osseous system — Digestive sys- tem — Blood — Circulation — Respiration — Nervous system — Organs of sense — Reproduction — Divisions, . . . 369-385 CHAPTER LIV. General characters of Fishes — Integumentary system— Osseous system — Fins — Respiration — Circulation — Digestive system — Swim- bladder— Nervous system— Olfactory organs — Reproduction, 386-399 CHAPTER LV. Pharyngobranchii — Marsipobranchii, 400-405 CHAPTER LVI. Teleostei — Sub-orders — Malacopteri — Anacanthini — Acanthopteri — Plectognathi — Lophobranchii, 405-412 CONTENTS. XV CHAPTER LVII. Ganoidei — Sub-orders — Lepidoganoidei— Placoganoidei, •. .412-418 CHAPTER LVIII. Elasmobranchii and Dipnoi — Sub-orders of Elasmobranchii — Holo- cephali — Plagiostomi — Dipnoi, 418-426 CHAPTER LIX. Distribution of Fishes in time, * 427-430 CHAPTER LX. General characters of the Amphibia, ...... 431-433 CHAPTER LXI. Orders of Amphibia — Ophiomorpha — Urodela — Anoura — Develop- ment of Frog — Families of Anoura — Labyrinthodontia — Distribu- tion of Amphibia in time, 433-443 CHAPTER LXII. General characters of Reptilia — Endoskeleton — Exoskeleton — Diges- tive system — Circulatory system — Respiratory system, . . 444-448 CHAPTER LXIII. Divisions of Reptilia — Chelonia — General characters of Chelonian Reptiles — Distribution of Chelonia in time — Ophidia — General characters of Snakes — Sub-orders — Distribution of Ophidia in time, 448-460 CHAPTER LXIV. Lacertilra — Families of Lacertilia — Distribution of Lacertilia in time — Crocodilia — Sub-orders of Crocodilia — Distribution of Croco- dilia in time, . 460-471 CHAPTER LXV. Extinct orders of Reptiles — Ichthyopterygia — Sauropterygia — Ano- modontia — Pterosauria — Dinosauria, ..... 471-479 CHAPTER LXVI. General characters of the class Aves — Feathers— Vertebral column — Skull — Pectoral arch and fore-limb — Pelvic arch and hind-limb — Digestive system — Respiratory system — Circulatory system — Reproductive organs — Nervous system and organs of sense, . 480-499 CHAPTER LXVII. General divisions of the class Aves— Characters and families of the order Natatores — Characters and families of Grallatore . 499'S11 XVI CONTENTS. CHAPTER LXVIII. Characters of Cursores — Characters and sections of Rasores — Galli- nacei — Columbacei, ........ 511-519 CHAPTER LXIX. Characters and families of Scansores — Characters of Insessores — Coni- rostres — Dentirostres — Tenuirostres — Fissirostres, . . . 519-528 CHAPTER LXX. Characters and sections of Raptores — Characters of Saururre, . 528-532 CHAPTER LXXI. Distribution of Aves in time, . . . . . * . 532-536 CHAPTER LXXII. General characters of the Mammalia — Skeleton — Pectoral arch and fore-limb — Pelvic arch and hind-limb — Teeth — Dental formula — Digestive system — Circulatory system — Respiratory system — Re- productive system — Mammary glands — Nervous system — Integu- mentary appendages, ........ 537-549 CHAPTER LXXIII. Classification of the Mammalia — Synopsis of the Mammalian orders, ........... 55°'554 CHAPTER LXXIV. Characters of Monotremata — Characters and divisions of Marsu- CHAPTER LXXV. Characters and families of Edentata, ..... , . 565-570 CHAPTER LXXVI. Characters of Sirenia — Characters and families of Cetacea, . . 570-580 CHAPTER LXXVII. General characters of Ungulata — Perissodactyla — Artiodactyla— Ru- minantia — Structure of the stomach in Ruminants— Dentition of Ruminants — Sections of Ruminants, ..... 580-599 CHAPTER LXXVIIL Characters of Hyracoidea — Characters of Proboscidea, . . 599-603 CHAPTER LXX IX. Characters of Carnivora — Pinnigrada — Plantigrada — Digitigrada, 603-616 CONTENTS. XVli CHAPTER LXXX. Characters of Rodentia — Families of Rodentia, . . • .617-622 CHAPTER LXXXI. Characters of Cheiroptera — Sections of Cheiroptera, . . . 623-626 CHAPTER LXXXII. Characters of Insectivora — Families of Insectivora — Galeopithe- cidae, 626-629 CHAPTER LXXXIII. Characters of Quadrumana — Sections of Quadrumana — Strepsirhina— Platyrhina— Catarhina, 629-637 CHAPTER LXXXIV. Characters of Bimana, . . ... ... . . 637-638 CHAPTER LXXXV. Distribution of Mammalia in time — Geographical succession of or- ganic forms — Tabular view of the chief sub-divisions of the Ver- tebrata, 638-651 GLOSSARY, 653-683 INDEX, •• 684-706 XV111 LIST OF ILLUSTRATIONS. 1. Ideal Section of the Crust of the Earth, 2. Gregarina of the Earth- worm, .... 3. Morphology of Rhizopoda, 4. Amoeba, .... 5. Actinophrys sol, 6. Nonionina and Gromia, . 7. Morphology of Foramini- fera, .... 8. Formation of the com- pound Foraminifera, . 9. Nummulites Itzvigatus, 10. Acanthometrina and Poly- cystina, 1 1 . Morphology of Radiolaria, 12. Diagrammatic section of Spongilla, . 13. Morphology and repro- duction of Spongida, . 14. Morphology of Infusoria, 1 5. Paramcecium bursaria and P. aurelia, . . . 1 6. Va^inicola, Slentor, and Vorticdla, . 17. Diagrammatic section of Actinia, 1 8. Morphology of Plydrida, 19. Morphology of Corynida, 20. Reproductive buds of Hydrozoa, . 21. Gonophore of Clytia Johnstoni, . 22. Tubularia indivisa, . 23. Hydractinia echinata, 24. Morphology of Sertularida, 25. Ovarian capsule of Sertu- laria operculata, »• 26. Clytia Johnstoni, 27. Morphology of Oceanic Hydrozoa, . . . 28. Diphyes appendiculata, . PAGE FIG. PAGE 29. Physalia and Velella, 109 46 Morphology of Medusida, in 31. Group of Naked-eyed 51 Medusce, 112 54 32. Lucernaria auricula, IJ5 55 33- Development of Aurelia, 117 57 34- Generative zooid of Chry- 59 saora hysoscella, . 118 35- Generative zooid of I\hi- 60 zostoma, 119 36. Morphology of Graptolites 61 priodon, 121 66 37. Monoprionidian and Di- prionidian Graptolites,. 122 67 38. Didymograpsus V-fractus,, 124 69 39- Transverse sections of Actinozoa and Hydrozoa, 125 71 40. Actinia Mesembryanthe- mum, and section of 72 Actinia, 126 77 41. Actinia rosea and Arach- nactis albida, 128 79 42. Cyathaxonia Dalmani, . 131 43- Diagrammatic sections of 82 Corals, 131 44. Sclerodermic and Sclero- 86 basic Corals, . ,• 132 92 45- Antipathes anguina, 133 93 46. Columnaria alveolata, 134 47- Calicular gemmation in 95 48. Lonsdalea Jloriformis, . Pennatula phosphorea, 136 139 96 49. Virgularia mirabilis, 139 97 5°- Strombodes pentagonus, 141 99 51. Calceola sandalina, . 141 100 52. 53- Pleurobrachia pileus, Morphology of Cteno- 143 101 phora, . . . '• . 144 102 54- Structure of Coral-reefs, . 148 55- Morphology of Echin- 104 oidea, .... 158 106 56. Cidaris papillata, 159 LIST OF ILLUSTRATIONS. XIX FIG. 57. Larva of Echinus. Dia- PAGE FIG. 94- gram of Echinus, 161 95- 58. Cribella oculala, . . 162 96. 59. Diagram of Goniaster, . 165 97- 60. Section of the ray of Uras- 98. ter rubens, . 166 61. Ophiura texturata and 99- Ophiocoma neglecta, 62. Rhizocrinus Lofotensis, . 169 171 63. Platycrinus tricontadac- 100. tylus, . . . 1 72 , J73 IOI. 64. Comatula rosacea and 102. young, 174 103. 65. Echinosphczrites auran- 104. tium, .... 176 105. 66. Holothuria tubulosa and young .... 178 106. 67. Thyone papillosa, . 68. Morphology of Tceniada, 179 187 107. 69. Trematoda, 190 108. 70. Morphology of Turbel- 109. laria .... 192 no. 71. Echinorhynchus gigas, . 194 Ill, 72. Anguillula aceti and /}'AGK FIG. 334 169. Diagram of the Lancelet, PAGE 4OI 336 i IJO. Lamprey, 4«>3 336 171. Heart of Teleostean and 337 Ganoid Fishes, 407 337 172. Gymnotus electricus, 408 338 173. Rhombus pit nctatuS) 410 174. Ostracion cornutus, 4II 342 175- Polypterus and Osteolepis, 415 345 I76. Cephalaspis Lyellii^ 417 346 177. Coccosteus z.\\&Ptcrichthys, 4l8 348 178. Head of Piked Dog-fish, 419 35° 179. Carcharias and Chimara, 421 352 1 80. Teeth of Cochliodus con- 354 tortus, 422 181. Raia marginata, 423 182. Lepidosiren annectens, 425 183. Spines and Teeth of Pal- aeozoic Elasmobranchii, 429 355 184. Hyla leucotcenia, 432 356 185. Siphonops annulatus, 434 1 86. Proteus aiiguinus, 436 360 187. Axolotl, 437 1 88. Triton cristatus. 438 189. Skeleton of the Frog, 439 196. Development of the Frog, 440 370 191. Footprints of a Labyrin- | thodont. 442 37i 192. Skull of a Serpent, 446 193- Diagram of the Circula- tion in Reptiles,. 447 374 194. Skeleton of Tortoise, 45° 375 195- Hawk's-bill Turtle, 452 196. Eye of Serpent and Head 377 of Viper, . 455 378 197. 198. Naja Haje, Head of Ringed Snake, 457 of Viper, and of Blind- 379 worm, 459 199. Iguana, 461 380 200. Blind-worm, 463 2OI. Common Skink, 464 38i 202. Head of Chameleon, 466 386 203. Crocodilus vulgaris, 469 204. Skull of Crocodtlus bipor- 388 catus, 470 389 205. Ichthyosaurus communis, 472 206. Plesiosaurus dolichodeirus , 473 39i 207. Dicynodon lacerticeps and 392 Oudenodon Bainii 474 208. Pterodactylus breviros- 394 tris, .... 476 209. Leg of Deinosaur, 478 394 210. Quill-feather, 482 211. Skull of Spur- winged 396 Goose, . . 485 LIST OF ILLUSTRATIONS. XXI 212. Pectoral arch and fore- limb of Penguin, 213. Fore-limb of Jer-falcon, . 214. Hind-limb of Loon, 215. Digestive System of the Common Fowl, Lung of Goose, Foot of Cormorant and Beak of Goose, 218. Jackass Penguin, . 219. Leg of Curlew, Head of Snipe, and Beak of Avocet, 220. Crested Heron, 221. Foot of Ostrich, and Breast-bone of Emeu, 222. Apteryx Australis, 223. Foot of Fowl, and Head of Guinea-fowl, . 224. Rock-pigeon, 225. Foot of Woodpecker, and Head of Love- bird, .... Purple-capped Lory, Feet and Heads of Inses- sores, 22%. Head of Bullfinch, 229. Foot of Peregrine Falcon, and Head of Buzzard, 230. Foot of Tawny Owl, and Head of White Owl, . 231. Head of Vulture, . 232. Arctuzopteryx macrura, . 233. Supposed footprint of Bird from the Trias of Connecticut, 234. Fore-limbs of Horse and Deer, . 235. Teeth of Chimpanzee, . 236. Ornithorhynchus para- doxus, 237. Pelvis of Kangaroo, 238. Koala or Kangaroo-bear, 239. Dentition of Thylacinns and Hypsiprymnus, . 240. Myrmecobius fasciatus, . 241. Hand of three -toed Sloth, . . . 242. Chlamyphoriis truncatus, 243. Dugong, . • .. / PAGE FIG. 244. 486 488 245- 490 246. 247. 492 248. 494 249. 502 250. 5°3 251. 252. 507 j 253. 509 254. 255- 512 256. 5H £ I N 257. 258. 259- 260. 520 26l. 521 262. 263. 523 264. 525 265. 266. 529 267. 529 268. 530 269. 531 270. 271. 533 272. 273- 542 546 556 274. 558 275" 560 276. 561 277. 564 278. 566 568 279. 280. Skull of Right Whale, . 573 Diagram of Baleen-plates of a Whale, . -575 Physeter macrocephalus, . 577 Delphinus defy his, . . 578 Tooth and vertebra 'of Zeuglodon cetoides, . 580 Feet of Ungulata, . 581 Head of Two -horned Rhinoceros, . . 583 Pal(zotherium magnum, . 584 Stomach of a Sheep, . 589 Skull of hornless Sheep, 590 Head of the Red-deer, . 593 Head of the Koodoo, . 596 Skull of the Indian Ele- phant, .... 600 Molarof Mastodon A rver- nensis, . . . 602 Skull of Deinotherium, . 603 Feet of Carnivora, . 604 Phoca grcenlandica, . 606 Skull of the Walrus, . 607 Skull of Jackal, . .614 Skull of Lion, . .615 Skull of Beaver, . .617 Common Hamster, . 621 Skeleton of Fox-bat, . 624 Head of Vampire-bat and Fox-bat, . . 625 Skull of Hedgehog, . 627 European Mole, . .627 Green Monkey, . . 630 Skulls of Orang and Euro- pean adult, . . 636 Jaw of Dromatherium, . 640 Jaws of Phascolotherium, Triconodon, Amphi- therium, and Plagi- aulax, . . .641 Skull of Diprotodon, . 642 Skeleton of Megathe- rium, • . • 643 Glyptodon clavipes, . 643 Skeleton of Megaceros Hibernicus, . . 644 Skeleton of Mastodon, . 646 Skeleton of Mammoth, . 647 Jaw of Trogontherium Cuvieri, . . • 648 ERRATA. age 58? H ie I, . ft >r garnules, re ad granules. 61, 17, • carcode, sarcode. 65, 42, . Foraminifera, Foramiiiifer . 103, 3; radiated, radiating. 112, 6, . Carsia, Sarsia. "7, 20, . Escholtz, Eschscholtz. 191, 23, • pervisceral, peri visceral. 273, 34, - movable, movably. 288, 41, . parthenogenical ly, parthenogenetically 293, 35, • Petropoda, Pteropoda. 316, 16, * . Trachiopoda, Brachiopoda. 37i? 1 8, . Allantoic, Allantois. 416, 22, . Lepadoganoids, Lepidoganoids. 577, 2, . Physteridtf, Physeteridff. 628, 39, • line, link. 635, 37, • hind-legs, hind-limbs. PART I. INVERTEBRATE ANIMALS. MANUAL OF ZOOLOGY. GENERAL INTRODUCTION, i. DEFINITION OF BIOLOGY AND ZOOLOGY. NATURAL HISTORY, strictly speaking, and as the term itself implies, should be employed to designate the study of all natural objects indiscriminately, whether these are endowed with life, or exhibit none of those incessant vicissitudes which collectively constitute vitality. So enormous, however, have been the conquests of science within the last century, that Natural History, using the term in its old sense, has of necessity been divided into several more or less nearly related branches. In the first place, the study of natural objects admits of an obvious separation into two primary sections, of which the first deals with the phenomena presented by the inorganic world, whilst the second is occupied with the investigation of the nature and relations of all bodies which exhibit life. The former department concerns the geologist and mineralogist, and secondarily the naturalist proper as well ; the latter department, treating as it does of living beings, is properly designated by the term Biology (from j§/o£, life, and Xoyos, a discourse). Biology, in turn, may be split up into the sciences of Botany and Zoology, the former dealing- with plants, the latter with animals; and it is really Zoology alone which is nowadays understood by the term Natural History. In determining, therefore, the limits and scope of Biology, we are brought at the very threshold of our inquiry to the question, What are the differences between dead and living bodies ? or rather, in the first place, what are the characteristics of an organised as compared with an unorganised body ? * * The differences between dead bodies on the one hand, and living bodies on the other, may be taken for all practical purposes as the same as those between unorganised and organised bodies. It is quite true that A MANUAL OF ZOOLOGY. 2. DIFFERENCES BETWEEN DEAD AND LIVING BODIES. In determining this somewhat difficult point, it will be best to examine the differences between organised and unorganised bodies seriatim, and to compare them together systematically under the following heads : — a. Chemical Composition. — Unorganised bodies are composed of many elements, which may be either simple or combined ; but the combinations are mostly limited to a small number of elements (forming binary and ternary compounds), and these are united in low combining proportions. Thus, carbonate of lime, or common limestone, is an excellent example of an in- organic body,* being a ternary compound composed of one atom of the metal calcium, three of oxygen, and one of carbon. Organised bodies, on the other hand, as well as those which, though dead, have been directly produced by the living organism, are composed of few chemical elements, and these are almost always combined. Furthermore, the combinations are always complex (ternary and quaternary compounds), and the elements enter into union in high combining proportions. Finally, the combinations are invariably characterised by the presence of water, and are prone to spontaneous decomposition. Thus, the great organic compound, albumen, is composed of 144 atoms of carbon, no of hydrogen, 18 of nitrogen, 2 atoms of sulphur, and 42 of oxygen. Iron, however, exists in the blood, very probably in its elemental condition ; and copper has been detected in the liver of certain Mammalia, and largely in the red colouring-matter of the feathers of certain birds. b. Arrangement of Parts. — Unorganised bodies are composed of an aggregation of homogeneous parts (when unmixed) which bear no definite and fixed relations to one another. Organised bodies are composed of heterogeneous parts, the relations of which amongst themselves are more or less definite. c. Form. — Unorganised bodies are either of no definite shape — when they are said to be "amorphous" — or they are crys- talline, in which case they are almost invariably bounded by certain living beings (Foraminiferd) cannot be said to be "organised" in the proper sense of the term ; still organisation is in such a vast proportion of cases the concomitant of vitality, that the purpose here in view will be fully served by assuming that all living bodies are organised, and all dead bodies are unorganised. * In another sense limestone may be said to be organic — namely, when it has been produced by the operations of living Beings ; but this does not affect the above definition. DEAD AND LIVING BODIES. 3 plane surfaces and straight lines. Organised bodies are always more or less definite in shape, presenting convex and concave surfaces, and being bounded by curved lines. d. Mode of Increase. — When unorganised bodies increase in size, as crystals do, the increase is produced simply by what is called " accretion ; " that is to say, by the addition of fresh particles from the outside. Organised bodies increase by what is often called the "in- tussusception " of matter ; in other words, by the reception of matter into their interior and its assimilation there. To this process alone can the term " growth " be properly applied. e. Cyclical Change. — Unorganised bodies exhibit no actions that are not purely physical or chemical, and they show no tendency to periodical vicissitudes. Organised bodies are pre- eminently distinguished by the tendency which they show to pass through spontaneous and cyclical changes. To sum up, all bodies which are composed of an aggrega- tion of diverse but definitely related parts, which have a defi- nite shape, bounded by curved lines and presenting concave and convex surfaces, which increase in size by the intussus- ception of foreign particles, and which pass through certain cyclical changes, are organised; and it is with the study of bodies such as these that Biology is concerned. In the foregoing it has been assumed, for the sake of sim- plicity, that all living bodies exhibit organisation. It is to be remembered, however, that there are living bodies (e.g., Fora- miniferd) to which the term of " organised/' as above defined, cannot be applied. Such bodies are living, but they are not organised. In these cases the distinction from dead matter depends wholly upon the mode of growth, and upon the presence of vital activity as shown by the occurrence of various periodic changes. The grand and fundamental characters by which living bodies are distinguished from dead bodies are these : — i. Every living body possesses the power of taking into its interior cer- tain foreign materials, and converting these into the substances required to build up fresh tissue or repair waste. By this power of " assimilation," as it is called, a living body grows. 2. Living bodies, as they are constantly assimilating fresh mat- ter, are incessantly losing portions of their substance — or, in other words, partial death is a constant accompaniment of life. 3. If our observation be continued for a sufficient length of time, we find that every living body has the power of repro- ducing its like. That is to say, every living body has, directly or indirectly, the power of giving origin to minute germs which 4 MANUAL OF ZOOLOGY. are developed into the likeness of the parent. 4. The matter of a living body is subject to the same physical and chemical forces as those which affect dead matter ; but it is further the seat of something in virtue of which the living body can over- ride the physical laws which control all dead matter. The living body is the seat of energy, and can overcome the pri- mary law of the inertia of matter. It has certain relations with the outer world other than those of mere passivity. However humble it may be, and even if it be permanently rooted to one place, some part or other of every living body possesses the power of spontaneous and independent move- ment— a power possessed by nothing that is dead. Living bodies, in short, possess the power of controlling and directing, and to some extent suspending, the action of the physical forces of the universe. 3. NATURE OF LIFE. We have next to determine — and the question is one of great difficulty — what connection exists between organisation and life. Is organisation essential to the manifestation of life, or can vital phenomena be exhibited by any body which is devoid of an organised structure ? In other words, is life the catftTVf- organisation, or the result of it ? And first, what do we mean by life ? Life has been variously defined by different writers. Bichat defines it as " the sum total of the functions which resist death ; " Treviranus, as " the constant uniformity of phenomena with diversity of external influences ; " Duges, as " the special acti- vity of organised bodies ; " and Beclard, as " organisation in action." All these definitions, however, are more or less objec- tionable, since they either really mean nothing, or the assump- tion underlies them that life is inseparably connected with organisation. In point of fact, no rigid definition of life appears to be at present possible, and it is best to regard it as being simply a tendency exhibited by certain forms of matter, under certain conditions, to pass through a series of changes in a more or less definite and determinate sequence. As regards the connection between life and organisation, it appears that whilst all organised bodies exhibit this ten- dency to change, and are therefore alive, all living beings are not necessarily organised. Many of the lowest forms of life (such as the Foraminifera amongst the Protozoa) fail to fulfil one of the most essential conditions of organisation, being devoid of definite parts or organs of any kind. Nevertheless, they NATURE OF LIFE. 5 are capable of manifesting all the essential phenomena of life ; they are produced from bodies . like themselves ; they eat, digest, and move, and exhibit distinct sensibility to many ex- ternal impressions. Furthermore, many of these little masses of structureless jelly possess the power of manufacturing for themselves, of lime, or of the still more intractable flint, external shells of surpassing beauty and mathematical regu- larity. In the face of these facts we are therefore compelled to come to the conclusion that life is truly the cause and not the consequence of organisation ; or, in other words, that organisation is not an intrinsic and indispensable condition of vital phenomena. Such an intrinsic and indispensable condition is, however, to be found in the1 presence of a " physical basis," to which has been applied the name of "protoplasm" (the "bioplasm" of Dr Beale). Without some such a material substratum or medium upon which to work, no one vital phenomenon can be exhibited. The necessary forces may be there, but in the absence of this necessary vehicle there can be no outward and visible manifestation of their existence. Life, therefore, as we know it, and as far as we know it, may be said to be insepar- ably connected with protoplasm.- In other words, protoplasm bears to life the same relation that a conductor does to the electric current. It is the sole medium through which life can be brought into relation with the external world. There is, however, as yet, no reason to believe that protoplasmic matter holds any other or higher relation to life, or that vital phenomena are in any way an inherent property of the matter by which alone they are capable of being manifested. As regards its nature, protoplasm, though capable of form- ing the most complex structures, does not necessarily exhibit anything which can be looked upon as organisation, or dif- ferentiation into distinct parts ; and its chemical composition is the only constant which can be approximately stated. It consists, namely, in all its forms, of the four elements, carbon, hydrogen, oxygen, and nitrogen, united into a proximate compound to which Mulder applied the name of " proteine," and which is very nearly identical with albumen or white-of- egg. It further appears probable that all forms of protoplasm can be made to contract by means of electricity, and " are liable to undergo that peculiar coagulation at a temperature of 4o°-5o° centigrade which has been called 'heat-stiffening'" (Huxley). If we admit, then, with Huxley— and the admission re- quires some qualifications— that "protoplasm, simple or 6 MANUAL OF ZOOLOGY. nucleated, is the formal basis of all life," * there, nevertheless, remain certain conditions equally indispensable to the external manifestation of vital phenomena; though life itself, or the power of exhibiting vital phenomena, may be preserved for a longer or shorter period, even though these conditions be ab- sent. These extrinsic conditions of vitality are, firstly, a cer- tain temperature varying from near the freezing-point to 1 20° or 130° ; secondly, the presence of water, which enters largely into the composition of all living tissues ; thirdly, the presence of oxygen in a free state — this, like water, appearing to be a sine qua non of life, though certain fungi are stated to offer an exception to this statement.t The non-fulfilment of any of these conditions for any length of time, as a rule, causes death, or the cessation of vitality ; but, as before remarked, life may sometimes remain in a dormant or " potential." condition for an apparently indefinite length of time. An excellent illustration of this is afforded by the great tenacity of life, even under unfavourable 'conditions, exhibited by the ova of some animals and the seeds of many plants ; but a more striking example is to be found in the Rotifera, or Wheel- animalcules. These are minute, mostly microscopic creatures, which inhabit almost all our -ponds and streams. Diminutive as they are, they are nevertheless, comparatively speaking, of a very high grade of organisation. They possess a mouth, masticatory organs, a stomach, and alimentary canal, a dis- tinct and well-developed nervous system, a differentiated reproductive apparatus, and even organs of vision. Repeated experiments, however, have shown the remarkable fact that, with their aquatic habits and complex organisation, the Roti- fers are capable of submitting to an apparently indefinite de- privation of the necessary conditions of their existence, without thereby losing their vitality. They may be dried and reduced to dust, and may be kept in this state for a period of many years ; nevertheless, the addition of a little water will at any time restore them to their pristine vigour and activity. It follows, therefore, that an organism may be deprived of all power of manifesting any of the phenomena which constitute * It has not yet been shown that the living matter which we designate by the convenient term of " protoplasm " has universally and in all cases a constant and undeviating chemical composition ; and there is, indeed, reason to believe that this is not the case. It is also certain that there are other materials, the exact use of which we do not at present know, which are absolutely essential to the maintenance of life, probably even in its humblest manifestations. t Recent experiments, as yet unconfirmed, would go to prove that these conditions of vitality are not of such essential importance. NATURE OF LIFK. 7 what we call life, without losing its hold upon the vital forces which belong to it. If, in conclusion, it be asked whether the term " vital force " is any longer permissible in the mouth of a scientific man, the question must, I think, be answered in the affirmative. Formerly, no doubt, the progress of science was retarded and its growth checked by a too exclusive reference of natural phenomena to a so-called vital force. Equally unquestionable is the fact that the development of Biological science has pro- gressed contemporaneously with the successive victories gained by the physicists over the vitalists. Still, no physicist has hitherto succeeded in explaining any fundamental vital phe- nomenon upon purely physical and chemical principles. The simplest vital phenomenon has in it something over and above the merely chemical and physical forces which we can demon- strate in the laboratory. It is easy, for example, to say that the action of the gastric juice is a chemical one, and doubt- less the discovery of this fact was a great step in physiological science. Nevertheless, in spite of the most searching inves- tigations, it is certain that digestion presents phenomena which are as yet inexplicable upon any chemical theory. This is exemplified in its most striking form, when we look at a simple organism like the Amoeba. This animalcule, which is structurally little more than a mobile lump of jelly, digests as perfectly — as far as the result to itself is concerned — as does the most highly organised animal with the most complex digestive apparatus. It takes food into its interior, it digests it without the presence of a single organ for the purpose; and, still more, it possesses that inexplicable selective power by which it assimilates out of its food such constituents as it needs, whilst it rejects the remainder. In the present state of our knowledge, therefore, we must conclude that even in the process of digestion, as exhibited in the Amoeba, there is some- thing that is not merely physical or chemical. Similarly, any organism when just dead consists of the same protoplasm as before, in the same forms, and with the same arrangement ; but it has most unquestionably lost a something by which all its properties and actions were modified, and some of them were produced. What that something is, we do not know, and perhaps never shall know ; and it is possible, though highly improbable, that future discoveries may demonstrate that it is merely a subtle modification of some physical force. _ In the meanwhile, as all vital actions exhibit this mysterious something, it would appear unphilosophical to ignore its exist- ence altogether, and the term " vital force" may therefore be MANUAL OF ZOOLOGY. retained with advantage. In using this term, however, it must not be forgotten that we are simply employing a con- venient expression for an unknown quantity, for that residual portion of every vital action which cannot at present be referred to the operation of any known physical force. It must, however, also be borne in mind that this residuum is probably not to be ascribed to our ignorance, but that it has a real existence. It appears, namely, in the highest degree probable that every vital action has in it something which is not merely physical and chemical, but which is conditioned by an unknown force, higher in its nature and distinct in kind as compared with all other forces. The presence of this " vital force " may be recognised even in the simplest phe- nomena of nutrition ; and no attempt even has hitherto been made to explain the phenomena of reproduction by the work- ing of any known physical or chemical force. 4. DIFFERENCES BETWEEN ANIMALS AND PLANTS. We have now arrived at some definite notion of the essen- tial characters of living beings in general, and we have next to consider what are the characteristics of the two great divisions of the organic world. What are the characters which induce us to place any given organism in either the vegetable or the animal kingdom ? What, in fact, are the differences between animals and plants ? It is generally admitted that all bodies which exhibit vital phenomena are capable of being referred to one of the two great kingdoms of organic nature. At the same time it is often extremely difficult in individual cases to come to any decision as to the kingdom to which a given organism should be referred, and in many cases the determination is purely arbitrary. So strongly, in fact, has this difficulty been felt, that some observers have established an intermediate kingdom, a sort of no-man's-land, for the reception of those debatable organisms which cannot be definitely and positively classed either amongst vegetables or amongst animals. Thus, Dr Ernst Haeckel has proposed to form an intermediate kingdom, which he calls the Regnum Protisticum, for the reception of all doubtful organisms. Even such a cautious observer as Dr Rolleston, whilst questioning the propriety of this step, is forced to conclude that " there are organisms which at one period of their life exhibit an aggregate of phenomena such as to justify us in speaking of them as animals, whilst at another they appear to be as distinctly vegetable." DIFFERENCES BETWEEN ANIMALS AND PLANTS. 9 In the case of the higher animals and plants there is no difficulty; the former being at once distinguished by the possession of a nervous system, of motor power which can be voluntarily exercised, and of an internal cavity fitted for the reception and digestion of solid food. The higher plants, on the other hand, possess no nervous system or organs of sense, are incapable of independent locomotion, and are not provided with an internal digestive cavity, their food being wholly fluid or gaseous. These distinctions, however, do not hold good as regards the lower and less highly organised members of the two kingdoms, many animals having no nervous system or internal digestive cavity, whilst many plants possess the power of locomotion ; so that we are compelled to institute a closer comparison in the case of these lower forms of life. a. Form. — As regards external configuration, of all charac- ters the most obvious, it must be admitted that no absolute distinction can be laid down between plants and animals. Many of our ordinary zoophytes, such as the Hydroid Polypes, the sea-shrubs and corals — as, indeed, the name zoophyte implies — are so similar in external appearance to plants that they were long described as such. Amongst the Molluscoida, the common sea-mat (Flustra) is invariably regarded by sea- side visitors as a sea-weed. Many of the Protozoa are equally like some of the lower plants (Protophyta) ; and even at the present day there are not wanting those who look upon the sponges as belonging to the vegetable kingdom. On the other hand, the embryonic forms, or "zoospores," of certain un- doubted plants (such as the Protococcus nivalis, Vaucheria, &c.) are provided with ciliated processes with which they swim about, thus coming so closely to resemble some of the Infusorian animalcules as to have been referred to that divi- sion of the Protozoa. b. Internal Structure. — Here, again, no line of demarcation can be drawn between the animal and vegetable kingdoms. In this respect all plants and animals are fundamentally similar, being alike composed of molecular, cellular, and fibrous tissues. c. Chemical Composition. — Plants, speaking generally, exhibit a preponderance of ternary compounds of carbon, hydrogen, and oxygen — such as starch, cellulose, and sugar — whilst nitrogenised compounds enter more largely into the compo- sition of animals. Still both kingdoms contain identical or representative compounds, though there may be a difference in the proportion of these to one another. Moreover, the most characteristic of all vegetable compounds — viz., cellulose — has been detected in the outer covering of the sea-squirts, IO MANUAL OF ZOOLOGY. or Ascidian Molluscs ; and the so-called " glycogen," which is secreted by the liver of the Mammalia, is closely allied to, if not absolutely identical with, the hydrated starch of plants. As a general rule, however, it may be stated that the presence in any organism of an external envelope of cellulose raises a strong presumption of its vegetable nature. In the face, however, of the facts above stated, the presence of cellulose cannot be looked upon as absolutely conclusive. Another highly charac- teristic vegetable compound is chlorophyll, the green colouring- matter of plants. Any organism which exhibits chlorophyll in any quantity, as a proper element of its tissues, is most probably vegetable. As in the case of cellulose, however, the presence of chlorophyll cannot be looked upon as a certain test, since it occurs normally in certain undoubted animals (e.g., Stentor, amongst the Infusoria, and the Hydra viridis, or the green Fresh-water Polype, amongst the Ccelenteratd). d. Motor Power. — This, though broadly distinctive of ani- mals, can by no means be said to be characteristic of them. Thus, many animals in their mature condition are permanently fixed, or attached to some foreign object ; and the embryos of many plants, together with not a few adult forms, are endowed with locomotive power by means of those vibratile, hair-like processes which are called " cilia," and are so characteristic of many of the lower forms of animal life. Not only is this the case, but large numbers of the lower plants, such as the Diatoms and Desmids, exhibit throughout life an amount and kind of locomotive power which does not admit of being rigidly separated from the movements executed by animals, though the closest researches have hitherto failed to show the mechanism whereby these movements are brought about. e. Nature of the Food. — Whilst all the preceding points have failed to yield a means of invariably separating animals from plants, a distinction which holds good almost without excep- tion is to be found in the nature of the food taken respectively by each, and in the results of the conversion of the same. The unsatisfactory feature, however, in this distinction is this, that even if it could be shown to be, theoretically, invariably true, it would nevertheless be practically impossible to apply it to the greater number of those minute organisms concerning which alone there can be any dispute. As a broad rule, all plants are endowed with the power of converting inorganic into organic matter. The food of plants consists of the inorganic compounds, carbonic acid, ammonia, and water, along with small quantities of certain mineral salts. From these, and from these only, plants are capable of elabo- DIFFERENCES BETWEEN ANIMALS AND PLANTS. I I rating the proteinaceous matter or protoplasm which consti- tutes the physical basis of life. Plants, therefore, take as food very simple bodies, and manufacture them into much more complex substances. In other words, by a process of deoxida- tion or unburning, rendered possible by the influence of sun- light only, plants convert the inorganic or stable elements — ammonia, carbonic acid, water, and certain mineral salts— into the organic or unstable elements of food. The whole problem of nutrition may be narrowed to the question as to the modes and laws by which these stable elements are raised by the vital chemistry of the plant to the height of unstable compounds. To this general statement, however, an exception must seem- ingly be made in favour of certain fungi, which require organ- ised compounds for their nourishment. On the other hand, no known animal possesses the power of converting inorganic compounds into organic matter, but all, mediately or immediately, are dependent in this respect upon plants. All animals, as far as is certainly known, require ready-made proteinaceous matter for the maintenance of exist- ence, and this they can only obtain in the first instance from plants. Animals, in fact, differ from plants in requiring as food complex organic bodies which they ultimately reduce to very much simpler inorganic bodies. The nutrition of animals is a process of oxidation or burning, and consists essentially in the conversion of the energy of the food into vital work ; this conversion being effected by the passage of the food into living tissue. Plants, therefore, are the great manufacturers in nature, — animals are the great consumers. Just, however, as this law does not invariably hold good for plants, certain fungi being in this respect animals, so it is not impossible that a limited exception to the universality of the law will be found in the case of animals also. Thus, in some recent investigations into the fauna of the sea at great depths, a singular organism, of an extremely low type, but occupying large' areas of the sea-bottom, has been discovered, to which Professor Huxley has given the name of Bathybius. As vegetable life is extremely scanty, or is altogether wanting, in these abysses of the ocean, it has "been conjectured that this organism is possibly endowed with the power — otherwise exclusively found in plants — of elaborating organic compounds out of inorganic materials, and in this way supplying food for the higher animals which surround it. The water of the ocean, however, at these enormous depths, is richly charged with organic matter in solution, and this conjecture is thereby rendered doubtful. I 2 MANUAL OF ZOOLOGY. Be this as it may, there remain to be noticed two distinc- tions, broadly though not universally applicable, which are due to the nature of the food required respectively by animals and plants. In the first place, the food of all plants consists partly of gaseous matter and partly of matter held in solution. They require, therefore, no special aperture for its admission, and no internal cavity for its reception. The food of almost all animals consists of solid particles, and they are therefore usually provided with a mouth and a distinct digestive cavity. Some animals, however, such as the tape-worm and the Gre- garinae, live entirely by the imbibition of organic fluids through the general surface of the body,, and many have neither a dis- tinct mouth nor stomach. Secondly, plants decompose carbonic acid, retaining the carbon and setting free the oxygen, certain fungi forming an exception to this law. The reaction of plants upon the atmo- sphere is therefore characterised by the production of free oxygen. Animals, on the other hand, absorb oxygen and emit carbonic acid, so that their reaction upon the atmosphere is the reverse of that of plants, and is characterised by the pro- duction of carbonic acid. Finally, it is worthy of notice that it is in their lower and not in their higher developments that the two kingdoms of organic nature approach one another. No difficulty is ex- perienced in separating the higher animals from the higher plants, and for these universal laws can be laid down to which there is no exception. It might, not unnaturally, have been thought that the lowest classes of animals would exhibit most affinity to the highest plants, and that thus a gradual passage between the two kingdoms would be established. This is not the case, however. The lower animals are not allied to the higher plants, but to the lower ; and it is in the very lowest members of the vegetable kingdom, or in the embryonic and immature forms of plants little higher in the scale, that we find such a decided animal gift as the power of independent locomotion. It is also in the less highly organised and less specialised forms of plants that we find the only departures from the great laws of vegetable life, the deviation being in the direction of the laws of animal life. 5. MORPHOLOGY AND PHYSIOLOGY. The next point which demands notice relates to the nature of the differences between one animal and another, and the question is one of the highest importance. Every animal — DIFFERENCES BETWEEN DIFFERENT ANIMALS. I 3 as every plant— may be regarded from two totally distinct, and, indeed, often apparently opposite, points of view. From the first point of view we have to look simply to the laws, form, and arrangement of the structures of the organism ; in short, to its external shape and internal structure. This con- stitutes the science of morphology (^oop^ form, and Xoyo?, dis- course). From the second, we have to study the vital actions performed by living beings and \htfunctions discharged by the different parts of the organism. This constitutes the science of physiology. A third department of zoology is concerned with the rela- tions of the organism to the external conditions under which it is placed, constituting a division of the science to which the term " distribution " is applied. Morphology, again, not only treats of the structure of living beings in their fully-developed condition (anatomy), but is also concerned with the changes through which every living being has to pass before it assumes its mature or adult charac- ters (embryology or development). The term " histology " is further employed to designate that branch of morphology which is specially occupied with the investigation of minute or micro- scopical tissues. Physiology treats of all the functions exercised by living bodies, or by the various definite parts or organs, of which most animals are composed. All these functions come under three heads : — i. Functions of Nutrition, divisible into func- tions of absorption and metamorphosis, comprising those func- tions which are necessary for the growth and maintenance of the organism. 2. Functions of Reproduction, whereby the per- petuation of the species is secured. 3. Functions of Correlation, comprising all those functions (such as sensation and voluntary motion) by which the external world is brought into relation with the organism, and the organism in turn reacts upon the external world. Of these three, the functions of nutrition and reproduction are often collectively called the functions of organic or vege- tative life, as being common to animals and plants ; while the functions of correlation are called the animal functions, as being more especially characteristic of, though not peculiar to, animals. 6. DIFFERENCES BETWEEN DIFFERENT ANIMALS. All the innumerable differences which subsist between dif- ferent animals may be classed under two heads, corresponding to the two aspects of every living being, morphological and 14 MANUAL OF ZOOLOGY. physiological. One animal differs from another either morpho- logically, in the fundamental points of its structure ; or physio- logically, in the manner in which the vital functions of the organism are discharged. These constitute the only modes in which any one animal can differ from any other; and they may be considered respectively under the heads of Specialisation of Function and Morphological type. a. Specialisation of function. — All animals alike, whatever their structure may be, perform the three great physiological functions ; that is to say, they all nourish themselves, repro- duce their like, and have certain relations with the external world. They differ from one another physiologically in the manner in which these functions are performed. Indeed, it is only in the functions of correlation that it is possible that there should be any difference in the amount or perfection of the function performed by the organism, since nutrition and repro- duction, as far as their results are concerned, are essentially the same in all animals. In the manner, however, in which the same results are brought about, great differences are observable in different animals. The nutrition of such a simple organism as the Amoeba is, indeed, performed perfectly, as far as the result to the animal itself is concerned — as perfectly as in the case of the highest animal — but it is performed with the simplest possible apparatus. It may, in fact, be said to be performed without any special apparatus, since any part of the surface of the body may be extemporised into a mouth, and there is no differentiated alimentary cavity. And not only is the nutritive apparatus of the simplest character, but the function itself is equally simple, and is entirely divested of those complexities and separations into secondary functions which characterise the process in the higher animals. It is the same, too, with the functions of reproduction and correlation ; but this point will be more clearly brought out if we examine the method in which one of the three primary functions is performed in two or three examples. Nutrition, as the simplest of the functions, will best answer the purpose. In the simpler Protozoa, such as the Amoeba, the process of nutrition consists essentially in the reception of food, its digestion within the body, the excretion of effete or indigestible matter, and the distribution of the nutritive fluid through the body. The first three portions of this process are effected with- out any special organs for the purpose, and for the last there is simply a rudimentary contractile cavity. Respiration, if it can be said to exist at all as a distinct function,, is simply effected by the general surface of the body. DIFFERENCES BETWEEN DIFFERENT ANIMALS. I 5 In a Ccelenterate animal, such as a sea-anemone, the func- tion of nutrition has not advanced much in complexity, but the means for its performance are somewhat more specialised. Permanent organs of prehension (tentacles) are present, there is a distinct mouth, and there is a persistent internal cavity for the reception of the food ; but this is not shut off from the general cavity of the body, and there are no distinct circulatory or respiratory organs. In a Mollusc, such as the oyster, nutrition is a much more complicated process. There is a distinct mouth, and an ali- mentary canal which is shut off from the general cavity of the body, and is provided with a separate aperture for the excre- tion of effete and indigestible matters. Digestion is performed by a distinct stomach with accessory glands ; a special contrac- tile cavity, or heart, is provided for the propulsion of the nutri- tive products of digestion through all parts of the organism, and the function of respiration is performed by complex organs specially adapted for the purpose. It is not necessary here to follow out this comparison further. In still higher animals the function of nutrition becomes still further broken up into secondary functions, for the due performance of which special organs are provided, the complexity of the organism thus necessarily increasing part passu with the complexity of the function. This gradual sub- division and elaboration is carried out equally with the other two physiological functions — viz., reproduction and correlation — and it constitutes what is technically called the " specialisa- tion of functions," though it has been more happily termed by Milne-Edwards " the principle of the physiological division of labour." It is needless, however, to remark that in the higher animals it is the functions of correlation which become most highly specialised — disproportionately so, indeed, when com- pared with the development of the nutritive and reproductive functions. b. Morphological Type. — The first point in which one animal may differ from another is the degree to which the principle of the physiological division of labour is carried. The second point in which one animal may differ from another is in its " morphological type ; " that is to say, in the funda- mental plan upon which it is constructed. By one not specially acquainted with the subject it might be readily imagined that each species or kind of animal was constructed upon a plan peculiar to itself and not shared by any other. This, how- ever, is far from being the case ; and it is now universally recognised that all the varied species of animals — however I 6 MANUAL OF ZOOLOGY. great the apparent amount of diversity amongst them — may be arranged under no more than half-a-dozen primary morpho- logical types or plans of structure. Upon one or other of these five or six plans every known animal, whether living or extinct, is constructed. It follows from the limited number of primitive types or patterns, that great numbers of animals must agree with one another in their morphological type'. It follows also that all so agreeing can differ from one another only in the sole remaining element of the question — namely, by the amount of specialisation of function which they exhibit. Every animal, therefore, as Professor Huxley has well expressed it, is the resultant of two tendencies, the one morphological, the other physiological. The six types or plans of structure, upon one or other of which all known animals have been constructed, are techni- cally called " sub-kingdoms," and are known by the names Protozoa, Ccelenterata, Annuloida, Annulosa, Mollusca, and Vertebrata. We have, then, to remember that every member of each of these primary divisions of the animal kingdom agrees with every other member of the same division in being formed upon a certain definite plan or type of structure, and differs from every other simply in the grade of its organisation, or, in other words, in the degree to which it exhibits specialisa- tion of function. VON BAER'S LAW OF DEVELOPMENT. — As the study of living beings in their adult condition shows us that the differences between those which are constructed upon the same morpho- logical type depend upon the degree to which specialisation of function is carried, so the study of development teaches us that the changes undergone by any animal in passing from the embryonic to the mature condition are due to the same cause. All the members of any given sub-kingdom, when examined in their earliest embryonic condition, are found to present the same fundamental characters. As development proceeds, however, they diverge from one another with greater or less rapidity, until the adults ultimately become more or less different, the range of possible modification being ap- parently almost illimitable. The differences are due to the different degrees of specialisation of function necessary to perfect the adult ; and therefore, as Von Baer put it, the pro- gress of development is from the general to the special. It is upon a misconception of the true import of this law that the theory arose, that every animal in its development passed through a series of stages in which it resembles, in turn, the different inferior members of the animal scale. With HOMOLOGY, ANALOGY, AND HOMOMORPHISM. I 7 regard to man, standing at the top of the whole animal kingdom, this theory has been expressed as follows : " Human organ ogenesis is a transitory comparative anatomy, as, in its turn, comparative anatomy is a fixed and permanent state of the organogenesis of man" (Serres). x In other words, the embryo of a Vertebrate animal was believed to pass through a series of changes corresponding respectively to the permanent types of the lower sub-kingdoms — namely, the Protozoa, Cce- lenterata, Annuloida, Annulosa, and Mollusca — before finally assuming the true vertebrate characters. Such, however, is not truly the case. The ovum of every animal is from the first impressed with the power of developing in one direction only, and very early exhibits the fundamental characters proper to its sub-kingdom, never presenting the structural peculiari- ties belonging to any other morphological type. Neverthe- less, the differences which subsist between the members of each sub-kingdom in their adult condition are truly referable to the degree to which development proceeds, the place of each individual in his own sub-kingdom being regulated by the stage at which development is arrested. Thus, many cases are known in which the younger stages of a given animal represent the permanent adult condition of an animal some- what lower in the scale. To give a single example, the young Gasteropod (amongst the Mollusca) transiently presents all the essential characters which permanently distinguish the adult Pteropod. The development of the Gasteropod, however, pro- ceeds beyond this point, and the adult is much more highly specialised than is the adult Pteropod. 7. HOMOLOGY, ANALOGY, AND HOMOMORPHISM. When organs in different animals agree with one another in fundamental structure, they are said to be " homologous ; " when they perform the same functions they are said to be " analogous." Thus the wing of a bird and the arm of a man are constructed upon the same fundamental plan, and they are therefore homologous organs. They are not analogous, however, since they do not perform the same function, the one being adapted for aerial locomotion, the other being an organ of prehension. On the other hand, the wings of a bird and the wings of an insect both serve for flight, and they are therefore analogous, since they perform the same function. They are not homologous, however, as they are constructed upon wholly dissimilar plans. There are numerous cases, however, in which organs correspond with one another both B I 8 MANUAL OF ZOOLOGY. structurally and functionally, in which case they are both homologous and analogous. A form of homology is often seen in a single animal in which there exists a succession of parts which are fundamentally identical in structure, but are variously modified to fulfil dif- ferent functions. Thus a Crustacean — such as the lobster — may be looked upon as being composed of a succession of rings, each of which bears a pair of appendages, these appen- dages being constructed upon the same type, and being there- fore homologous. They are, however, variously modified in different regions of the body to enable them to fulfil special functions, some being adapted for swimming, others for walk- ing, others for prehension, others for mastication, and so on. This succession of fundamentally similar parts in the same animal constitutes what is known as 'serial homology. When, however, the successive parts are similar to one another, both in structure and in function, the case becomes rather one of what is called "vegetative" or "irrelative repetition." An ex- cellent instance of this is seen in the common Millipede (lulus). Homomorphism. — Many examples occur, both among animals and among plants, in which families widely removed from one another as to their fundamental structure, nevertheless, pre- sent a singular, and sometimes extremely close, resemblance in their external characters. Thus the composite Hydroid Polypes and the Polyzoa are singularly like one another — so much so, that they have often been classed together; whereas, in reality, they belong to different sub-kingdoms. Many other cases of this resemblance of different animals might be adduced, and in many cases these " representative forms " appear to be able to fill each other's places in the general economy of nature. This is so far true, at any rate, that " homomorphous " forms are generally found in different parts of the earth's surface. Thus, the place of the Cacti of South America is taken by the Euphorbias of Africa ; or, to take a zoological illustration, many of the different orders of Mammalia are represented in the single order Marsupialia in Australia, in which country this order has almost alone to discharge the functions elsewhere performed by several orders. Many homomorphous forms, however, live peacefully side by side, and it is difficult to say whether in this case the resem- blance between them is for the advantage or for the disadvan- tage of either. In other cases we find certain animals putting on the external characters of certain other animals, to which they may be closely related, or from which they may be widely separated in zoological position. Such cases are said to be CORRELATION OF GROWTH. I g examples of "mimicry," and such animals are said to be " mimetic." Excellent examples of this may be found amongst certain Butterflies, or in the close resemblance of the clear- winged Moths to Bees and Hornets. In all these cases it appears that the mimetic species is protected from some enemy by its outward similarity to the form which it mimics. Finally, there are numerous cases in which animals mimic certain natural objects, and thus greatly diminish their chances of being detected by their natural foes. Excellent instances of this are afforded by the insects known as Walking-leaves (Phyllium) and Walking-sticks (Phasmida), which respectively present the most singular resemblance to leaves and dried twigs. The student, however, must carefully guard himself against supposing that the term "mimicry" implies any conscious action on the part of the mimetic species; there being no evidence to support such a view. 8. CORRELATION OF GROWTH. This term is employed by zoologists to express the empiri- cal law, that certain structures, not necessarily or usually con- nected together by any visible link, invariably occur in associa- tion with one another, and never occur apart — so far, at any rate, as human observation goes. Thus, all animals which possess two condyles on the occi- pital bone, and possess non-nucleated red blood-corpuscles, suckle their young. Why an animal with only one condyle on its occipital bone should not suckle its young we do not know, and perhaps we shall at some future time find mam- mary glands associated with a single occipital condyle. Again, the feet are cleft in all animals which ruminate, but not in any other. In other cases the correlation is even more appa- rently lawless, and is even amusing. Thus all, or almost all, cats which are entirely white and have blue eyes, are at the same time deaf With regard to these and similar gene- ralisations we must, however, bear in mind the following three points : — 1. The various parts of the organisation of any animal are so closely interconnected, and so mutually dependent upon one another, both in their growth and development, that the characters of each must be in some relation to the characters of all the rest, whether this be obviously the case or not. 2. It is rarely possible to assign any reason for correlations of structure, though they are certainly in no case accidental. 3. The law is a purely empirical one, and expresses nothing 2O MANUAL OF ZOOLOGY. more than the result of experience ; so that structures which we now only know as occurring in association, may ultimately be found dissociated, and conjoined with other structures of a different character. 9. CLASSIFICATION. Classification is the arrangement of a number of diverse objects into larger or smaller groups, according as they ex- hibit more or less likeness to one another. The excellence of any given classification will depend upon the nature of the points which are taken as determining the resemblance. Sys- tems of classification, in which the groups are founded upon mere external and superficial points of similarity, though often useful in the earlier stages of science, are always found in the long-run to be inaccurate. It is needless, in fact, to point out that many living beings, the structure of which is fundamentally different, may nevertheless present such an amount of adaptive external resemblance to one another, that they would be grouped together in any " artificial " classifi- cation. Thus, to take a single example, the whale, by its external characters, would certainly be grouped amongst the fishes, though widely removed from them in all the essential points of its structure. " Natural " systems of classification, on the other hand, endeavour to arrange animals into divi- sions founded upon a due consideration of all the essential and fundamental points of structure, wholly irrespective of external similarity of form and habits. Philosophical classifi- cation depends upon a due appreciation of what constitute the true points of difference and likeness amongst animals ; and we have already seen that these are morphological type and specialisation of function. Philosophical classification, therefore, is a formal expression of the facts and laws of Morphology and Physiology. It follows that the more fully the programme of a philosophical and strictly natural classifi- cation can be carried out, the more completely does it afford a condensed exposition of the fundamental construction of the objects classified. Thus, if the whale were placed by an arti- ficial grouping amongst the fishes, this would simply express the facts that its habits are aquatic and its body fish-like. When, on the contrary, we obtain a natural classification, and we learn that the whale is placed amongst the Mammalia, we then know at once that the young whale is born in a compa- ratively helpless condition, and that its mother is provided with special mammary glands for its support ; this expressing CLASSIFICATION. 2 I a fundamental distinction from all fishes, and being associated with other equally essential correlations of structure. The entire animal kingdom is primarily divided into some half-a-dozen great plans of structure, the divisions thus formed being called "sub-kingdoms." The sub-kingdoms are, in turn, broken up into classes, classes into orders, orders into families, families into genera, and genera into species. We shall examine these successively, commencing with the consideration of a species, since this is the zoological unit of which the larger divisions are made up. Species. — No term is more difficult to define than " species," and on no point are zoologists more divided than as to what should be understood by this word. Naturalists, in fact, are not yet agreed as to whether the term species expresses a real and permanent distinction, or whether it is to be regarded merely as a convenient, but not immutable, abstraction, the employment of which is necessitated by the requirements of classification. By Buffon, " species " is defined as " a constant succession of individuals * similar to and capable of reproducing each other/' De Candolle defines species as an assemblage of all those individuals which resemble each other more than they do others, and are able to reproduce their like, doing so by the generative process, and in such a manner that they may be supposed by analogy to have all descended from a single being or a single pair. M. de Quatrefages defines species as " an assemblage of individuals, more or less resembling one another, which are de- scended, or may be regarded as being descended, from a single primitive pair by an uninterrupted succession of families." Miiller defines species as "a living form, represented by in- dividual beings, which reappears in the product of generation with certain invariable characters, and is constantly repro- duced by the generative act of similar individuals." According to Pritchard, a species is constituted by "separate origin and distinctness of race, evinced by a constant trans- mission of some characteristic peculiarity of organisation." According to Woodward, "all the specimens, or individuals, which are so much alike that we may reasonably believe them to have descended from a common stock, constitute a species" From the above definitions it will be at once evident that * In using the term "individual," it. must be borne in mind that the " zoological individual " is meant ; that is to say, the total result of the development of a single ovum, as will be hereafter explained at greater length. 2 2 MANUAL OF ZOOLOGY. there are two leading ideas in the minds of zoologists when they employ the term species ; one of these being a certain amount of resemblance between individuals, and the other being the proof that the individuals so resembling each other have descended from a single pair, or from pairs exactly simi- lar to one another. The characters in which individuals must resemble one another in order to entitle them to be grouped in a separate species, according to Agassiz, " are only those determining size, proportion, colour, habits, and relations to surrounding circumstances and external objects." On a closer examination, however, it will be found that these two leading ideas in the definition of species — external resemblance and community of descent — are both defective, and liable to break down if rigidly applied. Thus, there are in nature no assemblages of plants or animals, usually grouped together into a single species, the individuals of which exactly resemble one another in every point. Every naturalist is compelled to admit that the individuals which compose any so-called species, whether of plants or animals, differ from one another to a greater or less extent, and in respects which may be regarded as more or less important. The existence of such individual differences is attested by the universal employment of the terms " varieties " and " races." Thus a "variety" comprises all those individuals which possess some distinctive peculiarity in common, but do not differ in other respects from another set of individuals sufficiently to entitle them to take rank as a separate species. A " race," again, is simply a permanent or " perpetuated " variety. The question, however, is this — How far may these differences amongst in- dividuals obtain without necessitating their being placed in a separate species ? In other words : How great is the amount r ° / two animals, one of which belongs to a lower morphological f type than the other, no degree of specialisation of function, however great, will place the former above the latter, as far as its type of structure is concerned, though it may make the former a more highly organised animal. Every Vertebrate animal, for example, belongs to a higher morphological type than every Mollusc ; but the higher Molluscs, such as cuttle- fishes, are much more highly organised, as far as their type is concerned, than are the lowest Vertebrata. In a linear classi- fication, therefore, the cuttle-fishes should be placed above the lowest fishes — such as the lancelet — in spite of the fact that the type upon which the latter are constructed is by far the highest of the two. It is obvious, therefore/ that a linear classification is not possible, since the higher members of each sub-kingdom are more highly organised than the lower forms of the next sub- kingdom in the series, at the same time that they are con- structed upon a lower morphological type. In the words of Professor Allen Thomson, " it has become more and more apparent in the progress of morphological research, that the different groups form circles which touch one another at certain points of greatest resemblance, rather than one continuous line, or even a number of lines which partially pass each other." In the same way the highest vegetables do not approximate to, or graduate into, the lowest animals ; but, " each kingdom presents, as it were, a radiating expansion into groups for itself, so that the relations of the ' two kingdoms might be represented by the divergence of lines spreading in two different directions from a common point." 10. REPRODUCTION. Reproduction is the process whereby new individuals are generated and the perpetuation of the species insured. The methods in which this end may be attained exhibit a good deal of diversity, but they may be all considered under two heads. I. Seocual Reprodtiction. — This consists essentially in the production of two distinct elements, a germ-cell or ovum, and a sperm-cell or spermatozoid, by the contact of which the ovum — now said to be " fecundated" — is enabled to develop itself into a new individual. As a rule, the germ-cell is pro- duced by one individual (female) and the spermatic element by another (male) ; in which case the sexes are said to be dis- tinct, and the species is said to be "dioecious." In other 26 MANUAL OF ZOOLOGY. cases the same individual has the power of producing both the essential elements of reproduction ; in which case the sexes are said to be united, and the individual is said to be " her- maphrodite," " androgynous," or "monoecious." In the case of hermaphrodite animals, however, self-fecundation — contrary to what might have been expected — rarely constitutes the re- productive process ; and, as a rule, the reciprocal union of two such individuals is necessary for the production of young. Even amongst hermaphrodite plants, where self-fecundation may, and certainly does, occur, provisions seem to exist by which perpetual self-fertilisation is prevented, and the influence of another individual secured at intervals.* Amongst the higher animals sexual reproduction is the only process whereby new individuals can be generated. II. Non-sexual Reproduction. — Amongst the lower animals fresh beings may be produced without the contact of an ovum and a spermatozoid ; that is to say, without any true generative act. The processes by which this is effected vary in different animals, and are all spoken of as forms of "asexual" or " agamic " reproduction. As we shall see, however, the true " individual " is very rarely produced otherwise than sexually, and most forms of agamic reproduction are really modifica- tions of growth. a. Gemmation and Fission. — Gemmation, or budding, con- sists in the production of a bud, or buds, generally from the exterior, but sometimes from the interior, of the body of an animal, which buds are developed into independent beings, which may or may not remain permanently attached to the parent organism. Fission differs from gemmation solely in the fact that the new structures in the former case are pro- duced by a division of the body of the original organism into separate parts, which may remain in connection, or may under- go detachment. The simplest form of gemmation, perhaps, is seen in the power possessed by certain animals of reproducing parts of their bodies which they may have lost. Thus, the Crustacea possess the power of reproducing a lost limb, by means of a bud which is gradually developed till it assumes the form and takes the place of the missing member. In these cases, how- * It seems to have been established as a strong probability by Darwin, Hildebrandt, and Delpino, that in the great majority of plants self-fecunda- tion never occurs, but the plant is fertilised by the intervention of insects. Thus, in many plants, the stamens and pistil arrive at maturity at different times, whilst in others the stamens and stigma are placed at different heights in the flower, and do not always occupy the same position even in a single species. REPRODUCTION. 2 J ever, the process is not in any way generative, and the pro- duct of gemmation can in no sense be spoken of as a distinct being (or zooid). Another form of gemmation may be exemplified by what takes place in the Foraminifera, one of the classes of the Protozoa. The primitive form of a Foraminifer is simply a little sphere of sarcode, which has the power of secreting from its outer surface a calcareous envelope ; and this condition may be permanently retained (as in Lagena). In other cases a process of budding or gemmation takes place, and the primi- tive mass of sarcode produces from itself, on one side, a second mass exactly similar to the first, which does not detach itself from its parent, but remains permanently connected with it. This second mass repeats the process of gemmation as before, and this goes on — all the segments remaining attached to one another— until a body is produced, which consists of a number of little spheres of sarcode in organic connection with one another, and surrounded by a shell, often of the most complicated description. In this case, however, the buds produced by the primitive spherule are not only not detached, but they can only remotely be regarded as inde- pendent beings. They are, in all respects, identical with the primordial segment, and it is rather a case of " vegetative " repetition of similar parts. Another form of gemmation is exhibited in such an organ- ism as the common sea-mat (Flustra), which is a composite organism composed of a multitude of similar beings, each of which inhabits a little chamber, or cell ; the whole forming a structure not unlike a sea-weed in appearance. This colony is produced by gemmation from a single primitive being (" poly- pide "), which throws out buds, each of which repeats the pro- cess, apparently almost indefinitely. All the buds remain in contact and connected with one another, but each is, neverthe- less, a distinct and independent being, capable of performing all the functions of life. In this case, therefore, each one of the innumerable buds becomes an independent being, similar to, though not detached from, the organism which gave it birth. This is an instance of what is called "continuous gemmation." In other cases — as in the common fresh-water polype or Hydra— the buds which are thrown out by the primitive or- ganism become developed into creatures exactly resembling the parent, but, instead of remaining permanently attached, and thus giving rise to a compound organism, they are De- tached to lead an entirely independent existence. This is a simple instance of what is termed "discontinuous gemmation." 28 MANUAL OF ZOOLOGY. The method and results of fission may be regarded as essen- tially the same as in the case of gemmation. The products of the division of the body of the primitive organism may either remain undetached, when they will give rise to a com- posite structure (as in many corals), or they may be thrown off and live an independent existence (as in some of the Hydrozoa). We are now in a position to understand what is meant, strictly speaking, by the term " individual." In zoological lan- guage, an individual is defined as " equal to the total result of the development of a single ovum" Amongst the higher animals there is no difficulty about this, for each ovum gives rise to no more than one single being, which is incapable of repeating it- self in any other way than by the production of another ovum ; so that an individual is a single animal. It is most import- ant, however, to comprehend that this is not necessarily or always the case. In such an organism as the sea-mat, the ovum gives rise to a primitive polypide, which repeats itself by a process of continuous gemmation until an entire colony is produced, each member of which is independent of its fellows, and is capable of producing ova. In such a case, therefore, the term " individual " must be applied to the entire colony, since this is the result of the development of a single ovum. The separate beings which compose the colony are technically called " zooids." In like manner the Hydra, which produces fresh and independent Hydrae by discontinuous gemmation, is not an " individual," but is a zooid. Here the zooids are not permanently united to one another, and the "individual " Hydra consists really of the primitive Hydra, plus all the detached Hydrae to which it gave rise. In this case, therefore, the " indi- vidual " is composed of a number of disconnected and wholly independent beings, all of which are the result of the develop- ment of a single ovum. It is to be remembered that both the parent zooid and the " produced zooids " are capable of giving rise to fresh Hydrae by a true generative process. It must also be borne in mind that this production of fresh zooids by a process of gemmation is not so essentially different to the true sexual process of reproduction as might at first sight appear, since the ovum itself may be regarded merely as a highly spe- cialised bud. In the Hydra, in fact, where the ovum is pro- duced as an external process of the wall of the body, this like- ness is extremely striking. The ovarian bud, however, differs from the true gemmae or buds in its inability to develop itself into an independent organism, unless previously brought into ' contact with another special generative element. The only REPRODUCTION. 29 exceptions to this statement are in the rare cases of true "par- thenogenesis," to be subsequently alluded to. b. Reproduction by Internal Gemmation. — Before . considering the phenomena of " alternate generations," it will be as well to glance for a moment at a peculiar form of gemmation ex- hibited by some of the Polyzoa, which is in some respects intermediate between ordinary discontinuous gemmation and alternation of generations. These organisms are nearly allied to the sea-mat, already spoken of, and, like it, can reproduce themselves by continuous gemmation (forming colonies), by a true sexual process, and rarely by fission. In addition to all these methods they can reproduce themselves by the formation of peculiar internal buds, which are called " statoblasts." These buds are developed upon a peculiar cord, which crosses the body-cavity, and is attached at one end to the fundus of the stomach. When mature they drop off from this cord, and lie loose in the cavity of the body, whence they are liberated on the death of the parent organism. When thus liberated, the statoblast, after a longer or shorter period, ruptures and gives exit to a young Polyzoon, which has essentially the same structure as the adult. It is, however, simple, and has to undergo a process of continuous gemmation before it can assume the compound form proper to the adult. As regards the nature of these singular bodies, " the in- variable absence of germinal vesicle and germinal spot, and their never exhibiting the phenomena of yelk-cleavage, inde- pendently of the conclusive fact that true ova and ovary occur elsewhere in the same individual, are quite decisive against their being eggs. We must then look upon them as gemmce peculiarly encysted, and destined to remain for a period in a quiescent or pupa-like state " (Allman). c. Alternation of Generations. — In the case of the Hydra and the sea-mat, which we have considered above, fresh zooids are produced by a primordial organism by gemmation ; the beings thus produced (as well as the parent) being capable not only of repeating the gemmiparous process, but also of producing new individuals by a true generative act. We have now to consider a much more complex series of pheno- mena, in which the organism which is developed from the primitive ovum produces by gemmation two sets of zooids, one of which is destitute of sexual organs, and is capable of per- forming no other function than that of nutrition, whilst the other is provided with reproductive organs, and is destined for the perpetuation of the species. In the former case the produced zooids all resembled each other, and the parent ^ 30 MANUAL OF ZOOLOGY. organism which gave rise to them ; in the latter case, the pro- duced zooids are often utterly unlike each other and unlike the parent, since their functions are entirely different. The simplest form of the process is seen in certain of the Hydroid Polypes, such as Hydractinia. The ovum of Hydrac- tinia is a free-swimming ciliated body, which, after a short locomotive existence, attaches itself to some submarine object, develops a mouth and tentacles, and commences to pro- duce zooids like itself by a process of continuous gemmation. These remain permanently attached to one another, with the result that a compound organism is produced, consisting of a number of zooids, or " polypites," organically connected to- gether, but enjoying an independent existence. None of the zooids, however, are provided with sexual organs ; and though there is theoretically no limit to the size which the colony may reach by gemmation, its buds are not detached, and the species would therefore die out, unless some special provision were made for its preservation. Besides these nutritive zooids, however, other buds are produced which differ con- siderably in appearance from the former, and which have the power of generating the essential elements of reproduction. These generative zooids derive their nourishment from the materials collected by the nutritive zooids, but only live until the ova are matured in their interior and liberated, when they disappear. The ova thus produced become free-swim- ming ciliated bodies, such as the one with which the cycle began. In this case, therefore, the " individual " consists of a series of nutritive zooids, collectively called the " trophosome," and another series of reproductive zooids, collectively called the " gonosome," the entire series remaining in organic con- nection. In other Hydroid Zoophytes allied to the preceding (such as Clytia), the process advances a step further. In Clytia the generative buds, or zooids, do not produce the reproduc- tive elements as long as they remain attached to the parent colony; but they require a preliminary period of independent existence. For this purpose they are specially organised, and when sufficiently mature they are detached from the stationary colony. The generative zooid now appears as an entirely independent being, described as a species of jelly-fish (or Medusa). It consists of a bell-shaped disc, by means of which it is enabled to swim freely ; from the centre of this disc depends a nutritive process, with a mouth and digestive cavity, whereby the organism is able to increase considerably ALTERNATION OF GENERATIONS. 3 I in size. The substance of the disc is penetrated by a complex system of canals, and from its margin hangs a series of tentacu- lar processes. After a period of independent locomotive existence, the Medusa attains its full growth, when it develops ova and spermatozoa. By the contact of these embryos are produced; but these, instead of resembling the jelly-fish by which they were immediately generated, proceed to develop themselves into the fixed Hydroid colony by which the Medusa was originally produced. Still more extraordinary phenomena have been discovered in other Hydrozoa, as in many of the Lucernarida. In these the ovum gives rise to a locomotive ciliated body, which ulti- mately fixes itself, becomes trumpet-shaped, and develops a mouth and tentacles at its expanded extremity, when it is known as the "hydra-tuba," from its resemblance to the fresh-water polype, or Hydra. The hydra-tuba has the power of multiplying itself by gemmation, and it can produce large colonies in this way; but it does not obtain the power of generating the essential elements of reproduction. Under certain circumstances, however, the hydra-tuba enlarges, and, after a series of preliminary changes, divides by transverse fission into a number of segments, each of which becomes detached and swims away. These liberated segments of the little hydra-tuba (it is about half an inch in height) now live as entirely independent beings, which were described by naturalists as distinct animals, and were called Ephyrae. They are provided with a swimming-bell, or "umbrella," by means of which they propel themselves through the water, and with a mouth and digestive cavity. They now lead an active life, feeding eagerly, and attaining in some instances a perfectly astonishing size (the Medusoids of some species are several feet in circumference). After a while they develop the essential elements of reproduction, and after the fecunda- tion and liberation of their ova they die. The ova, however, are not developed into the free-swimming and comparatively gigantic jelly-fish by which they were immediately produced, but into the minute, fixed, sexless hydra-tuba. We thus see that a small, sexless zooid, which is capable of multiplying itself by gemmation, produces by fission several independent locomotive beings, which are capable of nourish- ing themselves and of performing all the functions of life. In these are produced generative elements, which give rise by their development to the little fixed creature with which the series began. To the group of phenomena of which the above are examples, 32 MANUAL OF ZOOLOGY. the name "alternation of generations" was applied by Steen- strup ; but the name is not an appropriate one, since the process is truly an alternation of generation with gemmation or fission. The only generative act takes place in the repro- ductive zooid, and the production of this from the nutritive zooid is a process of gemmation or fission, and not a pro- cess of generation. The " individual," in fact, in all these cases, must be looked upon as a double being composed of two factors, both of which lead more or less completely inde- pendent lives, the one being devoted to nutrition, the other to reproduction. The generative being, however, is in many cases not at first able to mature the sexual elements, and is therefore provided with the means necessary for its growth and nourishment as an independent organism. It must also be remembered that the nutritive half of the " individual " is usually, and the generative half sometimes, compound — that is to say, composed of a number of zooids produced by con- tinuous gemmation ; so that the zoological individual in these cases becomes an extremely complex being. These phenomena of so-called " alternation of generations/' or " metagenesis," occur in their most striking form amongst the Hydrozoa ; but they occur also amongst many of the in- testinal worms (Entozoa), and amongst some of the Tunicata (Molluscoida). d. Parthenogenesis. — " Parthenogenesis" is the term employed to designate certain singular phenomena, resulting in the production of new individuals by virgin females without the intervention of a male. By Professor Owen, who first em- ployed the term, parthenogenesis is applied also to the processes of gemmation and fission, as exhibited in sexless beings ; or in virgin females ; but it seems best to consider these phenomena separately. Strictly, the term parthenogenesis ought to be confined to the production of new individuals from virgin females by means of ova, which are enabled to develop themselves without the contact of the male element. The difficulty in this definition is found in framing an exact definition of an ovum, such as will distinguish it from an in- ternal gemma or bud. No body, however, should be called an "ovum "which does not exhibit a germinal vesicle and germinal spot, and which does not exhibit the phenomenon known as segmentation of the yelk. Moreover, ova are almost invariably produced by a special organ, or ovary. As examples of parthenogenesis we may take what occurs in plant-lice (Aphides) and in the honey-bee ; but it will be seen that in neither of these cases are the phenomena so unequivo- PARTHENOGENESIS. JO cal, or so well ascertained, as to justify a positive assertion that they are truly referable to parthenogenesis in the above restricted sense of the term. The Aphides, or plant-lice, which are so commonly found parasitic upon plants, are seen towards the close of autumn to consist of male and female individuals. By the sexual union of these true ova are produced, which remain dormant through the winter. At the approach of spring these ova are hatched ; but instead of giving birth to a number of males and females, all the young are of one kind, variously regarded as neuters, virgin females, or hermaphrodites. Whatever their true nature may be, these individuals produce viviparously a brood of young which resemble themselves ; and this second generation, in like manner, produces a third, — and so the process may be repeated, for as many as ten or more generations, throughout the summer. When the autumn comes on, however, the vivi- parous Aphides produce — in exactly the same manner — a final brood, but this, instead of being composed entirely of similar individuals, is made up of males and females. Sexual union now takes place, and ova are produced and fecundated in the ordinary manner. The bodies from which the young of the viviparous Aphides are produced are variously regarded as internal buds, as " pseud- ova" (i.e., as bodies intermediate between buds and ova), and as true ova. Without entering into details, it is obvious that there is only one explanation of these phenomena which will justify us in regarding the case of the viviparous Aphides as one of true parthenogenesis, as above defined. If, namely, the spring broods arestrue females, and the bodies which they produce in their interior are true ova, then the case is one of genuine parthenogenesis, for there are certainly no males. The case might still be called one of parthenogenesis, even though the bodies from which these broods are produced be regarded as internal buds, or as "pseudova;" fora true ovum is essentially a bud. If, however, Balbiani be right, and the viviparous Aphides are really hermaphrodite, then, of course, the pheno- mena are of a much less abnormal character.* In the second case of alleged parthenogenesis which we are * According to Balbiani, the viviparous Aphides are always hermaphro- dite. As regards the oviparous Aphides, if the embryo is to become a female, the male organs remain undeveloped, and though present are merely rudimentary. On the contrary, if the hermaphrodite embryo is to become a male, the female organs, instead of remaining in a rudimentary condition, are transformed into a true testicle. C 34 MANUAL OF ZOOLOGY. about to examine — namely, in the honey-bee — the phenomena which have been described cannot be said to be wholly free from doubt. A hive of bees consists of three classes of indi- viduals— i. A " queen," or fertile female ; 2. The " workers/' which form the bulk of the community, and are really unde- veloped or sterile females ; and 3. The " drones," or males, which are only produced at certain times of the year. We have here three distinct sets of beings, all of which proceed from a single fertile individual, and the question arises, In what manner are the differences between these produced ? At a certain period of the year the queen leaves the hive, accompanied by the drones (or males), and takes what is known as her "nuptial flight " through the air. In this flight she is impregnated by the males, and it is immaterial whether this act occurs once in the life of the queen, or several times. Be this as it may, the queen, in virtue of this single impregnation, is enabled to pro- duce fresh individuals for a lengthened period, the semen of the males being stored up in a receptacle which communicates by a tube with the oviduct, from which it can be shut off at will. The ova which are to produce workers (undeveloped females) and queens (fertile females) are fertilised on their passage through the oviduct, the semen being allowed to escape into the oviduct for this purpose. The subsequent development of these fecundated ova into workers or queens depends entirely upon the form of the cell into which the ovum is placed, and upon the nature of the food which is supplied to the larva. So far there is no doubt as tothe nature of the phenomena which are observed. It is asserted, how- ever, by Dzierzon and Siebold, that the males or drones are produced by the queen from ova which she does not allow to come into contact with the semen as they pass through the oviduct. This assertion is supported by the fact that if the communication between the receptacle for the semen and the oviduct be cut off, the queen will produce nothing but males. Also, in crosses between the common honey-bee and the Ligu- rian bee, the queens and workers alone exhibit any intermediate characters between the two forms, the drones presenting the unmixed characters of the queen by whom they were pro- duced. If these observations are to be accepted as established — and, upon the whole, there can be no hesitation in accepting them as in the main correct — then the drones are produced by a true process of parthenogenesis ; but some observers main- tain that the development of any given ovum into a drone is really due — as in the case of the queens and workers — to DEVELOPMENT. 35 the special circumstances under which the larva is brought up* There are various other cases in which parthenogenesis is said to occur, but the above will suffice to indicate the general character of the phenomena in question. The theories of par- thenogenesis appear to be too complex to be introduced here ; and there is the less to regret in their omission, as naturalists have not yet definitely adopted any one explanation of the phenomena to the exclusion of the rest. First Law of Quatrefages. — From the phenomena of asexual reproduction in all its forms, M. de Quatrefages has deduced the following generalisation : — " The formation of new individuals may take place, in some instances, by gemmation from, or division of, the parent-being ; but this process is an exhaustive one, and cannot be carried out indefinitely. When, therefore, it is necessary to insure the continuance of the species, the sexes must present themselves, and the germ and sperm must be allowed to come in contact with one another." It should be added that the act of sexual reproduction, though it insures the perpetuation of the species, is very de- structive to the life of the individual. The formation of the essential elements of reproduction appears to be one of the highest physiological acts of which the organism is capable, and it is attended with a corresponding strain upon the vital energies. In no case is this more strikingly exhibited than in the majority of insects, which pass the greater portion of their existence in a sexually immature condition, and die almost immediately after they have become sexually perfect and have consummated the act whereby the perpetuation of the species is secured. ii. DEVELOPMENT, TRANSFORMATION, AND METAMORPHOSIS. Development is the general term applied to all those changes which a germ undergoes before it assumes the characters of the perfect individual ; and the chief differences which are ob- served in the process as it occurs in different animals consists simply in the extent to which these changes are external and visible, or are more or less completely concealed from view. * In the case of Polistes Gallica, Von Siebold appears to have proved beyond reasonable doubt that the males are produced by a process of par- thenogenesis. Landois, however, asserts that the eggs of insects are of no sex, that sex is only developed in the larva after its emergence from the egg, and that in each individual larva the sex is determined wholly by the nature of the food upon which it is brought up ; abundant nourishment producing females, and scanty diet giving rise to males. 30 MANUAL OF ZOOLOGY. For these differences the terms " transformation " and " meta- morphosis " are employed ; but they must be regarded as essen- tially nothing more than variations of development. Transformation is the term employed by Qiiatrefages to designate " the series of changes which every germ undergoes in reaching the embryonic condition ; those which we observe in every creature still within the egg ;v those, finally, which the species born in an imperfectly developed state present in the course of their external life." , Metamorphosis is defined by the same author as including the alterations which are "undergone after exclusion from the egg, and which alter extensively the general form and mode of life of the individual." Though by no means faultless, these terms are sufficiently convenient, if it be remembered that they are merely modifi- cations of development, and express differences of degree and not of kind. An insect, such as a butterfly, is the best illus- tration of what is meant by these terms. All the changes which are undergone by a butterfly in passing from the fecun- dated ovum to the condition of an imago, or perfect insect, constitute its development. The egg which is laid by a butter- fly undergoes a series of changes which eventuate in its giv- ing birth to a caterpillar, these preliminary changes constitut- ing its transformation. The caterpillar grows rapidly, and after several changes of skin becomes quiescent, when it is known as a "chrysalis." It remains for a longer or shorter time in this quiescent and apparently dead condition, during which period developmental changes are going on rapidly in its interior. Finally, the chrysalis ruptures, and there escapes from it the perfect winged insect. To these changes the term metamorphosis is rightly applied. These changes, however, do not differ in kind from the changes undergone by a Mammal ; the difference being that in the case of a Mammal the ovum is retained within the body of the parent, where it undergoes the necessary developmental changes, so that at birth it has little to do but grow, in order to be converted into the adult animal. From these considerations we arrive at the second law laid down by Qiiatrefages : " Those creatures whose ova — owing to an insufficient supply of nutritious contents, and an incapacity on the part of the mother to provide for their complete de- velopment within her own substance — are rapidly hatched, give birth to imperfect offspring, which, in proceeding to their definitive characters, undergo several alterations in structure and form, known as metamorphoses." SPONTANEOUS GENERATION. 37 Retrograde Development. — Ordinarily speaking, the course of development is an ascending one, and the adult is more highly ^organised than the young ; but there are cases in which there is an apparent reversal of this law, and the adult is to all appearance a degraded form when compared with the embryo. This phenomenon is known as "retrograde" or "recurrent" development; and Well-marked instances are found amongst the Cirripedia and Lernaeas, both of which belong to the Crustacea. Thus, in the Cirripedes (acorn-shells, &c.) and in the parasitic Lernaeae the embryo is free-swimming and provided with organs of vision and sensation, being in most respects similar to the permanent condition of certain other Crustacea, such as the Copepods. The adult, however, in both cases, is degraded into a more or less completely sedentary animal, more or less entirely deprived of organs of sense, and leading an almost vegetative life. As a compensation, reproductive organs are developed in the adult, and it is in this respect superior to the locomotive, but sexless, larva. 12. SPONTANEOUS GENERATION. Spontaneous or Equivocal generation is the term applied to the alleged production of living beings without the pre- existence of germs of any kind, and therefore without the pre- existence of parent organisms. The question is one which has been long and closely disputed, and is far from being settled ; so that it will be sufficient to indicate the facts upon which the theory rests. If an animal or vegetable substance be soaked in hot or cold water, so as to make an organic infusion, and if this infusion be exposed for a sufficient length of time to the air, the follow- ing series of changes is usually observed :— 1. At the end of a longer or shorter time, there forms upon the surface of the infusion a thin scum, or pellicle, which, when examined microscopically, is found to consist of an incalculable number of extremely minute molecules. 2. In the next stage these molecules appear, many of them, to have increased in size by endogenous division, till they form short staff-shaped filaments, called " bacteria." These increase in length by the same process until we get long filamentous bodies produced, which are termed " vibriones." "* Both the * By some authorities it is believed that the bacteria are produced by the fusion together of the primitive molecules in twos and threes ; and that the vibrios are produced out of the bacteria by the addition of fresh molecules to the extremities of the latter, or by their uniting with one another. 38 MANUAL OF ZOOLOGY. bacteria and the vibrios now exhibit a vibratile or serpentine movement through the surrounding fluid. 3. After a varying period, the bacteria and vibrios become motionless, and disintegrate so as to produce again a finely molecular pellicle. 4. Little spherical bodies now appear, each of which is pro- vided with a vibratile cilium'with which it moves actively through the infusion. (Monas lens.) 5. Varied forms of ciliated Infusoria — some of which pos- sess a mouth and are otherwise highly organised — make their appearance in the fluid. The above is the general sequence of the phenomena which have been observed, and the following are the two theories which have been advanced to account for them : — a. By the advocates of spontaneous generation, or " Hetero- geny," it is affirmed that the Infusoria, which finally appear in the infusion, are produced spontaneously out of the molecular pellicle, the molecules of which are also of spontaneous origin, and are not derived from any pre-existing germs. b. By the " panspermists," or the opponents of spontaneous generation, it is alleged, on the other hand, that the production of Bacteria, Vibrios, Monads, and Infusoria, in organic infu- sion, is due simply to the fact that the atmosphere, and pro- bably the fluid itself, is charged with innumerable germs — too minute, perhaps, to be always detectable by the microscope — which, obtaining access to the fluid, and finding their favour- able conditions, are developed into living beings. A large number of elaborate experiments have been carried out to prove that atmospheric air is absolutely necessary for the production of these living beings, and that if the air be pro- perly purified by passage through destructive chemical reagents, no such organisms will be produced, provided that the infusion have been previously boiled. As the results of all these experimental trials have hitherto proved more or less contra- dictory, it is unnecessary to enter into the question further, and it will be sufficient to indicate the following general considera- tions : — a. The primary molecules which appear in the fluid are extremely minute, and if they are developed from germs, these may be so small as to elude any power of the microscope yet known to us. As they subsequently become converted into bacteria and vibrios, and as there can be little dispute as to these being truly living organisms, we are obliged to believe that they must have had some definite origin. It appears, however, to be hardly philosophical to assume that they form SPONTANEOUS GENERATION. 39 themselves out of the inorganic materials of the infusion ; since this implies the sudden appearance, or creation, of new force, for which there seems to be no means of accounting. b. The nature of the vibrios and bacteria must be looked upon as quite uncertain. To say the least of it, they are quite as likely to be plants as animals ; and the most probable hypo- thesis would place the former near the filamentous Confervse, or would regard them as the mycelium of various species of Moulds (PtnidUium). c. What has been said above with regard to the origin of the bacteria and vibrios applies equally to the origin of the Monads, which appear in the infusion subsequently to the death of the vibrios. d. These Monads, as shown by recent researches, are pro- bably to be looked upon as the embryonic, or larval, forms of the higher Infusoria which succeed them. e. Many of the Infusoria which finally appear are of a comparatively high grade of organisation, being certainly the highest of the Protozoa, and being placed by some competent observers in the neighbourhood of the Trematode Worms (Annuloida). It is therefore very unlikely that these should be generated spontaneously ; since, if this ever occurs, it is reason- able to suppose that the creatures thus produced will be of the lowest possible organisation (such as the Gregarinidae or the Monera, for example), and will be far below the Infusoria in point of structure. f. The reproductive process in many of these same Infusoria is perfectly well known, and it consists either in a true sexual process, for which proper organs are provided (as in Paramce- cium), or in a process of gemmation or fission. It is therefore improbable that they should be generated in the manner maintained by the heterogenists, since this mode of reproduc- tion would appear to be superfluous. g. In the absence of any direct proof to the contrary, it is safer to adopt an explanation of the observed phenomena which does not have recourse to laws with which we are as yet unacquainted. Thus, it is not at variance with any known law to suppose that the primary molecules are the result of the development of germs which find in the inorganic infusion a suitable nidus ; that these primary molecules and the vibrios which they produce are referable to the Protophyta, and should probably be placed near the filamentous Confervae ; that by the death of these vegetable organisms the fluid is prepared for the reception and development of the germs of the Pro- tozoa, for which the former serve as pabulum ; and that many 4O MANUAL OF ZOOLOGY. of the forms which are observed are the larval stages of the higher Infusoria.* 13. ORIGIN OF SPECIES. It is impossible here to do more than merely indicate in the briefest manner the two fundamental ideas which are at the bottom of all the various theories as to the origin of species. The opinions of scientific men are still divided upon this sub- ject ; and it will be sufficient to give an outline of the two leading theories, without adducing any of the reasoning upon which they are based. I. Doctrine of Special Creation. — On this doctrine of the origin of species it is believed that species are immutable pro- ductions, each of which has been specially created at some point within the area in which we now find it, to meet the ex- ternal conditions there prevailing, subsequently spreading from this spot as far as the conditions of life were suitable for it. II. Doctrine of Development. — On the other hand, it is be- lieved that species are not permanent and immutable, but that they " undergo modification, and that the existing forms of life are the descendants by true generation of pre-existing forms " (Darwin). * Recent researches, especially those of Dr Bastian, have established some new facts as to the possibility of spontaneous generation, but they can by no means be said to have settled the question, if only upon the ground that they require confirmation by other experimentalists. The chief fact which appears to have been established upon a tolerably firm basis is, that living beings, vegetable or animal, may make their appearance in organic infusions which have been subjected to a temperature of considerably over the boiling-point, even though the said infusions have been hermetically sealed in a flask from which all atmospheric air has been previously with- drawn. The chief deduction which appears to flow from this — assuming its correctness — is, that there are low organisms which can exist, for a certain length of time at any rate, with an extremely small amount of air; for it is to be remembered that the production of a theoretically perfect vacuum is probably practically impossible. If it were conceded, in fact, that a perfect vacuum had been formed in the experiments in question, the sole result would be that we should have to alter all our beliefs as to the conditions under which life is a possibility. The only tangible result of these experiments, so far, is, that any supposed " pre-existent germs " must have been contained, if present at all, in the infinitesimal portion of air which could not be expelled from the flasks experimented on ; or, they must have been able to withstand without injury a temperature of over 212°. Mr Crace-Calvert, indeed, asserts that he has experimentally shown that vibrios can survive exposure to temperature exceeding 300° Fahren- heit. Neither of these hypotheses is wholly incredible ; but the question ought to be regarded as still sub judice, and there is grave doubt as to the reliability and accuracy of the experiments above alluded to. Under any circumstances the entire question is one of such complexity as to be entirely unsuited for discussion here. ORIGIN *F SPECIES. 4 I On Lamarck's theory of the development of species, the means of modification were ascribed to the action of external physical agencies, the inter-breeding of already existing forms, and the effects of habit. The doctrine of the development of species by variation and natural selection — propounded by Darwin, and commonly known as the Darwinian theory — is based upon the following fundamental propositions : — 1. The progeny of all species of animals and plants exhibit variations amongst themselves in all parts of their organisation, no two individuals being exactly and in all respects alike. In other words, in every species the individuals, whilst inheriting a general likeness to their progenitors, tend by variation to diverge from the parent-type in some particular or other. 2. Variations arising in any part of the organism, however minute, may be transmitted to future generations, under certain definite and discoverable laws of inheritance. 3. By " artificial selection," or by breeding from individuals possessing any particular variation, man, in successive genera- tions, can produce a breed in which the variation will be per- manent, the divergence from the parent-type being usually intensified by the process of inter-breeding. The races thus artificially produced by men are often as widely different as are distinct species of wild animals. 4. The world in which all living beings are placed is one not absolutely unchanging, but is liable, on the contrary, to subject them to very varying conditions. 5. All animals and plants give rise to more numerous young than can by any possibility be preserved, each species tending to increase in numbers in a geometrical progression. 6. As these young are none of them exactly alike in all respects, a process of " Natural Selection " will ensue, whereby those individuals which possess any variation, however slight, favourable to the peculiarities of the species will tend to be preserved. Those individuals, on the other hand, which do not possess any such favourable variation, will be placed at a disadvantage in the " struggle for existence," and will tend to be gradually exterminated. The individuals, therefore, com- posing any species are thus subjected to a rigid process of sifting, by which those least adapted to their environment are being perpetually weeded out, whilst "the survival of the fittest" is secured. 7. Other conditions remaining the same, the individuals which survive in the struggle for existence will transmit the variations, to which they owe their preservation, to future generations. 42 MANUAL OF ZOOLOGY. 8. By a repetition of this process, "varieties" are first established ; these become permanent, and " races " are pro- duced ; finally, in the lapse of time, the differences thus caused become sufficiently marked to constitute distinct " species." 9. If we grant that past time has been practically infinite, it is conceivable that all the different animals and plants which we see at present upon the globe, may have been produced by the action of Natural Selection upon the off- spring of a few primordial forms, or, it may be, of a single primitive being. Originally, Mr Darwin appears to have believed that " Natural Selection" would alone be found to be a sufficient cause to have given rise to all existing species by a process of Evolution from pre-existing forms. In view, however, of certain objections which had been brought forward, Mr Darwin seems to have abandoned this position ; and a cause supplementary to " Natural Selection " was sought for in what Mr Darwin terms " Sexual Selection." The action of Sexual Selection in a supposed process of Evolution, according to Mr Darwin's views, may be stated in the following two pro- positions : — a. The males of many species of animals are known to engage in very severe contests for the possession of the females, these latter yielding themselves to the victor. In such contests certain males will inevitably have certain advan- tages over the others, either in point of strength or activity, or in consequence of the possession of more efficient offensive weapons. There will therefore always be a probability that certain males will get possession of the females in preference to others : and thus there will be a tendency in the individuals of many species of animals to secure a preponderance of off- spring from the strongest males. The peculiarities which enable certain males to succeed in these contests will, cceteris paribus, be transmitted to their male offspring, and in this way variations may be perpetuated, initiated, or intensified. b. In the preceding cases, the females are believed to be perfectly passive, and the selection is a " natural " one, the final result depending solely upon the natural advantages which certain males possess over others in actual combat. It is alleged, however, that there are other cases in which the selection is truly " sexual," since its result is determined by spontaneous preference, and not by brute force alone. It is asserted, namely, that among certain species of animals, the females exercise a free choice as to the particular male with which they will pair \ the males being passive agents in the DISTRIBUTION. 43 matter, except in so far as each uses, or may use, his utmost exertions to secure that the choice of the female may fall upon him. The circumstances supposed to influence, and ulti- mately determine, the choice of the female, are of course, in the main, the personal attractions of some particular male, the female being captivated by some "beauty of form, colour, odour, or voice," which such a male may possess. If it be admitted that the females of some of the lower animals have the power of expressing and exercising a pre- ference in the manner above indicated, then it is easy to understand how variations might be transmitted or intensi- fied in this way. The male who is most attractive to the female will, other things being equal, have the best chance of propagating his species, and is likely to leave the largest number of descendants. His male offspring will inherit the peculiarities by which their sire was rendered pre-eminently attractive in the eyes of their mother, and thus a well-marked breed might be produced, by the preservation or intensifica- tion of characters of this nature. Mr Darwin is disposed to believe that colour and song in most, if not in all, animals are thus to be ascribed to the action of Sexual Selection, through numerous successive generations ; but other competent autho- rities are unable to concur in this view. 14. DISTRIBUTION. Under this head come all the facts which are concerned with the external or objective relations of animals — that is to say, their relations to the external conditions in which they are placed. The geographical distribution of animals is concerned with the determination of the areas within which every species of animal is at the present day confined. Some species are found almost everywhere, when they are said to be " cosmopolitan ; " but, as a rule, each species is confined to a limited and definite area. Not only are species limited in their distribution, but it is possible to divide the globe into a certain number of geo- graphical regions or u zoological provinces," each of which is characterised by the occurrence in it of certain associated forms of animal life. It is to be remembered, however, that the zoological provinces of the present day by no means corre- spond with those of former periods, and that they have only existed as such since comparatively recent times. The vertical or bathymetrical distribution of animals relates to the limits of depth within which each marine species of 44 MANUAL OF ZOOLOGY. animals is confined. As a rule it is found that each species has its own definite bathymetrical zone, and that its existence is difficult or impossible at depths greater or less than those comprised by that zone. Generalising on a large number of facts, naturalists have been able to lay down and name certain definite zones, each of which has its own special fauna. The four following zones are those generally accepted : — 1. The Littoral zone, or the tract between tide-marks. 2. The Laminarian zone, from low water to 15 fathoms. 3. The Coralline zone, from 15 to 50 fathoms. 4. The deep-sea Coral zone, 50 to 100 fathoms or more. 5. To these must now be certainly added a fifth zone, ex- tending from 100 fathoms to a depth of 2500 fathoms or more. Recent researches, however, have rendered it certain that after a certain depth, say 100 fathoms, the bathymetrical dis- tribution of animals is conditioned not by the depth, but by the temperature of the water at the bottom of the sea. Similar forms, namely, are always found inhabiting areas in which the bottom-temperature is the same, wholly irrespective of the depth of water in the particular locality in question. The supply of food, also, and the nature of the habitat, are important elements of the case. In the light, therefore, of these recent facts, it would perhaps be advisable to adopt the views of Mr Gwyn Jeffreys, and to consider that there are only two princi- pal bathymetrical zones — namely, the littoral and the submarine. In addition to the preceding forms of distribution, the zoologist has to investigate the condition and nature of animal life during past epochs in the history of the world. The laws of distribution in time, however, are, from the na- ture of the case, less perfectly known than are the laws of lateral or vertical distribution, since these latter concern beings which we are able to examine directly. The following are the chief facts which it is necessary for the student to bear in mind : — 1. The rocks which compose the crust of the earth have been formed at successive periods, and may be roughly divided into aqueous or sedimentary rocks, and igneous rocks. 2. The igneous rocks are produced by the agency of heat, are mostly unstratified (i.e., are not deposited in distinct layers or strata), and, with few exceptions, are destitute of any traces of past life. 3. The sedimentary or aqueous rocks owe their origin to the action of water, are stratified (i.e., consist of separate layers or strata), and mostly exhibit " fossils " — that is to say, the remains or traces of animals or plants which were in existence at the time when the rocks were deposited. DISTRIBUTION. 45 4. The series of aqueous rocks is capable of being divided into a number of definite groups of strata, which are technically called " formations." 5. Each of these definite rock groups, or " formations," is characterised by the occurrence of an assemblage of fossil remains more or less peculiar and confined to itself. 6. The majority of these fossil forms are " extinct" — that is to say, they do not admit of being referred to any species at present existing. 7. No fossil, however, is known, which cannot be referred to one or other of the primary subdivisions of the Animal Kingdom, which are represented at the present day. 8. When a species has once died out, it never reappears. 9. The older the formation, the greater is the divergence between its fossils and the animals and plants now existing on the globe. 10. All the known formations are divided into three great groups, termed respectively Palaeozoic or Primary, Mesozoic or Secondary, and Kainozoic or Tertiary. The Palaeozoic or Ancient-life period is the oldest, and is characterised by the marked divergence of the life of the period from all existing forms. In the Mesozoic or Middle-life period, the general fades of the fossils approaches more nearly to that of our existing fauna and flora ; but — with very few exceptions — the characteristic fossils are all specifically distinct from all existing forms. In the Kainozoic or New-life period, the approximation of the fossil remains to existing living beings is still closer, and some of the forms are now specifically identical with recent species ; the number of these increasing rapidly as we ascend from the lowest Kainozoic deposit to the Recent period. Subjoined is a table giving the more important subdivisions of the three great geological periods, commencing with the oldest rocks and ascending to the present day (Fig. i). MANUAL OF ZOOLOGY. IDEAL SECTION OF THE CRUST OF THE EARTH. Fig. i. Post-Tertiary and Recent. Pliocene. Miocene. Eocene. Cretaceous. Oolitic or Jurassic. L> Triassic. Permian. Carboniferous. Devonian or Old Red Sandstone. Silurian. Cambrian. Huronian. Lauren tian. DISTRIBUTION. 47 I. PALAEOZOIC OR PRIMARY ROCKS. 1. Laurentian. (Lower and Upper.) 2. Cambrian. (Lower and Upper, with Huronian Rocks?) 3. Silurian. (Lower and Upper.) 4. Devonian, or Old Red Sandstone. (Lower, Middle, and LTpper.) 5. Carboniferous. (Mountain-limestone, Millstone Grit, and Coal-measures.) 6. Permian. ( = the lower portion of the New Red Sand- stone.) II. MESOZOIC OR SECONDARY ROCKS. 7. Triassic Rocks. (Bunter Sandstein, or Lower Trias ; Muschelkalk, or Middle Trias ; Keuper, or Upper Trias.) 8. Jurassic Rocks. (Lias, Inferior Oolite, Great Oolite, Oxford Clay, Coral Rag, Kimmeridge Clay, Portland Stone, Purbeck beds.) 9. Cretaceous Rocks. (Wealden, Lower Greensand, Gault, Upper Greensand, White Chalk, Maestricht beds.) III. KAINOZOIC OR TERTIARY ROCKS. 10. Eocene. (Lower, Middle, and Upper.) 11. Miocene. (Lower and Upper.) 12. Pliocene. (Older Pliocene and Newer Pliocene.) 13. Post-tertiary. (Post-pliocene and Recent.) 48 INVERTEBRATE ANIMALS. PROTOZOA. CHAPTER I. i GENERAL CHARACTERS OF THE PROTOZOA. 2. CLASSIFICATION. 3. GREGARINID^E. i. Ge?ieral Characters. — The sub-kingdom Protozoa, as the name implies, includes the most lowly organised members of the animal kingdom. From this circumstance it is difficult, if not impossible, to give an exhaustive definition, and the fol- lowing is, perhaps, as exact as the present state of our know- ledge will allow : — The Protozoa may be defined as animals, generally of minute size, composed of a nearly or altogether structureless jelly-like substance (termed "sarcode"), showing no composition out of definite parts or segments, having no definite body-cavity, presenting no traces of a nervous system, and having either no differentiated alimentary apparatus, or but a very rudimentary one. The Protozoa are almost exclusively aquatic in their habits, and are mostly very minute, though they sometimes form colonies of considerable size. They are composed of a more or less contractile, jelly-like substance, called " sarcode " or "animal protoplasm," which is semi-fluid in consistence, and is composed of an albuminous base with oil-globules scattered through it. Granules are generally developed in the sarcode, and in many cases there is a definite internal solid particle, termed the " nucleus." In no Protozoan are any traces known of anything like the nervous and vascular arrangements which are found in animals PROTOZOA. 49 of a higher grade. A nervous system is universally and en- tirely absent, and the sole circulatory apparatus consists in certain clear spaces called "contractile vesicles," which are found in some species, and which doubtfully perform the functions of a heart. A distinct alimentary aperture is present in the higher Protozoa, but in many there is none ; and in all, the digestive apparatus is of the simplest character. Organs of generation, or at any rate differentiated portions of the body which act as these, are sometimes present ; but in many cases true sexual reproduction has not hitherto been shown to exist. The ^sarcode," which forms such a distinctive feature in all the Protozoa, is a structureless albuminous substance, not possessing " permanent distinction or separation of parts/' but nevertheless displaying all " the essential properties and char- acters of vitality," being capable of assimilation and excretion, of irritability and of the power of contraction, so as to produce movements, strictly analogous, in many cases, to the muscular movements of the higher animals. In some, too, the sarcode possesses the power of producing an external case or envelope, usually of carbonate of lime or flint, and often of a very com- plicated and mathematically regular structure. The power of active locomotion is enjoyed by a great many of fat Protozoa; but in some cases this is very limited, and in other cases the animal is permanently fixed in its adult condition. The apparatus of locomotion in the Protozoa is of a very varied nature. In many cases, especially in the higher forms, movements are effected by means of the little hair-like processes which are known as "cilia," and which have the power of lashing to and fro or vibrating with great rapidity. In other cases the cilia are accompanied or replaced by one or more long whip-like bristles, which act in the same fashion, and are known as " flagella." The most characteristic organs of locomotion amongst the lower Protozoa are known as " pseudopodia," and consist simply of prolongations of the sarcodic substance of the body, which can usually be emitted from the greater portion of the general surface of the body, and are capable of being again retracted, and of fusing com- pletely with the body-substance. 2. Classification of the Protozoa. The sub-kingdom Protozoa is divided into three classes — viz., the Gregarinida, the Rhizo- poda, and the Infusoria. In the Infusoria only 4s^ a mouth present, and hence these are sometimes spoken of as the " Stomatode" Protozoa, whilst the two former classes collec- tively constitute the " Astomata.?. ft 50 MANUAL OF ZOOLOGY. The following is a tabular view of the divisions of the Protozoa : — Class I. GREGARINID^. .N, f^fo***** Class II. RHIZOPODA. Order i. Monera. „ 2. Amcebea. ., 3. Foramini-fera. „ 4. Radiolaria. „ 5. Spongida. Class III. INFUSORIA. i Order i. Suctoria. „ 2. Cilia 'ta. „ 3. Flagellata. 3. CLASS I. GREGARINID^:. — The Gregarinidce may be defined as parasitic Protozoa, which are destitute of a mouth, and do not possess the pofoer of emitting " psendopodia^ They constitute the lowest class of the Protozoa, and comprise certain micro- scopic animals which are parasitic in the alimentary canal of both Invertebrate and Vertebrate animals. They have, how- ever, a special liking for the intestines of certain insects, being commonly found abundantly in the cockroach. As we shall see hereafter, in all probability a great deal of the degraded character of the Gregarinidce is due to the fact that they are internal parasites, and are therefore not dependent upon their own exertions for food. Nothing anatomically could be more simple than the struc- ture of a Gregarina, since it is almost exactly that of the un- impregnated ovum (fig. 2, a). An adult Gregarina, in fact, may be said to be a single cell, consisting of an ill-defined membraneous envelope rilled with a more or less granular sarcode with fatty particles, which contains in its interior a vesicular nucleus, this in turn enclosing a solid particle, or nucleolus. In some the body exhibits an approach to a more complex structure by the presence of internal septa ; but it is doubtful whether this appearance may not be due to the appo- sition and fusion of two separate individuals. A separate order, however, has been founded upon individuals of this kind, under the name of Dicystidea ; the name Monocystidea being retained for the ordinary forms. As regards the size of the Gregarince, they vary from about the size of the head of a small pin up to as much as half an inch in length, when they assume the PROTOZOA : GREGARINID^E. 5 I aspect of small worms. The integument or cuticle with which the protoplasmic body is inclosed may be quite smooth or striated, or it may be furnished with bristles or spines, or even in some cases with cilia. Sometimes one end of the body is furnished with uncinate processes, very similar in appearance to the hooked "head" of the common tape-worm (T&nia soliuni). Essentially, however, the structure of all appears to be the same. No differentiated organs of any kind beyond the nucleus and nucleolus exist, and both assimilation and excretion must be performed simply by the general surface of the body. The body is, nevertheless, contractile, and slow movements can be effected, not, however, by pseudopodia. Haeckel regards the Gregarince as Amoeba which have be- come degenerate by parasitism ; but this opinion is rejected by Van Beneden. In spite of their exceedingly simple structure, the following very interesting reproductive phenomena have been observed Fig. 2. — Gregarina of the earth-worm, a Adult Gregarina ; b The same encysted ; r With the contents divided into pseudonavicellse ; d Free pseudcnavicellse ; e Free amcebiform contents of the pseudonavicellae. (After Lieberkiihn.) sometimes in a single Gregarina without apparent cause, sometimes as the result of the apposition and coalescence of two individuals — the exact nature of the process being in either case obscure. In some species conjugation is invari- able j in others it never occurs ; and it may take place either by analogous or by opposite extremities. The Gregarina — or it may be two individuals which have come into contact and adhered together — assumes a globular form, becomes motion- less, and develops round itself a structureless envelope or cyst, when it is said to be "encysted" (fig. 2, b\ The central nucleus then disappears, apparently by dissolution, whereupon the granular contents of the cyst break up into a number of little rounded masses, which gradually elongate and become lanceolate, when they are termed "pseudonavicellae" (or 52 MANUAL OF ZOOLOGY. " pseudonaviculse ") (fig. 2, c}. The next step in the process consists in the liberation of the pseudonavicellae, which escape by the rupture of the enclosing cyst (fig. 2, d}. If they now find a congenial habitat, they give origin to little albuminous or sarcodic masses, which exhibit lively movements, and are endowed with the power of throwing out and retracting little processes of the body which closely resemble the " pseudo- podia " of the Rhizopoda ; so that the pseudonavicella in this condition is very similar to an a.d\AtAmozba (fig. 2, e). Finally, these amcebiform bodies are developed into adult Grcgarince. It will be seen from the above that the formation of the pseudonavicellae out of the granular contents of the body, subsequent to the disappearance of the nucleus, presents some analogy to the segmentation of the impregnated ovum which follows upon the dissolution of the germinal vesicle. In Gre- garina gigantea of the Lobster the embryo is a little mass of sarcode, quite like an Amoeba except that it wants a nucleus and contractile vesicle. It soon gives out two little contractile processes or arms, which become detached and move about like, little worms, when they are termed " pseudo- filariae," from their resemblance to free hematoids. After a period of activity, the pseudo-filarian becomes quiescent, shortens its dimensions, develops a nucleus and nucleolus, and becomes an adult Gregarina. PSOROSPERMI^E. — There occur as parasites on and within the bodies of fishes certain vesicular, usually caudate, bodies, termed Psorospermice, the exact nature of which is very pro- blematical. According to Lieberkiihn they occasionally give origin to amcebiform bodies, similar to those which are libe- rated from the pseudonavicellae of Gregarinidce. In this case they should probably be regarded as the embryonic forms of some Gregarina. By Balbiani, however, they are looked upon as properly belonging to the vegetable kingdom. PROTOZOA I RHIZOPODA. 53 CHAPTER II. RHIZOPODA. GENERAL CHARACTERS OF THE RHIZOPODA. — the Rhizopoda may be defined as Protozoa which are destitute of a mouth, are simple or compound, and possess the power of emitting "pseudo- podia" They are mostly small, but some of the composite forms, such as the sponges, may attain a very considerable size. Structurally, a typical Rhizopod — as an Amoeba — is composed of almost structureless sarcode, without any organs appropriated to the function of digestion, and possessing the power of throwing out processes of its substance so as to con- stitute adventitious limbs. These are termed " pseudopodia," or false feet, and are usually protrusible at will from different parts of the body, into the substance of which they again melt when they are retracted. They are merely filaments of sarcode, sometimes very delicate and of considerable length, at other times more like finger-shaped processes; and they are somewhat analogous to the little processes which can be thrown out by the white corpuscles of the blood and by pus- cells. Indeed, it has been remarked by Huxley that an Amoeba is structurally " a mere colourless blood-corpuscle, leading an independent life." The class Rhizopoda is divided into five orders — viz., the Monera, the Amcebea, the Foraminifera, the Radiolaria, and the Spongida, of which the last is occasionally considered as a separate class. ORDER I. MONERA. — This name has been proposed by Haeckel for certain singular organisms which may provisionally be regarded as the lowest group of the Rhizopoda. They are very minute in size, and are distinguished by the fact that the body is composed of structureless sarcode, capable of emit- ting thread-like prolongations or pseudopodia, but destitute of either nucleus or contractile vesicle. The pseudopodia are in the form of delicate filamentous processes of sarcode, which interlace and anastomose with one another in every direction, and which exhibit a circulation of minute molecules and gran- ules in their interior, and along their edges. The body, when at rest, is more or less nearly circular in form, but it is capable of undergoing manifold changes of figure. No hard covering or " test " is ever developed. Reproduction is mostly by fis- sion, with or without precedent encystation and quiescence. 54 MANUAL OF ZOOLOGY. So far as is known, all the Monera are marine, and their syste- matic position is still doubtful. From the absence of a nucleus and contractile vesicle, and from the nature of the pseudopodia, they would appear upon the whole to be most closely allied to the Foraminifera, from which they differ, chiefly if not entirely, in the absence of a shell defending the soft sarcode of the body. Fig. 3. — Morphology of Rhizopoda. a Amoeba, radiosa, showing the pseudopodia, contractile vesicle, and nucleus ; b Difflugia, with the pseudopodia protruded from the anterior end of the carapace; c Individual sponge-particles, or "sarcoids;" d Ciliated sponge-particles oiGrantia, showing the lesemblance to flagellate Infuso- rians ; e Mono-ciliated sarcoid of Spongilla. (After Carter.) ORDER II. AMCEBEA. — This order comprises those Rhizopoda which are, with one or two exceptions, naked, have usually short, blunt, lobose pseudopodia, which do not. anastomose with one another, and contain a " nucleus" and one or more " contractile vesicles" The Amoeba, or Proteus-animalcule, may be taken as the type, and a description of it will be sufficient to indicate the leading points of interest in the order. The Amoeba (fig. 3, a) is a microscopic animalcule which inhabits fresh water, and is composed of gelatinous sarcode, which admits of a separation into two distinct layers : an outer transparent layer, termed the " ectosarc ; " and an inner, more fluid and mobile, molecular layer, called the "endosarc." The "ectosarc" is highly ex- tensile and contractile, and is the layer of which the pseudo- podia are mainly composed ; whilst the " endosarc " contains the only organs possessed by the animal — viz., the " nucleus " and " contractile vesicle " or vesicles, along with certain for- tuitous cavities termed "food-vacuoles." It is believed by some that the ectosarc is surrounded by a colourless and structureless investing membrane or cuticle; but this is denied by others. Be this as it may, there is no oral cavity, so far as has ever been certainly observed, and the food is merely taken into the interior of the body by a process of intussusception — any portion of the surface being chosen for this purpose, and acting as an extemporaneous mouth. When the particle of food has been received into the body, the aper- ture by which it was admitted again closes up, and the dis- PROTOZOA I RHIZOPODA. 55 charge of solid excreta is effected in an exactly similar manner. In this case, however, the area of the general surface, within which an anus may be extemporised, appears to be more re- stricted, and to comprise a portion only of the body (" villous region "). Fig. 4.— A, Amoeba: developed in organic infusions (after Beale), greatly en- larged; B, Ainceba princeps (after Carter) ; v Villous region ; c Contractile vesicle; n Nucleus ; e Ectosarc. The "nucleus" (fig. 4) is a solid granular body, one or more of which is present within the endosarc of every Amoeba, but its function is not known with any certainty. The " contractile vesicles " are cavities within the endosarc, of which ordinarily one only is present in the same individual, though sometimes there are more. In structure it is a little cavity or vesicle filled with a colourless fluid apparently derived from the digestion, and exhibiting rhythmical movements of contraction (systole) and dilatation (diastole]. In some cases radiating tubes are said to have been seen proceeding from the vesicle at the moment of contraction. Regarded functionally, the contractile vesicle must be looked upon as a circulatory organ, and it offers therefore the most rudimentary form of a vascular system with which we are as yet acquainted. By others, however, the con- tractile vesicle is believed to be filled with water from the exterior, and it is regarded as a rudimentary form of water- vascular system. Besides these proper organs, the endosarc usually contains clear spaces, which are called " vacuoles," or, more properly, " food-vacuoles." These spaces are of a merely temporary character, and are simply produced by the presence of par- ticles of food, usually with a little water taken into the body along with the food. There are no traces of any organs of sense, or of a nervous 56 MANUAL OF ZOOLOGY. system, or, indeed, of any other organs in addition to those already described. Locomotion is effected with moderate activity, but in an irregular manner, by means of the blunt, finger-shaped processes of sarcode, or pseudopodia, which can be protruded at will from any part of the body, and can be again retracted within it. The pseudopodia also serve as pre- hensile organs ; but they do not interlace and form a net- work, nor do they exhibit any circulation of granules derived from the endosarc, as in many others of the Rhizopoda. As regards the reproductive process in the Amoeba, no dif- ferentiated sexual organs have hitherto been discovered, and the true sexual form of the process is therefore unknown. Fresh individuals, however, may be produced in three ways : — Firstly, by simple fission, the animal dividing into two parts, each of which becomes an independent organism. Secondly, by the detachment of a single pseudopodium, which becomes developed into a fresh Amoeba. Thirdly, by the production of little spherical masses of sarcode which may be derived from the nucleus by fission, or may be produced by a segmentation of the endosarc, the animal having previously become torpid, and the nucleus and contractile vesicle having disappeared. These little masses, however produced, develop themselves when liberated into ordinary Amcebce. This last method of repro- duction is obviously very closely analogous to the production of " pseudonavicellse ;; in an encysted Gregarina. It has been doubted, apparently with considerable reason, whether the so- called Amoeba are distinct species of animals, or whether they are not rather transitory stages in the life-history of other organisms. It is quite certain that several of the Protozoa pass through an Amoeboid stage, and it is also certain that vegetable matter not uncommonly assumes similar characters (e.g., the mycelium of certain fungi). It is therefore not impossible that the forms known to the microscopist as Amoeba may be ultimately discovered not to be permanent and distinct species ; but the evidence on this head is still defective. It is certain, at any rate, that many organisms, both vegetable and animal, pass through amoeboid stages — consist- ing, for a longer or shorter period, of protoplasm capable of emitting " pseudopodia." It is certain, also, that such amoeboid masses cannot be distinguished from true Amcebce, otherwise than by their life-history. When, therefore, we are informed that Amcebce can be shown to develop into different and higher organisms, we must construe the statement as meaning nothing more than that the higher organisms in question pass through an " amoeboid " stage in the course of their development. PROTOZOA ; RHIZOPODA. 57 The remaining members of the Amazbce are constructed more or less closely after the type of the Amoeba itself. In the nearly allied Difflugia, the sarcode forming the body of the animal is invested with a membranous envelope or " carapace," strengthened by grains of sand and other adventitious solid particles, and having a single aperture at one extremity, through which the pseudopodia are protruded (fig. 3, b). The animal generally creeps about head-downwards, so to speak ; that is to say, with the closed end of the carapace elevated above the surface on which it is moving. Difflugm often exhibit the phenomenon known as " conjugation " or " zygosis." Under these circumstances, two Difflugite come in contact ; the mouths of the two tests are brought together ; the two animals flow back- wards and forwards into each other's tests, with an apparently complete incorporation ; and finally they separate again, and each retires to its own test. In Arcella there is a discoid or basin-shaped carapace, secreted by the animal itself, and like- wise possessing but a single pseudopodial aperture, placed in this case on the flat surface of the body. In Pamphagus there is no carapace, but the pseudopodia are nevertheless protrusible from one extremity only of the body, the remainder of the surface appearing to be of too resistant a consistence to allow of this. The common sun-animalcule (Actinophrys sol) is another well-known Rhizopod which is Fig. 5.— Actinofhrys sol : showing the radiating pseudopodia. One specimen has swallowed a Diatom. usually placed in this order (fig. 5). It consists of a spherical mass of sarcode, about 1-1300 of an inch in diameter, and usually covered with long, radiating, filamentous pseudopodia, which are much less mobile than in the case of the Amceba. The division of the substance of the body into ectosarc and endosarc is tolerably evident, and the latter contains numerous 58 MANUAL OF ZOOLOGY. garnules and vacuoles. The pseudopodia are derived from the ectosarc alone, the endosarc not passing into them, and they exhibit a circulation of granules along their edges, though this is not nearly so marked a feature as in the case of the Foraminifera. A nucleus and contractile vesicle are also present. The long filamentous pseudopodia of Actinophrys make a decided approach to the Foraminifera, and for this reason the sun-animalcule is sometimes placed with the latter in a single order. The Amosbea may be divided into two sub-orders : i. Amoebina, including those forms which have the body naked ; and 2. Arcellina, comprising those in which the body is protected by a carapace. CHAPTER III. FORAMINIFERA. ORDER III. FORAMTNIFERA. — The Foraminifera may be defined as Rhizopoda in which the body is protected by a shell or " test" usually composed of carbonate of lime ; there is no distinct separation of the sarcode of the body into ectosarc and endosarc, and the nucleus and contractile vesicle are both absent. The pseu- dopodia are long and filamentous, and interlace with one another to form a network. The Foraminifera are specially characterised by the posses- sion of a " test " or external shell, which is usually composed of carbonate of lime, but is often composed of grains of sand or other adventitious solid particles cemented together by animal matter, or which, as in Gromia, may be simply chitin- ous. (If Lieberkuhnia is to be regarded as a Foraminifer, the possession of a test cannot be looked upon as essential, since this animalcule is naked. The Monera, also, differ from the present group mainly, if not altogether, by their naked and unprotected bodies.) The test is usually composed of an aggregation of chambers or "loculi" (fig. 7, c\ and its walls are usually pierced by numerous pores or " foramina" through which the pseudopodia are protruded ; the place of these being in some forms supplied by the large size of the terminal, or " oral" aperture of the shell (fig. 7, V). The presence or absence of foramina in the shell-walls is believed to constitute a genuine structural distinction, and the Foraminifera may be PROTOZOA : FORAMINIFERA. 59 thereby divided into two great groups (Perforata and Imfier- forata). As regards the soft parts of the Foraminifera, the body is composed of extensile and contractile sarcode — usually red- dish or yellowish in colour — which not only fills the interior of the shell, but generally invests its outer surface also with a thin film, from which the pseudopodia are emitted (fig. 6, b). The Fig. 6. — Foraminifera. a The animal of Nonionina, after the shell has been removed by a weak acid ; b Gromia (after Schultze), showing the shell surrounded by a network of filaments derived from the body-substance. test, therefore, in this case, is not a true cuticular secretion, like that of the Mollusca, but it is truly immersed within the sarcode of the body. The sarcode is not differentiated into a distinct ectosarc and endosarc, and is devoid of a nucleus and contractile vesicle, and, indeed, of any organs or specialised parts of any kind. From this uniformity in its composition there seems some reason to conclude that the Foraminifera — 6o MANUAL OF ZOOLOGY. in spite of the complexity and mathematical regularity of many of their shells — should be looked upon as the lowest forms of the Rhizopoda, or even of the Protozoa. The pseudopodia in all the Foraminifera (fig. 7, b, c} are fila- mentous and protrusible to a great length, and they possess the singular property of uniting together in various directions so as to form a kind of network, like an " animated spider's web." (Hence the name Reticulosa applied to the order by Dr Carpenter.) This property, however, is not peculiar to members of this order, but is seen also in Actinophrys and in the Thalassicollida, though to a less extent. Further, through- out the entire network formed by the inosculating pseudo- Fig- 7- — Morphology of Foraminifera. a Lagena vulgaris, a monothalamous Forami- nifer ; b Miliola (after Schultze), showing the pseudopodia protruded from the oral aperture of the shell ; c Discorbina (after Schultze), showing the nautiloid shell with the foramina in the shell-wall giving exit to pseudopodia ; d Section of Nodosaria (after Carpenter) ; e Nodpsaria hispida: f Globigerina bulloides. podia there is a constant circulation of granules in different directions. This singular phenomenon is in many respects analogous to the circulation of granules which is seen in many vegetable cells, and it is believed by Dr Carpenter that " the conditions of the two sets of phenomena are essentially the same." The shells of Foraminifera may be classed in three divisions, termed respectively the "porcellanous," the "hyaline" or " vitreous," and the " arenaceous." The porcellanous shell is quite homogeneous in its composition, is opaque-white when PROTOZOA I FORAMINIFERA. 6 I seen by reflected light, and is not perforated by pseudopodial foramina. In these forms (e.g., Miliola, fig. 4, b) the pseudo- podia are emitted solely from the mouth of the last-formed segment of the shell. The vitreous shell is transparent and glassy in texture, and its walls are perforated by numerous pseudopodial apertures. The arenaceous shell is, properly speaking, not a true shell secreted by the animal, since it is simply composed of particles of sand united together by some unknown cement. Its walls may or may not be traversed by pseudopodial foramina. As regards the form of the shell, the Foraminifera may be conveniently, though arbitrarily, divided into two sections : the Monothalamia and the Polythalamia. In the first of these sections (fig. 7, a), comprising the so-called " simple " or " uni- locular " Foraminifera, the shell consists of a single chamber, and the animal is, in fact, nothing .more than a little mass of carcode enveloped in a calcareous covering. Lagena (fig. 8, A) A B c Fig. 8. — Diagram to illustrate the formation of the compound Foraminffera. A, Simple form (Lagena), consisting of a sphere of sarcode, surrounded by a cal- careous shell ; B, Compound form, produced by linear gemmation from a primitive segment resembling A (Nodosarid) ; C, Compound form (Discorbina], in which the buds are thrown out in a spiral, the coils of which lie in one plane. with its beautiful flask-shaped shell, may be taken as the type of this division. Another well-known unilocular form is Entosolenia, which is like Lagena in shape, but has the tubular neck reversed, so as to be inserted into the interior of the test. In the Polythalamia, or " multilocular " Foraminifera, the shell is composed of many chambers separated from one another by divisional walls or "septa" (fig 7, c, d, e\ each of which is per- forated by one or more openings, "septal apertures," by means of which the sarcode occupying the different chambers is united into a continuous and organic whole, the connecting bands being called " stolons." Complex as their structure often is, the compound Foraminifera are, nevertheless, formed 62 MANUAL OF ZOOLOGY. by a process of continuous gemmation or budding from a single "primordial segment" in every respect identical with the permanent condition of a simple species. They commence their existence, therefore, as Monothalamia, and are converted into Polythalamia merely by a process of "vegetative" or "irre- lative repetition." As their development proceeds, the primitive mass of sarcode, or "primordial segment," throws out fresh segments in the form of buds according to a determinate law ; and it is upon the direction in which these segments are evolved that the ultimate form of the shell depends (fig. 8). The more important variations in this respect are as follows : — If the additional segments are added to the primordial chamber in a linear series, so as to form a straight or slightly curved line, we obtain respectively a Nodosaria (fig. 7, d, e) or a Den- talina. When the new chambers are added in a spiral direction, each being a little larger than the one which preceded it, and the coils of the spiral lying in one plane, then we get the " nauti- loid" shell, so common amongst the Foraminifera (fig. 7, c). This type of shell is so closely similar to the shape of the Pearly Nautilus, that the older naturalists were long in the habit of classing these forms along with the Cephalopoda, or Cuttlefish order. In the true nautiloid shell the convolutions of the spiral lie in a single plane, as in Rotating and the shell is said to be " equilateral." In other cases, however, the spiral passes obliquely round a central axis, and the shell becomes conical or turreted, when it is said to be " inequilateral " or " trochoid." In other forms, such as Nummulites (fig. 9) and Orbitolites, the structure of the shell> though regular, is much more compli- cated. Besides these symmetrical forms, there exist others in which the arrangement of the segments is very irregular, as is seen in Globigerina, Acervulina, &c. (fig. J,f). Besides the true pseudopodial foramina with which the walls of the test in most of the Foraminifera are pierced, there exists in some forms an additional system of complicated branching and anastomosing tubes, which are distributed between the laminae of the shell, and establish a communication between its external and internal surfaces. CLASSIFICATION OF FORAMINIFERA. — The classification of the Foraminifera has hitherto proved a matter of extreme diffi- culty, and probably none of the arrangements as yet proposed can be considered as more than provisional. The following is the classification adopted by Dr Carpenter, who is one of the greatest living authorities upon the group : — . ORDER RETICULOSA. (-FORAMINIFERA.) — Rhizopods show- PROTOZOA : FORAMINIFERA. 63 ing no differentiation, or a very imperfect one, into ectosarc and endosarc ; no nucleus or contractile vesicle ; pseudopodia filament- ous, minutely subdivided, and inosculating freely to form a net- work. * Section I. Imperforata. — Envelope membranous or calca- reous, the walls not perforated by apertures for the pseudo- podia, which are emitted solely from the single or multiple aperture of the shell. Families, i . Gromida. Test membranous. 2. Miliolida. Test porcellanous. 3. Lituolida. Test arenaceous. Section 2. Perforata. — Envelope calcareous (hyaline or vit- reous) or rarely arenaceous, its walls traversed by numerous foramina for the emission of pseudopodia. The following classifications by D'Orbigny and Schultze are founded merely upon the form of the shell, and, as such, are purely arbitrary. Of the two, Schultze's arrangement is pro- bably the more satisfactory. TABLE OF D'ORBIGNY'S ARRANGEMENT OF THE FORAMINIFERA. Order I. Monostega. — Body consisting of a single segment; the shell of a single chamber. Order 2. Stichostega. — Segments arranged in a single row, in a straight or slightly curved line. Order 3. Helicostega. — Segments arranged in a spiral, the shell forming a number of convolutions. (The "nautiloid " Foraminifera.} Order 4. Entomostega. — Segments arranged on two alternating axes, forming a spiral. Order 5- Enallostega. — Segments arranged on two or three alternating axes, not forming a spiral. Order 6. Agathistega. — Chambers wound round an axis, each segment embracing half the entire circumference. TABLE OF SCHULTZE'S ARRANGEMENT OF THE FORAMINIFERA. Section I. Helicoidea. — Segments arranged in a convolute series. Section 2. Rhabdoidea. — Segments placed in a direct line. Section 3. Soroidea. — Segments disposed in an irregular manner. AFFINITIES OF FORAMINIFERA. — The Foraminifera are re- lated on the one hand to the Amcebea, and on the other to the Spongida. From the former the " unilocular " Foraminifera differ, both in the possession of an external envelope, and in the much less highly differentiated characters of their sarcode ; but the points of resemblance are obvious, and in such forms as Actinophrys and Lieberkiihnia we are presented with an ap- parent transition between the two orders. From the shelled Amcebea, such as Arcdla, the Foraminifera are broadly sepa- 64 MANUAL OF ZOOLOGY. rated by the absence in the former of pseudopodial pores, and are fundamentally distinguished by the different nature of the sarcode-body. To the Sponges the Foraminifera are related in various ways, one of the most striking links being found in Carpenteria, a singular attached form of Foraminifer. The shell, namely, of Carpenteria is conical and calcareous, composed of an aggre- gation of chambers arranged in a spiral, and having its walls perforated by numerous foramina of minute size. The interior of the chambers, however, is filled with " a fleshy, sponge-like body," strengthened by numerous spicula. Another curious link between the Foraminifera and the Sponges is the Squa- mulina scopula of Carter, which is truly a Foraminifer, though originally referred to the latter. It consists of an arenaceous test, forming a pedestal surmounted by an obversely conical column. Both pedestal and column are more or less perfectly chambered, and are filled with semi-transparent yellowish sar- code. At the summit of the column is a minute aperture sur- rounded by a brush of spicules, and the whole structure is fixed by the pedestal to some solid object. To the Polycystina, the Foraminifera are obviously and closely allied. They agree in the nature of the sarcode-body, in the filamentous, inosculating pseudopodia, and in the phe- nomenon of a pseudopodial circulation of granules. They differ solely in the nature of the " test," which is calcareous or arenaceous in the Foraminifera, but is always siliceous in the Polycystina. BATHYBIUS, COCCOLITHS, AND COCCOSPHERES. — It may be as well to notice here a singular organism which is certainly referable to the Rhizopoda, though its exact affinities are doubtful. Certain minute oval or rounded bodies have long been known as occurring attached to the surface of the shells of Foraminifera, and they were originally described by Professor Huxley under the name of coccoliths. Subsequently it was discovered by Dr Wallich that these singular bodies occur not only in the free condition, but also attached to the external surface of little spherical masses of sarcode to which he gave the name of coccospheres. The coccospheres are enclosed in a delicate envelope apparently of a calcareous nature, and are studded at nearly regular intervals by the coccoliths. More recently still, it has been discovered by Professor Huxley that both the coccoliths and the coccospheres are embedded in masses of protoplasmic or sarcodic substance, covering wide areas of the sea-bottom, to which they bear the same relation that the spicules of sponges or of Radiolaria do to the soft parts of these animals. To this undefined and diffused protoplasm with its contained coccoliths and coccospheres the name Bathybius has been applied by Professor Huxley. Its exact position, as already said, is doubtful ; but it is believed by Dr Car- penter to be a rudimentary form of the Foraminifera, and to be somewhat allied to the ancient Eozo'dn* A curious point has recently been brought to light by Dr Gurnbel, the celebrated palaeontologist, who has succeeded PROTOZOA : FORAMINIFERA. 65 in demonstrating that bodies similar to, if not identical with, a*w/zV/b, occur in formations as old as the Potsdam Sandstone (Lower Silurian) of North America. More recently still, Mr Carter has shown that coccoliths occur in great numbers in the Laminarian zone, and he asserts them to be solitary, unicellular, calcareous Alga. He describes them under the name of Melobesia unicellularis and M. discus, according as they are oval or round ; and he believes that the coccospheres are most probably their "sporangia." Upon this view the term ''coccoliths" would be restricted to the fossil forms. DISTRIBUTION OF FORAMINIFERA IN SPACE. — The Forami- nifera are marine, and are found in almost all seas, though more abundantly in those of the warmer parts of the globe. It is concluded by Dr Carpenter that " the foraminiferous fauna of our own seas probably presents a greater range of variety than existed at any preceding period ; but there is no indication of any tendency to elevation towards a higher type." One of the most remarkable facts about their distribution at the present day, is the existence of a deposit at great depths in the Atlantic, but only in areas traversed by heated currents, formed almost entirely of the shells of Foraminifera, and very closely resembling chalk. It has further been quite recently established that there coexist with these Foraminifera various animals of a higher grade, some of which closely resemble, or are even specifically inseparable from, well-known Cretaceous species. There is therefore some reason to conclude that the bottom of the sea at great depths is peopled at the present day by a fauna which is very closely allied to that of the Chalk. Most living Foraminifera are very minute, but some of the extinct forms attained the size of as much as three inches in circumference (e.g., the Nummulite, fig. 9), and spheres of Parkeria may attain a circumference of nearly eight inches. Some forms may be obtained adhering to the roots of tangle at or near low-water mark, but they are mostly to be dredged from tolerably deep water. They have been found, in fact, in great abundance in the deepest parts of the ocean which have as yet been examined by the dredge — at a depth, namely, of nearly three miles. DISTRIBUTION OF FORAMINIFERA IN TIME. — Remains of Foraminifera have been found in Palaeozoic, Mesozoic, and Kainozoic formations. In the oldest stratified rocks with which we are acquainted — viz., the Laurentian rocks of Canada- there occurs a singular body which has been described as the remains of a gigantic Foraminifera, under the name of Eozob'n Canadense. If truly organic, as is doubted by some, it is the oldest fossil as yet discovered. It appears to have grown in reef-like masses resembling the sessile patches of Poly- E 66 MANUAL OF ZOOLOGY. trema* and Carpenteria, to both of which, as well as to the extinct Nummulites, it shows a decided affinity. In the Silurian rocks, remains of Foraminifera, some of which are apparently iden- tical with existing forms, have been detected in various places, and it is not improbable that the large Silurian fossils known as Receptaculites and Stromatopora should really be referred to this $rder. In the Carboniferous rocks of Russia whole beds are composed of a species of Fusulina. In the Secondary rocks Foraminifera occur in great abundance, the widely-spread for- mation known as the Chalk being crowded with these organ- isms. Chalk itself, in fact, is almost entirely composed of the cases of Foraminifera, some of which are identical with species now existing. Fig. 9. — Nummulites Icevigatus. Eocene. In the Tertiary rocks the Foraminifera attain their maximum of development, both as regards the size and the number of the forms which characterise them. The period of the Middle Eocene is especially distinguished by a very widely spread and easily recognised rock known as the Nummulitic Limestone, so called from the abundance in it of a large coin-shaped Fora- minifer termed the Nummulite (fig. 9). The Nummulitic Lime- stone stretches from the west of Europe to the frontiers of China; but in some cases, in place of Nummulites proper, it contains the remains of a mimetic form termed Orbitoides. Upon the whole, Dr Carpenter concludes that "there is no evidence of any fundamental modification or advance of the foraminiferous type from the Palaeozoic period to the present time." * Polytrema is a little branched coral-like Foraminifer, composed of a calcareous test forming a number of irregular chambers, which communicate with one another by wide orifices, and are filled with colourless sarcode. The walls of the chambers are also penetrated by an extensive system of capillary canals. PROTOZOA: RADIOLARIA. 67 CHAPTER IV. RADIOLARIA. ORDER IV. RADIOLARIA. —The order Radiolaria was founded by Miiller to include the Polycystina, the Acanthomet- rina, and the Thalassicollida, to which Dr Carpenter adds Actinophrys and its allies, chiefly on account of the form of the pseudopodia. Here, however, the term will be employed to designate the first three of these, and Actinophrys will be placed amongst the Amoebea, to which its alliance appears to be more decided. Most of the Radiolaria are marine, but some few forms of Thalassicollida have been described as occurring in fresh water. The order Radiolaria may be defined as comprising those Rhizopods which possess a siliceous test or siliceous spiciiles, and are provided with pseudopodia which stand out like radiating fila- ments, and occasionally run into one another. i. FAMILY ACANTHOMETRINA. — The Acanthometra (fig 10, a) are all minute, and are found floating near the surface in the open ocean, sometimes in great numbers. They consist of sarcode-bodies which are supported by a framework of radiat- ing siliceous spines, the extremities of which usually project Fig. 10.— a. Acanthometra lanceolata ; b Haliomma hexacantkum, one of the Polycystina, showing the radiating pseudopodia. (After Muller.) considerably beyond the body. The substance of the body admits of division into an outer membranous layer, or " ecto- sarc," and an internal granular layer, or " endosarc." The siliceous spines are hollow, being grooved at the base by a gutter, which is continued further up the spine by a canal ter- minating at the apex of the spine by a distinct aperture. The 68 MANUAL OF ZOOLOGY. spines, in consequence of this structure, are able to serve for the transmission of the pseud opodia, which gain the exterior by running through the canals and escaping at their apices. Many of the pseudopodia, however, do not occupy the canals of the spines. II. FAM. POLYCYSTINA. — The members of this family are closely related to the Foraminifera, differing from them chiefly in the fact that their shells are composed of flint instead of carbonate of lime, as in most of the latter. They possess a body of sarcode, which is enclosed in a foraminated siliceous shell, which is often furnished with spine-like processes, and is usually of great beauty (fig. 10, b). The sarcodic substance of the body is olive-brown in colour, with yellow globules, and often does not entirely fill the shell. The pseudopodia are emitted through the foramina in the test, and are long, ray-like filaments, which display a slow movement of granules along their borders. The Polycystina are all microscopic, and are all inhabitants of the sea, having a very wide distribution. They are also found abundantly in certain Tertiary deposits, being often erro- neously described as Diatomacea. III. FAM. THALASSICOLLIDA. — The 'Thalassicollida have been defined as being Rhizopoda which are " provided with structureless cysts containing cellular elements and barcode, and surrounded by a layer of sarcode, giving off pseudopodia, which commonly stand out like rays, but may and do run into one another, and so form networks'1'1 (Huxley). The Thalassicollida may be simple or composite, the latter consisting essentially of aggregations of the former; whilst these are fundamentally composed of a mass of granular proto- plasm, containing a nucleus, but without a contractile vesicle, " enclosed in a membranous capsule, which is in turn protected by a more or less thick gelatinous exudation, whilst numerous sarcoblasts occur scattered through the endosarc, and occa- sionally a few may be seen suspended within the external gela- tinous stratum " (Wallich). The whole organism is supported by more or less extensively developed skeletal structures. The skeleton may be simple, consisting of a delicate fenestrated shell ; or may be compound, consisting of a number of spicular masses. The three best-known genera of the family are Spharozoum, Collosphcera, and Thalassicolla. They are all marine, being found floating passively at the surface of most seas ; and they vary in size from an inch in diameter downwards. Sphcerozoum consists essentially of a number of spherical sarcode-bodies PROTOZOA I SPONGIDA. 69 (sometimes called " cellaeform bodies ") with distinct nuclei, surrounded by a zone of siliceous spicules, the whole being embedded in a common gelatinous matrix. The centre of the mass is vacuolated, sometimes to such an extent that it becomes a hollow sphere. In Collosphcera, the spherical body — which is very like that of the preceding form — is enclosed in a transparent siliceous Fig. n. — Morphology of Radiolaria. a Siliceous fenestrated test of Collosphara Hiixleyi j b Thaiassicolla mowtm, showing cellseform bodies, compound groups of spicules, and radiating pseudopodia. envelope, which is perforated by numerous rounded apertures or " fenestrae." This form, therefore, approaches very closely to the Polycystina, especially to those in which the foramina are so large that the test is reduced to a mere reticulate frame- work (fig. n, a). Thaiassicolla differs little from either of the above in fun- damental structure, but it contains a number of compound siliceous spicules embedded in its ectosarc (fig. n, b). CHAPTER V. SPONGIDA. ORDER V. SPONGIDA. — The true nature of sponges has long been a matter of dispute, but they are now almost universally referred to the animal kingdom, and placed either in or near the Rhizopoda. Some observers still maintain the vegetable nature of sponges, but this opinion has no real grounds for its support, and is chiefly founded upon loose analogies, and upon a certain similarity in outward form. The Spongida may be defined as " sar code-bodies, destitute of 70 MANUAL OF ZOOLOGY. a mouth, and united into a composite mass, which is traversed by canals opening on the surface, and is almost always supported by a framework of horny fibres, or of siliceous or calcareous spicula" (Allman). From the above definition it will be seen that a sponge is composed essentially of two elements — a soft, gelatinous, investing "flesh," and an internal supporting framework or " skeleton." Taking an ordinary horny sponge as the type of the order, we find it to be composed of a skeleton (fig 13, d) of horny reticulated fibres which interlace in every direction, and are pierced by numerous apertures, the whole surrounded exter- nally and internally by a gelatinous glairy substance, like white- of-egg, the so-called " sponge-flesh." The horny skeleton is composed of a substance called " keratode," and is often strengthened by spicula of lime or flint, which also occur less abundantly in the sponge-flesh. These must not, however, be confounded with the skeleton of the true calcareous or siliceous sponges in which the keratode is wanting. Of the apertures which penetrate the substance of the sponge in every direction, some are large crateriform openings, and are termed " oscules," or " exhalant apertures ; " whilst others, which occur in much greater numbers, are greatly smaller in size, and are termed " pores," or " inhalant apertures." Both the oscula and pores can be closed at the will of the animal ; but the oscula are permanent apertures, whereas the pores are not constant, but can be formed afresh whenever and wherever required. The " sponge-flesh," which invests the entire skeleton, is found upon a microscopical examination to be composed of an aggre- gation of rounded amcebiform bodies — the so-called " sponge- particles " or " sarcoids " (fig. 3, c, d, e). Some of these are ciliated ; whilst all are capable of emitting pseudopodia from all parts of their surface, and are provided with nuclei, thus coming closely to resemble so many Amoeba. Regard- ing the skeleton as something superadded, we may, in fact, look upon a sponge as being essentially nothing more than an aggregation of Amcebcz, since each " sarcoid " is capable of procuring and assimilating food for itself in a manner strictly analogous to what we have seen in the Amoeba. This view becomes still more easily comprehensible when we consider the simplest condition in which a sponge occurs in nature (as exemplified, for instance, in certain of the Calcispongice) ; the condition, namely, in which the entire sponge consists of a colony of amcebiform sarcoids, secreting a common skeleton, but provided with only a single " osculum," and a greater or PROTOZOA I SPONGIDA. 7 I less number of inhalant " pores." There are, in fact, many who hold that the more complex sponges are merely pro- duced by the aggregation together of a number of these simpler colonies. The "sarcoid" has been shown by Mr Carter to be "a granuliferous polymorphic body, possessing a nucleus and one or more contracting vesicles." It has also been shown that the monociliated sarcoids possess, in some cases at any rate, a membranous cylindrical collar round the base of the cilium, similar to that which has been observed in the Flagellate In- fusoria. To construct a typical sponge, therefore, we must imagine that a number of sarcoids, such as above described, are aggregated to form a community of a somewhat spherical shape, with a common circular aperture ; that each sarcoid has the power of taking food into its interior, and of discharging the indigestible portions, after the manner of an Amoeba; and that the circular aperture opens and closes itself as required by the needs of the colony. We have further to imagine that these spherical communities are the essential elements of the sponge, and that they are embedded in countless numbers in the sarcode of each individual sponge, constituting the so-called " ciliated chambers." In a living sponge a constant circulation of water is main- tained by means of an aquiferous system (fig. 12), which is Fig. 12.— Diagiammatic section o(Sfrngilta (after Huxley), a a Superficial layer or "dermal membrane ; " b b Inhalant apertures or " pores ; c c Ciliated chambers ; d An exhalant aperture or "osculum." The arrows indicate the direction ot currents. constituted by the oscula and pores— already alluded to— and by a system of canals excavated in the substance of the sponge, and uniting the two sets of apertures. The water passes in by the " pores " or inhalant apertures, and is con- veyed by a series of canals— the "incurrent" or " afferent''' 72 MANUAL OF ZOOLOGY. canals — to a second series of tubes — the " excurrent " or " efferent " canals — by which it reaches the " oscula " and is finally expelled from the body. These processes are regularly performed, and their mechanism was long a subject of specu- lation. It is now known, however, that beneath the super- ficial layer or " dermal membrane " of the sponge there exist chambers lined with sponge-particles which are provided with vibratile filaments or cilia (fig. 1 2, c, c). The pores open into these chambers, and from them proceed the incurrent canals, each being dilated at its commencement into a sac, which is also lined with ciliated sponge-particles. By the vibratile action of these cilia, currents of water are caused to set in by the pores ; and as out-going currents proceed from the oscula, a constant circulation of fresh water is maintained through the entire sponge. In this way each individual sponge-particle is enabled to obtain nutriment : the process being at the same time not improbably a rudimentary form of respiration. The chambers or sacs lined with ciliated sarcoids have been shown by Mr Carter to be the essential element in the organisation of the fresh-water and marine sponges, and to be the fundamental expression of the alimentary system. The reproduction of sponges may be effected either asexually or sexually, the following being a brief outline of J^g- 13-— a Gemmule of Spo ngilla : h Hilum ; b Diagrammatic section of the gem- mule, showing the outer layer of amphidiscs and the inner mass of cells ; c One of the amphidiscs seen in profile ; d Fragment of the skeleton of a horny sponge (after Bowerbank), showing the interlacing horny fibres with spicula. All much magnified. the phenomena which have been observed in the common fresh-water sponge (Spongilla), in which the process has been most accurately noticed. PROTOZOA : SPONGIDA. 73 In the first or asexual method of reproduction, which takes place in the winter, the deeper portions of the sponge are found to be filled with small seed-like rounded bodies, termed " gemmules " or " spores/' each of which possesses a small aperture or "hilum" at one point (fig. 13, //). Eachgemmule is composed of an outer coriaceous capsule surrounded by a layer of peculiar asteroid spicula, resembling two toothed wheels united by an axle, and termed "amphidiscs" (fig. 13, £, c). These amphidiscs are embedded in sarcode, whilst their inner surfaces rest upon the tesselated capsule already men- tioned. In the interior of the capsule thus formed is a mass of cells, of which the central ones contain numerous germs. When the spring comes, these masses of " ovi-bearing cells " are discharged through the "hilum" of the gemmule into the water, and are developed into new Spongillce. Spongilla also appears to reproduce itself in a somewhat ana- logous manner by means of what are termed " swarm-spores." These are small bodies, containing reproductive germs, and provided with numerous cilia by which they move about actively, becoming finally attached to some solid body, and developing themselves into the adult sponge. In the second or sexual method of reproduction, certain of the sponge-particles or " sarcoids " separate themselves and become nucleolo-nucleated, thus coming to resemble ova. At the same time other sarcoids become motionless, and their contents become molecular, and are finally converted into spermatozoa. By the rupture of these, and by the consequent contact of the different elements, embryos are produced, which are at first ciliated and move about freely, becoming eventually stationary, and developing into new individuals. CLASSIFICATION OF THE SPONGES. — The Spongida have been variously classed> and a good natural arrangement is still a desideratum. By Dr Bowerbank they are somewhat arbi- trarily arranged in three orders — viz., the Keralosa, the Silicea, and the Calcarea, of which the first is believed to hold the lowest place. In the Keratosa the skeleton is composed of interlacing horny fibres, often strengthened by spicula either of flint or lime. In the Calcarea or Caldspongia the skeleton is composed of carbonate of lime ; whilst in the Siliceous sponges it is composed either of spicules of silex, or " of solid, lami- nated, and continuous siliceous fibre/' By Professor Wyville Thomson the siliceous sponges are arranged in a separate order under the name of the " vitreous sponges " ( Vitred). The nature of the skeleton thus varies considerably, whilst the spicules show almost indefinite modifications of shape, though 74 MANUAL OF ZOOLOGY. they are constant for any given species, in any given part of its organisation. The sponge-flesh is much more uniform in its nature and composition. It may be noticed, however, that in Spongilla the sponge-particles are filled with green granules, which are apparently identical in chemical composition with the green colouring matter of plants (chlorophyll). In Grantia, too, the sarcoids are furnished with long filamentous appen- dages or cilia (fig. 3, d\ The siliceous sponges are mostly in- habitants of the deep sea, and many of them are remarkable for their long and slender spicules of flint. In Hyalonema^ or the glass-rope, long placed amongst the Zoophytes (Zoantharia sclerobasica), and still considered as such by competent authori- ties, there is a cup-shaped sponge-body, supported by a rope of long twisted siliceous fibres, which are sunk in the mud of the sea-bottom. In other " anchoring sponges," such as Pheronema and Holtenia, the body is sessile or stemless, and is moored to the mud by a beard of long delicate spicules. These sponges, in their single, long, chimney-like osculum, show a curious resemblance to the fossil Siphonias of the green sand. Similar root-fibres of flint, traversing the mud in every direc- tion, occur in the beautiful Venus' Flower-basket (Enplectelld), without any exception one of the most exquisite of all organic structures known to us. DISTRIBUTION OF SPONGES IN SPACE. — Sponges are almost exclusively marine, the SpongUl& alone being inhabitants of fresh water ; and they are of almost universal occurrence. The sponges of commerce are mostly obtained from the Grecian Archipelago and the Bahama Islands. Recently the existence of numerous siliceous sponges at great depths in the ocean has been demonstrated by Drs Carpenter and Wyville Thomson. They are associated with numerous Foraminifera and with Crinoidea, the whole assemblage bearing a singularly close re- semblance to the fauna of the Cretaceous epoch. The com- mon marine sponges are mostly found attached to some solid object between tide-marks or in deep water. The vitreous or siliceous sponges appear to be exclusively inhabitants 'of the deeper parts of the ocean. One genus (Cliona) inhabits branching cavities in shells, which the sponge excavates for itself apparently by means of its siliceous spicula. Fossil shells mined by a boring-sponge, allied to the recent Cliana, are found from the Silurian rocks upwards. DISTRIBUTION OF SPONGES IN TIME. — Remains of sponges are known to occur in formations belonging to the Palaeozoic, Mesozoic, and Kainozoic epochs. The keratose or horny sponges are obviously incapable of leaving any evidence of PROTOZOA: SPONGIDA. 75 their existence, otherwise than by the preservation of the spicula with which the skeleton is sometimes furnished ; and such are occasionally found, though they are of rare occurrence. The calcareous sponges are found from the Silurian rocks upwards, attaining their maximum in the seas of the Secondary epoch, the Chalk being especially characterised by their presence. The most important group of fossil sponges is that known as the Petrospongiadce, characterised by the possession of a stony reticulate framework or skeleton, and by the absence of spicula. The most important genera of this group are Sparsispongia (Devonian) and Ventriculites (Chalk). Of the Palaeozoic sponges, Archceocyathns is found in the Potsdam sandstone of North America (Upper Cambrian ?) ; Palaospongia and Acanthospongia are familiar Lower Silurian forms j and Amphispongia and Favospongia occur along with other forms in the Ludlow rocks. In the Devonian rocks sponges occur pretty frequently, Sparsispongia being the com- monest genus. (The Devonian Steganodictyum is really the cephalic buckler of a pteraspidean fish.) The most important Mesozoic genera of sponges are Ventriculites and Siphonia ; and the order appears, upon the whole, to attain .its maximum in the Cretaceous epoch. There seems no reason to doubt but that many of the chalk-flints owe their origin to sponges ; and in some sections of flint are found minute " spherical bodies covered with radiating and multicuspid spines," which have been termed Spiniferites or Xanthidia, and are probably the " gemmules " of sponges. (By some, however, these bodies are regarded as being the " sporangia " of Desmidice, an order of the Protophyta^) Many Cretaceous and Tertiary shells are found to be mined by a species of boring-sponge, which is nearly allied to the recent Cliona. AFFINITIES OF SPONGES. — As already pointed out, the sponges are allied both to the Amoeba and to the Foraminifera. Indeed the individual "sarcoids" or sponge-particles can scarcely be distinguished, when detached, from Amcebce. The sponges show likewise a decided relationship to the Radiolaria ; and by Professor James Clark they are believed to be nearly allied to the " flagellate " Infusoria. This observer, in fact, states his " conviction that the true ciliated Spongia are not Rhizopoda in any sense whatever, nor even closely related to them, but are genuine compound flagellate Protozoa." To prove this view, however, it should be shown that each sponge-particle possesses at any rate a distinct mouth, with or without a rudimentary alimentary canal. More recently Dr Ernst Haeckel and others have endeavoured to show that the sponges are most nearly 76 MANUAL OF ZOOLOGY. allied to the Sea-anemones (Actinozoa) ; but this seems to have arisen from a misconception as to the compound nature of the former. Three views, namely, may be held as to the " indi- viduality" of a sponge. Firstly, it may be held that the entire organism which we call a sponge is a single animal. The microscope has rendered this view wholly untenable. Secondly, it may be held that the entire sponge-mass is a single " zoological individual," of which each sarcoid is a single " zooid." As each sponge-mass is certainly in most cases the product of a single ovum, this is the most probable and reasonable view. Thirdly, it may be held that each sponge mass consists of a number of aggregated " individuals," each of which is con- stituted by a single exhalant " osculum," together with the greater or less number of inhalant " pores " thereto apper- taining. Upon no other view than this does there appear to be any relation of affinity between the sponges and the Ccslen- terata ; and even on this view the general affinities between the two are not of a very striking nature. In some cases (such as Euplectella amongst the Silicispongice, and Sycum and Ute amongst the Calcispongue) the adult sponge never consists of more than a single osculum and the pores belonging to it, con- stituting what Haeckel terms a single " person." Most sponges, however, form a " stock," consisting of several such " persons " united together. CHAPTER VI. INFUSORIA. » THE Infusoria of many writers comprise many of the lowest forms of plants — such as the Diatoms — together with the Roti- fera, a class of minute animals now known to belong to the Annuloida. By modern writers, however, the term Infusoria is used strictly to designate those Protozoa which possess a mouth and rudimentary digestive cavity. They are, for this reason, often called collectively the " stomatode " Protozoa, in contradistinction to the remaining members of the sub-kingdom, which are all " astomatous." The so-called " suctorial " Infu- soria (Acinetce), however, appear to have no definite oral aper- ture ; and the same is the case with the parasitic Opalina, though there is great doubt as to the propriety of placing this in the Infusoria at all. The name Infusoria itself is derived from PROTOZOA : INFUSORIA. 77 the fact that the members of the class are often developed in organic infusions. The Infusoria, or Stomatode Protozoa, maybe defined as Pro- tozoa which are mostly provided with a mouth and rudimentary digestive cavity, which do not possess the power of emitting pseu- dopodia, but which are furnished with vibratile cilia, or with contractile filaments. They are mostly microscopic in size, and their bodies usually consist of three distinct layers. The Infusoria may be divided into three orders — viz., Suctoria, Ciliata, and Flagellata — of which the second comprises the majority of the members of the class, and alone requires much consideration. I. ORDER CILIATA. — This order comprises those Infusoria in which the outer layer of the body is more or less abundantly furnished with vibratile cilia, which serve either for locomotion or for the procuring of food. Besides cilia, properly so called, some of the ciliated Infusoria are provided with styles or jointed bristles, which are movable, and subserve locomotion ; whilst others have little hooks or uncini, with which they can attach themselves to foreign bodies. As types of the order, Paramos- cium and Vorticella may be selected, the former being free, whilst the latter is permanently fixed in its adult condition. Paramctcium (fig. 14, c] is a slipper-shaped animalcule, com- posed externally of a structureless transparent pellicle — the Fig. 14. — Morphology of Infusoria ; a Epistylis, a stalked Infusorian ; b A single calyx of the same greatly magnified, showing the ciliated disc which protrudes at will, and the ciliated internal cavity into which the particles of food are received. In the substance of the body are the contractile vesicle and smaller food-vactioles. c Diagrammatic representation of Paramceciurn, showing the funnel-shaped gullet, the nucleus and nucleolus, food-vacuoles, and two contractile vesicles, d Aspidisca. lynceus : e Peranema globulosa, a flagellate Infusorian. " cuticle " — which is lined by a layer of firm and consistent sar- code, which is termed the " cortical layer," or the " parenchyma 78 MANUAL OF ZOOLOGY. of the body," this in turn passing into a central mass of softer and more diffluent sarcode, known as the " chyme-mass," or " abdominal cavity." The " cuticle " is covered with vibratile cilia, and is perforated by the aperture of the mouth. The mouth leads into a funnel-shaped gullet, which is not continued into any distinct digestive sac, but is lost in the central " chyme- mass." Within the " cortical layer " are the " nucleus " and "nucleolus," and the "contractile vesicle" (or vesicles). The nucleus is usually a solid band or rod-shaped body, having a small spherical particle applied to its exterior, or immersed in its substance. This latter is the so-called " nucleolus," which must be carefully distinguished from the nucleolus of a cell, which occurs in the interior of the nucleus. The contractile vesicles are clear spaces, which contract and dilate at intervals, and occasionally exhibit radiating canals passing into the sur- rounding sarcode. Ordinarily one contractile vesicle is present, or at most two, but in some cases there may be several. It has also been maintained that the contractile vesicles com- municate with the exterior of the body, but proofs are wanting on this point. Whether this should ultimately be established or not, there can be little doubt but that the vesicles are a rudi- mentary form of vascular apparatus. Others, however, hold, with some probability, that the contractile vesicles are to be regarded as excretory in function, and that they correspond more with the water- vascular system of the Annuloida than with the true blood-vascular system of higher animals. Certain other spaces termed " vacuoles " are generally visible in addi- tion to the contractile vesicles. These, however, are probably merely collections of water surrounding the particles of ingested food, and performing with them a circulation in the abdominal cavity, something like the circulation of granules which is seen in certain vegetable cells. It was the appearance of these " vacuoles " — which are certainly not permanent organs of any kind — which induced Ehrenberg to term the Infusoria the " Polygastrica," upon the belief that they were so many stomachs. Param&cium obtains its food by means of the currents of water which are set up by the constantly- vibrating cilia. The nutritive particles thus brought to the mouth pass into the central abdominal cavity, along with the contents of which they undergo the circulation above spoken of. Indigestible and faecal particles appear to be expelled by a distinct anal aperture, which is situated near the mouth. Reproduction in Paramacium (fig. 15) is effected either non-sexually by fission (/>., by a simple division of its substance), PROTOZOA ! INFUSORIA. 79 or by a true sexual process. In this latter method two Para- mcetia come together, and adhere closely to one another by their ventral surfaces. The " nucleus," which is truly an ovary, enlarges, and a number of ovules are formed in its interior. In like manner, the " nucleolus " of each, which is really a testis or spcrmarium, also enlarges, and develops in its interior a number of fusiform, or rod-like bodies, which are believed to be sperma- tozoa. The nucleolus of each then passes into the body of the other, the act of transference being effected through the Fig. 15. — A, Paramcecium, showing the nucleus («) and two contractile vesicles (v) ; JB, ParamcEcium bursaria. (after Stein), dividing transversely ; n Nucleus ; it Nucleolus ; v Contractile vesicle. C, Paramcecium aurelia (after Ehrenberg), divid- ing longitudinally. mouth. Contact of the two reproductive elements then takes place, and a number of germs are produced, which, after their liberation from the body of the parent, are developed into adult Param&cia. Vorticella (fig. 16, c] is a beautiful flower-like Infusorian which is commonly found in fresh water, adhering to the stems of aquatic plants. It consists of a bell-shaped body or " calyx," supported upon the extremity of a slender contractile stem or "pedicle." The other extremity of the pedicle is fixed to some foreign body, and its power of contraction is due to the presence in its interior of a spiral contractile fibre, which is sometimes called the " stem-muscle." The edge of the bell or calyx is surrounded by a projecting rim or border, called the " peristome," within which is a circular surface, the " disc," forming the upper extremity of the so-called " rotatory organ." The disc is surrounded by a fringe of vibratile cilia, forming a spiral line which is prolonged into the commencement of the digestive canal. Near the edge of the disc is situated 8o MANUAL OF ZOOLOGY. the mouth, which conducts by its entrance or " vestibulum " into a fusiform canal or " pharynx," which terminates abruptly in the abdominal cavity. The particles of food are taken in at the mouth, descend through the short alimentary canal, and enter the abdominal cavity, where they are subjected to the general rotation of the " chyme-mass," being finally excreted by an anal aperture which is situated near the mouth and within the vestibule. As in Param&cium, the body in Vorticella is composed of an outer " cuticle," a central " chyme-mass," and an intermediate " cortical layer," which contains a contractile vesicle and a band-like nucleus. The cortical layer appears to be furnished with muscular fibres, and the contractile stem- fibre is almost certainly a muscle. Reproduction in Vorticella may take place by fission, or by gemmation, or by a process of encystation and endogenous division. In the first of these modes the calyx becomes in- dented in a longitudinal direction — viz., from the pedicle to the disc ; and the groove thus formed becomes gradually deeper until the calyx is finally divided into two halves supported upon the same pedicle. On one of these cups a " posterior " circlet of cilia is then formed in addition to the " anterior " circlet already existing (/>., a fringe of cilia is developed round that end of the calyx which is nearest the attachment of the pedicle and furthest from the disc). The cup (fig 16, d}, thus furnished with a circlet of cilia at both extremities, is then detached, and swims about freely. Finally, the anterior circlet of cilia disappears, and this end of the calyx puts forth a pedicle and becomes attached to some foreign object. A new mouth is now formed within what was before the posterior circlet of cilia; so that the position and function of the two extremities of the calyx are thus reversed. In the second mode of reproduction — namely, that by gem- mation— exactly the same phenomena take place, with this single difference, that in this case the new individual is not produced by a splitting into two of the adult calyx, but by means of a bud thrown out from near its proximal extremity. This bud is composed of a prolongation of the cuticular and cortical layers of the adult with a caecal diverticulum of the abdominal cavity or chyme-mass. It soon develops a posterior circlet of cilia, the connection with the parent is rapidly constricted until complete separation is effected, and then the process differs in no respect from that described as occur- ring in the fissiparous method of reproduction. According to Stein and Greif, however, these so-called "buds" are really small calyces, produced by fission of one Vorticella and then PROTOZOA : INFUSORIA. 8 I attaching themselves to the outside of the calyx of another individual. In the third mode of reproduction the Vorticella encysts itself in a capsule, the cilia and pedicle disappear, and the nucleus breaks up into a number of rounded germs, which are ultimately liberated by the rupture of the cyst, and, after a short locomotive stage, develop themselves into fresh Vorticella. How far this process may be truly sexual is not known, and no form of un- equivocal sexual reproduction has hitherto been shown to occur in the case of Vorticella. Epistylis is a not uncommon form of fixed Infusorian which is nearly allied to Vorticella, and differs chiefly in the fact that the pedicle is much branched, and is rigid and not contractile. Epistylis (fig. 14, a) usually occurs in the form of a greyish- white nap on the stems of water-plants, or on the head of the common water-beetle, the Dytiscus marginalis. It consists of a plant-like branching and re-branching frond, the stems of which are quite transparent and faintly striated, but are not contractile, though capable of movement from side to side. Each branch of the entire colony terminates in an oval calyx, articulated to the stem by a distinct joint, upon which it can move from side to side. The calyces are oval or somewhat campanulate, but have the power of altering their dimensions, and especially of contracting so as to shorten their antero- posterior diameter. Each calyx, in some species, terminates distally in a slightly-elevated annular aperture, the margins of which are regularly toothed. The calyx appears to be formed by a hardening of the cuticle, and to form a distinct case, with a double margin, enclosing the animal. The sarcode-body enclosed within this outer envelope is of a light-brown colour, and full of minute granules, with larger food-vacuoles and a well-marked contractile vesicle, which contracts and dilates two or three times a minute. The animal can retract itself entirely within its cup, and can at will exsert a ciliated disc. This disc (fig. 14, b) is inversely conical, and acts as a kind of plug, and it is provided with two tufts of long cilia, one on each side. On one side of the protrusible disc is the oral aperture, which is continued by a distinct and well-.marked gullet into a central ill-defined cavity. Both the entrance of the gullet and the bottom of the central cavity are provided with very long, actively-vibrating cilia, some of which are almost setiform. The entire granular contents of the abdominal cavity undergo a constant though slow rotation. Carchesium is another form which is like Epistylis in consist- ing of a number of calyces supported upon a branched pedicle, F 82 MANUAL OF ZOOLOGY. but differs from Epistylis and agrees with Vorticella in the fact that the pedicle is contractile. Stentor, or the trumpet-animalcule (fig. 16, b\ is another common Infusorian which is closely related to Vorticella. It Fig. 16. — a Vaginicola crystallina ; b Steutor Mulleri ; c Group of Vorticellce ; d Detached bud of Vorticella, showing the posterior circlet of cilia. consists of a trumpet-shaped calyx, devoid of a pedicle, but possessing the power of attaching and detaching itself at will. When detached it swims by means of the anterior circlet of cilia, just as the calyx of Vorticella will, if broken from its stalk. True muscular fibres appear to be present in the cor- tical layer of Stentor. In Vaginicola (fig. 16, a) the essential structure is much the same as in Vorticella, but the body is protected by a membranous or horny case (" carapace " or " lorica "), within which the animal can retire. In this beautiful Infusorian the carapace is certainly a cuticular secretion, but it appears at the same time to be quite distinct from the true cuticle itself. Amongst the structures of the Infusoria which require some notice are the "pigment spot" and the " trichocysts." The pigment spot is a brightly-coloured solid particle, generally red, of very common occurrence in many Infusoria, but of quite unknown function. The " trichocysts " are vesicular bodies, capable of emitting thread-like filaments, and greatly resembling the urticating cells of many of the Ccelenterata. They have been detected in Bursaria, as well as in various other members of this order ; and they are very like certain cells which are found in the integument of many Planarians. II. ORDER SUCTORIA. — This order includes a series of In- fusoria of a very anomalous nature. In Acineta,* which may be taken as the type, the body is covered wi.th a number PROTOZOA I INFUSORIA. 8 1 o of radiating filamentous tubes, which are furnished at their extremities with suctorial discs, and are capable both of exser tion and retraction. These retractile tubes both seize the prey and serve as vehicles for the ingestion of food ; hence the term " polystome," or many-mouthed, has been proposed for the order by Professor Greene. III. ORDER FLAGELLATA. — This order comprises those In- fusoria which, like Peridinium, find their means of locomotion in long, flexible, lash-like filaments, termed " flagella ; " cilia occasionally being present as well. In some, as in Peranema (fig. 14, e)t there is only a single one of these appendages ; in others, as in Anisonema, there are two flagella ; whilst in Hetero- mastix and Pleuronema we have forms apparently transitional between the Ciliata and the Flagellata, since both cilia and flagella are present in these genera. In all their other essen- tial characters the flagellate Infusoria do not differ from the more typical members of the class. They have, however, the peculiarity that the base of the flagellum is surrounded by a cup-like or cylindrical membranous collar, which can be retracted at will. In one singular form (Phalansterium intes- tinale), the organism consists of numerous zooids, each with a single flagellum and projecting membranous collar, enveloped basally in slimy sarcode, so as to form a cylindrical colony. NOCTILUCA. — Amongst the numerous organisms which con- tribute to the phosphorescence of the sea,* one of the com- monest is the animalcule known as Noctiluca, the true position of which has not yet been determined. It is nearly spherical in shape, having an indention, or " hilum," at one side, close to which is fixed a long filament, probably used in locomotion. The body consists of a " cuticle " and " cortical layer," en- closing a central mass of sarcode. Near the filament there is a minute oral aperture leading into a short digestive cavity. A nucleus and vacuoles are also present. From the presence of a mouth, and from its general structure, Noctiluca should * The diffused luminosity of the sea is mainly due to the Noctiluca miliaris ; but its partial luminosity is due to various phosphorescent ani- mals, amongst which are the Physalia utriculus (the Portuguese man-of- war), Medttstz, Tunicata, Annelides^ &c. The cause of phosphorescence is variously stated, being supposed very generally to be caused by a process of slow combustion analogous to that which takes place in phosphorus when exposed to the atmosphere. Upon the whole, however, it appears that the phenomenon is a vital process, consisting essentially in the conver- sion of nervous force (or vital energy) into light ; just as the same force can be converted by certain fishes into electricity. This transformation often requires a special apparatus for its production, but it appears to be sometimes effected by the entire organism. 84 MANUAL OF ZOOLOGY. probably be looked upon as a flagellate Infusorian, but it is placed by M. de Quatrefages amongst the Rhizopoda. AFFINITIES OF THE INFUSORIA. — Though generally placed amongst the Protozoa, of which they form the highest division, the position of the Infusoria cannot be looked upon as defi- nitely settled. There is a growing opinion amongst competent authorities that the Infusoria should be entirely removed from the Protozoa, and that they should be placed amongst the An- nuloida, having their nearest allies in the Turbellarian Worms. If this change be carried out, the Infusoria &&& Rotifera, which older naturalists grouped together, and which modern ob- servers have placed widely apart, will be again brought nearly together. If the sponges also should be removed from the Protozoa, as is maintained by some modern observers, then the entire sub-kingdom of the Protozoa would contain only the Gregarinida, Amcebea, Foraminifera, and Radiolaria. At pre- sent, however, there certainly do not appear to be sufficiently decisive grounds for such a step ; and the affinities of the Spongida are certainly more intimate with the typical Rhizopods than with the Ccel&itirata. CCELENTERA TA. CHAPTER VII. THE SUB-KINGDOM CCELENTERATA. T. CHARACTERS OF THE SUB-KINGDOM. 2. DIVISIONS. 3. GENERAL CHARACTERS OF THE HYDROZOA. 4. EX- PLANATION OF TECHNICAL TERMS. THE Sub-kingdom Ccelenterata (Frey and Leuckhart) may be considered as the modern representative of the Radiata of Cuvier. From the Radiata, however, the Echinodermata and Scoledda have been removed to form the Annuloida, the entire sub-kingdom of the Protozoa has been taken away, and the Polyzoa have been relegated to their proper place amongst the Mollusca. Deducting these groups from the old Radiata, the residue, comprising most of the animals commonly known as Polypes or Zoophytes, remains to constitute the modern Ccelenterata. The Ccelenterata may be defined as animals whose alimentary canal communicates freely with the general cavity of the body (" somatic cavity "). The substance of the body is made up of two fundamental membranes — an outer layer, called the "ecto- derm" and an inner layer, or " endoderm? There are no distinct neural and hcemal regions, and in the great majority of the members of the sub-kingdom there are no traces of a nervous system. Peculiar urticating organs, or " thread-cells" are usually present ; and, generally speaking, a radiate condition of the organs is perceptible, especially in the tentacles with which most are provided. In all the Ccelenterata distinct reproductive organs have been shown to exist. By Professor Allman the Ccelenterata have been defined as follows : — " Animals composed of numerous merosomes (body-segments), which are disposed radially round a longitudinal (antero-posterior) axis ; frequently with a de- terminable antero-posterior and dorso ventral plane (bilateral) ; a distinct body-cavity, which always communicates with the outer world through the mouth." 86 MANUAL OF ZOOLOGY. The leading feature which distinguishes the Ccelcnterata, and the one from which the name of the sub-kingdom is derived, is the peculiar structure of the digestive system. In the Protozoa, as we have seen, a mouth is only present in the higher forms, and in no case is there any definite internal cavity bounded by the walls of the body to which the name of " body-cavity " or "somatic cavity" could be properly applied. In animals higher than the Coelenterata, on the other hand, there is not only generally a permanent mouth, but the walls of the body usually enclose a permanent chamber or " body-cavity." Fur- ther, in most cases, the mouth conducts into an alimentary Yig. 17 — Diagrammatic vertical section of a Sea-anemone (Actinia), a Stomach ; b Mesentery; c Convoluted cord or " craspedum ;" d Tentacle. The dark line indicates the " ectoderm," the fine line and clear space adjacent mark the " endo- derm. canal, which is always distinct from the body-cavity, never opening into it, but usually passing through it to open on the surface by another distinct aperture (the anus). In most cases, therefore, the alimentary canal is a tube which communicates with the outer world by two apertures — a mouth and anus — but which simply passes through the body-cavity without in anyway communicating with it. In the Ccelenterata (fig. 17) there is an intermediate condition of parts. There is a distinct and permanent mouth, and a distinct and permanent body- cavity, but the mouth opens into, and communicates freely with/ the body-cavity. In some cases (Hydrozoa) the mouth opens directly into the general body-cavity, which then serves as a digestive cavity as well (fig. 18). In other cases there intervenes between the mouth and the body-cavity a short alimentary tube, which communicates externally with the outer world through the mouth, and opens below by a wide aperture into the general cavity of the body (Actinozoa, fig. 17). In no case is there a distinct intestinal canal which runs through the CCELENTERATA : HYDROZOA. 87 body and opens on the surface by a mouth at one end and an excretory aperture or anus at the other. Though of the true " radiate " type, some Coelenterates show traces of bilateral symmetry. Thus, in some Sea-anemones one of the tentacles is larger than, or differently coloured from, the others; and in some corals two of the primary septa, opposite one another, are larger than the rest, and divide the animal into two halves. With regard to the fundamental tissues of the Ccelenterata, there exist two primary membranes, of which one forms the outer surface of the body, and is called the " ectoderm ; " whilst the other lines the alimentary canal, the general cavity of the body, and the tubular tentacles, and is termed the " endoderm." These membranes correspond with the primi- tive serous and mucous layers of the germinal area, and become differentiated in opposite directions, the ectoderm growing from within outwards, the endoderm from without inwards. Each consists of numerous nuclear bodies, or " endoplasts," embedded in a granular " intercellular substance " or " peri- plast ; " and each may be rendered more or less complex by vacuolation or fibrillation. Between the ectoderm and endo- derm there is sometimes a third layer, which appears to be muscular. In connection with the integument of the Cozlenterata, the organs termed "thread-cells" ("cnidae," or " nematocysts ") must be noticed. These are peculiar cellular bodies, of various shapes, which probably serve as weapons of offence and defence, and which communicate to many members of the sub- kingdom (e.g., the Sea-blubbers) their well-known power of stinging. In the common Hydra the thread-cells consist of " oval elastic sacs, containing a long coiled filament, barbed at its base, and serrated along its edges. When fully developed the sacs are tensely filled with fluid, and the slightest touch is sufficient to cause the retroversion of the filament, which then projects beyond the sac for a distance, which is not uncommonly equal to many times the length of the latter " * (Huxley). (Fig. 18, d.) Many beautiful modifications of shape are known in the thread-cells of different Ccelenterates, but their essential structure in all cases is much the same as in the Hydra. It is only in few cases, comparatively speaking, * Thread-cells, though very commonly, if not universally, present in the Ccelenterata, are nevertheless not peculiar to them. Similar organs have been shown to exist in several of the Nudibranchiate Mollusca, as well as in some Annelides (Spio selicornis}. There likewise exist analogous organs (trichocysts) in several of the Infusoria, and in the Planarida. 55 MANUAL OF ZOOLOGY. that the thread-cells have the power t>f piercing and irritating the human skin • but even in the diminutive Hydra it is probable that they exercise some benumbing and deleterious influence on the living organisms which may be captured as prey. Besides the thread-cells, the tentacles of some Hydroids are furnished with rigid hair-like processes, which are probably tactile in function, and which are known as " paipocils." The Cczlenterata are divided into two classes, termed respectively the Hydrozoa and the Actinozoa. CLASS I. HYDROZOA. The Hydrozoa are defined as Ccelenterata in which the walls of the digestive sac are not separated from that of the general body-cavity, the two coinciding with one another ; the reproductive organs are in the form of external processes of the body-wall. (Fig. 1 8, a, b.) It follows from the above, that, since there is but a single internal cavity, the body of a Hydrozoon on transverse section appears as a single tube, the walls of which are formed by the limits of the combined digestive and somatic cavity. The Hydrozoa are all aquatic, and the great majority are marine. The class includes both simple and composite organ- isms, the most familiar examples being the common Fresh-water Polype (Hydra), the Sea-firs (Sertularida), the Jelly-fishes (Medusa), and the Portuguese man-of-war (Physalia). Owing to the great difficulty which is ordinarily experienced by the student in mastering the details of this class of animals, it has been thought advisable to introduce here a short explana- tion of some of the technical terms which are in more general use in describing these organisms. GENERAL TERMINOLOGY OF THE HYDROZOA. Individual. — We have already seen (see Introduction) the term "individual," in its zoological sense, must stricted to " the entire result of the development of a fertilised ovum," and that in this sense an individual ^kijay either be simple, like Amoeba, or may be composite, like a Sponge, which is produced by an aggregation of amoebiform particles. If all the parts composing an individual remain mutually connected, its development is said to be " continu- ous ; " but if any of these parts become separated as inde- pendent beings, the case becomes one of "discontinuous" development. We have seen, also, that however long zooidal CCELENTERATA : HYDROZOA. 89 multiplication may go on, there ultimately arrives in the history of every individual a period at which sexual reproduction must be called in to ensure the perpetuation of the species through- out time. This truth is expressed by Steenstrup's celebrated law of the " alternation of generations." Amongst the Hydrozoa, the individual may be either simple or compound, and the development may be either continuous or discontinuous, the following terms being employed to denote the phenomena which occur. Hydrosoma. — This is the term which is employed to desig- nate the entire body of a Hydrozoon, whether it be simple, as in the Hydra, or composite, as in a Sertularian. Polypite. — The alimentary region of a Hydrozoon is called a "polypite ;" the term "polype" being now restricted to the same region in the Actinozoa. In the simple Hydrozoa the entire organism may be called a " polypite ; " but the term is more appropriately applied to the separate nutritive factors which together make up a compound Hydrozoon. Distal and Proximal. — These are terms applied to different extremities of the hydrosoma. It is found that one extremity grows more quickly than the other, and to this free-growing end — at which the mouth is usually situated — the term "distal" is applied. To the more slowly growing end of the hydrosoma — which is at the same time usually the fixed end — the term "proximal" is applied. These terms maybe used either in relation to a single polypite in the compound Hydrozoa, or to the entire hydrosoma, whether simple or compound. Caznosarc. — This is the term which is employed to designate the common trunk, which unites the separate polypites of any compound Hydrozoon into a single organic whole. Polypary. — The term " polypary ;' or " polypidom" is applied to the horny or chitinous outer covering or envelope with which many of the Hydrozoa are furnished. These terms have also not uncommonly been applied to the very similar structures produced by the much more highly organised Sea- mats and their allies (Polyzoa), but it is better to restrict their use entirely to the Hydrozoa. Zob'ids. — In continuous development the partially inde- pendent beings which are produced by gemmation or fission by the primitive organism, to which they remain permanently attached, are termed " zooids." In other words, " zooids " are the more or less individualised members of which the Hydroid colony is made up. In discontinuous development, where certain portions of the "individual" are separated as completely independent 9O MANUAL OF ZOOLOGY. beings, these detached portions are likewise termed " zooids ; " that which is first formed being distinguished as the "pro- ducing zooid," whilst that which separates from it is known as the " produced zooid." In a great number of Hydrozoa there exist two distinct sets of zooids, one of which is destined for the nutrition of the colony, and has nothing to do with generation, whilst the functions of the other, as far as the colony is concerned, are wholly reproductive- For the whole assemblage of the nutritive zooids of a Hydrozoon Professor All- man has proposed the term " trophosome," applying the term " gonosome " to the entire assemblage of the reproductive zooids. In such Hydrozoa^ therefore, as possess these two distinct sets of zooids the " individual," zoologically speaking, is composed of a trophosome and a gonosome. It follows from this that neither the trophosome nor the gonosome, however apparently independent, and though endowed with intrinsic powers of nutrition and locomotion, can be looked upon as an "indi- vidual." in the scientific sense of this term. As a rule, the zooids of the trophosome are all like one another, or are " homomorphic ; " but there are some cases (as in Hydrac- tinia, and in the nematophores of the Plumularida) in which some of the zooids of the trophosome are unlike the others. The zooids of the gonosome, on the other hand, are normally unlike, or are " heteromorphic," consisting of two or three different sets of zooids, each with its special duty in the gener- ative functions of the Hydroid Colony. CHAPTER VIII. DIVISIONS OF THE HYDROZOA. SUB-CLASS HYDROIDA. THE Hydrozoa are divided into four sub-classes — viz., the Hy- droida^ the Siphonophora^ the Lucernarida, and the Discophora. SUB-CLASS I. HYDROIDA. — This sub-class comprises those Hydrozoa which consist of an alimentary region or " polypite" which is provided with an adherent disc or " hydrorhiza" and prehensile tentacles. In some few cases the hydrosoma is composed of a single polypite only, as in the Hydrida and in some of the Corynida; but usually there are several polypites united together by CCELENTERATA : HYDROZOA. 9 I means of a common trunk or "ccenosarc," as in most of the Corynida and in the orders Sertularida and Campcnmlarida. Further, in the great majority of cases the " hydrorhiza " is permanently attached to some foreign object. The Hydroida comprises four orders — viz., the Hydrida, the Corynida, the Sertularida, and the Campanularida. ORDER I. HYDRIDA (Gymnochroa, Hincks).— This order comprises those Hydrozoa whose " hydrosoma " consists of a single locomotive polypite, with tentacles and " hydrorhiza" and with reproductive organs which appear as simple external pro- cesses of the body-wall. The hydrorhiza is discoid, and ?io hard cuticular layer is at any time developed. The order Hydrida comprises a single genus only (Hydra), including the various species of " Fresh-water Polypes," as they are often called. The common Hydra (fig. 18, c] is found abundantly in this country, and consists of a tubular cylindrical body, the " proximal " extremity of which is ex- panded into an adherent disc or foot — the " hydrorhiza" — by means of which the animal can attach itself to some foreign body. It possesses, however, the power of detaching the hydrorhiza at will, and thus of changing its place. At the opposite or " distal " extremity of the body is placed the mouth, surrounded by a circlet of tentacles, which arise a little distance below the margin of the oral aperture. The tentacles vary in number from five to twelve or more, and they vary considerably in length in different species, being much shorter than the body in the Hydra viridis, but being extremely long and filamentous in Hydra fusca. They are highly extensile and contractile, and serve as organs of pre- hension, being capable of retraction till they appear as nothing more than so many warts or tubercles, and of being extended to a length which is in some species many times longer than the body itself. (In the Hydra fusca the tentacles can be protruded to a length of more than eight inches.) Each con- sists of a prolongation of both ectoderm and endoderm, en- closing a diverticulum of the somatic cavity, and they are abundantly furnished with thread-cells. The cylindrical hydro- soma is excavated into a single large cavity, lined by the en- doderm, and communicating with the exterior by the mouth. This— the " somatic cavity ;?— is the sole digestive cavity with which the Hydra is provided, the indigestible portions of the food being rejected by the mouth. The Hydra possesses a most extraordinary power of resist- ing mutilation, and of multiplying artificially when mechani- cally divided. Into however many pieces a Hydra may be MANUAL OF ZOOLOGY. divided, each and all of these will be developed gradually into a new and perfect polypite. The remarkable experiments of Trembley upon this subject are well known, and have been Fig. 18. — Morphology of Hydrozoa. a Diagrammatic section of Hydra. The dark line is the ectoderm, the fine line and clear space adjacent are the endodeim. b Hydra viridis, showing a single ovum contained in the body-wall near the proximal extremity, and two elevations containing spermatozoa near the bases of the tentacles ; c Hydra vulgaris, >with an undetached bud ; d Thread-cell of the Hydra, greatly magnified. often repeated, but space will not permit further notice of them here. Reproduction is effected in the Hydra both asexually by gemmation, and sexually — the former process being followed in summer, and the latter towards the com- mencement of winter, few individuals surviving this season. In the first method the Hydra throws out one or more buds, generally from near its proximal extremity. These buds at first consist simply of a tubular prolongation of the ectoderm and endoderm, enclosing a caecal diverticulum of the body- cavity ; but a mouth and tentacles are soon developed, when the new being is usually detached as a perfect independent Hydra. The Hydra thus produced throw out fresh buds, often before they are detached from the parent organism, and in this way reproduction is rapidly carried on. In the second or sexual mode of reproduction, ova and spermatozoa are produced in outward processes of the body- wall (fig. 1 8, b). The spermatozoa are developed in little conical elevations, which are produced near the bases of the tentacles, and the ova are enclosed in sacs of much greater size, situated nearer the fixed or proximal extremity of the animal. Ordinarily there is but one of these sacs containing a single ovum, but sometimes there are two. When mature, the ovum is expelled through the body- wall, and is fecundated CCELENTERATA I HYDROZOA. 93 by the spermatozoa, which are simultaneously liberated. The embryo appears as a minute, free-swimming, ciliated body. The serous and mucous layers of the blastoderm (germinal area) correspond to the ectoderm and endoderm, and for the forma- tion of the perfect Hydra nothing further seems wanting than the modification of one end of the body into a hydrorhiza, and the formation of a mduth and tentacles at the other. ORDER II. CORYNIDA ( = TUBULARIDA, the Athecata of Hincks). — The order Corynida comprises those Hydrozoa whose hydrosoma is fixed by a hydrorhiza, and consists either of a single polypite, or of several united by a ccenosarc, which usually develops a firm outer layer or "polypary" No " hydrothecce " are present. " The reproductive organs are in the form of gono- phores, which vary much in structure, and arise from the sides of the polypites, from the coenosarc, or from gonobla stidia " (Greene). The hydrosoma of the Corynida may consist of a single polypite, as in Coryomorpha and Vorticlava, or it may be com- posed of several united by a ccenosarc, as in Cordylophora (fig. 19, a). The order is entirely confined to the sea, with the single exception of Cordylophora, which inhabits fresh water. In Tubularia and its allies the organism is protected by a well- developed external chitinous envelope or "polypary;" but in the other genera belonging to the order the polypary is either rudimentary or is entirely absent. The polypary of the Corynida, when present, is readily distinguished from that of the Sertularida, by the fact that in the former it extends only Fig. 19.— Morphology of Corynida. a Fragment of Cordylophora lacustris, slightly enlarged ; b Fragment of the same considerably enlarged, showing a polypite and three gonophores in different stages of growth, the largest containing ova ; c Portion of Syncoryne Sarsii with medusiform zooids budding from between the tentacles. to the base of the polypites ; whereas in the latter it expands to form little cups for the reception of the polypites, these cups being called " hydrothecae." 94 MANUAL OF ZOOLOGY. As regards the reproductive process in the Corynida, the reproductive elements are developed in distinct buds or sacs, which are external processes of the body-wall, and have been aptly termed " gonophores" by Professor Allman. Strictly speaking, Dr Allman understands by the term " gonophore " only the ultimate generative zooid, that which immediately pro- duces the generative elements.* Great variations exist in the form and development of these generative buds, and an exami- nation of these leads us to some of the most singular pheno- mena in the entire animal kingdom. In some species of Hydractinia and Coryne, the generative buds or " gonophores" exist in their simplest form — namely, as sacciform protuber- ances of the endoclerm and ectoderm, enclosing a diverticulum of the somatic cavity. In this form they are attached to the " trophosome " by a short stalk, and they are termed " sporo- sacs " (rig. 20, a). They are exactly like the buds which we have already seen to exist in the Hydra, with this difference, that they are not themselves developed into fresh polypites, but are simply receptacles in \vhich the essential elements of generation — the ova and spermatozoa — are prepared, by the union of which the young Corynid is produced. In Cordylophora (fig. 19, b) a further advance in structure is perceptible. The gonophore now consists of a closed sac, from the roof of which depends a hollow process or peduncle — the " manubrium " — which gives off a system of tubes which run in the walls of the sac. For reasons which will be imme- diately evident, the gonophore in this case is said to have a "disguised" medusoid structure (fig. 20, ^). In certain Corynida, however, we meet with a still higher form of structure, the gonophores being now said to be " medusoid." In these cases the generative bud is primitively a simple sac — such as the " sporosac " — but ultimately develops itself into a much more complicated structure. The gono- phore (fig. 19, c) is now found to be composed of a bell- shaped disc, termed the "gonocalyx," which is attached by its base to the parent organism (the trophosome), and has its cavity turned outwards. From the roof of the gonocalyx, * According to Mr Hincks, the "gonophore" is the bud in which the reproductive elements are formed. "It consists of an external envelope (ectotheca), enclosing either a fixed generative sac between the walls of which the ova and spermatozoa are developed, or a free sexual zooid. " The actual sexual zooid is termed by Mr Hincks the "gonozooid," whether it be fixed or free — in other words, it is the gonophore minus its external invest- ment. The gonozooid is sometimes male, sometimes female ; and the same colony may produce one or both — the former being most commonly the CGELENTERATA : HYDROZOA. 95 like the clapper of a bell, there depends a peduncle or " manubrium," which contains a process of the somatic cavity. The manubrium gives out at its fixed or proximal end four prolongations of its cavity, in the form of radiating lateral tubes which run to the margin of the bell, where they com- municate with one another by means of a single circular canal which surrounds the mouth of the bell. This system of tubes constitute what is known as the system of the " gonocalycine canals." The gonophore, thus constituted, may remain per- manently attached to the parent organism, as in Tubularia indivisa (fig. 20, c] ; but in other cases still further changes ensue. In the higher forms of development (fig. 20, d) the Fig. 20. — Reproductive processes of Hydrozoa. a Sporosac ; b Disguised medusoid ; c Attached medusiform gonophore ; d Free medusiform gonophore. The cross shad- ing indicates the reproductive organs, ovaria or spermaria. The part completely black indicates the cavity of the manubrium and the gonocalycine canals. manubrium acquires a mouth at its free or distal extremity, and the gonocalyx becomes detached from the parent. The gonophore is now free, and behaves in every respect as an independent being. The gonocalyx is provided with marginal tentacles and with an inward prolongation from its margin, which partially closes the mouth of the bell, and is termed the "veil" or "velum." By the contractions of the gonocalyx, which now serves as a natatorial organ, the gonophore is pro- pelled through the water. The manubrium, with the shape, assumes the functions of a polypite, and its cavity takes upon itself the office of a digestive sac. Growth is rapid, and the gonophore may attain a comparatively gigantic size, being now absolutely identical with one of those organisms which are com- monly called "jelly-fishes," and are technically known as Medusa*. (fig. 21). In fact, as we shall afterwards see, most, if not all of the gymnophthalmate Medusa, originally described as a distinct order of free-swimming Hydrozoa, are in truth merely the liberated generative buds, or " medusiform gonophores," of the permanently rooted Hydroids. Finally, the essential generative elements — the ova and spermatozoa — are developed in the walls of the manubrial sac, between its endoderm and ectoderm 96 MANUAL OF ZOOLOGY. and embryos are produced. These embryos, however, instead of resembling the organism which immediately gave them birth, develop themselves into the fixed Corynid from which the gonophore was produced, thus completing the cycle. The swimming-bell of the medusiform gonophore is believed to be formed by a great development of an inter-tentacular web, such as is sometimes present, in a rudimentary form, in the nutritive zooids. Sometimes the medusoid becomes quies- cent towards the close of its existence, and the swimming-bell becomes reversed or atrophied. Lastly, in Clavatella, the sexual zooid, though free and locomotive, is not provided with a swimming-bell, but creeps about by means of suctorial discs developed on branches of the tentacles. As we have seen, the generative buds of the Corynida may exist in the following chief forms: — i. As "spo- rosacs," or simple closed sacs, con- sisting of ectoderm and endoderm, with a central cavity in which ova and spermatozoa are produced. 2. As " disguised medusoids," in which there is a central manubrial process and a rudimentary system of gonocalycine canals ; but the gonocalyx remains closed. 3. As complete medusoids, which have a central manubrium, a complete sys- tem of gonocalycine canals, and an open gonocalyx ; but which never become detached. 4. As perfect medusiform gonophores (fig. 21), which are detached, and lead an independent existence for a time, until the generative elements are matured. In whichever of these forms the gonophore may be pre- sent, the place of its origin from the a Central poiypite or trophosome may vary in different manubrium; b £ Radiating gastro- r . r . J. * _,. vascular canals ;cCircular canal; SpCClCS Of the Order. I. 1 hey may m Marginal bodies ;* Tentacles. arise from the gides of the poly_ pites, as in C0ry«* and Stauridia; 2. They may be produced from the ccenosarc, as in Cordylophora ; 3. They may be produced upon certain special processes, which are termed "gonoblastidia," as in Hydractinia and Dicoryne. These gonoblastidia are processes from the body-wall or coenosarc, which closely COiLENTERATA I HYDROZOA. 97 resemble true polypites in form, but differ from them in being usually devoid of a mouth, and in having shorter tentacles. They are, in truth, atrophied or undeveloped polypites. As regards the development of the Corynida, the embryo is very generally, though not always, ciliated at first, and becomes developed into a hydra-form polypite, which fixes itself to some foreign body, and then (if not belonging to one of the simple forms) proceeds to produce by gemmation the com- posite adult. In one species the embryo leaves the gono- phore as a free and locomotive polypite, and in another form it is. non-ciliated and amoeboid. The development of the Corynida (as well as that of the Sertularida and Lucernarida) obeys the general law, that the new polypites are developed at, or near, the distal end of the hydrosoma ; so that the distal polypites are the youngest, the reverse of this obtaining amongst the oceanic Hydrozoa. The subject of the reproduction of the Corynida having been treated at some length, so as to apply to the re- maining Hydroida, we shall now give a brief description of the leading types of structure exhibited by the order. Eudendrium, a genus of the Cory- nida^ which is not uncommonly found attached to submarine objects, usually in tolerably deep water, may be taken as a good example of the fixed and composite division of the order. The hydrosoma consists of numerous polypites, united by a coenosarc, which is more or less branched, and is defended by a horny tubular polypary. The poly- pites are borne at the ends of the branches and branchlets, and are not contained in "hydrothecae," the polypary ending abruptly at their bases. The polypites are non- retractile, of a reddish colour, and provided with about twenty ten- tacles, arranged round the mouth in a single row. Tubularia (fig. 22) is very similar to Eudendrium, but the hydrosoma is either undivided or is very slightly branched. The hydrosoma consists of clustered homy G Fig. 22 — Corynida. Fragment of Tubularia indivisa, natural size. 98 MANUAL OF ZOOLOGY. tubes, of a straw colour, and not unlike straws to look at ; hence the common name of pipe-coralline given to this zoophyte. Each tube is filled with a soft, semi-fluid, reddish ccenosarc, and gives exit at its distal extremity to a single polypite. The polypites are bright red in colour, and are not retractile within their tubes, the horny polypary extending only to their bases. The polypites are somewhat conical in shape, the mouth being placed at the apex of the cone, and they are furnished with two sets of tentacles. One set consists of numerous short tentacles placed directly round the mouth ; the other is com- posed of from thirty to forty tentacles of much greater length, arising from the polypite about its middle or near the base. Near the insertion of these tentacles the generative buds are produced at proper seasons. The generative buds remain permanently attached, but each is furnished with a swimming- bell, in which canals are present. The manubrium is destitute of a mouth, and " the swimming-bell is converted into a nursery in which the embryo passes through the later stages of its development" (Hincks). Coryomorpha nutans maybe taken to represent those Cory- nida in which there is no polypary and the hydrosoma is simple. It is about four inches in length, and is fixed by filamentous roots to the sands at the bottom of the sea. It consists of a single whitish polypite, striped with pink, and terminating upwards in a spear-shaped head, round the thickest part of which is a circlet of from forty to fifty long white tentacles. Above these comes a series of long branching gonoblastidia. bearing gonophores, and succeeded by a second shorter set of tentacles which surround the mouth. The gonophores become ultimately detached as free-swimming medusoids. Another remarkable example of the Corynida is Hydractinia (fig. 23). In this genus the polypites are gregarious, and the polypary forms a horny crust which spreads over shells and other foreign bodies. The tentacles of the nutritive zooids form a single sub-alternate series. The generative buds are produced upon imperfect, non-tentaculate polypites ; and are mere sac-shaped protuberances, enclosing diverticula from the body-cavity, but not detached from the parent organism. ORDER III. SERTULARIDA (Thecaphora, Hincks). — This order comprises those Hydrozoa " whose hydrosoma is fixed by a hydrorhiza, and consists of several polypites, protected by hydro- thecce, and connected by a ccenosarc, which is usually branched and invested by a very firm outer layer. Reproductive organs in the form of gonophores arising from the ccenosarc or from gonoblas- tidia" (Greene). CCELENTERATA I HYDROZOA. 99 The Sertnlarida resemble the Corynida in becoming perma- nently fixed after their embryonic condition by a hydrorhiza, which is developed from the proximal end of the ccenosarc '; Fig. 23. — Group of zooids of Hydractinia echiiiata. Enlarged (after Hincks). a a Nutritive zooids ; b b Generative zooids, carrying sacs filled with ova. but they differ in the fact that the polypites are invariably pro- tected by " hydrothecae," or little cup-like expansions of the polypary (fig. 24, a, b} ; whilst the hydrosoma is in all cases composed of more than a single polypite. The mouth of the hydrotheca is generally furnished with an operculum or valve for its closure. The ccenosarc generally consists of a main stem — or " hydrocaulus " — with many branches ; and it is so plant-like in appearance that the common Sertularians are almost always mistaken for sea-weeds by visitors at the seaside. It is invested by a strong corneous or chitinous covering, often termed the "periderm." The polypites are sessile or subsessile, hydra-form, and in all 100 MANUAL OF ZOOLOGY. essential respects identical with those of the Corynida though usually smaller. Each polypite consists of a soft, contractile, and extensile body, which is furnished at its distal extremity with a mouth and a circlet of prehensile tentacles, richly fur- nished with thread-cells. The tentacles have an indistinctly alternate arrangement. The mouth is simple or lobed, and is placed, in many cases, at the extremity of a more or less pro- minent extensile and contractile proboscis. The mouth opens into a chamber which occupies the whole length of the polypite, and is to be regarded as the combined body-cavity and digestive sac. At its lower end this chamber opens by a constricted aperture into a tubular cavity which is everywhere excavated in the substance of the coenosarc (fig. 24, b). The nutrient Fig. 24. — a Sertularia (Diphasia) pinuata, natural size ; a' Fragment of the same enlarged, carrying a male capsule (o), and showing the hydrothecse (k) ; b Fragment of Campanularia neglecta (after Hincks), showing the polypites contained in their hydrothecae (h), and also the point at which ;the coeuosarc communicates with the stomach of the polypite (o}. particles obtained by each polypite thus serve for the support of the whole colony, and are distributed throughout the entire organism. The nutritive fluid prepared in the interior of each polypite gains access through the above-mentioned aperture to the cavity of the coenosarc, which by the combined exertions of the whole assemblage of polypites thus becomes filled with a granular nutritive liquid. This ccenosarcal fluid is in con- stant movement, circulating through all parts of the colony, and thus maintaining its vitality, the cause of the movement CCELENTERATA : HYDROZOA. 101 being probably due in part, at any rate, to the existence of vibrating cilia. The generative buds (gonophores or ovarian vesicles) are usually supported upon gonoblastidia, and do not become detached in the true Sertularids. They are developed in chitinous receptacles known as "gonothecag" (fig. 24, o). The young Sertularian on escaping from the ovum appears as a free-swim- ming ciliated body, which soon loses its cilia, fixes itself, and develops a young coenosarc, by gemmation from which the branching hydrosoma of the perfect organism is produced. In Phimularia and some of its allies there occur certain peculiar organs, probably offensive, to which the name of " nematophores " has been applied. Each of these consists of a process of the ccenosarc, which is invested by the horny polypary, with the exception of the distal extremity, which remains uncovered, and contains many large Fi thread-cells embedded in it. The nematophores are sometimes fixed, sometimes movable. They "constitute cup-like appendages, formed of chitine, and filled with protoplasm, which has the power of emitting pseudopodia or amoeboid prolongations of its substance, and having their cavity in communication with that of the common tube of the hydrocaulus " (Allman). ORDER IV. CAMPANULARIDA. — The members of this order are closely allied to the Sertuiarida • so closely, indeed, that they are very often united together into a single group. The chief difference consists in the fact that the hydrothecae of the Campanularida with their contained polypites are supported upon conspicuous stalks, thus being terminal in position (fig. 24, b); whilst in the Sertuiarida they are sessile or subsessile, and are placed laterally upon the branchlets. The gonophores also in the Campanularida are usually detached as free-swim- ming medusoids, whereas they remain permanently attached in the Sertularians. Each medusoid consists of a little trans- parent glassy bell, from the under surface of which there is suspended a modified polypite, in the form of a "manubrium " (fig. 21). The whole organism swims gaily through the water, propelled by the contractions of the bell or disc (gonocalyx) ; and no one would now suspect that it was in any way related to the fixed plant-like zoophyte from which it was originally £. 25. — Ovarian capsule of Diphasia (Sertularia) oper- cu/a/a,~L'mn. (AfterHincks.) Greatly enlarged. IO2 MANUAL OF ZOOLOGY. budded off. The central polypite is furnished with a mouth at its distal end, and the mouth opens into a digestive sac. From the proximal end of this stomach proceed four radiating canals Fig. 26. — Portion of the colony of Clytia (Campanularia)'Johnstoni, magnified; p Nutritive zooid ; g Capsules in which the reproductive zooids are produced. which extend to the circumference of the disc, where they all open into a single circular vessel surrounding the mouth of the bell. From the margins of the disc hang also a number of delicate extensile filaments or tentacles; and the circum- ference is still further adorned with a series of brightly-coloured spots, which are probably organs of sense. The mouth of the bell is partially closed by a delicate transparent membrane or shelf, the so-called "veil." Thus constituted, these beautiful little beings lead an independent and locomotive existence for CCELENTERATA I HYDROZOA. 103 a longer or shorter period. Ultimately, the essential elements of reproduction are developed in special organs, situated in the course of the radiated canals of the disc. The resulting embryos are ciliated and free-swimming, but ultimately fix themselves, and develop into the plant-like colony from which fresh medusoids may be budded off. The ova in the medu- siform gonophores are usually developed in the course of the gonocalycine canals, and not between the ectoderm and endoderm of the manubrium, as is the case in the Corynida. Examples of the order are Campamuaria, Laomedea, &c. The distinctions between the Sertularida and Campanularida are certainly insufficient to justify their being placed in separate orders. If united together, it would probably be best to adopt the name Thecaphora (Hincks) for the order, and to employ the names Sertularida and Campanularida for the sub-orders. CHAPTER IX. SIPHONOPHORA. SUB-CLASS II. SIPHONOPHORA. — The members of this sub- class constitute the so-called "Oceanic Hydrozoa;" and are characterised by the possession of a "free and oceanic hydro- soma, consisting of several polypites united by a flexible, contrac- tile, unbranched or slightly -branched ccenosarc, the proximal end of which is usually furnished with ' nectocalyces] and is dilated into a l somatocyst' or into a ' pneumatophore '" (Greene). All the Siphonophora are unattached, and permanently free, -and all are composite. They are singularly delicate organisms, mostly found at the surface of tropical seas, the Portuguese man-of-war (Physalia) being the most familiar member of the group. The sub-class is divided into two orders — viz., the Calycophoridce and the Physophoridce. ORDER I. CALYCOPHORID^E. — This order includes those^ Siphonophora whose hydrosoma is free and oceanic, and is pro- pelled by ' * nectocalyces ' ' attached to its proximal end. The hydro- soma consists of several polypites, united by an unbranched cceno- sarc, which is highly flexible and contractile, and never develops a hard cuticular layer. The proximal end of the hydrosoma is modified into a peculiar cavity called the " somatocyst" The re- productive organs are in the form of medusiform gonophores pro- duced by budding from the peduncles of the polypites. MANUAL OF ZOOLOGY. In all the Calycophoridce the coenosarc is filiform, cylindrical, imbranched, and highly contractile, this last property being due to the presence of abundant muscular fibres. " The proximal end of the coenosarc dilates a little, and becomes ciliated in- ternally, forming a small chamber" which communicates with the nectocalycine canals. " At its upper end this chamber is a little constricted, and so passes, by a more or less narrowed channel, into a variously-shaped sac, whose walls are directly continuous with its own, and which will henceforward be termed the somatocy'st (fig. 27, 3 b). The endoderm of this sac is cili- ated, and it is generally so immensely vacuolated as almost to Fig. 27.— Morphology of the Oceanic Hydrozoa. i. Diagram of the proximal ex- tremity of a Physophorid. a Pneumatocyst. 2. Vo%tia pentacantha, one of the Calycophoridee. n Nectpcalyces ; p Polypites ; t Tentacles. 3. Diagram of a Calycophorid. _ a a' Proximal and distal nectocalyces ; b Somatpcyst ; c Coenosarc ; d Hydrophyllium or bract ; e Medusiform gonophore ; / Polypite. The dark lines in figs, i and 3 indicate the endoderm, the lig the ectoderm. (After Huxley.) ight line with the clear space indicates obliterate the internal cavity, and give the organ the appearance of a cellular mass " (Huxley). The polypites in the Calyco- fhorida often show a well-marked division into three portions, termed respectively the proximal, median, and distal divisions. Of these, the " proximal" division is somewhat contracted, and forms a species of peduncle, which often carries appendages. The " median " portion is the widest, and may be termed the " gastric division," as in it the process of digestion is carried on. It is usually separated from the proximal division by a valvular inflection of the endoderm, which is known as the "pyloric valve." The polypites have only one tentacle " de- CCELENTERATA : HYDROZOA. loq \j veloped near their basal or proximal ends, and provided with lateral branches ending in saccular cavities," and furnished with numerous thread-cells. The proximal ends of the poly- pites usually bear certain overlapping plates, of a protective nature, which are termed " hydrophyllia " or " bracts." They are composed of processes of both ectoderm and endoderm (fig. 27, 3 d\ and they always contain a diverticulum from the somatic cavity, which is called a " phyllocyst." The Calyco- phoridcR always possess swimming-bells, or " nectocalyces," by the contractions of which the hydrosoma is propelled through the water (fig. 27, 2). The nectocalyx in structure is very similar to the " gonocalyx " of a medusiform gonophore, as already described ; but the former is devoid of the gastric or genital sac — the "manubrium" — possessed by the latter. Each nectocalyx consists of a bell-shaped cup, attached by its base to the hydrosoma, and provided with a muscular lining in the interior of its cavity, or "nectosac." There is also always a "velum" or " veil," in the form of a membrane attached to the mouth of the nectosac round its entire margin, and leaving a central aperture. The peduncle by which the nectocalyx is attached to the hydrosoma conveys a canal from the somatic cavity, which dilates into a ciliated chamber, and gives off at least four radiating canals, which proceed to the circumference of the bell, where they are united by a circular vessel ; the entire system constituting what is known as the system of the " nectocalycine canals." In the typical Calycophorida two nectocalyces only are present, but in some genera there are more. In Praya the two nectocalyces are so apposed to one another that a sort of canal is formed by the union of two grooves, one of which exists on the side of each nectocalyx. This chamber, which is present in a more or less complete form in all the genera, is termed the " hydrcecium," and the ccenosarc can be retracted within it for protection. The reproductive bodies in the Calycophorida are in the form of medusiform gonophores, which are budded from the peduncles of the polypites, becoming, in many instances, de- tached to lead an independent existence. In some Calycopho- rida, as in Abyla, " each segment of the ccenosarc, provided with a polypite, its tentacle, reproductive organ, and hydro- phyllium, as it acquires a certain size, becomes detached, and leads an independent life — the calyx of its reproductive organ serving it as a propulsive apparatus. In this condition it may acquire two or three times the dimensions it had when at- tached, and some of its parts may become wonderfully altered in form" (Huxley). To these detached reproductive por- io6 MANUAL OF ZOOLOGY. tions of adult Calycophoridce the term " Diphyozooids" has been applied. As regards the development of the Calycophoridce, "not only the new polypites, but the new nectocalyces and repro- ductive organs, and even the branches of the tentacles, are developed on the proximal side of the old ones ; so that the distal appendages are the oldest" (Huxley). The process of de- velopment is therefore the reverse of what obtains amongst the Hydroida. Diphyes (fig. 28), which may be taken as the type of the Calycophoridce, consists of a delicate filiform coenosarc, provided proximally with two large mitre-shaped nec- tocalyces (z/, z/), of which one lies entirely on the distal side of the other. The pointed apex of the distal nectocalyx is received into a special cavity in the proximal nectocalyx. The "hydroecium" (h) is formed partially by this chamber in the nectocalyx, and par- tially by an arched groove prolonged upon the inner surface of the distal nectocalyx, within which the ccenosarc moves freely up and down, and can be entirely retracted if necessary. The upper part of the coenosarc dilates into a small ciliated cavity, from which are given off two tubes, which pro- ceed respectively to the distal and proximal nectocalyces, where they open into the cen- tral chamber from which the nectocalycine canals take their rise. The upper portion of this small ciliated cavity is prolonged c'aiyx ; k Hydroecium ; proximally into the larger chamber of the " somatocyst." The coenosarc (c) bears polypites, each of which is protected by a Fig. 28. — Calycophori- dse. Diphyes appetidi- culata (after Kolliker). 7.1 Proximal nectoca- lyx ; v' Distal necto- bract and tentacle. delicate glassy " hydrophyllium." DIVISIONS OF THE CALYCOPHORID^E. — (AFTER HUXLEY.) Fam. I. Diphydce. — Nectocalyces not more than two in number, and of a polygonal shape. Hydroecium of the proximal nectocalyx complete, or closed posteriorly. Hydrophyllia well developed. Fam. II. Spharontctida. — Nectocalyces probably not more than two in number ; the proximal netocalyx spheroidal, with a complete hydrcecium. No hydrophyllia (?). Fam. III. Pray idee. — Nectocalyces two in number ; hydrcecia incom- plete and groove-like. Polypites protected by hydrophyllia. CCELENTERATA : HYDROZOA. 1 07 Fam. IV. Hippopodida. — Nectocalyces numerous ; hydrcecia incomplete. Polypites not protected by hydrophyllia. ORDER II. PHYSOPHORID^E. — This second order of the Oceanic Hydrozoa comprises those Siphonophora in which the hydrosoma consists of several polypites united by a flexible, con- tractile, unbranched or very slightly branched coznosarc, the proxi- mal extremity of which is modified into a " pneumatophore" and is sometimes provided with " nectocalyces." The polypites have either a single basal tentacle, or the tentacles arise directly from the ccenosarc. " Hydrophyllia " are commonly present. The reproductive bodies are developed upon gonoblastidia. The ccenosarc in the Physophoridce, like that of the Calyco- phoridce, is perfectly flexible and contractile ; but it is not necessarily elongated, being sometimes spheroidal or discoidal. The proximal end of the coenosarc " expands into a variously- shaped enlargement, whose walls consist of both ectoderm and endoderm, and which encloses a wide cavity in free communi- cation with that of the ccenosarc, and like it, full of the nutri- tive fluid. From the distal end, or apex, of this cavity depends a sac, variously shaped, but always with tough, strong, and elastic walls, composed of a substance which is stated to be similar to chitine in composition, and more or less completely filled with air" (Huxley). The large proximal dilatation of the ccenosarc is termed the " pneumatophore," whilst the chiti- nous air-sac which it contains is termed the " pneumatocyst " (fig. 27, i). The pneumatocyst is held in position by the reflection of the endoderm of the pneumatophore over it, and it doubtless acts as a buoy or "float." In the Portuguese man-of-war (Physalia) the pneumatocyst communicates with the exterior by means of an aperture in the ectoderm of the pneumatophore. In Velella and Porpita the pneumatocyst communicates with the exterior by means of several openings called "stigmata ; " and from its distal surface depend numerous slender processes, containing air, and known as " pneumatic filaments." The polypites of the Physophoridce resemble those of the Calycophoridce in shape, but the tentacles have a much more complicated structure, and are sometimes many inches in length, as in Physalia. The " hydrophyllia " have essentially the same structure as those of the former order. There occur also in the Physophoridce certain peculiar bodies, termed " hydrocysts " or " feelers " (" fiihler " and " taster " of the Ger- mans). These resemble immature polypites in shape, consisting of a prolongation of both ectoderm and endoderm, usually with a tentacle, and containing a diverticulum of the somatic IOS MANUAL OF ZOOLOGY. cavity, the distal extremity being closed, and furnished with numerous large thread-cells. They are looked upon as " organs of prehension and touch/' and they are somewhat analogous to the " nematophores " of some of the Sertnlarida. As regards the reproductive organs, they are developed upon special processes or " gonoblastidia," and they may remain permanently attached, or they may be thrown off as free- swimming medusoids. In many of the Physophorida the male and female gonophores differ from one another in form and size, and they are then termed respectively "andro- phores" and "gynophores." As regards their development, the Physophoridce obey the same general law as the Calyco- phoridce. In Physophora the hydrosoma consists of a filiform ccenosarc. which bears the polypites and their appendages, and dilates proximally into a pneumatophore. Below this point the ccenosarc bears a double row of nectocalyces, which are channelled on their inner faces to allow of their attachment to the ccenosarc. There are no hydrophyllia, but there is a series of "hydrocysts" on the proximal side of the poly- pites. Physalia, or the Portuguese man-of-war (fig. 29, a), is com- posed of a large bladder-like, fusiform " float " or pneumato- phore— sometimes from eight to nine inches in length — upon the under surface of which are arranged a number of polypites, together with highly contractile tentacles of great length, " hy- drocysts," and reproductive organs. Physalia is of common occurrence, floating at the surface of tropical seas ; and fleets of it are not uncommonly driven upon our own shores. In Velella (fig. 29, b) the hydrosoma consists of a widely- expanded pneumatophore of a rhomboidal shape, carrying upon its upper surface a diagonal vertical crest. Both the horizontal disc and the vertical crest are composed of a soft marginal "limb," and a central more consistent "firm part." " To the distal surface of the firm part of the disc are attached the several appendages, including, i. a single large polypite, nearly central in position ; 2. numerous small gonoblastidia, which resemble polypites, and are termed " phyogemmaria ; " and 3. the reproductive bodies to which these last give rise. The tentacles are attached, quite independently of the poly- pites, in a single series along the line where the firm part and limb of the disc unite. There are no hydrocysts, nectocalyces, or hydrophyllia. . . . On all sides the "limb is traversed by an anastomosing system of canals, which are ciliated, and communicate with the cavities of the phyogemmaria and large CCELENTERATA : HYDROZOA. central polypite " (Greene). Velella is about two inches in length by one and a half in height. It is of a beautiful blue colour and semi-transparent, and it floats at the surface of the sea, with its vertical crest exposed to the wind as a sail. Fig. -2C).—Phyfophorid(e. a Portuguese man-of-war (Physalia utricnlus), showing the fusiform float and the polypites and tentacles (after Huxley) ; b Velella vulgaria (after Gosse). DIVISIONS OF THE PHYSOPHORID^E. — (AFTER HUXLEY.) Fam. \.Apolemiadce. — Hydrosoma with nectocalyces and hydrophyllia, the latter united with the other organs into groups which are arranged at considerable intervals along the ccenosarc. Coenosarc filiform. Pneuma- tocyst small. Fam. II. Stephanomiadce. — Hydrosoma with nectocalyces and hydro- phyllia, the latter arranged with the other organs in a continuous series. Coenosarc filiform. Pneumatocyst small. Fam. III. Physophoriadce. — Hydrosoma with nectocalyces, but without hydrophyllia. Distal end of the filiform coenosarc dilated. Pneumatocyst small. Fam. IV. Athorybida. — Hydrosoma without nectocalyces, but with hydrophyllia. Pneumatocyst occupying almost the whole of the globular I IO MANUAL OF ZOOLOGY. Fam. V. Rhizophysiadce. — Hydrosoma without either nectocalyces or hydrophyllia. Coenosarc filiform, Pneumatocyst small. Fam. VI. Physaliada, — Pneumatocyst occupying almost the whole of the thick and irregularly fusiform ccenosarc. No nectocalyces or hydro- phyllia. Fam. VII. Velellidce. — Hydrosoma without nectocalyces or hydrophyllia ; with short, simple, or branched submarginal tentacles. A single central principal polypite. Pneumatocyst flattened, divided into chambers by numerous concentric partitions, and occupying almost the whole of the discoidal ccenosarc. CHAPTER X. DISCOP HORA. SUB-CLASS III. DISCOPHORA (Acalepha * in part). — Since the sub-class contains only a single order, that of the Medusida, a single definition necessarily suffices for both. The Medusidce are defined as " Hydrozoa whose hydrosoma is free and oceanic, consisting of a single nectocalyx, from the roof of which a single polypite is suspended. The nectocalyx is furnished with a system of canals. The reproductive organs are as processes either of the sides of the polypite or of the nectocalycine canals " (Greene). The Medusidce comprise most of the organisms commonly known as Jelly-fishes or Sea-nettles, the last name being de- rived from the property which some of them possess of severely stinging the hand, this power being due to the presence of numerous thread-cells. As employed by modern naturalists, the order is very much restricted, and it is by no means impro- bable that it will ultimately be entirely done away with, very many of its members having been shown to be really the free generative buds of other Hydrozoa. As used here, it corre- sponds to part of the Gymnophthalmate Medusce of Professor E. Forbes, the Steganophthalmate Medusce of the same author being now placed in the sub-class Lucemarida. * The old sub-class of the Acalephce contained the Gymnophthalmate Medusa ( = the Discophora}, and the Steganophthalmate Medusa ( = the Lucemarida in part), the two being placed in a single order under the name of Pulmograda . The Acalepha also contained the Ctenophora and the Calycophoridce and Physophoridte, of which the former constituted the order Ciliograda, whilst the two latter made up the order Physograda. The Ctenophora, however, are now generally placed amongst the Actinozoa, whilst the Calycophoridce and Physophoridcz constitute the Hydrozoal sub- class Siphonophora . CCELENTERATA : HYDROZOA. 1 II The hydrosoma of one of the Discophora ( = a Gymnoph- thalmate Medusa) is composed of a single, gelatinous, bell-shaped swimming organ, the "nectocalyx" or "disc," from the roof of which a single polypite is suspended (fig. 30). The interior of the nectocalyx is often called the " nectosac," and the term " codonostoma " has been proposed to designate the open Fi.?. 30. — Morphology of Meclusidae. a A Medusid (Tkaumantias) seen in profile, showing the central polypite, the radiating and circular gonocalycine canal, the marginal vesicles and tentacles, and the reproductive organs ; b The same viewed from below. The dotted line indicates the margin of the velum. mouth of the bell. The margin of the nectocalyx is produced inwards to form a species of shelf, running round the margin of the mouth of the bell, and termedthe " veil " or "velum," by the presence of which the nectocalyx is distinguished from the somewhat similar "umbrella" of the Lucernarida. The en- dodermal lining of the central polypite or " manubrium " (some- times called the " proboscis ") is prolonged into four, sometimes more, radiating canals, which run to the periphery of the nec- tocalyx, where they are connected by a circular canal which runs round its circumference, the whole constituting the system of the " nectocalycine canals " (formerly called the " chylaqueous canals "). From the circumference of the nectocalyx depend marginal tentacles, which are usually hollow processes, com- posed of both ectoderm and endoderm, and in immediate connection with the canal system. Also round the circum- ference of the nectocalyx are disposed certain " marginal bodies," of which two kinds may be distinguished. Of these the first are termed " vesicles," and consist of rounded sacs lined by epithelium, and containing one or more solid, motion- less concretions — apparently of carbonate of lime — immersed in a transparent fluid. The second class of marginal bodies, variously termed " pigment-spots," " eye-specks," or " ocelli," consists of little aggregations of pigment enclosed in distinct cavities. The " vesicles " are probably rudimentary organs of hearing, and possibly the eye-specks are a rudimentary form of I 12 MANUAL OF ZOOLOGY. visual apparatus. The oral margin of the polypite may be simple, or it may be produced into lobes, which are most frequently four in number. The essential elements of genera- tion are produced in simple expansions either of the wall of the manubrium or of the radiating nectocalycine canals. Fig- 31-— Group of naked-eyed Medusez. a Carsia gemmifera, with medusoids arising from the sides of the central polypite (after Greene) ; b Modeeria formosa (after Forbes) ; c Polyxenia A Ideri (after Gosse). From the above description it will be evident that the Medusa is in all essential respects identical in structure with the free-swimming generative bud or gonophore of many of the fixed and oceanic Hydrozoa. Indeed, a great many forms which were previously included in the Medusidce, have now been proved to be really of this nature, and it may fairly be doubted if this will not ultimately be found to apply to all. As to the value, however, of the order Medusidce, the present state of our knowledge is well expressed by the following con- clusions which have been drawn up by Professor Greene : — " i. That several of the organisms formerly described as Medusidce are the free gonophores of other orders of Hydrozoa. "2. That the homology of these free gonophores with those simple expansions of the body-wall which in Hydra and some other genera are known to be reproductive organs by their contents alone, is proved alike by the existence of numerous CCELENTERATA : HYDROZOA. I I 3 transitional forms and by an appeal to the phenomena of their development. " 3. That many of the so-called Medusidce may, from ana- logy, be regarded as, in like manner, medusiform gonophores. " 4. But that there may exist, nevertheless, a group of Medu- sid forms which may give rise by true reproduction to organisms directly resembling their parents, and therefore worthy of being placed in a separate order under the name Medusida" The same authority concludes by remarking that to the order as above defined " may be referred provisionally that large assemblage of forms anatomically similar to true Medu- sidcz, but whose development is unknown." Besides the large group of forms thus temporarily admitted, all the Trachynemidce and sEginidce are stated by Gegenbauer to fulfil the conditions of the above definition, and should, therefore, be looked upon as true Medusidce. As to the development of these true Medusidce, little is known for certain. It appears, however, that in Trachynema, sEginopsis, and other genera, the embryo is directly developed into a form resembling its parent, without passing through any intermediate changes of form. It is hardly necessary to re- mark that this is not the case with the embryos of a medusiform gonophore, these being developed into the sexless Hydrozoon by which the medusoid was produced. In this connection, allusion may be made to the long-known fact that certain medusiform gonophores are capable of pro- ducing independent forms directly resembling themselves, but this is by a process of gemmation, and not by one of true reproduction. Technically these are called " tritozooids," as being derived from organisms which are themselves but the generative zooids of another being. This singular phenomenon has been observed in various medusiform gonophores (e.g., Sarsia gemmifera, fig. 31, A), the buds springing in different species from the gonocalycine canals, from the tentacles, or from the sides of the polypite or manubrium. The " naked-eyed ;' Medusa, though mostly very diminutive in point of size, are exceedingly elegant and attractive when examined in a living condition, resembling little bells of trans- parent glass adorned here and there with the most brilliant colours. They occur in their proper localities and at proper seasons in the most enormous numbers. They are mostly phosphorescent, or capable of giving out light at night, and they appear to be one of the principal sources of the lumi- nosity of the sea. It does not seem, however, that they phos- phoresce, unless irritated or excited in some manner. H I 14 MANUAL OF ZOOLOGY. CHAPTER XI. LUCERNARIDA AND GRAPTOLITID^E. SUB-CLASS IV. LUCERNARIDA (Acalephce, in part). — The mem- bers of this sub-class may be defined as Hydrozoa " whose hydrosoma has its base developed into an ' umbrella] in the walls of which the reproductive organs are produced" (Greene). A large number of forms included in the Lucernarida were described by Edward Forbes under the name of Steganophthal- mate Medusa, being in many external characters closely similar to the MedusidcR. These " hidden-eyed " Medusa are familiar to every one as "sea-blubbers" or "sea-jellies," and they occur in great numbers round our coasts during the summer months. The resemblance to the little jelly-fishes is especially strong between the disc or "nectocalyx" of the true Medusidcz and the " umbrella" of the Lucernarida, the latter being often a bell-shaped swimming organ, with marginal tentacles, and containing one or more polypites. These analogous structures (figs. 31 and 34) are, however, distinguished as follows : — i. The "umbrella''* of the Lucernarida is never furnished with a "velum," as is the nectocalyx of the Medusida. 2. The radiating canals in the former are never less than eight in number, and they send off numerous anastomosing branches, which join to form an intricate network ; whereas in the latter they are rarely more than four in number, and though they may subdivide, they do not anastomose. 3. In the place of the separate and unprotected " vesicles " and " ocelli " of the Medusidce, the marginal bodies of the Lucernarida consist of these bodies combined together into single organs, which are termed " lithocysts," and which are protected externally by a sort of hood. The Lucernarida admit of being divided into three orders — viz., the Lucernariadcz, the Pelagidce, and the Rhizostomida. ORDER I. LUCERNARIAD^:. — This order includes those Lucer- narida which have only a single polypite, are fixed by a proximal hydrorhiza, and possess short tentacles on the margin of the tim- brella. The reproductive elements " are developed in the primitive hydrosoma without the intervention of free zooids" (Greene). In Lucernaria (fig. 32), which may be taken as the type of the order, the body is campanulate or cup-shaped, and is attached proximally at its smaller extremity by a hydrorhiza, which, however, like that of the Hydra, is not permanently CCELENTERATA : HYDROZOA. I i 5 fixed. When detached, the animal is able to swim with toler- able rapidity by means of the alternate contraction and expan- sion of the umbrella. Around the margin of the umbrella are tufts of short tentacular processes, and in its centre is a poly- pite with a quadrangular, four-lobed mouth. " In transverse section the polypite may be described as some- what quadrilateral, with a sinuous out- line which expands at its four angles to form as many deep longitudinal folds, within which the simple gener- ative bands are lodged " (Greene). Wide longitudinal canals are formed by septa passing from the walls of the polypite to the inner surface of the cup, and a circular canal runs immediately beneath the insertion of the tentacles. The reproductive elements are pro- duced within the body of Lucernaria itself, without the intervention of any generative zooid. ORDER II. PELAGID^E. — This order is defined as including Lucernarida which possess a single polypite only, and an umbrella with marginal tentacles. The reproductive elements " are developed in a free umbrella, which either consti- Fig. 32.— Lucemariadae. z«- tutes the primitive hydrosoma, or is STT^ffStSSS produced by fission from an attached Johnston). Lucernaroid" (Greene). Two types, therefore, exist in the Pelagida. The one type is represented by a fixed " trophosome," resembling Lucernaria, but distinguished from it by the fact that the generative ele- ments are not developed in the primitive hydrosoma, but in a free " gonosome," which is produced for the purpose. The second type, represented by Pelagia itself, is permanently free, thereby differing from Lucernaria, which it approaches, on the other hand, in the fact that its generative elements are pro- duced in its' own umbrella without the intervention of free generative zooid s. Pelagia, however, differs considerably in structure from Lucernaria, and in all essential characters is not anatomically separable from a Stegatwphthalmate Medusid. The process of reproduction as displayed in the first section of the Pelagidcz will be considered when treating of that of the Rhizostomida, there being no important difference between I 1 6 MANUAL OF ZOOLOGY. the two, except as concerns the structure of the generative zooids. ORDER III. RHIZOSTOMID^E. — The members of this order are defined as being Lucernarida in which the reproductive elements are developed in free zooids, produced by fission from attached Lucernaroids. The umbrella of the generative zooids is without marginal tentacles, and the polypites are "numerous, modified, forming with the genitalia- a dendriform mass depending from the umbrella" (Greene). The following is a brief summary of the life-history of a member of this extraordinary order (fig. -33), the illustration, however, representing the development of Aurelia, one of the Pelagida, in which the phenomena are essentially the same. The embryo is a free-swimming, oblong, ciliated body, termed a "planula" (d), of a very minute size, .and composed of an outer and inner layer, enclosing a central cavity. The planula soon becomes pear-shaped, and a depression is formed at its larger end. " Next, the narrower end attaches itself to some submarine body, whilst the depression at the opposite extremity, becoming deeper and deeper, at length communi- cates with the interior cavity. Thus, a mouth is formed, around which may be seen four small protuberances, the rudiments of tentacula. In the interspaces of these four new tentacles arise ; others in quick succession make their appearance, until a circlet of numerous filiform appendages, containing thread-cells, surrounds the distal margin of the ' Hydra-tuba ' (b), as the young organism at this stage of its career has been termed by Sir J. G. Dalyell. The mouth, in the meantime, from being a .mere quadrilateral orifice, grows and lengthens itself so as to constitute a true polypite, occupying the axis of the inverted umbrella or disc, which supports the marginal tentacles. The space between the walls of the polypite and umbrella is divided into longitudinal canals, whose relations to the rest of the organism, and, indeed, the whole structure of -Hydra-tuba, closely resemble what may be seen in Lucernaria" (Greene, Manual of Ccelenteratd). The Hydra-tuba thus constitutes the fixed " Lucernaroid," or the " trophosome " of one of the Rhizosto- midce. In height it is less than half an inch, but it possesses the power of forming, by gemmation, large colonies, which may remain in this condition for years, the organism itself being incapable of producing the essential elements of generation. Under certain circumstances, however, reproductive zooids are produced by the following singular process (fig. 33). The Hydra-tuba becomes elongated, and becomes marked by a CCELENTERATA I HYDROZOA. 117 series of grooves or circular indentations, extending transversely across the body from a little below the tentacles to a little above the fixed extremity. At this stage the organism was described as new by Sars, under the name " Scyphistoma" The annula- tions or constrictions go on deepening, and become lobed at their margin, till the Scyphistoma assumes the aspect of a pile of saucers, arranged one upon another with their concave Fig. 33. — Development of Aurelia, one of the Luceniarida. a. Ciliated free-swim- ming embryo, or "planula;" b Hydra-tuba; c Hydra-tuba in which fi>sion has considerably advanced, and the " Strobila " stage has been reached ; d Hydra-tuba in which the fission has proceeded still further, and a large number of the segments have been already detached to lead an independent existence. surfaces upwards. ' This stage was described by Sars under the name of "Strobila" (c). The tentacular fringe which originally surrounded the margin of the Hydra-tuba now dis- appears, and a new circlet is developed below the annulations, at a point a little above the fixed extremity of the Strobila (c). " The disc-like segments above the tentacles gradually fall off, and, swimming freely by the contractions of the lobed margin which each presents, they have been described by Escholtz as true Medusidce. under the name of Ephyrcz" (d}> Each Ephyra, however, soon shows its true nature by becoming developed into a free-swimming reproductive body, usually of large size, with umbrella, hooded lithocysts and tentacles, constituting, in fact, a Steganophthalmate Medusa. The re- productive zooid now swims freely by the contractions of its umbrella, and it eats voraciously and increases largely in size. The essential elements of generation are then developed in special cavities in the umbrella, and the fertilised ova, when liberated, appear as free- swimming, ciliated "planulae," which n8 MANUAL OF ZOOLOGY. fix themselves, become Hydra-tuba, and commence again the cycle of phenomena which we have above described. As regards the size of these reproductive zooids as compared with the organism by which they are given off, it may be men- tioned that the umbrella of Cyanea arctica -has been found in one specimen to be seven feet in diameter, with tentacles more than fifty feet in length, the fixed Lucernaroid from which it was produced not being more than half an inch in height. As regards the special structure of these gigantic reproductive bodies, con- siderable differences obtain between the Rhizostomi- dce and that section of the Pelagidce in which this method of reproduction is employed. In the Pelagi- dce, namely, the generative zooids possess a general, though chiefly mimetic, re- semblance both to the genuine Medusidce and to the free-swimming medu- siform gonophores of so many of the Hydrozoa, and they have the following Fig. 34.-Hidden-eyed Medusa,. Generative Structure. Each (fig. 34) zooid of one of the Pelagidce (Chrysaora COnSlStS of a bell-Shaped hysoscelld), after Gosse. -, .• , • , ,/ gelatinous disc, the " um- brella," from the roof of which is suspended a large polypite. the lips of which are extended into lobed pK>cesses often of considerable length, "the folds of which serve as temporary receptacles for the ova in the earlier stages of their develop- ment." The polypite — manubrium or proboscis — is hollowed into a digestive sac, which communicates with a cavity in the roof of the umbrella, from which arise a series of radiating canals, the so-called "chylaqueous canals." These canals, which are never less than eight in number, branch freely and anastomose as they pass towards the periphery of the umbrella, where the entire series is connected by a circular marginal canal. This, in turn, sends tubular processes into the marginal tentacles, which are often of great length. Besides the tentacles, the margin of the umbrella is furnished with a series of peculiar CGELENTERATA I HYDROZOA. I i 9 bodies, termed " lithocysts," each of which is protected by a sort of process or hood derived from the ectoderm, and consists essentially of a combined "vesicle" and "pigment-spot," such as have been described as occurring in the Medusida. 'These marginal bodies likewise communicate with the chylaqueous canals. The reproductive elements " are lodged in saccular processes of the lower portion of the central cavity, imme- Fig. 35- — Rhizostomidae. Generative zooid of Rhizostoma (after Owen). a Um- brella ; b b " Stomatodendra," covered with clavate tentacles and minute polypites ; c c Anastomosing network of canals. diately above the bases of the radiating canals, and, being usually of some bright colour, form a conspicuous cross shining through the thickness of the disc" (Greene). In the Rhizostomidcz the reproductive zooids (fig. 35), differ from those we have just described as occurring in the first section of the Pelagidcz, in not possessing tentacles on the margin of the umbrella, and in having the simple central polypite replaced by a composite dendriform process, which bears numerous polypites, projects far below the umbrella, and is thus described by Professor Huxley : — " In the Rhizostomida (fig- 35)5 a complex, tree-like mass, whose branches, the ' stoma- todendra,' end in, and are covered by, minute polypites, inter- spersed with clavate tentacula, is suspended from the middle of the umbrella in a very singular way. The main trunks of I 2O MANUAL OF ZOOLOGY. the dependent polypiferous tree, in fact, unite above into a thick, flat, quadrate disc, the ' syndendrium/ which is suspended by four stout pillars, the ' dendrostyles,' one springing from each angle, to four corresponding points on the under surface of the umbrella, equidistant from its centre. Under the middle of the umbrella, therefore, is a chamber, whose floor is formed by the quadrate disc, whilst its roof is constituted by the under wall of the central cavity of the umbrella, and its sides are open. The reproductive elements are developed within radiating folded diverticula of the roof of this genital cavity." It appears, finally, that amongst the old Pulmograde Aca- lephae, or amongst what would commonly be called Jelly-fishes, we have the following distinct sets of beings, which resemble each other more or less closely in appearance, but differ in their true nature : — 1. Free medusiform gonophores of various Corynida, Campa- nularidct) and the Oceanic Hydrozoa. 2. True Medusidce, entirely resembling the former in anato- mical structure, but differing in the fact that their ova do not give rise to a fixed zooid, but to free-swimming organ- isms exactly like the parent hydrosoma (Trachynemidce. and 3. Hydrozoa, which are provided with an " umbrella " (with all the peculiarities belonging to this structure), but which re- produce themselves without the intervention of free generative zooids produced by fission (Pelagid). 4. The free generative zooids of most of the Pelagidce, with an umbrella and a single polypite, the primitive hydrosoma being fixed and sexless (Aurelia, Cyanea, &c.) 5. The free generative zooids of the Rhizostomida, with an umbrella and a complex central tree bearing many polypites (Rhizostoma, Cephea, &c.) Of these five classes of organisms, Nos. i and 2 constitute the Gymnophthalmate Medustz of Professor E. Forbes, whilst Nos. 3, 4, and 5 are the Steganophthalmate Medusa of the same naturalist. SUB-CLASS V. GRAPTOLITJD^:. — The organisms included at present under this head are all extinct, and they are in many respects so dissimilar, and their structure is so far from being entirely understood, that it is doubtful if any definition can be framed which will include all the supposed members of the family. The following "definition, however, will include all the most typical Graptolites : — Hydrosoma compound, occasionally branched, consisting of numerous polypites united by a ccenosarc ; the latter being CCELENTERATA : HYDROZOA. 121 enclosed in a strong tubular polypary, whilst the former were protected by hydrothecae. In the great majority of Graptolites the hydrosoma was certainly unattached ; but in some aberrant forms — doubtfully belonging to the sub-class — there is reason to believe that the hydrosoma was fixed. The polypites are never separated from the coenosarc by any partition. In many cases the hydrosoma was strengthened by a chitinous rod, the " solid axis," somewhat analogous to the chitinous rod recently described by Professor Allman in the singular Polyzoon Rhabdopleura. From the above definition it will be seen that the nearest living allies to the Graptolites are the Sertularians. In point of fact, if we do not insist upon the presence of a " solid axis " as part of the definition, the Graptolites differ from the Sertularians in no essential point, save that the hydro- soma is always attached in the latter, and was certainly free in the most typical examples of the former. Indeed, certain forms at present placed among the Graptolites — such as Ptilo- grapsus and Dendrograpsus — are so similar to some living Sertularians, that it might be well to remove them alto- gether from the GraptolititUe, and to regard them as extinct representatives of the Sertularida. As regards the value of the " solid axis " as an element in defining Grap- tolites, we fear that much stress cannot be laid up on its presence or absence. It is true that it is present in all the most characteristic members of the sub-class, but it seems to be certainly absent in some — e.g., in Retiolites Geinitzianus, and in all species of Rastrites— and there do not seem to be sufficient grounds for excluding these from the Graptolitida on this account alone. Taking such a simple Graptolite as G. priodon (fig. 36) as the type of the sub-class, the hydrosoma is found to consist of the " solid axis," the " common canal," and the "cellules." The entire polypary is corneous and flexible, Fig. 36. — A, Graptolites prio- don, Bronn, preserved in relief. Lateral view slightly enlarged. B, Dorsal view of a fragment of the same species : considerably en- larged. C, Front view of a fragment of the same, showing the mouths of the cellules : much enlarged. D, Transverse section of the same. All from the base of the Coniston Flags, (Original.) 122 MANUAL OF ZOOLOGY. and the solid axis is a cylindrical fibrous rod, which gives support to the entire organism, and is often prolonged beyond one or both ends of the hydrosoma. There is, however, every reason for believing that the so-called " solid axis " is truly hollow. The common canal is a tube which encloses the ccenosarc, and gives origin to a series of cellules, these being little cups corresponding to " hydrothecae," and enclosing the polypites. Not only are the essential details of the structure — with the exception of the solid axis — strictly comparable with that of a Sertularian, but there is a good evidence, as shown by Hall and the author, that the reproductive process was also carried on in a manner similar to what we have seen in the other Hydroida — namely, by generative buds or gonophores. No Graptolite, however, has hither- to been certainly proved to have been fixed by a " hydrorhiza," and it is only in certain aberrant forms that there are any traces of a " hy- drocaulus." Besides the simple forms of Graptolites with ,a row of cellules on one side (monoprionidian) (fig. 37, 2), there are others with a row of cellules on each side (dip- rionidian) (fig. 37, 3). Many other curious modifications are known ; but there is only another peculi- arity which is worthy of notice here. This is the occurrence in several genera of a basal cor- neous disc or cup, which is pro- bably the homologue of the " float " or " pneumatophore " of the Physo- phoridae. (For distribution of Grap- rius enlarged ;« Solid axis J {Com- tolitCS SC6 ' Distribution of HydrO- mon canal ; c Cellules. 2. Mono- . * prionidian Graptolite (G- argen- ZOa in lime.) tens). 3. Diprionidian Graptolite \ rAcyorrlc rVipir mrn-lp. r»f nr (Diplograpsus pristis, variety with AS regards tneiF mOdC long basal spines). currence, Graptolites are usually found as glistening, pyritous impressions, with a silvery lustre. In some cases, however, they are found in relief. CCELENTERATA : HYDROZOA. 123 CHAPTER XII. DISTRIBUTION OF THE HYDROZOA. I. DISTRIBUTION OF HYDROZOA IN SPAC£. — The genera of Hydrozoa have a wide distribution, the mode of reproduction amongst the fixed forms being such as to ensure their extension over considerable areas. The various species of Hydra are of common occurrence in the fresh waters of Europe. Cordylo- phora, the sole remaining fresh-water genus, has not been found to occur out of the north temperate zone. All the other Hydrozoa, without a known exception, are marine in their habits. The fixed forms — viz., the Corynida, Sertularida, and Campannlarida — are represented more or less abundantly in almost all seas, extending from the littoral zone to con- siderable depths. The oceanic Hydrozoa, Calycophoridcz and Physophorukz, are chiefly characteristic of tropical seas ; but they are found also in the Mediterranean, and even in seas not far from, or even within, the Arctic circle. II. DISTRIBUTION OF HYDROZOA IN TIME. — The fine-grained lithographic slates of Solenhofen and Eichstadt have yielded impressions of Meduscz belonging to the existing families of the SEquoridcz and Trachynemidiz ; and the Lucer?iarida are represented by an ancient form of the Rhizostomidcz in the same formation. With these exceptions, however, there are hardly any fossil remains which would universally be conceded to be of a Hydrozoal nature. The Oldhamia of the Cambrian rocks of Ireland has, indeed, been regarded as belonging to the Hydrozoa; but it is believed by Mr Salter to be really a plant It consists of a main stem with numerous secondary branches, springing from the axis in an umbellate manner, but exhibiting no traces ofhydro- thecae. The occurrence of Corynida in a fossil condition can hardly be said to be free from doubt. Remains probably referable to this order have been, however, recently discovered in the Pal- aeozoic Rocks. The oldest of these was described by the Author some years ago from the Lower Silurian rocks of Dum- friesshire under the name of Corynoides. More lately a form called Palaocoryne has been described from the Carboniferous rocks of Scotland. Species of Hydractinia have also been described from the Cretaceous, Miocene, and Pliocene deposits. 124 MANUAL OF ZOOLOGY. The Sertularida and Campanularida are not certainly known to occur in a fossil condition. The fossils called Dendrograms us, Callograpsus, Ptilograpsus, and Dictyonema, all at present placed amongst the Graptolites, are, however, not improbably truly referable to the Sertularida. There can be little doubt but that the large and singular family of the Graptolitidce, should really be looked upon as extinct Hydrozoa, though good authorities still place them amongst the Polyzoa. As regards their distribution two facts are chiefly noticeable. In the first place, no Graptolite, except the doubtful genus Dictyonema, has hitherto been found to occur above the Silurian rocks. * lie Graptolites may therefore be regarded as characteristic fossils of the Silurian period, though they commence their existence in the Upper Cam- Fig. &.--Didy*nograpSus V-fractus. ^-^ Rockg> Secondlyj the diprionidian Graptolites, or those with a row of cellules on each side (genera Diplograpsus, Climacograpsus, and Dicranograpsus], have in Bohemia alone been certainly shown to occur above the horizon of the Lower Silurian rocks. The common genus Didymograpsus (comprising the " twin " Graptolites, fig. 38) is still more characteristic of the Lower Silurian period. In Didymograpsus the polypary consists of two lateral symmetrical branches, with cellules on one side only, springing from a central point or base, which is usually marked by a little spine or " radical." CHAPTER XIII. ACTINOZOA. i. GENERAL CHARACTERS OF THE ACTINOZOA. 2. CHAR- ACTERS OF THE ZOANTHARIA. 3. ZoANTHARIA MALACO- DERMATA. 4. ZoANTHARIA SCLEROBASICA. 5. ZOAN- THARIA SCLERODERMATA. CLASS II. ACTINOZOA. — The Actinozoa are defined an Ccelen- terata with a differentiated digestive sac opening below into the somatic cavity, but separated from the body-walls by an interven- CCELENTERATA : ACTINOZOA. 125 ing "perivisceral space" which is divided into a series of compart- ments by vertical partitions, or " mesenteries" to the faces of which the reproductive organs are attached. The Actinozoa (fig. 40), therefore, differ fundamentally from the Hydrozoa in this, that whereas in the latter the digestive cavity is identical with the somatic cavity, in the former there is a distinct digestive sac, which opens, indeed, into the somatic cavity, but is, nevertheless, separated from it by an intervening perivisceral space. As a result of this, the body of a typical Actinozoon (fig. 39), exhibits on transverse section two concentric tubes, one formed by the digestive sac, the other by the parietes of the body • whereas the transverse section of a Hydrozoon exhibits but a single tube, formed by the walls of the combined digestive and somatic cavity. Histologically, the tissues of the Actinozoa are essentially the same as those of the Hydrozoa, consisting of the two funda- mental layers, the " ectoderm " and the " endoderm." In the Actinozoa, however, there is a much greater tendency to a differentiation of these into specialised structures, and in some members of the class muscular fibres are well developed. Thus, the Sea-anemones have a well-developed series of longitudinal and circular muscular fibres, of which the former become radial in the disc and base. The ectoderm, especially, shows a tendency to break up into two layers, which are differentiated in opposite directions from an intermediate zone, and are termed by Huxley the " ecderon " and "enderon," corresponding respectively to the epidermis and derma of man. Cilia are often present, especially in the Fig. 39.— A, Transverse section of an Actinozoon. a. Digestive sac ; b Wall of the body ; m Mesenteries connecting the stomach with the body-walls, and dividing the space between them into a number of vertical compartments. B, Transverse section of a. Hydrozoon, showing the single tube formed by the walls of the body. interior of the somatic cavity, where they serve to promote a circulation of the digestive fluids contained therein. The sole 126 MANUAL OF ZOOLOGY. digestive apparatus in the Actinozoa consists of a tubular stomach-sac, which communicates freely with the outer world by means of the mouth, and opens inferiorly directly into the general body-cavity. In most, the " perivisceral space " be- tween the body-walls and the digestive sac is subdivided into compartments by a series of vertical lamellae, which are called the "mesenteries" (fig. 40, m). Upon the faces of these are Fig. 40. — A, Actinia mesembryanthemum, one of the Sea-anemones (after Johnston) ; B, Section of the same, showing the mouth (a), the stomach ($), and the body- cavity (c). borne the reproductive organs in the form of band-like ovaria or spermaria. There are no differentiated respiratory organs as a rule. Some forms, however, which live half-buried in sand or mud, have lobed and crimped organs attached to or near the tentacles, which have been supposed to act as breathing-organs ; whilst structures supposed to be gills are developed in some Zoanthids on either side of the primary mesenteries. Thread-cells, often of very complicated structure, are almost universally present, some of the Ctenophora having been asserted to be without them ; and some of the Actinozoa are able to sting very severely. A nervous system has not yet been proved to exist in any of the Actinozoa, except in the Ctenophora, and in none are there any traces of a vascular system. Some Actinice, are said to have short optic nerves distributed to the pigment-masses at the bases of the tentacles; and these masses possess crystalline lenses. Distinct reproductive organs occur in all the Actinozoa^ but CCELENTERATA I ACTINOZOA. I 2 7 these are internal, and are never in the form of external pro- cesses as in the Hydrozoa. Sexual reproduction occurs in all the members of the class, but in many forms gemination or fission constitutes an equally common mode of increase. Some Actinozoa, therefore, such as the common Sea-anemones, are simple organisms ; whilst others, such as the reef-building corals, are composite, the act of gemmation or fission giving rise to colonies composed of numerous zooids united by a ccenosarc. In these cases the separate zooids are termed " polypes," the term " polypite " being restricted to the Hydrozoa. In the simple Actinozoa, however, the term "polype" is employed to designate the entire organism. In other words, the "aetinosoma," or entire bodyofany^'«, may be composed of a single " polype," or of several such, produced by a process of continuous gemmation or fission, and united by a common connecting structure, or ccenosarc. Most of the Actinozoa are permanently fixed ; some, like the Sea-anemones, possess a small amount of locomotive power ; and one order, the Ctenophora, is composed of highly active, free-swimming organism. Some of the Actinozoa are un- ' provided with any hard structure or support, as in the Sea- anemones and in all the Ctenophora; but a large number secrete a calcareous or horny, or partially calcareous and partially horny, framework or skeleton, which is termed the " coral," or " corallum." The Actinozoa are divided into four orders — viz., the Zo- antharia, the Alcyonaria, the Rugosa, and the Ctenophora ; but the last is sometimes placed amongst the Hydrozoa, and it has been recently proposed to remove the Rugosa also to the same class. ORDER I. ZOANTHARIA. — The Zoantharia or " Helianthoid Polypes" are defined by the disposition of their soft parts in multiples of five or six, and by the possession of simple, usually numerous, tentacles. There may be no corallum, or rarely a " sclerobasic" one. Usually there is a " sclerodermic " corallum, in which the septa in each corallite, like the mesenteries, are arranged in imdtiphs of five or six. The Zoanmaria are divided into three sub-orders — the Zoan- tharia malacodermata, the Z. sclerobasica, and the Z. scleroder- mata; according as the corallum is entirely absent or very rudimentary, is " sclerobasic," or is " sclerodermic." SUB-ORDER I. ZOANTHARIA MALACODERMATA. — In this sec- tion of the Zoantharia there is either no corallum or 3, Very rudimentary one, in the form of a few scattered spicules. The "actinosoma" is usually composed of but a single polype. 128 MANUAL OF ZOOLOGY. (The term " actinosoma " is a very convenient one to express in the Actinozoa what " hydrosoma" expresses in the Hydrozoa — namely, the entire organism, whether simple or compound.) There are three families in this section, of which the Acti- nidce will require a somewhat detailed examination, since they may be taken as typical of the entire class of the Actinozoa. FAMILY I. ACTINID.E. — The members of this family are commonly known as Sea-anemones, and are distinguished by having no evident coralium, by being rarely compound, and by having the power of locomotion. The body of a Sea-anemone (fig 41, a) is a truncated cone, or a short cylinder, termed the " column," and is of a soft, leathery consistence. The two extremities of the column are Fig. 41. — Morphology of Actinidse. a Actinia rosea : b Arachnactis albida, (After Gosse.) termed respectively the "base" and the "disc," the former constituting the sucker, whereby the animal attaches itself at will, whilst the mouth is situated in the centre of the latter. Most Sea-anemones fix themselves by the base to some foreign object — a stone or a living animal — but others (Peachta and Edwardsia) bury themselves more or less completely in the sand. In a few cases (Cerianthus and Peachia) the centre of the base is perforated, but the object of this arrangement is unknown. Between the mouth and the circumference of the disc is a flat space, without appendages of any kind, termed the " peristomial space." Round the circumference of the disc are placed numerous tentacles, usually retractile, arranged in alternating rows, and amounting to as many as 200 in number in the common Actinia. The tentacles are tubular prolongations of the ectoderm and endoderm, containing diverticula from CCELENTERATA : ACTINOZOA. I 29 the somatic chambers, and sometimes having apertures at their free extremities. The mouth leads directly into the stomach, which is a wide membranous tube, opening by a large aper- ture into the general body-cavity below, and extending about half-way between the mouth and the base. The wide space between the stomach and column-wall is subdivided into a number of compartments by radiating vertical lamellae, termed the " primary mesenteries/' arising on the one hand from the inner surface of the body-wall, and attached on the other to the external surface of the stomach. In reality, the mesenteries are arranged in pairs, the chamber between each pair opening above into the cavity of a tentacle. As the stomach is considerably shorter than the column, it follows that the inner edges of the primary mesenteries below the stomach are free ; and these free edges, curving at first outwards and then down- wards and inwards, are ultimately attached to the centre of the base. Besides the primary mesenteries, there are other lamellae which also arise from the body-wall, but which do not reach so far as the outer surface of the stomach, and are called " secondary " and " tertiary " mesenteries, according to their breadth. The reproductive organs are in the form of reddish bands, which contain ova and spermatozoa, and are situated on the faces of the mesenteries. ' Most of the Actinia are dioecious — that is to say, the same individual does not develop both ova and spermatozoa. Along the free margins of the mesenteries there also occur certain singular convoluted cords, charged with thread-cells, and termed " craspeda," the function of which is not yet understood. It is believed, however, that the apertures, termed " cinclides," in the column-walls of some of the Actinidce, are for the emission of the craspeda. No traces of a nervous system, except the previously mentioned " optic nerves," have as yet been proved to exist in any Actinia. The embryo of the Actinia is a free-swimming ciliated body, at first rounded, but afterwards somewhat ovate. The rudimentary mouth is soon marked out by a depression at the larger extremity thread-cells appear as a layer in the ecto- derm ; a fold is prolonged inwards from the mouth to form the digestive sac ; and the primitive tentacles are at first either five or six in number, but usually double themselves rapidly. FAMILY II. ILYANTHID^E. — In this family there is no corallum, and the polypes are single and free, with a rounded or tapering base (fig. 41, b). Ilyanthus is in all essential respects identi- cal with the ordinary Actinia, but it is of a pointed or conical shape, the base being much attenuated, though whether its habit of life is free or not, is a matter of some uncertainty. * I I3O MANUAL OF ZOOLOGY. Arachnactis is certainly free, and, according to Professor E. Forbes, it can not only swim like a jelly-fish, but " it can convert its posterior extremity into a suctorial disc, and fix itself to bodies in the manner of/ an Actinia" It is by no means certain, however, that Arachnactis is a mature form, and there is some reason to suppose that it is merely the young stage of some at present unknown Actinozoon. FAMILY III. ZOANTHID^E. — In the Zoanthida there is a spicular corallum, and the polypes are attached by a fleshy or coriaceous base or coenosarc. The base is not muscular, and they possess no power of locomotion. In Zoanthits the sepa- rate polypes closely resemble small Actinitz, but they are united together at their bases by a thin fleshy coenosarc. SUB-ORDER II. ZOANTHARIA SCLEROBASICA. — The members of this sub-ord^r are always composite, and always possess a corallum, but this is " sclerobasic," and there are no spicular tissue-secretions. It appears advisable to explain here what is understood by the terms "sclerobasic" and " sclerodermic," as applied to corals. The "corallum" is the term which is applied to the hard structures deposited by the tissues of any Actinozoon^ many of which are so familiarly known as " corals." Usually the corallum is composed of carbonate of lime ; but it may be corneous, or partly corneous and partly calcareous. Whatever their composition may be, all coralla may be divided into two sections, termed respectively "sclerobasic" and "sclerodermic," which must be carefully distinguished from one another. The " sclerobasic " corallum, of which the red coral of commerce may be taken as the type, is in reality an exoskeleton, some- what analogous to the shell of a Crustacean, being a true tegumentary secretion. At the same time it is not a shell or external envelope, but it forms an axis, upon which the entire actinosoma is spread, much as the bark of a tree encloses the wood. The actinosoma, in fact, is inverted, and the " sclerobasis " is secreted by the outer surface of the ectoderm. The sclerobasic corallum is therefore truly " outside the bases of the polypes and their connecting coenosarc, which, at the same time, receive support from the hard axis which they serve to conceal " (Greene). Upon this view the sclerobasis is termed " foot-secretion " by Mr Dana. In other words, the sclerobasic coral is a hard skeleton which belongs solely to the ccenosarc of the actinosoma, and which can therefore be produced by a compound organism only. The " sclerodermic " corallum, on the other hand, is secreted within the bodies of the polypes, apparently by the inner layer CCELENTERATA I ACTINOZOA. of the ectoderm — the " enderon" of Huxley — and it is there- fore termed " tissue-secretion " by Mr Dana. In the sclero- dermic corallum each polype has a complete skeleton of its own, and the entire coral may consist of one such skeleton, or of several such united by the calcareous matter of the coenosarc. A sclerodermic corallum, therefore, like the animal which produces it, may be simple or composite, according as it is produced by a single polype or by several united by a coanosarc. It consists, therefore, of a single calcareous cup, or " corallite \ " or of several such united by a common calcareous bond or basis, the "coenenchyma." Taking a single " corallite " (fig. 42) as the type, we find that it shows its origin and nature plainly in its form. It consists of a cylindrical or conical tube of carbonate of lime, the outer wall of which is called the " theca." The upper part of the space included by the " theca " is vacant, and it is termed the cup or " calice ; " but the lower part is subdivided into a series of chambers, or " loculi/' by a series of radiating, vertical, calcareous plates, which are called the " septa " (figs. 42, 43). The septa extend from the inner surface of the theca towards its centre, where they usually unite to form an axial column, called the "columella." Many of the septa, however, do not reach the centre, but stop short at some distance from . — Cyathaxonia A simple sc'erodermic coral, showing the theca, with its co«tae, the calice, with the columella in its centre, and the septa. A portion of wall of the theca is broken, in order to show the interior of the calice. Fig. 43. — Diagrammatic sections of corals. A, Section of sclerodermic coral, showing five primary septa, the columella, and costa; (c). B, Section of Rugosa coral, showing four primary septa. Between the primary septa are seen the secondary and tertiary septa. the columella, often being broken up into upright pillars, called " pali." The parts thus described as essentially com- posing a corallite in a typical sclerodermic corallum are 132 MANUAL OF ZOOLOGY. related in the most obvious manner to the soft structures of the animal by which they are secreted. Thus, the "theca" clearly corresponds to the "column-wall," or the general wall of the body ; the " columella," when present, cor- responds to " that part>-of the enderon which forms the floor of the somatic cavity below the digestive sac ; " whilst the " septa " correspond to the "mesenteries," and, like them, are called "primary" and " secondary " according as they reach the colu- mella or fall short of it. When there are several corallites, the bond of union between them, the " coenenchyma," is secreted by the " coenosarc," to which it corresponds. In many Actinozoa, however, the sclerodermic corallum is not present in the typical form above described, but simply in the form of calcareous spicules or nodules scattered through the tissues of the animal. There are, also, members of the class in which both a scleroder- mic and a sclerobasic corallum are present, the latter constituting the main skeleton, whilst the former is represented by scattered spicules. The coral tissue itself is known as " sclerenchyma," and it varies considerably in texture, being sometimes extremely compact, and at other times very loosely put together. From what has been said it will be seen that a sclerobasic corallum can easily be distinguished from a schlerodermic by Fig. 44. — Sclerodermic and Sclerobasic Corals, a Portion of branch of Deudrophyllia, nigrescens, a compound sclerodermic coral (after Dana) ; b Longitudinal section of Isis hippuris, a sclerobasic coral, exhibiting the external bark or coenosarc, with its embedded polypes, supported by the internal axis or skeleton (after Jones). inspection ; the former (fig. 44, b) being usually more or less smooth, and being invariably devoid of the cups or receptacles CCELENTERATA : ACTINOZOA. 133 for the separate polypes, which are always present in the latter (fig. 44, a). The more important variations of detail which occur in both classes of corals will be noticed under the differ- ent families in which they occur. It only remains to add that doubt has been thrown by eminent zoologists upon the validity of the general distinction between sclerobasic and sclerodermic corals, as above denned. Returning now to the Zoantharia Sderobasica, we find the sub-order to contain the two families of the Antipathidce and the Hyalonemadce, (or Hyalochcetida!). Of these the Arttipatkida are chiefly noticeable because of their likeness to some of the Gorgonidce, from which, however, they are readily distinguished by the fact that the number of their tentacles is a multiple of six, whereas in the latter it is a multiple of four. Antipathes itself (fig. 45), possesses a horny sclerobasic corallum, which may be simple or branched, and is covered with numerous small polypes, united together by a ccenosarc, and possessing six tentacles each. Fig- 45- — Part °f a living stem of Antipathes an^uina, of the natural size. (After Dana.) The second family, that of the Hyalommada, contains the so-called " Glass-zoophytes," the true nature and position of which has been a subject of much controversy. By Dr Gray the Hyalonemadce are believed to be true Actinozoa, and he defines them as follows : — " Social Zoanthoid polypes secreting a central, siliceous, internal, axial coil for their support. The upper half of the coil covered by a uniform cylindrical bark, regularly studded with retractile polypes." The lower portion of the siliceous rope-ljfe axis, which looks exactly like a skein of threads of glass, is sunk in the sand at the bottom of the sea. The upper portion of the Hyalonema is often occupied by a cup-shaped sponge, called Carteria, which Dr Gray believes to be a parasitic growth. By Professors Loven, Perceval Wright, Wyville Thomson, and others, the sponge Carteria is looked upon as the true artificer of the siliceous rope, and the polypes are regarded as paraskic, and as referable to Palythoa. This last view, by which Hyalonema would be placed amongst the siliceous sponges, appears, upon the whole, to be most probably the correct one. In this case there is no I 34 MANUAL OF ZOOLOGY. Actinozoon, as far as is yet known, which possesses the power of secreting a siliceous skeleton, in this respect presenting a striking contrast to the Protozoa. SUB-ORDER III. ZOANTHARIA SCLERODERMATA. — The mem- bers of this sub-order include the great bulk of the coral-pro- ducing or " coralligenous " zoophytes of recent seas. They are defined by the possession of a sclerodermic corallum, the parts of which are arranged in multiples of five or six. The actinosoma may be simple, consisting of a single polype, or it may be composite, consisting of several polypes united by a ccenosarc. The divisions of the sub-order are founded upon the nature of the corallum, for the due comprehension of which it will be necessary to consider some points in connection with these structures somewhat more minutely. As already described, a typical corallite consists of an outer wall or " theca," with a cup or " calice " above, and divided below into numerous chambers or " loculi " by vertical partitions or " septa." Often the larger or "primary" septa coalesce centrally to form a median calcareous rod or " columella." The chief additional structures to be remarked are what are known as " tabulae," and "dissepiments." The "tabulae" (fig. 46) are transverse Fig. 46. — Columnaria. alveolata, showing the corallites partitioned off into stories by tabulae. plates or floors running at right angles to the axis of the coral- lite, and dividing the theca into so many horizontal compart- ments or stories, each of which is vertically subdivided by the septa, when these exist. As a rule, however, the septa are absent when there are tabulae, though the two structures co- exist in many extinct corals. The " dissepiments " are incom- plete transverse plates, which, " growing from the sides of the septa, interfere, to a greater or less extent, with the perfect CCELENTERATA I ACTINOZOA. I ^ ^ o pular name of Brain-stone Coral has hp^n rW,' to indicate.53 v-r t to suggest that resemblance to the convolutions of the brain which _ its popular name of Brain-stone Coral has been devised CHAPTER XIV. ALCYONARIA. ORDER II. ALCYONARIA. — The second great division of living Actinozoa is that of the Alcyonaria, defined by the possession of polypes with eight pinnately -fringed tentacles, the mesenteries and somatic chambers being also some multiple of four. The corallum, when present, is usually sclerobasic, or spicular; if " thecce " are prese?it, as is rarely the case, there are no septa. The Alcyonaria or " Asteroid Polypes " differ numerically from the Zoantharia in having their soft parts arranged in multiples of four, instead si five or six, as in the latter, whilst the septa are not in pairs. Their tentacles, too, are pinnate, and are not simply rounded. Numerically the Alcyonaria agree with the extinct order Rugosa, but the latter invariably possess a well-developed sclerodermic corallum, the thecae of which exhibit either septa or tabulae, or both combined. With the exception of the single genus Haimeia, the Alcyon- aria are all composite, their tubular polypes being connected together by a common ccenosarc, " through which permeate prolongations of the somatic cavity of each, forming a sort of canal system, whose several parts freely communicate," and permit of a free circulation of nutrient fluids. As a rule, the entire colony forms a lobate or branched mass. Anatomically the polypes of the Alcyonaria do not differ in any essential particular from those of the Zoantharia ; the numerical dis- tinction being the one by which they are chiefly separated from one another. The Alcyonaria are divided into four families — viz., the Alcyonidce, the Tubiporidce, the Pennatulidce, and the Gorgonidce. FAMILY I. ALCYONID^:. — This family is characterised by the possession of a fixed actinosoma, which is provided with a sclerodermic corallum in the form of calcareous spicula embedded in the tissues. The spicules are mostly fusiform in shape, and are generally present both in the polypes them- selves and in the connecting ccenosarc ; but there is no central solid axis. 13$ MANUAL OF ZOOLOGY. Alcyonium may be taken as the type of the family, and it is well known to fishermen under the name of " Dead-men's fingers." It forms spongy-looking, orange-coloured crusts or lobate masses, which are attached to submarine objects, and are covered with little stellate apertures, through which the delicate polypes can be protruded and retracted at will. The polypes communicate with one another by an anastomosing system of aquiferous tubes, and the corallum is in the form of cruciform, calcareous spicula scattered through its substance. In the allied Sarcodictyon the actinosoma is creeping and linear. FAMILY II. TUBIPORID^. — In the Tubiporidce, or "organ- pipe corals/' of which T. musica is a familiar example, there is a well-developed sclerodermic corallum, with thecae, but with- out septa. The corallum is composed of a number of bright- red, tubular, cylindrical thecae, which are united together externally by horizontal plates or floors, which are termed " epithecae," and represent external tabulae. The polypes are usually bright green in colour, and possess eight tentacles each. FAMILY III. PENNATULID^E. — The Pennatulida, or " Sea- pens," are defined by their free habit, and by the possession of a sclerobasic, rod-like corallum, sometimes associated with sclerodermic spicules. Pennatula (fig. 48), or the " Cock's-comb,'; consists of a free coenosarc, the upper end of which is fringed on both sides with feather-like lateral pinnae, which bear the polypes j whilst its proximal end is smooth and fleshy, and is probably sunk in the mud of the sea-bottom. This latter portion of the coeno- sarc is likewise strengthened by a long, slender styliform sclerobasis, resembling a rod in shape, whilst spicula occur also in the tentacles and ectoderm. The general colour of Pennatula is a deep reddish purple, the proximal extremity of the coenosarc being ^orange-yellow. Our British species (Pen- natula phosphored) varies from two to four inches in length, and is found on muddy bottoms in tolerably deep water. Its specific name is derived from the fact that it phosphoresces brilliantly when irritated. In Virgularia- (fig. 49), which, like Pennatula^ occurs not uncommonly in British seas, the actinosoma is much longer and more slender than in the preceding, and the polype-bear- ing fringes are short. The polypes have eight tentacles. The sclerobasis is in the form of a long calcareous rod, like a knit- ing-needle, and part of it is usually naked. No spicula are found in the tissues of Virgularia. In the nearly-allied Pavo- naria the polype-mass is quadrangular in shape. CCELENTERATA : ALCYONARIA. 139 FAMILY IV. GORGONID*:.— In the Gorgonida, or "Sea- shrubs," there is an arborescent ccenosarc permanently rooted Fig. 48. — Pennatula phosphorea (after Johnston). b Fig. 49. — Pennatulidse. Virgularia mirabilis. a A portion of the stem in the living con- dition, enlarged ; b Portion of the stem in its dead condition. and provided with a grooved, or silicate, branched sclerobasis, which is sometimes associated with true tissue-secretions, termed " dermo-sclerites." The sclerobasis of the Gorgonidcz varies a good deal in its composition. In some it is corneous, and these have often been confounded with the AntipathidcR^ amongst the Zoantharia. The distinction, however, between them is easy, when it is remembered that the polypes in the Gorgonidcz have tentacles in multiples oifour, whilst in the Antipathidce they are in sixes. The sclerobasis, too, in the former is always marked by grooves, whereas in the latter it is always either smooth or spinulous. In Isis (fig. 44, b) and Mopsea the sclerobasis consists of alter- nate calcareous and horny segments, branches being developed in the former from the calcareous, and in the latter from the horny segments. In Corallium rubrum, the "red coral" of commerce, the sclerobasis is unarticulate, or unjointed, and is entirely cal- 140 MANUAL OF ZOOLOGY. careous. It is the most familiar member of the family, and is largely imported for ornamental purposes. Red coral consists of a branched, densely calcareous sclerobasis, which is finely grooved upon its surface, and is of a bright-red colour. The corallum is invested by a ccenosarc, also of a red colour, which is studded by the apertures for the polypes, which are white, and possess eight pinnately-fringed tentacles. The entire ccenosarc is channelled out by a number of anastomos- ing canals, which communicate with the somatic cavities of the polypes, and are said to be in direct communication with the external medium by means of numerous perforations in their walls. The entire canal system is filled with a nutrient fluid, containing corpuscles, and known as the " milk." CHAPTER XV. RUGOSA. ORDER III. RUGOSA. — Until quite recently all the members of the Rugosa were believed to be extinct, and with the excep- tion of Holocystis elegans of the Lower Cretaceous rocks, it was believed that no example of the order had survived the close of the Palaeozoic period. Some Tertiary forms have, however, been now discovered ; whilst the recent Guynia of the Medi- terranean, and Haplophyllia of Florida, are Rugose corals. With the soft parts of the Rugosa we are, of course, almost entirely unacquainted, and the definition of the order must therefore be founded upon the characters of the corallum. The corallum-in the Rugosa is highly developed, sclerodermic, with true thecse, and often presenting both septa and tabulae com- bined. The septa are in multiples of four (fig. 43, B), unlike the recent sclerodermic coralla, in which they are in multiples of five or six. There is, further, no true ccenenchyma. Some of the Rugosa are simple ; but others are composite, increasing either by parietal or by calicular gemmation. Recently it has been shown that some very abnormal Rugose corals were provided with a lid or operculum, closing the mouth of the calice. In the genus Calceola (fig. 51), formerly referred to the Brachiopoda, and very abundant in certain parts of the Devonian System, the operculum consisted of a single valve or piece. In Goniophyllum four valves were present, and in Cystiphyllum prismaticum there were four or more valves in CCELENTERATA I ACTINOZOA. 141 the operculum. It is worthy of notice that some recent corals (species of Primnoa, Paramuricea, and others) exhibit also a more or less complete operculum. According to Professor Agassiz, the Rugosa and the Tabulate division of the Zoantharia ought not to be considered as belonging to the Actinozoa, but should be placed amongst the Hydrozoa. This radical Fig. 50. — Strombodes pentagonus. A Silurian Rugose Coral. Fig. 51. — Calceolasandalina. An operculate Rugose Coral. Devonian. change, however, cannot be accepted without the production of very conclusive evidence in its favour. A strong argument against referring the Rugose and Tabulate Corals, as proposed by Agassiz, to the Hydrozoa, is their possession in most cases of well-developed septa, implying, of course, the existence in the living animal of mesenteries, structures which are wholly wanting in the Hydrozoa. DISTINCTIONS BETWEEN THE CORALLA OF THE ORDERS OF ACTINOZOA. — Having now considered all the orders of the Actinozoa in which coralla are developed, it may be as well briefly to review their more striking differences. In the first place, a sclerobasic corallum may be distin- guished by inspection from a sclerodermic corallum by the fact that the latter, unless composed simply of spicules, presents the cups or "'thecse/' in which the polypes were contained ; the surface of the former being invariably destitute of these receptacles. A sclerobasic corallum is found in the families Antipathidce and Hyalonemadce (?) amongst the Zoantharia, and in the families Pennatulidcz and Gorgonidce amongst the Alcyonaria ; the following being the differences between them : — 1. Antipathid(E. — Sclerobasis spinulous or smooth; tentacles and soft parts in multiples of six. 2. Hyalonemadce (.?). — Sclerobasis siliceous, composed of numerous threads ; tentacles in multiples of five. 142 MANUAL OF ZOOLOGY. 3. PennatulidcR. — Sclerobasis sulcate, free; soft parts in mul- tiples of four. 4. Gorgonidce. — Sclerobasis sulcate, attached proximally ; soft parts in multiples of four. Sclerodermic coralla fall under two heads, according as they are simply composed of scattered spicules, or are provided with true thecce. I. Spicular coralla occur in the Zoantharia Malacodermata (occasionally), and in the Alcyonida ; and no differences can be stated between the coralla themselves. The animals, how- ever, differ entirely, the soft parts of the former being in mul- tiples of five or six, those of the latter being in multiples of four. II. A thecal sclerodermic corallum occurs in three distinct sections of Actinozoa: — i. In \h& Zoantharia Sclerodermata ; 2. In the Tvbiporidce, amongst the Alcyonaria; and, 3. In the Rugosa ; and the following are the distinctions between them : — 1. Zoantharia Sclerodermata. — Septa in multiples of five or six, sometimes absent ; tabulae often present. 2. Tubiporida. — Septa absent; thecae united externally by distinct, horizontal " epithecae." 3. Rugosa. — Septa in multiples of four; tabulae usually present. CHAPTER XVI. CTENOPHORA. ORDER IV. CTENOPHORA. — The Ctenophora comprise " trans- parent, oceanic, gelatinous Actinozoa, swimming by means of ' ctenophores] or parallel rows of cilia disposed in comb-like plates. No corallum " (Greene). The members of this order are all free-swimming organisms, and they are placed by many amongst the Hydrozoa, from which, however, they appear to be clearly separated by the possession of a differentiated digestive sac, as well as by their analogies with the Actinozoa, and their generally superior degree of organisation. Pleurobrachia (Cydippe, fig. 52) may be taken as the type of the order, the structure of all being similar to this in essential points. Pleurobrachia possesses a transparent, colourless, gelatinous, melon-shaped body, or " actinosoma," in which the CCELENTERATA I ACTINOZOA. 143 two poles of the sphere are termed respectively the " oral " and " apical," and the rest of the body constitutes the interpolar region. At the oral pole is the transverse mouth, bounded by lateral, slightly protuberant margins. " Eight meridional bands, or * ctenophores ' bearing the comb-like fringes, or characteristic organs of locomotion, traverse at definite in- tervals the interpolar region, which they divide into an equal number of lune-like lobes, termed the " actinomeres ; " but this division of the body does not extend into the immediate vicinity of the poles, before reaching which the ctenophores gradually diminish in diameter, each terminating in a point " (Greene). The normal number of the ctenophores appears to be eight, and each consists of a band of surface elevated transversely into a number of ridges, to each of which a fringe Fig. 52. — Ctenophora. Pleurobrach ia pileiis. of cilia is attached, so as to form a comb-like plate. The cilia in the middle of these transverse ridges are the longest, and they gradually diminish in length towards the sides, so that the form of each comb is somewhat crescentic. Beside the comb-like groups of vibratile cilia, Pleurobrachia is pro- vided with two very long and flexible tentacular processes, which are fringed on one side with smaller cirrhi. These filamentous processes arise each from a sac, situated on one of the lateral actinomeres, within which they can be completely and instantaneously retracted at the will of the animal. The mouth of Pleurobrachia (fig. 53, a) opens into a fusiform digestive sac, or stomach (b), the lower part of which is provided with brown cells, supposed to discharge the functions of a liver. The stomach opens below into a shorter 144 MANUAL OF ZOOLOGY. and wider cavity (c), termed the " funnel," from which two canals diverge in the direction of the vertical axis of the organism, to open at the " apical pole." These canals are known as the " apical canals " (e), and their apertures as the " apical pores." From the funnel two other pairs of canals are given off. Of these, one pair — known as the " paragastric canals " — turns upwards, one running parallel to the digestive sac on each side (d), and " terminating caecally before quite reaching the oral extremity." The second pair of canals (/) — the so-called "radial canals" — branch off from the funnel laterally, each dividing into two, and then again into two, as they proceed towards the periphery of the body. Thus, the two " primary " radial canals produce four " secondary " canals (/£), and these, in turn, give rise to eight " tertiary " radial canals (/), which finally terminate by opening " at Fig- S3- — Morphology of Ctenophora. i. Diagrammatic transverse section of Pleu^ robrachia, b Digestive cavity ; i i Primary radial canals ; k k Secondary radial canals ; / / Tertiary radial canals ; £• Tentacle. 2. Longitudinal section of P leurobrachia. a Mouth ; b Digestive cavity ; e Fun- nel ; d d Paragastric canals ; e e Apical canals ; f Ctenophoral canal ; g Tentac le ; h Ctenocyst. (After Greene.) right angles, into an equal number of longitudinal vessels, the 'ctenophoral canals' (/), whose course coincides with that of the eight locomotive bands. These canals end caecally both at their oral and apical extremities " (Greene). The whole of this complex canal-system is lined by a ciliated endoderm, and a constant circulation of the included nutrient fluid is thus maintained. Immediately within the apical pole is situated a small cyst or vesicle, supposed to be an organ of sense, and termed the " Ctenocyst " (h). In structure the " ctenocyst " consists of a spherical vesicle, lined with a ciliated epithelium, and filled with a clear fluid, which contains mineral particles, probably of carbonate of lime. Resting upon the ctenocyst is a small ganglionic mass, giving origin to a number of delicate filaments, CCELENTERATA I ACTINOZOA. I 45 and generally admitted to be a rudimentary form of nervous system. The reproductive organs of Pleurobrachia are in the form of folds, containing either ova or spermatozoa, and situated beneath the endodermal lining of the ctenophoral canals, one on each side. The embryo Pleurobrachia is at first rudely cylindrical in form, a belt of cilia passing round the middle of its body. This soon breaks up into two lateral groups, which eventually disappear altogether, " the ctenophores, at first very broad and few in number, at an early period taking on the performance of their special function " (Greene). As regards thehomologies between Actinia and Pleurobrachia, the following may be quoted from Professor Greene : — " If now a comparison be made between this nutrient system " (the canal-system of the Ctenophora} " and that of Actinia, the digestive sacs of the two organisms are clearly seen to correspond in form, in relative size, and mode of communication with the somatic cavity. The funnel and apical canals of Pleurobrachia, though more distinctly marked out, are the homologues of those parts of the general cavity, which in Actinia are central in position, and underlie the free end of the digestive sac. So also the paragastric and radial canals may be likened to those lateral portions of the somatic cavity of Actinia which are not included between the mesen- teries. Lastly, the ctenophoral canals of Pleurobrachia and the somatic chambers of Actinia appear to be truly homologous, the chief difference between the two forms being, that while in the latter the body-chambers are wide and separated by very thin partitions, they are in Pleurobrachia reduced to the con- dition of tubes ; the mesenteries which intervene becoming very thick and gelatinous, so as to constitute, indeed, the principal bulk of the body." The " apical " canals, again, by which the digestive sac communicates ififeriorly with the external medium, may be compared with the perforation which is found in some of the Actinidce, (Cerianthus and Peachid] traversing the axis of the base or foot. The remaining members of the Ctenophora conform in most essential respects with Pleurobrachia, the most important dif- ferences being found in the canal-system. For purposes of comparison this system may be divided into four portions as follows: — i. The "axial system," consisting of the mouth, stomach, funnel, and apical canals. 2. The "paraxial system/' comprising the paragastric canals. 3. The " radial system," comprising the primary, secondary, and tertiary radial canals. K 146 MANUAL OF ZOOLOGY. 4. The " ctenophoral system," consisting of the tubes which run underneath the locomotive bands. In Beroe, which is in other respects very similar to Pleuro- brachia, the axial system of canals is the same as we have seen in the latter. The paraxial system, however, consists of two pairs of paragastric canals, which, instead of terminating caecally, open into a circular canal which surrounds the mouth. The ctenophoral canals, likewise, open into the oral vessel, instead of terminating caecally as in Pleurobrachia. Lastly, the radial system is not developed, the ctenophoral canals simply curving round towards their apical extremities, and opening into the funnel directly. Amongst the Beroidcz the mouth extends entirely across the oral extremity of the body; hence they have been termed Eurystomata, the term Stenostomata being applied collectively to all the other Ctenophora. The Beroidcz further differ from Pleurobrachia in being destitute of the long tentacular appendages so characteristic of the latter, In Cestum^ or " Venus's Girdle," " elongation takes place to an extraordinary extent, at right angles to the direction of the digestive track, a flat, ribbon-shaped body, three or four feet in length, being the result." DIVISIONS OF THE CTENOPHORA. — The following arrange- ment of the Ctenophora has been adopted by Gegenbaur (see Greene) : — Order CTENOPHORA. Sub-order I. Stenostomata. Family T. CALLYMMID^E. Body furnished with a pair of antero-posterior oral lobes, and other smaller lateral appendages. Tentacles various, turned towards the mouth. Family II. CESTID^:. Body ribbon-shaped, extended in a lateral direction, without oral lobes. Tentacles two in number, antero-posterior, turned towards the mouth. Family III. CALLIANIRID^E. Body produced into a pair of wing-like lateral lobes, bearing the ctenophores. Tentacles two in number, lateral, turned from the mouth. Family IV. PLEUROBRACHIAD^E. Body oval or spheroidal, without oral lobes. Tentacles two in number, lateral, turned from the mouth. Sub-order II. Eurystomata . Family V. BEROID^:. Body oval, elongated, without oral lobes. Tentacles absent. CCELENTERATA : ACTINOZOA. 147 CHAPTER XVII. DISTRIBUTION OF ACTINOZOA. T. DISTRIBUTION OF ACTINOZOA IN SPACE. 2. CORAL-REEFS. 3. DISTRIBUTION OF ACTINOZOA IN TIME. 4. APPENDIX. DISTRIBUTION OF ACTINOZOA IN SPACE. — The Zoantharia mala- codermata appear to have an almost cosmopolitan range, Sea- anemones being found on almost every coast ; some of the tropical forms attaining a very large size. The Ctenophora, too, have an almost world-wide distribution, occurring in all seas from the equator to within the arctic circle. In habit all the Ctenophora are pelagic, being found, like the oceanic Hy- drozoa, swimming near the surface far from land. Pennatulidcz and GorgonidcR are found in the seas of the temperate zone, but the latter attain their maximum within the tropics. The Red Coral of commerce (Corallium rubrum) is derived from the Mediterranean, most abundantly in depths of from 25 to 50 feet, but extending to a depth of 1000 feet. The so-called "reef-building" corals have their distribution conditioned by the mean winter temperature of the sea, a tem- perature of not less than 66° being necessary for their existence. The seas, therefore, which possess the necessary temperature may be said to be all comprised within a distance of about 1800 miles of the equator on each side. Within these limits, however, apparently owing to the influence of arctic currents, no coral-reefs are found on the western coasts of America and Africa. They are found chiefly on the east coast of Africa, the shores of Madagascar, the Red Sea and Persian Gulf, throughout the Indian Ocean and the whole of Polynesia, and around the West Indian Islands and the coast of Florida. All known Acfinozoa are marine, no member of the class having hitherto been found in fresh water. CORAL-REEFS. — A " coral-reef" is a mass of coral, sometimes many hundred miles in length, and it may be two thousand feet or more in thickness, produced by the combined growth of different species of coralligenous Acfinozoa. As before said, a mean winter temperature of not less than 66° is necessary for their existence, and, therefore, nothing worthy of the name of a "coral-reef" is to be found in seas so far removed from the equator as to possess a lower winter temperature than the above. The headquarters of the reef-building Corals may be said to be around the islands and continents of the 148 MANUAL OF ZOOLOGY. Pacific Ocean. According to Darwin, coral-reefs may be divided into three principal forms — viz., Fringing-reefs, Barrier- reefs, and Atolls, distinguished by the following characters : — 1. Fringing-reefs (fig. 54, i). — These are reefs, seldom of great size, which may either surround islands, or skirt the shores of continents. These shore-reefs have no channel of any great depth intervening between them and the land, and the soundings on their seaward margin indicate that they repose upon a gently-sloping surface. 2. Barrier-reef s (kg. 54, 2). — These, like the preceding, may either encircle islands, or may skirt continents. They are dis- tinguished from fringing-reefs by the fact that they occur usually Fig. 54. — Structure of coral-reefs, i. F ringing-reef ; 2. Barrier-reef; 3. Atoll, a Sea level ; b Coral-reef; c Primitive land? d Portion of sea within the reef, forming a channel or lagoon. at a much greater distance from land, that there intervenes a channel of deep water between them and the shore,, and that soundings taken close to their seaward margin indicate enor- mous depths. If the barrier-reef surround an island, it is some- times called an " encircling barrier-reef," and it constitutes with its island what is called a " lagoon island." As an example of this class of reefs may be taken the great barrier-reef on the N.E. coast of Australia, the structure of which is on a perfectly colossal scale. This reef runs, with a few breaches in its continuity, for a distance of more than a thousand miles, its average distance from the shore being CCELENTERATA : ACTINOZOA. 149 between twenty and thirty miles, and the depth of the inner channel being from ten to sixty fathoms, whilst the sea outside is " profoundly deep" (in some places over 1800 feet). 3. Atolls (fig. 54, 3). — These are oval or nearly circular reefs of coral, enclosing a central expanse of water or lagoon. They seldom form complete rings, the reef being usually breached by one or more openings, which are always situated 'on the lee- ward side, or on that side which is most completely sheltered from the prevailing winds. In their structure they are iden- tical with " encircling barrier-reefs," and differ from these only in the fact that the lagoon which they enclose does not contain an island in its centre. If a coral-reef be observed — say a portion of an encircling barrier-reef — the following are the general phenomena which may be noticed. The general shape of the reef is triangular, presenting a steep and abrupt wall on the seaward side, and having a long and gentle slope towards the land. The outer margin of the reef is exposed to the beating of a tremendous surf, whilst the soundings taken just outside the line of breakers always indicate great depths. The longer inner slope is washed by the calm waters of the inner lagoon or channel. The reef is only very partially composed of living corals, which are found to occupy a mere strip, or zone, along the seaward margin of the reef, whilst all above this, as well as all below, is constituted by dead coral, or " coral-rock." As to the method in which such a reef is produced, the following facts have been established :— A. The coral-producing polypes cannot exist at levels higher than extreme low water, exposure to the sun, even for a short period, proving rapidly fatal. It follows from this that no coral-reef can be raised above the level of the sea by the efforts of its builders. The agency whereby reefs are raised above the surface of the sea, is the denuding power of the breakers which constantly fall upon their outer margins. These detach large masses of dead coral, and heap them up in particular places, until an island is gradually produced. The fragments thus accumulated are compacted together by the finer detritus of the reef, and are cemented together by the percolation of water holding carbonate of lime in solution. In this way the upper surface of the reef, along a line of greater or less breadth, is more or less completely raised above the level of high water. It is obvious, however, that the- reef might be entirely destroyed by a continuation of this process — the sea being quite competent to undo what it had done — unless some counteracting force were brought into play. This counteract- I 50 MANUAL OF ZOOLOGY. ing force is found in the vital activity of the living corals which form the seaward margin of the reef, and which, by their growth, prevent the sea from always destroying the masses of sediment which it may have thrown up. B. The coral-producing polypes cannot exist at depths exceeding some 15 to 30 fathoms. It follows from this that no coral-reef can be commenced upon a sea-bottom deeper than about 30 fathoms. The question now arises — In what way have reefs been produced, which, as we have seen, rise out of depths of 300 fathoms or more? This question has been answered by Darwin, who showed that the production of barrier-reefs and atolls was really to be ascribed to a gradual subsidence of the foundations upon which they rest. Thus, if a fringing-reef which surrounds an island is supposed gradually to sink beneath the sea, the upward growth of the corals will neutralise the downward movement of the land, so far, at any rate, that the reef will appear to be stationary, whilst it is really growing upwards. The island, however, as subsidence goes on, will gradually diminish in size, and a channel will be formed between it and the reef. If the depression should be still continued, the island will be reduced to a mere peak in the centre of a lagoon ; and the reef, from a " fringing-reef," will have become converted into an "encircling barrier-reef." As the growth of the reef is chiefly vertical, the continued depression will, of course, have produced deep water all round the reef. If the subsidence be continued still further, the central peak will disappear altogether, and the reef will become a more or less complete ring surrounding a central expanse of water; thus becoming converted into an "atoll." The production, therefore, of encircling barrier-reefs and atolls is thus seen to be due to a process of subsidence of the sea- bottom. The existence, however, of fringing-reefs is only possible when the land is either slowly rising, or is stationary ; and, as a matter of fact, fringing-reefs are often found to be conjoined with upraised strata of post-tertiary age. Atolls and encircling barrier- reefs, on the other hand, are not found in the vicinity of active volcanoes — regions where geology teaches us that the land is either stationary, or is undergoing slow upheaval. C. Different portions of a coral reef are occupied by differ- ent kinds of corals. According to Agassiz, the basement of a coral-reef is formed by a zone of massive Astraans. These cannot flourish at depths of less than six fathoms of water, and consequently when the surface of the reef has reached this level, the Astrczans cease to grow. Their place is now taken by Meandrinas (Brain-corals) and Forties; but these, too, CCELENTERATA : ACTINOZOA. I 5 I cannot extend above a certain level. Finally, the summit of the reef is formed by an aggregation of less massive corals, such as Madreporidcz, Milleporidce, and Gorgonidtz. DISTRIBUTION OF ACTINOZOA IN TIME. — With the single exception of the Mollusca, no division of the animal kingdom contributes such important and numerous indications of its past existence as the Actinozoa. In the Palaeozoic rocks the majority of corals belong to the division Rugosa, these seeming to have filled the place now taken by the sclerodermic Zoantharia. Until quite recently it was believed that all the Rugosa were Palaeozoic, with the exception of the genus Holocystis, represented in the Cretaceous period (Upper Greensand) by the single species H. elegans. Recent researches, however, have brought to light the existence in our present seas of at least two genera (Haplophyllia and Guynia) which belong to the Rugose family of the Cyathax- onidiz; and certain Tertiary Rugose Corals have also been described (Martin Duncan). As the Rugosa are in no funda- mental structural character to be distinguished from the Zoantharia Sclerodermata, save in the number of their septa, there would thus seem to be no good ground for maintaining that there is any essential difference between the Palaeozoic corals and those of more modern times. The Cyathophyllidce. and Cystiphyllida are exclusively Palaso- zoic ; the Cyathaxonida are Palaeozoic, but are represented by two living genera ; and the Stauridcz are represented in the Silurian Rocks (Stauria\ Devonian (Metriophyllurn), Permian (Polycalia), and in Tertiary deposits (Conosmilia). The Zoantharia Sclerodermata, though attaining their maxi- mum at the present day, nevertheless are well represented in past time, beginning in the Silurian period. One subdi- vision of this group, the Tubulosa, is entirely confined to the Palaeozoic Rocks, and another, the Tabulata, is chiefly Palaeo- zoic. The Perforata and Aporosa, on the other hand, are more abundant in the Mesozoic and Kainozoic Epochs. The Zoantharia Sclerobasica are hardly known as fossils, but the Miocene deposits of Piedmont (Middle Tertiary) have yielded a species of Antipathes. The Zoantharia Malacodermata, from the soft nature of their bodies, are obviously incapable of leaving any traces of their existence ; though we are by no means therefore justified in asserting that they did not exist in past geological epochs. The Alcyonaria are very doubtfully represented in rocks older than the Chalk; the Lower Silurian fossil called Pro- tovirgularia being more probably referable to the Hydrozoa. I 5 2 MANUAL OF ZOOLOGY. One of the Ptnnatulidce (viz., Graphularia) has been found in the London Clay (Eocene), and the same formation has like- wise yielded two species of Gorgonidce. (Mopsea and Websteria}. The genus Corallium has likewise been found in deposits of Miocene age. The Ctenophora, being entirely destitute of any hard structures, are not known at all as occurring in the fossil condition. APPENDIX GIVING A TABULAR VIEW OF THE DIVISIONS OF THE ZOANTHARIA SCLERODERMATA AND RUGOSA (AFTER MILNE-EDWARDS AND JULES HAIME). A. The Zoantharia Sderodermata are defined by the possession of a sclerodermic corallum, the parts of which are arranged in multiples of five or six. Septa generally well developed, but not combined, as a rule, with tabulae. The following chief divisions of the Zoantharia Sderodermata are, with few alterations, those adopted by the above-mentioned authorities : — I. TABULATA.— Septa rudimentary or absent; tabulae well developed, dividing the visceral chamber into a series of stories. 1. Thecidce, — Corallum massive ; a dense spurious ccenenchyma formed by the lateral union of the septa ; tabulae numerous. 2. Favositida. — Septa and corallites distinct ; little or no true ccenen- chyma. 3. Seriatoporidce. — Corallum arborescent ; sclerenchyma abundant and compact ; tabulae few. 4. Milleporidce. — Corallum massive or foliaceous ; septa not numerous ; sclerenchyma tabular or cellular. II. PERFORATA, — Septa well developed; no tabulae; dissepiments rudi- mentary ; sclerenchyma porous. 5. EupsammidcE. — Corallum simple or composite ; septa well developed and lamellar ; columella spongiose. 6. Poritidce. — Corallum composed of spongy, reticulated sclerenchyma. Septa never lamellar, but consisting wholly of a more or less definite series of trabeculae ; no tabulae. 7. Madreporida. — Corallum usually composite ; cosnenchyma abundant and spongy ; thecae porous, not distinct from the ccenenchyma ; septa distinct, but slightly perforate. III. APOROSA.— Septa well developed, completely lamellar, and primitively consisting of six elements ; no tabulae ; sclerenchyma imperforate. 8. Fungidce. — Corallum simple or compound ; thecae ill developed, and somewhat porous) no dissepiments or tabulae ; synapticulae numerous. 9. AstrceidcE. — Corallum simple or compound ; no proper ccenenchyma ; numerous dissepiments ; no synapticulas. Corallites well denned, and separated from one another by perfect walls. 10. Oculinidce. — Corallum composite ; ccenenchyma abundant and com- pact ; dissepiments few in number. Walls of the corallites without perforations, not distinct from the ccenenchyma. 11. Turbinolidtz. — Corallum usually simple ; no ccenenchyma ; septa well developed ; no dissepiments, nor synapticulae. IV. TUBULOSA. — Septa indicated by mere striae ; thecae pyriform ; corallites sometimes connected by a creeping basal ccenenchyma. 12. Auloporida. — This being the only family in the 7~ubulosa, its charac- ters are necessarily the same as those of the division itself. CCELENTERATA : ACTINOZOA. 153 B. ORDER RUGOSA. — Characterised by the possession of a sclerodermic corallum, usually with septa and tabulae combined, the former being in multiples of four. The corallites are always distinct, and are never united together by a cosnenchyma. The septa are usually incomplete, but are never porous, and never bear synapticulse. The order is divided into the following four families : — Family I. Stauridce. Corallum simple or composite ; septa incomplete ; united by lamellar dissepimnts ; four large primary septa, forming a cross. Family 2. Cyathaxonidce.. Corallum simple ; septa complete ; no dissepiments or tabulae ; with- out four primary septa. Family 3. • Cyathophyllida. Corallum simple or composite ; septa incomplete ; tabulse generally present. Family 4. Cystiphyllida. Corallum simple, composed chiefly of a vesicular mass, with but slight traces of septa. J54 ANNULOIDA. CHAPTER XVIII. T. GENERAL CHARACTERS OF THE ANNULOIDA. 2. GENERAL CHARACTERS OF THE ECHINODERMATA. SUB-KINGDOM III. ANNULOIDA ( = Echinozoa^ Allman). — This sub-kingdom was proposed by Professor Huxley for the recep- tion of the two groups of the Echinodermata and the Scolecida, of which the former belonged to the old sub-kingdom Radiata, whilst the latter was formerly classed with the Annulosa. The same sections have been grouped by Professor Airman together, under the name Echinozoa; the Rotifera, however, being ex- cluded from this division and classed with the Annulosa. By others again, the Annuloida are looked upon as a section of the Annulosa, and not as a distinct sub-kingdom. Provisionally, however, it seems best to regard the Annuloida as one of the primary divisions of the animal kingdom, it being impossible, in the meanwhile, to frame a definition common to it and to the Annulosa. The name Vermes has sometimes been em- ployed to designate the sub-kingdom Annuloida, certain classes being sometimes removed elsewhere, or certain others being added. In its most modern signification, the term Vermes may be held as synonymous with Annuloida, minus the Echino- dermata and plus the whole of the Anarthropodous division of the Annulosa. The Annuloida are distinguished by the presence of a distinct nervous system, and the possession of an alimentary canal which is entirely shut off from the general cavity of the body. A peculiar system of canals, usually communicating with the exterior, and termed the "water-vascular" or "aquiferous" system, is present in all; and a true vascular apparatus is sometimes present. In none is the body of the adult composed of definite segments, or provided with " bilaterally disposed successive pairs of appendages." The union of the Echinodermata with the Scolecida in a single sub-kingdom, as proposed by Huxley, must be regarded as a ANNULOIDA : ECHINODERMATA. 155 purely provisional arrangement. Many other classifications have been proposed, each with some obvious advantages and some disadvantages. Perhaps the most natural arrangement would be to establish a separate sub-kingdom for the Echino- dermata, and to group the Scolecida with the Anarthropoda under the name of Vermes. In the confessedly imperfect state of our knowledge, however, it will be as well to retain for the present the sub- kingdom Annuloida. The Anmdoida are divided into two great classes, the Echino- dermata and the Scolecida. CLASS I. — ECHINODERMATA. The members of this class are known commonly as Sea- urchins, Star-fishes, Brittle-stars, Feather-stars, Sea-cucumbers, &c., and the following are their leading characteristics. They are all animals which, in the adult condition, show a more or less distinctly radiate condition of their parts, especially of those around the mouth ; whilst in their embryonic stages they are more or less distinctly bilaterally symmetrical. Whilst radial symmetry in the great majority of cases preponderates in the adult Echinoderm, there are, nevertheless, many instances in which the fully-grown animal shows distinct traces of bilateral symmetry. The external envelope of the body (" perisome ") is either composed of numerous calcareous plates, articulated together, or of a coriaceous integument, in which calcareous granules and spicules are usually developed. In all adult Echinoderms there is a system of tubes, termed the "ambu- lacral system," which generally subserves locomotion, and usually communicates with the exterior. This water-vascular system surrounds the commencement of the alimentary canal, and in almost all cases gives off secondary vessels in a radiating manner. An alimentary canal is always present, and is com- pletely shut off from the body-cavity. The nervous system in all the adult Echinoderms is a ring-like gangliated cord, which surrounds the oesophagus and sends branches parallel to the radiating ambulacral canals. The special features of the structure of the Echinodermata will be noticed under each order, but it will be as well to give here an abstract of Professor Huxley's description of the pro- cess of development in the members of the class. In the great majority, if not in all, of the Echinodermata the impregnated ovum is developed into a free-swimming, ciliated, ovoid embryo. Soon the cilia become restricted to one, two, or more bands, which are generally disposed transversely to the long axis of 156 MANUAL OF ZOOLOGY. the body, and are in all cases bilaterally symmetrical. The parts of the body which support the cilia are usually developed into protuberances, or processes, which are symmetrically dis- posed upon the two sides of the body. " The larvae of Asteridea and Holothuridea are devoid of any continuous skeleton, but those of Ophiuridea and Echinidea possess a very remarkable, bilaterally symmetrical, continuous, calcareous skeleton, which extends into and supports the processes of the body." In this stage the larva form of the two orders last mentioned was described by Miiller as a distinct animal under the name of Pluteus, from its resemblance to a painter's easel. (See fig. 57, i.) An alimentary canal soon appears in the larva, forming a curve with an open angle towards the ventral surface of the organism. The parts of the alimentary canal consist of a mouth, gullet, globular stomach, and short intestine, with a distinct anal aperture ; the whole being " disposed in a longitudinal and vertical plane, dividing the larval body into two symme- trical halves." Besides the digestive canal, no other organs have hitherto been discovered in these larvae. In the further process of development, " an involution of the integument takes place upon one side of the dorsal region of the body, so as to give rise to a caecal tube, which gradually elongates inwards, and eventually reaches a mass of formative matter, or blastema, aggregated upon one side of the stomach. Within this, the end of the tube becomes converted into a circular vessel, from which trunks pass off, radially, through the enlarging blastema. The latter, gradually expanding, gives rise, in the Echinidea, the Asteridea, the Ophiuridea, and the Crinoidea, to the body-wall of the adult ; the larval body and skeleton (when the latter exists), with more or less of the primitive intestine, being either cast off as a whole, or dis- appearing, or becoming incorporated with the secondary development, while a new mouth is developed in the centre of the ring formed by the circular vessel. The vessels which radiate from the latter give off diverticula to communicate with the cavities of numerous processes of the body — the so- called feet — which are the chief locomotive organs of the adult. The radiating and circular vessels, with all their appendages, constitute what is known as the ' ambulacral system ; ' and in Asterids and Echinids this remarkable system of vessels remains in communication with the exterior of the body by canals, connected with perforated portions of the external skeleton — the so-called ' madreporic canals,' and 'tubercles.' In Ophitirids the persistence of any such com- ANNULOIDA I ECHINODERMATA. 157 mimication of the ambulacral system with the exterior is doubtful, and still more so in Crinoids. In Holothurids no such communication obtains ; the madreporic canals and their tubercles depending freely from the circular canal into the peri visceral cavity." By Professor Wyville Thomson the larva of the Echinoder- mata is termed the " pseud-embryo," since it leads a perfectly independent existence, and the true Echinoderm is usually developed out of a portion only of its substance. The great peculiarity, therefore, in the development of the Echinodermata is found in the possession by the larva of provisional organs, which may be either absorbed or cast off, but which are not converted into the corresponding structures of the adult. 'Thus the Pluteus of an Echinoid possesses a mouth and alimentary canal which are not converted into, and in no way correspond with, the mouth and alimentary canal of the adult. The Echinodermata are divided into seven orders — viz., the Crinoidta, Cystoidea, Blastoidea, Ophiuroidea, Asteroidea, Echi- noidea, and Holothuroidea. Of these, the first is almost extinct, and the two next are entirely so ; they are really the lowest orders ; but their structure will be better understood if the higher orders are considered first. CHAPTER XIX. ECHINOIDEA. ORDER ECHINOIDEA. — The members of this order — commonly known as Sea-urchins — are characterised by the possession of a subglobose, discoidal, or depressed body, encased in a " test " or shell, which is composed of numerous, immovably connected, calcareous plates. The intestine is convoluted, and there is a distinct anus. The mouth is usually armed with calcareous teeth, and is always situated on the inferior surface of the body, but the position of the anal aperture varies. The larva is pluteiform, and has a skeleton. The " test "of the Echinoidea is composed of numerous cal- careous plates, firmly united to one another by their edges, and bearing different names according to their position and function. In one or two exceptional -cases (Echinothurida), though the essential structure of the shell is the same as in the ordinary forms, the plates of the test are so thin, and are so 153 MANUAL OF ZOOLOGY. united together, that the entire test becomes flexible and soft. In the typical recent members of the order the test is composed of twenty rows of these plates, arranged in ten alternating- zones, which pass from the one pole of the animal to the other, each zone being composed of two similar rows. Five of these double rows are composed of large plates, which are not per- forated by any apertures (fig. 55) ; the zones formed by these imperforate plates being termed the " inter-ambulacral areas." The other five double rows of plates alternate regularly with the former, and are termed the " ambulacral areas," or " pori- ferous zones." Each of these zones is composed of two rows Fig- 55- — Morphology of Echinoidea. i. Portion of the test of Galerites hemispheric-its enlarged, showing an iriter-ambulacral area («), and an ambulacral area (£). 2. Galerites hemispheric-its viewed from above, a Inter-ambulacra ; b Ambulacra. 3. Genital and ocular disc of Hemicidaris intermedia enlarged, c Ocular plate ; ^ Genital plate ; e Anal aperture ; yMadreporiform tubercle.- 4. Spine of the same. (After Forbes.) The tubercles are mostly omitted on figs. 2 and 3 for the sake of clearness. * of small plates, which are perforated by minute apertures for the emission of the " ambulacral tubes," or " tube-feet." In one great group of the Echinoids, the ambulacral areas pass from the centre of the base of the shell to its summit, when they are said to be " perfect" (ambulacra perfecta) or " simple." In another great group the ambulacral areas are not thus con- tinuous from pole to pole, but simply form a kind of rosette upon the upper surface of the shell. In these cases — as in the common Heart-urchins — the ambulacral zones are said to be " circum script " (ambulacra circumscripta] or " petaloid." Growth of the test is carried on by additions made to the edge of each individual plate, by means of an organised membrane which passes between the sutures, where the plates come into ANNULOIDA I ECHINODERMATA. 159 contact with one another. The plates of the test are studded with large tubercles, which are more numerous on the inter- ambulacral areas than on the ambulacral, and are wanting on all the plates which do not belong to either area. These tubercles carry spines (fig. 56), used defensively and in loco- motion, which are articulated to their apices by means of a sort of " universal " or " ball-and-socket " joint. Occasionally a small ligamentous band passes between the head of the tubercle and the centre of the concave articular surface of the spine, thus closely resembling the " round ligament" of the hip-joint of man. Besides the main rows of plates just described, form- ing the so-called " corona," other calcareous pieces go to make up the test of an Echinus. The mouth is surrounded by a coriaceous peristomial membrane, which contains a series of Fig. 56.— Cidaris papillata. (After Gosse.) small calcareous pieces, known as the " oral plates ; " whilst a corresponding series of " anal plates " is found in the mem- brane surrounding the opposite termination of the alimentary canal. Surrounding the aperture of the anus at the summit of the test is the " apical disc," composed of the so-called genital and ocular plates (fig. 55, 3). The "genital plates" are five large plates of a pentagonal form, each of which is perforated by the duct of an ovary or testis. One of the genital plates is larger than the others, and supports a spongy tubercle, per- forated by many minute apertures, like the rose of a watering- pot, and termed the " madreporiform tubercle." The genital plates occupy the summits of the interambulacral areas. Wedged in between the genital plates, and occupying the summits of the ambulacral areas, are five smaller, heart-shaped, l6o MANUAL OF ZOOLOGY. or pentagonal plates, known as the " ocular plates," each being perforated by a pore for the reception of an " ocellus " or " eye." Besides the spines, which are sometimes of a very great length, the test often bears curious little appendages, called " pedicellariae," and often supposed to be parasitic. Each of these consists of a stem, bearing two or three blades or claws, which snap together and close upon foreign objects like the beak of a bird. Their action appears to be independent of the will of the animal, and their true function is not known ; but they may be regarded as peculiarly modified spines. One function performed by the pedicellarise, in some species at any rate, is the removal of excrementitions particles of food. Such particles, on being ejected from the vent, are seized by the pedicellarise, passed on from one to another, and ultimately entirely got rid of. Locomotion in the Echinoidea is effected by means of a singular system of contractile and retractile tubes, which constitute the " ambulacral tubes," or " tube-feet," and are connected with the "ambulacral system" of aquiferous canals (%• 57)- From the perforated " madreporiform tubercle" on the largest of the genital plates, there proceeds a membranous canal, known as the " stone," or " sand canal/' whereby water is conveyed from the exterior to a circular tube, surrounding the oesophagus, and constituting the centre of the water- vascular, or ambulacral system. The function of the madre- poriform tubercle appears to be that of permitting the ingress of water from the exterior, but of excluding any solid particles which might be injurious. The "circular canal," surrounding the gullet, is situated between the nervous and blood-vascular rings, and gives off five branches — the " radiating canals " — which proceed 'radially along the "ambulacral areas "in the interior of the shell. In this course they give off numerous short lateral tubes — the "tube-feet" — which pass through the " ambulacral pores " to gain the exterior of the test, and terminate in suctorial discs. Besides the radiating ambulacral canals, there are connected with the circular canal certain vesicles of unknown functions, known as the " Polian vesicles " (ampulla Poliancz). The ambulacral tubes, or tube-feet, can be protruded at the will of the animal through the pores which perforate the ambulacral areas, and can be again retracted. By means of these locomotion is effected, the tube-feet being capable of protrusion to a length greater than that of the longest spines of the body. The mechanism by which the tube-feet are protruded and retracted is as follows : — Each ANNULOIDA : ECHINODERMATA. 161 tube-foot, shortly after its origin, gives rise to a secondary lateral branch, which terminates in a vesicle. These vesicles or " ampullae " are provided with circular muscular fibres, by the contraction of which their contained fluid is forced into the tube-feet, which are thus protruded. Retraction of the ambulacral tubes is effected by proper muscular fibres of their own, which expel again the fluid which has been forced into them by the vesicles. According to Owen, the terminal sucker in each tube-foot of the Echinus is " supported by a circle of five, or sometimes four, reticulate calcareous plates, which intercept a central foramen, and by a single, delicate, reticulated, perforate plate on the proximal side of the preced- ing group. The centre of the suctorial disc is perforated by an aperture conducting to the interior of the ambulacral tube- foot." This perforation of the suctorial discs of the ambulacra, though affirmed by Valentine, is denied by Miiller ; and it is difficult to believe that it would not impair the functions of the feet in the act of protrusion. jrjg. 57 — Morphology of Echinoidea. i. Echinid larva, a Mouth ; b Stomach ; c In- testine ; s Skeleton. 2. Diagram of Echinus. The spines and the ambulacra are represented over a small portion of the test ; the vascular system is cross-shaded ; the nervous system is represented by the black line, a Anus ; b Stomach ; c Mouth ; d and / Vas- cular rings round the alimentary canal ; e Heart ; g Test ; h Nervous ring round the gullet ; i Ambulacral ring or "circular canal" round the gullet ; k k Pohan vesicles ; / Sand canal ; m m Radiating ambulacral canal ; n Secondary ambula- cral vesicles ; o Ambulacral tubes, or "tube-feet;" p Spines; r Madreponform tubercle. The digestive system of the Echinus consists of a mouth, armed with five long, calcareous, rod-like teeth, which perforate five triangular pyramids, the whole forming a singular structure, known as " Aristotle's Lantern." The mouth conducts by a pharynx and a tortuous oesophagus to a stomach, opening into a convoluted intestine, which winds * L 1 62 MANUAL OF ZOOLOGY. round the interior of the shell, and terminates in a distinct anus. The mouth is always situated at the base of the test, and may be central, sub-central, or altogether excentric in position. The anus varies considerably in its position, being usually situated within the apical disc, and surrounded by the genital and ocular plates, when the test is said to be " regular." Sometimes, however, the anal aperture is with- out the apical disc, and is removed to some distance from the genital plates, when the test is said to be " irregular." In this last case, the anus, instead of being apical, is marginal or sub-marginal. The convolutions of the alimen- tary canal are attached to the interior of the test by a delicate mesentery ; the surface of which, as well as that of the lining-membrane of the shell, is richly ciliated, and subserves the purposes of respiration. The proper blood-vascular system (fig. 57, 2) consists of a central, fusiform, contractile vesicle, or heart. This gives off one vessel, which forms a ring round the intestine near the anus, and another which passes downwards, and forms a circle round the gullet, above the "circular canal;'of the ambulacral system. From the anal vessel proceed five arterial branches, which run along the ambulacral spaces, and return their blood by five branches, which run alongside of them in an opposite direction. This blood-vascular system has been thought to be homologous with the pseudohaemal system of the Annelida, rather than with the true circulatory system of higher animals. By Huxley, however, the pseudohsemal vessels of the Anne- lides are looked upon as homologous with the water- vascular system of the Scoledda, to which the water-vascular or am- bulacral system of the Echinoderms is unquestionably com- parable. The haemal system, therefore, of the Echinoderms must be regarded as something not represented amongst the Annelides. The nervous system consists of a ganglionated circular cord, which surrounds the gullet below, or superficial to, the " circular canal" of the ambulacral system, and which sends five branches along the ambulacral spaces, in company with the radiating ambulacral canals. There is no distinct respiratory organ, but the function of aeration of the blood appears to be performed partly by the vascular lining of the test and the mesentery, and partly by the secondary ambulacral vesicles. The perivisceral cavity is filled with sea-water, but the mode in which this is admitted, or renovated, is not known with certainty. According to Tiede- mann, the water gains access to the interior by means of short, ANNULOIDA : ECHINODERMATA. 163 branched processes, which are attached to the extremities of the inter-ambiilacral areas round the mouth ; but others deny that these are perforated by any apertures. These processes are apparently nothing more than greatly-developed tube-feet, and they are probably homologous with the crown of feathery tentacles surrounding the mouth in the Holothurians. The sexes are distinct in all the Echinoidea, and the repro- ductive organs are in the form of five membranous sacs, which occupy the inter-ambulacral areas, and open on the exterior by means of the apertures in the genital plates. In the " irregular " Echinoids (such as the "heart-urchins") there are only four genital glands, and, therefore, only four genital plates in the apical disc. .The irregular Echinoids, further, are distinguished by having the anus marginal or sub-marginal, by being mostly destitute of a masticatory apparatus, and by being generally of an oblong, pentagonal, heart-shaped, or discoidal figure. The "regular" Echinoids, on the other hand, have the anus placed at the summit of the test, surrounded by the genital disc ; the test is almost always circular or spheroidal ; and the mouth is armed with a complicated masticatory apparatus. The Echinoidea may be divided into the following principal families : — SYNOPSIS OF THE FAMILIES OF ECHINOIDEA (AFTER POMEL). SUB-ORDER I. ECHINIDA. — Test composed of no more than twenty rows of plates. a. Spatiformes. — Mouth excentric, in front; anus behind; anterior am- bulacrum obliterated ; form obovate. (The so-called " Spantan- goid" Sea-urchins.) 1. Ananchytida. — With simple ambulacra. 2. Spantangida. — With petaloid ambulacra. b. Lampadi formes. — Mouth central, or nearly so ; toothed or toothless ; anus more or less posterior, but oiten mounting high enough to enter into the genital disc ; ambulacra similar. 3. Echinoneida. — Toothless ; ambulacra simple. 4. Cassidulida. — Toothless ; ambulacra petaloid. 5. Clypeastrida. — Toothed ; ambulacra petaloid. 6. Echinoconida. — Toothed ; ambulacra simple. c. Globiformes. — Mouth central ; anus opposite the mouth, surrounded by the genital plates. 7. Cidarida. — Ambulacra prolonged on the buccal membrane and destitute of buccal branchiae. 8. Echinidce. — Ambulacra not prolonged on the buccal membrane, but provided with buccal branchiae. SUB-ORDER II. PERISCHOECHINID/E OR TESSELATA. — Corona of the test, consisting of more than twenty rows of plates. (The Palaeozoic Sea- urchins, Archaocidaris and Palcechinus.] 164 MANUAL OF ZOOLOGY. CHAPTER XX. ASTEROIDEA AND OPHIUROIDEA. ORDER ASTEROIDEA (Stellerida). — This order comprises the ordinary star-fishes, and is defined by the following characters : —The body (fig. 58) is star shaped or pentagonal, and consists of a central body or " disc," surrounded by five or more lobes, or " arms," which radiate from the body, are hollow, and con- tain prolongations of the viscera. The body is not enclosed in an immovable box, as in the Echinoidea, but the integument (" perisome ") is coriaceous, and is strengthened by irregular calcareous plates, or studded by calcareous spines. No dental apparatus is present. The mouth is inferior, and central in position; the anus either absent or dorsal. The ambulacral tube- feet are protruded from grooves on the under surface of the rays, The larva is vermiform, and has no pseudembryonic skeleton. Fig. $>.—Cribella oculata. (After Forbes.) The skeleton of the A steroidea is composed of a vast number of small calcareous plates, or ossicula, united together by the coriaceous perisome, so as to form a species of chain-armour. Besides these, the integument is abundantly supplied with spines, tubercles, and " pedicellariae." Lastly, the radiating ambulacral vessels run underneath a species of internal skele- ton, occupying the axis of each arm, and composed of a great number of bilateral " vertebral ossicles " or calcareous plates, which are movably articulated to one another, and are provided with special muscles by which they can be brought together or ANNULOIDA I ECHINODERMATA. drawn apart. The upper surface of a star-fish corresponds to the combined inter-ambulacral areas of an Echinus, and exhibits the aperture of the anus (when present), and the " madreporiform tubercle," which is situated near the angle between two rays. The inferior or ventral surface corresponds to the ambulacral areas of an Echinus, and exhibits the mouth and ambulacral grooves. The mouth is central in position, and is not provided with teeth ; it leads, by a short gullet, into a large stomach, from which a pair of sacculated diverticula are prolonged into each ray. A distinct intestine and anus may, or may not, be pre- sent • but the anus is sometimes wanting (in the genera, Astro- pecten, Ctenodiscus, and Luidia}. The ambulacral system is essentially the same as in the Echinoidea, and is connected with the exterior by means of the "madreporiform tubercle," or "nucleus," two, three, or more of these being occasionally present. The ambulacral tube-feet are arranged in two or four rows, along grooves in the under surface of the arms. Each ambulacral groove is continued along the lower surface of one of the arms, tapering gradually towards the extremity of the latter. The floor of each groove is con- stituted by a double row of minute calcareous pieces — the " ambulacral ossicles" — which are movably articulated to one another at their inner ends. At the bottom of each groove-is lodged one of the radiating canals of the water- vascular system or ambulacral system, from which are given orT the rows of suctorial feet, or " tube-feet." It follows from this that the radiating vessels of the ambulacral system are outside the chain of ambulacral ossicles, so that these latter are to be regarded as an internal skeleton, and they do not correspond with any part of the skeleton of Echinoids* — at least they do not correspond with the per- forated ambulacral plates of the Sea-urchins. The am- ig- 59- — Diagram of a star-fish (Gonias- ter), showing the under surface, with the mouth and ambulacral grooves, a Am- bulacral ossicles, with the ambulacral pores between them, b Adambulacral plates, bounding the ambulacral grooves ; m Marginal plates (wanting in many species) ; o Oral plates, placed at the angles of the mouth. * The structures in the Echinus, which are truly homologous with the ambulacral ossicles of the Asteroidea and Ophiuroidea, are the so-called " auriculae." 1 66 MANUAL OF ZOOLOGY. bulacral ossicles, however, of the Star-fishes are of such a form that by their apposition an aperture or pore is formed between each pair. By means of these pores (fig. 59, a) the tube-feet communicate with a series of little bladders placed above the chain of ossicles. These perforations, however, do not corre- spond with the perforated plates of the Echinoid test, and the tube-feet of the Star-fishes pass through no " poriferous " plates on their way to the exterior. • This may be rendered more intelligible by examining a section of the arm of a Star-fish from which the soft parts have been removed (fig. 60). In such a section the ambulacral ossicles (a, a) are seen in the centre of the lower surface, united along the middle line by their inner extremities. They are so placed as to form a kind of elongated pent-house, and Fig. 60. — Section of the ray of Uraster ritbens. a a Ambulacral ossicles; b Position of the ambulacral vessel ; c c Plates of the external skeleton ; n Nerve-cord. The dotted lines show the tube-feet proceeding from the ambulacral vessel. immediately beneath the line where the ossicles of one side are articulated with those of the other side is placed the ambulacral vessel (b). Superficial to this, again, is a nerve- cord ; so that the whole chain of ambulacral ossicles is placed in the midst of the soft parts of the animal, and is thus clearly an internal skeleton. At their outer extremities the ambulacral ossicles are articulated by the intervention of the " adambulac- ral plates" (fig. 59, b), with plates belonging to the external or integumentary skeleton, to be immediately described. As before said, the shape of the ambulacral ossicles is such that a pore is formed by the apposition of each pair ; and by these apertures each tube-foot communicates with a vesicle placed internal to the chain of ossicles. It will be seen, however, that the tube-feet (indicated by the dotted lines in the figure) do not pass through these apertures, or through any other pores of the skeleton, on their way to the surface. The " poriferous zones " of the Sea-urchins are part of the external skeleton, and are not represented in the Star-fishes. On the ANNULOIDA : ECHINODERMATA. 167 other hand, the integumentary skeleton in the Star-fishes is absent along the ambulacral areas, or along the areas occupied by the ambulacral grooves. The blood-vascular system consists, as in the Echinus, of two circular vessels, one round the intestine, and one round the gullet, with a dilated tube, or heart, intervening between them. There are no distinct respiratory organs, but the sur- faces of the viscera are abundantly supplied with cilia, and doubtless subserve respiration ; the sea-water being freely admitted into the general body-cavity by means of numerous contractile ciliated tubes, which project from the dorsal surface of the body. The nervous system consists of a gangliated cord, surround- ing the mouth, and sending filaments to each of the rays. At the extremity of each ray is a pigment-spot, corresponding to one of the ocelli of an Echinus, and, like it, supposed to be a rudimentary organ of vision. The eyes are often surrounded by circles of movable spines, called "eyelids." The generative organs are in the form of ramified tubes, arranged in pairs in each ray, and emitting their products either into the surrounding medium, by means of efferent ducts which open round the mouth, or into the general body-cavity, by dehiscence, the external medium in this latter case being ultimately reached through the respiratory tubes. In their development, the Asteroidea show the same general phenomena as are characteristic of the class ; but the larvae are not pro- vided with any continuous endoskeleton. In some Asteroids the larval forms have been described under the name of Bipin- naria, and in these, as in the Pluteus of the Echinoids, a large portion of the larva is cast off as useless. In Bipinnaria asteri- gera (Sars) the digestive cavity is a simple sac which sends no prolongations into the rays, and the mouth is inter-radial, instead of being placed in the centre of the ambulacral system. The mouth of the adult is at this stage closed by the soft exter- nal skin of the larva. The general shape of the body varies a good deal in different members of the order. In the common star-fish ( Uraster rubens) the disc is small, and is furnished with long, finger-like rays, usually five in number. In the Cribellce. (fig. 58) the general shape of the body is very much the same. In the Solasters the disc is large and well marked, and the rays are from twelve to fifteen in number, and are narrow and short (about half the length of the diameter of the body). In the Goniasters the body is in the form of a pentagonal disc, flattened on both sides ; the true " disc " and rays being only I 68 MANUAL OF ZOOLOGY. visible on the under surface of the body. In none of the true star-fishes, however, are the arms ever sharply separated from the disc, as in the Ophiuroidta, but they are always an imme- diate continuation of it. The order Asteroidea has been divided by Dr Gray as fol- lows : — ORDER ASTEROIDEA. Section a. Ambulacra -with four rows of feet. Family I. Aster iadce. Dorsal wart simple. Section b. Ambulacra with t^vo rorvs of feet. Family 2. Astropectinidce. Back flattish, netted with numerous tuber- cles, crowned with radiating spines at the tip, called " paxillse." Family 3. Pentacerotida. Body supported by roundish or elongated pieces, covered with a smooth or granular skin, pierced with minute pores between the tubercles. Family 4. Asterinidce. Body discoidal or pyramidal ; sharp-edged ; skeleton formed of flattish, imbricate plates ; dorsal wart single, rarely double. ORDER OPHIUROIDEA. — This order comprises the small but familiar group of the " Brittle-stars " and " Sand-stars," often considered as belonging to the Asteroidea, to which they are nearly allied. The body in the Ophiuroidea (fig. 61) is dis- coidal, and is covered with granules, spines, or scales, but pedicellarise are wanting. From the body — which contains all the viscera — proceed long slender arms, which may be simple or branched, but which do not contain any prolongations from the stomach, nor have their under surface excavated into ambulacral grooves. The arms, in fact, are not simple pro- longations of the body, as in the Asteroidea, but are special appendages, superadded for locomotive and prehensile pur- poses. Each arm is enclosed by four rows of calcareous plates, one on the dorsal surface, one on the ventral surface, and two lateral. The lateral plates generally carry more or less well- developed spines. In the centre of each arm is a chain of quadrate ossicles, forming a central axis, and between this axis and the row of ventral plates is placed the ambulacral vessel. Each ossicle of the central chain is composed of two symmetrical halves, but these are immovably articulated together, and are not movable upon one another, as in the Asteroidea. The mouth is situated in the centre of the inferior surface of the body, is provided with a masticatory apparatus, and is surrounded by tentacles. It opens directly into a sac- like ciliated stomach, which is not continued into an intestine, the mouth serving as an anal aperture. The stomach is destitute of lateral diverticula. The reproductive organs are ANNULOIDA I ECHINODERMATA. 169 situated near the bases of the arms, and open by orifices on the ventral surface of the body or in the interbrachial areas. It is very questionable whether the ambulacral system in the adult Ophiuroidea communicates with the exterior; its place as a locomotive apparatus being taken by the arms. The radial vessels of the ambulacral system are not provided with secondary vesicles or " ampullae," as they are in the Echinoidea and Asteroidea, and the lateral " feet " which they give off have no terminal suckers. The madreporiform tubercle is either Fig. 61.— Ophiuroidea. a Ophiura texturata, the common Sand-star ; b Ophiocoma neglecta, the grey Brittle-star (after Forbes). placed on the inferior surface of the body or is partially con- cealed by one of the plates surrounding the mouth.^ The larva of the Ophiuroidea is pluteiform, and is furnished with a continuous endoskeleton ; and in some, as in Ophiolepis squamata, the echinoderm-body appears within the larva, when the latter has attained but a very imperfect degree of develop- ment. In Euryale the body is in the form of a sub-globose disc I 70 MANUAL OF ZOOLOGY. with five obtuse angles, and the arms are prehensile. In Asterophyton, the Medusa-head star, the arms are divided from the base, first dichotomously, and then into many branches. In Ophiura, the sand-star, the arms serve for reptation (creep- ing), and are undivided, often exceeding the diameter of the disc many times in length. The order Ophiuroidea may be divided into two families, as follows : — Family I. Ophiuridea. Genital fissures two or four in number. Arms five, always simple. Family 2. Asierophydia. Genital fissures ten in number. Arms five, simple or branched. CHAPTER XXL CRINOIDEA, CYSTOIDEA, AND BLASTOIDEA. ORDER CRINOIDEA. — The members of this order are Echino- dermata, in which the body is fixed, during the whole or a portion of the existence of the animal, to the sea-bottom by means of a longer or shorter, jointed, and flexible stalk. The body is dis- tinct, composed of articulated calcareous plates, bursiform, or cup-shaped, and provided with solid arms, which are primarily from five to ten in number, are independent of the visceral cavity, and are grooved on their upper surfaces for the ambulacra. (The position of the body being reversed, the upper surface is ventral ; whilst the dorsal surface is inferior, and gives origin to the pedicle.) The tubular processes, however, which are given off from the radiating ambulacral canals of the Crinoidea, unlike those of the Echinoidea and Asteroidea, are not used in locomotion, but have probably a respiratory function. The mouth is central, and looks upwards, an anal aperture being sometimes present, sometimes absent. The ovaries are situated beneath the skin in the grooves on the ventral surfaces of the arms or pinnules, as are also the ambulacral or respiratory tubes. The arms are furnished with numerous lateral branches or " pinnulae." The embryo is "free ANNULOIDA I ECHINODERMATA. 171 and ciliated, and develops within itself a second larval form, which becomes fixed by a peduncle " (Huxley). If we take such a living Crinoid as Rhizocrinus (fig. 62), we shall be able to arrive at a comprehension of the leading characters of this order. Rhizocrinus is one of those Crinoids which is permanently rooted to some foreign object by the base of a stalk which is composed of a number of calcareous pieces or articulations. In some cases (as in Apiocrinus) the base of the stem or " column " is considerably expanded. In other cases the column is simply "rooted by a whorl of terminal cirri in soft mud" (Wyville Thom- son). The joints of the columns are rnovably articu- lated to one another, the joint-surfaces often having a very elaborate structure, so that the entire stem possesses in the living state a greater or less amount of flexibility. Each joint is perforated centrally by a canal, which is very inappropriately termed the " alimentary canal," but which in truth has nothing to do with the digestive system of the animal. At the summit of the stem is placed the body, which is termed the " calyx," and which is usually more or less cup-shaped, pyriform, bursiform, or discoidal. The calyx exhibits two surfaces, a dorsal and a ventral, of which the dorsal is composed of calcareous plates articulated by their margins, whilst the former is composed of a more or less leathery integument strengthened by the deposition in it of numerous small plates of carbonate of lime. Fig. 62 — Crinoidea : Rhizocrimis Lofoten- sis, a living Crinoid (after Wyville Thomson), four times the natural size. a Stem, b Calyx, c c Arms. 1/2 MANUAL OF ZOOLOGY. The ventral surface exhibits the aperture of the mouth, which . may be sub-central or may be very excentric, and which in many extinct forms is wholly concealed from view. The ventral surface also exhibits the aperture of the anus, which is usually placed excentrically in one of the spaces between the arms, and which is generally, if not universally, carried at the end of a longer or shorter tubular eminence or process, which is called the " proboscis." Owing to the animal being sup- ported on a stalk, it is evident that the "ventral" surface is turned upwards, and the " dorsal " surface downwards. The column springs from the centre of the dorsal surface ; and a stalked Crinoid may, therefore, be compared to a Star- fish turned upside down, with its lower or ambulacral surface superior, and its dorsal surface looking downwards. The calyx contains the digestive canal, and the central portions of the nervous and water-vascular (ambulacral) systems ; but it does not contain the reproductive organs, as is the case with the visceral cavity of the other Echino- derms. From the margins of the calyx, where the dorsal and ventral surfaces join one another, arise a series of longer or shorter flexible processes, which are composed of a great number of small calcareous articulations, and which are termed the "arms" (fig. 63). The arms are usually primarily five in number, but they generally divide almost immediately into two branches, each of which may again subdivide ; the branches thus pro- duced perhaps again dividing, until a crown of delicate graceful filaments is formed. The arms carry smaller lateral branches or "pinnulse" on both sides; and they are not hollow like the arms of the Star- fishes, nor do they contain any prolongations of the stomach. The upper surface of the arms and pinnulae is covered with a soft membrane, and below this are placed the reproductive organs. The generative organs are, therefore, not placed within the calyx, and it follows of necessity that there is no generative opening or " ovarian aperture " in the walls of the calyx. The ventral surfaces of the arms and pinnulae are furnished with grooves, which in the living species are seen to be covered with vibratile cilia. The brachial grooves coalesce till they con- stitute five primary grooves, which are continued from the bases ANNULOIDA : ECHINODERMATA. 173 of the arms to the mouth. The action of the cilia gives rise to a constant current of sea-water, bearing organic matter in solu- and this current proceeds from the brachial grooves to tion Fig. &•),.— Platycrinus tricontadactylns. Carboniferous. The left-hand figure shows the calyx, arms, and upper part of the stem, and the figure next this shows the surface of one of the joints of the column. The right-hand figure shows the proboscis ; and on p. 172 is a magnified figure of part of one arm with its pinnulse. the mouth. In this way the animal obtains its food. As the bases of the arms are separated from the mouth by an inter- vening space, it follows that the brachial grooves are continued over the ventral surface of the calyx, till they reach the oral opening. There is no doubt that it is by the above arrangement that the living Crinoids obtain their food, and the mechanism seems to have been essentially the same in many extinct species. In the Palaeozoic Crinoids, however, there seems to have been a modification of this arrangement. In these forms, the arms have much the structure of those of the recent Crinoids, and are deeply grooved on their ventral surfaces. The ventral surface of the calyx, however, exhibits no central aperture, but only a proboscidiform tube, which arises from one of the inter- radial spaces (i.e., one of the intervals between two of the arms). This tube is probably anal, but good observers regard it as discharging the functions of both mouth and amis. However this may be, the brachial grooves are certainly not 174 MANUAL OF ZOOLOGY. continued over the ventral surface of the calyx, but stop short at the bases of the arms. Hence they are continued as covered passages or tunnels to a central point in the ventral surface of the disc. Here, it is believed, is placed the mouth, concealed by the calcareous plates of the perisome. Of the living stalked Crinoids, the best known is the Penta- crinus Caput-Medusce, of the Caribbean Sea. More recently a stalked Crinoid has been discovered in the Atlantic and North Sea, and has been described under the name of Rhizocrinns Lofotensis (fig. 62). The chief interest of this form is the fact that it belongs to a group of the Crinoidea hitherto believed to be exclusively confined to the Mesozoic Rocks — viz., the Apiocrinidce or " Pear-encrinites." In fact, Rhizocrinus is very closely allied to the Cretaceous genus Bourgutticrinus, and it may even be doubted if it is generically separable from it. The late remarkable researches into the life of the deeper parts of the ocean have brought to light several new Crinoids, which will doubtless, when fully investigated, still further fill up the interval between the living and extinct Crinoidea. Fig. 64. — Crinoidea. Comatula rosacea, the Feather-star; a Free adult ; b Fixed young. (After Forbes.) In the second type of the Crinoidea — represented in our seas by the 'Comatula (fig. 64), or Feather-star— the animal is not ANNULOIDA: ECHINODERMATA. 175 permanently fixed, but is only attached by a stalk when young (fig. 64, /;), in which condition it was described as a distinct species under the name of Pentacrinus Europeans. In its adult condition, however, the Comatula is free, and consists of a pen- tagonal disc, which gives origin to ten slender arms, which are fringed with many marginal pinnulae or " cirri." The mouth and anus are on the ventral surface of the disc, which in this case is again the inferior surface, since the animal creeps about by means of its pinnated arms. The arms, in fact, of Comatula appear to be purely locomotive in function, and to be never employed as prehensile organs. The animal lives upon very minute organisms, drawn into the mouth by the action of the cilia lining the alimentary canal. The dorsal cirri, however, are employed to moor the animal temporarily to solid objects. The mouth is central in position, and the anus, which in some species forms a tubular projection, is situated on one side. Both the arms and the lateral pinnulae are grooved on their ventral surfaces for the ambulacral vessels ; and the pinnules also serve for the support of the reproductive organs. It is extremely doubtful if the ambulacral system, in the adult, has any communication with the exterior. The function, in fact, of the water-vascular system appears to be wholly respiratory, locomotion being entirely effected by means of the arms. The alimentary canal is confined entirely to the disc, and the stomach sends no diverticula along the arms as it does in the Aster oidea. The larva or pseudembryo of Comatula rosacea is a small ovate organism, with four transverse ciliated bands, a key-hole-shaped mouth, and a small vent and rudimentary in- testine, the whole showing no traces of radiation. The young Crinoid is produced within the pseudembryo, and develops a fresh mouth, anus, and stomach for itself; the first being originally oro-anal in function, and being placed in the centre of the ambulacral system. Several species of Comatula are known, and the genus appears to be cosmopolitan in its distribution. The genus Ophicrinus has been formed for species said to possess no more than five undivided arms. ORDER CYSTOIDEA ( Cystidea).— The members of this order are all extinct,* and are entirely confined to the Palaeozoic period. The body (fig. 65) was more or less spherical, and was pro- tected by an external skeleton, composed of numerous poly- * Recently Professor Loven has described a singular Australian Echino- derm as being most closely allied to, if not truly referable to, the order Cystoidea. He has named this curious form Hyponome Sarsi, and believes it to be nearly related to the Cystidean genus Agelacrinites. 176 MANUAL OF ZOOLOGY. gonal calcareous plates, accurately fitted together, and enclosing all the viscera of the animal. The body was in most cases permanently attached to the sea-bottom by means of a jointed calcareous "column" or pedicle, but this was much shorter than in the majority of Crinoids, and was rarely altogether absent. Upon the upper surface of the body were two, sometimes three apertures, the functions of which have been a matter of consider- able controversy. One of these is lateral in position, is defended by a series of small valvular plates, and is believed by some to be the mouth, whilst by others it is asserted to have been an ovarian aperture. The view advocated by Mr Billings is that this aperture was the mouth, or rather that it was oro-anal, as was also the proboscis of the Palseocrinoids. The second opening is central in position, and is believed by Mr Billings to be the " ambulacral orifice," as it is always in the centre of the arms when these are present. The third aperture is only occasionally present, and doubtless discharged the func- ]?ig. 65.— Cystidea. Ecki- tions of an anus. High authorities, how- nospfuerites anrantium, ever regard the lateral valvular aperture a Cystidean from the , . . Baia Limestone (Lower as the anus, and the central aperture as the mouth — a view which is supported by the analogies of recent forms. In some Cystoidea there were no arms, properly speaking, but only small pinnulae. In a second section true arms were present, but these were bent backwards, and were immovably soldered down to the body. In one single species (Comarocystites punctatus, Billings) the development has gone further, the arms being free, and provided with lateral pinnulse, as in the true Crinoids. Many Cystideans are likewise provided with a system of pores, or fissures, penetrating the plates of the body, and usually arranged in definite groups. These groups are termed " pectinated rhombs," but their exact function is doubtful. By Mr Billings, however, they are believed, and apparently with good reason, to have admitted water to the body-cavity, and to have thereby subserved a respiratory function. ORDER BLASTOIDEA. — The members of this order, like those of the preceding, are all extinct, and are entirely confined to the Palaeozoic period. The body was fixed to the bottom of the sea by means of a short jointed pedicle ; it was globular or oval in shape, and composed of solid polygonal calcareous ANNULOIDA : ECHINODERMATA. 177 plates, firmly united together, and arranged in five inter-ambu- lacral and as many ambulacral areas. (These ambulacral areas are termed by M'Coy "pseud-ambulacra," upon the belief that they were not pierced for tube-feet, but that they carried a double row of little jointed tentacles or arms.) The pseud- ambulacra are petaloid in shape, having a deep furrow down the centre, and striated transversely. They converge to the summit of the calyx, and each appears to have carried a row of small jointed " pinnulae " upon each side. The five pseud- ambulacra, radiating from the summit of the calyx, give the upper surface of the body somewhat the appearance of a flower- bud ; hence the- name applied to the order (Gr. blastos, a bud ; eidos, form). Upon the whole, it would seem most probable that the pseud-ambulacra of the Pentremites represent the arms of the Crinoids, anchylosed with r the calyx, and that the longitudinal furrows of the pseud-ambulacra represent the "brachial grooves" of the Crinoids. At the summit of the calyx are six apertures, of which one is the mouth, four are ovarian, and the sixth is probably partly ovarian and partly anal. The Blastoidea are kn6wn more familiarly under the name of Pentremites, and they occur most commonly in the Carboni- ferous Rbclts. CHAPTER XXII. HOLOTHUROIDEA. ORDER HOLOTHUROIDEA. — The members of this order are commonly known by the name of "sea-cucumbers," "tre- pangs," or " beches-de-mer," and are the most highly organised of all the Echinodermata. The body is elongated and vermi- form, or rarely slug-shaped, and is not provided with a distinct test, but is enclosed in a coriaceous skin, sometimes containing scattered calcareous granules or spicules, or even imbricated scales. The ambulacral tube-feet, when present, are usually dis- posed in five rows, which divide the body into an equal number of longitudinal segments or lobes. The mouth is surrounded by a circlet of feathery tentacles, containing prolongations from the central ring of the water-vascular system ; and an anus is situated at the opposite extremity of the body. There is a long, convoluted intestine. A special respiratory, or waterv vascular, system is usually developed, in the form of a systf ~ M i78 MANUAL OF ZOOLOGY. of arborescent tubes, which admit water from the exterior. The larva is vermiform, and has no skeleton. At a certain period of their existence, the young Holothurians are barrel-shaped, with transverse rings of cilia (fig. 66, c). They rotate rapidly on their long axis, and have at this stage been described as a distinct genus under the name of Auricularia. In the Holothnricz proper, locomotion is chiefly effected by means of rows of ambulacral tube-feet, or by alternate ex- tension and contraction of the worm-like body ; but in the Synaptidce there are no ambulacra, but only the central circular canal of the ambulacral system, and the animal moves by means of anchor-shaped spictila, which are scattered in the Fig. 66. — Annuloida. a Holothuria tubulosa, one of the Sea-cucumbers ; b and c Young stages of the same. integument. When developed, the ambulacral system consists of a " circular canal," surrounding the mouth, bearing one or more " Polian vesicles," and giving off branches to the tenta- cula ; and of five " radiating canals " which run down the interspaces between the great longitudinal muscles. These radiating canals give off the tube-feet and their secondary vesicles, just as in the Echinus. In the typical forms there are five rows of tube-feet, but these may be scattered over the whole body, or may be restricted to the ventral surface. There is also a " sand-canal," which arises from the circular canal, and is terminated by a madreporiform tubercle ; but this, instead of opening on the exterior, hangs down freely in the perivisceral cavity. The fluid, therefore, with which the ANNULOIDA : ECHINODERMATA. 179 ambulacral system is filled, is derived from the perivisceral cavity, and not from the exterior, as is usually the case. The mouth in Holothnria is situated anteriorly, and is sur- rounded by a beautiful fringe of branched, retractile tentacles (fig. 67), which arise from a ring of calcareous plates, and into which are sent prolongations from the circum-oral ring of the ambulacral system. The mouth opens into a pharynx, which conducts to a stomach. The intestine is long and convoluted, and opens into a terminal dilatation, termed the " cloaca," which serves both as an anus and as an aperture for the admission of sea-water to the respiratory tubes. From the cloaca arise two branched and arborescent tubes, the termina- tions of which are probably caecal. These run up towards the anterior extremity of the body, and together constitute the so-called " respiratory tree." They are highly contractile, and they perform the function of respiratory organs, sea-water being admitted to them from the cloaca. The nervous system Fig. 67. — Holothuroidea. Thyone papillosa. (After Forbes.) consists of a cord, surrounding the gullet, and giving off five branches, which run alongside of the radiating ambulacral canals. The generative organs are in the form of long, rami- fied, caecal tubes, which open externally by a common aper- ture, situated near the mouth. There is thus no trace of that radial symmetry which is observed in the arrangement of the reproductive organs in the other orders of the Echinodermata. The vascular system consists of two main vessels — one dorsal, and the other ventral — connected with a circum-cesophageal ring. The skin in the Holothuria is highly contractile, and the body is provided with powerful longitudinal and circular muscles, in compensation for the absence of any rigid integu- mentary skeleton. Many of the Sea-cucumbers, in fact, are endowed with such high contractility that they can eject their internal organs entirely, if injured or alarmed. In Synapta there is no ambulacral system of tube-feet, nor respiratory tree. Locomotion is effected by means of little. ISO MANUAL OF ZOOLOGY. anchor-shaped, calcareous spicules, placed upon little papillae of the integument. Respiration is effected in the abdominal cavity; into which the water is admitted by five openings between the tentacles. The Synapta live in the mud, but they form for themselves a kind of case or tube composed of particles of sand. They obtain their food by swallowing sand or mud, from which they extract any nutrient particles which may be contained therein. The order Holothuroidea may be divided into the following two families : — Family I. Holothuridce. Body free, cylindrical, with a coriaceous integument containing scattered calcareous particles. An ambulacral system always, and a respiratory tree usually, present. Family II. Synaptida. Body free, covered with a coriaceous, sometimes soft, integument, containing minute, anchor-shaped spicules, by means of which the animal moves. The ambulacral system rudimentary, not giving rise to tube-feet, and not connected with locomotion. A respiratory tree sometimes present, sometimes absent. CHAPTER XXIII. DISTRIBUTION OF ECHINODERMATA IN SPACE AND TIME. DISTRIBUTION OF ECHINODERMATA IN SPACE. — The Crinoidea are represented by very few forms in recent seas, and these have a very local distribution. The Comatula are the com- monest, and species have been found in most seas. The Pentacrinus Caput-Meduscz is exclusively confined, as far as is known, to the Caribbean Sea. Rhizocrinus Lofotensis has been dredged on the coast of Norway, and in the North Atlantic, and a form believed to be the same has been found in the Gulf of Mexico. In the North Atlantic also, has been found another Apiocrinoid, which has been described under the name of Bathycrinus grarilis. The Asteroidea, Ophiuroidea, and Echinoidea are represented in almost all seas, whether in tropical or temperate zones, some occurring very far north. The Holothuroidea have their metropolis in the Pacific Ocean, occurring abundantly on the coral-reefs of the Polynesian Archipelago. One species is col- lected in large numbers, and is exported to China, where it is regarded as a great delicacy. ANNULOIDA : ECHINODERMATA. l8l DISTRIBUTION OF ECHINODERMATA IN TIME. — Numerous remains of Echinodermata occur in most sedimentary rocks, beginning with the Upper Cambrian Rocks, and extending up to the recent period. The two orders Cystoidea and Blastoidea, which are the most lowly organised of the entire class, are exclusively Palaeozoic ; and the Crinoidea are mostly referable to the same epoch. The more highly organised Asteroidea and Ophiuroidea commenced to be represented in the Silurian period j but the Echinoidea, with few exceptions, have no representative earlier than the Carboniferous Rocks. The following exhibits the geological distribution of the different orders of the Echinodermata in somewhat greater detail : — 1. CRINOIDEA.*- — The Crinoidea attained their maximum in the Palaeozoic period, from which time they have gradually diminished down to the present day. As has already been described, the Palaeozoic Crinoidea differ in some important particulars from those which succeeded them. The order is well represented in the Silurian, Devonian, and Carboniferous Rocks, but especially in the latter ; many Carboniferous lime- stones (crinoidal limestones and entrochal marbles) being almost entirely made up of the columns and separate joints of Crinoids. In the Secondary Rocks Crinoids are still abundant. In the Trias the beautiful " Stone-lily " (Encrinus liliiformis) is peculiar to its middle division (Muschelkalk). In the Juras- sic period occur many species of Apiocrinus (Pearencrinite), Periiacrinus, and Extracrinus. The Chalk also abounds in Crinoids, amongst which is a remarkable unattached form (the Tortoise-encrinite or Marsupites). Of the non-pediculate Crinoidea, which are a decided advance upon the stalked forms, there are few traces ; but remains of Comatula have been discovered in the lithographic slate of Solenhofen (Oolite) and in the Chalk, and the genus Saccosoma is Oolitic. 2. BLASTOIDEA. — The Blastuidea, or Pentremites, are entirely Palaeozoic, and attain their maximum in the Carboniferous Rocks, some beds of which in America are known as the * As regards the calyx of the fossil Crinoidea, the following terms are employed to designate its different parts. The base of the cup, or calyx, is termed the "pelvis," and it is made up of five, four, or sometimes three plates, which are termed the "basals." To the "basals" succeed two or three rows of plates, which are termed respectively the "primary radials," "secondary radials," and "tertiary radials," according to their distance from the basals. The axillary radials, which are the furthest removed, give origin to the arms, and are occasionally called the " scapulae ' (for this reason), whilst the primary and secondary radials are. called the "costse." 1 82 MANUAL OF ZOOLOGY. Pentremite Limestone, from the abundance of these organisms. They are, however, also found in the Silurian and Devonian Rocks. 3. CYSTIDEA. — These, like the preceding, are entirely Palaeo- zoic ; but they are, as far as is yet known, exclusively confined to the Upper Cambrian and Silurian Rocks, being especially characteristic of the horizon of the Bala Limestone. Forms supposed to be Cystideans have been described from the Devo- nian Rocks, but their true nature is doubtful. The oldest known Echinoderms are two extremely simple Cystideans (Trochocystites and Eocystites) which have been discovered in the primordial zone of North America. 4. ASTEROIDEA. — These have a very long range in time, extending from the Lower Silurian period up to the present day. In the Silurian Rocks the genera Pa/ceaster, Stenaster, Pal&odiscus, and Petraster are among the more important, the greater number of forms being Upper Silurian. The next period in which star-fishes abound is the Oolitic (Mesozoic) ; the more important genera being Ur aster, Luidia, Astropecten, Plumaster, and Goniaster, some of which have survived to the present day. Many star-fishes occur, also, in the Cretaceous Rocks, the genera Greasier, Goniodiscus, and Astrogonium being among the more noticeable. In the Tertiary Rocks few star- fishes are known to occur, but Goniaster and Astropecten are represented in the London Clay (Eocene). 5. OPHIUROIDEA. — The " brittle-stars " are represented in the Silurian Rocks by the single genus Protaster. In the Triassic, Oolitic, Cretaceous, and Tertiary Rocks several genera of Ophiuroidea are known ; some being extinct, whilst others (such as Ophioderma, Ophiolepis, and Ophiocoma) still survive at the present day. 6. ECHINOIDEA. — This order is represented in the Palaeozoic Rocks by a single aberrant family ; but it is numerously repre- sented in the Mesozoic and Kainozoic periods. For the Palaeozoic Echinoidea the formation of a separate sub-order has been proposed by Professor M'Coy under the name of Perischoechinidce, since they differ in some funda- mental points from all the other known members of the order. The test is composed of more than twenty rows of calcareous plates, divided into five ambulacral and five inter-ambula- cral areas. The five ambulacra are continuous from pole to pole, and are surmounted dorsally by the ocular plates. The five inter-ambulacra are composed, each, of three, five, or more rows of plates, and are surmounted dorsally by the ovarian plates. The two genera, Archceocidaris and Pal&chinus, ANNULOIDA : SCOLECIDA. 183 comprise all the known forms of the family, the former occur- ring in the Devonian Rocks, the Carboniferous Limestone, and the Permians, whilst the latter occurs also in the Upper Silurians. The Secondary and Tertiary Echinoidea resemble those now living in being composed of not more than twenty rows of calcareous plates. The Oolitic and Cretaceous Rocks are especially rich in forms belonging to this order, many genera being peculiar ; but the number of forms is too great to permit of any selection. 7. HOLOTHUROIDEA. — This order, comprising, as it does, soft-bodied animals, can hardly be said to be known as occurring in the fossil condition. Some calcareous plates and spicules, supposed to belong to a Holothurid, have, however, been described as occurring in the • Secondary Rocks, and the shield of Psolus has been found in Post-tertiary deposits in Bute. CHAPTER XXIV. SCOLECIDA. CLASS II. SCOLECIDA. — This class was proposed by Professor Huxley for the reception of the remaining members of the Annuloida, comprising the Rotifera, the Turbellaria, the Trematoda, the Tceniada, the Nematoidea, the Acanthocephala, and the Gordiacea. Of these the Rotifera stand alone, whilst the Turbellaria, Trematoda, and Tceniada constitute the old division of the Platyelmia (Flat Worms), and the Nematoidea, Acanthocephala, and Gordiacea make up the old Nematelmia (Round Worms or Thread-worms). For some purposes these old divisions are sufficiently convenient to be retained, though they are of little scientific value. The term Entozoa has acquired such a general currency that it is necessarily employed occasionally, but it has been used in such widely different senses by different writers, that it would be almost better to discard it altogether. It certainly cannot be used as synony- mous with Scolecida, many of these not being parasitic at all. It will, therefore, be employed here, in a restricted sense, to designate those orders of the Scolecida which are internal parasites, comprising the Trematoda, Ttzniada, Nematoidea (in part), Acanthocephala, and Gordiacea. The Turbellaria "184 MANUAL OF ZOOLOGY. and Rotifera, with a section of the Nematoidca, lead a free existence, and are not parasitic within other animals. The Scolecida are defined by the possession of a "water- vascular system," consisting of a " remarkable set of vessels which communicate with the exterior by one or more apertures situated upon the surface of the body, and branch out, more or less extensively, into its substance " (Huxley). No proper vascular apparatus is present, and the nervous system (when present) " consists of one or two closely approximated ganglia." The habits and mode of life of the different mem- bers of the Scolecida are so different, that no other character, save the above, can be predicated which would be common to the entire class, and would not be shared by some other allied division. DIVISION I. PLATYELMIA. — This section includes those Scole- cida which possess a more or less flattened body, usually some- what ovate in shape, and not exhibiting anything like distinct segmentation. The division includes two parasitic orders — the Tceniada and the Trematoda ; and one non-parasitic order — viz., the Turbellaria. A sub-order, however, of this last, the Nemertidce, does not conform to the above definition ; but their other characters are such as to forbid their separation. ORDER I. T^ENIADA (Cestoidea). — This order comprises the internal parasites, called Tape-worms (Cestoid worms), and the old order of the "Cystic worms" (Cystica); the latter being now known to be merely immature forms of the Tape- worms. In their mature condition, the Tceniada (see fig. 68) are always found inhabiting the alimentary canal of some warm- blooded vertebrate animal ; and they are distinguished by their great length, and by being composed of a number of flattened joints or articulations. These joints are not, how- ever, an example of true segmentation, nor do they really constitute the Tape-worm ; the true animal being found in the small, rounded, anterior extremity, the so-called " head," or "nurse," whilst the joints are simply hermaphrodite, generative segments, which the " head " throws off by a process of gemmation. The "head" (fig. 68, 3), which constitutes the real Tape-worm, is a minute, rounded body, which is furnished with a circlet of hooks or suckers, or both, whereby the parasite is enabled to maintain its hold upon the mucous membrane of the intestines of its host. No digestive organs of any kind are present, not even a mouth ; and the nutrition of the animal is entirely effected by imbibition. The nervous system consists of two small ANNULOIDA : SCOLECIDA. 185 ganglia, which se^hd filaments backwards ; but there is con- siderable obscurity on this point, and it has been asserted that the nervous system is entirely wanting, or that there is only a single ganglion. The " water-vascular system " con- sists of a series of long vessels which run down each side of the body, communicating with one another at each articula- tion by means of a transverse vessel, and opening in the last joint into a contractile vesicle. It thus appears that all the joints are organically connected together. Whilst the "head5' constitutes the real animal, it, nevertheless, contains no repro- ductive organs, and these are developed in the joints or segments (fig. 68, 4), which are produced from the head poste- riorly by budding. After the first joint, each new segment is intercalated between the head and the segment, or segments, already formed ; so that the joints nearest the head are those latest formed, and those furthest from the head are the most mature. Each segment, when mature, contains both male and female organs of generation, and is, therefore, sexually perfect. To such a single segment the term " proglottis " is applied, from its resemblance in shape to the tip of the tongue. The ovary is a branched tube, which occupies the greater part of the proglottis, and opens, along with the efferent duct of the male organ, at a common papilla, which is perforated by an aperture, termed the " generative pore." The position of this pore varies, being placed in the centre of one of the lateral margins of the proglottis in the common Tape-worm (T(E?iia solium), but being situated upon the flat surface of the segment in the rarer Bothrioccphalus latus. These two elements — namely, the minute head, with its hooklets and suckers, and the aggregate of the joints, or proglottides — together compose what is commonly called a " Tape-worm," such as is found in the alimentary canal of man, and of many animals. The length of this composite organism varies from a few inches to several yards. Singular as is the composition of the mature Tape-worm, still more extraordinary are the phenomena observed in its development, of which the following is a brief account : — " Proglottides," or the sexually mature segments of a Tape- worm, are only produced within the alimentary canal of man, or of some other warm-blooded vertebrate. The development of the ova which are contained in the proglottides, cannot, however, be carried out in this situation ; hence the compara- tive harmlessness of this parasite, and hence the name of " solitary worm." which is sometimes applied to it. For the production of an embryo, it is necessary that the ovum should I 86 MANUAL OF ZOOLOGY. be swallowed by some animal other than the one inhabited by the mature Tape-worm. If this does not take place, the fecun- dated ovum is absolutely unable to develop itself. To secure this, however, the dispersion of the ova is provided for by the expulsion of the ripe proglottides from the bowel, all their contained ova having been previously fertilised. After their discharge from the body, the proglottides decompose, and the ova are liberated (fig. 68, i), when they are found to be covered by a capsule which protects them from all ordinary mechanical, and even chemical, agencies, which might prove injurious to them. In this stage, the embryo is often so far developed within the ovum that its head may be recognised by its possession of three pairs of siliceous hooklets. For further development, it is now necessary that the ovum be swallowed by some warm-blooded vertebrate, and should thus gain access to its alimentary canal. When this takes place, the protective capsule or covering of the microscopically minute ovum is ruptured, either mechanically during mastication, or chemically by the action of the gastric juice ; and the embryo is thus liberated. The liberated embryo is now called a " proscolex," and consists of a minute vesicle, which is pro- vided with three pairs of siliceous spines, fitted for boring through the tissues of its host. Armed with these, the pro- scolex perforates the wall of the stomach, and may either penetrate some contiguous organ, or may gain access to some blood-vessel, and be conveyed by the blood to some part of the body, the liver being the one most likely. Having by one of these methods reached a suitable resting- place, the proscolex now proceeds to surround itself with a cyst, and to develop a vesicle, containing fluid, from its pos- terior extremity, when it is called a "scolex" (fig. 68, 2). In some of the T&niada the scolices are called " hydatids," and it is these, also, which constituted the old order of the " Cystic Worms." When thus encysted within the tissues of an animal, the " scolex " consists simply of a taenioid head, with a circlet of hooklets and four "oscula" or suckers, united by a con- tracted neck to a vesicular body. It contains no reproductive organs, or, indeed, organs of any kind, and cannot attain any further stage of development, unless it be swallowed and be taken for the second time into the alimentary canal of a warm- blooded vertebrate. It may increase, and produce fresh scolices, but this takes place simply by a process of gemma- tion. In some cases, however, a very partial and limited de- velopment does actually take place In the scolex prior to this change of abode, but this is an exceptional occurrence. In ANNULOIDA : SCOLECIDA. I 87 these cases the " neck " of the scolex becomes partially seg- mented, so that it comes to resemble an imperfectly developed Tcenia, and is called a " strobila-embryo." The series of changes, however, whereby the scolex is converted into the " strobila," or adult tape-worm, cannot be carried out unless the scolex gain access to the alimentary canal of a warm- blooded vertebrate. In this case, the scolex attaches itself to the mucous membrane of the intestinal tube by means of its cephalic booklets (when these are present) and suckers. The caudal vesicle now drops off, and the scolex is thus converted Fig. 68. — Morphology of Taeniada. i. Ovum containing the embryo in its leathery case. 2. Cysticercus longicollis. 3. "Head" of adult Teenia solium enlarged, showing the hooklets and cephalic suckers. 4. A single generative joint, or pro- glottis, magnified, showing the dendritic ovary (o), the generative pore (a), and the water-vascular canals (b). 5. A portion of a tape-worm (strobila), snowing the alternate arrangement of the generative pores. into the " head " of the tape-worm. Gemmation then com- mences from its posterior extremity, the first segments being immature. As the first-formed joints, however, are pushed further from the head by the constant intercalation of fresh articulations, they become sexually mature, thus constituting the " proglottides " of the adult tape-worm with which the cycle began. To the entire organism, with its " head " and its mature and immature joints (" proglottides "), the term " stro- bila" is now applied. In the development, therefore, of the tape-worm we have to remember the following stages : — 1 88 MANUAL OF ZOOLOGY. 1. The ovum, set free from a generative joint, or proglottis. 2. The proscolex, or the minute embryo which is liberated from the ovum, when this latter has been swallowed by any warm-blooded vertebrate. 3. The scolex, or the more advanced, but still sexually im- perfect, embryo, into which t\\e proscolex develops, when it has encysted itself within the tissues of its host. (Under this head come the so-called " Cystic Worms.") 4. The strobila, or adult tape-worm, into which the scolex develops itself, when received into the alimentary canal of a warm-blooded vertebrate. The strobila is constituted by the " head," and by a number of immature and mature generative segments or joints, termed the " proglottides." The subject will, perhaps, be more clearly understood by following the development of one of the common tape-worms of man — viz., the Tcznia solium. Commencing with an indivi- dual who is already suffering from the presence of this para- site, one of the most distressing symptoms of the case is found to be the escape of the joints of the animal from the bowel. These joints are the ripe " proglottides," containing the fecun- dated ova. When the ova — which are microscopic in size — are liberated by the decomposition of the proglottis, they may gain access to water, or be blown about by the wind. In many ways, it is easy to understand how one of them may be swallowed by a pig. When this occurs, a " proscolex w is libe- rated from the ovum, and bores its way through the walls of the stomach, to become a "scolex." It now takes up its abode, generally in the muscles, in which position it was originally described as a cystic worm under the name of Cysticercus cellu- losce, constituting what is commonly known as the " measles " of the pig. In this state the scolex will continue for an in- definite period ; but if a portion of " measly " pork be eaten by a man, then the scolex will develop itself into a tape-worm. The scolex fixes itself to the mucous membrane of the intes- tine, throws off its caudal vesicle, and commences to produce " proglottides " instead, becoming, thus, the " strobila " of the Tcenia solium, with which we originally started. The other common tape-worm of man — viz., the Tcenia mediocanellata — is derived in an exactly similar manner from the " m'easles " of the ox. The young, however, of another of the tape-worms of man (viz., the Bothriocephahis latus) is said not to be " cystic." In like manner, the tape-worm of the cat (Tcznia crassicollis] is the mature form of the cystic worm of the mouse (Cysticercus fasciolaris) ; the tape-worm of the fox (Tania pisiformis] is derived from the cystic worms of hares and rabbits (Cysticercus ANNULOIDA I SCOLECIDA. I 89 pisiformis) ; and the tape-worm of the dog (Ttznia serrata) is the developed form of the Ccenurus cerebralis of the sheep, the cystic worm which causes the " staggers " in the latter animal Besides tape-worms, however, man is liable to be affected with " scolices," which are the larvae of the tape-worms of other animals. Thus, what are professionally called " hydatids " in the human subject, are really the scolices of the tape-worm of the dog. The disease is indicated by the presence of the so- called " hydatid-tumour," which consists of a strong membran- ous cyst — the " hydatid " proper — situated in some solid organ, most commonly the liver, and filled with a watery fluid. To the interior of the cyst are attached numerous minute scolices, many others also floating freely in the contained fluid. These " Echinococci," as they are called, do not differ in structure from other scolices, consisting of a head, provided with four suckers and a circlet of recurved hooklets, a vesicular body, and an intermediate contracted portion or neck. The Echi- nococci multiply within the hydatid cyst by gemmation, but they develop no reproductive organs. If, however, an Echi- nococcus should gain access to the alimentary canal of a dog, it then becomes the tape-worm peculiar to that animal — the Tcenia echinococcus. CHAPTER XXV. TREMATODA AND TURBELLARIA. ORDER TREMATODA. — This order includes a group of animals, which, like the preceding, are parasitic, and are commonly known as " suctorial worms," or " Flukes." They inhabit vari- ous situations in different animals — mostly in birds and fishes — and they are usually flattened or roundish in shape. The body is provided with one or more suctorial pores for adhesion. An intestinal canal, with one exception, is always present, but this is simply hollowed out of the substance of the body, and does not lie in a free space, or " perivisceral cavity." The intestinal canal is often much branched, and possesses but a single external opening, which serves alike as an oral and an anal aperture, and is usually placed at the bottom of an an- terior suctorial disc. The sexes are united in the same indi- vidual. A " water-vascular system " is always present, and is sometimes " divided into two portions, one with contractile and non-ciliated walls, the other with non-contractile and ciliated walls " (Huxley). 1 90 MANUAL OF ZOOLOGY. The Trematode Worms are all hermaphrodite, and they pass through a series of changes in their development somewhat analogous to those observed in the Tceniada. This subject, however, is still involved in great obscurity, and it is too com- plicated to admit of description in this place. The larvae are often tailed, but never possess cephalic hooklets, and are never " cystic." From the absence of a perivisceral cavity, the Trematoda were formed by Cuvier into a separate division of Entozoa, under the name of Vers Intestinaux parenchymateux, along with the T&niada and Acanthocephala^ in which no alimentary canal is present. By Owen, for the same reason, they are included in a distinct class, under the name of Sterelmintha. The Distoma hepaticum (fig. 69) may be taken as the type of the Trematoda. It is the common " Liver-fluke " of the sheep, Fig. 69. — Trematoda. i. Distoma hepaticum, the " Liver-fluke," showing the branched alimentary canal. 2. Anterior extremity of Distoma lanceolatum. a An- terior sucker ; b Posterior sucker ; c Generative pore ; d GEsophagus ; e Alimentary canal. (After Owen.) and inhabits the gall-bladder or biliary ducts, giving rise to the disease known as the " rot." In form it is ovate, and flattened on its two sides, and it presents two suctorial discs, the ante- rior of which is perforated by the aperture of the mouth, whilst the posterior is impervious. Between the suckers is the ".genital pore," at which the efferent ducts of the reproductive organs open on the exterior. A branched water-vascular system is present, and opens posteriorly, by a small aperture. The alimentary canal bifurcates shortly behind the mouth, the two divisions thus produced giving off numerous lateral diverticula, and terminating posteriorly in blind extremities. The nervous system consists of a ring round the gullet, giving off filaments both forwards and backwards. The larvae of Distoma are tailed or " cercariform," and are found in the interior of fresh-water snails. ANNULOIDA : SCOLECIDA. JQJ In Distoma lanceolatum (fig. 69, 2) the intestine has not the ramose, complex character of that of D. hepaticum. On the other hand, the alimentary canal, after its bifurcation, is con- tinued on each side of the body to the posterior extremity without giving off any branches on the way, and it terminates simply in blind extremities. Diplostomum, in its essential characters, does not differ much from Distoma ; but it is found living gregariously in the vitreous humour and lens of the eyes of certain fresh-water fishes, such as the common Perch. Other members of the order infest the intestines of birds and Batrachians, the gills of fishes, or the paunch of Ruminants. ORDER TURBELLARIA. — The members of this order are almost all aquatic, and are all non-parasitic ; thus differing entirely from the animals which compose the two preceding orders. Their external surface is always and permanently cili- ated, and they never possess either suctorial discs or a circlet of cephalic hooklets. A " water- vascular system " is always present, opening externally by one or more apertures, or appearing to be entirely closed in the adult (Nemertida). As in the Trematoda, the alimentary canal is imbedded in the parenchyma of the body, and except in the Nemertida, there is no " pervisceral cavity." The intestine is either straight or branched, and a distinct anal aperture may, or may not, be present. The nervous system consists of ganglia situated in the fore-part of the body, united to one another by transverse cords, and sending filaments backwards. The Turbellaria are divided into two sections, termed respectively the Planar ida and the Nemertida. SUB-ORDER I. PLANARIDA. — The Planarians (fig. 70) are mostly ovoid or elliptical in shape, flattened and soft-bodied. They are for the most part aquatic in their habits, occurring in fresh water, or on the sea-shore, but occasionally found in moist earth. The integument is abundantly provided with vibratile cilia, which subserve locomotion, and 'it also contains numerous cells which have been compared to the " cnidae,"or nettle cells, of the Ccelentcrata. There is always a considerable portion of the body situated in front of the mouth, constituting the so-called "prae-oral region," or " prostomium •" and this is often modified into'a singular protrusible and retractile organ, called the " proboscis," the exact use of which is not known. The mouth opens into a muscular pharynx, which is often evert- ible ; and the intestine may be either straight or branched, but always terminates caecally behind, and is never provided with an anal aperture. The " water- vascular system" commu- MANUAL OF ZOOLOGY. nicates with the exterior by two or more contractile apertures. The nervous system consists of two ganglia, situated in front of the mouth, united by a commissure, and giving off filaments in various directions. Pigment-spots, or rudimentary eyes, from two to sixteen in number, are often present, and are always placed in the prae-oral region of the body. The male and female organs are united in the same individual, and the pro- cess of reproduction may be either sexual, by means of true ova, or non-sexual by internal gemmation or transverse fission. Fig. 70. — Morphology of Turbellaria. i. Pint/aria torva (Muller); m Mouth ; ? Nerve-ganglion; ^Eyes: ov Ovary ; t Testis ; gn Genital opening. 2. Planaria lactea, showing the branched (dendrocoel) intestine. 3. Microscopic larva of Alaii- rina. a marine Turbellarian. 4. Pilidium, the " pseudembryo" of a Nemertid ; a The alimentary canal ; b Rudiment of the Nemertid. The Planarians have been divided into two sections, as follows : — Section A. RHABDOCCELA. — Intestine straight, not branched. Body elongated, rounded, or oval. Section B. DENDROCCELA. — Intestine branched or arbores- cent. Body flat and broad. SUB-ORDER II. NEMERTIDA. — The Nemertida, or " Ribbon- worms/' agree in most essential respects with the Planarida. They are distinguished, however, by their elongated, vermi- form shape, by the presence of a distinct anus, by the posses- sion of a distinct perivisceral cavity, by the absence of an external aperture to the water-vascular system of the adult, and by the fact that the sexes, with one or two exceptions, are distinct. The Nemertida further differ from the other Platyel- mia in possessing a pseudohasmal system in addition to, and distinct from, the water-vascular system. Reproduction takes place by the formation of true ova, by internal gemmation, or by transverse fission. In Nemertcs, however, the egg gives rise to a larva, from which the adult is ANNULOIDA I SCOLECIDA. 193 developed in a manner closely analogous to that described as characteristic of the Echinodermata. The larval form of Nejnertes was described by Johannes Miiller, under the name of Pilidium (fig. 70, 4). It is " a small helmet-shaped larva, with a long flagellum attached like a plume to the summit of the helmet, the edges and side-lobes of which are richly ciliated. A simple alimentary canal opens upon the under surface of the body between the lobes. In this condition the larva swims about freely; but, after a while, a mass of formative matter appears on one side of the alimentary canal, and, elongat- ing gradually, takes on a worm-like figure. Eventually it grows round the alimentary canal, and, appropriating it, detaches itself from the Pilidium as a Nemertid — provided with the characteristic proboscis, and the other organs of that group of Turbellaria " (Huxley). CHAPTER XXVI. NEMATELMIA. I. ACANTHOCEPHALA. 2. GORDIACEA. 3. NEMATODA. DIVISION II. NEMATELMIA. — This section may be considered as comprising those Scolecids in which the body has an elon- gated and cylindrical shape. Strictly speaking, it should include the Nemertida, but the division is not founded upon anatomical characters, and is employed here simply for con- venience. Most of the Nematelmia possess an annulated in- tegument ; but there is no true segmentation, and there are rarely any locomotive appendages attached to the body. The majority are unisexual, and parasitic during the whole or a part of their existence. Three orders are comprised in this division — viz., the Acanthocephala, the Gordiacea, and the Nema- toda. ORDER I. ACANTHOCEPHALA. — The Acanthocephala are en- tirely parasitic, vermiform in shape, and devoid of any mouth or alimentary canal. They are provided with a kind of snout or proboscis armed with recurved hooks, which is continued backwards into a bandlike structure (ligamentum suspensorium\ to which the reproductive organs are attached. " Immediately beneath the integument lies a series of reticulated canals con- taining a clear fluid, and it is difficult to see with what these N i94 MANUAL OF ZOOLOGY. can correspond if not with some modification of the water- vascular system " (Huxley). This system of water-vascular canals, however, does not communicate, so far as is known, in any way with the exterior. At the base of the proboscis is placed a single nervous ganglion, which gives off radiating filaments in all directions. Besides the presence of a water- vascular system and the absence of any 'alimentary canal, another point of affinity between the Acanthocephala and the Tceniada has recently been established by the discovery that the adult worm is developed within a hooked embryo, from which it is secon- darily produced. The "Thorn-headed worms" include some of the most formidable parasites with which we are acquainted. The Echinorhynchus (fig. 71) is found in the intestinal canal of many vertebrate animals, especially of birds and fishes. ORDER II. GORDIACEA. — The Gordiacea, or "Hair-worms," are thread-like parasites, which in the earlier stages of their existence inhabit the bodies of various insects, chiefly of beetles and grasshoppers. They possess a mouth and alimentary canal, but they are not provided with a distinct anal aper- ture. In Gordius itself the gullet is . said to open directly into the body-cavity ; but it is more probable that this is an error, and that there is a complete intestine open- ing posteriorly into a cloaca. The sexes are distinct, and they leave the bodies of the insects which they infest in order to breed ; subsequently depositing their ova in long chains, either in water or in some moist situation. At the time of its migra- Fig. 71. — Acanthoce- . . _ , , . „ °. phaia. a Echino- tion the mouth ot the adult Gordius SeTl'' Vh'f headnai appears to be obliterated, and the anterior the same magnified, portion of the alimentary canal becomes atrophied. The embryo of Gordius pos- sesses a snout armed with booklets, and retractile, thus present- ing a close resemblance to the proboscis si Echinorhynchus. It at first leads a free existence in water, but soon penetrates the tissues of the larva of some aquatic insect, by means of the cephalic armature, and becomes encysted. In form the Gordiacea are singularly like hairs, and they often attain a length many times greater than that of the insect which harbours them. ANNULOIDA I SCOLECIDA. 195 ORDER III. NEMATODA (or Nematoidea). — The Nematoda — " Thread-worms" or " Round- worms " — are of an elongated and cylindrical shape ; and are often, though by no means always, parasitic in the interior of other animals. They possess a distinct mouth and an alimentary canal which is freely sus- pended in an abdominal cavity, and terminates posteriorly in a distinct anus. They also possess a system of canals, in some cases contractile, which open externally near the anterior part of the body, on the ventral surface, or by lateral pores, and are probably homologous with the water-vascular system of the Tceniada and Trematoda. The sexes are distinct, and the males are usually less frequently met with, and of smaller size, than the females. The nervous system is mostly well developed, and is in the form of a ganglionic ring, surrounding the oesophagus, and sending filaments backwards. As before said, most of the Ne- matoda are internal parasites, in- habiting the alimentary canal, the pulmonary tubes, or the areolar tissue, in man and in many other vertebrate animals ; but a large section of the order are of a permanently free habit of existence. The most familiar examples of the parasitic Nematoda are the Ascaris lumbricoides, the little Oxyuris, the Trichina, and the Guinea-worm, The Ascaris lumbricoides, or com- mon Round-worm, inhabits the intes- tine of man, often attaining a length of several inches. The ova are pro- bably expelled with the faeces, and the embryo is developed within the ovum prior to its rupture. When fully formed, the embryo is about one-hundredth of an inch in length, and its development is not exactly known, though it appears to be di- rectly transferred from river or pond water to the alimentary canal of some vertebrate animal. The Oxyuris vermmilaris, or "Small Thread-worm," is a grega- rious worm, which inhabits the rectum, especially of children. It is the smallest of the intestinal worms of man, its average Fig. 72. — Nematoda. A, Angn- illula aceti ; B, Dorylaimus stagnates. Magnified. 196 MANUAL OF ZOOLOGY. length not being more than a quarter of an inch, but the females are much bigger than the males. The Trichina spiralis is a singular Nematoid, which gives rise to a painful and very generally fatal train of symptoms, somewhat resembling rheumatic fever, and known as Trichiniasis. The Trichina is known in two different conditions, sexually imma- ture or mature. In its sexually immature condition it inhabits the muscles, usually of the pig, in vast numbers, each worm being coiled up in a little capsule or cyst. In this condition the worm is incapable of further development, and may remain, apparently for an indefinite period, without change, and without seeming to produce any injurious results to the animal affected. If, however, a portion of trichinatous muscle be eaten by a warm-blooded vertebrate, and so introduced into the alimentary canal, an immediate development of young Trichinae is the result. The immature worms escape from their enveloping cysts, grow larger, develop sexual organs, and give birth to numerous progeny, which they produce viviparously. The young Trichina thus produced perforate the walls of the alimentary canal, and, after working their way amongst the muscles, become encysted. If the animal in which these changes go on has sufficient vitality to bear up under the severe symptoms which are produced by the migration of the Trichina, he is now safe ; since they cannot become sexually mature, or develop themselves further, until again transferred to the alimentary canal of some other animal. The Guinea-worm (Dracunculus or Zilaria medinensis) is a Nematode worm, which inhabits, during one stage of its existence, the cellular tissue of the human body, generally attacking the legs, and often attaining a length of several feet. All known specimens of this parasite are impregnated females, containing a large number of young. The worm remains imbedded in the body, in a more or less quiescent condition, for a year or more, at the end of which time it seeks the surface, in order to get rid of its young. No external aperture to the genital organs has hitherto been proved to exist, and it seems possible that the young are produced within the body of the parent by a process of internal gemmation. The young Filaria consists of a vermiform body, terminating in a hair-like tail ; and when set free from the parent, its further development probably takes place in water, when it is believed to be con- verted into one of the " Tank-worms " so common in India. In this condition, it is possible, as some believe, that sexual organs are developed, and that the females are impregnated. The worm is believed to gain access to the body of bathers, ANNULOIDA : SCOLECIDA. 197 when still extremely minute. According to Dr Bastian, how- ever, it appears probable that the Guinea-worm " is a parasite only accidentally, and that it and its parents were originally free Nematoids." The second section of the Nematoda comprises worms, which are not at any time parasitic, but which are permanently free. These "free Nematoids " (fig. 72) constitute the family of the Anguittulidtf) of which about two hundred species have been already described, mostly inhabiting fresh water or the shores of the sea. They resemble the parasitic Nematoids in all the 'essential features of their anatomy, but they differ in often possessing pigment-spots, or rudimentary eyes, in being mostly provided with a terminal sucker, and in bringing forth com- paratively few ova at a time ; the dangers to which the young are exposed being much less than in the parasitic forms. Amongst the more familiar Nematoids are the Vinegar Eel (Anguillula aceti, fig. 72, A) and the Tylenchus (or Vibrio] tritid, which produces a sort of excrescence or gall upon the ear of wheat, causing the disease known to farmers as the " Purples," or " Ear Cockle." The parasitic and free Nematoids are connected together by an Ascaris (A. nigrovenosd), which in succeeding generations is alternately free and parasitic. This Ascaris has long been known as inhabiting the lungs of the frog, but it has been shown by Mecznikow that " the young of this animal become real, free Nematoids ; for, after passing from the intestine of the frog into damp earth or mud, they grow rapidly, and actually develop in the course of a few days, whilst still in this external medium, into sexually mature animals. Young, differ- ing somewhat in external characters from their parents, are soon produced by them, and these attain merely a certain stage of development whilst in the moist earth, arriving at sexual maturity only after they have become parasites, and are ensconced in the lung of the frog" (Bastian). This extraor- dinary history is rendered still more remarkable, if it should be proved that the young of the parasitic forms of this Ascaris are produced by a process of parthenogenesis \ and this seems to be highly probable, since none of the individuals which are found as parasites are males, but are universally females. 198 MANUAL OF ZOOLOGY. CHAPTER XXVII. ROTIFERA. SUB-CLASS ROTIFERA (Rotatoria). — The Rotifera, or " Wheel- animalcules," constitute a very natural group, the exact position of which has been a good deal disputed, and is still doubtful. They are looked upon here as a distinct division of the Scole- cida, following Huxley ; but they are very frequently placed with the Annelida amongst the lower division of the Annulosa (Anarthropoda}. The Rotifera are Annuloida of a minute size, never parasitic, inhabiting water, and usually provided ivith an anterior ciliated disc, capable of inversion and eversion. In the females there is a distinct mouth, intestinal canal, and anus. A nervous system is also present, consisting of ganglia, situated near the anterior extremity of the body, and sending filaments backwards. A water- vascular system is also present. Most of the Rotifera are entirely invisible to the naked eye, and they are all extremely minute, none of them attain- ing a greater length than i-36th of an inch. Nevertheless, as remarked by Mr Gosse, "so elegant are their outlines, so brilliantly translucent their texture, so complex and yet so patent their organisation, so curious their locomotive wheels, so unique their apparatus for mastication, so graceful, so vigorous, so fleet, and so marked with apparent intelligence their move- ments, so various their forms and types of structure," that they form one of the most interesting departments of zoological and microscopical study. They are all aquatic in their habits, and in the great majority of cases are free-swimming animals, some, however, being permanently fixed, as is the case with Stephana- ceros Melicerta (fig. 73, B), and Floscularia. They are usually simple, but are occasionally composite, forming colonies, as in Megalotrocha. As a rule, the male and female Rotifera differ greatly from one another, the males being smaller than the females, destitute of any masticatory or digestive apparatus, and more or less closely resembling the young form of the species. The most characteristic organ in the great majority of the Rotifera is the so-called " wheel-organ," or " trochal disc," which is always situated at the cephalic or distal end of the body, and consists of a retractile disc surrounded by a circlet of cilia, which, when in action, vibrate so rapidly as to produce the illusory impression that the entire disc is rotating. ANNULOIDA : ROTIFERA. 199 The disc, which carries the cilia, is capable of eversion and inversion, and may be circular, reniform, bilobed, four-lobed, or divided into several lobes. It serves the purpose of loco- motion in the free-swimming forms, acting somewhat like the propeller of a screw-steamer, and in all it serves to produce currents in the water, which convey the food to the mouth. In Chatonotus, and one or two other forms, there is no true wheel-organ, capable of protrusion and retraction, but the cilia are variously disposed over the surface of the body. The Chatonoti or Hairy-backed Animalcules have no jaws, and have the ventral surface of the body clothed with cilia. They have usually been placed in the Turbellaria, but there seem to be good reasons for regarding them as an aberrant group of Rota- toria. Fig. 73. Rotifera A, Diagrammatic representation of Hydatina sent a (generalised trom Pritchard). a Depression in the ciliated disc leading to the digestive canal ; b Mouth : c Pharyngealbulb or mastax, with the masticatory apparatus ; d Stomach ; e Cloaca : /"Contractile bladder : g g Respiratory or water-vascular tubes ; h Nerve- ganglion giving filament to ciliated pit (Jt) ; o Ovary. B, Melicerta ringens. (After Gosse.) The proximal extremity of the body in the free forms ter- minates in a caudal process, or " foot," sometimes telescopic, which ends in a suctorial disc, or in a pair of diverging " toes," which act as a pair of forceps (fig. 73, A). The mouth usually opens into a pharynx, or " buccal funnel," which is generally provided with a muscular coat, constituting the " mastax " or " pharyngeal bulb," and which generally con- 2OO MANUAL OF ZOOLOGY. tains a very complicated masticatory apparatus. * The parts of this apparatus are horny, and are believed by Mr Gosse to be homologous with the parts of the mouth in Insects. In the females of almost all known species of Rotifera the intestinal canal is a more or less simple tube, extending through a well-developed perivisceral cavity, and terminat- ing posteriorly in a dilatation, or " cloaca/' which forms the common outlet for the digestive, generative, and water-vascular systems. In both sexes there is a well-developed water-vascular system, usually consisting of the following parts : — In the hinder part of the body, close to the cloaca, and opening into it, is a sac or vesicle, which is termed the " contractile bladder," and exhibits rhythmical contractions and dilatations. From the contractile bladder proceed two tubes — " the respiratory tubes " — which pass forwards along the sides of the body, and terminate anteriorly in a manner not quite ascertained. Attached to the sides of the respiratory tubes, in all the larger Rotifera, is a series of ovate or pyriform vesicles, each of which is fur- nished internally with a single central cilium, which is fixed to the free end of the vesicle. It is asserted, however, that these ciliated vesicles communicate internally with the perivisceral cavity with its contained corpusculated fluid. The exact func- tion of this water- vascular system is not known, but it is most probably respiratory and excretory. Dr Leydig believes that water enters the perivisceral cavity by endosmose, where it mingles with the absorbed products of digestion, to form the so-called "chylaqueous fluid;" and that the effete fluid is excreted by the respiratory tubes, and ultimately discharged into the cloaca by the contractile bladder. Taking this view of the subject, Mr Gosse believes that " the respiratory tubes represent the kidneys, and that the bladder is a true urinary bladder ;" and consequently that "the respiratory and urinary functions are in the closest relation with one another." This observer, further, finds a decided analogy between the above system in the Rotifera and the long and tortuous renal tubes of the Insecta, to which class he believes the Rotifera to be most nearly allied. No central organ of the circulation or heart and no organs of respiration are present, but the perivis- ceral cavity is filled with a corpusculated fluid. The nervous system of the Rotifera constitutes a bilobate * The lower jaws, or "incus," consist of a fixed portion, the "fulcrum," to which are attached two movable blades — the " rami." The upper jaws, or " mallei," consist each of a handle, or " manubrium," to which is hinged a toothed blade, or "uncus." ANNULOIDA I ROTIFERA. 20 1 cerebral mass, " which for its proportionate volume may com- pare with the brain of the highest vertebrates." It is placed anteriorly, and usually on the dorsal aspect of the body, and the eye — in the shape of a red pigment spot or spots — is invariably situated like a wart upon it. Other sense- organs, probably tactile, are often present in the form of two knobs surmounted by tufts or bristles, placed at the back of the head. The ovaries constitute conspicuous organs in the female Rotifera, but in summer the young Rotifers appear to be produced by the females without having access to the males. The muscular system of the Rotifera is well developed, con- sisting of bands which produce the various movement of the body and foot, whilst others act upon the various viscera, and others effect the movements of the jaws. The typical group of the Rotifera is that of the Notommatina {Hy da- tinea of Ehrenberg). In this group (fig. 74) the animals are all perma- nently free, and are never combined into colonies, while the integument is flexible, and the body is never encased in a tube. Stephanoceros and Floscularia, on the other hand, are fixed, and are enclosed in a gelatinous tube which is secreted by the animal Melicerta (fig. 53, B) inhabits a tubular case, which the animal forms for itself by means of a special organ for the purpose ; whilst Polyarthra and Triarthra are protected by a stiff shell, or " lorica." In Triarthra there are twelve en- siform fins, jointed to the body by distinct shelly tubercles, and moved by powerful muscles. These natatory organs are considered by Mr Gosse to be homologous F^4oT,hew£,S±TSler t'- With the articulated limbS OI the larged about 250 diameters. (After Arthropoda. In Asplanchna, whilst the masticatory organs, gullet, and stomach are well developed, there is no intestine, the stomach 2O2 MANUAL OF ZOOLOGY. " hanging like a globe in the centre of the body-cavity," but not communicating with the body-cavity. AFFINITIES OF ROTIFERA. — In their external appearance the Rotifera approximate closely to the Infusoria, but the organisa- tion of the former presents a very striking advance when com- pared with that of the latter. Thus, in the Infusoria there is no differentiated body-cavity, bounded by distinct walls, and the alimentary canal is imperfect, the digestive sac simply opening inferiorly into the diffluent sarcode of the centre of the body. Further, there are no traces of a nervous system, and the contractile vesicles, if looked upon as representing the water-vascular system, are a very rudimentary form of this apparatus. In the Rotifera, on the other hand, the alimentary canal forms a complete tube, having an oral and an anal aper- ture, and not communicating with the surrounding perivisceral cavity; and there is a well-developed nervous system, and a highly complex water-vascular system. A real affinity is found to subsist, however, between the Rotifera and the Planarida ; both possessing external cilia, a nervous system, and a well- developed water- vascular apparatus, the characters of which are not dissimilar in the two groups. In the Planarida, how- ever, the sexes are united in the same individual, and there is no anal aperture ; whereas in the Rotifera the sexes are dis- tinct, and there is a distinct anus. To the true Arthropoda^ as already pointed out, the Rotifera shows some points of affinity, but these are hardly sufficiently numerous or decided to war- rant the removal of the group from the Annuloida to the Annulosa. A N N U L OS A. CHAPTER XXVIII. ANNULOSA. i. GENERAL CHARACTERS OF ANNULOSA. 2. GENERAL CHARACTERS OF ANARTHROPODA. 3. CLASS GEPHYREA. 4. GENERAL CHARACTERS OF THE CLASS ANNELIDA. SUB- KINGDOM ANNULOSA. — The members of this sub-kingdom are distinguished by the possession of a body which is composed of numerous segments, or " somites" arranged along a longitudinal axis. A nervous system is always present, and consists of a double chain of ganglia, running along the ventral surface of the body, and traversed anteriorly by the (Esophagus (fig. 75). The limbs (when present) are turned towards the neural aspect of the body. The sub-kingdom Annulosa may be divided into two primary divisions, according as the body is provided with articulated appendages, or not ; these divisions being termed respectively Fig- 75- — Diagram of an Annulose Animal, a Blood-vascular or haemal system ; b Digestive system ; <: Neural system. the Arthropoda and Anarthropoda. The first of these com- prises Crustaceans, Spiders, Scorpions, Centipedes, and Insects : whilst the latter includes the Spoon-worms, Leeches, Earth- worms, Tube-worms, and Sand -worms. DIVISION I. ANARTHROPODA. — In this division of the Annu- losa the locomotive appendages are never distinctly jointed or arti- culated to the body. In this division are included three classes — viz., the Gephyrea, the Annelida, and the Chcetognatha. CLASS I. GEPHYREA ( = Sipunculoided). — This class includes certain worm -like animals in which the body is sometimes 2O4 MANUAL OF ZOOLOGY. obviously annulated, sometimes not ; but there are no ambulac- ral tubes nor foot-tubercles, though there are sometimes bristles concerned in locomotion. The nervous system consists of an oesophageal nerve-collar, and a cord placed along the ventral surface of the body ; but the ventral nerve-cord is not provided with any ganglionic enlargements. The Sipunculus and its allies (fig. 76) make up this class, and from their affinity to the worm-like Holothurians they have often been placed amongst the EcMnodermata. They are not, however, provided with an ambulacral system, the integument is not capable of secreting calcareous matter, and there are no traces of any radiate arrangement of the nervous system. The Sipunculus is a worm which is found burrowing in the sand of the coasts of most of our European seas, or which inhabits the cast-away shells of dead univalve Molluscs. The different species differ much in length, varying from half an inch to a foot or more. The body is cylindrical, covered by a delicate cuticle, beneath which is a thick, muscular, and highly Fig. 76. — Gephyrea. Syrinx nitdus. (After Forbes.) contractile coat. The anterior portion of the body forms a retractile trunk or proboscis, at the extremity of which is the mouth surrounded by a circlet of simple tentacles. The ali- mentary canal is proportionately of great length, and is much convoluted. Upon reaching the posterior extremity of the body it is reflected forwards, and it terminates in a distinct anus, which is placed anteriorly near the junction of the body with the proboscis. The sexes are distinct in all the Gephyrea, and the young pass through a metamorphosis. In Echiurus, which is found on the coasts of the North Sea, the body is provided posteriorly with zones of horny bristles ; and in the Sternaspis of the Adriatic similar zones of bristles are found anteriorly as well as posteriorly. In the Echiuridce, also, there are branched tubes connected with the termination of the intestine, which are doubtless homologous with the " respiratory tree" of the Holothurians. In Bonellia there is a ANNULOSA : ANNELIDA. 205 proboscis formed by a folded fleshy plate, susceptible of great elongation, and forked at its extremity. The vent is at the opposite end of the body, and the intestine is very long, and folded several times. The British species of the class are grouped by Professor E. Forbes as follows : — Fam. I. Sipunculacea, having a retractile proboscis, at the base of which the anus is placed, and round the extremity of which is seen a circlet of tentacles. Fam. II. Priapulacea, having a retractile proboscis but no tentacula, and having the anus placed at the extremity of a long, filiform, caudal appendage. Fam. III. Thalassemacea, having a proboscis to which a long fleshy appendage is attached. There are no oral tentacula, and the anus is placed at the posterior extremity of the body. CLASS II. ANNELIDA ( = Annulata).—rY\\z Annelida are dis- tinguished from the preceding by the possession of distinct external segmentation ; the nervous system is composed of a ventral, double, gangliated cord, with an cesophageal collar and pras-cesophageal ganglion. This class comprises elongated, worm-like animals, in which the integument is always soft, and the body is more or less distinctly segmented, each segment usually corresponding with a single pair of ganglia in the ventral cord. All the segments are similar to one another except those at the anterior and posterior extremities of the body. Each segment may also be provided with a pair of lateral appendages, but these are never articulated to the body, and are never so modified in the region of the head as to be converted into masticatory organs. Fig. 77. — Diagrammatic transverse section of an Annelida, d Dorsal arc ; # Ventral arc ; « Branchiae ; a Notopodium or dorsal oar ; b Neuropodiumor ventral oar. both carrying setae and a jointed cirrhus. In the higher Annelida each segment (fig. 77) consists of two arches, termed, from their position, respectively the " dorsal arc " and the " ventral arc ; " and each bears two lateral pro- 2O6 MANUAL OF ZOOLOGY. cesses, or "foot-tubercles" (parapodia), one on each side. Each "foot-tubercle" is double, being composed of an upper process, called the "notopodium," or "dorsal oar," and a lower process, termed the " neuropodium," or "ventral oar." The foot-tubercles, likewise, support bristles, or " setse," and a soft cylindrical appendage, which is termed the " cirrhus" (fig. 77). The number of the segments varies much, being as many as 400 in Eunice gigantea ; and, generally, there is not a distinct head which is separable from the succeeding rings of the body. When such a distinct head appears to be present, it is not com- parable with the head of the Arthropoda, but is really a greatly modified prae-oral region, or " prostomium," as is shown by the position of the mouth. The digestive system of the Annelides consists of a mouth, sometimes armed with horny jaws, a gullet, stomach, intestine, and a distinct anus. Except in the ffirudinea, the alimentary canal is suspended in a capacious perivisceral space, divided into compartments by more or less complete partitions. The alimentary canal is, with one exception, not convoluted, and extends straight from the mouth to the anus ; but lateral diver- ticula are often present. As regards the vascular system, " no Annelide ever possesses a heart comparable to the heart of a Crustacean or Insect; but a system of vessels, with more or less extensively contrac- tile walls, containing a clear fluid, usually red or green in colour, and in some cases only corpusculated, is very generally developed, and sends prolongations into the respiratory organs, when such exist" (Huxley). This system has been termed the " pseudo-haemal system," and its vessels are considered by Professor Huxley as being " extreme modifications of organs homologous with the water- vessels of the Scolecida : " since the perivisceral cavity, with its contained corpusculated fluid (chy- laqueous fluid), is believed by M. de Quatrefages to be the true homologue of the vascular system of Crustacea and in- sects. The pseudo-haemal system, therefore, of the Annelides is to be regarded as essentially respiratory in function. The pseudo-haemal vessels are sometimes wanting, and in these cases respiration appears to be effected by the cilia lining the perivisceral cavity. Respiration is effected by the general surface of the body, by saccular involutions of the integument, or by distinct external gills, or branchiae. The nervous system consists of a double, ventral, gangliated cord, which is traversed anteriorly by the oesophagus ; the " prae-cesophageal," or " cerebral," ganglia being connected by ANNULOSA : ANNELIDA. m lateral cords or commissures with the " post-oesophageal " ganglia. Pigment-spots, or " ocelli," are present in many, generally upon the proboscis, sometimes in each segment, or on the branchiae, or on the tail ; and the head often supports two or more feelers which differ from the " antennae " of Insects and Crustacea in not being jointed. The sexes in the Annelida are sometimes distinct, and some- times united in the same individual. The embryos are almost universally ciliated, and even in the adult cilia are almost always, if not always, present, in both of which respects this class differs from the Arthropoda. The Annelida may be divided into two sections, characterised by the presence or absence of external respiratory organs or branchiae. The Abranchiate section comprises the Leeches and the Earth-worms ; whilst the Branchiate division includes the Tube-worms (Tubicola) and the Sand-worms (Errantia). The Annelida are also often divided into two sections, called Ch&tophora and Discophora, according as locomotion is effected by chitinous setae (Earth-worms, Tube-worms, and Sand-worms) or by suctorial discs (Leeches). CHAPTER XXIX. ORDERS OF ANNELIDA. ORDER I. HIRUDINEA (Discophora or Suctoria}. — This order includes the Leeches, and is characterised by the possession of a locomotive and adhesive sucker, posteriorly or at both extremities, and by the absence of bristles and foot-tubercles. The sexes are united in the same individual, and the young do not pass through any metamorphosis. The Leeches are aquatic, vermiform animals, mostly in- habiting fresh water, though a few species are marine. Loco- motion is effected either by swimming by means of a serpentine bending of the body, or by means of one or two suctorial discs. In those forms in which there is only a single sucker (posterior), the head or anterior extremity of the body can be converted into a suctorial disc. The body is ringed, as many as one hundred annulations being present in the common Leech ; but it is not divided into distinct sornites, and, with one exception, there are no lateral appendages of any kind. The mouth is sometimes edentulous, but it is usually armed with teeth. The 208 MANUAL OF ZOOLOGY. alimentary canal is short, and is united to the skin by means of a spongy vascular tissue. The pseudo-haemal system con- sists principally of four great longitudinal trunks, connected by lateral vessels, and devoid of any special dilatations.* Re- spiration appears to be partly effected by means of a number of sacs, which are formed simply by an involution of the integu- ment, and which open externally by minute apertures, termed "stigmata." In the common Leech there are about seventeen of these vesicles on each side of the body, their openings being placed on the abdominal surface. These saccular involutions of the integument certainly secrete the mucus with which the body of the animal is lubricated ; and it is believed by some that their function is solely excretory, and that they answer to the kidneys of higher animals. In this case respiration must be effected by the general surface of the body ; but there is no reason why the same organs should not perform both func- tions, since a close relationship subsists between the two. These sacculi are generally known as the " segmental organs," and in most of the Hirudinea they are closed inter- nally, and only open externally by the " stigmata." In some of the Hirudinea, however, the "segmental organs" agree with those of the great majority of the Annelides in not only opening exter- nally, but in also communicating inter- nally with the perivisceral cavity. The segmental organs of the Leeches differ further from those of the other Annelida in not being in any way connected with the process of reproduction. The nervous system consists of a prae-cesophageal ganglion, which gives branches to a number of simple eyes, or ocelli, which are placed on the head, Fig. 78.-Hirudinea. a The and which is united by lateral oesopha- Medidnai Leech (San? uisn- g^al cords to the ventral gangliated ga.officina.lis), natural size; ° £ Anterior extremity of the same magnified, showing the sucker and triradiate jaws ; ....... , T , c One i of the jaws detached, individual, but the Leeches are never- semicircular theless incapable of self-fertilisation. The sexes are united in the same ts0^°thedsmar|in. * If Branchiobdella be regarded as a true Leech, then the absence of gills is not universal in this order, for it possesses branchiae. It has two suckers, and is parasitic on the Torpedo and on the gills of the Cray-fish. ANNULOSA : ANNELIDA. 2OQ Reproduction, also, is always effected by means of the sexes, and never by fission or gemmation. The common Horse-leech is only provided with a few blunt teeth ; but the Medicinal Leech (Sanguisuga medicinalis, fig. 78) has its mouth furnished with three crescentic jaws, the con- vex surfaces of which are serrated with minute teeth. This species is chiefly imported from Hungary, Bohemia, and Russia. In Sanguisuga officinalis, also used in medicine, the abdomen has numerous black spots. In both species the oral and caudal extremities are narrowed before dilating into the suckers, and the body has from ninety to one hundred rings. The marine Pontobddla have the body tuberculated, and attach themselves to the bodies of fishes, especially skates. The anterior sucker is separated in these from the body by a distinct constriction or neck. In the little fresh-water Clepsines the anterior sucker is wanting, and there is a pro- boscidiform mouth. They are found attached to the stems of water-plants. ORDER II. OLIGOCH^ETA (Terricola), — The members of this order, comprising the Earth-worms (Lumbruidas) and the Water-worms (Na'ididce), are distinguished by the fact that their locomotive appendages are in the form of chitinous setae or bristles, attached in rows to the sides and ventral surface of the body. They are all hermaphrodite. The Oligochceta are divided into the two groups of the Terricolce or Earth-worms, and the Limicolce. or Mud-worms and Water-worms (Sanurida. and Ndididce). In the common Earth-worm (Lumbricus) the body is cylin- drical, attenuated at both extremities, and carrying in the adult a thickened zone, which occupies from six to nine rings in the anterior part of the body, is connected with reproduc- tion, and is termed the " clitellum," or "saddle." Locomo- tion is effected by eight rows of short bristles or setae, four of which are placed laterally and four on the ventral surface of the body; these representing the foot-tubercles of the higher Annelides. The mouth is edentulous, and opens into a short oesophagus, which leads to a muscular crop, or " pro-ventricu- lus," succeeded by a second muscular dilatation, or gizzard. The intestine is continued straight to the anus, and is con- stricted in its course by numerous transverse septa, springing from the walls of the perivisceral cavity. The perivisceral cavity (as in all the Oligochatd) is lined by a cellular mem- brane, which is continuous with a yellow cellular layer cover- ing the intestine and large vessels, and which casts off its cells into the perivisceral fluid. The pseudo-haemal system is well O 2IO MANUAL OF ZOOLOGY. developed ; and there exists, in even greater numbers, the same series of lateral sacculi or " segmental organs " which we have seen in the Leeches, and which have either a respiratory or a renal function. In all the Oligochczta the segmental organs communicate internally with the perivisceral cavity as well as externally with the outer medium. A portion of the segmental organs is ciliated, and in all cases the segmental organs of certain of the segments have the special function of acting as efferent ducts for the generative organs. Of the little Naididcz, the most familiar is the Tubifex rivu- lorum, which is of common occurrence in the mud of ponds and streams. It is from half an inch to one inch and a half in length, and of a bright-red colour. The pseudo-haemal system is provided with two contractile cavities or hearts ; and there is present the same system of lateral tubes, opening externally by pores, as occurs in the Earth-worms. The Ndididce are chiefly noticeable on account of the sin- gular process of non-sexual reproduction which they present before they attain sexual maturity. In this process the Ndis throws out a bud between two rings, at a point generally near the middle of the body. Not only is this bud developed into a fresh individual, but the two portions of the parent marked out by the budding point likewise become developed into separate individuals. The portion of the parent in front of the bud develops a tail, whilst the portion behind the bud develops a head. Prior to the detachment of the bud, other secondary buds are formed from the same segment, each in front of the one already produced ; and in this way, before separation takes place, a chain of organically connected individuals is produced, all of which are nourished by the anterior portion of the primi- tive worm. Besides their non-sexual reproduction, the Naididcz possess generative organs when adult, and exhibit true sexual reproduction. With the development of the generative organs, a new segment is added to the body, and certain other modifi- cations take place ; so that the process of attaining sexual maturity is actually attended with a species of metamorphosis. ORDER III. TUBICOLA (Cephalobranchiata). — The Annelides which are included in this order inhabit tubes, which may be calcareous, and secreted by the animal itself, or may be com- posed of grains of sand or pieces of broken shell, cemented together by a glutinous secretion from the body. The body- rings are mostly provided with fasciculi of bristles set upon lateral foot-tubercles or parapodia, by means of which the animal is enabled to draw itself in and out of its tube. The alimentary canal is loosely attached to the integument. The ANNULOSA I ANNELIDA. 21 Tubicola are unisexual, and the young pass through a meta- morphosis. The protecting tube of the Tubicolous Annelides may be composed of carbonate of lime (Serpuld), of grains of sand (Sabellaria), or of sand, pieces of shell, and other adventitious particles cemented together by a glutinous secretion from the body (Terebelld) • or it may be simply membranaceous or lea- thery (Sabella). Sometimes the tube is free and non-adherent (Pectinarid) ; more commonly it is attached to some submarine object by its apex or by one side (Serpula and Spirorbis). Sometimes the tube is single (Spirorbis) ; sometimes the animal is social, and the tubes are clustered together in larger or smaller masses (Sabellaria). When the tube is calcareous, it presents certain resemblances to the shells of some of the Molluscs, such as Vermetus and Dentalium. In the living state it is easy to make a distinction between these, for the Tubicolar Annelides are in no way organically attached to their tubes, whereas the Molluscs are always attached to their shell by proper muscles. The pseudo-haemal system has its usual arrangement, and the contained fluid is usually red in colour, but is olive-green in Sabella. The respiratory or- gans are in the form of filament- ous branchiae, attached to, or near, the head, generally in two lateral tufts, arranged in a funnel- shaped or spiral form. Each fila- ment is fringed with vibrating cilia, and the tufts are richly sup- plied with fluid from the pseudo- haemal system. There is no spe- cial apparatus required to drive the blood back to the heart, but this is effected by the con- tractile power of the gills them- selves. From the position of the branchiae upon, or near, the head, the Tubicola are often known as the " cephalobranchiate " Annelides (fig. 79). Reproduction in the Tubicola is generally sexual, the sexes being in different individuals ; but spontaneous fission has also been observed. As regards their development, the process has been thus described, as it occurs in Terebella : — The embryo, which is at first a free-swimming, ciliated body, "lengthens, and the cilia, which were at first generally diffused, become Fig. 79. — Tubicola. a Serpula con tortuplicata, showing the branchiae and operculum ; b Spirorbis com- •munis. 212 MANUAL OF ZOOLOGY. confined to a cincture behind the head, a transverse ventral band near the tail, and a small circle round that part. The head is distinguished by two red eye-specks ; new segments are successively added, one behind the other, and always in front of the anal one ; but as yet the embryo is apodal. The tubercles and setae are next developed in the same order, and a free-swimming or ' errant ' Annelida ensues. Finally, the cilia of the buccal rings are lost, the young Terebella reposes, and envelops itself in a mucous tube" (Owen). As the young tubicolar Annelide is thus free, or " errant," before it becomes finally enveloped in a tube, it is generally believed that the Tubicola should be looked upon as really higher than the next order of Annelida — viz., the Errantia. It appears, however, more probable that the stationary condition of the adult Tubicola should rather be regarded as an instance of " retrograde development." The most familiar of the Tubicola is the Serptila (fig. 79, a), the contorted and winding calcareous tubes of which must be known to almost every one as occurring on shells or stones on the sea-shore. One of the cephalic cirrhi in Serpula is much developed, and carries at its extremity a conical plug, or oper- culum, whereby the mouth of the tube is closed, when the animal is retracted within it. The operculum of Serpula has a more than ordinary interest in the fact that it is the only in- stance in the Annelida in which calcareous matter is deposited within the integument. In Spirorbis (fig. 79, b] the shelly tube is coiled into a flat spiral, one side of which is fixed to some solid object. It is of extremely common occurrence on the fronds of sea-weed and on other submarine objects. Equally familiar with Serpula is Terebella, the animal of which is included in a tube composed of sand and fragments of shell, cemented together by a glutinous secretion. In the Sabellidce the tube is composed of granules of sand or mud. In Pectinaria the tube is free, membranous, or papyraceous, and in the form of a reversed cone of considerable length. ORDER IV. ERRANTIA (Nereidea). — This order comprises free Annelides,* which possess setigerous foot-tubercles. The respiratory organs are generally in the form of tufts of external branchiae, arranged along the back or the sides of the body. They are unisexual, and the young pass through a metamor- phosis. This order includes most of the animals which are * Fritz Miiller describes an errant Annelide belonging to the Amphinomida as living parasitically within the shell of the common Barnacle (Lepas), showing that; the members of this group may sometimes lose their free habit. ANNULOSA I ANNELIDA. 2 1 3 commonly known as Sand-worms and Sea-worms, together with the familiar Sea-mice. The integument is soft, and the body is very distinctly divided into a great number of rings or segments, each of which, in the typical forms, possesses the following structure. The segment consists of two arches, a lower or " ventral arc," and an upper or " dorsal arc," with a " foot-tubercle " on each side. Each foot-tubercle consists of an upper process, or " notopodium," and a lower process, or " neuropodium," each of which carries a tuft of bristles, or " setae," and a species of tentacle termed the "cirrhus" (fig. 77). The anterior extremity of the body is usually so modified as to be distinctly recognisable as the head, and is provided with eyes, and with two or more feelers, which are not jointed, and are, therefore, not comparable with the antennae of Crus- tacea and Insects. The mouth is placed on the inferior sur- face of the head, and is often furnished with one or more pairs of horny jaws, working laterally. The pharynx is muscular, and forms a sort of proboscis, being provided with special muscles, by means of which it can be everted and again re- tracted. In most there is no distinction between stomach and intestine, and the epithelium of the alimentary canal, like that of the preceding orders, is ciliated. The perivisceral cavity is filled with a colourless corpusculated fluid — the " chylaqueous fluid " — which " performs one of the functions of an internal skeleton, acting as the fulcrum or base of resistance to the cutaneous muscles, the power of voluntary motion being lost when the fluid is let out" (Owen). The pseudo-haemal system is well developed, and consists essentially of a long dorsal vessel, and a similar ventral one, connected by transverse branches, and furnished at the bases of the branchiae with pulsating dilatations. The contained fluid is mostly red, but is yellow in Aphrodite and Polynoe. Respiration is carried on by means of a series of external branchiae or gills, arranged in tufts upon the sides of the body on its dorsal aspect, along the middle of the body only, or along its entire length. From the position of the branchiae, the members of this order are often spoken of as the " Dorsi- branchiate" (or more properly " Notobranchiate ") Annelides. The "segmental organs," with few exceptions, communicate with the perivisceral cavity internally, and in certain segments they are always specialised to act as efferent ducts for the reproductive organs. In the Sea-mouse (Aphrodite, fig. 81, B), the back is covered with a double row of membranous imbricated plates, which 214 MANUAL OF ZOOLOGY. are called " elytra," or " squamae," and respiration is effected by the periodical elevation and depression of these plates, whereby water is alternately admitted into, and expelled from a space beneath them. This space is separated by a membrane from the perivisceral cavity below, and contains the gills in the form of small fleshy crests. The pharynx is thick and muscular, and can be everted like a proboscis, and the intestine has a number of lateral branched cseca. The nervous system in the Errantia has its typical form, consisting of a double gangliated ventral cord, two ganglia of which are appropriated to each segment. The prae cesopha- geal, or cerebral, ganglia are of large size, and send filaments to the ocelli and feelers. The sexes in the Errantia are in different individuals, and reproduction is usually sexual, though in some cases gemma- tion is known to occur. The process of gemmation is carried on by a single segment, and so long as it continues, the bud- ding individual remains sexually immature, though the young Fig. 80. — " Errant" Annelide. Nereis, showing the "head" with its appendages, and the setigerous parapodia. thus produced develop generative organs. Thus, there is in these cases a kind of alternation of generations, or rather an alternation of generation and gemmation ; the oviparous indi- viduals producing eggs from which the gemmiparous indi- viduals are born ; these, in their turn, but by a non-sexual process, producing the oviparous individuals. The embryo usually appears, on its liberation from the ovum, as a free-swimming, ciliated body, possessing a mouth, intestine, and anus. The cilia are primarily diffused, but become aggre- gated so as to form a single median belt, or two bands, one about each extremity. The head, with its feelers and eye- specks, appears at one extremity, whilst the segments of the body begin to be formed at the other. Each segment is deve- loped in four parts, the two principal ones forming half-rings, united by shorter side-pieces, from which the setigerous foot- ANNULOSA I ANNELIDA. 215 tubercles are developed. The ciliated band or bands finally disappears, and new rings are rapidly added by intercalation between the head and the segments already formed. Amongst the best known of the Errantia is the common Lob-worm (Arenicola piscatorum, fig. 81, C), which is used by fishermen for bait. The Lob-worm lives in deep canals which it hollows out in the sand of the sea-shore, literally eating its way as it proceeds, and passing the sand through the alimen- tary canal, so as to extract from it any nutriment which it may contain. It possesses a large head, without eyes or jaws, and with a short proboscis. There are thirteen pairs of branchiae placed on each side in the middle of the body. Fig. 81.— Errant Annelidas. A, Hairy-bait (Nephthys) ; B, Sea-mouse (Aphrodite]: C, Lob-worm (A renicola). (After Gosse.) In the Nereidce, or " Sea-centipedes," the body is greatly elongated, and consists of a great number of similar segments, with rudimentary branchiae. The head is distinct, and carries eyes and feelers, whilst the mouth is furnished with a large proboscis, and often with two horny jaws (fig. 80). In the Eunicea the branchiae are usually well developed and of large size, and the mouth is armed with seven, eight, or nine horny jaws. Eunice gigantea attains sometimes a length of over four feet, and may consist of more than four hundred rings. DISTRIBUTION OF ANNELIDA IN TIME. — Of the Annelida the only orders which are known to have left any traces of their existence in past time are the Tubicola and the Errantia ; of which the former are known by their investing tubes, whilst 2l6 MANUAL OF ZOOLOGY. the latter are only recognised by the tracks which they left upon ancient sea-bottoms, or by their burrows in sand or mud. These tracks and burrows of Annelides are found commonly in rocks of almost all ages from the Cambrian period upwards. Those tracks which have been caused simply by the passage of the worm over the surface of the mud are termed by Mr Salter Helminthites, whilst the burrows are called Scolites (or Scolithus). Tubicolar Annelides are known to occur from the Silurian Rocks upwards. The well-known Silurian fossil, Tentaculites, has been often referred to the Tubifola^\3n\. is almost certainly Pteropodous. ComulitfS, Serpulites, Ortonia, Trachy derma, Spirorbis, and Conchicolites are, however, genuine Silurian Tubicola. The Microconchus carbonarius is a little spiral Tubicolar Annelide, nearly allied to the Spirorbis (fig. 79, /;) of our seas, which is not uncommonly found in strata belong- ing to the Carboniferous period ; and the genus Spirorbis itself is represented even in the Silurian period. TABULAR VIEW OF THE ANNELIDA. Division A. ABRANCHIATA. — No external organs of respiration. Order I. Hirudinea. — No bristles or foot- tubercles : locomotion by means of a suctorial disc at one or both extremities. 111. Gen. Hirudo, Clepsine, Pontobdella. Order II. Oligochata. — Locomotion by means of rows of stiff bristles, or "setae ;" no foot-tubercles. 111. Gen. Lumbricus, JVais, Tubifex. Division B. BRANCHIATA. — Respiratory organs in the form of external branchiae. Order III. Tubicola. — Body protected by a calcareous or arenaceous tube. Branchiae attached to, or near, the head (Cephalobranchiata}. 111. Gen. Serpula, Terebella, Sabella. Order IV. Errantia. — Animal free, with setigerous foot-tubercles. Branchiae in tufts, attached on the sides of the body, in the middle of dorsal region only, or along its entire length (Dorsibranchiatd). 111. Gen. Arenicola (Lob-worm), Nereis (Sea-centipede), Aphrodite (Sea-mouse). CLASS III. CH^TOGNATHA (Huxley). — The remaining class of the Anarthropoda has been recently constituted by Professor Huxley tinder the name of Chcetognatha, for the reception of the single genus Sagitta, which had been formerly placed amongst the Annelida. By Professor Rolleston, however, the Chcetognatha are placed in the division Nematelmia of the Annuloida, in the immediate neighbourhood of the Nema- toidea. The Sagitta are singular marine animals, transparent, and elongated in form, and usually not more than an inch in ANNULOSA I CH^TOGNATHA. 2 I J length. The following are the characters ascribed to the class by Huxley : — " The head is provided with several, usually six, sets of strong, bilaterally symmetrical oral setae, two of which, long and claw-like, lie at the sides of the mouth ; while the other four sets are short, and lie on that part of the snout which is produced in front of the oral aperture. The posterior part of the body is fringed on each side by a delicate striated fin-like membrane, which seems to be an expansion of the cuticle. In some species the body is beset with fine setae. The intestine is a simple, straight tube, extending from the rnouth to the anus ; the latter opens on the ventral surface, just in front of the hinder extremity. A single oval ganglion lies in the abdomen, and sends, forwards and backwards, two pairs of lateral cords. The lateral cords unite in front of and above the mouth into a hexagonal ganglion. This gives off two branches which dilate at their extremities into the spheroidal ganglia, on which the darkly pigmented imperfect eyes rest. The ovaries, saccular organs, lie on each side of the intestine and open on either side of the vent ; receptacula seminis are present. Behind the anus, the cavity of the tapering caudal part of the body is partitioned into two compartments ; on the lateral parietes of these, cellular masses are developed which become detached, and floating freely in the compartment, develop into "sperma- tozoa. These escape by spout-like lateral ducts, the dilated bases of which perform the part of vesiculce. seminales. The embryos are not ciliated, and undergo no metamorphosis " (See Introduction to the Classification of Animals, p. 52). CHAPTER XXX. ARTHROPODA. DIVISION II. ARTHROPODA, OR ARTICULATA. — The remaining members of the sub-kingdom Annulosa are distinguished by the possession of jointed appendages, articulated to the body ; and they form the second primary division — often called by the name Articulata. As this name, however, has been employed in a wider sense than is understood by it here, it is, perhaps, best to adopt the more modern term Arthropoda. The members of this division, comprising the Crustacea, (Lobsters, Crabs, &c.), the Arachnida (Spiders and Scorpions), 2 I 8 MANUAL OF ZOOLOGY. the Myriapoda (Centipedes), and the Insecta, are distinguished as follows : — The body (fig. 75) is composed of a series of segments, arranged along a longitudinal axis ; each segment, or " somite," occasionally, and some always, being provided with articulated appendages. Both the segmented body and the articulated limbs are more or less completely protected by a chitinous exoskeleton, formed by a hardening of the cuticle. The appendages are hollow, and the muscles are prolonged into their interior. The nervous system in all, at any rate in the embryonic condition, consists of a double chain of ganglia, placed along the ventral surface of the body, united by longi- tudinal commissures, and traversed k anteriorly by the oeso- phagus. The hsemal system, when differentiated, is placed dorsally, and consists of a contractile cavity, or heart, provided with valvular apertures, and communicating with a perivis- ceral cavity, containing corpusculated blood. Respiration is effected by the general surface of the body, by gills, by pulmonary sacs, or by tubular involutions of the integument, termed " tracheae." In no member of the division are vibra- tile cilia known to be developed. According to Professor Huxley, an additional constant character of the Ai'thropoda is to be found in the structure of the head, which is typically composed of six segments, and never contains less than four. The Arthropoda are divided into four great classes — viz., the Crustacea, the Arachnida, the Myriapoda, and the Insecta; which are roughly distinguished as follows : — 1. CRUSTACEA. — Respiration by means of gills, or by the general surface of the body. Two pairs of antenna. Locomotive appendages, more than eight in number, borne by the segments of the thorax, and usually of the abdomen also. 2. ARACHNIDA. — Respiration by pulmonary vesicles, by trachea, or by the general surface of the body. Head and thorax united into a cephalothorax. Antenna (as such) absent. Legs eight. Abdomen without articulated appendages. 3. MYRIAPODA. — Respiration by trachea ; head distinct ; re- mainder of the body composed of nearly similar somites. One pair of antenna. Legs numerous. 4. INSECTA. — Respiration by trachea. Head, thorax, and abdomen distinct. One pair of antenna. Three pairs of legs borne on the thorax. Abdomen destitute of limbs. Generally two pairs of wings on the thorax. ANNULOSA : CRUSTACEA. CHAPTER XXXI. CRUSTACEA. CLASS I. CRUSTACEA. — The members of this class are com- monly known as Crabs, Lobsters, Shrimps, King-crabs, Bar- nacles, Acorn-shells, &c. They are nearly allied to the suc- ceeding order of the Arachnida (Spiders and Scorpions) ; but may usually be distinguished by the possession of articulated appendages upon the abdominal segments, by the possession of two pairs of antennae, and by the presence of branchiae. The body is composed of a number of definite rings or segments (" somites "), each of which may be provided with a pair of jointed appendages. With rare exceptions, some of the somites of the adult always carry appendages \ and one or more pairs are almost invariably adapted for mastication. The nervous system of the embryo has the typical Annulose form of a chain of ventral ganglia, between the first two pairs of which the gullet passes. No water-vascular system is present ; but there is generally a true blood-vascular system. The heart, when present, is placed on the opposite side of the alimentary canal to the ventral nerve-chain, and communicates by valvular apertures with a surrounding venous sinus— the so-called "pericardium." When differentiated breathing-organs are present, these are always in the form of branchiae or gills, adapted for respiring air dissolved in water. In addition to these characters, the body in the Crustacea is always protected by a chitinous or sub-calcareous exoskele- ton, or " crust," and the number of pairs of articulated limbs is generally from five to seven. They all pass through a series of metamorphoses before attaining their adult condition, and ever}7 part that is found in an embryonic form, even though only temporarily developed, may be represented in a permanent condition in some member of a lower order. , The classification of the Crustacea is extremely complicated, and hardly any two writers adhere to the same arrangement. The tabular view which follows embodies the arrangement which appears to be most generally adopted, and the diagnostic characters of each order will be briefly given, a more detailed description being reserved for the more important divisions of the class. Before proceeding further, however, it will be as well to give a description of the morphology of a typical Crustacean, selecting the lobster as being as good an example as any. 22O MANUAL OF ZOOLOGY. The body of a typical Crustacean may be divided into three regions — a head, a thorax, and an abdomen, each of which is composed of a certain number of somites, though opinions differ both as to the number of segments in each region, and as to their number collectively. By the majority of writers the body is looked upon as being typically composed of twenty-one segments, of which seven belong to the head, seven to the thorax, and seven to the abdomen. In many Crustacea, how- ever, the segments of the head and thorax are welded together into a single mass, called the " cephalothorax ; " in which case the body shows only two distinct divisions, of which the cephalo- thorax claims fourteen segments, whilst the remaining seven are allotted to the abdomen. By Professor Huxley, on the other hand, the terminal joint of the abdomen, termed the " telson," is regarded as an appendage, and not as a somite. Upon this view, the body of a typical Crustacean will consist of twenty segments only. Professor Huxley, further, differs from the above-mentioned view in the allotment of the somites, and he divides the body into six cephalic, eight thoracic, and six abdominal somites.* Fritz Miiller and Glaus deny that the eyes are limbs, or that there is an ocular segment. The telson, on the other hand, is regarded by the former as a true somite, chiefly because the intestine usually opens in this piece. Whilst the normal number of segments in the body of any Crustacean may thus be regarded as being twenty-one, or twenty, there occur cases in which this number is exceeded, and others in which the number of somites is apparently less. In these latter cases, however, the apparent diminution in the number of segments is really due to some having been fused together, as is shown by the number of appendages, since each pair of appendages indicates a separate somite. In other cases, however, in which the number of somites is really less than the normal, this is due to an arrest of development. Accord- ing to Milne-Edwards : — " In the embryo these segments are formed in succession from before backwards, so that, when their evolution is checked, the latter, rather than the earlier, rings are those which are wanting ; and, in fact, it is generally easy to see in those speci- mens of full-grown Crustaceous animals, whose bodies present fewer than twenty-one segments, that 'the anomaly depends on * In reality the five hindmost segments of the eight somites here allotted to the thorax, should alone be regarded as constituting the abdomen proper, — that is, the region corresponding to the " abdomen " of insects and Arach- nida. The six somites allotted above to the abdomen belong to what is strictly called the " post abdomen " of the Crustacea. ANNULOSA : CRUSTACEA. 221 the absence of a certain number of the most posterior rings of the body." According to Dana, however, the abortion of segments, with their appendages, almost always takes place at the posterior end of the cephalothorax. In no single example can a general view be obtained of the different segments and their appendages in the Crustacea. " Indeed, the only segment that may be said to be persistent, is that which supports the mandibles, for the eyes may be wanting, and the antennae, though less liable to changes than the remaining appendages, are nevertheless subject to very extraordinary modifications, and have to perform functions equally various. Being essentially and typically organs of touch, hearing, and perhaps of smell, in the highest Decapods, they become converted into burrowing organs in the Scyllaridce, organs of prehension in the Merostomata, claspers for the male in the Cydopoidea, and organs of attachment in the Cirripedia. Not to multiply instances, we have presented to us in ,the Crustacea, probably the best zoological illustration of a class, constructed on a common type, retaining its general character- istics, but capable of endless modification of its parts, so as to suit the extreme requirements of every separate species " (H. Woodward). Taking the common Lobster (fig. 95) as a good and readily obtainable type of the Crustacea, the body is at once seen to be composed of two parts, familiarly called the "head" and the " tail," the latter being jointed and flexible. The so-called " head " is really composed of both the head, properly so called, and the thorax, which have coalesced so as to form a single mass, technically called the •' cephalothorax." The so-called " tail," on the other hand, is truly the "abdomen." The various appendages .....^ of the animal are arranged along the ? Ik V lower surface of the body, and consist -/ of the feelers, jaws, claws, legs, &c. s * The entire body, with the articu- Fig. 82.— Theoretical figure iiius- , , . J . , -, • tratmg the composition or the lated appendages, IS enclosed in a tegumentary skeleton of the strong chitinous "shell," or exo- S^t^^^T^ Skeleton, and the Cephalothorax IS Tergal pieces; e e Epimeral covered by a great cephalic shield geeS ^n//^it4a1 or plate, which is termed the " cara- pieces ; / p insertion of the F ,, * extremities. pace. Each segment of the body may be regarded as essen- tially composed of a convex upper plate, termed the "ter- gum," which is closed below by a flatter plate, called the 222 MANUAL OF ZOOLOGY. " sternum," the line where the two unite being produced downwards and outwards, into a plate, which is called the " pleuron," or " pleura " (fig. 83, 2). Strictly speaking, the composition of the typical somite is considerably more complex, each of the primary arcs of the somite being really com- posed of four pieces. The tergal arc is composed of two central pieces, one on each side of the middle line of the body, united together, and con- stituting the " tergum " proper. The superior arc is completed by two lateral pieces, one on each side of the tergum, which are termed the "epimera." In like manner the ventral or sternal arc is composed of a central plate, composed of two pieces united together in the middle line, and constituting the " sternum " proper; the arc being completed by two lateral pieces, termed the " episterna." These plates are usually more or less completely anchylosed together, and the true structure of the somite in these cases is often shown by what are called "apodemata." These are septa which proceed inwards from the internal surface of the somite, penetrating more or less deeply between the various organs enclosed by the ring, and always proceeding from the line of junction of the different pieces of the segment (fig. 82). It must be borne in mind that though the so-called " head " — that is to say, the " cephalothorax " — of the Lobster is pro- duced by an amalgamation of the various somites of the head and thorax, this is not the case with the great shield which covers this portion of the body. This shield — the so-called "cephalic buckler," or " carapace " — is not produced by the union of the tergal arcs of the various cephalic and thoracic segments, as would at first sight appear to be the case. On the contrary, the " carapace " in the higher Crustacea is pro- duced by an enormous development of the tergal pieces, or of the " epimera" of one or two of the cephalic segments : the tergal arcs of the remaining somites being overlapped by the carapace and remaining undeveloped. Examining the somites from behind forwards (for simpli- city's sake), the last segment comes to be first described. This is the so-called "" telson," which forms the last articulation of the abdomen, and never bears any appendages. For this reason, many authorities do not regard it as a somite, properly speaking, but simply as an azygous appendage — that is to say, as an appendage without a fellow. In the next segment (the last but one, or the last, of the abdomen, according to the view which is taken of the " telson "), there is a pair of natatory ap- pendages, called " swimmerets." Each swimmeret (fig. 83, 2) consists of a basal joint, which articulates with the sternum, and is called the " protopodite " or propodite, and of two diverging joints, which are attached to the former; the outer of these being called the " exopodite," and the inner the ANNULOSA : CRUSTACEA. 223 " endopodite." In this particular segment, the exopodite and endopodite are greatly expanded, so as to form powerful pad- dles, and the exopodite is divided into two by a transverse joint. In the succeeding somites of the abdomen — with the Fig. 83. — Morphology of Lobster, i. Lobster with all the appendages, except the terminal swimmerets, removed, and the abdominal somites separated from one another, ca Carapace; t Telson. 2. The third abdominal somite separated. / Tergum ; .$• Sternum ; p Pleiiron ; a Protopodite ; b Exopodite ; c Endopodite One of the last pair of foot-jaws or maxillipedes. e Epipodite ; g Gill : the c letters as before. other exception of the first, in which there is some modification— the appendages are in the form of swimmerets, essentially the same as those attached to the penultimate segment, and differ- 224 MANUAL OF ZOOLOGY. ing only in the fact, that the exopodite and endopodite are much narrower, and the former is undivided (fig. 83, 2). The last thoracic somite — immediately in front of the abdomen — carries a pair of the walking or ambulatory legs, each consist- ing of a short basal piece, or " propodite," and of a long jointed "endopodite,'7 the "exopodite" not being developed. The next thoracic segment carries another pair of ambulatory limbs, quite similar to the last, except for the fact that the protopo- dite bears a process which serves to keep the gills apart, and is termed the " epipodite." The succeeding segment supports a pair of limbs similar to the last in all respects, except that its extremities, instead of being simply pointed, are converted into nipping claws, or " chelae." The next segment of the thorax carries a pair of chelate limbs, just like the preceding, and the next is furnished with appendages, which are essen- tially the same in structure, but are much larger, constituting the great claws. The next two segments of the thorax, and the segment in front of these (by some looked upon as belong- ing to the head, by others as referable to the thorax), bear each a pair of modified limbs, which are termed " maxillipedes," or " foot-jaws." These are simply limbs with the ordinary structure of protopodite, exopodite, endopodite, and epipodite, but modified to serve as instruments of mastication, the hind- most pair being less altered than the two anterior pairs (fig. 83, 3). The next two somites carry appendages, which are in the form of jaws, and are termed respectively the first and second pairs of " maxillae." Each consists of the parts aforementioned, but the epipodite of the first pair of maxillae is rudimentary, whilst that of the second pair is large, and is shaped like a spoon. It is termed the " scaphognathite," and its function is to cause a current of water to traverse the gill-chamber by con- stantly baling water out of it. The next segment carries the biting jaws, or " mandibles ; " each of which consists of a large protopodite, and a small endopodite, which is termed the " palp," whilst the exopodite is undeveloped. The aperture of the mouth is situated between the bases of the mandibles, bounded behind by a forked process, called the " labium," or " metastoma," and in front by a single plate, called the " labrum " (upper lip). The next segment bears the long antennae, or feelers (fig. 95, ga), each consisting of a short pro- topodite, and a long, jointed, and segmented endopodite, with a very rudimentary exopodite. In front of the great antennae are the next pair of appendages, termed the " antennules," or smaller antennae (fig. 95, #), each composed of a protopodite, and a segmented endopodite and exopodite, which are nearly ANNULOSA : CRUSTACEA. 225 of equal size. Finally, attached to the first segment of the head are the eyes, each of which is borne upon an eye-stalk formed by the protopodite. The gill-chamber is formed by a great prolongation downwards of the pleura of the thoracic segments, and the gills are attached to the bases of the legs. As regards the digestive system of the Crustacea, the ali- mentary canal is, with few exceptions, continued straight from the mouth to the aperture of the anus. There are no salivary glands, but a large and well-developed liver is usually present. A heart is generally, but not always, present. In most of the lower forms it is a long vasiform tube, very like the " dorsal vessel" of Insects. The exact course of the circulation has been differently stated by different writers, but the following appear to be the facts of the case : In some of the lower forms (e.g., Copepoda) there are no arterial vessels, and the venous blood returned from the body is collected into a venous sinus — the so-called " pericardium," which surrounds the heart and opens into it by valvular apertures. In the higher forms, the heart gives off a number of arteries by which the blood is driven to all parts of the body and to the gills. The arteries do not terminate in a system of capillary Vessels, but in a series of irregular lacunae occupying all the interstices between the different organs of the body. From this interstitial lacunar system arise the venous trunks, which are generally dilated into more or less extensive sinuses. Whether the whole of the venous blood is submitted to the action of the gills, or whether the blood sent to the gills is derived mainly from the heart, is a matter of question ; but the former is the more probable view. Be this as it may, the blood is invariably returned to a large venous sinus which surrounds the heart, and opens into it by a number of valvular apertures. It follows from this description, that the heart of the Crustacea is mainly, if not altogether, a systemic heart, being concerned chiefly, if not entirely, in driving the aerated blood to all parts of the body. Distinct respiratory and circulatory organs may be altogether wanting ; but, as a rule, distinct branchiae are present. The exact form and structure of the gills differ in different cases, but their leading modifications will be alluded to in treating of the different orders. TABULAR VIEW OF THE DIVISIONS OF THE CRUSTACEA, Sub-class I. EPIZOA (Haustellata\ Order i. Ichthyophthira. „ 2. Rhizocephala. P 226 MANUAL OF ZOOLOGY. Sub-class II. CIRRIPEDIA. Order 3. Thoracica. „ 4. Abdominalia. „ 5. Apod a. ( Balanidae. < Verrucidae. ( Lepadidge. Sub-class III. ENTOMOSTRACA. Order 6. Ostracoda. \ T . T , , » 7. Copepoda. } Le$mi> Lophyropoda. „ 8. Cladocera. \ „ 9. Phyllopoda. ,- Legion, Branchiopoda. „ 10. TrUobita. j „ ii. Merostomata. Sub-class IV. MALACOSTRACA. Division A. EDRIOPHTHALMATA. Order 12. Lcemodipoda. „ 13. Isopoda. „ 14. Amphipoda. Division B. PODOPHTHALMATA. Order 15. Stomapoda. „ 1 6. Decapoda. Tribe a. Macrnra. „ b. Anomura. „ Maxillary palpi greatly developed, and forming strong chelae. 2. Telson of the Scorpion. 3. One of the abdominal segments of the Scorpion, showing the " stig- mata," or apertures of the pulmonary sacs. 4. Tegenariadomestica,\ht common Spider (male), viewed fiom below ; .$• Spinnerets ; in Mandibles with their perforated hooks — below the mandibles are the maxillae, and between the bases of these is the labium ; p The maxillary palpi with their enlarged tumid extremities. of the antenna. The antennae, therefore, of the Spiders are converted into prehensile and offensive weapons ; whilst in the Scorpions, as in the King-crabs, they are developed into nip- ping-claws, or chelae. In the lower Arachnida, the organs of the mouth, though essentially the same as in the higher forms, are enveloped in a sheath, formed by the labium and maxillae, whilst the man- dibles are often joined together so as to constitute a species of lancet. The mouth opens into a pharynx, which is of remarkably small calibre in the true spiders, all of which live simply on ANNULOSA : ARACHNIDA. 257 the juices of their prey. The intestinal canal is usually short and straight, no convolutions intervening between the mouth and the aperture of the anus. Often, however, lateral caeca are appended to the alimentary tube. Salivary glands are also present, as well as ramified tubes, supposed to perform the functions of a kidney, and to correspond to the " Malpighian vessels " of Insects. The circulation in the Arachnida is maintained by a dorsal heart, which is situated above the alimentary canal. Usually the heart is greatly elongated, and resembles the " dorsal vessel " of the Insecta. In the lower Arachnida, however, there is no central organ of the circulation, and there are no dif- ferentiated blood-vessels. All the Arachnida, except, perhaps, some of the lowest, breathe the air directly, and the respiratory function is performed by the general surface of the body (as in the lowest members of the class), or by ramified air-tubes, termed " tracheae," or by distinct pulmonary chambers or sacs ; or, lastly, by a combination of tracheae and pulmonary vesicles. The " tracheae " consist of ramified or fasciculated tubes, opening upon the surface of the body by distinct apertures, called " stigmata." The walls of the tube are generally pre- vented from collapsing by means of a chitinous fibre or filament, which is coiled up into a spiral, and is situated beneath their epithelial lining. The pulmonary sacs are simple involutions of the integument, abundantly supplied with blood ; the vascular surface thus formed being increased in area by the development of a number of close set mem- branous lamellae, or vascular plates, which project into the interior of the cavity. Like the tracheae, the pulmonary sacs communicate with the exterior by minute apertures, or " stig- mata "(fig. 98, 3). The nervous system is of the normal articulate type, but is often much concentrated. In the Spiders there is a cephalic or " cerebral" ganglion, a large thoracic ganglion, and in some instances a small abdominal ganglion. In some of the lower forms the articulate type of nervous system is lost, and there is merely a ganglionic mass which is traversed by the gullet. In none of the Arachnida are compound eyes present, and in none are the eyes supported upon foot-stalks. The organs of vision, when present, are in the form of from two to eight or more simple eyes, or " ocelli." In all the Arachnida, with the exception of the Tardigrada, the sexes are distinct. The great majority of the Arachnida are oviparous, and in most cases the larvae are like the adult in all except in size. In some cases, however (Acarina), the R 258 MANUAL OF ZOOLOGY. larvae have only six legs, and do not attain the proper four pairs of legs, until after some moults. The Arachnida may be divided into two great sections or sub-classes — viz., the Trachearia, in which respiration is effected by the general surface of the body, or by tracheae, and there are never more than four ocelli ; and the Pulmonaria, in which respiration is effected by pulmonary sacs, either alone or com- bined with tracheae, and there are six or more eyes. CHAPTER XXXVII. DIVISIONS OF THE ARACHNIDA. DIVISION A. TRACHEARIA. — Respiration cutaneous, or by trachea. Eyes never more than four in number. The Trachearia comprise three orders — viz., the Podosomata. the Acarina or Monomerosomata, and the Adelarthrosomata. ORDER I. PODOSOMATA (Pantopoda}. — The members of this order, sometimes called " Sea-spiders/' have been placed alter- nately amongst the Arachnida and the Crustacea, their true position being rendered doubtful by the fact that, though marine in their habits, they possess no differentiated respira- tory organs. They possess, however, no more than four pairs of legs, and would therefore appear to be properly referable to the Arachnida. The commoner forms of the Podosomata (such as Nymphon and Pycnogonuni) may be found on the sea- coast at low water, crawling about amongst marine plants or hiding beneath stones. Some species of the latter genus are asserted to be parasitic upon fishes and other marine animals, but the common British species (P. littorale} is free when adult, and does not appear to be parasitic at any stage of its existence (fig. 99, a). The legs consist of four pairs, some- times greatly exceeding the body in length, and sometimes containing caecal prolongations of the digestive cavity for a portion of their length. The mouth is provided with a pair of " chelicerae," or chelate mandibles, and with two well-developed maxillary palpi, behind which in the female are a pair of false legs which carry the ova. The abdomen is rudimentary. Though there are no respiratory organs, there is a distinct heart. The sexes are in different individuals. ORDER II. ACARINA or MONOMEROSOMATA. — The members of this order possess an unsegmented abdomen which is fused ANNULOSA I ARACHNIDA. 259 with the cephalothorax into a single mass. Respiration is effected by tracheae. Most of the Acarina are parasitic, and the most familiar are the Mites and Ticks. Family i. Linguatulina or Pentastomida. — The members of this family are singular vermiform animals, found as parasites in the frontal sinuses and lungs of some Vertebrates. In their adult condition they possess no external organs except two pairs of hooks, representing limbs, placed near the mouth. They thus closely approximate to the Tceniada, beside which they have been generally placed. In the young condition, however, they possess four articulated legs, and even in the adult state the characters of the nervous system are higher than those of the Scolecida. There are no differentiated organs of respiration, and there are no circulatory organs, but the sexes are distinct. Family 2. Macrobiotida (Tardigrada or Arctisca). — The Fig. 99. — Arachnida. a Pycnogon um lit tor ale : b Tetranychus telarius, one of the " Sociable " mites ; c Hydrachna globulns, one of the " Water-mites." "Sloth" or "Bear animalcules," which compose this family, are microscopic animals, very much like Rotifers, found in damp moss and in the gutters of houses. The nervous system consists of four ganglia, and there is a suctorial mouth, with rudimentary jaws or stilets. The abdomen is undeveloped, and there are four pairs of rudimentary legs. They exhibit no traces of either circulatory or respiratory organs, and the sexes are united in the same individual. Family 3. Acarida. — This family includes the Mites, Ticks, and Water-mites, some of which are parasitic, whilst others are free, and some are even aquatic in their habits. The mouth is formed for suction. There is no definite line of demarcation between the unsegmented abdomen and the cephalothorax. In the true Acari (fig. 99, £), of which the Cheese-mite may be taken as an example, there are four pairs of legs, adapted for walking, and the mouth is provided with distinct mandibles. 26O MANUAL OF ZOOLOGY. Besides the Cheese-mite (A. domesticus], another well-known species is the Acarus destructor, which feeds upon various zoo- logical specimens, and is very annoying to the naturalist. In the Sarcoptes scabiei — the cause of the skin-disease known as the " itch " — the two anterior pairs of legs are provided with suckers, and the two posterior are terminated by bristles ; the mouth, also, is furnished with bristles. In the Ticks (Ixodes] the mouth is provided with a beak, or "rostrum," which enables them to pierce the skin, and retain their hold firmly. In the Hydrachnidce. (fig. 99, c\ or Water-mites, the head is fur- nished with two or four ocelli, and there are four pairs of hairy natatory legs. They are parasitic, during at least a portion of their existence, upon Water-beetles and other aquatic insects. They pass through a metamorphosis, the larva being hexapod, or having only three pairs of legs. The Garden-mites (Trom- bididce) and Spider-mites (Ganasida) live upon plants; the Wood-mites ( Oribatidce) and Harvest-ticks (Leptida) are to be found amongst moss and herbage, or creeping upon trees or stones ; whilst the true Ticks (Ixodidce) attach themselves para- sitically by means of their suctorial mouth to the bodies of various Mammals, such as sheep, oxen, dogs, &c. Several Mites (Thalassarachna, Pontarachna, &c.) have been found to inhabit salt water, and several species of Trombididcz live habit- ually between tide-marks. Another member of the Acarina is the curious little Demodex folliculorum, which is found in the sebaceous follicles of man, especially in the neighbourhood of the nose. It is probable that very few, if any, individuals are exempt from this harmless parasite. ORDER III. ADELARTHROSOMATA. — The members of this order, comprising the Harvest-spiders, the Book-scorpions, &c., are distinguished from the preceding by the possession of an abdomen, which is more or less distinctly segmented, but generally exhibits no line of separation from the cephalothorax, the two regions being of equal breadth and conjoined together. The mouth is furnished with masticatory appendages, and respiration is effected by tracheae, which open on the lower surface of the body by two or four stigmata. Family i. Phalangidcz. — The well-known "Harvest-spiders" belong to this family. They are characterised by the great length of the legs, and by the filiform maxillary palpi, terminated by simple hooks. Family 2. Pseudoscorpionida (Cheliferidcz). — The "Book- scorpion" (CJielifer) is a common little animal in old books. It is distinguished by the fact that the maxillary palpi are of ANNULOSA : ARACHNIDA. 26 I large size, and are converted into nipping-claws or chelae, thus giving the animal the appearance of a Scorpion in miniature. Family 3. Solpugidce. — In this family the abdomen is not only very distinctly segmented, but is also clearly separated from the abdomen. The mandibles in Gakodes, which is the type of the group, are chelate, but the maxillary palpi constitute long feet. DIVISION B. PULMONARIA. — Respiration by pulmonary sacs alone, or by pulmonary sacs conjoined with trachece. Eyes six or more in number. Abdomen usually distinct from the cephalo- thorax. This division comprises the higher Arachnida, such as the Scorpions, and the majority of what are commonly known as Spiders ; the former constituting the order of the Pedipalpi, the latter that of the Araneida or Dimerosomata. ORDER I. PEDIPALPI. — In this order are the true Scorpions, together with certain other animals which are in some respects intermediate between the Scorpions and the true Spiders. The members of this order are distinguished by the fact that the abdomen in all is distinctly segmented, but is not separated from the cephalothorax by a well-marked constriction. They agree in this character with the Adelarthrosomata ; hence the two are sometimes united into a single order (Arthrogastrd). but they are separated by the nature of the respiratory organs, the latter breathing by tracheae, and not by pulmonary sacs. Family i. Scorpionidce. — The Scorpions are amongst the best known of the Arachnida, as well as being amongst the largest. Fig. 100. — Scorpion (reduced). They are distinguished by their long, distinctly segmented ab- domen, terminating in a hooked claw (figs. 98, 100). This claw, which is really a modified " telson," is the chief offensive weapon of the Scorpion, and is perforated at its point by the duct of a 262 MANUAL OF ZOOLOGY. poison-gland which is situated at its base. The abdomen is composed of twelve somites, but there is no evident line of de- marcation between this region and the cephalothorax. The thoracic segments carry four pairs of ambulatory feet. There are six, eight, or twelve simple eyes. The maxillary palpi are greatly developed, and constitute strong nipping-claws, or "chelae" (figs. 98. 100). The mandibles (antennae) also form claws, or " chelicerae." The respiratory organs are in the form of pulmonary sacs, four on each side, opening upon the under surface of the abdomen by as many stigmata, each of which is surrounded by a raised margin, or " peritrema " (fig. 98, 3). The Scorpions are mostly inhabitants of warm regions, and their sting, though much exaggerated, is of a very severe nature. They live under stones or in dark crevices, and run swiftly, carrying the tail curved over the back. They feed on Insects, which they hold in the chelate palpi and sting to death. Family 2. Thelyphonidce. The members of this family in external appearance closely resemble the true Spiders, from which they are separated by the possession of a segmented abdomen, and long spinose palpi, and by the absence of spin- nerets. They are distinguished from the Scorpionida by the amalgamation of the head and thorax into a single mass, which is clearly separated from the abdomen by a slight constriction, as well as by the fact that the maxillary palpi terminate in movable claws instead of chelae. Further, the extremity of the abdomen is not furnished with a terminal hook, or " sting." ORDER II. ARANEIDA or SPH^EROGASTRA. — This order in- cludes the true Spiders, which are characterised by the amal- gamation of the cephalic and thoracic segments into a single mass, and by the generally soft, unsegmented abdomen, attached to the cephalothorax by a constricted portion, or peduncle. Respiration is effected by pulmonary sacs usually in combina- ation with tracheae. (Hence the name Pulmotrachearia, some- times applied to the order.) The number of the pulmonary sacs is smaller in the true Spiders than in the Scorpions, being either two or four, opening by as many stigmata upon the under surface of the abdomen. The head bears from six to eight simple eyes ; the man- dibles are simply hooked, and are perforated by the duct of a gland which secretes a poisonous fluid ; and the maxillary palpi are never chelate. Spiders (fig. 101) are all predaceous animals, and many of them possess the power of constructing webs for the capture ANNULOSA I ARACHNIDA. 263 of their prey or for lining their abodes. For the production of the web, Spiders are furnished with special glands, situated at the extremity of the abdomen. The secretion of these glands is a viscid fluid, which hardens rapidly on exposure to air, and which is cast into its proper, thread-like shape, by being passed through what are called the "spinnerets." These are little conical or cylindrical organs, four or six in number, situated below the extremity of the abdomen. The excretory ducts of the glands open into the spinnerets, each of which has its apex perforated by a great number of minute tubes, through which the secretion of the glands has to pass before reaching the air. Many spiders, however, do not construct any web, unless it be for their own habitations, but hunt their prey for themselves. As regards the reproductive process in the Spiders, it appears certain that the act of copulation, so to speak, is performed by Fig. 101. — Araneida. Theridion ripariutn (female). the males by means of the maxillary palpi, the extremities of which are specially modified for this purpose. The testes are abdominal, but the semen appears to be stored up in the enlarged extremities of the maxillary palps, which thus per- form the part of the vesiculae seminales. " The most careful observations, repeated by the most attentive and experienced entomologists, have led to the conviction that the ova are fertilised by the alternate introduction into the vulva of the appendages of the two palpi of the male. Treviranus's sup- position that these acts are mere preliminary stimuli, has received no confirmation, and is rejected by Duge's, Westwood, and Blackwall ; and with good reason, as the detection of the spermatozoa in the palpal vesicles has shown. . . . Duges offers the very probable suggestion that the male himself may apply the dilated cavities of the palpi to the abdominal aper- ture (of the testes), and receive from the vasa deferentia the 204 MANUAL OF ZOOLOGY. fertilising fluid, preparatory to the union. . . . Certain it is that an explanation of this singular condition of the male apparatus, in which the intromittent organ is transferred to the remote and outstretched palp, is afforded by the insatiable proneness to slay and devour in the females of these most predaceous of articulated animals " (Owen). The Spiders are oviparous, and the young pass through no metamorphosis ; but they cast their skins, or moult, repeatedly, before they attain the size of the adult. DISTRIBUTION OF ARACHNIDA IN /TIME. — The Arachnida are only very rarely found in a fossil condition. As far as is yet known, both the Scorpions and the true Spiders appear to have their commencement in the Carboniferous epoch, the former being represented by the celebrated Cyclophthalmus senior from the Coal-measures of Bohemia. Spiders are also known to occur in the Jurassic Rocks (Solenhofen Slates) and in the Tertiary period. The Mites, Harvest-spiders, and Book- scorpions have been detected in amber. CHAPTER XXXVIII. MYRIAPODA. CLASS III. MYRIAPODA. — The Myriapoda are defined as ar- ticulate animals in which the head is distinct, and the remainder of the body is divided into nearly similar segments, the thorax exhibiting no clear line of demarcation from the abdomen. There is one pair of antennce, and the number of the legs is always more than eight pairs. Respiration is by trachece. In this class — comprising the Centipedes (fig. 102) and the Millipedes — the integument is chitinous, the body is divided into a number of somites provided with articulated appendages, and the nervous and circulatory organs are constructed upon a plan similar to what we have seen in Crustacea and Arachnida. The head is invariably distinct, and there is no marked line of demarcation between the segments of the thorax and those of the abdomen. The body, except in Pauropus, always consists of more than twenty somites, and those which correspond to the abdomen in the Arachnida and Insecta are always provided with locomotive limbs. " The head consists of at least five, and probably of six, coalescent and modified somites ; and some of the anterior segments of the body are, in many genera, ANNULOSA : MYRIAPODA. coalescent, and have their appendages specially modified to subserve prehension" (Huxley). Pauropus has only nine pairs of legs ; but, with this exception, eleven pairs of legs is the smallest number known in the order. The respiratory organs, with one exception, agree with those of the Inserta and of many of the Arachnida in being "tracheae" — that is to say, tubes, which open upon the surface of the body by minute apertures, or " stigmata/' and the walls of which are strengthened by a spirally- coiled filament of chitine. The tracheae may or may not anastomose with one another as they do in Insects. The somites, with the exception of the head and the last abdominal segment, are usually undistinguishable from one another, and each bears a single pair of limbs. In some cases, however, each segment appears to be provided with two pairs of appendages (fig. 103). This is really due to the coales- cence of the somites in pairs, each apparent segment being in reality composed of two amalgamated somites. This is shown, not only by the bigeminal limbs, but also by the arrangement of the stigmata, which in the normal forms occur on every alternate ring only, whereas in these aberrant forms they are found upon every ring. The head always bears a pair of jointed antennae, resembling those of many Insects, and behind the antennae there is gene- • rally a variable number of simple sessile eyes. In one species (Scutigera) compound facetted eyes are present ; and in Pauro- pus the antennae are bifid, and carry many-jointed appendages, thus differing wholly from the antennae of Insects, and pre- senting a decided approximation to the Crustacea. The young in some cases, on escaping from the egg, possess nearly all the characters of the parents, except that the number of somites, and consequently of limbs, is always less, and in- creases at every change of skin (" moult " or " ecdysis "). In most cases, there is a species of metamorphosis, the embryo being at first either devoid of locomotive appendages, or pos- sessed of no more than three pairs of legs, thus resembling the true hexapod Insects. It is believed, however, that the legs of these hexapod larvae do not correspond homologically with the Fig. 102. — Centipede (Scolopendra) . 266 MANUAL OF ZOOLOGY. three pairs of legs proper to adult Insects. In these cases the number of legs proper to the adult is not obtained until after several moults, the entire process being stated to occupy in some species as much as two years, before maturity is reached. The Myriapoda are divided into three orders — viz., the Chi- lopoda, the Chilognatha, and the Pauropoda, ORDER I. CHILOPODA. — This order comprises the well- known carnivorous Centipedes and their allies, and is charac- terised by the number of legs being rarely indefinitely great (usually from 15 to 20 pairs), by the composition of the an- tennae out of not less than 14 joints (14 to 40 or more), and by the structure of the masticating organs. These consist of a pair of mandibles with small palpi, a labium, and two pairs of " maxillipedes," or foot-jaws, of which the second is hooked, and is perforated for the discharge of a poisonous fluid. There is not more than one pair of legs to each somite, and the last two limbs are often directed backwards in the axis of the body, so as to form a kind of tail. The body in all the Chilopoda is flattened, and the generative organs open at the posterior end of the body. Scolopendra (fig. 102), Lithobius, and Geophilus are common European genera of this order. The ordinary Centipedes of this country are perfectly harmless, but those of tropical regions sometimes attain a length of a foot, or more, and these are cap- able of inflicting very severe, and even dangerous, bites. ORDER II. CHILOGNATHA. — This order comprises the vege- table-eating Millipedes (lulidcR) and the Gallyworms (Polydes- mus). The order is characterised by the great number of legs, — each segment, except the six or seven anterior ones, bearing Fig. 103. — Millipede (lulus). two pairs ; by the composition of the antennae out of six or seven joints ; and by the structure of the masticating organs, which consist of a pair of mandibles without palps, covered by a lower lip, composed of the confluent maxillae. The genera- tive apertures are placed in the anterior portion of the body In the common Millipede (lulus) the body is composed of from forty to fifty segments, each of which bears two pairs of minute, thread-like legs. The lull of this country are of small size, but an American species attains a length of more than half a foot. ANNULOSA I INSECTA. 267 ORDER III. PAUROPODA. — In this order is only an extra- ordinary little Myriapod, described by Sir John Lubbock under the name of Pauropus. The body is only one-twentieth of an inch in length, and consists of ten somites, furnished with scattered setae. There are only nine pairs of legs, of which one pair is carried by the 3d segment, whilst the 4th, 5th, 6th, and yth segments carry each two pairs of legs, and may there- fore be regarded as really double. The head is composed of two segments, and is not provided with jaw-feet. The witennae are five-jointed, bifid, with three long multi-articulate appen- dages. The body is white and colourless, and there are no tracheae, so that respiration must be effected entirely by the skin. Pauropus is found amongst decaying leaves in damp situations, and species have been described both from Britain and America. It is separated from the Chilopoda by its small number of legs, the absence of foot-jaws, and the composition of the antennae out of no more than five joints. DISTRIBUTION OF MYRIAPODA IN TIME. — About twenty species of Myriapoda are known as fossils, the oldest example of the order having been found in the Carboniferous epoch. From rocks of this age several species of Chilognathous Myria- pods have been discovered. They belong to the genera Xylobius and Archiulus, and have been placed in a special family under the name of Archiulidce. The occurrence of air-breathing articulate animals (both Arachnida and Myria- poda] in the Carboniferous period is noticeable, as being con- temporaneous with the earliest known terrestrial Molluscs. CHAPTER XXXIX. INSECTA. GENERAL CHARACTERS OF THE INSECTA. CLASS IV. — INSECTA. — The Insecta are defined as articulate animals in which the head, thorax, and abdomen are distinct ; there are three pairs of legs borne on the thorax ; the abdomen is destitute of legs ; a single pair of antenna is present ; mostly, there are two pairs of ivings on the thorax. Respiration is effected by trachece. In the Insecta the body is divided into a variable number of definite segments, or somites, some of which are furnished 268 MANUAL OF ZOOLOGY. with jointed appendages, and the nervous and circulatory systems are constructed upon essentially the same plan as in the Crustacea, Arachnida, and Myriapoda. The head, thorax, and abdomen are distinct (fig. 104), and the total number of somites in the body never exceeds twenty. " Of these, five certainly, and six probably, constitute the head, which pos- sesses a pair of antennae, a pair of mandibles, and two pairs of maxillae, the hinder pair of which are coalescent, and form the 'labium.' Three, or perhaps, in some cases, more, somites unite and become specially modified to form the thorax, to which the three pairs of locomotive limbs, characteristic of perfect Insects, are attached. Two additional pairs of loco- motive organs, the are developed, in most insects, from the tergal walls of the second and third thoracic somites. No locomotive limbs are ever developed from the abdomen of the adult insect, but the ventral portions of the abdominal somites, from the eighth backwards, are often metamorphosed in- to apparatuses ancillary to the generative func- tion " (Huxley). The integument of the Insecta, in the mature condition, is more or less hardened by the deposi- tion of chitine, and usu- ally forms a resisting exo- skeleton, to which the muscles are attached. The segments of the head are amalgamated into a single piece, which bears a pair of jointed feelers or an- tennae, a pair of eyes, usually compound, and Fig. 104.— Diagram of Insect, a Head, carrying the appendages of the the eyes and antennae ; b - Prothorax, carrying mOuth. The SCffmentS of t-Vip. fii-sf- nail- nf >>«<:• r MpcntVini-Q v. <-ar-rTrincr r^O the first pair of legs ; c Mesothorax, carrying legs a b Metathorax, with the the thorax are aiSO the second pair of legs and first pair of wings ; third pair of legs and o-e>mnt-p>r1 infr\ the second pair of wings ;* Abdomen, without grated mtO limbs, but having terminal appendages subser- piece I but thlS, never- vient to reproduction. ^^ ^^ Qf sepa_ ration into its constituent three somites (fig. 104). These are termed respectively, from before backwards, the "pro- ANNULOSA I INSECTA. 269 thorax," " mesothorax," and "m eta thorax/' and each bears a pair of jointed legs. In the great majority of Insects, the dorsal arches of the mesothorax and metathorax give origin each to a pair of wings. Each leg consists of from six to nine joints. The first of these, which is attached to the sternal surface of the thorax, is called the " coxa/' and is succeeded by a short joint, termed the " trochanter." The trochanter is followed by a joint, often of large size, called the "femur," and this has articulated to it the " tarsus," which may be composed of from two to five joints. The wings of Insects are membranous " flattened vesicles, sustained by slender but firm hollow tubes, called ' nervures/ along which branches of the tracheae and channels of the circulation are continued " (Owen). According to New- port, the wings of Insects are " expanded portions of the common integuments of the sides of the meso- and meta- thorax, occasioned by the enlargement and extension of numerous tracheae and the accompanying passages for the circulatory fluids, and their motions are intimately connected with the function of respiration." In the Coleoptera (Beetles) the anterior pair of wings become hardened by the deposition of chitine, so as to form two protective cases for the hinder membranous wings. In this condition the anterior wings are known as the "elytra," or "wing-cases." In some of the Hemiptera this change only affects the inner portions of the anterior wings, the apices of which remain membranous and to these the term " hemelytra " is applied. In the Diptera the posterior pair of wings are rudimentary, and are converted into two capitate filaments, called "halteres," or "balancers." In the Strepsiptera the anterior pair of wings are rudimentary, and are converted into twisted filaments. The primitive number of somites in the abdomen of insects is said to be eleven (Orthoptera), but nine is the number ordi- narily present ; and though these are distinct in most larvae, it is seldom that more than seven or eight are recognisable in the adult. The abdominal somites are usually more or less freely movable upon one another, and never carry locomotive limbs. The extremity of the abdomen is, however, not infrequently furnished with appendages, which are connected with the generative function, and not infrequently serve as offensive and defensive weapons. Of this nature are the ovipositors of Ichneumons and other insects, and the sting of Bees and Wasps. In the Earwig (Forficula) these caudal appendages form a pair of forceps ; whilst in many Insects they are in the 270 MANUAL OF ZOOLOGY. form of bristles, by which powerful leaps can be effected, as is seen in the Springtails (Podurce). In some insects (as the Mole-cricket and Cockroach), the 9th or roth abdominal seg- ment carries jointed antenniform appendages, which, though perhaps partially or even primarily generative in function, are certainly organs of sense, being connected with smell or hearing. The organs about the mouth in Insects are collectively termed the "trophi," or "instrumenta cibaria." Two principal types require consideration — namely, the masticatory and the suctorial — both types being sometimes modified, and occasion- ally combined. In the Masticatory Insects, such as the Beetles (fig. 105, i), Fig. 105. — Organs of the mouth in Insects, i. Trophi of a masticating Insect (Beetle): a Labriim or upper lip ; b Mandibles; c Maxillae with their palpi; d Labium or lower lip with its palpi. 2. Mouth of a Butterfly: o Eye ; f Base of antennae : g Labial palp; h Spiral trunk or "antlia." 3. Mouth of a Hemipterous Insect (Nepa cinerea)'. /Labium; in Maxillae; n Mandibles. the trophi consist of the following parts, from before back- wards: — (i.) An upper lip, or "labrum," attached below the front of the head. (2.) A pair of biting-jaws, or "mandibles." (3.) A pair of chewing-jaws, or "maxillae," provided with one or more pairs' of "maxillary palps," or sensory and tactile filaments. (4.) A lower lip, or "labium," composed of a second coalescent pair of maxillae, and also bearing a pair of palpi, the " labial palps." The primitive form of the labium, that, namely, of a second pair of maxillae, is more or less per- fectly retained by the Orthoptera and some of the Neuroptera. The lower or basal portion of the labium is called the "men- turn " or chin, whilst the upper portion is more flexible, and is termed the " ligula." The upper portion of the ligula is often ANNULOSA : INSECTA. 2 7 I developed into a kind of tongue, which is very distinct in some Insects, and is termed the "lingua." In the typical suctorial mouth, as seen in the Butterflies (fig. 105, 2), the following is the arrangement of parts: — The labrum and the mandibles are now quite rudimentary; the first pair of maxillae is greatly elongated, each maxilla forming a half-tube. These maxillae adhere together by their inner surfaces, and thus form a spiral " trunk," or " antlia " (inappro- priately called the "proboscis"), by which the juices of flowers are sucked up. Each maxilla, besides the half-tube on one side, contains also a tube in its interior ; consequently on a transverse section the trunk is found really to consist of three canals, one in the interior of each maxilla, and the third formed between them by their apposition. To the base of the trunk are attached the maxillary palpi, which are extremely small. Behind the trunk is a small labium, com- posed of the united second pair of maxillae. The "labial palpi" are greatly developed, and form two hairy cushions, between which the trunk is coiled up when not in use. In the Bee there exists an intermediate condition of parts, the mouth being fitted partly for biting, and partly for suction. The labrum and mandibles are well developed, and retain their usual form. The maxillae and the labium are greatly elongated ; the former being apposed to the lengthened tongue in such a manner as to form a tubular trunk, which cannot be rolled up, as in the Butterflies, but is capable of efficient suc- tion. The labial palpia are also greatly elongated. In the Hemiptera, the " trophi" consist of four lancet-shaped needles, which are the modified mandibles and maxillae, en- closed in a tubular sheath formed by the elongated labium, (fig. 105, 3). Lastly, in the Diptera — as in the common House-fly — there is an elongated labium, which is channelled on its upper surface for the reception of the mandibles and maxillae, these being modified into bristles or lancets. The mouth in the Masticating Insects leads by a pharynx and oesophagus into a membranous, usually folded, stomach — the " crop," or " ingluvies " — from which the food is trans- mitted to a second muscular stomach, called the "gizzard" (fig. 1 06). The gizzard is adapted for crushing the food, often having plates or teeth of chitine developed in its walls, and is succeeded by the true digestive cavity, called the "chylific stomach " (ventriculus chylopoieticus). From this an intestine of variable length proceeds, its terminal portion, or rectum, opening into a dilatation which is common to the ducts of the generative organs, and is termed the " cloaca." The oesophagus MANUAL OF ZOOLOGY. is furnished with salivary glands of varying size and complexity, and is provided in some of the Suctorial Insects with a dilata- tion called the "sucking sto- mach." Behind the pyloric aperture of the stomach, with very few exceptions, is a vari- able number of caecal convo- luted tubes (fig. 1 06, e), which open into the intestine, and are called the " Malpighian tubes." These are often looked upon as representing the liver, but are by some believed to have a renal function. If the Mal- pighian vessels truly perform the functions of a liver — as their position would appear to prove — then the kidneys will be represented by a series of cse- cal tubes which are only occa- sionally present, and which open into the rectum, close to the cloaca. There are no absor- bent vessels, and the products of digestion simply transude through the walls of the alimen- tary canal into the sinuses or irre- gular cavities which existbetween the abdominal organs. The ap- paratus of digestion does not differ essentially from the above in any of 'the Insects ; but the alimentary canal is, generally speaking, considerably lengthened in the herbivorous species. There is no definite and regular course of the circulation in the Insects. The propulsive organ of the circulation is a long contractile cavity, situated in the back and termed the " dorsal vessel." This is composed of a number of sacs (ordinarily eight), opening into one another by valvular apertures, which allow of a current in one direction only — viz., towards the head. The blood is collected from the irregular venous sinuses which are formed by the lacunae and interstices between the tissues, and enters the dorsal vessel from behind ; it is then driven forwards, and is expelled at the anterior extremity of the body. Respiration is effected by means of " trachea:;," or branched tubes, which commence at the surface of the body by lateral ig. 1 06.— Digestive system of a Beetle (Carabus auratus). a CEsophagus ; b Crop ; c Gizzard : d Chylific stomach ; e Malpighian tubes ; f Intestine ; g Cloaca ; h Supposed renal vessels. ANNULOSA I INSECT A. 273 apertures called " stigmata," or " spiracles," and ramify through every part of the animal. In structure the tracheae are mem- branous, but their walls are strengthened by a chitinous fila- ment, which is rolled up into a continuous spiral coil. In the aquatic larvae of many insects, and in one adult insect, branches of the tracheae are sent to temporary outgrowths which are termed " tracheal gills," and in which the blood is oxygenated. In all, however, except the single insect above mentioned, these temporary external appendages fall off when maturity is attained. The wings, also, whilst acting as loco- motive organs, doubtless subserve respiration, the nervures being hollow tubes enclosing tracheae. The nervous system in Insects, though often concentrated into special masses, consists essentially of a chain of ganglia, placed ventrally, and united together by a series of double cords or commissures. The cephalic or " prae-oesophageal" ganglia are of large size, and distribute filaments to the eyes and antennae. The post-oesophageal ganglia are united to the preceding by cords which form a collar round the gullet, and they supply the nerves to the mouth, whilst the next three ganglia furnish the nerves to the legs and wings. In larvae, thirteen pairs of ganglia, one to each segment, can be recog- nised. In the imago, however, of the Coleoptera, several of these primitive ganglia have coalesced, so that this number is considerably reduced. The organs of sense are the eyes and antennae. The eyes in Insects are usually " compound," and are composed of a number of hexagonal lenses, united together, and each supplied with a separate nervous filament. Besides these, simple eyes — " ocelli," or " stemmata," — are often present, or, in rare cases, may be the sole organs of vision. In structure these resemble the single elements of the compound eyes. In a few cases the eyes are placed at the extremities of stalks or pedun- cles, but in no case are these peduncles movable articulated to the head, as is the case in the Podophthalmous Crustaceans. The antennae are movable, jointed filaments, attached usually close to the eyes, and varying much in shape in different Insects. They doubtless discharge the functions of tactile organs, but are probably the organ of other more recondite senses in addition. The sexes in Insects are in different individuals, and most are oviparous. Generally speaking, the young insect is very different in external characters from the adult, and it requires to pass through a series of changes, which constitute the " meta- morphosis," before attaining maturity. In some Insects, how- S 274 MANUAL OF ZOOLOGY. ever, there appears to be no metamorphosis, and in some the changes which take place are not so striking or so complete as in others. By the absence of metamorphosis, or by the degree of its completeness when present, Insects are divided into sections, called respectively Ametabola, Hemimetabola, and Holometabola, which, though not, perhaps, of a very high scien- tific value, are nevertheless very convenient in practice. Section i. Ametabolic Insects. — These pass through no meta- morphosis, and also, in the mature condition, are destitute of wings. The young of these insects (Apterd) on escaping from the ovum resemble their parents in all respects except in size ; and though they may change their skins frequently, they undergo no alteration before reaching the perfect condition, except that they grow larger. Section 2. Hemimetabolic Insects. — In the insects belonging to this section there is a metamorphosis consisting of three stages. The young on escaping from the ovum is termed the " larva ; " when it reaches its second stage it is called the " pupa," or " nymph ; " and in its third stage, as a perfect insect, it is called the " imago." In the Hemimetabola, the "larva," though of course much smaller than the adult, or " imago,'; differs from it in little else except in the absence of wings. It is active and locomotive, and is generally very like the adult in external appearance. The "pupa," again, is a little larger than the larva, but really differs from it in nothing else than in the fact that the rudiments of wings have now appeared, in the form of lobes enclosed in cases. The " pupa" is still active and locomotive, and the term " nymph " is usually applied to it. The pupa is converted into the perfect insect, or " imago," by the liberation of the wings, no other change being requisite for this purpose. From the comparatively small amount of difference between these three stages, and from the active condition of the pupa, this kind of metamorphosis is said to be "incomplete." In some members of this section however — such as the Dragon-flies — the larva and pupa are aquatic, whereas the imago leads an aerial life. In these cases there is necessarily a .considerable difference between the larva and the adult ; but the larva and pupa are closely alike, and the latter is active. Section 3. Holometabolic Insects. — These — comprising the Butterflies, Moths, Beetles, &c. — pass through three stages which differ' greatly from one another in appearance, the metamorphosis, therefore, being said to be " complete." In these insects (fig. 107) the "larva" is vermiform, seg- mented, and usually provided with locomotive feet, which ANNULOSA : INSECTA. 275 do not correspond with those of the adult, though these latter are usually present as well (fig. 107). In some cases the larva is destitute of legs, or is "apodal." The larva is also provided with mastica- tory organs, and usually eats voraciously. In this stage of the metamorphosis the larvae constitute what are usually called " caterpillars " and " grubs." Having remained in this condition for a longer or shorter length of time, and having undergone repeated changes of skin, or " moults," necessitated by its rapid growth, the larva passes into the second stage, and becomes a " pupa." The insect is now perfectly quiescent, unless touched or otherwise irritated; is incapable of changing its place ; and is often attached to some foreign object. This Fig. 107. — Metamorphosis of the Magpie- moth (Phalcena grossulariata) . constitutes what — in the case of the Lepidoptera — is gene- rally known as the "chrysalis," or "aurelia" (fig. 114). The body of the pupa is usually covered by a chitinous pellicle, which closely invests the animal. In some cases (e.g., in many Dipterous insects) no traces can be detected in the pupa of the future insect ; but in the Lepidoptera the thorax and abdomen are distinctly recognisable in the pupae; whilst in others (\ imago, larva, and eggs. wings four in number, all membranous, generally nearly equal in size, traversed by numerous delicate nervures, having a longitudinal and transverse direction, and giving them a reticulated, lace-like aspect Metamorphosis generally in- complete, rarely complete. The larva active, hexapod, rarely with pro-legs. This order includes the Dragon - flies (Libellulidce), Caddis - flies (Phryganeidce}, May-flies (Ephemeridce)* the Ant - lion (Myrmeleo\ Ter- mites, &c. The last of these — namely, the Termites or White Ants — are social, and live in communities, and their hahitc IT-A cr» cinmilar tl-iof o naDltS are SO Singular that a short description of them will not be out of place here. They are mostly inhabitants of hot countries, where they are commonly known as " White Ants ; " but it must be borne in mind that they have nothing to do with the Insects commonly called Ants, which belong, indeed, to a different order (Hymenoptera). The following account is taken from Mr Bates's work on the Amazons, where there is an excellent description of the habits of these remarkable insects. Termites are small, soft-bodied insects, which live in large communities, as do the true Ants. They differ, however, from the Ants in the fact that the workers are individuals of no fully developed sex, whereas amongst the latter they are unde- veloped females. Further, the neuters of the Termites are always composed of two distinct classes or " castes " — the workers and the soldiers. Lastly, the Ants undergo a quiescent pupa-stage ; whereas the young Termites, on their emergence from the egg, do not differ from the adult in any respect except in size. Each species of Termites consists of several distinct orders or castes, which live together, and constitute populous, or- ganised communities. They inhabit structures known as * By some the Dragon-flies (Libenulidce), the May-flies (Ephemeridula cleracea). under surface of the head. Ocelli are present in addition to the compound eyes. The wings are generally horizontal and transparent, the nervures not very numerous, and for the most part longitudinally disposed. The antennae are generally small and three-jointed, sometimes many-jointed (Tipulidcf), or feathery ( Culiddce). The larva is soft and fleshy, with a soft indistinct head, usually apodal, never with thoracic legs, and rarely with pro-legs. The larval skin mostly forms a hardened case for the pupa, but the larvae sometimes cast their skin when becoming pupae, or even spin cocoons. In some the eggs are hatched within the body of the mother, so ANNULOSA : INSECTA. that the insect appears first in the larval state ; and in Pupipara not only is this the case, but the larvae continue to reside with- in the mother until they become pupae. In the Hessian Fly (Ceridomyia) the larva produces asexually a number of second- ary larvae, which are developed within the body of the primitive larva, and feed upon its tissues, ultimately causing its death. The Diptera constitute one of the largest of the orders of the Insecta; the House-flies and Flesh-flies (Musca\ Gnats (Culex), Forest-flies (Hippoboscd], Crane-flies (Ttpulidce^ and Gad-flies (Tabanidtz), constituting good examples. ORDER IX. LEPIDOPTERA. — Mouth suctorial, consisting of a spiral trunk or " antlia," composed of the greatly-elongated maxillae, and protected, when not in use, by the cushion-shaped hairy labial palpi. Maxillae forming two sub-cylindrical tubes, Fig. 114. — Large White Cabbage" Butterfly (Pontia brassicee). a Larva or caterpillar b Pupa or chrysalis ; c Imago or perfect insect. united together by inosculating hooks, and constituting an in- termediate tube by their junction. Maxillary palpi minute ; labrum and mandibles rudimentary. Head, thorax, and ab- domen more or less covered with hair. Wings, four in num- ber, covered with modified hairs or scales ; wanting in the females of a few species. Nervures not very numerous, mostly longitudinal. Antennae almost always distinct, and composed of numerous minute joints. This well-known and most beautiful of all the orders of Insects comprises the Butterflies (fig. 114) and the Moths (fig. 115) ; the former being diurnal in their habits, the latter mostly crepuscular or nocturnal. 286 MANUAL OF ZOOLOGY. The larvae of Lepidoptera (fig. 115), commonly called "cater- pillars," are vermiform in shape, normally composed of thirteen segments, the anterior portion forming a distinct horny head, with antennae, jaws, and usually simple eyes. The mouth of the caterpillar, unlike that of the perfect insect, is formed for mastication. The labium, also, is provided with a tubular organ — the " spinneret " — which communicates with two internal glands, the functions of which are to furnish the silk, whereby the animal constructs its ordinary abode 'or spins its cocoon. The three segments behind the head correspond with the pro- thorax, meso-thorax, and meta-thorax of the perfect insect, and Fig. 115. — Goat-moth (Cossus ligniperda) and Caterpillar. each carries a pair of jointed walking-legs. Besides these thoracic legs, there is a variable number (generally ten) of soft fleshy legs, which are borne by the segments of the abdomen, and are known as " pro-legs." Each is usually furnished with a crown of small horny hooks, and they are never attached to the 4th, 5th, loth, and nth abdominal segments. In the Diurnal Lepidoptera, or Butterflies proper (fig. 114), the antennae are knobbed ; the wings are usually held erect when the insect is in a state of repose ; the larvae have six ANNULOSA I INSECTA. 287 thoracic legs, and ten pro-legs ; and the pupae are always naked, attached by the posterior extremity, or head downwards, and usually angular. In the Crepuscular Lepidoptera, including those forms which are active during the twilight, the antennae are fusiform, or grow gradually thicker from the base to the apex ; the wings are horizontal or little inclined when the insect is at rest ; the posterior wings have their front margins furnished with a rigid spine (" retinaculum ") which is received into a hook on the under surface of the anterior wings ; and the pupae are never angular. The Nocturnal Lepidoptera have the antennae setaceous, or diminishing gradually from the base to the apex, often serrated or pectinated (fig. 115) ; the wings in repose are horizontal or deflexed, and the hind- wings are furnished with a "retinaculum,'' as in the preceding section ; the pupae are mostly smooth, sometimes spiny, and often enclosed in a cocoon. ORDER X. HYMENOPTERA. — Wings four, membranous, with few nervures ; sometimes absent. Mouth always provided Fig. 116. — Gooseberry Saw-fly (Tentftredo grossularue), larva, pupa, and imago. with biting-jaws, or mandibles ; the maxillae and labium often converted into a suctorial organ. Females having the ex- 288 MANUAL OF ZOOLOGY. tremity of the abdomen mostly furnished with an ovipositor (terebra or acnleus], consisting chiefly of three elongated pro- cesses, of which two serve as a sheath for the third. Besides the compound eyes, there are usually three ocelli placed on the top of the head. The antennae are generally filiform or setaceous. The metamorphosis is complete, but the various parts of the pupa are visible through the delicate enclosing mem- brane. The larvae are sometimes provided with feet, and live on vegetable food (as in the Tenthredinidce, fig. 1 16); but they are mostly footless, without a distinct head, and fed by the adult. The Hymenoptera form a very extensive order, comprising the Bees, Wasps, Ants, Ichneumons, Saw-flies (fig. Ti6), &c. The ovipositor, which is very generally present in the females of this order, is sometimes a boring organ (terebra), or in other cases a " sting " (aculeus}. Amongst the Hymenoptera we find social communities, in many respects resembling those of the Termites, of which a description has already been given. The societies of Bees and Ants are well known, and merit a short description. The social Bees, of which the common Honey-bee (Apis mellifica) is so familiar an example, form organised communities, consisting of three classes of individuals — the males, females, and neuters. As a rule, each community consists of a single female — " the queen " — and of the neuters, or " workers." The impregnation of the female is effected by the production of males, or " drones," during the summer. After impregnation has been effected, the aiunes, us being then useless, are de- stroyed by the workers. The eggs produced by the fecundated queen are mostly intended to give origin to neuters, to which end they are placed in the ordinary cells. The ova which are to give origin to females — the " queens " of future colonies — are placed in cells of a peculiar construction, and the larvae are fed by the workers with a special food. The ova which are to produce males are likewise placed in cells, which are slightly larger than those allotted to the workers. It is asserted, however, that this is not the sole or true cause of the production of the males ; but that the ova which are intended to produce drones are not fertilised by the female with the semen which she has stored up in her spermatheca, and are therefore produced by a process of Parthenogenesis. That the males are produced parthenogenically in some, at any rate, of the Hymenoptera, appears to have been placed beyond a reasonable doubt by the researches by Von Siebold. (See Introduction.) In the Humble-bees (Bombid(z\ and in the Wasps ( Vespidcz), ANNULOSA : INSECTA. 289 we have societies essentially the same as in the Honey-bee. In a large community of Wasps, or " vespiary," there may be several hundred females, of which few survive the winter, and live to found fresh colonies next spring. The number of males is about equal to that of the females, but, unlike the drones of the Bees, the males work actively and defend the nest. As amongst the Bees, solitary species are not uncommon. The Ants (Formicidce) likewise form communities, consisting of males, females, and neuters (fig. 117). The males and females, as we have seen in the case of the Termites, are winged, and are produced in great numbers at a particular period of the year. They then quit the nest and pair, after which the males die. The females then lose their wings and fall to the ground, when they become the queens of fresh societies. In some Ants, as in the Termites, the neuters are Fig. 117. — Red Ant (Myrmica ntfa\. a Winged male ; b Wingless neuter. Much magnified. divided into two classes — the workers and the soldiers — of which the former perform all the duties necessary for the pre- servation of the society except defending the nest, this being left to the soldiers. In other cases, as many as three distinct orders or " castes " of neuters may be present in the same nest. Amongst the more singular of the habits and instincts of Ants two may be mentioned — the instinct of making slaves, and that of milking, so to speak, the little Plant-lice (Aphides}. As regards the first of these, it is found that certain Ants pos- sess the extraordinary instinct of capturing the pupae of other species of Ants, and bringing them up as slaves. The rela- tions between the master and the slaves vary a good deal in different species. In the case of Formica rufescens, for instance, the masters are entirely dependent upon their slaves ; the males and females do nothing except reproducing the species, and the neuters perform no other labour except that of captur- * T 290 MANUAL OF ZOOLOGY. ing fresh slaves. The masters are in this case unable even to feed themselves, and their existence is maintained entirely by the devotion of the slaves. In Formica sanguinea, on the other hand, the number of slaves is much less, and both masters and slaves occupy themselves in performing most of the duties necessary for the community. The masters, how- ever, go alone when on slave-making expeditions ; and in case of a migration, the masters carry the slaves in their mouths. A second singular fact in the history of Ants is found in the relations which subsist between them and the Aphides, or Plant-lice. The Aphides secrete, or rather excrete, a peculiar viscid and sweet liquid, by means of a gland which is situated towards the extremity of the abdomen, and communicates with the exterior by two tubular filaments. Ants are extremely fond of this excretion, and it is a well-established fact that the Aphides allow themselves to be milked, as it were, by the Ants. For this purpose the Ant touches and caresses the abdomen of the Aphis with its antennae, whereupon the latter voluntarily exudes a drop of the coveted fluid. Ordinarily the Ants seek the Aphides upon plants ; but it is asserted that in some cases they keep Aphides, much in the same way as human beings keep cows, though this is probably partly imaginary. ORDER XI. STREPSIPTERA. — Females without wings or feet, parasitic. Males possessing the posterior pair of wings, which are large, membranous, and folded longitudinally like a fan. The anterior pair of wings rudimentary, represented by a pair of singular twisted organs. Jaws abortive. ThzStrepsiptera constitute a small order, which includes certain parasites of minute size, found on Bees and other Hymenoptera. The female is a soft vermiform grub, without feet, but with a horny head, which it pro- trudes from between the abdominal segments of its host. The larvae are active, and possess six feet \ whilst the males (fig. 118) are winged, and fly about with great activity. ORDER XI. COLEOPTERA. — Mouth masticatory, furnished with an upper lip or labrum, two mandibles, two maxillae, with maxillary palpi (generally four-jointed), and a movable lower lip Fig. 118.— Strepsiptera. Stylops Spencii, greatly magnified (after Westwood). ANNULOSA : INSECTA. 29 I or labium,with two jointed labial palpi. The four wings are usually present, and the anterior pair are not adapted for flight, but are hardened by chitine, so as to form protective cases (ely- tra) for the posterior wings (fig. 119). The inner margins of the elytra are generally straight, and when in contact they form a longitudinal suture. The posterior wings are membranous, and when not in use, are folded transversely beneath the elytra. (Amongst deviations from this state of parts may be mentioned the occasional absence or rudimentary condition of the hinder wings, the soldering together of the elytra, the soft and yielding condition of the elytra, or the absence of both elytra and wings.) The eyes are always compound, Fig. 119. — Coleoptera. Common Cockchafer (Melolonthavulgaris). generally circular, oval, or reniform, but sometimes completely divided. The antennae are extremely variable in form, gene- rally of eleven joints, sometimes of fewer, rarely of twelve. The thorax is composed of a pro- meso- and meta-thorax, but when the elytra are closed, only the pro-thorax and a little plate (" scutellum") belonging to the meso-thorax are visible. The tarsus is generally composed of five joints, sometimes fewer, never more, and its last joint is usually furnished with two hooked claws. The larvae of Coleoptera are generally composed of thirteen segments, including the head. The body is generally soft and fleshy, the head horny, and the mouth adapted for mastication. The antennae are small, usually of three or four joints, with ocelli at their base. They have three pairs of legs attached to the thorax, and sometimes anal pro-legs or fleshy tubercles. The pupa is sometimes enclosed in a cocoon, and the parts of the perfect insect are always distinctly recognisable in the pupa. The order Coleoptera includes all those insects commonly 292 MANUAL OF ZOOLOGY. known as "Beetles," and comprises an enormous number of genera and species. They are remarkable, as a general rule, for their hard polished integument, their glittering, often me- Fig. 120. — a Rose-chafer (Cetoin'a aura to) and larva ; b Vine weevil (Curculio sulcatus). tallic colour, and their voracious habits. They are grouped by Latreille in the following four sections : — 1. Pentamera. — Tarsus five-jointed. 2. Heteromera. — Tarsus of two anterior pairs of legs five- jointed, of the posterior pair four-jointed. 3. Tetramera. — Tarsus four-jointed. 4. Trimera. — Tarsus three -jointed. DISTRIBUTION OF INSECTA IN TIME. — The earliest known insects have been discovered in the Devonian Rocks of America, and consist of the remains of Neuroptera* Others, as might have been anticipated, have been found in the Coal- measures. In the Secondary Rocks remains of insects haye been found abundantly in certain beds of the Oolitic and Liassic formations. In some Tertiary strata Lepidoptera and other in- sects have been found in a good state of preservation. Amber, which is a fossil resin, has long been known to contain many insects in its interior (in certain specimens) ; and all of these appear to belong to extinct species, though amber, geologically speaking, is not an ancient product. * The Devonian Ne-uroptera of North America are most closely allied to the Ephemeridce; but one form is in many respects transitional between the orders Orthoptera and Neuroptera, Insects belonging to the Neurop- tera (viz., Miamia and Hemeristid), to the Orthoptera (Blattina), and to the Hemiptera (Eugereon), have also been described from the Carboniferous Rocks of North America. 293 MOLL USC A. CHAPTER XLI. SUB-KINGDOM MOLLUSCA. SUB-KINGDOM MOLLUSCA. — The Mollusca may be defined as in- cluding soft-bodied animals, which are usually provided with an exoskeleton. The intestinal canal is bounded by its own proper walls, and is completely shut off from the perivisceral cavity. The alimentary canal is situated between the haemal system, which lies dorsally, and the neural system, which is situated towards the ventral aspect of the body. The nervous system (fig. 121) in its highest de- velopment consists of three principal ganglia, which are reduced to one in the lower forms. Usually there is a distinct propulsive organ by which the circulation is carried on, but this is oc- casionally absent. Distinct respiratory organs may or may not be present. Re- production is sexual, though gemmation is also occa- sionally superadded. The higher Mollusca are all simple ani- mals, but many of the lower forms are capable of forming colonies by continuous gemmation. The digestive system in all the Mollusca consists of a mouth, gullet, stomach, intestine, and anus — though in some of the Brachiopoda, and in a few other forms, the intestine ends caecally. In some the mouth is surrounded by ciliated ten- tacles (Polyzoa, fig. 124); in others it is furnished with two ciliated arms (Brachiopoda, fig. 128) ; in the bivalves (Lamelli- branchiata) it is mostly furnished with four membranous pro- cesses or palpi (fig. 130) ; in others it is provided with a com- plicated apparatus of teeth (Gasteropoda, fig. 132, and Petro- Fig. 121. — Diagram of a Mollusc, a Alimen- tary canal ; k Heart ; f Foot ; n Cerebral ganglion ; «' Pedal ganglion ; n" Parieto- splanchnic ganglion. 294 MANUAL OF ZOOLOGY. poda] ; and, lastly, the Cephalopoda have, in addition, horny or calcareous mandibles, forming a kind of beak. Well-developed salivary glands are usually present ; the liver in the higher forms is of large size, and pours its secretion either into the stomach or into the commencement of the intestine ; and a renal organ has been detected in most of the Mollusca proper. There is no distinct absorbent system, but the products of digestion pass by exosmose into the general abdominal cavity, and thence into the larger veins, which are sometimes pierced by numerous round holes for this purpose. The blood is colourless, or nearly so. In the Polyzoa the circulation is carried on by ciliary action, and there is no dis- tinct propulsive organ, or definite course of the circulating fluid. In the Tunicata the heart is a simple tube, open at both ends, and the course of the circulation is periodically reversed. In the Brachiopoda the course of the circulation is not defi- nitely ascertained, and it is doubtful if a true heart is present in all. In the higher Mollusca a distinct heart is always present, and consists of an auricle which receives the aerated blood from the breathing-organ, and a muscular ventricle which propels it through the systemic vessels. That a system of capillaries in many cases intervenes between the arteries and veins, appears from recent researches to be probable. In all cases the heart of the Mollusca is systemic, distributing the aerated blood to the body, and in no case is it respiratory, propelling the non-aerated blood to the breathing-organ. In the Polyzoa there is no differentiated respiratory organ, and the function of respiration is discharged mainly by the oral crown of ciliated tentacles. In the Tunicata respiration is effected by means of the pharyngeal or branchial sac ; and in the Brachiopoda by the oral arms, and possibly, to some extent, by an "atrial" or " water-vascular " system, furnished with contractile dilatations. In the higher Mollusca a distinct breathing-organ is always present, a portion of the mantle being specialised for this purpose. In the Lamellibranchiata, and the branchiate Gasteropoda, the breathing-organs are in the form of lamellar and pectinate gills ; and the same is the case with the Cephalopoda. In the pulmonate Gasteropoda, in which respiration is aerial, a pulmonary sac or air-chamber is produced by the folding of a portion of the mantle, over the interior of which the pulmonary vessels are distributed. The chamber thus formed communicates with the exterior by a round aperture which can be opened or closed at will ; and the renovation of the effete air within the sac appears to be effected mainly or entirely by simple diffusion. MOLLUSCA : GENERAL CHARACTERS. 2Q5 The nervous system varies considerably in its development. In the Polyzoa, Tunicata, and Brachiopoda — which collectively constitute the Molluscoida — the nervous system consists of a single ganglion, or of a principal pair with accessory ganglia, placed between the oral and anal apertures, or on the ventral surface of the body. The true Molluscan type (fig. 121), how- ever, of nervous system is constituted by the presence of three pairs of ganglia, connected with one another by commissures, but distributed in a characteristically scattered manner (hetero- gangliate type). One of these ganglia is situated above the oesophagus, and is called the "supra-cesophageal " or " cerebral" ganglion. A second is placed below the oesophagus, and is termed the " infra-cesophageal " or "pedal" ganglion (from its supplying the nerves to the " foot "). The third pair is the most persistent, and is termed the " branchial " or " parieto- splanchnic " ganglion. Organs of sight exist in some of the lower, and in the majo- rity of the higher, Mollusca. In the Cephalopoda, and in some of the Gasteropoda (e.g., Strombidcz), the eyes are of a very high type of organisation. In the Lamellibranchiata the adults are either destitute of organs of vision, or possess numerous simple eyes (" ocelli ") placed along the margins of the mantle-lobes. Similar ocelli are also found in some of the Tunicata, placed between the oral tentacles. Organs of hearing exist in the more highly organised Mollusca, especially in the Gasteropoda and Cephalopoda, and supposed olfactory organs occur in some of the latter. Reproduction amongst the Mollusca is almost invariably sexual, but it is by continuous gemmation that the colonies of the Polyzoa, and the social and compound Tunicata, are pro- duced, and the " statoblasts " of the former offer a good ex- ample of non-sexual reproduction. The sexes are usually dis- tinct, but are in many cases united in the same individual. In many forms the ova are arranged in rows, so as to form a strap or ribbon-shaped structure, termed the " nidamental ribbon." As implied by their scientific name, the Mollusca are mostly soft-bodied animals ; but their popular name of " Shell-fish " expresses the fact, that the presence of a shell, protecting the soft body, is likewise a very characteristic feature in the sub- kingdom. At the same time, a shell is not universally present, and many of the Mollusca are either permanently naked, or possess nothing that would be ordinarily looked upon as a shell. When there is either no shell at all, or merely a rudi- mentary shell enclosed in the mantle, the Mollusc is said to be "naked." The shell of the "testaceous" Mollusca is very 296 MANUAL OF ZOOLOGY. closely related to the respiratory organs ; " indeed it may be regarded as a pneumoskeldon, being essentially a calcified por- tion of the mantle, of which the breathing-organ is at most a specialised part. ... In its most reduced form the shell is only a hollow cone or plate, protecting the breathing-organ and heart, as in Limax, Testacella, and Carinaria. Its peculiar features always relate to the condition of the breathing-organ, and in Terebratula and Pelonaia it becomes identified with the gill. In the Nudibranchs the vascular mantle performs, wholly or in part, the respiratory office. In the Cephalopods the shell becomes complicated by the addition of a distinct, internal, chambered portion (phragmacone), which is properly a visceral skeleton " (Woodward). In a great many of the Mollusca proper the shell consists of but a single piece, and they are called " univalves." In many others the shell consists of two separate plates or " valves," and these are called " bivalves." In others, again, as in the Chiton, the shell consists of more than two pieces, and is said to be " multivalve." Most, how- ever, of the multivalve shells of older writers are in reality referable to the Cirripedia. All the testaceous Mollusca (except the Argonaut), and most of the " naked " forms, acquire a rudimentary shell before their liberation from the ovum. In the latter this rudimentary shell is cast off as the embryo grows, but in the former it be- comes the " nucleus " of the adult shell. In the bivalves the embryonic shell or "nucleus" is situated at the beak or " umbo " of each valve, and is often very irnlike the remainder of the shell. In composition the shell of the Mollusca consists of carbon- ate of lime — usually having the atomic arrangement of calcite — with a small proportion of animal matter. In the Phola- didce, however, the calcareous matter exists in the allotropic condition of arragonite, which is very much harder than calcite. As regards their texture, three principal varieties of shells may be distinguished — viz., the " porcellanous," the "nacreous," and the " fibrous." In the " nacreous " or pearly shells, as seen in "mother-of-pearl," the shell has a peculiar lustre, due to the minute undulations of the edges of alternate layers of car- bonate of lime and membrane. The "fibrous" shells are composed of successive layers of prismatic cells. The " por- cellanous " shell has a more complicated structure, and is com- posed of three layers or strata, each of which is made up of very numerous plates, " like cards placed on edge." The direction in which the vertical plates are placed, is sometimes transverse in the central layer, and lengthwise in the two MOLLUSCA : GENERAL CHARACTERS. 297 others; or longitudinal in the middle, and transverse in the outer and inner strata. All living shells have an outer layer of animal matter, which is known as the "epidermis," or " periostracum." This is sometimes of extreme tenuity, but is sometimes very thick, the latter being especially the case with those shells which are found in fresh water. In many of the spiral univalves, as the animal grows it withdraws itself from the upper portion of the shell, often par- titioning off the space thus left vacant. In many instances the portion thus abandoned falls off, and the shell becomes " truncated," or " decollated ; " this being the normal condition in fully -grown examples of some shells. In the great majority of univalves the shell is coiled into a spiral, the direction of which is right-handed, but in some cases the spiral is left-handed, and the shell is said to be " re- versed," or " sinistral." The reversed shell may occur as the normal condition of the species, or it may occur simply as a variety of a form which is normally right-handed, or " dextral." The sub-kingdom Mollusca is divided into two great divi- sions, termed respectively the Molluscoida^ and the Mollusca proper. In the former of these the nervous system consists of a single ganglion or principal pair of ganglia, and there is either no circulatory organ or an imperfect heart. In the latter the nervous system consists of three principal pairs of ganglia, and there is a well-developed heart, consisting of at least two chambers. 298 MOLL USCO I D A. CHAPTER XLII. POLYZOA. DIVISION A. MOLLUSCOIDA. — Nervous system consisting of a single ganglion, or of a principal pair with accessory ganglia; no distinct organ of the circulation, or an imperfect heart. This division includes three classes — viz., the Polyzoa, the Tunicata, and the Brachiopoda. CLASS I. POLYZOA (Bryozod). — The members of this class are defined as follows: — " Alimentary canal suspended in a double-walled sac, from which it may be partially protruded by a process of evagination, and into which it may be again retracted by invagination. Mouth surrounded by a circle or crescent of hollow, ciliated tentacles ; animals always forming composite colonies " (Allman). All the Polyzoa live in an associated form in colonies or " polyzoaria," which are sometimes foliaceous (fig. 122), some- times branched and plant-like, sometimes encrusting, and very rarely are free. Each " polyzoarium " consists of an assem- blage of distinct but similar zooids arising by continuous gem- mation from a single primordial individual. The colonies thus produced are in very many respects closely similar to those of . many of the Hydroid Polypes, with which, indeed, the Polyzoa were for a long time classed. The "polyzoarium," however, of a Polyzoon differs from the polypidom of a composite Hy- droid in the general fact that the separate cells of the former do not communicate with one another otherwise than by the continuity of the external integument ; whereas the zooids of the latter are united by an organic connecting medium, or " ccenosarc," from which they take their origin. On this point Mr Busk observes : — "It has been before said that the Polyzoa are always asso- ciated into compound growths, made up of a congeries of in- dividuals, which, though distinct, yet retain some degree of MOLLUSCOIDA I POLYZOA. 299 intercommunication, comparable in kind perhaps, though not in degree, to what obtains in many of the compound Ascidians. That this community exists is proved by the otherwise inex- plicable circumstance that the polyzoaria in many instances present elements common to the whole growth, and not be- longing specially to any individual. The chief bond of con- nection would appear to reside partly in the continuity of the external integument, and partly also, in all probability, in a slow interchange of the vital fluid with which the cavities of the cells are charged." Fig. 122. — Flustra foliacea, one of the Sea-mats, a Portion of the colony, natural size ; b A fragment magnified, to show the cells in which the separate polypides are contained. In one sub-order of the Polyzoa (Ctenostomata,} the polyzo- arium consists of a series of cells arising from a common tube, but this exception does not affect the value of the above general distinction between the Polyzoa and the Hydroida. A second point of difference is found in the invariably cor- neous (or chitinous) texture of the polypidoms of the Hydroida, whereas those of the Polyzoa may be corneous or fleshy, but 300 MANUAL OF ZOOLOGY. are in the majority of instances more or less highly charged with carbonate of lime. The homomorphism, however, which subsists between the Polyzoa and the Hydroida is shown most decisively not to be a true affinity, when the structure of the individual zooids is examined. The polypite of a Hydroid Zoophite, as we have already seen, possesses no alimentary canal distinct from the general cavity of the body ; there are no traces of a nervous system, and the reproductive organs are in the form of exter- nal processes of the body-wall. In the zooid of all the Polyzoa (fig. 123, 2), on the other hand, there is a distinct alimentary canal, completely shut off from the somatic cavity ; a nervous system is present, and the reproductive organs are contained within the body. The following are the more important differences in the ter- minology employed to designate the various parts of the com- pound growths of the Polyzoa and the Hydrozoa. In the Hydroida the entire colony is called the " hydrosoma,'; and its investing layer, when present, is called the " polypary," or " polypidom ;" whilst the individuals composing the hydrosoma are called the " polypites," and the cups in which these are in some cases contained are called " hydrothecae." In the Polyzoa the entire colony — or its entire dermal system — is called the " polyzoarium " or " ccencecium ; " the separate zooids a.re called "polypides;" and the little chambers in which each is contained are called the " cells." It will be seen, therefore, that the term polypite is restricted to the zooid of a compound Hydrozoon, or to the entire hydro- soma of a simple member of the class. The term polype is applied to a simple Actinozoon, or to the zooids of a compound actinosoma. Lastly, the tercn. polypidt is exclusively employed to designate the zooid of one of the Polyzoa. The construction of a typical polypide of a Polyzob'n is thus described by Professor Allman (fig. 123, 2) : — " Let us imagine an alimentary canal, consisting of oeso- phagus, stomach, and intestine, to be furnished at its origin with long ciliated tentacula, and to have a single nervous gan- glion placed upon one side of the oesophagus. Let us now suppose this canal to be bent back upon itself towards the side of the ganglion, so as to approximate the termination to the origin. Let us further imagine the digestive tube thus constituted to be suspended in a fluid contained in a mem- branous sac with two openings, one for the mouth and the other for the vent, the tentacula alone being external to the sac. Let us still further suppose the alimentary tube, by means MOLLUSCOIDA : POLYZOA. 301 of a system of muscles, to admit of being retracted or pro- truded according to the will of the animal ; the retraction being accompanied by an invagination of the sac, so as par- tially or entirely to include the oral tentacles within it ; and if to these characters we add the presence of true sexual organs in the form of ovary and testis, occupying some portion of the interior of the sac, and the negative character of the absence of all vestige of a heart, we shall have, perhaps, as correct an idea — apart from all considerations of homology or deriva- tion from an archetype — as can be conveyed of the essential structure of a Polyzoon in its simplest and most generalised condition. Fig. 123. — Morphology of Polyzoa. i. Portion of the ccencecium of Flustra. truttcata, magnified. 2. Diagram of a Polyzoon (after Allman) : a Region of the mouth surrounded by tentacles; b Alimentary canal; c Anus; d Nervous ganglion; e Investing sac (ectocyst) ; f Testis ; _/' Ovary ; g Retractor muscle. 3. Bird's-head process, or "avicularium," of a Polyzoon. "To give, however, more actuality to our ideal Polyzoon, we may bear in mind that the immediately investing sac has the power, in almost every case, of secreting from its external surface a secondary investment, of very various constitution in the different groups ; and we may, moreover, conceive of the entire animal with its digestive tube, tentacula, ganglion, muscles, generative organs, circumambient fluid, and investing sacs, repeating itself by gemmation, and thus producing one or more precisely similar systems, holding a definite position relatively to one another, while all continue organically united, 3O2 MANUAL OF ZOOLOGY. and we shall then have the actual condition presented by the Polyzoa in their fully-developed state/' The vast majority of the Polyzoa are fixed, but this is not universally the case. Thus the singular fresh-water Cristatella is free and locomotive, creeping about by means of a flattened discoid base, not unlike the foot of the Gasteropoda. The two fundamental structures of the " ccencecium " of a Polyzoon — viz., the immediately investing sac, and its secon- dary investment — are sometimes termed the " endoderm " and " ectoderm ; " but as these terms are employed in describing the Hydrozoa, it is better to make use of the terms " endocyst " and " ectocyst," proposed by Dr Allman. The " ectocyst," or external investment of the coenoecium, is usually a brown, pergamentaceous. probably chitinous, but often highly calcareous, membrane ; and it is by the ectocyst that the " cells n are formed. In Cristatella, alone of the Polyzoa, there is no ectocyst, and in Lophopus (fig. 124, 3) the ectocyst is gelatinous in its consistence. In many cases the ectocyst is provided with singular appendages, supposed to be weapons of offence and defence, termed " avicularia " (fig. 123, 3) and "vibracula." The avicularia, or "bird's head processes," differ a good deal in shape, but consist essentially of " a movable mandible and a cup furnished with a horny beak, with which the point of the mandible is capable of being brought into apposition " (Busk). In shape the avicularia often closely resemble the head of a bird, and they are in many respects comparable with the " pedicellariae " of the Echinoder- mata* In the "vibracula," the place of the mandible of the avicularium is taken by a bristle, or seta, which is capable of extensive movement. The endocyst is always soft, contractile, and membranous. It lines the interior of the cells formed by the ectocyst, and is reflected backwards at the mouth of the cell, so as to be inva- ginated, or inverted into itself; and it finally terminates by being attached to the base of the circlet of tentacles. This invagination of the endocyst is more or less permanently pre- sent in all the fresh-water Polyzoa. A portion of the inner surface of the endocyst, if not the whole, is furnished with vibratile cilia. The mouth of each polypide is surrounded by a crown of * There is great reason, however, as shown by Huxley, to regard the avicularia, not as mere appendages or organs of any kind, but as peculiarly- modified zooids, having many singular points of affinity with the Brachio- poda. The avicularia, like the pedicellarice of the Echinodermata, continue their movements long after the death of the animal. MOLLUSCOIDA I POLYZOA. 303 tubular, non-retractile tentacles, which have their sides ciliated, and are arranged sometimes in a circle and sometimes in a crescent. In the fresh-water Polyzoa the tentacles are united towards their bases by a funnel-shaped membrane, known as the " calyx." The tentacles are borne upon a kind of disc, or stage, which is termed by Professor Allman the " lophophore." In the majority of Polyzoa — including almost all the marine species — the lophophore is circular (fig. 124, 2) ; but in most of the fresh-water forms it has its neural side extended into two long arms, so that the entire lophophore becomes crescentic or " horse-shoe-shaped " (fig. 124, 3); hence this section is Fig. 124. — i. Fragment of Flustra iruncata, one of the Sea-mats, natural size. 2. A single polypide of Valkeria, magnified, showing the ortrcular crown of tentacles. 3. A polypide of Lophopus crystallinus, a fresh-water Polyzoon, highly magnified, showing the horse-shoe-shaped crown of tentacles : a Tentacular crown ; b Gullet ; c Stomach ; d Intestine ; e Anus ; g Gizzard ; k Endocyst ; / Ectocyst ; f Funiculus. sometimes collectively termed the " Hippocrepian " Polyzoa. In all, or almost all, the Polyzoa in which this crescentic con- dition of the lophophore exists, there is also a singular valve- like organ which arches over the mouth, and is termed the " epistome." The only marine forms in which the lophophore is bilateral are Pedicellina and Rhabdopletira ; the only fresh- water species in which the lophophore is orbicular are Paludi- cella and Urnatella. The mouth conducts by an oesophagus into a dilated stomach. In some cases a pharynx may be present, and in others there 304 MANUAL OF ZOOLOGY. is in front of the stomach a muscular proventriculus, or giz- zard. From the stomach proceeds the intestine, which shortly turns forward to open by a distinct anus close to the mouth. As the nervous ganglion is situated on that side of the mouth towards which the intestine turns in order to reach its termina- tion, the intestine is said to have a "neural flexure;" and this relation is constant throughout the entire class. Respiration in the Polyzoa appears to be carried on by the ciliated tentacles, and by the " perigastric space," which is filled with a clear fluid, containing solid particles in suspen- sion. A kind of circulation is kept up in this "perigastric fluid" by means of the cilia lining the inner surface of the endocyst. Beyond this there is nothing that could be called a circulation, and there are no distinct circulatory organs of any kind. The nervous system in all the Polyzoa consists of a single small ganglion (fig. 123, 2), placed upon one side of the oeso- phagus, between it and the anal aperture. Besides the single ganglion which belongs to each polypide, there is also in many, if not in all of the Polyzoa, a " colonial nervous system ; " that is to say, there is a well-developed nervous system, which unites together the various zooids composing the colony, and brings them into relation with one another. It is probably in virtue of this system that the avicularia are enabled to con- tinue their movements, and retain their irritability after the death of the polypides. The muscular system is well developed, and consists of various muscular bands, with special functions attaching to each. The most important fasciculi are the retractor muscles (fig. 123, 2, £•), which retract the upper portion of the polypide within the cell. These muscles arise from the inner surface of the endocyst near the bottom of the cell, and are inserted into the upper part of the oesophagus. The polypide, when re- tracted, is again exserted, chiefly by the action of the "parietal muscles," which are in the form of circular bundles running transversely round the cell. As far as is known, all the Polyzoa are hermaphrodite, each polypide containing an ovary and testis (fig. 123, 2). The ovary is situated near the summit of the cell, and is attached to the inner surface of the endocyst. The testis is situated at the bottom of the cell, and a curious cylindrical appendage, called the " funiculus," usually passes from it to the fundus of the stomach. There are no efferent ducts to the reproductive organs ; and the products of generation — i.e., the spermatozoa and ova — are discharged into the perigastric space, where MOLLUSCOIDA I POLYZOA. 305 fecundation takes place ; but it is not certainly known how the impregnated ova escape into the external medium. As already mentioned, continuous gemmation occurs in all the Polyzoa, the fresh zooids thus produced remaining attached to the organism from which they were budded forth, and thus giving rise to a compound growth. A form of discontinuous gemmation, however, occurs in many of the Polyzoa, in which certain singular bodies, called " statoblasts," are developed in the interior of the polypide. The statoblasts are found in certain seasons lying loose in the perigastric cavity. In form " they may be generally described as lenticular bodies, varying, according to the species, from an orbicular to an elongated-oval figure, and enclosed in a horny shell, which consists of two concavo-convex discs united by their margins, where they are further strengthened by a ring which runs round the entire margin, and is of different struc- ture from the discs. . . . When the statoblasts are placed under circumstances favouring their development, they open by the separation from one another of the two faces, and' there then escapes from them a young Polyzoon, already in an advanced stage of development, and in all essential respects resembling the adult individual in whose cell the statoblasts were produced" (Allman). The statoblasts are formed as buds upon the " funiculus " — the cord already alluded to as extending from the testis to the stomach — upon which they may usually be seen in different stages of growth. They do not appear to be set free from the perigastric space prior to the death of the adult, and when liberated they are enabled to float near the surface of the water, in consequence of the cells of the marginal ring, or " annulus," being spongy and filled with air. They must be looked upon as "gemma pecu- liarly encysted, and destined to remain for a period in a qui- escent or pupa-like state " (Allman). As regards the development of the Polyzoa, the embryo upon its emergence from the ovum presents itself as a ciliated, free-swimming, sac-like body, from which the polypide is sub- sequently produced by a process of gemmation. In the sin- gular Rhabdopleura the primitive bud is enclosed between two fleshy lobes or valve-like plates, attached along their dorsal margin, and giving exit in front to the rudimentary lophophore. As the development proceeds, these plates cease to keep pace in their growth with the rest of the bud ; till ultimately they appear as a peculiar shield-like organ on the haemal side of the lophophore. These lobes have been compared by Dr Allman with the mantle-lobes of the Lamellibranchiata. U 306 MANUAL OF ZOOLOGY. DIVISIONS OF THE POLYZOA. — The Polyzoa are Divided into two divisions or orders — the Phylactol&mata (fig. 124, 3), dis- tinguished by the possession of a bilateral horse-shoe-shaped lophophore, and of an " epistome " arching over the mouth ; and the Gymnol&ntata (fig. 124, 2), in which the lophophore is orbicular, and there is no epistome. TABLE OF THE DIVISIONS OF THE POLYZOA. ORDER I. PHYLACTOL^EMATA. Lophophore bilateral ; mouth with an epistome. Sub-order I. Lophopea (fresh-water). Arms of lophophore free or obsolete ; consistence horny, sub-cal- careous. Sub-order 2. Pedicellinea (marine). Arms of lophophore united at their extremities ; consistence soft, fleshy. Sub-order 3. Rhabdopleiirea (marine). Coencecium branched, adherent, membranous, with a solid chili- nous rod on its adherent side, to which the polypites are attached by their funiculi. Lophophore completely hippocrepian, with a peculiar shield-like body on its haemal side. No epistome (?). ORDER II. GYMNOL^EMATA. Lophophore orbicular, or nearly so ; no epistome. Sub-order 4. Paludicellea (fresh-water). Polypide completely retractile ; evagination of tentacular sheath imperfect ; consistence horny or sub-calcareous. Sub-order 5. Cheilostomata (marine). Polypide completely retractile ; evagination perfect ; orifice of cell sub-terminal, of less diameter than the cell, and usually closed with a movable lip or shutter, sometimes by a contractile sphincter ; cells not tubular ; consistence calcareous, horny, or fleshy. Sub-order 6. Cyclostomata (marine). Cell tubular ; orifice terminal, of the same diameter as the cell, without any movable apparatus for its closure; consistence cal- careous. Sub-order 7. Ctenostomata (marine). Orifice of the cell terminal, furnished with a usually setose fringe for its closure ; cells distinct, arising from a common tube ; consist- ence horny or carnose. CHAPTER XLIII. TUN 1C AT A. CLASS II. TUNICATA (Ascidioida). — The members of this class of the Molluscoida are defined as follows : — Alimentary canal suspended in a double-walled sac, but not capable of protru- MOLLUSCOIDA : TUNICATA. 307 sion and retraction ; mouth opening into the bottom of a respiratory sac, whose walls are more or less completely lined by a network of blood-vessels " (Allman). Animal simple or composite. An imperfect heart in the form of a simple tube open at both ends. The Tunicaries are all marine, and are protected by a lea- thery, elastic integument, which takes the place of a shell. In appearance a solitary Ascidian (fig. 125), may be compared to a double-necked jar with two prominent apertures situated close to one another at the free extremity of the animal, one of these being the mouth, whilst the other serves as an excre- tory aperture. The covering of an Ascidian is composed of two layers. Of these the outer is called the "external tunic," h- Fig. 125. — Morphology of Tunicata. i. Diagram of a Tunicary (after Allman) : a Oral aperture ; b Atrial aperture ; c Pharyngeal or branchial sac, with its rows of ciliated apertures ; d Alimentary canal, with its haemal flexure ; e Anus ; f Atrium ; g Ner- vous ganglion. 2. Cynilua papillosa, a simple Ascidian (after Woodward). or " test," and is distinguished by its coriaceous or cartilaginous consistence. It is also remarkable for containing a substance which gives the same chemical reactions as cellulose, and is probably identical with this characteristic vegetable product. The test is lined by a second coat, which is termed the " second tunic," or " mantle," and which is mainly composed of longi- tudinal and circular muscular fibres. By means of these the animal is endowed with great contractility, and has the power of ejecting water from its branchial aperture with considerable force. The mantle lines the test, but is only slightly and loosely attached to it, especially near the apertures. The mouth is generally surrounded by a circlet of small, non-ciliated, 308 MANUAL OF ZOOLOGY. non-retractile tentacles, and opens into a large chamber (fig. 125, i, c), which usually occupies the greater part of the cavity of the mantle, and has its walls perforated by numerous aper- tures. This is known variously as the " pharynx," the " respi- ratory sac," or the " branchial sac." (It must be remembered that the aperture here spoken of as the mouth can only be looked upon in this light provided that the respiratory sac is looked upon as the pharynx. By Professor Allman, whose definition is given at the head of this chapter, this view is not accepted, and consequently the internal or inferior opening of the respiratory sac is regarded as the true mouth.) Inferiorly the respiratory sac leads by a second aperture into an oeso- phagus, which opens into a capacious stomach. From the stomach an intestine is continued, generally with few flexures, to the anal aperture, which does not communicate directly with the exterior, but opens into the bottom of a second cham- ber, which is called the "cloaca" (fig. 125, i,/). Superiorly the cloaca communicates with the external medium, by means of the second aperture in the test. The first bend of the intestine is such that, if continued, it would bring the anus on the opposite side of the mouth to that on which the nervous ganglion is situated. The intestine, therefore, is said to have a " haemal flexure ; " whereas the flexure in the case of the Polyzoa is "neural." The intestine, however, in the Tunicata does not preserve this primary haemal flexure, but is again bent to the neural side of the body, the nervous ganglion coming finally to be situated between the mouth and the rectum. As just stated, the anus is not in direct communication with the exterior, but opens into a large cavity, called the " cloaca," or " atrial chamber," which, in turn, opens externally by the second aperture of the animal. This cloaca is a large sac lined by a membrane which " is reflected like a serous sac on the viscera, and constitutes the ' third tunic/ or ' peritoneum.' " From the cloaca " it is reflected over both sides of the pharynx," (respiratory sac), " extending towards its dorsal part very nearly as far as that structure which has been termed the ' en- dostyle.' It then passes from the sides of the pharynx to the body-walls, on which the right and left lamellae become con- tinuous, so as to form the lining of the chamber into which the second aperture leads, or the ' atrial chamber.' Posteriorly, or at the opposite end of the atrial chamber to its aperture, its lining membrane (the ' atrial tunic ') is reflected to a greater or less extent over the intestine and circulatory organs. . . . Where the 'atrial tunic' is reflected over the sides of the pharynx, the two enter into a more or less complete union. MOLLUSCOIDA I TUNICATA. 309 and the surfaces of contact become perforated by larger or smaller, more or less numerous, apertures. Thus the cavity of the pharynx acquires a free communication with that of the atrium ; and as the margins of the pharyngo-atrial apertures are fringed with cilia working towards the interior of the body, a current is produced, which sets in at the oral aperture and out by the atrial opening, and may be readily observed in a living Ascidian ;' (Huxley). As regards some points in the above description, Professor Allrnan does not agree with Huxley, but believes, on the other hand, " that the walls of the atrium simply surround the branchial sac, without being reflected on its sides, and that the branchial sac is therefore properly within the cavity of the atrium." In structure, the pharyngeal or " branchial " sac is composed of a- series of longitudinal and transverse bars, which cross each other at right angles, and thus give rise to a series of quadrangular meshes, the margins of which are fringed with vibratile cilia. These bars are hollow, and are really vessels which open on each side into two main longitudinal sinuses, the so-called " branchial " or " thoracic " sinuses — one of which is placed along the haemal side of the pharynx, whilst the other runs along its neural aspect. The function of the entire perforated pharynx is clearly respiratory. The Tunicata possess a distinct heart, consisting of a simple muscular tube, which is open at both ends, and is not provided with valves. In consequence of this, the circulation in the majority of Tunicaries is periodically reversed, the blood being propelled in one direction for a certain number of con- tractions, and being then driven for a like period in an oppo- site direction ; " so that the two ends of the heart are alter- nately arterial and venous." The nervous system consists of a single ganglion placed on one side of the oral aperture, between it and the anus, in all known Tunicata, except in the aberrant form Appendicularia. The only organs of sense are pigment-spots, or ocelli, placed between the oral tentacles, and an auditory capsule, some- times containing an otolith. These organs, however, do not appear to be constantly present. With the exception of Doliolum and Appendicularia, all the Tunicata are hermaphrodite. Mr Saville Kent, however, is of opinion that Appendicularia is the free reproductive zooid of an Ascidian, bearing to the adult the same relation that the Medusae do to the Hydroid colony. The reproductive organs are situated in the fold of the intestine, and their efferent duct 31O MANUAL OF ZOOLOGY. opens into the atrium. The embryo Tunicate is at first gene- rally free, and is mostly shaped like the tadpole of a frog, swimming by means of a long caudal appendage. In one species (Molgula tubulosa) the larval form is destitute of a tail, inactive, and amoeboid, and it almost immediately, attaches itself by means of little outward processes which it develops. Lastly, in several instances the larval caudal appendage has been shown to exhibit a cylindrical rod-like body, which has been paralleled with the chorda dorsalis of Vertebrates. The body in question is a kind of cellular rod, which agrees with the notochord of Vertebrates in giving insertion by its sheath to muscles, and which holds an analogous position to the nervous system. Amongst the Salpians a species of alternation of generations has been' observed. A solitary Salpian produces long chains of embryos, which remain organically connected throughout their entire life. Each individual of these associated speci- mens produces solitary young, which are often very unlike their parents, and these again give rise to the aggregated forms. The Tunicata are often spoken of as exhibiting thre^ main types of structure, which give origin to as many sections, known respectively as the solitary, the social, and the compound forms. In the " solitary " Tunicaries, the individuals, however produced, remain entirely distinct, or, if not so primitively, they become so. In the "social" Ascidians the organism consists of a number of zooids, produced by gemmation and permanently connected together by a vascular canal, or "stolon," composed of a prolongation of the common tunic, through which the blood circulates. Finally, in the " compound" forms, the zooids become aggregated into a common mass, their tests being fused together, but there being no internal union. The Botrylli, which are familiar examples of the compound Tuni- cates, form semi-transparent masses, often of brilliant colours, attached to various submarine objects, and consisting of numerous zooids arranged in star-shaped groups. They are almost always " very small, soft, irritable, and contractile, changing their form with the slightest movement " (Stark). HOMOLOGIES OF THE TUNICATA. — The general resemblance between a solitary Ascidian and a single polypide of a Polyzoon is extremely obvious ; each ^consisting of a double-walled sac, containing a freely suspended alimentary canal, with a distinct mouth and anus, and a nervous ganglion placed between the two. The chief feature in the Tunicata, as 'to the exact nature of which there is much difference of opinion, is the branchial or respiratory sac. By Professor Allman this is "believed to be MOLLUSCOIDA I TUNICATA. 3 I I truly homologous with the tentacular crown of the Polyzoa, and the oral tentacles of the Tunicaries are believed to be something superadded, and not represented at all in the Poly- zoa. fBy Professor Huxley, on the other hand, the branchial sac is looked upon as an enormously developed pharynx, and the oral tentacles are regarded as a rudimentary representative of the tentacular crown of the Polyzoa. Probably the most correct view of the homologies of the Tunicata is taken by Rolleston, who regards the " branchial sac " as the homologue of the gills of the ordinary Bivalve Molluscs (Lamdlibranchiata), whilst the oral and atrial apertures are looked upon as corre- sponding to the respiratory apertures of these same animals. DIVISIONS OF THE TUNICATA. — By Professor Huxley the following arrangement of the Tunicaries is adopted : — CLASS TUNICATA. Order I. A scidia Branchialia. Branchial sac occupying the whole, or nearly the whole, length of the body ; intestine lying on one side of it. (Ascidiada, Botryllus, dry.) Order II. A scidia Abdominalia. Alimentary canal completely behind the branchial sac, which is comparatively small. (Clavellina, Doliolum, Order III. A scidia Larvalia. Permanent larval form. (Appendicularia.} The following subdivisions are those adopted by Mr Wood- ward : — CLASS TUNICATA. Fam. I. Ascidiada (Simple Ascidians). Animal simple, fixed, solitary, or gregarious ; oviparous ; sexes united ; branchial sac simple ; or disposed in (8- 1 8) deep and regular folds. Fam. II. ClceuettinicUt (Social Ascidians). Animal compound, fixed ; individuals connected by creeping tubular prolongations of the common tunic through which the blood circulates (or by a common gelatinous base). Reproduction effected by ova, or by gemmation from the common tube ; the new individuals remaining attached to the parent, or becoming completely free. Fam. III. Botryllidtz (Compound Ascidians). Animals compound, fixed, their tests fused, forming a common mass in which they are imbedded in one or more groups. Individuals not connected by any internal union ; oviparous and gemmiparous. Fam. IV. Pyrosormda. Animal compound, free and oceanic. Fam. 'V. Salpidcz. Animals free and oceanic ; alternately solitary and aggregated. 312 MANUAL OF ZOOLOGY. CHAPTER XLIV. BRACHIOPODA. CLASS III. — BRACHIOPODA (Palliobranchiata). — The members of this class are defined by the possession of a body protected by a bivalve shell, which is lined by an expansion of the in- tegument, or " mantle." The mouth is furnished with two long cirriferous arms. The nervous system consists of a single ganglion, placed in the re-entering angle between the gullet and the rectum, so that the intestine has a " neural flexure.'7 The Brachiopoda are essentially very similar in structure to the Polyzoa, from which they are distinguished by the fact that they are never composite, and by the possession of a bivalve, calcareous, or sub-calcareous shell. They are commonly known as " Lamp-shells," and are all inhabitants of the sea. All the living forms are fixed to some solid object in their adult condi- tion ; but there is good reason to believe that many of the Fig. 126. — Rhynchonella sn>cata. A, Profile view. B, View of the dorsal surface. C, View of the base, a Ventral valve ; b Dorsal valve ; f Base ; c Beak ; h. Foramen. Lower Cretaceous. fossil forms were unattached and free in their fully-grown con- dition. From the presence of a bivalve shell, the Brachiopods have often been placed near the true bivalve Mollusca (the Lamellibranchiata) but their organisation is very much inferior, and there are also sufficient differences in the shell to justify their separation. The two valves of the shell of any Brachiopod (fig. 126) are articulated together by an apparatus of teeth and sockets, or are kept in apposition by muscular action alone. One of the valves is always slightly, sometimes greatly, larger than the other, so that the shell is said to be " inequivalve." As regards the contained animal, the position of the valves is anterior and posterior, so that they are therefore termed respectively the u ventral " and " dorsal " valves. In the ordinary bivalve MOLLUSCOIDA I BRACHIOPODA. 313 Mollusca (Lamellibranchiatd), on the other hand, the two valves of the shell are usually of the same size (equivalve), and they are situated upon the sides of the animal ; so that, instead of being dorsal and ventral, they are now termed "right" and " left " valves. The ventral valve in the shell of the Brachio- poda is usually the largest, and usually possesses a prominent curved beak. The beak (fig. 126) is sometimes perforated by a "foramen," or terminal aperture, through which there is trans- mitted a muscular peduncle, whereby the shell is attached to some foreign object. In some cases, however (as in Lingula, fig. 127), the peduncle simply passes between the apices of the valves, and there is no foramen ; whilst in others (as in Crania) the shell is merely at- tached by the substance of the ventral valve. The dorsal or smaller valve is always free, and is never perforated by a foramen. In intimate structure, the shell of most of the Brachiopoda consists " of flattened prisms, of considerable length, arranged parallel to one another with great regularity, and at a very acute -angle — usually only about 10° or 1 2° — with the surfaces of the shell " (Carpen- ter). In most cases, also, the shell is perfo- rated by a series of minute canals, which pass from one surface of the shell to the other, in a more or less vertical direction, usually widen- ing as they approach the external surface'. These canals give the shell a " punctated " structure, and in the living animal they con- tain caecal tubuli, or prolongations, from the mantle, which are considered by Huxley as Fis- I27-— Lingula. analogous to the vascular processes by which in many Ascidians the muscular tunic, or " mantle," is attached to the outer tunic, or " test." In some of the Brachiopoda (as in the Rhynchondlida) the shell is " impunctate," or is devoid of this singular canal system. The inner surface of the valves of the shell is lined by expansions of the integument which secrete the shell, and are called the "lobes " of the " pallium," or "mantle." The diges- tive organs and muscles occupy a small space near the beak of the shell, which is partitioned off by a membranous septum, which is perforated by the aperture of the mouth. The re- mainder of the cavity of the shell is almost filled by two long anatina, showing the muscular ped- uncle by which the shell is attached. 314 MANUAL OF ZOOLOGY. oral processes, which are termed the " arms," and from which the name of the class has been derived (fig. 128, i). These organs are lateral prolongations of the margins of the mouth, usually of great length, closely coiled up, and fringed on one side with lateral processes, or " cirri." In many Brachiopods the arms are supported upon a more or less complicated inter- nal calcareous framework or skeleton, which is sometimes called the " carriage -spring apparatus." The mouth conducts by an oesophagus into a distinct stomach, surrounded by a well-developed granular liver. The intestine has a " neural flexure," and " either ends blindly in the middle line, or else terminates in a distinct anus between the pallial lobes " (Huxley). Within the pallial lobes there is a remarkable system of more or less branched tubes, anastomising with one another, and ending in caecal extremities. This, which has been termed by Huxley the " atrial system," communicates with the peri- Fig. 128. — Brachiopoda (Terebrattda vitrea). i. Showing the ciliated 2. Showing the shell with its loop. (After Woodward.) arms visceral cavity by means of two or four organs which are called " pseudo-hearts," and which were at one time supposed to be true hearts. " Each pseudo-heart is divided into a narrow, elongated, external portion (the so-called ' ventricle '), which communicates, as Dr Hancock has proved, by a small apical aperture, with the pallial cavity ; and a broad, funnel-shaped, inner division (the so-called * auricle ') communicating, on the one hand, by a constricted neck, with the so-called ' ventricle ; ' and, on -the other, by a wide, patent mouth, with a chamber which occupies most of the cavity of the body proper, and sends more or less branched diverticula into the pallial lobes " (Huxley). This system of the atrial canals has been looked upon as a rudimentary respiratory apparatus ; but its function is more probably to act as an excretory organ, and also to convey away the reproductive elements, the organs for which are developed in various parts of its walls. By Woodward MOLLUSCOIDA : BRACHIOPODA. 3 I 5 the pseudo-hearts are regarded as oviducts, and it is stated that they have been found to contain mature ova, so that there can be little doubt but that this view of their nature is the correct one. By Rolleston the pseudo-hearts are looked upon as corresponding with the so-called " organ of Bojanus" of the Lamellibranchiata. The function of respiration is probably performed, mainly, if not entirely, by the cirriferous oral arms, as it appears chiefly to be by the homologous tentacular crown of the Polyzoa. A true vascular system and a distinct heart are present in some, at any rate, of the Brachiopoda, but this subject is still involved in considerable obscurity. In Terebratula the heart is in the form of a unilocular, pyriform vesicle, placed on the dorsal surface of the stomach. The nervous system consists of a principal ganglion of no great size, placed in the re-entering angle between the gullet and the rectum. In those Brachiopods in which the valves of the shell are united by a hinge, the nervous system attains a greater development, and consists of a gangliated cesophageal collar. The sexes are said to be ordinarily distinct, but in some cases they appear to be united in the same individual. The development of the Brachiopoda is still shrouded in consider- able obscurity, but in some cases the young have been observed to move from place to place, either by protruding their ciliated arms, or by means of spines developed in the ventral lobe of the mantle. As regards the development of Terebratulina septentrionalis, the changes observed by Mr Morse show the close affinity which subsists between the Brachiopoda and the Polyzoa. The arms, namely, in this species commence as a series of ciliated tentacles placed round the mouth, most strik- ingly similar to the lophophore of such a Polyzoon as Pedicellina. The lophophore becomes horse-shoe-shaped, and the "arms" are finally produced by the growth and development of the free ends of the horse-shoe. The Brachiopoda may be divided into two groups, called respectively the Articulata and Inarticulata. In the former the valves of the shell are united along a hinge-line, the lobes of the mantle are not completely free, and the intestine ends cascally. In this group are the recent Tcrebratulida and Rhyn- chonellidce. In the Inarticulata the valves of the shell are not united along a hinge- line, the mantle-lobes are completely free, and the intestine terminates in a distinct anus. In this group are the Craniadce, Discinidcz, and Lingulida, AFFINITIES OF THE BRACHIOPODA. — There can be no ques- 3 I 6 MANUAL OF ZOOLOGY. tion as to the close relationships subsisting between the Brachio- poda and Polyzoa, and until recently most naturalists held that both these groups had strongly-marked affinities with the La- mellibranchiata. This view is still held by the generality of naturalists ; but recently Mr Edward Morse has brought forward evidence to show that the Brachiopoda and Polyzoa are most nearly related to the Tubicolar Annelidas ; and this opinion has been previously advanced as regards the latter group by Leuckhart. Amongst the more striking facts adduced in sup- port of this view may be mentioned the assertion that the long and worm-like peduncle of Lingula pyramidata is normally encased in a sand-tube resembling that of a Tubicolous Anne- lide. The peduncle of this form is also contractile and hollow, admitting the blood into its interior, and the blood is stated to be red. In the meanwhile, however, the affinities between the Trachiopoda and Polyzoa, on the one hand, and the Tunicata on the other, are too strong to allow of our unhesitating accept- ance of this sweeping change. CLASSIFICATION OF THE BRACHIOPODA (AFTER DAVIDSON). CLASS BRACHIOPODA. Fam. I. Terebratulida. Shell minutely punctate ; ventral valve with a prominent beak per- forated by a foramen for the emission of a muscular peduncle, whereby the animal is fixed to some solid object. Foramen partially surrounded by a deltidiutn of one or two pieces. Oral appendages entirely or partially supported by calcified processes, usually in the form of a loop, and always fixed to the dorsal valve. Genera. — Terebratula (with Terebratulina and Waldheimia), Tere- bralella.) Stringocephalus, &c. Fam. II. Thecidid(e. Shell fixed to the sea-bottom by the beak of the larger or ventral valve ; structure punctated. Oral processes united in the form of a bridge over the visceral cavity ; cirrated arms folded upon themselves, and supported by a calcareous loop. Genus. — Thecidium. Fain. III. Spiriferidtz. Animal free, or rarely attached by a muscular peduncle. Shell punctated or unpunctated. Arms largely developed, and entirely supported by a thin, shelly, spirally rolled lamella. Genera. — Spirifer, Spiriferina, Cyrtia, Athyris, &c. Fam. IV. KoninckinidcE. Animal unknown. Shell free ; valves unarticulated (?). Oral arms supported by two lamellae, spirally coiled. Genus. — Koninckia. Fam. V. Rhynchonellida. Animal free, or attached by a muscular peduncle issuing from an aperture situated under the extremity of the beak of the ventral valve. Arms spirally rolled, flexible, and supported only at their origin by a MOLLUSCOIDA I BRACHIOPODA. 3 I 7 pair of short, curved, shelly processes. Shell-structure fibrous and impunctate. Genera. — Rhynchonella, Pentamerus, Porambonites, &c. Fam. VI. Strophomenida. Animal unknown ; some probably free, others attached, during the whole or a portion of their existence, by a muscular peduncle. No calcified supports for their arms. Shell with a straight hinge-line, and a low triangular area in each valve. Shell-structure fibrous and punctated. Genera. — Orthis, Orlhisina, Strophomena, and Lept&na, Fam. VII. Productida. Animal unknown. Shell entirely free, or attached to marine bottoms by the substance of the beak ; valves either regularly articulated, or kept in place by muscular action. No calcified support for the oral appendages. Genera. — Producta, Chonetes, Strophalosia, Aulosteges. Fam. VIII. Craniada. Animal fixed to submarine objects by the substance of the shell of the ventral valve. Arms fleshy and spirally coiled ; no hinge or articulating processes ; upper or dorsal valve patelliform (i.e., limpet- shaped). Genus. — Crania . Fam. IX. Discinida. Animal attached by means of a muscular peduncle passing through the ventral or lower valve by means of a slit in its hinder portion, or a circular foramen excavated in its substance. Arms fleshy, valves unarticulated. Genera. — Discina, Trematis, Siphonotreta, Acrotreta. Fam. X. Lingulidtz* Animal fixed by a muscular peduncle passing out between the beaks of the valves ; arms fleshy, unsupported by calcified processes. Shell unarticulated, sub-equivalve, texture horny. Genera. — -J^ingula, Obohis. Fam. XI. Trimeretlidcz . Shell calcareous, not horny ; hinge-area well developed ; deltidium wide, bounded by two ridges, the inner edges of which serve as teeth ; limbs generally very prominent, usually massive, and often divided by a partition into two chambers. Each valve with muscular platforms, which are typically elevated and vaulted. Genera. — Trimerella, Dinobolus, Monomerella. * Another family was formerly constituted for the reception of the sin- gular Devonian fossils known as Calceolce. It has been shown, however, that these are probably operculate Corals. 3l MANUAL OF ZOOLOGY. CHAPTER XLV. DISTRIBUTION OF MOLL US CO ID. 1 . DISTRIBUTION OF MOLLUSCOIDA IN SPACE. — The Polyzoa, like all the Molluscoida, are exclusively aquatic in their habits, but, unlike the remaining two classes, they are not exclusively con- fined to the sea. The marine Polyzoa are of almost universal occurrence in all seas. The fresh-water Polyzoa, however, not only differ materially from their marine brethren in structure, but appear to have a much more limited range, being, as far as is yet known, confined to the north temperate zone. Britain can claim the great majority of the described species of fresh- water Polyzoa, but this is probably due to the more careful scrutiny to which this country has been subjected. The Tunicata are cosmopolitan in their distribution, and are found in all seas, the Mediterranean appearing to be especially rich in members of this class. Four genera are pelagic in their habits, and several are found in the Arctic regions. The Brachiopoda, though of very partial occurrence, have a wide range in space, being found both in tropical seas and in the Arctic Ocean. Their bathymetrical range is also very wide, extending from the littoral zone almost to the greatest depths at which animal life has hitherto been detected. DISTRIBUTION OF MOLLUSCOIDA IN TIME. — The Polyzoa have left abundant traces of their past existence in the stratified series, commencing in the Lower Silurian Rocks and extending up to the present day. The Oldhamia of the Cambrian Rocks of Ireland, and the Graptolites, have been supposed to belong to the Polyzoa ; but the former is very possibly a plant, and the latter should be referred to the Hydrozoa. Of undoubted Poly- zoa, the marine orders of the Cheilostomata and C'yclostomafa are alone known with certainty to be represented. Several Palaeozoic genera— such as Fenestella (the Lace-coral), Ptilo- dictya, Ptilopora, &c. — are exclusively confined to this epoch, and do not extend into the Secondary Rocks. Amongst the Mesozoic formations, the Chalk is especially rich in Polyzoa, over two hundred species having been already described from this horizon alone. In the Tertiary period, the Coralline Crag (Pleiocene) is equally conspicuous for the great number of the members of this class. The Tunicata, from the nature of their bodies, are not known to occur in a fossil condition. The Brachiopoda are found from the Cambrian Rocks up to MOLLUSCOIDA ! DISTRIBUTION. 3 I 9 the present day, and present us with an example of a group which appears to be slowly dying out. Nearly two thousand extinct species have been described, and the class appears to have attained its maximum in the Silurian epoch, which is, for this reason, sometimes called the " Age of Brachiopods." Numerous genera and species are found also in both the Devonian and Carboniferous formations. In the Secondary Rocks Brachiopoda are still abundant, though less so than in the Palaeozoic period. In the Tertiary epoch a still further diminution takes place, and at the present day we are not acquainted with a hundred living forms. Of the families of Brachiopoda, the Productidce, Strophomenidce, and Spiriferidce are the more important extinct types. Of the genera, the most persistent is the genus Lingtila, which commences in the Cam- brian Rocks, and has maintained its place up to the present day, though it appears to be gradually dying out. According to Woodward : — " The hingeless genera attained their maximum in the Palaeozoic age, and only three now sur- vive (Lingula, Discina, Crania] — the representatives of as many distinct families. Of the genera with articulated valves, those provided with spiral arms appeared first, and attained their maximum while the Tere.bratulidce were still few in number. The subdivision with calcareous spires disappeared with the Liassic period, whereas the genus Rhynchonella still exists. Lastly, the typical group, Terebratnlidce. attained its maximum in the Chalk period, and is scarcely yet on the decline." Of the families of the Brachiopoda, the Productidce and Strophomenidce are exclusively Palaeozoic. The Spiriferida are mainly Palaeozoic, but extend into the Lias, where they finally disappear. The Lingulida commence in the Cambrian period, and have survived to the present day. The Rhyncho- nellidce, Craniadce, and Discinidcz commence in the Silurian period, and are represented by living forms in existing seas. The Koninckidce are exclusively Triassic. The Thecididce ex- tend from the Trias to the present day ; and the Terebratulida appear to commence in the Devonian, and are well represented by living forms. 320 MOLLUSC A PROPER. CHAPTP:R XLVI. LAMELLIBRANCHIA TA. DIVISION II. MOLLUSCA PROPER. — This division includes those members of the sub-kingdom Mollusca in which the nervous system consists of three principal pairs of ganglia ; and there is always a well-developed heart, which is never composed of fewer than two chambers. The Mollusca proper may be roughly divided into two great sections, respectively termed the Acephala and the Encephala (or Cephalophord], characterised by the absence or presence of a distinctly differentiated head. The headless, or Acephalous, Molluscs correspond to the class Lamellibranchiata ; also dis- tinguished, at first sight, by the possession of a bivalve shell. The Encephalous Molluscs are more highly organised, and are divided into three classes — viz., the Gasteropoda, the Pteropoda, and the Cephalopoda. The shell in these three classes is of very various nature, but they all possess a singular and com- plicated series of lingual teeth • hence they are grouped to- gether by Professor Huxley under the name of Odontophora. CLASS I. LAMELLIBRANCHIATA, or CONCHIFERA. — The members of this class are characterised by the absence of a distinctly differentiated head, and by having the body more or less completely protected in a bivalve shell. There are two lamellar gills on each side of the body, the intestine has a neural flexure, and there is no odontophore. The Lamellibranchiata are commonly known as the bivalve shell-fish, such as Mussels, Cockles, Oysters, Scallops, &c., and they are all either marine or inhabitants of fresh water. Though they agree with the Brachiopoda in possessing a shell which is composed of two pieces or valves, there are, nevertheless, many points in which the shell of a Lamelli- branch is distinguishable from that of a Brachiopod, irrespec- tive of the great difference in the structure of the animal in MOLLUSCA : LAMELLIBRANCHIATA. 321 each. The shell in the Brachiopoda, as we have seen, is rarely or never quite equivalve, and always has its two sides equally developed (equilateral) ; whilst the valves are placed antero- posteriorly as regards the animal, one in front and one behind, so that they are "dorsal" and "ventral." In the Lamellibran- chiata, on the other hand, the two valves are usually of nearly equal size (equivalve), and are more developed on one side than on the other (inequilateral) ; whilst their position as re- gards the animal is always lateral, so that they are properly termed "right" and "left" valves, instead of "ventral" and " dorsal." It is to be remembered, however, that many of the Bivalves, such as the Oysters, habitually lie on one side, in which case Fig. 129. — Left valve of Cytherea chione. (After Woodward.) A, Anterior margin ; B, Posterior margin ; C, Ventral margin or base ; u Umbo ; k Ligament; / Lunule ; c Cardinal tooth ; / t Lateral teeth ; a Anterior adductor ; a Posterior adductor ; / Pallial line ; s Pallial sinus, caused by the retractor muscles of the siphons. the valves, though really right and left, are called " upper " and "lower." It is to be borne in mind also that the two valves, especially in the attached Bivalves, maybe very imsymmetrical, one valve being much larger or deeper than the other. Lastly, there are some cases in which the shell becomes very nearly equilateral, the line drawn from the beaks to the base dividing the shell into two almost equal halves. The following are the chief points to be noticed in connection with the shell of any Lamellibranch (fig. 129) : Each valve of the shell may be regarded as essentially a hollow cone, the apex of which is turned more or less to one side ; so that more of the shell is situated on one side of the apex than on the other. * x 322 MANUAL OF ZOOLOGY. The apex of the valve is called the "umbo," or "beak," and is always turned towards the mouth of the animal. Conse? quently, the side of the shell towards which the umbones are turned is the "anterior" side, and it is usually the shortest half of the shell. The longer half of the shell, from which the umbones turn away, is called the "posterior" side, but in some cases this is equal to, or even shorter than, the anterior side. The side of the shell where the beaks are situated, and where the valves are united to one another, is called the "dorsal" side ; and the opposite margin, along which the shell opens, is called the " ventral" side, or "base." The length of the shell is measured from its anterior to its posterior margin, and its breadth from the dorsal margin to the base. At the dorsal margin the valves are united to one another, for a shorter or longer distance, along a line which is called the " hinge-line." The union is effected in most shells by means of a series of parts which interlock with one another (the "teeth"), but these are sometimes absent, when the shell is said to be " edentulous." Posterior to the umbones, in most Bivalves, is another structure passing between the valves, which is called the " ligament," and which is usually composed of two parts, either distinct or combined with one another. These two parts are known as the " external ligament" (or the liga- ment proper) and the "cartilage," and they constitute the agency whereby the shell is opened, but one or other of them may be absent. The ligament proper is outside the shell, and consists of a band of horny fibres, passing from one valve to the other just behind the beaks, in such a manner that it is put upon the stretch when the shell is closed. The cartilage, or internal ligament, is lodged between the hinge-lines of the two valves, generally in one or more " pits," or in special processes of the shell. It consists of elastic fibres placed perpen- dicularly between the surfaces by which it is contained, so that they are necessarily shortened and compressed when the valves are shut. To open the shell, therefore, it is simply necessary for the animal to relax the muscles which are provided for the closure of the valves, whereupon the elastic force of the ligament and cartilage is sufficient of itself to open the shell. Generally the hinge-line is curved, but it is sometimes straight. The beaks are mostly more or less contiguous, but they may be removed from one another to a greater or less distance, and in some anomalous forms they are not near one another at all. In the Arcadce. the two beaks are separated from one another by an oval or lozenge-shaped MOLLUSCA : LAMELLIBRANCHIATA. flat space or area. When teeth are present, they differ much in their form and arrangement. In some forms (fig. 129) the teeth are divisible into three sets — one group of one or more teeth, placed im- mediately beneath the umbo, and known as the " cardinal teeth;" and two groups on either side of the preceding, termed the " lateral teeth." Sometimes there maybe lateral teeth only ; sometimes the cardinal teeth alone are pre- sent ; and in some cases (Arcadc. Fam. 2. Aviculidcz. — Shell inequivalve, very oblique, attached by a byssus ; hinge nearly, or quite, edentulous. Mantle-lobes free ; anterior adductor small, leaving its impression within the umbo ; posterior adductor large and sub- central. Foot small. 111. Gen. Avicula, Inoceramus, Pinna. Fam. 3. Mytilidce. — Shell equivalve, umbones anterior, hinge eden- tulous ; anterior muscular impression small, posterior large. Shell attached by a byssus. Mantle-lobes united between the siphonal apertures. Foot cylindrical, grooved, and byssiferous. 111. Gen. Mytilus, Modiola, Dreissena. Fam. 4. Arcades. — Shell equivalve ; hinge long, with many comb- like equal teeth. Muscular impressions nearly equal. Mantle- lobes separated ; foot large, bent, and deeply grooved. 111. Gen. Area, Pectunculus, Cucullcea. Fam. 5. Trigoniadce. — Shell equivalve trigonal; hinge-teeth few, diverging ; umbones directed posteriorly. Mantle open ; foot long and bent. 111. Gen. Trigonia, Axinus. Fam. 6. Unionidce. — Shell usually equivalve, with a large external ligament. Anterior hinge-teeth thick and striated ; posterior laminar, or wanting. Mantle-lobes united between the siphonal apertures. Foot very large, compressed, byssiferous in the fry, 111. Gen. Unio, Anodon, Midler ia. SECTION B. SIPHONIDA. Subdivision I. Integro-pallialia. — Siphons short, pallial line simple. Fam. 7. Chamidce. — Shell inequivalve, attached ; hinge-teeth 2-1 (two in one valve and one in the other). Adductor impressions large. Mantle closed ; pedal and siphonal orifices small and nearly equal. Foot very small. 111. Gen. Chama, Diceras. Fam. 8. Hippuritidce. — " Shell inequivalve, unsymmetrical, thick, attached by the right umbo ; umbones frequently camerated ; structure and sculpturing of valves dissimilar ; ligament internal ; hinge-teeth 1-2 ; adductor impressions 2, large, those of the left valve on prominent apophyses ; pallial linefsimple, sub-marginal " (Woodward). 111. Gen. Hippurites, Radiolites, Caprinella. 328 MANUAL OF ZOOLOGY. Fam. 9. Tridacnidce. — Shell equivalve ; ligament external ; muscular impressions blended, sub-central. Animal attached by a byssus, or free. Mantle lobes extensively united ; pedal aperture large ; siphonal orifices surrounded by a thickened pallial border. Foot finger-like and byssiferous. 111. Gen. Tridacna. Fam. 10. Cardiadce. — Shell equivalve, heart-shaped, with radiating ribs ; cardinal teeth 2 ; lateral teeth I-I, in each valve. Mantle open in front, siphons usually very short ; foot large, sickle- shaped. 111. Gen. Cardium, Hemicardium, Conocardium. Fam. II. Lucinidce. — Shell orbicular, and free ; hinge-teeth I or 2 ; lateral teeth i-i, or obsolete. Mantle lobes open below, with one or two siphonal orifices behind ; foot elongated, cylindrical, or strap-shaped. 111. Gen. Lucina, Diplodonta, Kellia. Fam. 12. Cyclqdidce. — Shell sub-orbicular, closed ; hinge with cardinal and lateral teeth ; ligament external. Mantle open in front ; 1-2 siphons, more or less united. Foot large, tongue- shaped. 111. Gen. Cyclcis, Cyrena. Fam. 13. Cyprinidce. — Shell equivalve, closed ; ligament external ; cardinal teeth 1-3 in each valve, and usually a posterior tooth. Mantle-lobes united behind by a curtain pierced with two siphonal orifices. Foot thick and tongue-shaped. 111. Gen. Cyprina, Astarte, Isocardia. Subdivision II. Sinu-pallialia. — Respiratory siphons large; pallial line sinuated. Fam. 14, Venerida. — Shell regular, sub-orbicular or oblong ; liga- ment external ; hinge with usually 3 diverging teeth in each valve. Animal usually free and locomotive ; mantle with a rather large anterior opening ; siphons unequal, more or less united. Foot tongue-shaped, compressed, sometimes grooved and byssiferous. 111. Gen. Venus, Cytherea, Venerupis. Fam. 15. Mactridce. — Shell equivalve, trigonal ; hinge with two diverging cardinal teeth, and usually with anterior and posterior lateral teeth. Mantle more or less open in front ; siphons united, with fringed orifices ; foot compressed. 111. Gen. Mactra, Lutraria. Fam. 16. Tettinidce. — Shell free, usually equivalve and closed; cardinal teeth 2 at most, laterals I-I, sometimes wanting. Liga- ment on the shortest side of the shell, sometimes internal. Mantle widely open in front. Siphons separate, long and slender; foot tongue-shaped, compressed. 111. Gen. Tdlina, Psammobia, Donax. Fam. 17. Solenidce. — Shell elongated, gaping at both ends ; ligament external ; hinge-teeth usually 2-3. Siphons short and united (in the long-shelled genera), or longer and partly separate (in the genera with shorter shells). Foot very large and powerful. Gills prolonged into the branchial siphon. 111. Gen. Solen^ Cultellus, Solecurtus. Fam. 1 8. Myaddce. — Shell gaping posteriorly. Mantle almost entirely closed ; siphons united, partly or wholly retractile. Foot very small. 111. Gen. Mya, Panopcea, Glycimeris. Fam. 19.. Anatinida. — Shell often inequivalve, with an external ligament. Mantle-lobes more or less united ; siphons long, more or less united. Foot small. 111. Gen. Anatina, Pholadomya, Myochama. MOLLUSCA : GASTEROPODA. 329 Fam. 20. Gastrochtznidce. — Shell equivalve, gaping, with thin eden- tulous valves sometimes cemented to a calcareous tube. Mantle- margins thick in front, united, with a small pedal aperture. Siphons very long, united. Foot finger-shaped. 111. Gen. Gas- troch&na, Saxicava, Aspergillum. Fam. 21. Pholadidce. — Shell gaping at both ends, without hinge or ligament, often with accessory valves. Animal club-shaped or worm-like, with a short truncated foot. Mantle closed in front. Siphons long, united to near their extremities. 111. Gen. Pholas, Xylophaga, 7"eredo. CHAPTER XLVII. GASTEROPODA. DIVISION ENCEPHALA, or CEPHALOPHORA. — The remaining three classes of the Mollusca proper all possess a distinctly differentiated head, and are all provided with a peculiar masti- catory apparatus, which is known as the " odontophore." For the first of these reasons they are often grouped together under the name Encephala ; and for the second reason they are united by Huxley into a single great division, under the name of Odontophora. Whichever name be adopted, the three classes in question (viz., the Gasteropoda, Pteropoda, and Cephalopoda) certainly show many points of affinity, and form a very natural division of the Mollusca. The Pteropoda, as being the lowest class, should properly be treated of first, but it will conduce to a clearer understanding of their characters if the Gasteropoda are considered first. CLASS II. GASTEROPODA. — The members of this class are characterised by being never included in a bivalve shell ; loco- motion being effected by means of a broad, horizontally flat- tened, ventral disc — the "foot;" or by a vertically flattened, ventral, fin-like organ. Flexure of intestine haemal or neural. This class includes all those Molluscous animals which are commonly known as " univalves," such as the land-snails, sea- snails, whelks, limpets, &c. The shell, however, is sometimes composed of several pieces (multivalve), and in many there is •either no shell at all, or nothing that would be generally recog- nised as such. In none is there a bivalve shell. In their habits the Gasteropods show many differences, some being sedentary, but the great majority being free and locomo- tive. In these latter, locomotion may be effected by the sue- 33° MANUAL OF ZOOLOGY. cessive contractions and expansions of a muscular foot; but some possess the power of swimming freely by means of a modified fin-like foot. In most of the Gasteropoda the body is unsymmetrical, and is coiled up spirally, " the respiratory organs of the left side being usually atrophied " (Woodward). The body is enclosed in a " mantle," which is not divided into two lobes as in the Lamel- libranchiala, but is continuous round the body. Locomotion is effected by means of the " foot," which is usually a broad muscular disc, developed upon the ventral surface of the body, and not exhibiting any distinct division into parts. In the Hctcropoda, however, and in the Wing-shells (Strombickz), the foot exhibits a division into three portions — an anterior, the " propodium ; " a middle, the " mesopodium ; " and a posterior lobe, or " me'tapodium." In some, again, the upper and lateral surfaces of the foot are expanded into muscular side-lobes, which are called " epi- podia." In many cases the metapodium, or posterior portion of the foot, secretes a calcareous, homy, or fibrous plate, which is called the " operculum " (fig. 134, d), and which serves to close the orifice of the shell when the animal is retracted within it. The head in most of the Gasteropoda is very distinctly marked out, and is provided with two tentacles and with two eyes, which are often placed upon long stalks. Very often there is an elongated retractile proboscis with ear-sacs, contain- ing otoliths, at its base. The mouth is some- times furnished with horny jaws, and is always provided with a singular masticatory appara- tus, called the "tongue" or " odontophore" (fig. 132). " It consists essentially of a cartila- ginous cushion, supporting, as on a pulley, an elastic strap, which bears a long series of trans- versely-disposed teeth. The ends of the strap are connected with muscles attached to the upper and lower surface of the hinder extremi- ties of the cartilaginous cushions ; and these muscles, by their alternate contractions, cause the toothed strap to work backwards and for- odonto- wards over the end of the pulley formed by its k6 (Buc- anterior end. The strap consequently acts, after mag^fieT(After ^ fasmon °f a chain-saw, upon any substance Woodward.) to which it is applied, and the resulting wear and tear of its anterior teeth are made good by the incessant development of new teeth in the secreting sac in which the MOLLUSCA : GASTEROPODA. 331 hinder end of the strap is lodged " (Huxley). The teeth of the odontophore (" lingual teeth ") are composed of silica, and are usually arranged in a central ("rachidian ") and two lateral (" pleural ") rows. The mouth leads by a gullet into a distinct stomach (fig. 133), which is sometimes provided with calcareous plates for the trituration of the food. The intestine is long, and its first flexure is commonly " haemal," or towards that side of the body on which the heart is situated ; though in some the flexure is " neural." Distinct salivary glands are usually present, and the liver is well developed. A distinct heart (fig. 133, //) is usually present, composed of Fig. 133. — Diagrammatic section of a Whelk, a Mouth, with masticatory apparatus ; b Salivary glands; c Stomach; d d Intestine, surrounded by the liver, and ter- minating in the anus (e) ; g Gill ; h Heart ; ./Nervous ganglion. an auricle and ventricle. In many Gasteropods it has been shown that the blood-vessels form closed tubes, and that the arteries and veins are connected by an intermediate system of capillaries, instead of merely communicating through the inter- stices and lacunae between the tissues. It seems also certain that, in general at any rate, there is no direct connection between the blood-vessels and the outer medium, though, in some cases, such a communication seems undoubtedly to exist. Respira- tion is very variously effected ; one great division (Branchio- gasteropodd) being constructed to breathe air by means of 332 MANUAL OF ZOOLOGY. water ; whilst in another section (Ptdmogasteropoda) the respi- ration is aerial. In the former division respiration may be effected in three ways. Firstly, there may be no specialised respiratory organ, the blood being simply exposed to the water in the thin walls of the mantle-cavity (as in some of the Hetero- podd). Secondly, the respiratory organs may be in the form of outward processes of the integument, exposed in tufts on the back and sides of the animal (as in the Nudibranchiatd}. Thirdly, the respiratory organs are in the form of pectinated or plume-like branchiae, contained in a more or less complete branchial chamber formed by an inflection of the mantle. In many members of this last section the water obtains access to the gills by means of a tubular prolongation or folding of the mantle, forming a " siphon/' the effete water being expelled by another, posterior siphon similarly constructed. In the air- breathing Gasteropods, the breathing organ is in the form of Fig. 1-3,4,.— Ampullaria canaliculata, one of the Apple-shells, o Operculum ; j Respiratory siphon. a pulmonary chamber, formed by an inflection of the mantle, and having a distinct aperture for the admission of air. The nervous system in the Gasteropoda has its normal com- position of three principal pairs of ganglia, the supra-cesopha- geal or cerebral, the infra-oesophageal or pedal, and the parieto- splanchnic ; but there is a tendency to the aggregation of these in the neighbourhood of the head. The organs of sense are the two eyes, and auditory capsules placed at the bases of the tentacles, the latter being tactile organs. The sexes are mostly distinct, but in some they are united in the same individual. The young, when first hatched, are always provided with an embryonic shell, which in the adult may become concealed in a fold of the mantle, or may be entirely lost. In the branchiate Gasteropods the embryo (fig. 135) is protected by a small nautiloid shell, within which it can MOLLUSC A : GASTEROPODA. 333 entirely retract itself; and it is enabled to swim freely by means of two ciliated lobes arising from the sides of the head ; thus, in many respects, resembling the permanent adult condition of the Pteropoda. In the branchiate Gasteropoda, however, of fresh waters, the young do not possess these ciliated buccal lobes. Shell of the Gasteropoda. — The shell of the Gasteropods is composed either of a single piece (univalve), or of a number of plates succeeding one another from before backwards (mul- tivalve). The univalve shell is to be regarded as essentially a cone, the apex of which is more or less oblique. In the simplest form of the shell the conical shape is retained without any alteration, as is seen in the common Limpet (Patella]. In the great majority of cases, however, the cone is consider- ably elongated, so as to form a tube, which may retain this shape (as in Dentalium}, but is usually coiled up into a spiral. The "spiral univalve" (figs. 136, 137) may, in fact, be looked upon as the typical form of the shell in the Gasteropoda. In Fig. 135. — A, Young of Eolis, a water-breathing Gasteropod, showing the provi- sional buccal lobes. B, Adult Pteropod (Limacina Antarctica). (After Wood- ward.) some cases the coils of the shell — termed technically the " whorls " — are hardly in contact with one another (as in Vermetus\ More commonly the whorls are in contact, and are so amalgamated that the inner side of each convolution is formed by the pre-existing whorl. In some cases the whorls of the shell are coiled round a central axis in the same plane, when the shell is said to be " discoidal " (as in the common fresh- water shell Planorbis\ In most cases, however, the whorls are wound round an axis in an oblique manner, a true spiral being formed, and the shell becoming " turreted," " trochoid," " turbinated," &c. This last form is the one which may be looked upon as most characteristic of the Gasteropods, the shell being composed of a number of whorls passing obliquely round a central axis or " columella," having the embryonic shell or " nucleus " at its apex, and having the mouth or " aperture " of the shell placed at the .extremity of the last and largest of 334 MANUAL OF ZOOLOGY. the whorls, termed the " body-whorl" (fig. 136). The lines or grooves formed by the junction of the whorls are termed the " sutures," and the whorls above the body- whorl constitute the " spire" of the shell. The axis of the shell (columella) round which the whorls are coiled is usually solid, when the shell is said to be " imperforate ; " but it is sometimes hollow, when the shell is said to be " perforated," and the aperture of the axis near the mouth of the shell is called the " umbilicus/' The margin of the " aperture " of the shell is termed the "peristome," and is composed of an outer and inner lip, of which the former is often expanded or fringed with spines. When these expansions or fringes are periodically formed, the place of the mouth of the shell at different stages of its growth is marked by ridges or rows of spines, which cross the whorls, be e b Fig. 136.— Anterior and posterior views of Cassis cancellata, a Spiral Gasteropod. a " Spire," placed at the posterior end of the shell ; b " Mouth, " placed at the anterior end of the shell ; c Inner or collumellar lip ; d Outer lip ; e Notch for the passage of a respiratory siphon. and are called " varices." In most of the phytophagous Gasteropods (Holostomatd) the aperture of the shell (fig. 137) is unbrokenly round or " entire," but in the carnivorous forms (Siphonostomatd] it is notched, or produced into a canal (fig. 138). Often there are two of these canals, an anterior and a posterior, but they do not necessarily indicate the nature of the food, as their function is to protect the respiratory siphons. The animal withdraws into its shell by a retractor-muscle, which passes into the foot, or is attached to the operculum ; its scar or impression being placed, in the spiral univalves, upon the columella. In the multivalve Gasteropods, the shell is composed of eight transverse imbricated plates, which succeed one another from before backwards, and are imbedded in the leathery or fibrous border of the mantle, which may be plain, or may be beset with bristles, spines, or scales. MOLLUSCA : GASTEROPODA. 335 CHAPTER XLVIII. DIVISIONS OF THE GASTEROPODA. THE Gasteropoda are divided into two primary sections or sub-classes, according as the respiratory organs are adapted for breathing air directly, or dissolved in water : termed respectively the Pulmonifera or Pulmogasteropoda, and the Branchifera or Branchiogasteropoda. SUB-CLASS A. BRANCHIFERA or BRANCHIOGASTEROPODA. — In this sub-class respiration is aquatic, effected by the thin walls of the mantle-cavity, by external branchial tufts, or by pectinated or plume-like gills, contained in a more or less complete branchial chamber. Flexure of intestine hczmal. This sub-class comprises three orders — viz., the Proso- branchiata, the Opisthobranchiata, and the Nudeobranchiata or Heteropoda. ORDER I. PROSOBRANCHIATA. — The members of this order are defined as follows: — "Abdomen well developed, and pro- tected by a shell, into which the whole animal can usually retire. Mantle forming a vaulted chamber over the back of the head, in which are placed the excretory orifices, and in which the branchiae are almost always lodged. Branchice pectinated or plume-like, situated (prosori) in advance of the heart. Sexes distinct" (M.-Edwards). (See Woodward's " Manual") The order Prosobranchiata includes all the most character- istic members of the Branchiate Gasteropods, and is divisible into two sections, termed respectively Siphonostomata, and Holostomata, according as the aperture of the shell is notched or produced into a canal, or is simply rounded and " entire." The Siphonostomata, of which the common Whelk (Bucci- num undatum} may be taken as an example, are all marine, and are mostly carnivorous in their habits. The following families are comprised in this section : — Strombidcz (Wing- shells), Muricidce, Bucrinida. (Whelks), Conidce (Cones), Volu- tidce, and Cyprceidce (Cowries). The Holostomata, of which the common Periwinkle (Litto- rina littored) is a good example, are either spiral or limpet- shaped, in some few instances tubular, or multivalve ; the aper- ture of the shell being in most cases entire. They are mostly plant-eaters, and they may be either marine or inhabitants of fresh water. The following families are included in this sec- tion : — Natirida, Pyramidellida, Cerithiada, Melaniada, Turn- 336 MANUAL OF ZOOLOGY. tellidcE, Littorinidcz (Periwinkles), Paludinida (River-snails), Neritida, Turbinidcz (Top-shells), Haliotidce (Ear-shells), Fis- surellida (Key-hole Limpets), Calyptrceidcz (Bonnet Limpets), Patellida (Limpets), Dentalidtz (Tooth-shells), and Chitonidce. ORDER II. OPISTHOBRANCHIATA. — This order is defined as follows : — " Shell rudimentary, or wanting. Branchice arbores- cent or fasciculated, not contained in a special cavity, but more or less completely exposed on the back and sides, towards the rear (ppistheti) of the body. Sexes united " (Milne- Edwards). (See Woodward's " Manual.") The Opisthobranchiata, or " Sea-slugs," may be divided into two sections, the Tcetibranchiata and Nudibranckiata, accord- ing as the branchiae are protected or are uncovered. Fig. 137. — Scalar ia Grcenlandica, a Ho- lostomatous Univalve. Fig. 138. — Fusus tantalus^ a Si- phonostomatous shell. Post- Pliocene. The first section, that of the Tectibranchiata, is distinguished by the fact that the animal is usually provided with a shell, both in the larval and adult state, and that the branchiae are protected by the shell or by the mantle. Under this family are included the families of the Tornatettida, Bullida ($\fo\At- sheD&^^^ft^(Sea-bares)^^ In the second section, that of the Nudibranchiata (fig. 139), the animal is destitute of a shell, except in the embryo condi- tion, and the branchiae are always placed externally on the back or sides of the body. This section comprises the families Dorida (Sea-lemons), Tritoniadce, ^olida, Phyllirhoidat, and MOLLUSCA : GASTEROPODA. Elysiadce. Specimens of the Sea-slugs and Sea-lemons may at any time be found creeping about on sea-weeds, or attached to the under surface of stones at low water. The head is furnished with tentacles, which appear to be rather connected with the sense of smell than to be used as tactile organs ; and behind the tentacles are generally two eyes. The ner- Fig. i39.— Nudibranchiata. Doris vous system is extremely well de- ***"*«'• on veloped, and would lead to the belief that the Nudibranchs are amongst the highest of the Gasteropoda. Locomotion is effected, as in the true Slugs, by creeping about on the flat- tened foot. ORDER III. NUCLEOBRANCHIATA or HETEROPODA. — This order is denned by the following characteristics: — Animal provided with a shell, or not, free-swimming and pelagic ; locomotion effected by a fin-like tail, or by a fan-shaped, ver- tically flattened, ventral fin. Fig. 140. — Heteropoda. Carinariacymbiuin. ^Proboscis; /Tentacles; $ Branchiae ; j Shell ; f Foot ; d Disc. (After Woodward). The Heteropoda are pelagic in their habits, and are found swimming at the surface of the sea. They are to be regarded as the most highly organised of all the Gasteropoda, at the same time that they are not the most typical members of the class. Some of them can retire completely within their shells, closing them with an operculum ; but most have large bodies, and the shell is either small or entirely wanting. They swim by means of a flattened ventral fin, or by an elongated tail, and adhere at pleasure to sea-weed by a small sucker situated on the side of the fin. These organs are merely modifications of the foot of the ordinary Gasteropods ; the fin-like tail being Y 338 MANUAL OF ZOOLOGY. the " metapodium " (as shown by its occasionally carrying an operculum), the sucker being the " mesopodium," and the ven- tral fin being a modified " propodium." The " epipodia" are apparently altogether wanting. Respiration is sometimes car- ried on by distinct branchiae, but in many cases these are wanting, and the function is performed simply by the walls of the pallial chamber. The Heteropoda are divided into the two families Firolida and Atlantidcz, the former characterised by having a small shell covering the circulatory and respiratory organs, or by having no shell at all; whilst in the latter there is a well- developed shell, into which the animal can retire, and an oper- culum is often present. SUB-CLASS B. PULMONIFERA or PULMOGASTEROPODA. — In this sub-class of the Gasteropoda respiration is aerial, and is carried on by an inflection of the mantle, forming a pulmonary chamber into which air is admitted by an external aperture. The flexure of the intestine is neural, and the sexes are united in the same individual. Fig. 141. — Limax Soiuerbyi, one of the Slugs. (After Woodward.) The Pulmonifera include the ordinary land-snails, slugs, pond-snails, &c., and are usually provided with a well-developed shell, though this may be rudimentary (as in the slugs), or. even wanting. Though formed to breathe air directly, many of the members of this sub-class are capable of inhabiting fresh water. The common Pond-snails are good examples' of these last. The condition of the shell varies greatly. Some, such as the common Land-snails, have a well-developed shell, within which the animal can withdraw itself completely. Others, such as the common Slugs (fig. 141) have a rudimen- tary shell, which is completely concealed within the mantle. Others are entirely destitute of a shell. They are divided into two sections as follows : — Section I. Inoperculata. — Animal not provided with an oper- culum to close the shell. In this section are included the families MOLLUSCA : GASTEROPODA. 339 Helidda (Land-snails), Limacida (Slugs), Oncidiada, Limnceida (Pond-snails), and Auriculida. Section II. Operculata. — Shell closed by an operculum. In this section are included the families Cydostomida and Adcuiidtz. SYNOPSIS OF THE FAMILIES OF THE GASTEROPODA. (AFTER WOODWARD.) SECTION A. BRANCHIFERA. Respiration aquatic, by the walls of the mantle-cavity, or by branchiae. ORDER I. PROSOBRANCHIATA. The branchiae situated (prosori) in advance of the heart. Division a. Siphonostomata. Margin of the shell-aperture notched or produced into a canal. Fain. i. Strombidcc. Shell with an expanded lip, deeply notched near the canal. Operculum claw-shaped. Foot narrow, adapted for leaping. 111. Gen. Strombus, Pteroceras. Fam. 2. Muricidcz. Shell with a straight anterior canal, the aperture entire posteriorly. Foot broad. 111. Gen. Murex, Triton, Pyrula, Fusus. Fam. 3. Buccinidce. Shell notched anteriorly, or with the canal abruptly reflected, producing a kind of varix on the front of the shell. 111. Gen. Buccinum, Nassa, Purpura, Cassis, Harpa, Oliva. Fam. 4. Conidce. Shell inversely conical, with a long narrow aper- ture, the outer lip notched at or near the suture. Operculum minute, lamellar. 111. Gen. Conus, Pleurotoma. Fam. 5. Volutidcz. Shell turreted or convolute, the aperture notched in front ; the columella obliquely plaited. No operculum. Foot very large ; mantle often reflected over the shell. 111. Gen. Valuta. Mitra, Marginella. Fam. 6. Cyprceidt?. Shell convolute, enamelled ; spire concealed, aperture narrow, channelled at each end. Outer lip thin m the young shell, but thickened and inflected in the adult. Foot broad ; mantle forming lobes which meet over the back of the shell. 111. Gen. Cyprcea, Ovulum. Division b. Holostomata. Margin of the shell-aperture " entire" rarely notched or produced into a canal. Fam. i. Naticidce. Shell globular, of few whorls, with a small spire, outer lip acute, pillar often callous. Foot very large ; mantle- lobes hiding more or less of the shell. Gen. Natica, Sigaretus. Fam. 2. Pyramidellidte. Shell turreted, with a small aperture, sometimes with one or more prominent plaits on the columella. Operculum horny, imbricated. 111. Gen. Pyramidella, Chemnitzia. Eulima. Fam. 3. CerithiadcB. Shell spiral, turreted ; aperture channelled in front, with a less distinct posterior canal. Lip generally expanded in the adult. Operculum horny and spiral. 111. Gen. Cei ithium, Potamides, Aporrhais. Fam. 4. Melaniada. Shell spiral, turreted ; aperture often chan- nelled or notched in front ; outer lip acute. Operculum horny and spiral. 111. Gen. Melanta, Paludomus. 34-O MANUAL OF ZOOLOGY. Fam. 5. Turritellida . Shell tubular, or spiral, often turreted ; upper part partitioned off; aperture simple. Operculum horny, many- whorl ed. Foot very short. Branchial plume single. 111. Gen. Turritella, Vermetus, Scalaria. Fam. 6. Littorinidce. Shell spiral, top-shaped, or depressed ; aper- ture rounded and entire ; operculum horny and pauci-spiral. 111. Gen. Littorina, Solarium, Itissoa, Phorus. Fam. 7. Paludinidce. Shell conical or globular ; aperture rounded and entire ; operculum horny or shelly. 111. Gen. Paludina, Ampullaria, Valvata. Fam. 8. Neritida. Shell thick, globular, with a very small spire ; aperture semi-lunate, its columellar side expanded ; outer lip acute. Operculum shelly, sub-spiral. 111. Gen. Nerita, Pileolus, Net itina. Fam. 9. Turbinidce. Shell turbinated (top-shaped), or pyramidal, nacreous inside. Operculum horny and multi-spiral, or calca- reous and pauci-spiral. 111. Gen. Turbo, Trochus, Delphinula, Euomphalus. Fam. 10. Haliotidcz. Shell spiral, ear-shaped, or trochoid ; aperture large, nacreous. Outer lip notched or perforated. No operculum. Mantle-margin with a posterior fold or siphon, occupying the slit or perforation in the shell. Metapodium rudimentary. 111. Gen. Haliotis, Scissurella, Pleurotomana, Murchisonia, lanthina. Fam. II. Fissurellidtz . Shell conical, patelliform, with a notch in the anterior margin, or a perforation at its apex, which is occupied by an anal siphon. Muscular impression horse-shoe-shaped, open in front. 111. Gen. Fissurella, Emarginula, Parmophorus. Fam. 12. Calyptrczidce. Shell patelliform, with a more or less spiral apex ; interior simple, or divided by a shelly process to which the adductor muscles are attached. 111. Gen. Calyptrcea, Pileopsis. Fam. 13. Patellidce. Shell conical, with the apex turned forwards ; muscular impression horse-shoe-shaped, open in front. Foot as large as the margin of the mantle. Respiratory organ in the form of one or two branchial plumes, lodged in a cervical cavity ; or of a series of lamellae surrounding the animal between the body and the mantle. 111. Gen. Patella, Acmcea. Fam. 14. Dentalidce. Shell tubular, symmetrical, curved, open at both ends. Aperture circular. Foot pointed, with symmetrical side-lobes. Gen. Dentalium* Fam. 15. Chitonidce. Shell multivalve, composed of eight transverse imbricated plates. Animal with broad creeping foot ; branchiae forming a series of lamellae between the foot and the mantle, round the posterior part of the body. 111. Gen. Chiton, Crypto- chiton. ORDER II. OPISTHOBRANCHIATA. Branchiae placed towards the rear (ppistheri) of the body- Section a. Tectibranchiata. Branchice covered by the shell or mantle; a shell in most. Sexes united. Fam. i. Tornatellid(E. Shell external, spiral, or convoluted ; aper- ture long and narrow ; columella plaited. 111. Gen. Tornatella, Cinulia. * Dentalium is placed by Professor Huxley amongst the Pteropoda, from its rudimentary head, the neural flexure of the intestine, the nature of the epipodia, and the characters of the larva. MOLLUSCA : GASTEROPODA. 341 Fain. 2. Bullida. Shell convoluted, thin ; spire small or concealed, lip sharp. Animal more or less investing the shell. 111. Gen. Bulla, Cylichna, Philine. Fam. 3. Aplysiadte. Shell absent, or rudimentary and concealed by the mantle. Animal slug-like, with extensive side-lobes (epipodia), reflected over the back and shell. 111. Gen. Aplysia, Dolabella. Fam. 4. Pleurobranchidcc. Shell patelliform. or concealed, rarely wanting. Mantle or shell covering the back of the animal. 111. Gen. Pleurobranchus, Umbrella, Tylodina. Fam. 5. Phyllidiadce. Animal shell-less, covered by a mantle. 111. Gen. Phyllidia, Dlphyllidia. Section b. Nudibranchiata. Animal destitute of a shell in the adult condition. Branchice external, on the back or sides of the body. Fam. 6. Doridee. 111. Gen. Doris. Fam. 7. Tritoniada. 111. Gen. Tritonia, Scyllaa. Fam. 8. Ai.olidce. 111. Gen. SEolis, Glaucus. Fam. 9. Phyllirhoidce. Gen. Phyllirhoe. Fam. 10. Elysiad;TA r?otte%i° nr"°' fh-e " Paper 1Sa-u' . sometimes attain to a ^reat tilus, female. 1 he animal is represented in . „,, T • i its shell, but the webbed dorsal arms are se- ' S1ZC. 1 hey may DC divided embrace^0"1'1116 SheU' Whi°h ^ °rdinarUy into tWO Sections, Octopodd and Decapoda, according as they have simply eight arms, or eight arms and two additional " tentacles." MOLLUSCA : CEPHALOPODA. 351 SECTION A. OCTOPODA. — The Cephalopods comprised in this section are distinguished by the possession of not more than eight arms, which are provided with sessile suckers. The shell is internal and rudimentary ; in one instance only (the Argonaut) external. The body is short and bursiform, and ordinarily without fins. This section comprises the two families of the Argortautida, and the Odopodida, In the former of these there is only the single genus Argonauta, (the Paper Sailor, or the Paper Nau- tilus), of which the female and male differ greatly from one another. The female Argonaut (fig. 146) is protected by a thin single- chambered shell, in form symmetrical and involuted, which is secreted by the webbed extremities of the dorsal arms, but is not attached in any way to the body of the animal. It sits in its shell with the funnel turned towards the keel, and the webbed arms applied to the shell. The male Argonaut is much smaller than the female (about an inch in length), and is not protected by any shell. The third left arm is developed in a cyst, and ultimately becomes a " hectocotylus," and is deposited by the male in the pallial chamber of the female. In the Octopodidtz (or Poulpes) there are eight arms, all similar to one another, and united at the base by a web. There is an internal rudimentary shell, represented by two short styles encysted in the substance of the mantle (Owen). The body is seldom provided with lateral fins. The third right arm of the male is primarily developed in a cyst, and ultimately becomes " hectocotylised." SECTION B. DECAPODA. — The Cephalopods of this section have eight arms and two additional " tentacles," which are much longer than the true arms, are retractile, and have ex- panded, club-shaped extremities (fig. 143). The suckers are pedunculated ; the body is always provided with lateral fins, and the shell is always internal. This section comprises the three living families of the TenthidcE, 'Sepiadce, and the Spirulida, and the extinct family of the Belemnitidcz. The family of the Teuthidce. comprises the Calamaries or Squids, characterised by the possession of an elongated body with lateral fins. The shell is internal and horny, consisting of a median shaft and of two lateral wings; it is termed the " gladius " or " pen," and in old specimens several may be found lodged in the mantle, one behind the other. In the common Calamary (Loligo] the fourth left arm of the male is metamorphosed towards its extremity to subserve repro- duction. 352 MANUAL OF ZOOLOGY. In the family of the Sepiadce. the internal shell is cal- careous (" cuttle-bone " or " sepiostaire "), and is in the form of a broad plate, having an imperfectly chambered apex. The broad laminated plate is extremely light and spongy, and the chambered apex is called the " mucro." In the living members of the family the body is provided with long lateral fins, sometimes as long and as wide as the body itself. In the singular family of the Spirn- HdcE the internal skeleton is in the form of a nacreous, discoidal shell, the whorls of which are not in contact with one another, and which is di- vided into a series of chambers by means of partitions or septa which are pierced by a ventral tube or " siphuncle." The body is provided with minute terminal fins, and the arms have six rows of small suckers. The shell of the Spirula — commonly known as the " post-horn " — is similar in structure to the shell of the Nau- tilus, but it is lodged in the posterior part of the body of the animal, and is therefore internal, whereas the shell of the latter is external. It really cor- responds to the "phragmacone" of the Belemnite. Though the shell occurs in enormous numbers in cer- tain localities, a single perfect speci- men of the animal is all that has been hitherto obtained. In the extinct family of the Belem- nitidce, our knowledge is chiefly con- fined to the hard parts. Certain specimens, however, have been dis- covered, which show that the Belem- nite had essentially the structure of a Cuttle-fish, such as the recent Calamary. The body was provided with lateral fins ; the arms were eight, furnished with horny hooks, with two "tentacles ; " and probably the mouth was provided with horny mandibles. .-v g. 147 nite (after Professor Phillips). r Horny pen or " pro-ostra- cum '," p Chambered "phrag- macone" in its cavity (a) or " alveolus ; " g- " Guard." MOLLUSCA : CEPHALOPODA. 353 An ink-bag was present. The internal skeleton of a Belem- nite (fig. 147) consists of a chambered cone — the "phragma- cone " — the septa of which are pierced with a marginal tube, or " siphuncle." In the last chamber of the phragmacone is contained the ink-bag, often in a well-preserved condition. Anteriorly the phragmacone is continued into a horny lamina or " pen " (the " pro-ostracum " of Huxley), and posteriorly it is lodged in a conical sheath or " alveolus/' which is excavated in the substance of a nearly cylindrical, fibrous body, the "guard" (fig. 147, g) which projects backwards for a longer or shorter distance, and is the part most usually found in a fossil condition. ORDER II. TETRABRANCHIATA. — The members of this order of the Cephalopoda are characterised by being creeping animals, protected by an external, many-chambered shell, the septa between the chambers of which are perforated by a membra- nous or calcareous tube, termed the " siphuncle." The arms are numerous, and are devoid of suckers ; the branchiae are four in number, two on each side of the body ; the funnel does not form a complete tube ; and there is no ink-bag. Though abundantly represented by many and varied extinct forms, the only living member of the Tetrabranchiata is the Pearly Nautilus, which has been long known by its beautiful chambered shell, but the soft parts of which can hardly be said to be known by more than one perfect specimen, which was examined by Professor Owen. The soft structures in the Pearly Nautilus may be divided into a posterior, soft, membranous mass (metasoma), contain- ing the viscera, and an anterior muscular division, comprising the head (prosoma) ; the whole being contained in the outer- most, capacious chamber (the body-chamber) of the shell, from which the head can be protruded at will. The shell itself (fig. 148) is involuted and many-chambered, the animal being con- tained successively in each chamber, and retiring from it as its size becomes sufficiently great to necessitate the acquisition of more room. Each chamber, as the animal retires from it, is walled off by a curved, nacreous septum ; the communication between the chambers being still kept up by a membranous tube or siphuncle, which opens at one extremity into the peri- cardium, and is continued through the entire length of the shell. The position of the siphuncle is in the centre of each septum. Posteriorly the mantle of the Nautilus is very thin, but it is much thicker in front, and forms a thick fold or collar sur- rounding the head and its appendages. From the sides of the z 354 MANUAL OF ZOOLOGY. head spring a great number of muscular prehensile processes or "arms," which are annulated, but are not provided with cups or suckers. In the centre of the head is the mouth, sur- rounded by a circular fleshy lip, external to which is a series of labial processes. The mouth opens into a buccal cavity, armed with two horny mandibles, partially calcined towards their extremities, and shaped like the beak of a parrot, except that the under mandible is the longest. There is also a "tongue," which is fleshy and sentient in front, but is armed with recurved teeth behind. The gullet opens into a large crop, which in turn conducts to a gizzard, and the intestine terminates at the base of the funnel. On each side of the crop is a well- developed liver. Fig. 148.— Pearly Nautilus (Nautilus pompilins). a Mantle ; b Its dorsal fold ; c Hood ; o Eye ; t Tentacles ; f Funnel. The heart is contained in a large cavity, divided into several chambers, and termed the " pericardium " (Owen). The respi- ratory organs are in the form of four pyramidal branchiae, two on each side. The chief masses of the nervous system are the cerebral and infra-cesophageal ganglia, which are partially protected by a cartilaginous plate, which is to be regarded as a rudimentary cranium, and which sends out processes for the attachment of muscles. The organs of sense are two large eyes, attached by short stalks to the sides of the head, and two hollow MOLLUSCA I CEPHALOPODA. 355 plicated subocular processes, believed to be olfactory in their function. The reproductive organs of the female consist of an ovary, oviduct, and accessory nidamental gland. There is no ink-bag, and the funnel does not form a com- plete tube, but consists of two muscular lobes, which are simply in apposition. It is the organ by which swimming is effected, the animal being propelled through the water by means of the reaction produced by the successive jets emitted from the funnel. The function of the chambers of the shell appears to be that of reducing the specific gravity of the animal to near that of the surrounding water, since they are most probably filled with some gas secreted by the animal. Good authorities, how- ever, believe that the chambers of the shell are filled with water. The function of the siphuncle is unknown, except in so far as it doubtless serves to maintain the vitality of the shell. SHELL OF THE TETRABRANCHIATA. — The shells of all the Tetrabranchiata agree in the following points : — 1. The shell is external. 2. The shell is divided into a series of chambers by plates or " septa," the edges of which, where they appear on the shell, are termed the " sutures." 3. The outermost chamber of the shell is the largest, and is the one inhabited by the animal. 4. The various chambers of the shell are united by a tube, termed the " siphuncle." Agreeing in all these fundamental points of structure, two ,0 0-Q,Q Fig. 149. — Diagram to illustrate the position of the siphuncle and the form of the septa in various Tetrabranchiate Cephalopoda. The upper row of figures represents transverse sections of the shells, the lower row represents the edges of the septa. a a A mmonite or Baculite ; bb Ceratite ; c c Goniatite ; d d Ciymenia ; e e Nau- tilus or Orthoceras. very distinct types of shell may be distinguished as character- istic of the two families Nautilida and Ammonitidce, into which the order Tetrabranchiata is divided. 356 MANUAL OF ZOOLOGY. In the family Nautilida (fig. 149), the " septa " of the shell are simple, curved, or slightly lobed ; the " sutures " are more or less completely plain ; and the " siphuncle J; is central, sub-central, or internal (i.e., on the concave side of the curved shells). In the family Ammonitidce (fig. 149), on the other hand, the septa are folded and complex ; the sutures are angulated, zig- zag, lobed, or foliaceous; and the siphuncle is external (i.e., on the convex side of the curved shells). In both these great types of shell, a series of representative forms exists, resembling each other in the manner in which the shell is folded or coiled, but differing in their fundamental structure. All these different forms may be looked upon as produced by the modification of a greatly elongated cone, the structure of which may be in conformity with the type either of the Nautilidce. or of the Ammonitidce. The following table (after Woodward) exhibits the representative forms in the two families : — Nautilidfs. Ammonitidtz. Shell straight Orthoceras . . Baculites. ., bent on itself . . . Ascoceras . . Ptychoceras. ,, curved Cyrtoceras . . Toxoceras. ,, spiral Trochoceras . Turrilites. ,, discoidal .... Gyroceras . . Crioceras. ,, discoidal and produced Lituites . . . Ancyloceras. „ involute .... Nautilus . . Ammonites. After the Nautilus itself, the most important form of the Nautilidce. is the Orthoceras (fig. 150). In structure this was Fig. 150. — Orthoceras exploratory Billings, i. Side view of a fragment, showing the septa. 2. Transverse section of the same, showing (s) the siphuncle. doubtless essentially identical with the Nautilus, but the shell, instead of being coiled into a spiral lying in one plane, was ex- tended in a straight, or nearly straight, line. Orthoceratites of more than six feet in length, have been discovered, but in all, the body-chamber, in which the animal was lodged, appears to have been comparatively small. , The siphuncle is usually very MOLLUSCA: CEPHALOPODA. 357 complex in structure, and was calcareous throughout its entire length. The structure of the shell in the Ammonitidce is exactly that of the Pearly Nautilus, consisting of an outer porcellanous and an inner nacreous layer. The body-chamber was rather elongated than laterally expanded or dilated. The simplest form of the Ammonitidce is the Baculite, in which the shell is straight, like that of an Orthoceras, whilst the septa have the characters of those of an Ammonite, and the siphuncle is ex- ternal. In the Turrilite the structure of the shell is the same, but it is coiled into a turreted spiral. In the Ammonite itself, the shell is discoidal and involuted, corresponding (mform) to the shell of the Nautilus ; the body-chamber was of compara- tively large size, and had its aperture closed, in some species at any rate, by an operculum. The shell sometimes attained a gigantic size, and several hundred species of the genus have been described. In Crioceras the shell was a fiat spiral, like that of the Ammonites, but the whorls are not in contact. In Toxoceras the shell is shaped like a bow. In Ancyloceras the shell is at first discoidal, with separate whorls, then produced into a straight line, and finally bent forwards into a hook. SYNOPSIS OF THE FAMILIES OF THE CEPHALOPODA. CLASS CEPHALOPODA. ORDER I. DIBRANCHIATA. Animal with two branchiae ; not more than eight or ten » arms,*provided with suckers ; an ink-bag ; shell commonly internal and rudimentary ; rarely external, but not cham- bered. SECTION A. OCTOPODA. Arms eight, suckers sessile. Fam. i. Argonautidtoura. Hyla leucota-Hia, one of the Tree-frogs (after Giiuther). period. As maturity is approached, true lungs adapted for breathing air are developed. The development, however, of the lungs varies with the completeness with which aerial respi- ration has to be accomplished ; being highest in those forms which lose their gills when grown up (Cadutibranchiatd), and lowest in those in which the branchiae are retained throughout life (Perennibranchiata). In accordance with the change from an aquatic or branchial to a more or less completely aerial or pulmonary mode of respiration, considerable changes are effected in the course and distribution of the blood-vessels. In the larval condition, when the respiration is entirely effected by means of the gills, the circulation is carried on very much as it is in Fishes. The heart is composed of a single auricle and ventricle, and the blood is propelled through a bulbus arteriosus and bran- chial artery to the gills. The aerated blood is then collected in the branchial veins, and instead of being returned to the heart, is forthwith propelled to all parts of the body, the de- scending aorta being formed out of the branchial veins. At this stage, therefore, the heart is a branchial one, and the single contraction of the heart is sufficient to drive the blood through both the branchial and systemic circulations, just as we saw was permanently the case with all the Fishes except the Lepi- ORDERS OF AMPHIBIA. 433 dosiren. The pulmonary arteries are at first very small, and take their origin from the last pair of branchial arteries. When the lungs, however, are developed, and the respiration commences to be aerial, the pulmonary arteries increase pro- portionately in size, and more and more blood is gradually diverted from the gills and carried to the lungs, so that the branchiae surfer a proportionate diminution in size. In those Amphibians in which branchiae are permanently retained {Pertnnibranchiata), this state of affairs remains throughout life — that is to say, a portion of the venous blood is sent by the pulmonary artery to the lungs, and a portion goes to the gills. In those Amphibians, however, in which the adult breathes by lungs alone (Cadudbranchiatd), further changes ensue. In these the pulmonary arteries increase so much in size that they ultimately divert all the blood from the branchiae, and these or- gans, having fulfilled their temporary function, become atrophied and disappear. The vessels which return the aerated blood from the lungs (the pulmonary veins) increase in size proportionately with their increased work, and ultimately come to open into a second auricle formed at their point of union. The heart, therefore, of the Amphibia in their adult state consists of two auricles and a common ventricle. The right auricle receives the venous blood from the body, and the left receives the arterial blood from the lungs, and both empty their contents into the single ventricle. As in Reptiles, therefore, the ventri- cular cavity of the heart in adult Amphibians contains a mixed fluid, partly venous and partly arterial, and from this both the body and the lungs are supplied with blood. As regards the digestive system of the Amphibia there is little to say, except that the rectum opens, as it does in Reptiles, into a common chamber or " cloaca," into which are also dis- charged the secretions of the kidneys and generative organs. A liver, gall-bladder, spleen, and pancreas are always present. Singular pulsating cavities, belonging to the lymphatic system, and known as " lymph-hearts," are also present in the higher Amphibians. CHAPTER LXI. ORDERS OF AMPHIBIA. THE Amphibia are usually divided by modern writers into four orders, the old order Lepidota, comprising the Lepidosiren , 2 E 431 MANUAL OF ZOOLOGY. being now placed at the head of the Fishes, under the name of Dipnoi. Whilst there is a general agreement as to the number and characters of the Amphibian orders, the names employed to designate them are very various, and it really matters little which are adopted. ORDER I. OPHIOMORPHA, Owen (_= Gymnophiona, Huxley ; Apoda of older writers ; Ophidobatrac.hia\ — This is a small order, including only certain snake-like, vermiform animals (fig. 185) which are found in various tropical countries, burrowing in marshy ground, something like gigantic earth-worms. They form the family Caciliadce (so called by Linnaeus from their supposed blindness), and are characterised by their snake-like form, and by having the anus placed almost at the extremity of the body. Fig. 185. — Ophiomorpha. a Siphonops annulatus, one of the Csecilians, much reduced ; b Head ; c Mouth, showing the tongue, teeth, and internal openings of the nostril.-, ; d Tail and cloaca! aperture. (After Dumeril and Bibron.) The skin is quite soft, but differs from that of the typical Amphibians in mostly having small horny scales embedded in it. Another fish-like character is that the vertebrae are amphi- ccelous or biconcave, and the cavities formed by their apposi- tion are filled with the cartilaginous or gelatinous remains of the notochord. The. body is cylindrical and worm-like, and is completely destitute of limbs. The skin is glandular, naked, and viscous, thrown into numerous folds, and containing nu- merous delicate, rounded, horny scales, which are dermal in their character, and are wanting in Siphonops annulatus. The mandibular rami are short, and are united in front by a sym- physis. The teeth are long, sharp, and generally recurved ; ORDERS OF AMPHIBIA. 435 and a row of palatine teeth forms a concentric series with the maxillary teeth. The tongue is fleshy, fixed to the concavity of the lower jaw, and not protrusible (fig. 185). The ribs are numerous, but there is no sternum. The adult possesses lungs. one of which is smaller than the other, and the nose opens behind into the mouth. The eyes are rudimentary, nearly concealed beneath the skin, or altogether wanting. The position of the Ccecilitz was long doubtful ; but their Amphibian character was ultimately proved by the discovery that whilst the adult breathes by lungs, the young possess internal branchiae, communicating with the external world by a branchial aperture on each side of the neck. Only a few species of Ccedlia are known, and they are all inhabitants of hot climates, such as South America, Java, Ceylon, and the Guinea coast. They sometimes attain a length of several feet. ORDER II. URODELA ( - Ichthyomorpha, Owen ; Sauro- batrachia). — This order is commonly spoken of collectively as that of the " Tailed " Amphibians, from the fact that the larval tail is always retained in the adult. The Urodela are characterised by having the skin naked, and destitute of any exoskeleton. The body is elongated posteriorly to form a compressed or cylindrical tail, which is permanently retained throughout life. The dorsal vertebrae are biconcave (amphi- ccelous], or concave behind and convex in front (ppisthoc&lous], and they have short ribs attached to the transverse processes. The bones of the fore-arm (radius and ulna) on the one hand, and those of the shank (tibia and fibula] on the other, are not anchylosed to form single bones. In one section of the order — formerly called Amphipneusta — the gills are retained throughout life, and the animal is there- fore " perennibranchiate." In this section are the Proteus, Siren, and Menobranchus. In the remaining members of the order the gills disappear at maturity, and the animal is there- fore " caducibranchiate." In this section are the land and water salamanders. One form, however — the Axolotl of Mexico — appears to be sometimes caducibranchiate, though generally perennibranchiate. The genera Amphiuma and Menopoma, also, exhibit a partially intermediate state of parts ; for though they lose their branchiae when adult, they never- theless retain the branchial apertures behind the head. Of the perennibranchiate Urodela, one of the best known is the singular Proteus (Hypochthon) anguinus (fig. 186), which is only found inhabiting pools in certain caves in Illyria and Dalmatia. It is of a pale flesh-colour, or nearly white, with three pairs of scarlet branchiae on each side of the neck. It 43^ MANUAL 0F ZOOLOGY. attains a length of about a foot, and has two pairs of weak limbs, of which the anterior have three toes, and the posterior only two. From its habitat, the power of vision must be quite unnecessary, and, as a matter of fact, the eyes are altogether rudimentary, and are covered by the skin. Several varieties of Proteus are known, and the one figured below has been described as a distinct species (P. xanihostictus}. The blood- corpuscles in Proteus are oval in shape, and are larger than those of any other Vertebrate animal. Fig. 186. — Head and fore-part of the body of Pro feus angidnus, showing the external branchiae and tridactylous fore-limb. Of the Sir&iidee, the most familiar are the Sirens and the Axolotls. The Siren, or Mud-eel, is found abundantly in the rice-swamps of South Carolina, and attains a length of three feet. The branchiae are persistent, and the hinder pair of legs wholly wanting. Two other species are known, but they are likewise confined to North America. • The Mexican Axolotl (Siredon pisciforme, fig. 187) is a native of the Mexican lakes, and attains a length of about a foot or fourteen inches. It possesses both pairs of limbs, the anterior pair having four toes, and the hinder pair five toes. As ordi- narily known in its native country, the Axolotl is certainly perennibranchiate, and they breed in this condition freely. There is no doubt, however, that individual specimens may lose their gills, without thereby suffering any apparent change, except it be one of colour. The Axolotl, therefore, is in the singular position of being sometimes " caducibranchiate," whilst it is ordinarily " perennibranchiate." * Nearly allied * Professor Marsh of New Haven has recently shown that the Siredon lickenoides of the western States of America, when kept in confinement, loses its gills, and dorsal and caudal fins, whilst it changes much in colour, and undergoes various minor modifications in structure. Its habits, also, become less aquatic, and it becomes apparently absolutely identical with Amblystoma mavortiiun, a Salamandroid. This discovery has thrown con- siderable doubt upon the value of the distinction bet ween perennibranchiate and caducibranchiate Amphibians, and has rendered it probable that all the species of Siredon are merely larval Salamanders, as long ago suspected by Cuvier. At the same time, the Axolotls certainly breed freely whilst in possession of their branchiae, and there is as yet no proof that they lose their gills whilst in a state of nature. ORDERS OF AMPHIBIA. 437 to the Axolotl is the Mbnobranchus of North America, in which the branchiae are persistent. Amphiuma and Menopoma, as already remarked, differ from the form just mentioned in losing the gills when adult, but in retaining the external bran- chial apertures on the side of the neck. The former is exclusively North American, whilst the latter is represented by different but nearly-related species in both North America and Java. Both possess the normal two pairs of limbs. The Javanese species (Menopoma maxima) has the gill-slit closed in the adult. It is about three feet long, and is the nearest living relative of the extinct Andrias. In the second section of the Urodela, comprising those forms in which the gills are caducous, and both pairs of limbs are always present, are the Water- salamanders or Tritons, and the Land -salamanders. The Tri- tons are the only examples of the aquatic Salamanders which occur in Britain, and every one, probably, is acquainted with the common Newt. The Water-salamanders or Newts (fig. 1 88) are distin- guished from the terrestrial forms by being furnished with a compressed fish-like tail, and by being strictly oviparous. The larvae are tadpole-like, with external branchiae, which they retain till about the third month. The adult is destitute of gills, and breathes by lungs alone, but the larval tail is re- tained throughout the life of the animal. The tongue is small, free, and pointed be- hind, and there are two rows of palatine teeth. The fore-feet are four-toed, the hind -feet five-toed : and the males have a crest on the back and tail. Fig. 187. — The Axolotl (Siredon pisci- Jorme] — after Tegetmeier. The ordi- nary form, with persistent branchi se. 438 MANUAL OF ZOOLOGY. The development of the Newts 'is so like that of the Frogs that it is unnecessary to dilate further upon it here ; but there are these two points of difference to be noticed :— u//x, That the embryonic tail is not cast off in the adult ; and, 2(ily, That the fore-limbs are developed sooner than the hind-limbs — the reverse of this being the case amongst the Anoura. Fig. 188.— Great Water-newt {Triton cristatu*) — after Bell. The Land-salamanders form the genus Salamandra, and are distinguished from their aquatic brethren by having a cylindri- cal instead of a compressed tail, and by bringing forth their young alive, or by being ovo-viviparous, in which case the larvae have sometimes shed their external branchiae prior to birth. The head is thick, the tongue broad, and the palatine teeth in two long series. The skin is warty, with many glands secreting a watery fluid. The best known species is the S. maculosa of Southern Europe. Another species (S. alpina) lives upon lofty mountains. The chief thing to remember about the Land-salamanders, and, indeed, about all the Uro- dela, is their complete distinctness from the true Lizards (Lacer- tilia]. They are often completely lizard-like in form when adult, but they always possess gills in the earlier stages of their exist- ence, and this distinguishes them from all the Lacertilians. ORDER III. ANOURA ( = Batrachia, Huxley ; Theriotnorpha, Owen ; Chelonobatrachia, &c.) — This order includes the Frogs and Toads, and is perhaps best designated by the name of Anoura, or "Tail-less" Amphibians. The name Batrachia, employed by Huxley, is inexpedient, partly because it is used by Owen to designate the entire class Amphibia, and partly because, in common language, it is usual to understand by a " Batrachian " any of the higher Amphibians — such, for instance, as a Labyrinthodont. The Anoura, or Tail-less Amphibians, are characterised by the following points : — The adult is destitute of both gills and tail, both of which structures exist in the larva, whilst the two ORDERS OF AMPHIBIA. 439 pairs of limbs are always present. The skin is soft, and there are rarely any traces of an exoskeleton. The dorsal vertebrae are " proccelous," or concave in front, and are furnished with long transverse processes, which take the place of ribs, which are only present in a rudimentary form. The radius and ulna in the fore-limb, and the tibia and fibula in the hind-limb, are anchylosed to form single bones (fig. 189). The mouth is sometimes edentulous, but the upper jaw has usually small teeth, and the lower jaw sometimes. The hind-limbs usually have the digits webbed for swimming, and are generally much larger and longer than the fore-limbs. The vertebral column is short (of ten vertebrae in the Frogs, but only eight in Pipa). Fig. 189. — Skeleton of the common Frog (Rana temporaria}- d Dorsal Vertebrae, with long transverse processes. The tongue is soft and fleshy, not supported by an os hyoides, but fixed to the symphysis of the lower jaw in front. Pipa has a sort of valve over the tympanum ; Hyla and Rana have the tympanum shown externally ; and Bufo has the tympanum concealed. In the adult Anoura, respiration is purely aerial, and is car- ried on by means of lungs, which are, comparatively speaking, well developed. As there are no movable ribs by which the thoracic cavity can be expanded, the process of respiration is somewhat peculiar. The animal first closes its mouth, and fills the whole buccal cavity with air taken in through the 440 MANUAL OF ZOOLOGY. nostrils. The posterior nares are then closed, and by the con- traction of the muscles of the cheeks and pharynx the inspired air is forcibly driven into the windpipe through the open glottis. The process, in fact, is one of swallowing ; and it is possible to suffocate a frog simply by holding its mouth open, and thereby preventing the performance of the above-mentioned actions. There can be no doubt, also, that the skin in these animals plays a very important part in the aeration of the blood, and that the frogs especially can carry on their respiration cutane- ously, without the assistance of the lungs, for a very lengthened period. This undoubted fact, however, should not lead to any credence being given to the often-repeated stories of the occur- rence of frogs and toads in cavities in solid rock, no authen- ticated instance of such a phenomenon being as yet known to science. Fig. 190. — Development of the common Frog (Rana. temporaria). a Tadpole, viewed from above, showing the external branchiae (g) ; b Side view of a somewhat older specimen, showing the fish-like tail ; c Older specimen, in which the hind-legs have appeared ; d Specimen in which all the limbs are present, but the tail has not been wholly absorbed. (After Bell.) The young or larvae of the Frogs and Toads are familiarly known as " Tadpoles." The ova of the Frog are deposited in masses in water, and the young form, upon exclusion from the egg, presents itself as a " tailed " Amphibian, completely fish- like in form, with a broad rounded head, a sac-like abdomen, and a compressed swimming-tail (fig. 190, a). There are at first two sets of gills, one external and the other internal. The external branchiae (fig. 190, a) have the form of filaments at- tached to the side of the neck, and they disappear very shortly after birth. The internal branchiae are attached to cartilaginous arches, which are connected with the hyoid bone, and they are ORDERS OF AMPHIBIA. 441 contained in a gill-cavity, protected by a flap of integument, which differs from the gill-cover of fishes in never developing any opercular bones or branchiostegal rays. Within the bran- chial chamber thus formed the fore-limbs are budded forth, but the hind-limbs are the first to appear, instead of the fore-limbs, as in the case with the Urodela. Even after the first appear- ance of the limbs, the tail is still retained as an instrument of progression ; but as the limbs become fully developed, the tail is gradually absorbed (fig. 190, d), until in the adult it has wholly disappeared. The development of the Frog is thus a good illustration of the general zoological law that the transient embryonic stages of the higher members of any division of the animal kingdom are often represented by the permanent condition of the lower members of the same division. Thus the transitory condition of the young Frog in its earliest stage, when the branchiae are external, is permanently represented by the adult perenni- branchiate Urodela, such as the Proteus or the Siren. The final stage, again, when the gills have disappeared and the limbs have been developed, but the tail has not been wholly absorbed, is represented by the caducibranchiate Urodela, such as the common Newt. The order Anoura comprises a considerable number of forms, but may be divided into the three sections of the Pipidce, Bufonidcz, and JRanida. In the Pipidce, or Surinam Toads, there are rarely teeth, and the mouth is destitute of a tongue. A singular and hideous species (Pipa Americana] is the best known, and it inhabits Brazil and Surinam. In this curious Amphibian the eggs are placed by the male on the back of the female, in the integument of which, in cell-like cavities, the eggs are hatched and the young developed. In the aberrant form Dadylethra the upper jaw is furnished with small teeth, and the three inner toes of the hind-feet are fur- nished with nails, as is the case with no other Amphibian, except Salamandra unguiculata amongst the Urodela. This curious form is found at the Cape of Good Hope and in Mozambique. In the Toads, or Btifonidce, a tongue is present, but the jaws are not armed with teeth. The tongue agrees with that of the Frogs in being fixed to the front of the mouth, whilst it is free behind, so that it can be protruded for some distance from the mouth. The hind-limbs are not disproportionately developed, whilst the toes are only imperfectly webbed, and the toes of the fore-limb are free. The skin is warty and glan- dular. The common Toad (Bufo vulgaris] is an excellent 442 MANUAL OF ZOOLOGY. example of this family. The Natter-jack Toad is the only other British species, but about fifty other forms are known, of which many are American. In the Ranida the tongue has the same form as in the Toads, but the upper jaw always carries teeth. The hind- limbs are much larger than the fore-limbs, and are fitted for leaping, whilst the toes are webbed. The toes of the fore- limbs are free. The common Frog (Rana temporaries) is a good example of the typical Ranidce. Larger than the common Frog is the Eatable Frog (Rana esculenta) of Europe, and larger again than this is the Bull-frog (Rana pipiens) of North Ame- rica. The Tree-frogs (Hyla] are adapted for a wholly different mode of life, having the toes of all the feet furnished with ter- minal suckers, by the help of which they climb with ease. They are mostly found in warm countries, especially in America, but one species (Hyla arbored) is European (fig. 154). ORDER IV. LABYRINTHODONTIA. — The members of this, the last order of the Amphibia, are entirely extinct. They were Batrachians, probably most nearly allied to the Urodela, ™*/>2» ' * ^* V I ^^ ^.^-i^ ' 7* V ^^ Fig. 191. — Footprints of a Labyrinthodont (Cheirotherinm}. but all of large size, and some of gigantic dimensions, the skull of one species (Labyrinthodon Jagaeri ) being upwards of three feet in length and two feet in breadth. The Labyrinthodonts were first known to science simply by their footprints, which were found in certain sandstones of the age of the Trias. These footprints consisted of a series of alternate pairs of hand-shaped impressions, the hinder print of each pair being much larger than the one in front (fig. 191). So like were these impressions to the shape of the human hand that the unknown animal which produced them was at once christened C heir ot her ium, or " Hand-beast." Further discoveries, however, soon showed that the footprints of Cheirothermm had been produced by different species of Batrachians, to which the name of Labyrinthodonts was applied, in consequence of the complex microscopic structure of the teeth. The Labyrinthodonts were " salamandriform, with relatively weak limbs and a long tail " (Huxley). The vertebral centra and arches were ossified, and the bodies of the dorsal vertebrae ORDERS OF AMPHIBIA. 443 are biconcave (amphiccelous). " In the thoracic region three superficially-sculptured exoskeletal plates, one median and two lateral, occupy the place of the interclavicle and clavicles. Between these and the pelvis is a peculiar armour, formed of rows of oval dermal plates, which lie on each side of the middle line of the abdomen, and are directed obliquely for- wards and inwards to meet in that line" (Huxley). The head was defended by an external covering or helmet of hard and polished osseous plates, sculptured on their exter- nal surface, and often exhibiting peculiar, smooth, symmetrical grooves — the so-called " mucous canals." The skull was arti- culated to the vertebral column by two occipital condyles. The teeth are rendered complex by numerous foldings of their parietes, giving rise to the "labyrinthine" pattern, from which the name of the order is derived. The Labyrinthodonts are known to occur from the Carboni- ferous to the Triassic or Liassic period inclusively ; but they are most characteristically and distinctively Triassic. DISTRIBUTION OF AMPHIBIA IN TIME. — From a geological point of view, by far the most important of the Amphibia are the Labyrinthodontia, the distribution of which has just been spoken of. The living orders of Amphibia are of much more modern date, being, as far as known, wholly Tertiary and Post-tertiary. The Anoura are represented by both Toads and Frogs in Miocene times, and they have survived to the present day. The " Tailed " Amphibians are best known to geologists by a singular fossil, which was described by its ori- ginal- discoverer as human, under the name of Homo diluvii testis. The fossil in question is of Miocene age, and it is now known to belong to a Salamander, nearly allied to the giant- salamander of Java (Mcnopoma). It is termed the Andrias Scheuchzeri. If the Palceosiren of Geinitz be not truly re- ferable to the Labyrinthodonts, then the Urodela date from the Permian period. 444 DIVISION II. SAUROPSIDA. CHAPTER LXIL CLASS III.—REPTILIA. THE second great division of the Vertebrate sub-kingdom, according to Huxley, is that of the Sauropsida, comprising the true Reptiles and the Birds. It is, no doubt, at first sight an almost incredible thing that there should be any near bond of relationship between the Birds and the Reptiles, no two classes of animals being more unlike one another in habits and ex- ternal appearance. It is, nevertheless, the fact that the Birds are more nearly related to the Reptiles than to any other class of the Vertebrata, and it will shortly be seen that many affini- ties and even transitional forms are known to exist between these great sections. The Reptiles and Birds, then, may be naturally included in a single primary section of Vertebrates, which may be called Sauropsida after Huxley, and which is denned by the possession of the following characters : — At no period of existence are branchiae, or water-breathing respiratory organs, developed upon the visceral arches ; the embryo is furnished with a well-developed amnion and allantois ; the red corpuscles of the blood are nucleated (fig. 159, <£, c) ; the skull articulates with the vertebral column by means of a single articulating surface or condyle ; and each half or " ramus " of the lower jaw is composed of several pieces, and articulates with the skull, not directly, but by the intervention of a pecu- liar bone, called the " quadrate bone," or " os quadratum " (fig. 192). These being the common characters of Reptiles and Birds by which they are collectively distinguished from other Verte- brates, it remains to inquire what are the characters by which they are distinguished from one another. The following, then, are the characters which separate the Reptiles from the Birds : — The blood in Reptiles is cold — that is to say, slightly warmer than the external medium — owing mainly to the fact that the pulmonary and systemic circulations are always directly con- CHARACTERS OF REPTILIA. 445 nected together, either within the heart or in its immediate neighbourhood, so that the body is supplied with a mixture of venous and arterial blood, in place of pure arterial blood alone. The terminations of the bronchi at the surface of the lung are closed, and do not communicate with air-sacs, placed in dif- ferent parts of the body. When the epidermis develops horny structures, these are in the form of horny plates or scales, and never in the form of feathers. The fore-limbs are formed for various purposes, including in some cases even flight, but they are never constructed upon the type of the " wings " of Birds. Lastly, with one or two doubtful exceptions, whilst the ankle- joint is placed between the distal and proximal portions of the tarsus, the tarsal and metatarsal bones of the hind-limb are never anchylosed into a single bone. These are the leading characters by which Reptiles are dis- tinguished from Birds, but we must not forget the other dis- tinctive peculiarities in which Reptiles agree with Birds, and differ from other Vertebrates — namely, the presence of an amnion and allantois in the embryo, the absence of branchiae at all times of life, the possession of only one occipital condyle, and the articulation of the complex lower jaw with the skull by means of a quadrate bone. It is now necessary to consider these characteristics of the Reptilia a little more minutely. The class includes the Tor- toises and Turtles, the Snakes, the Lizards, the Crocodile^, and a number of extinct forms ; and with the exception of th£ Tor- toises and Turtles they are mostly of an elongated cylindrical shape, provided posteriorly with a long tail. The limbs may be altogether absent, as in the Snakes, or quite rudimentary, as in some of the Lizards ; but, as a general rule, both pairs of limbs are present, sometimes in the form of ambulatory legs, sometimes as swimming-paddles, and in some extinct forms modified to subserve an aerial life. The endoskeleton is always well ossified, and is never cartilaginous or semi-carti- laginous, as in many fishes and some Amphibians. The skull articulates with the atlas by^a single condyle.. The lower jaw is complex, each half or ramus being composed of from four to six pieces, united to one another by sutures (fig. 192). In the tortoises, however, these are anchylosed into a single piece, and the two rami are also anchylosed. In most reptiles, how- ever, the two rami of the lower jaw are only loosely united — in the Snakes by ligaments and muscles only, in the Lizards by nbro-cartilage, and in the Crocodilia by a regular suture. In all, the lower jaw articulates with the skull by a quadrate bone (fig. 192, a) ; and as this often projects backwards, the 446 MANUAL OF ZOOLOGY. opening of the mouth is often very extensive, and may even extend beyond the base of the skull. Teeth are usually pre- sent, but are not sunk in separate sockets or alveoli, except in the Crocodiles, and in some extinct forms. In the Tortoises and Turtles alone of living types there are no teeth, and the jaws are simply sheathed in horn, constituting a kind of beak like that of a bird. Ribs are always present, and always well. .developed, hni- thpy differ much in form. It is not correct, however, to regard the presence of ribs as separating the true Reptiles from the Amphibia, as is sometimes stated. Some of the most Lizard- like of the Amphibians, such as the Siren, possess short but well-developed ribs, and rudiments of ribs are traceable in other orders ; whilst in the CcecilicE they are large and well developed. As regards the exoskeleton, most Reptiles have horny 6 Fig. 192.— Skull of a Serpent (Python}, b Articular portion of the lower jaw ; a Quadrate bone ; c Squamosal portion of the temporal bone. epidermic scales, and they are divided into two great sections — called respectively Squamata and Loricata — according as the integumentary skeleton consists simply of these scales, or there are osseous plates developed in the derma as well. In the Tortoises, the epidermic plates unite with the bony exoskeleton and with the true endoskeleton to form the case or box in which the body of these animals is enclosed. The digestive system of the Reptilia possesses few characters of any special importance, except that the rectum opens, as in Amphibia, into a common cavity or " cloaca," which not only receives the faeces, but also serves for the discharge of the products of the urinary and generative organs. Thetieartm the Reptiles consists of two completely separate auricles, and a ventricular cavity, which is divided into two by an incomplete partition. In the Crocodilia alone is the septum CHARACTERS OF REPTILIA. 447 between the ventricles a perfect one, and even in these, as in all other Reptiles, the heart consists functionally of no more than three chambers. The ordinary course of the circulation, where the ventricular septum is imperfect, is as follows : — The impure venous blood returned from the body is, of course, poured by the venae cavae into the right auricle (fig. 193, a), and thence into the ventricle. The pure arterialised and aerated blood that has passed through the lungs, is, equally of course, poured into the left auricle (a), and thence propelled into the ventricle (?'). As the ventricular cavity is single, and not divided by a complete partition, it fol- lows of necessity that there is a mixture in the ventricle, resulting in the production of a mixed fluid, consisting partly of venous and partly of arterial blood. This mixed fluid, then, occupies the common ventricular cavity, and by this it is driven both to the lungs (through the pulmonary artery), and to the body (through the systemic aorta). Conse- quently, in Reptiles, both the lungs and the various tissues and organs of the body are supplied with a mixture of arterial and venous blood, and not with un- mixed blood — the lungs with purely venous, and the body with purely arterial blood — as is the case with the higher Vertebrata. said, the partition between the ventricles is a complete one, and consequently this mixture of the arterial and venous blood cannot take place within the heart itself. In these Reptiles, however, a direct communication exists between the pulmonary artery and aorta (the right and left aortae) by the so-called " foramen Panizzae," close to the point where these vessels spring respectively from the right and left ventricle. In these Reptiles, therefore, the same mixture of arterial blood with Fig- 193.— Diagram of the circulation in Reptiles. (The venous system is left light, the arterial system is black, and the vessels containing mixed blood are cross-shaded.) a Right auricle, receiv- ing venous blood from the body ; a1 Left auricle, receiving arterial blood from the lungs ; -v Arterio-venous ven- tricle, containing mixed blood, which is driven by (/) the pulmonary artery to the lungs, and by \o) the aorta to the body. In the Crocodilia, as before MANUAL OF ZOOLOGY. venous takes place as in the lower Reptilia, though probably not to so complete an extent. It is this peculiarity of the circulation in all Reptiles which conditions their low tempera- ture, slow respiration, and generally sluggish vital actions. The lungs in all Reptiles, except the Crocodiles, are less completely cellular than in the Birds and Mammals, and they often attain a very great size. In no Reptile is the cavity of the thorax shut off from that "of the abdomen by a complete muscular partition or " diaphragm ; " though traces of this structure are found in the Crocodiles. The lungs, therefore, often extend along the whole length of the thoracico-abdominal cavity. In no case are the lungs connected with air-receptacles situated in different parts of the body ; and not uncommonly there is only a single active lung, the other being rudimentary or completely atrophied (Ophidid). Lastly, all reptiles are essentially oviparous, but in some cases the eggs are retained within the body till the young are ready to be excluded, and the animals are then ovo-viviparous. The egg-shell is usually parchment-like, but sometimes contains more or less calcareous matter. CHAPTER LXIII. DIVISIONS OF REPTILES. CHELONIA AND OPHIDIA. THE class Reptilia is divided into the following nine orders, of which the first four are represented by living forms, whilst the remaining five are extinct : — :. Chelonia (Tortoises and Turtles). ^ 2. Ophidia (Snakes). V. Recent 3. Lacertilia (Lizards). ( * 4. Crocodilia (Crocodiles and Alligators). ) 5. Ichthyopterygia. ] 6. Sauropterygia. 7. Anomodontia. \ Extinct. 8. Pterosauria. 9. Deinosauria. ORDER I. CHELONIA. — The first order of living Reptiles is that of the Chelonia^ comprising the Tortoises and Turtles, and DIVISIONS OF REPTILES. 449 distinguished by the following characters : — There is an osseous exoskeleton which is combined with the endoskeleton to form a kind of bony case or box in which the body of the animal is enclosed, and which is covered by a leathery skin, or, more usually, by horny epidermic plates. The dorsal vertebrae, with the exception of the first, are immovably connected together, and are devoid of transverse processes. The ribs are greatly expanded (fig. 194, r\ and are united to one another by sutures, so that the walls of the thoracic cavity are immovable. All the bones of the skull except the lower jaw and the hyoid bone are immovably united together. There are no teeth, and the jaws are encased in horn so as to form a kind of beak. The tongue is thick and fleshy. The heart is three-chambered, the ventricular septum being imperfect. There is a large uri- nary bladder, and the anal aperture is longitudinal or circular. The lungs are voluminous, and respiration is by swallowing air, as in the Frogs. All will pass prolonged periods without food, and will live and move, even for months, after the removal of the entire brain (Redi). Of these characters of the Chelonia, the most important and distinctive are the nature of the jaws, and the structure of the exoskeleton and skeleton. As regards the first of these points, the lower jaw in the adult appears to consist of a single piece, its complex character being masked by anchylosis. The sepa- rate pieces which really compose each ramus of the jaw are immovably anchylosed together, and the two rami are also united in front by a true bony union. There are also no teeth, and the edges of the jaws are simply sheathed in horn, constituting a sharp beak. In the Chelydidce, and Trionycidce, however, the horny jaws are covered with soft skin, constituting a kind of lips. As regards the second of these points, the bony case in which the body of a Chelonian is enclosed consists essentially of two pieces, a superior or dorsal piece, generally convex, called the "carapace," and an inferior or ventral piece, generally flat or concave, called the "plastron." The carapace and plastron are firmly united along their edges, but are so excavated in front and behind as to leave apertures for the head, tail, and fore and hind limbs. The limbs and tail can almost always be withdrawn at will under the shelter of the thoracico-abdominal case formed in this way by the carapace and plastron, and the head is also generally retractile. The carapace or dorsal shield is composed of the following elements : — i. The spinous processes of the dorsal vertebra, which are much flattened out laterally and form a series of broad plates. 2 F 450 MANUAL OF ZOOLOGY. 2. The ribs, which are also much flattened and expanded, and constitute what are known as the "costal plates " (fig. 194, ;-). They are generally eight in number on each side, and are commonly united throughout the whole of their lateral margins by sutures. In some cases, however, they leave marginal apertures towards their extremities, and these openings are simply covered by a leathery skin or by horny plates. 3. The margin of the carapace is completed by a series of bony plates, Fig. 194.— Skeleton of Tortoise (Emys Enropcea), the plastron being removed, ca Carapace ; r Ribs, greatly expanded, and united by their edges ; j Scapular arch, placed within the carapace, and carrying the fore-limbs ; p Pelvic arch, also placed within the carapace, and carrying the hind-limbs. which are called the "marginal plates." These are variously regarded as being dermal bones belonging to the exoskeleton, or as being endoskeletal, and as representing the ossified cartilages of the ribs (in this last case the marginal plates would correspond with what are known as the " sternal ribs " of Birds). The " plastron " or ventral shield is composed of a number of bony plates (nine in number), the nature of which is doubt- CHELONIA. 45 I ful. By some, the plastron is still regarded as a greatly-devel- oped breast-bone or sternum. By others, again, the Chelonia are regarded as being wholly without a sternum, and the bones of the plastron are looked upon as exclusively integu- mentary ossifications. Of the nine pieces of the plastron, eight are in pairs, whilst the ninth is odd, and is placed between the four anterior ones. Both the carapace and the plastron are covered by a leathery skin, or more generally by a series of horny plates (fig. 195), which roughly correspond with the bony plates below, and which constitute in some species the " tortoise-shell " of commerce. These epidermic plates, however, must on no account be confounded with the true bony box in which the animal is enclosed, and which is pro- duced partly by the true endoskeleton and partly by dermal integumentary ossifications. The other points of importance as regards the end«skeleton are these : — Firstly, The dorsal vertebrae are immovably joined together, and have no transverse processes, the heads of the ribs uniting directly with the bodies of the vertebrae. Secondly, The scapular and pelvic arches, supporting the fore and hind limbs respectively (fig. 194, s and /), are placed within the carapace, so that the scapular arch is thus inside the ribs, instead of being outsider as it normally is. The scapular arch consists of the shoulder-blade or scapula, and two other bones, of which one corresponds with the acromion process of human anatomy, and the other to the coracoid process, or to the " coracoid bone" of the Birds. The clavicles, as is also the case with the Crocodilia, are absent. The order Chelonia is conveniently divided into three sec- tions, according as the limbs are natatory, amphibious, or ter- restrial. In the first of these, the limbs are converted into most efficient swimming-paddles, all the toes being united by a common covering of integument. In this section are the well- known Turtles (Cheloniida), all of which swim with great ease and power, but are comparatively helpless upon the land (fig. 195). The legs are of unequal length, and the carapace is much depressed and flattened. The best-known species are the "edible" or Green Turtle (Chelone my das], the Loggerhead Tur- tle ( Chelone caonanna), the Hawk's-bill Turtle (C. imbricata), and the Leathery Turtle (Sphargis coriaced). The Green Turtle is largely imported into this country as a delicacy, and occurs abundantly in various parts of the Atlantic and Indian Oceans. The Hawk's-bill Turtle is of even greater commercial impor- tance, as the horny epidermic plates of the carapace constitute 452 MANUAL OF ZOOLOGY. the l< tortoise-shell " so largely used for ornamental purposes. The Leathery Turtle is remarkable in having the carapace covered with a leathery skin in place of the horny plates which are found in other species. In the second section of the Chelonia^. in which the limbs are adapted for an amphibious life, are the Mud-turtles or soft Tortoises (Trir of Mexico, only the fore-limbs are present, and in the African genus Bipes only the hind-limbs are present. In the Amphisbana of South America the tail is very short,, and the vent is placed nearly at the end of the body, whilst there are no limbs. In the Glass Snake (Ophi- saurus} of the United States there are also- no limbs. The next great family is that of the Scincida, including a number of small Lacertilians, some of which are completely snake-like, whilst others possess two limbs, and others again have the normal two pairs of limbs in a well-developed condi- tion. All possess movable eyelids, and in all the conforma- tion of the lower jaw is Lacertilian, and not Ophidian. All the Scincoidean Lizards have the body covered by similar scales overlapping one another like the scales of fishes, whilst TACERTILIA AND CROCODILIA. 46. the head is protected by larger plates. The tongue is free, fleshy, and slightly notched. Of the snake -like forms of this group, none is more familiarly known than the Blind-worm or Slow-worm (Anguis fragiUs, fig. 200), which is found over almost the whole of Europe, in western Asia, and northern Africa, and which is one of the most abundant of the British Reptiles. The Blind-worm possesses no external appearance of limbs, though the scapular and pelvic arches are present in a rudimentary condition. Its appearance is completely serpentiform, and it is vulgarly regarded as a dan- gerous and venomous animal, but quite erroneously, as it is even unable to pierce the human skin. It is a perfectly harm- less animal, living upon worms, insects, and snails, and hyber- Fig. 200. — The Blind-worm (Angitisfragilis] — after Bell. nating during the winter. It derives its specific name of fragilis from the fact that when alarmed it stiffens its muscles to such an extent that the tail can be readily broken off, as if it were brittle. Numerous other small Lizards are referable to the Scinridce, but it is only necessary to mention the Skinks themselves (Scincus], in which both pairs of limbs are present in a well- developed state. The Skinks are found in almost all the warmer parts of the Old World, and closely-allied forms (such as the West Indian " Galliwasp ") are found in the New World. The common Skink (fig. 201) is a native of Arabia and Africa. 464 MANUAL OF ZOOLOGY. It attains a length of eight or nine inches, and was formerly used in various diseases as a remedy. The next family is that of the Lacertida, comprising the typical Lizards, in which there are always four well-developed limbs, each terminated by five free toes of unequal lengths. The body is covered with scales, which assume the form of shields or " scuta" over the abdomen and on the head. The tail is rounded. The tongue is slender, bifid, and protrusible. The only truly British Lizards are the Sand-lizard (Lacerta agilis], and the Viviparous Lizard (Zootoca vivipard) ; and the commonest form upon the Continent is the graceful little Green Lizard (Lacerta viridis], which also occurs in Jersey. The Fig. 201.— The common Skink (Seine us officlnalis). Lizards of the Old World are represented in America by the Ameivce, some of which attain a length of several feet. Very closely allied to the true Lizards are the Varanida or Monitors, which indeed are chiefly separated by the compara- tively trivial fact that the abdomen and head are covered with ordinary scales, and not with large " scuta." The tongue is protrusible and fleshy, like that of the Snakes. The teeth are lodged in a common alveolar groove, which has no internal border ; and there are no palatal teeth. The tail has a double row of carinated scales, and is cylindrical in the terrestrial forms, and compressed in those whose habits are aquatic. The Monitors are exclusively found in the Old World, and are the largest of all the recent Lacertilia; the Varanus Niloticus of Egypt attaining a length of six feet, and the Varanus bivittatus LACERTILIA AND CROCODILIA. 465 of Java attaining to as much as eight feet. The Safe-guards (Salvator) are the Monitory Lizards of the New World, and are also of large size. The Geckotidce form a large family of Lizards, comprising a great number of species, occurring in almost all parts of the world. The tongue is wide, flat, scarcely notched at its free extremity, and hardly at all protrusible. The eyes are large, with extremely short lids, the pupil mostly linear, but some- times circular. The teeth are numerous, small, compressed, and implanted on the inner edge of the jaw. The nails are mostly hooked and retractile, and the toes are furnished below with imbricated plates. The animal is capable of running on the smoothest surfaces, or suspending itself back-downwards. They feed on insects, and are found in abundance in the warmer parts of both the Old and New Worlds. The Igtianidce constitute another large family of Lizards, also belonging partly to the Old and partly to the New World. The tongue is thick, fleshy, notched at its extremity only, and not protrusible. M'ostly there is a dorsal crest, and a goitre or throat-pouch. The body is covered with imbricated scales. Only one species of the family is European, but the group is represented by numerous species in N. and S. America, Asia, Africa, and Australia. They are often divided into "ground- iguanas," in which the body is flat and depressed, and " tree- iguanas," in which the body is compressed. The members of the genus Iguana itself (fig. 199) are confined to the New World, and are distinguished by having the throat furnished with a pendulous dewlap or fold of skin, the edge of which is toothed. The back and tail, too, are furnished with an erect crest of pointed scales. The Iguana attains a length of from four to five feet, and though not of a very inviting appearance, is highly esteemed as food. The Basilisks (Basiliscus) have the top of the head furnished with a membranous sac, which can be distended with air at will. The Agamidce, agree with the Iguanas in most respects, but have two rows of teeth on the hinder margin of the palate, and the tail is covered with imbricated scales. Good examples are the Tapayaxin (Agama orbicularis) of South America, and the hideous Moloch horridus of Australia. Here also belongs the curious little Frill Lizard (Chlamydosaurus] of Australia, which has the neck furnished on each side with a membranous plaited frill, which can be erected at will. More remarkable than the true Iguanas is the little Flying Dragon (Draco volans) of the East Indies and Indian Archipelago. In this singular little Lizard there is a broad membranous expansion on each side, formed by a fold 2 G 466 MANUAL OF ZOOLOGY. of the integument, supported upon the anterior false ribs, which run straight out from the spinal column. By means of these lateral expansions of the skin, the Draco volans can take long flying leaps from tree to tree, and can pursue the insects on which it feeds; but the lateral membranes simply act as parachutes, and there is no power of true flight, properly so called. The last family of the living Lizards which requires notice is that of the Chamaleontida, containing the familiar little Chamtzleo Africamis, which occurs abundantly in the north of Africa and in Egypt, and is so well known for its power of changing its colour under irritation or excitement. In this genus the eye (fig. 202) is of large size, and is covered by a single circular lid, formed by a coalescence of the two lids, and perforated centrally by a small aperture, by which the rays of light reach the pupil. The Chameleon is naturally a sluggish Fig. 202. — Head of a Chameleon (C. Petersii) — after Gray. animal, but it catches its food, consisting of insects, by darting out its long, fleshy, and glutinous tongue — an operation which it effects with the most extraordinary rapidity. The tail in the Chameleons is round and prehensile, the body compressed, and the skin like shagreen. The toes are adapted for the arboreal life and scansorial habits of the animal, being so arranged as to form two equal and opposable sets. The lungs are excessively voluminous. The Chameleons are exceedingly sluggish and slow in their movements, and are confined to the warmer parts of the Old World. DISTRIBUTION OF LACERTILIA IN TIME. — It is hardly pos- sible, with our present knowledge, to speak very positively as to the exact range of the Lacertilia in time. This uncertainty arises from two causes — firstly, that there is some doubt as to the exact age of some deposits which have yielded Lacertilian remains ; and, secondly, that the affinities of some extinct LACERTILIA AND CROCODILIA. 467 Reptiles are a matter of considerable question. Upon the whole, the oldest known Lacertilian would appear to be the Protorosaurus of the Middle Permian Rocks; though good authorities have placed this form in the Crocodilian group of the Thecodontia. Protorosaurus attained a length of between three and four feet, and differs from all existing Lizards in having its teeth implanted in distinct sockets — this being a Crocodilian character. In other respects, the Permian reptile approximates closely to the living Monitors ( Varanidce}, and its slightly cupped vertebrae would lead to the belief that it was aquatic in its habits. In rocks known, or supposed, to be of Triassic age, numerous Lacertilian reptiles have been discovered, of which the most important are Telerpeton, Hyperodapedon, and Rhynchosaurus, of which the last is generally referred to the group of the Anomodontia, to be subsequently spoken of. In the Jurassic period, the remains of Lacertilians are not unknown, but call for little special notice. Several forms of little importance have been described from the Middle Oolites. In the fresh- water strata of the Purbeck series (Upper Oolites), occur the remains which have been referred to the genera Nuthetes, Macellodon, Saurillus, and Echinodon. These are, perhaps, the first traces in the stratified series of remains, the affinities of which to the typical Lacertidce cannot be disputed. In the Cretaceous Rocks, and almost exclusively confined to strata of this age, occur the singular Lacertilians which form the group of the " Mosasauroids." These remarkable Reptiles were of gigantic size, Mosasaurus princeps being believed to have attained the enormous length of not less than seventy- five feet. The teeth of these reptiles are long, pyramidal, and slightly curved ; but they are anchylosed to the jaw, and are not sunk into distinct sockets as in the living Crocodiles. From the shortness of the humerus, and the indications that the vertebral column was unusually flexible, and that the tail was laterally compressed, it was early conjectured that the Mosasauroids were marine and aquatic in their habits. This conjecture has been raised to the rank of a certainty by the discovery that the fore and hind limbs of the Mosasauroids were in the form of fin-like paddles, like those of the Ichthyo- saur and Plesiosaur. There can, therefore, be no doubt that Mosasaurus — like the living Amblyrhynchus — was aquatic in its habits, and frequented the sea-shore, coming, in fact, only occasionally to the land. Professor Marsh has also recently shown that some species possess bony dermal scutes, thus rendering their Lacertilian affinities somewhat dubious. 468 MANUAL OF ZOOLOGY. ORDER IV. CROCODILIA. — The last and highest order of the living Reptilia is that of the Crocodilia, including the living Crocodiles, Alligators, and Gavials, and characterised by the following peculiarities : — The body is covered with an outer epidermic exoskeleton composed of horny scales, and an inner dermal exoskeleton consisting of squared bony plates or scutes, which may be con- fined to the dorsal surface alone, or may exist on the ventral surface as well, and which are disposed on the back of the neck into groups of different form and number in different species. The bones of the skull and face are firmly united together, and the two halves or rami of the lower jaw are united in front by a suture. There is a single row of teeth, which are implanted in distinct sockets, and hollowed at the base for the germs of the new teeth, by which they are successively pushed out and replaced during the life of the animal. The centra of the dorsal vertebrae in all living Crocodilia are procoelous, or concave in front, but in the extinct forms they may be either amphiccelous (concave at both ends) or opisthocoelous (con- cave behind). The vertebral ends of the anterior trunk-ribs are bifurcate. There are two sacral vertebras. The cervical vertebrae have small ribs (hence the difficulty experienced by the animal in turning quickly) ; and there are generally false abdominal ribs produced by the ossification of the tendinous intersections of the recti muscles. There are no clavicles. The heart consists of four completely distinct and separate cavities, two auricles, and two ventricles, the ventricular sep- tum— as in no other Reptiles— being complete. The right and left aortae, however — or, in other words, the pulmonary artery and systemic aorta — are connected together close to their origin by a small aperture (foramen Panizzcz), so that the two sides of the heart communicate with one another. The aperture of the cloaca is longitudinal, and not transverse, as in the Lizards. All the four limbs are present, the anterior ones being penta- dactylous, the posterior tetraclactylous. All are oviparous. The chief points by which the Crocodiles are distinguished from their near allies, the Lacertilians, are the possession of a partial bony dermal exoskeleton in addition to the ordinary epidermic covering of scales, the lodgment of the teeth in distinct sockets, and the fact that the mixture of venous and arterial blood, which is so characteristic of Reptiles, takes place, not in the heart itself, but in its immediate neighbour- hood, by a communication between the pulmonary artery and aorta directly after their origin. The only other points about the Crocodiles which require LACERTILIA AND CROCODILIA. 469 special notice are that the eyes are protected by movable eye- lids; the ear is covered by a movable ear-lid; the nasal cavities open in front by a single nostril, and are shut off from the cavity of the mouth, but open far back into the cavity of the pharynx ; and lastly, the tongue is large and fleshy, and is im- movably attached to the bottom of the mouth. (Hence the belief of the ancients that the Crocodile had no tongue.) The tail is long and compressed, with two rows of keeled plates, which unite about its middle to form a single crest, which is continued to its extremity. The feet are palmate or semi- palmate, and only the three inner toes on each foot possess claws. The eyes possess three distinct lids, and there are two glands under the throat secreting a musky substance. The Crocodilia abound in the fresh waters of hot countries, and are the largest of all living Reptiles, not uncommonly attaining a length of twenty feet or upwards. They are divided by Owen into three sub-orders, according to the shape of the Fig. 203. — Crocodilia. Head and fore-part of the body of the Common Crocodile (Crocodilus vulgaris). dorsal vertebrae, termed the Proccelia^ Amphic&lia, and Opis- thoccelia. Sub-order i. Procoslia. — In this sub-order are all the living members of the Crocodilia distinguished by having the bodies of the dorsal vertebrae concave in front (proccelous). Three distinct types may be distinguished amongst the living Croco- dilia. The Gavial is distinguished by its elongated snout, at the extremity of which the nostril is placed, and by the fact that the teeth are pretty nearly equal in size and similar in form in the two jaws. In the true Crocodiles (fig. 204) the fourth tooth in the lower jaw is larger than the others, and forms a canine tooth, which is received into a notch excavated in the side of the alveolar border of the upper jaw, so that it is visible externally when the mouth is closed. In the Caimans or Alligators the same tooth in the lower jaw forms a canine, but it is received into a pit in the palatal surface of the upper jaw, where it is entirely concealed when the mouth is shut. 470 MANUAL OF ZOOLOGY. The Crocodiles have the hind-legs bordered by a toothed fringe, and the toes completely united by membrane. They are essentially natives of fresh water, but sometimes frequent the mouths of rivers. They occur chiefly in Asia and Africa, but species are found in some of the West Indian Islands. The Alligators have the hind-legs simply rounded, and the feet not completely webbed. They are essentially aquatic, and are voracious animals, living upon fish or Mammals. The best- known species are the Alligator of the Southern United States (A. Mississippiensis), the Caiman (A . palpebrosus) of Surinam and Guiana, and the " Jacare " or Spectacled Alligator (A. sclerops) of Brazil. The Ga vials inhabit fresh waters, and appear to be exclusively confined to the Ganges and other large rivers of India. The Gangetic form (Gavialis Gangeticus], in spite of its numerous pointed teeth, is not so highly carnivorous as the true Crocodiles. Fig. 204. — Skull of young Crocodiles biporcatiis (after Van cler Hoven). True proccelian Crocodiles occur for the first time in the Greensand (Cretaceous series) of North America. In Europe, however, the earliest remains of proccelian Crocodiles are from the Lower Tertiary rocks (Eocene), It is a curious fact that in the Eocene rocks of the south-west of England, there occur fossil remains of all the three living types of the Crocodilia — namely, the Gavials, true Crocodiles, and Alligators ; though at the present day these forms are all geographically restricted in their range, and are never associated together. Stib-order 2. Amphicoelia. — The Amphiccelian Crocodiles, with biconcave vertebrae, are entirely extinct. They have but a limited geological range, extending only from the Lias to the Chalk inclusive, and being therefore strictly Mesozoic.* The biconcave vertebrae show a decided approach to the * If the so-called "Thecodont" Reptiles, such as Thecodontosaurits and Belodon, belong to this sub-order, then the Amphicoelian Crocodilia date from the age of the Triassic rocks ; as is also the case if Stagonolepis be included here. EXTINCT ORDERS OF REPTILES. 47 I structure of the backbone in fishes ; and as the rocks in which they occur are marine, there can be little doubt but that these Crocodiles were, in the majority of cases at any rate, marine. The most important genera belonging to this order are Teleo- saurus, Steneosaurus, Dakosaurus, Makrospondylus, and Sucho- saurus, the last being from the fresh-water deposits of the Wealden (Cretaceous). Sub-order 3. Opisthoccelia. — The sub-order of the Opisthocai- lian Crocodiles, including those forms in which the anterior trunk vertebrae are concave behind, is one which can be only provisionally retained. Professor Owen includes in this section the two genera Streptospondylus and Cetiosaurus ; but the latter is referable to the Deinosauria, and will be treated of when that order is considered. The genus Streptospondylus has been founded on vertebrae obtained from the Oolitic and Wealden formations ; but there are doubts as to the true position of the reptile to which these belonged. CHAPTER LXV. EXTINCT ORDERS OF REPTILES. IT remains now to consider briefly the leading characters of five wholly extinct orders of Reptiles, the peculiarities of which are very extraordinary, and are such as are exhibited by no living forms. ORDER V. ICHTHYOPTERYGIA, Owen ( — Ichthyosauria, Hux- ley). The gigantic Saurians forming this order were distin- guished by the following characters: — The body was fish-like, without any distinct neck, and pro- bably covered with a smooth or wrinkled skin, no horny or bony exoskeleton having been ever discovered. The vertebrae were numerous, deeply biconcave or amphiccelous, and having the neural arches united to the centre by a distinct suture. The anterior trunk-ribs possess bifurcate heads. There is no sacrum, and no sternal ribs or sternum, but clavicles were pre- sent as well as an interclavicle (episternum) ; and false ribs were developed in the walls of the abdomen. The skull had enormous orbits separated by a septum, and an elongated snout. The eyeball was protected by a ring of bony plates in the sclerotic. The teeth were not lodged in distinct sockets, but in a common alveolar groove. The fore and hind limbs 472 MANUAL OF ZOOLOGY. were converted into swimming-paddles, the ordinary number of digits (five) remaining recognisable, but the phalanges being greatly increased in number, and marginal ossicles being added as well. A vertical caudal fin was in all probability present. The order Ichthyopterygia includes only the gigantic and fish-like Ichthyosauri (fig. 205), all exclusively Mesozoic, and abounding in the Lias, Oolites, and Chalk, but especially char- acteristic of the Lias. If, however, the Eosaurus Acadiensis (Marsh) of the Coal-measures of Nova Scotia be rightly re- ferred to this order, then the Ichthyopterygia date from the Car- boniferous period. There is no doubt whatever but that the Ichthyosauri were essentially marine animals, and they have been often included with the next order (Sauropterygia] in a common group, under the name of Enaliosauria or Sea- lizards. In the biconcave vertebrae and probable presence of a ver- tical tail-fin, the Ichthyosaurus approaches the true fishes. There is, however, no doubt as to the fact that the animal was strictly an air-breather, and its reptilian characters cannot be Fig. lo*,.— Ichthyosaurus communis. questioned, at the same time that the conformation of the limbs is decidedly Cetacean in many respects. Much has been gathered from various sources as to the habits of the Ichthyo- saurus, and its history is one of great interest. From the re- searches of Buckland, Conybeare, and Owen, the following facts appear to be pretty well established : — That the Ichthyo- sauri kept chiefly to open waters may be inferred from their strong and well-developed swimming-apparatus. That they occasionally had recourse to the shore, and crawled upon the beach, may be safely inferred from the presence of a strong and well-developed bony arch, supporting the fore-limbs, and closely resembling in structure the scapular arch of the Orni- thorhynchus or Duck-mole of Australia. That they lived in stormy seas, or were in the habit of diving to considerable depths, is shown by the presence of a ring of bony plates in the sclerotic, protecting the eye from injury or pressure. That they possessed extraordinary powers of vision, especially in the dusk, is certain from the size of the pupil, and from the enor- EXTINCT ORDERS OF REPTILES. 473 mous width of the orbits. That they were carnivorous and predatory in the highest degree is shown by the wide mouth, the long jaws, and the numerous, powerful, and pointed teeth. This is proved, also, by an examination of their petrified drop- pings, which are known to geologists as " coprolites," and which contain numerous fragments of the scales and bones of the Ganoid fishes which inhabited the same seas. ORDER VI. SAUROPTERYGIA, Owen ( — Plesiosauria, Hux- ley). This order of extinct reptiles, of which the well-known Plesiosaurus may be taken as the type, is characterised by the following peculiarities : — The body, as far as is known, was naked, and not furnished with any horny or bony exoskeleton. The bodies of the ver- tebrae were either flat or only slightly cupped at each end, and the neural arches were anchylosed with the centra, and did not remain distinct during life. The transverse processes of the vertebrae were long, and the anterior trunk-ribs had simple, not bifurcate, head. No sternum or sternal ribs are known to have existed, but there were false abdominal ribs. The neck in Fig. 206. — Plesiosaurus dolichodeirus. most was greatly elongated, and composed of numerous verte- brae. The sacrum was composed of two vertebrae. The orbits were of large size, and there was a long snout, as in the Ichthyo- sauri, but there was no circle of bony plates in the sclerotic. The limbs agree with those of the Ichthyosauri in being in the form of swimming-paddles (fig. 206), but differ in not possess- ing any supernumerary marginal ossicles. A pectoral arch, formed of two clavicles and an interclavicle (episternum) appears to have been sometimes, if not always, present. The teeth were simple, and were inserted into distinct sockets, and not lodged in a common groove. The most familiar and typical member of the Sauropterygia is the Plesiosaurus (fig. 206), a gigantic marine reptile, chiefly characteristic of the Lias and Oolites. As regards the habits of the Plesiosaurus, Dr Conybeare arrives at the following con- clusions : — " That it was aquatic is evident from the form of its paddles ; that it was marine is almost equally so from the remains with which it is universally associated ; that it may 474 MANUAL OF ZOOLOGY. have occasionally visited the shore, the resemblance of its ex- tremities to those of the Turtles may lead us to conjecture ; its movements, however, must have been very awkward on land ; and its long neck must have impeded its progress through the water, presenting a striking contrast to the organisation which so admirably fits the Ichthyosaurus to cut through the waves." As its respiratory organs were such that it must of necessity have required to obtain air frequently, we may conclude " that it swam upon or near the surface, arching back its long neck like a swan, and occasionally darting it down at the fish which happened to float within its reach. It may, perhaps, have Fig. 207. — A, Skull of Dicynodon lacerticeps, showing the maxillary tusk. B, Skull of Oudenodon Bainii. From the Trias of South Africa. (After Owen.) lurked in shoal water along the coast, concealed amongst the sea-weed ; and raising its nostrils to a level with the surface from a considerable depth, may have found a secure retreat from the assaults of powerful enemies ; while the length and flexibility of its neck may have compensated for the want of strength in its jaws, and its incapacity for swift motion through the water." The geological range of the Plesiosaurus is from the Lias to the Chalk inclusive, and specimens have been found indicating a length of from eighteen to twenty feet. Of the other genera of the Sauropterygia, Simosaurus and EXTINCT ORDERS OF REPTILES. 475 Nothosaunis are from the Trias, and are chiefly characteristic of its middle division, the Muschelkalk. Placodus is another genus, also from the Muschelkalk, and is characterised by the extraordinary form of the teeth, which resembled those of many fishes in forming broad crushing plates, constituting a kind of pavement. ORDER VII. ANOMODONTIA, Owen ( = Dicynodontia^ Hux- ley). The leading characters of this order are to be found in the structure of the jaws, which appear to have been sheathed in horn so as to constitute a kind of beak, very like that of the Chelonians. • In the genera Rhynchosaurus and Oudenodon (fig. 207), both jaws seem to have been altogether destitute of teeth ; but in Dicynodon (fig. 207) there were two long tusks, growing from persistent pulps, placed one on each side in the upper jaw. The pectoral and pelvic arches were very strong, and the limbs were well developed and fitted for walking, and not for swimming. Dicynodon and Oudenodon are known only from strata of supposed Triassic age in South Africa and India, but Rhyncho- saurus occurs in the Trias of Europe. This last genus, however, is placed by Huxley amongst the Lacertilia. ORDER VIII. PTEROSAURIA. — This order includes a group of extraordinary flying Reptiles,' all belonging to the Mesozoic epoch, and exhibiting in many respects a very extraordinary combination of characters. The most familiar members of the order are the so-called " Pterodactyles," and the following are the characters of the order : — No exoskeleton is known to have existed. The dorsal ver- tebrae are proccelous, and the anterior trunk-ribs are double- headed. There is a broad sternum with a median ridge or keel, and ossified sternal ribs. The jaws were always armed with teeth, and these were implanted in distinct sockets. In some forms (Ramphorhynchus} there appear to have been no teeth in the anterior portion of the jaws, and these parts seem to have been sheathed in horn, so as to constitute a kind of beak. A ring of bony plates occurs in the sclerotic coat of the eye. The pectoral arch consists of a scapula and distinct coracoid bone, articulating with the sternum as in Birds, but no clavicles have hitherto been discovered. The fore-limb (fig. 208) consists of a humerus, ulna and radius, carpus, and hand of four fingers, of which the inner three are short and un- guiculate, whilst the outermost is clawless and is enormously elongated. Between this immensely-lengthened finger, the .side of the body, and the comparatively small hind-limb, there must have been supported an expanded flying-membrane or 476 MANUAL OF ZOOLOGY. " patagium," which the animal must have been able to employ as a wing, much as the bats of the present day. Lastly, most of the bones were " pneumatic " — that is to say, were hollow and filled with air. By the presence of teeth in distinct sockets, and, as will be seen hereafter, especially in the structure of the limbs, the Pterodactyles differed from all known Birds, and there can be little question as to their being genuine Reptiles. The only Reptile, however, now existing, which possesses any power of sustaining itself in the air, is the little Draco volans, but this can only take extended leaps from tree to tree, and cannot be said to have any power of flight properly so called. That the Pterodactyles, on the other hand, possessed the power of genuine flight, is shown by the presence of a median keel upon the sternum, proving the existence of unusually -developed pectoral muscles ; by the articulation of the coracoid bones with the top of the sternum, providing a fixed point or fulcrum Fig. 208. — Pterodactylus brevirostris. Skeleton and restoration. for the action of the pectoral muscles ; and, lastly, by the existence of air-cavities in the bones, giving the animal the necessary degree of lightness. The apparatus, however, of flight was not a " wing," as in Birds, but a flying membrane, very similar in its mode of action to the patagium of the Mam- malian order of the Bats. The patagium of the Bats, however, differs from that of the Pterodactyles in being supported by the greatly-elongated fingers, whereas in the latter it is only the outermost finger which is thus lengthened out. The diffi- culty as to the position of the Pterosanria is evaded by Mr Seeley by placing them in a distinct class, which he terms Ornithosauria, and which he regards as most nearly related to, but coequal with, the class Aves. The Pterosauria are exclusively Mesozoic, being found from EXTINCT ORDERS OF REPTILES. 477 the Lower Lias to the Middle Chalk inclusive, the Lithographic Slate of Solenhofen (Upper Oolite) being particularly rich in their remains. Most of them appear to have attained no very great size, but the remains of a species from the Cretaceous rocks have been considered to indicate an animal with more than twenty feet expanse of wing, counting from tip to tip. In the genus Pterodactylus proper, the jaws are provided with teeth to their extremities, all the teeth being long and slender. In Dimorphodon, the anterior teeth are large and pointed, the posterior teeth small and lancet-shaped. In Ramphorhynchus, the anterior' portion of both jaws is edentulous, and may have formed a horny beak, but teeth are present in the hinder portion of the jaws. ORDER IX. DINOSAURIA. — The' last order of extinct Reptiles is that of the Dinosauria, comprising a group of very remarkable Reptiles, which are in some respects intermediate in their characters between the Struthious Birds and the typical Rep- tiles ; whilst they have been supposed to have affinities to the Pachydermatous Mammals. Most of the Dinosauria were of gigantic size, and the order is defined by the following characters : — The skin was sometimes naked, sometimes furnished with a well-developed exoskeleton, consisting of bony shields, much resembling those of the Crocodiles. A few of the anterior ver- tebrae were opisthocoelous, the remainder having flat or slightly biconcave bodies. The anterior trunk-ribs were double-headed. The teeth were confined to the jaws and implanted in distinct sockets. There were always two pairs of limbs, and these were strong, furnished with claws, and adapted for terrestrial pro- gression. In some cases the fore-limbs were very small in proportion to the size of the hind-limbs. No clavicles have been discovered. The teeth are sometimes implanted in distinct sockets, and they are never anchylosed with the jaws. The ischium and pubes are much elongated ; the inner wall of the acetabulum is formed by membrane ; the tibia has its proximal end pro- longed anteriorly into a strong crest ; and the astragalus is bird-like (Huxley). The most remarkable points in the organisation of the Dinosauria are connected with the structure of the pelvis and hind-limb, the characters of which, as pointed out by Huxley, approximate to those of the same parts in the Birds, and especially in the Struthious Birds. This approximation is especially seen in the prolongation of the ilium in front of the 478 MANUAL OF ZOOLOGY. o between forty and fifty femur and tibia acetabulum (fig. 209), the elongation and slenderness of form of the ischium, and the slenderness of the pubes. The astra- galus is like that of a bird, and in some cases appears to have become anchylosed with the distal end of the tibia. The metatarsal bones, however, remain distinct, and are not an- chylosed with any of the tarsalbones to forma "tarso- metatarsus. The most familiar ex- amples of the Dinosauria are Megalosaurus and Igua- nodon. Megalosaurus is a gigantic Oolitic Reptile, which oc- curs also in the Cretaceous series (Weald Clay). Its length has been estimated at feet, the each measuring about three feet in length. As the head of the femur is set on nearly at right angles with the shaft, whilst all the long bones contain large medul- lary cavities, there can be no doubt but that Megalosaurus was terrestrial in its habits. That it was carnivorous and destructive in the highest degree is shown by the powerful, pointed, and tren- Fibula ; as " ' f Astragalus ; ca Calcaneum ; m Metatarsus. Cliant teettl. (After Huxley.) The fguanojon is rnainly, if not exclusively, Cretaceous, being especially characteristic of the great delta-deposit of the Wealden. The length of the Iguanodon has been estimated as being probably from fifty to sixty feet, and from the close resemblance of its teeth to those of the living Iguanas, there is little doubt that it was herbivo- rous and not carnivorous. The femur of a large Iguanodon measures from four to five feet in length, with a circumference of twenty-two inches in its smallest part. From the dispro- portionately small size of the fore-limbs, and from the occur- rence of pairs of gigantic three-toed footsteps in the same beds, it has been concluded, with much probability, that Iguanodon. Fig. 209. — Leg of Deinosatir. il Iliur Ischium ; f Femur ; t Tibia ; EXTINCT ORDERS OF REPTILES. 479 in spite of its enormous bulk, must have walked temporarily or permanently upon its hind-legs, thus coming to present a most marked and striking affinity to the Birds. The most remarkable, however, of the Dinosauria, is the little Compsognathns longipes, from the Lithographic Slate of Solenhofen, referred to this order by Professor Huxley. This Reptile is not remarkable for its size, which does not seem to have been much more than two feet, but for the remarkable affinities which it exhibits to the true Birds. The head of Compsognathus was furnished with A?0/£o/ in the Ostrich, Emeu, and Cassowary. We have next to consider the structure of the bones which compose the fore-limb or " wing " of the bird ; and as this organ is the one which chiefly conditions the peculiar life of the bird, it is in it that we find some of the most characteristic points of structure in the whole skeleton. Though consider- ably modified to suit its function as an organ of aerial progres- sion, the wing of the bird is readily seen to be homologous with the arm of atman or the fore-limb of a Mammal (fig. 212, A, and fig. 213). The upper arm (brachium) is supported by a single bone, the humerus, which is short and strong, and articulates above with the articular cavity formed partly by the scapula and partly by the coracoid (fig. 213, K). The humerus is succeeded distally by the fore-arm (antibrachium\ constituted by the normal two bones, the radius and ulna (fig. 213, r, «), of which the radius is much the smaller and more slender, and the ulna much the larger and stronger. The ulna and radius are followed inferiorly by the bones of the wrist or carpus ; but these are reduced in number to two small bones, " so wedged in between the antibrachium and metacarpus as to limit the motions of the hand to those of abduction and adduction necessary for the folding up and 488 MANUAL' OF ZOOLOGY. expansion of the wing ; the hand is thus fixed in a state of pronation ; all power of flexion, extension, or of rotation, is removed from the wrist-joint, so that the wing strikes firmly, and with the full force of the contraction of the depressor muscles, upon the resisting air " (Owen). One other bone of the normal carpus (namely, the " os magnum ") is present, but this is anchylosed with one of the metacarpals. There are thus really three carpal bones, though only two appear to be present. The carpus is followed by the metacarpus, the condition of which agrees with that of the carpal bones. Fig. 213. — Fore-limb of the Jer-falcon. h Humerus ; r Radius ; u Ulna ; / " Thumb ; " m Metacarpals, anchylosed at their extremities ; //Phalanges of fingers. The two outermost of the normal five metacarpals are absent, and the remaining three are anchylosed — together with the os magnum — so as to form a single bone (fig. 213, m). This bone, however, appears externally as if formed of two meta- carpals united to one another at their extremities, but free in their median portion. The metacarpal bone which cor- responds to the radius is always the larger of the two (as being really composed of two metacarpals), and it carries the digit which has the greatest number of phalanges. This digit corresponds with the "index" finger, and it is com- CHARACTERS OF AYES. 489 posed of two, or sometimes three, phalanges (fig. 213, p\ At the proximal end of this metacarpal, at its outer side, there is generally attached a single phalanx, constituting the so-called "thumb" (fig. 213, /), which carries the "bastard- wing." The digit which is attached to the ulnar metacarpal corresponds to the " ring-finger," and never consists of more than a single phalanx (fig. 213). As regards the structure of the posterior extremity or hind- limb, the pieces which compose the innominate bones (namely, the ilium, ischium, and pubes) are always anchylosed with one another; and the two innominate bones are also always an- chylosed, by the medium of the greatly-elongated ilia, with the sacral region of the spine. In no living bird, however, with the single exception of the Ostrich, are the innominate bones united in the middle line in front by a symphysis pubis. The stability of the pelvic arch, necessary in animals which sup- port the weight of the body on the hind-limbs alone, is amply secured in all ordinary cases by the anchylosis of the ilia with the sacrum. As in the higher Vertebrates, the lower limb (fig. 214, A) consists of a femur, a tibia and fibula, a tarsus, metatarsus, and phalanges ; but some of these parts are considerably obscured by anchylosis. The femur or thigh-bone (fig. 214, A,/) is generally very short, comparatively speaking. The chief bone of the leg is the tibia (/), to which a thin and tapering fibula (r) is anchylosed. The upper end of the fibula, however, articu- lates with the external condyle of the femur. The ankle-joint is placed, as in Reptiles, between the proximal and distal portions of the tarsus. The proximal portion of the tarsus is undistinguishably amalgamated with the lower end of the tibia. The distal portion of the tarsus is anchylosed with the whole of the metatarsus to constitute the most characteristic bone in the leg of the Bird — the " tarso-metatarsus " (m). In most of the long-legged birds, such as the waders, the disproportionate length of the leg is given by an extraordinary elongation of the tarso-metatarsus. The tarso-metatarsus is followed inferiorly by the digits of the foot. In most birds the foot consists of three toes directed forwards and one backwards — four toes in all. In no wild bird are there more than four toes, but often there are only three, and in the Ostrich the number js reduced to two. In all birds which have three anterior and one posterior toe, it is the posterior thumb or hallux (that is to say, the innermost digit of the hind-limb) which is directed backwards ; and it invariably consists of two phalanges only. The most internal 49O MANUAL OF ZOOLOGY. of the three toes which are directed forwards, consists of three phalanges; the next has four phalanges ; and the outermost toe is made up sifive phalanges (fig. 214, A). This increase in an arithmetical ratio of the phalanges of the toes, in proceeding from the inner to the outer side of the foot, obtains in almost all birds, and enables us readily to detect which digit is sup- pressed, when the normal four are not all present. Variations of different kinds exist, however, in the number and disposi- P Fig. 214. — A, Hind-limb of the Loon (Colymbus glacialis) — after Owen ; i Innominate bone ; f Thigh-bone or femur ; t Tibia, with the proximal portion of the tarsus an- chylosed to its lower end ; r Fibula ; m Tarso-metatarsus, consisting of the distal portion of the tarsus anchylosed with the metatarsus ; pp Phalanges of the toes ; B, Tail of the Golden Eagle ; s Ploughshare-bone, carrying the great tail-feathers. tion of the toes. In many birds — such as the Parrots — the outermost toe is turned backwards, so that there are two toes in front and two behind. In others, again, the outer toe is normally directed forwards, but can be turned backwards at the will of the animal. In the Swifts, on the other hand, all four toes are present, but they are all turned forwards. In many cases — especially amongst the Natatorial birds — the CHARACTERS OF AVES. 491 hallux is wholly wanting, or is rudimentary. In the Emeu, Cassowary, Bustards, and other genera, the hallux is invariably absent, and the foot is three-toed. In the Ostrich both the hallux and the next toe (" index ") are wanting, and the foot consists simply of two toes, these being the outer toe and the one next to it. The toes are mechanically flexed during the sleep of the Bird, in virtue of an arrangement by which, whilst all the flexor tendons pass behind the heel, one of them runs in front of the knee. As the muscles, therefore, are relaxed during sleep, and the weight of the body tends to flex the knee, the tendon of this flexor is thereby put on the stretch, and the toes are again bent involuntarily. The digestive system of birds comprises the beak, tongue, gullet, stomach, intestines, and cloaca. Teeth are invariably wanting in birds, and the jaws are encased in horn, constituting the bill. The form of the bill varies enormously in different birds, and it is employed for holding and tearing the prey, for prehensile purposes, for climbing, and in some birds as an organ of touch. In these last-mentioned cases the bill is more or less soft, and is supplied with filaments of the fifth nerve. In many birds, too, in which the bill is not soft, the base of the upper mandible is surrounded by a circle of naked skin, constituting what is called the " cere," and this, no doubt, serves also as a tactile organ. The tongue of birds can hardly be looked upon as an organ of taste, since it is generally cased in horn like the mandibles. It is, in fact, principally employed as an organ of prehension ; but in some cases — as in the Parrots — it is soft and fleshy, and then, doubtless, is to some extent connected with the sense of taste. It is essentially composed of a prolongation of the hyoid bone (the glosso-hyal), which is sheathed in horn, and is variously serrated or fringed. Salivary glands are invariably present, but they are rarely of large size, and they have often a very simple structure. In accordance with the structure of the neck, the gullet in birds is usually of great length, and it is generally very dilatable. In the carnivorous, or Raptorial, and in the granivorous birds, the gullet (fig. 215, o), is dilated into a pouch, which is situated at the lower part of the neck, just in front of the merry-thought. This is what is known as the " crop " or " ingluvies " (c), and it may be either a mere dilatation of the tube of the gullet, or it may be a single or double pouch. The food is detained in the crop for a longer or shorter time, according to its nature, before it is subjected to the action of the proper digestive organs. The oesophagus, after leaving the crop, shortly opens 492 MANUAL OF ZOOLOGY. into a second cavity, which is known as the " proventriculus " or " ventriculus succenturiatus " (/). This is the true digestive cavity, and its mucous membrane is richly supplied with gastric follicles which secrete the gastric juice. The proventriculus, however, corresponds, not with the whole stomach of the Mammals, but only with its cardiac portion ; and it opens into a second, muscular cavity, which corresponds to the pyloric division of the Mammalian stomach. The gizzard (g) is situ- ated below the liver, and forms in all birds an elongated sac, having two apertures above, of which one conducts into the Fig. 215.— Digestive System of the common Fowl (after Owen), o Gullet ; c Crop : / Proventriculus ; g Gizzard ; sm Small intestine ; k Intestinal cseca ; / Large in- testine ; cl Cloaca. duodenum or commencement of the small intestine, whilst the other communicates with the proventriculus. The two chief forms of gizzard are exhibited respectively by the Raptorial birds, which feed on easily - digested animal food, and the Rasores and some of the Natatores, which feed on hardly- digested grains. In the birds of Rapine the gizzard scarcely deserves the name, being, as a rule, -nothing more than a wide membranous cavity with thin walls. In the granivorous birds, whose hard food requires crushing, the gizzard is enormously developed ; its lining coat is formed of a thick, horny epithe- CHARACTERS OF AVES. , 493 Hum, and its walls are extremely thick and muscular. This constitutes a grinding apparatus, like the stones of a mill ; whilst the " crop " or oesophageal dilatation may be compared to the "hopper" of a mill, since it supplies to the gizzard " small successive quantities of food as it is wanted " (Owen). Supplementing the action of the muscular walls of the gizzard, and acting in the place of teeth, are the small stones or peb- bles, which, as is so well known, so many of the granivorous birds are in the habit of swallowing with their food, or at other times. In fact, there can be no doubt but that the gravel and pebbles swallowed by these birds are absolutely essential to existence, since the gizzard, without this assistance, is unable properly to triturate the food. The intestinal canal extends from the gizzard to the cloaca, and is, comparatively speaking, short. The secretions of the liver and pancreas are poured into the small intestine, as in Mammals. The commencement of the large intestine is al- most always furnished with two long " caeca " or blind tubes, the length of which varies a good deal in different birds (fig. 215, /£). They are sometimes wanting; and their exact func- tion is uncertain ; though they are most probably connected partly with digestion and partly with excretion. The large intestine is always very short — seldom more than a tenth part of the length of the body — and it terminates in the " cloaca " (fig. 215, d). This is a cavity which in all birds receives the termination of the rectum, the ducts of the generative organs, and the ureters ; and serves, therefore, for the expul- sion of the faeces, the generative products, and the urinary secretion. Respiration is effected in Birds more completely and actively \ tharr in any other class of the Vertebrata, and as the result of this, their average temperature is also higher. This extensive development of the respiratory process is conditioned by the fact that, in addition to true lungs, air is admitted into a greater or less number of the bones and into a number of cavities — the so-called air-receptacles — which are distributed through various parts of the body. By this extensive penetration of air into various parts of the body, the aeration of the blood is effected not only in the lungs, but also over a greater or less extent of the systemic circulation as well ; and hence in Birds this process attains 4t^m'gh^sl£erje£tioja. The cavities of the thorax and abdomen are not separated from one another by a complete partition, the diaphragm being only present in a rudimentary form. The lungs are two in number, of a bright- red colour, and spongy texture. They are confined to the 494 MANUAL OF ZOOLOGV. back of the thorax, extending along each side of the spine, from the second dorsal vertebra to the kidney. They differ from the lungs of the Mammals in not being freely suspended in a pleural membrane. The pleura, on the other hand, is reflected only over the anterior surface of the lungs. The bronchi, or primary divisions of the wind- pipe (fig. 216), diminish in size as they pass through the lung, by giving off branches, which, in turn, give off the true air-vesicles of the lung. When the bronchial tubes reach the surface of the lung, they open, by a series of distinct apertures, into a series of (i air-sacs." These are a series of membranous sacs formed by the continuation of the lining mem- brane of the bronchi, and sup- ported by reflections of the serous membrane of the thoracico-abdo- minal cavity. In those aquatic birds which, like the Penguin, do not enjoy the power of flight, the air-cells are restricted to the ab- domen ; but in most birds, they are continued along the sides of Fig-2/6.—Lungof Goose (after Owen), the neck and limbs. In some a Mam bronchus dividing into secon- . _ ,. „, dary branches as it enters the lung, CaSCS as the Pelican and GanilCt these giving off smaller branches, the air rprpntarlps arp dfnatprl hp openings of which are seen on the air rCCCptaClCS are SltliatCQ DC- back of the bronchial tubes ; bb Bris- neatll alniOSt the whole of the Hl- tles passed from the bronchi through , /-r>i 11 i the apertures on the surface of the tegument. The air-Cells not Only lung by which the bronchi communi- greatly reduce the specific gravity* cate with the air-receptacles. r-u-j j ^ r^ ^ r of birds, and thus fit them for an aerial life, but also assist in the mechanical work of respiration, and must also greatly promote the aeration of the blood. In connection with the air-receptacles, and as an extension of them, is a series of cavities occupying the interior of a greater or less number of the bones, and also containing air. In young birds these air-cavities do not exist, and the bones are filled with marrow as in the Mammals. The extent also to which the bones are " pneumatic " varies greatly in different birds. In the Penguin — which does not fly — all the bones contain marrow, and there are no air-cavities. In the large CHARACTERS OF AVES. 495 Running birds (Cvrsores), such as the Ostrich, the bones of the leg, pelvis, spine, ribs, skull, and sternum are pneumatic ; but the bones of the wings, with the exception of the scapular arch, are without air-cavities, and permanently retain their marrow. All birds \vhich fly, with the singular exception of the Woodcock, have air admitted to the humerus. In the Pelican and Gannet, all the bones of the skeleton, except the phalanges of the toes, are penetrated by air ; and in the Horn- bill even these are pneumatic. The functions discharged by the air-cavities of the bones appear to be much the same as those of the air-receptacles — namely, that of diminishing the specific gravity o*f the body and subserving the aeration of the blood. The heart in all Birds consists of four chambers, two auricles and two ventricles. The right auricle and ventricle, constitut- ing the right side of the heart, are wholly concerned with the pulmonary circulation ; the left auricle and ventricle, forming the left side of the heart, are altogether occupied with the systemic circulation ; and no communication normally exists in adult life between the two sides of the heart. In all essen- tial details, both as regards the structure of the heart itself and the course taken by the circulating fluid, Birds agree with Mammals. The venous blood — namely, that which has circu- lated through the body — is returned by the venae cavae to the right auricle, whence it is poured into the right ventricle. The right ventricle propels it through the pulmonary artery to the lungs, where it is aerated, and becomes arterial. It is then sent back by the pulmonary veins to the left auricle, whence it is driven into the left ventricle. Finally, the left ventricle pro- pels the aerated blood to all parts of the body through the great systemic aorta. The chief difference between Birds and Reptiles as regards the course of the circulation is, that in the Birds the two sides of the heart are completely separated from one another, the blood sent to the lungs being exclusively venous, whereas that which is sent to the body is exclusively arterial. In Reptiles, on the other hand, the pulmonary and systemic circulations are connected together either in, or in the immediate neigh- bourhood of, the heart ; so that mixed venous and arterial blood is propelled both through the lungs and through every part of the body. In accordance with their extended respiration and high mus- cular activity, the complete separation of the greater and lesser circulations, and the perfect structure of the heart, Birds main- tain a higher average temperature than is the case with any 496 MANUAL OF ZOOLOGY. other class of the Vertebrata. This result is also to a consider- able extent conditioned by the non-conducting nature of the combined down and feathers which form the integumentary covering of Birds. The urinary organs of Birds consist of two elongated kid- neys and two ureters, but there is no urinary bladder. The ureters open into the cloaca, or into a small urogenital sac which communicates with the cloaca. As regards the reproductive organs, the males have two testes placed above the upper extremities of the kidneys, and their efferent ducts (vasa deferentia) open into the cloaca alongside of the ureters. A male organ (penis] may or may not be pre- sent, but there no perfect urethra. The female bird, as a general rule, is provided with only one ovary and oviduct — that of the left side — the corresponding organs of the right side being rudimentary or absent. The oviduct is very long and tortuous, and the egg, during its passage through it, receives the albuminous covering which serves for the nutrition of the embryo, and which is known as the " white " of the egg. The lower portion of the oviduct is dilated, and the egg receives here the calcareous covering which constitutes the "shell/' Finally, the oviduct debouches into the cloaca, into which the egg, when ready, is expelled. The further development of the chick is secured by the process of " incubation" or brooding, for which birds are peculiarly adapted, in consequence of the high temperature of their bodies. The development of the ovum belongs to physiology, and does not concern us here. It is sufficient to notice the means by which in many cases the chick is ultimately enabled to escape from the egg. When development has reached a stage at which external life is possible, it is of course necessary for the chick to be liberated from the egg, the shell of which is. often ex- tremely hard and resistant. To this end, in very many in- stances, the young bird is provided with a little calcareous knob on the point of the upper mandible, and by means of this it chips out an aperture through the shell. Having effected its purpose, this temporary appendage then disappears, without leaving a trace behind. The state of the young upon exclusion from the egg is very different in different cases, and in accordance with this, Birds have been divided into the two sections of the Autophagi or Aves prcecoces, and the Heterophagi or Aves altrices. In the Aulophagi the young bird is able to run about and help itself from the moment of liberation from the egg. In the Hetero- phagi the young are born in a blind and naked state, unable to CHARACTERS OF AVES. 497 - feed themselves, or even to maintain unassisted the necessary vital heat. In these birds, therefore, the young require to be brooded over and fed by the parents for a longer or shorter period after exclusion from the egg. As regards their nervotis system, the brain of Birds is rela- tively larger, especially as regards the size of the cerebrum proper, than the brain of Reptiles, but its chief mass con- sists of the corpora striata. The cerebellum, though always present, consists simply of the central lobe (the "vermiform process "), and is not provided with the lateral lobes which occur in the Mammals, or they are only present in a rudimen- tary form. The corpus callosum is absent, and the surface of the cerebral hemispheres is devoid of convolutions. As regards the organs of the senses, the eyes are always well developed, and in no bird are they ever rudimentary or absent. The chief peculiarity of the eye is that the cornea forms a segment of a much smaller sphere than does the eyeball pro- per, so that the anterior part of the eye is obtusely conical, whilst the posterior portion is spheroidal. Another peculiarity is that the form of the eye is maintained by a ring of from thirteen to twenty bony plates, which are placed in the anterior portion of the sclerotic coat. Eyelashes are almost universally absent ; but in addition to the ordinary upper and lower eye- lids, Birds possess a third membranous eyelid — the "membrana nictitans " — which is sometimes pearly-white, sometimes more or less transparent* This third eyelid is placed on the inner side of the eye, and possesses a special muscular apparatus, by which it can be drawn over the anterior surface of the eye like a curtain, moderating the intensity of the light. As to the organ of hearing, most birds possess no external ear or concha, by which sounds can be collected and transmitted to the in- ternal ear. In some birds, however, as in the Ostrich and Bustard, the external meatus auditorius is surrounded by a circle of feathers, which can be raised and depressed at will. The Nocturnal Birds, also, especially Owls, have the external meatus auditorius protected by a musculo-membranous valve, which foreshadows the cartilaginous concha of the majority of Mammals. The external nostrils in Birds are usually placed on the sides of the upper mandible, near its base, in the form * The membrana nictitans is simply a fold of the conjunctiva on the inner side of the eye. It occurs in some Fishes (e.g., Sharks), in some Reptiles and Amphibians, in Birds, in Monotremes and Marsupials, and in some of the higher Mammals. In Man, however, in Monkeys, and in most of the higher Mammals, it is rudimentary, and constitutes the so-called " plica semilunaris." 2 I 498 MANUAL OF ZOOLOGY. of simple perforations, which sometimes communicate from side to side by the deficiency of the septum narium. In the singular Apteryx of New Zealand, the nostrils are placed at the extreme end or tip of the elongated upper mandible. Some- times the nostrils are defended by bristles, and sometimes by a scale (Rasores}. Taste must be absent, or almost absent, in the great majority of birds, the tongue being nothing more than a horny sheath surrounding a process of the hyoid bone, and serving for deglutition or to seize the prey. In the Parrots, however, the tongue is thick and fleshy, and some perception of taste may be present. Touch or tactile sensibility, too, as already remarked, is very poorly developed in Birds. The body is entirely, or almost entirely, covered with feathers ; the anterior limbs are converted into wings, and rendered thereby useless as organs of touch ; and the posterior limbs are covered with horny scales or feathers. The bill certainly officiates as an organ of touch, but it cannot possess any acute sensibility, as in most birds it is encased in a rigid horny sheath. In some birds, however, such as the common Duck, the texture of the bill is moderately soft, and it is richly supplied with filaments of the fifth nerve ; so that in these cases the bill doubtless con- stitutes a tolerably efficient tactile organ. The " cere," too, or the fleshy scale found at the base of the bill in some birds, is in all probability also used as a tactile organ. The last anatomical peculiarity of Birds which requires notice is the peculiar apparatus known as the "inferior larynx," by which the song of the singing birds is conditioned. "The air-passages of birds commence by a simple superior larynx, from which a long trachea extends to the anterior aperture of the thorax, where it divides into the two bronchi, one for each lung. At the place of its division, there exists in most birds a complicated mechanism of bones and cartilages, moved by appropriate muscles, and constituting the true organ of voice; this part is termed the inferior larynx" (Owen). The structure of the vocal apparatus is extremely complicated, and there is no necessity for entering upon it here. It is to be remembered, however, that those modifications of the voice which constitute the song of birds, are produced in a special and complex cavity placed at the point where the trachea divides into the two bronchi, and not in a true larynx situated at the summit of the windpipe. Lastly, the trachea of birds is always of considerable proportionate length, and it is often twisted or dilated at intervals, this structure, doubtless, having something to do with the production of vocal sounds.* * The student desirous of fuller information as to the anatomy of Birds DIVISIONS OF BIRDS. 499 Before passing on to the consideration of the divisions of Birds, a few words may be said as to the migration of birds. In temperate and cold climates comparatively few birds remain constantly in the same region in which they were hatched. Those which do so remain, are called " permanent birds " (aves manentes). Other birds, such as the Woodpeckers, wander about from place to place, without having any fixed direction. These are called " wandering birds " (aves erratic^}, and their irregular movements are chiefly conditioned by the scarcity or abundance of food in any particular locality. Other birds, however, at certain seasons of the year undertake long jour- neys, usually uniting for this purpose into large flocks. These birds — such as the swallows, for instance — are properly called " migratory birds " (aves migrator itz). The movements of these birds are conditioned by the necessity of having a cer- tain mean temperature, and consequently they leave the cold regions at the approach of winter, and return again for the warmer season. CHAPTER LXVII. DIVISIONS OF BIRDS. i. GENERAL DIVISIONS OF AVES. 2. NATATORES. 3. GRALLATORES. OWING to the extreme compactness and homogeneity of the entire class Aves, conditioned mainly by their adaptation to an aerial mode of life, the subject of their classification has been one of the greatest difficulties of the systematic Zoologist. By Professor Huxley the Birds are divided into the following three orders : — 1. SAURUR^. — In this order the caudal vertebrae are nume- rous, and there is no ploughshare-bone. The tail is longer than the body, and the metacarpal bones are not anchylosed together. This order includes only the single extinct bird the ArchtKOpteryx macrura, in which the long lizard-like tail is only the most striking of several abnormalities. 2. RATIIVE. — This order comprises the Running birds, should consult the masterly article by Owen on " Aves " in the " Cyclo- paedia of Anatomy and Physiology," or the second volume of the " Verte- brata " of the same author, from which the preceding summary has been chiefly derived. 5OO MANUAL OF ZOOLOGY. which cannot fly, such as the Ostriches, Emeus, and Casso- waries. It is characterised by the fact that the sternum has no median ridge or keel for the attachment of the great pectoral muscles. The sternum is therefore raft-like (from the Lat. rates, a raft), hence the name of the order. 3. CARINATTE. — This comprises ail the living Flying birds, and is characterised by the fact that the sternum is furnished with a prominent median ridge or keel (carina) ; hence the name of the order. This is probably the nearest approach to a strictly natural classification of Birds which has yet been proposed ; but the order Carinatce is so disproportionately large as compared with the other two, that it would lead to considerable inconvenience if it were to be adopted here. For the purposes of the present work it will be better to adhere, with some modifications, to the classification .of the Birds originally proposed by Kirby, and since sanctioned by the adoption of other distinguished naturalists. In this more generally current, but certainly artificial, arrangement, the Birds are divided into the following seven orders, founded chiefly on the habits and mode of life, and on the resulting anatomical or structural peculiarities. To these an eighth order must be added for the reception of the Mesozoic bird, the Archceopteryx, the discovery of which dates from a recent period. Before entering upon a consideration of the indivi- dual orders, it will be as well to present to the student, synop- tically and in an easily-remembered form, the leading differences between these eight orders. 1. Natatores or Swimmers. — These are characterised by the fact that the toes are united by a membrane or web ; the legs are short, and are placed behind the point of equilibrium of the body. The body is closely covered with feathers, and with a thick coating of down next the skin. (Ex. Ducks, Geese, Pelicans, Gulls.) 2. Gr allator es or Waders. — The Wading birds are charac- terised by the possession of long legs, which are naked or are not covered with feathers from the distal end of the tibia downwards. The toes are long, straight, and not united to one another by a membrane or web. (Ex. Curlews, Herons, Storks.) 3. Cursores or Runners. — The Cursorial birds have very short wings which are not used in flight, and the sternum is without a ridge or keel. The legs are exceedingly robust, and there are only two, or at most three developed toes, the hind- toe or hallux being always absent or quite rudimentary. The DIVISIONS OF BIRDS. 50 I order agrees with the Ratitce of Huxley. (Ex. Ostrich, Emeu, Apteryx.) 4. Rasores or Scratchers. — The Rasorial birds have usually strong feet with powerful blunt claws adapted for scratching, but sometimes for perching. All the four toes are present. The upper mandible is vaulted, and the nostrils are pierced in a membranous space at its base, and are covered by a cartila- ginous scale. (Ex. Fowls, Game-birds, Pigeons.) 5. Scansores or Climbers. — The Climbing birds are charac- terised by the structure of the foot, in which two toes are turned backwards and two forwards, so as to give the bird unusual facilities in climbing trees. (Ex. Parrots, Toucans, Woodpeckers.) 6. Insessores or Perchers. — The Insessorial or Passerine birds are characterised by having slender and short legs, with three toes before and one behind, the two external toes generally united by a very short membrane, and the whole foot being adapted for perching. This is by far the largest order of birds, and includes all our ordinary songsters, such as the Thrushes, Linnets, Larks, &c., together with the Swallows, Humming- birds, and many others. 7. Raptores or Birds of Prey. — The Birds of Rapine are characterised by their strong, curved, sharp-edged and sharp- pointed beak, adapted for tearing animal food ; and by their robust legs armed with four toes, three in front and one be- hind, all furnished with long, strong, crooked claws or talons. (Ex. Eagles, Hawks, Owls.) 8. Saururce. — The metacarpal bones are not anchylosed together, and the tail is longer than the body, and consists of numerous free vertebrae, without a terminal ploughshare-bone. The only member of this order is the extinct Arcfuzopteryx. ORDER I. NATATORES. — The order of the Natatores, or Swimmers, comprises a number of birds which are as much or even more at home in the water than upon the land. In accordance with their aquatic habit of life, the Natatores have a boat-shaped body, usually with a long neck. The legs are short, and placed behind the centre of gravity of the body, this position enabling them to act admirably as paddles, at the same time that it renders the gait upon dry land more or less awkward and shuffling. In all cases the toes are " webbed " or united by membrane to a greater or less extent (fig. 217, A). In many instances the membrane or web is stretched com- pletely from toe to toe, but in others the web is divided or split up between the toes, so that the toes are fringed with 5O2 MANUAL OF ZOOLOGY. membranous borders, but the feet are only imperfectly webbed. As their aquatic mode of life exposes them to great reductions of temperature, the body of the Natatorial birds is closely covered with feathers and with a thick coating of down next the skin. They are, further, prevented from becoming wet in the water by the great development of the coccygeal oil-gland, by means of which the lustrous plumage is kept constantly lubricated and waterproof. They are usually polygamous, each male consorting with several females ; and the young are hatched in a condition not requiring any special assistance from the parents, being able to swim and procure food for themselves from the moment they are liberated from the egg. Fig. 217. — Natatores. A. Foot of Cormorant (Phalacrocorajc) ; B, Beak of the Bean-goose (Anser ssgetuin). The Natatores are divided into the following four families : — Fam. i. Brevipennatcz. — In this family of the swimming birds the wings are always short, and are sometimes useless as organs of flight, the tail is very short, and the legs are placed very far back, so as to render terrestrial progression very difficult or awkward. The family includes the Penguins, Auks, Guillemots, Divers, and Grebes. In the Penguins (Sphenisridce] the wings are completely rudimentary, without quills, and covered with a scaly skin. They are useless as far as flight is concerned, but they are employed by the bird as fins, enabling it to swim under water with great facility, and they are also used on the land as fore-legs. The feet are webbed, and the hinder toe is rudimentary or wanting. The Penguins live gregariously in the seas of the southern hemisphere, on the coasts of South Africa and South America, especially at Terra del Fuego, and in the solitary islands of the South Pacific. When on land the Penguins stand bolt upright, and as they usually stand on the shore in long lines, they are said to present a most singular appearance. The best-known species are the NATATORES. 503 Jackass Penguin (Spheniscus demersus) of the Falkland Islands, and the King Penguin (Aptenodytes Patagonica) of the Straits of Magalhaens. In the Auks (Altidcz) the wings are better developed than in the Penguins, and they contain true quill feathers ; but they are still short as compared with the size of the body, and are of more use as fins than for flight. The Great Auk or Gare-fowl (Alca impennis) is remarkable for being one of the birds which appear to have become entirely extinct Fig. 218. — Jackass Penguin (Spheniscus demers us). within the human period, having been, in fact, destroyed by man himself. It used to abound in the arctic regions, and occasionally visited our own shores in the winter. The little Auk (Mergulus alba) occurs still in abundance in the seas of the arctic regions. Other well-known members of this group are the Razor-bill, the Puffins (Fratercula arctica], and the Guillemots ( Uria). The Guillemots have a short tail, narrow and pointed wings, short feet, and no hallux. Like the other 504 MANUAL OF ZOOLOGY. members of the family, they inhabit northern and polar re- gions. In the Divers (Colymbidcz), comprising the true Divers and the Grebes, the power of flight is pretty well developed, but the bird still is much more active in the water, swimming or diving, than on land. The Grebes are not uncommon in Bri- tain, and are largely killed for making muffs, collars, and other articles of winter dress. They have the membrane between the toes deeply incised. They haunt the sea as well as lakes and rivers, and swim and dive admirably. In the Divers pro- per the front toes are completely united by a membrane. The Northern Diver or Loon ( Colymbus glarialis) is a familiar ex- ample, and is found on the coasts of high northern latitudes. Fam. 2. Longipennatce. — This family of Natatores is charac- terised by the well-developed wings, the pointed, sometimes knife-like, sometimes hooked bill, and by never having the hallux united with the anterior toes by a membrane. The following are the more important groups coming under this head : — a. Laridce, or Gulls and Terns, having powerful wings, a free hinder toe, and the three anterior toes united by a membrane. The gulls form an exceedingly large and widely distributed group of birds ; and the Terns or Sea-swallows are equally beautiful, if not quite so common. The Terns are distinguished by their long and pointed wings, forked tail, and comparatively short legs. They fly with great rapidity over the surface of the sea, from which they pick up their food. b. Procellaridce, or Petrels, closely resembling the true Gulls, but having a rudimentary hinder toe, and having the upper mandible strongly hooked. . The smaller species of Petrel are well known to all sailors under the name of Storm-birds and Mother Carey's Chickens. They are nocturnal or crepuscular in their habits, breed in holes in the rocks, lay but one egg, and are almost all of small size and more or less sombre plumage. The largest member of the group is the gigantic Albatross (Diomedea exulans), not uncommonly found far from land in both the northern and southern oceans. The Albatross sometimes measures as much as fifteen feet from the tip of one wing to that of the other, and the flight is powerful in proportion. Fam. 3. TotipalmatcE, characterised by having the hinder toe or hallux more or less directed inwards, and united to the innermost of the anterior toes by a membrane (fig. 217, A). In this family are the Pelicans, Cormorants, Gannets, Frigate- birds, Darters, and others. They all fly well, and have short NATATORES. 505 legs, and amongst them are almost the only Natatorial Birds which ever perch upon trees. The Pelicans (Pdicamdx) are large birds, which subsist on fish, and are found in Europe, Asia, Africa, and the New World. They sometimes measure as much as from ten to fif- teen feet between the tips of the wings, and most of the bones are pneumatic, so that the skeleton is extremely light. The lower mandible is composed of two flexible branches which serve for the support of a large "gular" pouch, formed by the loose unfeathered skin of the neck. The bill is long and straight, and the upper mandible is strongly hooked at the tip. The fish captured by the bird -are temporarily deposited in this pouch, and the parent birds feed their young out of it. In the Cormorants (Phalacr.ocorax) there is no pouch be- neath the lower mandible, but the skin of the throat is very lax and distensible ; the nail of the middle toe is serrated. They are widely distributed over the world, one species being very abundant in many parts of Europe. The Gannets (Sula) have a compressed bill, the margins of which are finely crenate or toothed. They occur abundantly on many parts of the coasts of northern Europe, one of the most noted of their stations being the Bass Rock at the mouth of the Frith of Forth. Another species (Sula variegata) is of greater import- ance to man, as being one of the birds from the accumulated droppings of which guano is derived. The Frigate-birds (Tachypetes) are chiefly remarkable for their extraordinary powers of flight, conditioned by their enormously long and powerful wings and long forked tail. They occur on the coasts of tropical America, and are often found at immense distances from any land. The Tropic-birds {Phaeton) inhabit inter- tropical regions, and are found far out at sea. They have short feeble feet, and long pointed wings. The Darters or Snake-birds (Plotus) are somewhat aberrant members of this group, characterised by their elongated necks and long pointed bills. They occur in America, Africa, and Australia, and catch fish by suddenly darting upon them from above. Fam. 4. Lamdlirostres. — The last family of the Natatores is that of the Lamellirostres, including the Ducks, Geese, Swans, and Flamingoes ; and characterised by the form of the beak (fig. 211, 217), which is flattened in form and covered with a soft skin. The edges of the bill are further furnished with a series of transverse plates or lamellae, which form a kind of fringe or " strainer," by means of which these birds sift the mud in which they habitually seek their food. The bill is 506 MANUAL OF ZOOLOGY. richly supplied with filaments of the fifth nerve, and doubtless serves as an efficient organ of touch. The feet are furnished with four toes, of which three are turned forwards, and are webbed, whilst the fourth is turned backwards, and is free. The trachea in the males is often enlarged or twisted in its lower part, and co-operates in the production of the peculiar clanging note of most of these birds. The body is heavy, and the wings only moderately developed. The groups of the Ducks (Anatida), Geese (Anserince], and Swans (Cygnidtf), are too familiar to require much special notice. The Anatidtz, or true Ducks, have the hallux fur- nished with a very narrow membranous lobe, and the laminae of the upper mandible generally projecting. As examples may be taken the Mallards and Teals (Boschas), the Widgeons (Mareca), the Shoveller (Anas), and the Pin-tail Ducks (Dafila). The Sea-ducks (Fiiligulintz] frequent the sea chiefly, and have the hallux furnished with a wide membranous lobe. Good examples are the Eider-duck (Somateria\ the Surf-duck (Oidemia), the Canvass-back Duck, and Pochard (Fuligula), and the Golden-eye (Clanguld). The Anserince are distinguished from the Ducks chiefly by their stronger and longer legs, arid comparatively shorter wings. Good examples are the Grey Lag (Anser ferus\ the Canada Goose (A. Canadensis], the Bean-goose (A. Segetum), and the Snow-goose (A. hyperboreus). All the domesticated varieties of Geese appear to be undoubtedly descended from the " Grey Lag " Goose, a common wild species which is found in marshy districts in Europe generally, in [Northern Africa, and as far east as Persia. In the Swans the neck is extremely long, and the legs are short. In the Hooper Swan \Cygnus ferus) the sternal keel is double, and forms a cavity for the reception of a convoluted portion of the trachea. This is not the case, however, with the Mute Swan (C. olor\ the Black Swan (C. atratus), or the Trumpeter Swan (C. buccinator), all well-known members of the group. The Flamingoes, however, forming the group of the Phcenicop- terida, require some notice, if only for the fact that the legs are so long and slender that they have often been placed in the order Grallatores on this account. The three anterior toes, however, are webbed or completely united by membrane, and the bill is lamellate, so that there can be little hesitation in leaving the Flamingo in its present position amongst the Nata- tores. The bill is singularly bent, both mandibles being sud- denly curved downwards from the middle. The common GRALLATORES. 50/ Flamingo (Phcenicopterus ruber) occurs abundantly in various parts of southern Europe. It stands between three and four feet in height, the general plumage being rose-coloured, the wing-coverts red, and the quill-feathers of the wings black. The tongue is fleshy, and one of the extravagances of the Romans during the later period of the Empire was to have dishes composed solely of Flamingoes' tongues. Other species occur in South America and Africa. ORDER II. GRALLATORES. — The birds comprising the order of the Grallatores, or Waders, for the most part frequent the banks of .rivers and lakes, the shores of estuaries, marshes, lagoons, and shallow pools, though some of them keep almost exclusively to dry land, preferring, however, moist and damp situations. In accordance with their semi-aquatic amphibious Fig. 219. — Grallatores. A, Leg and foot of the Curlew ; B, Head of Snipe ; C, Beak of the Avocet. habits, the Waders are distinguished by the great length of their legs ; the increase in length being mainly due to the great elon- gation of the tarso-metatarsus. The legs are also unfeathered from the lower end of the tibia downwards. The toes are elongated and straight (fig. 219, A), and are never completely palmate, though sometimes semi-palmate. There are three anterior toes, and usually a short hallux, but the latter may be wanting. The wings are long, and the power of flight usually considerable ; but the tail is short, and the long legs are stretched out behind in flight to compensate for the brevity of the tail. The body is generally slender, and the neck and beak usually of considerable length (fig. 219, B). They are sometimes polygamous, sometimes monogamous, and the young of the former are able to run about as soon as they are hatched. 508 MANUAL OF ZOOLOGY. The most -typical Waders — those, namely, which are semi- aquatic in their habits — spend most of their time wading about in shallow waters or marshes, feeding upon small fishes, worms, shell-fish, or insects. Others, such as the Storks, live mostly upon the land, and are more or less exclusively vegetable- feeders. The Grallatores are divided into the four families of the Macrodactyli, the Cultirostres, the Longirostres, and the Pressi- rostres. Fam. i. Macrodactyli. — In this family the feet are furnished with four elongated, sometimes lobate, toes, and the wings are of moderate or less than average size. In many of their char- acters a considerable number of the birds of this family ap- proach the Rasorial birds, and differ from the true Waders. The beak is mostly short, rarely longer than the head, and is compressed from side to side, or wedge-shaped. The legs are strong and not particularly lengthy ; but the toes are often of great length, and are furnished with long claws. The neck is not very long, and the tail is very short. Some of them are strictly aquatic in their habits, and, like the Coots, approach in many respects to the Natatores ; others, again, are exclusively terrestrial. The most familiar members of this family are the Rails (Rallus), Water-hens (Gallinultz), the Coots (Fulica), and the Jacana (Parra jacana). The Water-hens and Coots are aquatic or semi-aquatic, swimming and diving with great ease. In the Coots the toes are semi-palmate, being bordered by membranous lobes, like the toes of the Grebes, but the toes are not fringed in the Gallinules. Amongst the Coots should probably be placed the Notornis (Owen), long supposed to be extinct, but recently proved to be still living in the Middle Island of New Zealand. The Notornis is much larger than the ordinary Coots, and is remarkable in the fact that, like many extinct and some living New Zealand birds, the wings are so rudimentary as to be useless for flight. The true Rails, comprising the common Land-rail (Rallus aquatints), and the Corn-crake (Crex pratensis) of Britain, and the Marsh Hen (Rallus elegans), and Virginian Rail (fi. Virginianus] of North America, live almost exclusively on land, though the former usually frequents damp or marshy places. In the Jacanas, lastly, the feet are furnished with excessively long and slender toes, which enable the bird to run about upon the leaves of aquatic plants ; whilst the carpus is armed with for- midable spurs. They are natives of South America, Africa, and India. Closely allied to the Jacanas are the Screamers (Palamedea) of South America, of which the Horned Screamer GRALLATORES. 509 (P. cornuta) is the best known. It has a long frontal horn, and has spurs implanted on the edge of the wing. Fam. 2. Cultirostres. — In this family of the Grallatores are some of the most typical and familiar forms contained in the entire order. The bill in this family is long — usually longer than the head — and is compressed from side to side ; the legs are long and slender, having a considerable portion of the tibiae unfeathered ; and the feet have four toes, which are usually connected to a greater or less extent at their bases by membrane. In this family are the Cranes, Herons, Stork, Ibis, Spoonbill, and others of less importance. Fig. 220. — Crested Heron (A rdea cinerea). Europe. The Cranes (Gruida) are large and elegant birds, and are chiefly remarkable for their long migrations, which were noticed by many classical authors. In these journeys the Cranes usually fly in large flocks, led by a single leader, so that the whole assemblage assumes a wedge-like form ; or they fly in long lines. The common Crane (Grus cinerea) breeds in the north of Europe and Siberia, and migrates southwards at the approach of winter. The Numidian Crane or Demoiselle in- habits Asia and Africa, the Stanley Cranes (Anikropoides] are 5IO MANUAL OF ZOOLOGY. natives of the East Indies, and the Crowned Cranes (Balearica) are African. The Herons (Ardeidce) are familiarly known to every one in the person of the common Grey or Crested Heron (Ardea cinerea, fig. 220). It was one of the birds most gene- rally pursued in the now almost extinct sport of falconry. Various species of Heron are found over the whole world, both in temperate and hot climates. Here, also, belong the various species of Night Heron (Nycticorax\ the Bitterns (Botaurus), and the Boat-bills (Cancroma). The Ibises (Tantalina) form a group of beautiful birds, species of which occur in all the warm countries of the world. They are distinguished by their metallic colours, long, cylin- drical, curved bill, and more or less naked head. One, the Ibis religiosa, was regarded by the ancient Egyptians as a deity, and was treated with divine honours, being often embalmed along with their mummies, or figured on their monuments. The Storks (dconina) are large birds, of which one, the common Stork (Ciconia alba), is rarely found in Britain, but occurs commonly on the Continent, where it is often semi- domesticated. The Storks live in marshes, and feed on frogs, fishes, &c. Nearly related to the true Storks are the gigantic Marabout (Ciconia Maraboii], and Adjutant (C Argala] of Africa and India, which possess a sausage-shaped appendage in front of the neck. The Spoonbills (Plataleadce), are also large birds, very like the Storks, but the bill is flattened out so as to form a broad spoon-like plate. The common White Spoonbill (Platalea leucorodid) is found commonly on the Continent, but is of very rare occurrence in Britain. fam. 3. Longirostres. — The third family of Waders is that of the Longirostres, characterised by the possession of long, slender, soft bills, grooved for the perforations of the nostrils (fig. 219, B). The legs are sometimes rather short, sometimes of great length ; the toes are of moderate length, and the hallux is usually short, and is sometimes absent. The bill in these birds serves as an organ of touch, being used as a kind of probe to feel for food in mud or marshy soil. To fulfil this purpose, the tip of the bill is furnished with numerous filaments of the fifth nerve. They feed mostly upon insects and worms, and are not strictly aquatic in their habits, mostly frequenting marshy districts, moors, fens, the banks of rivers or lakes, or the shores of the sea. In this family of the Long-billed Waders are the various species of Snipe and Woodcock (Scolopaddce\ the Sandpipers (Tringa), the Curlews (Numenius\ the Turnstones (Strepsilas), CURSORES AND RASORES. 5 I I the Ruffs (Machetes], the Redshanks (Totanus\ the Godwits (Limosa), and others which need no special notice. JFam. 4. Pressirostres. — The members of this family are characterised by the moderate length of the bill, which is seldom longer than the head, and has a compressed tip. The legs are long, but the toes are short, and are almost always partially connected together at their bases by membrane. The hallux is short, and is often wanting. The wings are long, and they can both fly powerfully and run with great swiftness. In this section are two very distinct sub-families, the Charadriidce or Plovers, and the Otida or Bustards. In the former of these the legs are long and slender, the toes are united at their bases by a small membrane, and the hind-toe is very small and raised above the ground, or is entirely wanting. In this group are the true Plovers and Lapwings \Charadrius and Vanellus\ the Pratincoles (Glareola), the Long-shanks (Himantopus\ the Oyster-catcher (H&matopus], and the Thick-knee (CEdicnemus). In the Otidtz, or Bustards, the legs are long and the toes are short and furnished with stout claws. The hinder toe or hallux is entirely wanting ; and these birds are chiefly interesting from the affinities which they exhibit to the Rasores on the one hand, and to the Cur sores (Ostrich, &c.) on the other. The wings, however, are of ample size, and the tail is long, the reverse being the case in the Cursores. The Bustards are entirely confined to the Old World, and two species were for- merly not uncommon in Britain. They are found in plains and downs, and rarely fly, but run with great swiftness, using the wings to accelerate their course. They are polgamous, and the males are generally brighter and more variegated in plumage than the females. CHAPTER LXVIII. CURSORES AND RASORES. ORDER III. CURSORES. — The third order of Birds is that of the Cursores, or Runners, comprising the Ostriches, Rheas, Cassowaries, Emeus, and the singular Apteryx of New Zealand. In many respects the Cursores are to be looked upon as an artificial assemblage ; but in the meanwhile it will be most convenient to consider them as forming a distinct division. The Cursores are characterised by the rudimentary condition 5 I 2 MANUAL OF ZOOLOGY. of the wings, which are so short as to be useless for flight, and by the compensating length and strength of the legs. In accordance with this condition of the limbs, many of the bones retain their marrow, and the sternum (fig. 221, B) is destitute of the prominent ridge or keel, to which the great pectoral muscles are attached (hence the name of Ralita, applied by Huxley to the order). In the Ostrich, the pubic bones of the pelvis unite to form a symphysis pubis, as they do in no other bird ; and in all, the pelvic arch possesses unusual strength and stability. The legs are extremely robust and powerful, and the hind-toe is entirely wanting, except in the Apteryx, in which it is rudimentary. The anterior toes are two or three in num- ber, and are provided with strong blunt claws or nails. The plumage presents the remarkable peculiarity that the barbs of the feathers, instead of being connected to one another by hooked barbules, as is usually the case, are remote and disconnected from one another, presenting some resemblance to hairs. Fig. 221. — Cursores. A, Foot of the Ostrich (Strnthio camehts) ; B, Sternum of the Emeu {Dromaius Novce-Hollandice). The order Cursores may be divided into the t\vo families of the Struthionidcz and the Apterygidce — the former characterised by the absence of the hallux, and comprising the Ostrich, Rhea, Emeu, and Cassowary,* with several extinct forms ; the latter comprising only the Apteryx of New Zealand, and char- acterised by the possession of a rudimentary hallux. The African Ostrich (Struthio camelus) occurs in the desert plains of Africa and Arabia, and is the largest of all living birds, attaining a height of from six to eight feet. The head and neck are nearly naked, and the quill-feathers of the wings and tail have their barbs wholly disconnected, constituting the ostrich-plumes of commerce. The legs are extremely strong, and are terminated by two toes only (fig. 221, A), these con- sisting respectively of four and five phalanges, showing that it is the hallux and the innermost toe which are wanting. The CURSORES AND RASORES. 5 I 3 internal one of the two toes is much the largest, and is clawed. the outer toe is small and clawless. The Ostriches run with extraordinary speed, and can outstrip the fastest horse. They are polygamous, each male consorting with several females, and they generally keep together in larger or smaller flocks. The eggs are of great size, averaging three pounds each in weight, and the hens lay their eggs in the same nest, this being nothing more than a hole scratched in the sand. The eggs appear to be hatched mainly by the exertions of both parents, relieving each other in the task of incubation, but also partly by the heat of the sun.* The American Ostriches or Rheas are much smaller than the African Ostrich, and have the head feathered, whilst the feet are furnished with three toes each. The wings are rudi- mentary, and the phalanges are plumed and terminated by a spur. They inhabit the great plains of South America, and are polygamous. The Emeu (Dromaius Novcz-HollandicB} is exclusively found in the Australian continent, and nearly equals the African Ostrich in size, attaining a height of from five to seven feet. The feet are furnished with three toes each, and the head is feathered. The throat, however, is naked, and the general plumage resembles long hairs, the feathers hanging down on both sides of the body from a central line or parting which runs down the middle of the back. The Emeus are mono- gamous, and the eggs are dark green in colour. The male Emeu is smaller than the female, and undertakes all the duties of incubation. The last of the Struthionidcz is the Cassowary (Casuarius galeatus], which inhabits the Moluccan Islands and New Guinea, and was first brought alive to Europe by the Dutch. It stands about five feet in .height, and possesses a singular horny crest upon its head. The head and neck are naked, with pendant wattles, and the feet have three toes each. The general plumage is black, and the feathers more or less closely resemble hairs. The wings are rudimentary, each with five naked pointed quills. The male is much the smallest, and sits upon the eggs. Besides the Galeated Cassowary, other species have been described from New Britain and North Australia. The second family of the Cursorial birds is that of the Apttrygida, comprising only the singular Apteryx of New Zealand. The beak in the Apteryx is long, slender, and slightly curved, the tip being obtuse, and the nostrils placed * Mr Sclater. however, states that the duty of incubation is entirely taken by the males. 2 K 514 MANUAL OF ZOOLOGY. at the extremity of the upper mandible. The legs are com- paratively short, and there is a rudimentary hind-toe or hallux, forming a kind of spur, furnished with a claw. The wings are entirely rudimentary, and are quite concealed by the feathers, each terminating in a sharp claw. The feathers are long and narrow, and the tail is short and inconspicuous. The Apteryx is wholly confined to New Zealand, and is nocturnal in its habits, living upon insects and worms. Three species of Apteryx have been described, of which A. australis (fig. 222) is the best known. Fig. 222. — Apteryx australis. (Gould.) Besides the above-mentioned living forms, the order Cursores comprises several gigantic extinct forms, which will be treated of when describing the geological distribution of Birds as a class. ORDER IV. RASORES. — The fourth order of Birds is that of the Rasores, or Scratchers, often spoken of collectively as the "Gallinaceous" birds, from the old name of "Gallinge," given to the order by Linnaeus. The Rasores are characterised by the convex, vaulted upper mandible, having the nostrils pierced in a membranous space at its base. The nostrils are covered by a cartilaginous scale. The legs are strong and robust, mostly covered with feathers as far as the joint between the tibia and tarso-metatansus. There are four toes, three in front RASORES. 5 I 5 and one behind, the latter being short, and placed at a higher level than the other toes. All the toes terminate in strong blunt claws suitable for scratching (fig. 223, A). The food of the Scratchers or Gallinaceous birds consists chiefly of hard grains and seeds, and in accordance with this they have a ca- pacious crop and an extremely strong and muscular gizzard. They mostly nidificate, or build their nests, upon the ground, and the more typical members of the order are polygamous. The males take no part in either nidification or incubation, and the young are generally "precocious," being able to run about and provide themselves with food from the moment they quit the egg. The young of the Pigeons and Doves, however, are brought forth in a comparatively helpless condition. The wings in the majority of the Rasores are more or less weak, and the flight is feeble and accompanied with a whirring sound. Many of the Pigeons, however, are capable of very powerful and sustained flight. The order Rasores is divided into two sub-orders, called re- ^;; T> A Fig. 223.— Rasores. A, Foot of Fowl (Callus Bankiva) ; B, Head of Guinea-fowl. spectively the Gallinacei and the Columba&i, or sometimes, from the characters of the sounds which they utter, the Clama- tores and the Gemitores. Sub-order i. Gallinacei or Clamatores. — This sub-order comprises the typical members of the order Rasores, such as the common Fowls, Turkeys, Partridge, Grouse, Pea-fowl, and a number of allied forms. Its characters are therefore those of the order itself, but it is especially distinguished from the Columbacei by being less fully adapted for flight. The body is much heavier comparatively speaking, the legs and feet are stronger, and the wings shorter and less powerful. On the whole, therefore, these birds are worse fliers than the Columbacei, and are better adapted for living upon the ground. The hallux is elevated above the anterior toes, and merely touches the ground in walking. The back of the tarsus, too, is usually furnished in the males with a spur (calcar), which is used as an 5l6 MANUAL OF ZOOLOGY. offensive weapon, and has sometimes been looked upon as a rudimentary toe.* Lastly, the Gallinacei are mostly polygamous, and the males are usually much more brilliantly coloured than the females, this being an adaptive modification of the plumage to meet this peculiarity in their mode of life.t The following are the most important families of the Gal- linacei : — The TetraonidcK, or Grouse family, comprises the various species of Grouse (Tetrao), the Ruffed Grouse (Bonasa}, the Cock of the Plains (Centrocercus), and the Ptarmigans (Lagopus). The Perdiadcz, or Partridge family, comprises the Par- tridges (Perdix], the Francolins (Francolinus), the Quails (Co- turnix], the Maryland Quail (Orfyx), the Tufted Quails (Lophortyx\ &c. The Phasianidce or Pheasant family, comprises the Turkeys and Guinea-fowl (Meleagrinte), the common Pheasant (Phasi- anus Colchicus}, the Golden and Silver Pheasants, the common Fowl (Gallus domesticus\ and the Pea-fowl (Pavonintz). None of these birds — all of which can be domesticated, and most of which are of- great value to man — are natives of this country, though they will all breed readily, and thrive even in confine- ment. The domestic Turkey (Meleagris gallopavo] is originally a native of North America, where it still occurs in a wild con- dition, having been brought to Europe about the beginning of the sixteenth century. The Guinea-fowl (Numida Meleagris] is originally an African bird. The common Pheasant (Phasianus Colchicus], though now regarded as an indigenous bird, truly belongs to Asia, and it is asserted that it was really brought to Europe from Colchis by the Greeks ; hence its specific name. The common Fowl is certainly not a native of Europe, and it is almost as certainly a native of Asia or of some of the Asiatic islands ; but its exact original habitat is uncertain, as is the species from which the domestic breeds are descended (com- monly said to be the Gallus Bankiva of Java). The introduc- tion of the Fowl into Europe is lost in the mists of antiquity, and it is wholly unknown whence the original stock may have been brought ; though there is really every ground for believing that the typical breed — the Game breed — is truly descended from the Jungle Cock, or Gallus Bankiva. The Pea-fowl (Pavo) are really natives of Thibet and Hindostan, and were originally brought to Greece by Alexander the Great. They were for- * In some cases (as in the Java . Peacock) the female possesses spurs as well as the male ; and sometimes (as in Polyplectron} there are two or more spurs on each leg of the male. t The Guinea-fowl, Red Grouse, Ptarmigan, and Partridge are mono- gamous, in a state of nature at any rate. RASORES. 517 merly much esteemed as food, but are now regarded merely from an ornamental point of view. The Megapodickz, or Mound-birds, belong to India and Aus- tralia, and have very large feet and long claws. They build immense mounds, often six or eight feet high, and twenty or thirty feet in diameter. They lay their eggs in the centre of these mounds at a depth of two or three feet, and leave them to be hatched by the heat produced by the fermentation of the vegetable matter of the mass. The Craddce, or Curassows, are large heavy birds, belonging to Central and South America, and to a great extent arboreal in their habits. The best-known species is the Crested Curas- sow (Crax alector} of Mexico and Brazil, Fig. 224. — Columbidae. Rock-pigeon (Columba livia). The second sub-order of the Rasores is that of the Cohimbacei or Gemitores, comprising the Doves and Pigeons, and often raised to the rank of a distinct order under the name of Co- lumbce. The Columbacei are separated from the more typical members of the Rasores by being furnished with strong wings, so as to endow them with considerable powers of flight. In place, therefore, of being chiefly ground-birds, they are to a 5 I 8 MANUAL OF ZOOLOGY. great extent arboreal in their habits, and in accordance with this the feet are slender, and are well adapted for perching. There are four toes, three in front and one behind, and the former are never united towards their bases by a membrane, though the base of the outer toe is sometimes united to that of the middle toe. The hallux is articulated on the same plane as the other toes, and touches the ground in walking. Lastly, they are all monogamous, and pair for life ; in consequence of which fact, and of their being readily susceptible of domesti- cation, they present an enormous number of varieties, often so different from one another that they would certainly be de- scribed as distinct species if found in a wild state. It seems certain, however, that all the common domestic breeds of Pigeons, however unlike one another, are really descended from the Rock-pigeon (Columba livia\ which occurs wild in many parts of Europe, and has retained its distinguishing peculiarities unaltered for many centuries up to the present day. Finally, the young of the Columbacei are born in a naked and helpless state, whilst those of the Gallinacei are "preco- cious," and can take care of themselves from the moment of their liberation from the egg. Of the various living birds included in this section, the true Pigeons (Columbidce) are too well known to require any de- scription; but the Ground-pigeons (Gourida] depart to some extent from this type, being ground-loving birds, more closely allied to the ordinary Gallinacei. The only other member of the sub-order which requires special notice, is the remarkable extinct bird, the Dodo (Didus ineptus), which seems certainly to belong here, though its size was gigantic, and some of its characters very anomalous. The Dodo may, properly speak- ing, be said to be extinct, since it no longer occurs in a living state ; but it is not extinct in the sense that geologists speak of " fossils " as extinct ; since it has been extirpated by man him- self within quite a recent period — in fact, not more than three centuries ago. The Dodo was an inhabitant of the Island of the Mauritius up to the commencement of the seventeenth cen- tury, and was a large bird, considerably over the size of a swan. All that remain nowadays to prove the existence of the Dodo are two or three old, but apparently faithful, oil-paintings, two heads, a foot, and some feathers, to which a few bones have recently been added. The Dodo owed its extermination to the fact that it was unable to fly. The body must have been extremely weighty, and the wings were rudimentary and com- pletely useless as organs of flight. The legs, were short and stout, the feet had four toes each, and the tail was extremely SCANSORES. 5 1 9 short, carrying, as well as the wings, a tuft of soft plumes. The beak (unlike that of any of the Columbacei except the little Didunculus strigirostris) was strongly arched towards the end, and the upper mandible had a strongly-hooked apex, not at all unlike that of a bird of prey. The nearest living ally of the Dodo appears to be the little Diduncnlus just alluded to, which inhabits the Navigator Islands, and is little bigger than a partridge. It is worthy of notice, that in the little Island of Rodriguez, lying to the east of Mauritius, there existed one large wingless bird, the Solitaire or Ptzophdps, which has likewise become ex- tinct during the human period. In the Mauritius, also, occur the remains of the Aphanapteryx, a wingless bird believed to have strong Grallatoriai affinities, and to have been extermi- nated by man. Other cases in which wingless birds have been, or are being, exterminated by man, lead us to the belief that the absence of wings is not compatible with the coexistence of birds and human beings. In other words, the sole protection possessed by birds against the destructive propensities of man is to be found in their power of flight. CHAPTER LXIX. SCANSORES AND INSESSORES. ORDER V. SCANSORES. — The order of the Scansorial or Climb- ing birds is easily and very shortly defined, having no other distinctive and exclusive peculiarity except the fact that the feet are provided with four toes, of which two are turned back- wards and two forwards. Of the two toes which are directed backwards, one, of course, is the hallux or proper hind-toe, and the other is the outermost of the normal three anterior toes. This arrangement of the toes (fig. 225, A) enables the Scansores to climb with unusual facility. Their powers of flight, on the other hand, are generally only moderate and below the average. Their food consists of insects or fruit. Their nests are usually made in the hollows of old trees, but some of them have the remarkable peculiarity that they build no nests of their own, but deposit their eggs in the nests of other birds. They are all monogamous. The most important families of the Scansores are the Cuckoos (Cuculida), the Woodpeckers and Wrynecks (Picida), the 52O MANUAL OF ZOOLOGY. Parrots (Psittadda), the Toucans (Rhamphastida*}, and the Trogons (Trogonidce). The Cuculidce, or Cuckoos, are chiefly remarkable for the extraordinary fact that many of them, instead of nidificating and incubating for themselves, lay their eggs in the nests of other birds. The only bird not belonging to this family which has the same "parasitic" habit, is the Cow Bunting (Molothrns pecoris) of the United States. As a rule, only one egg is deposited in each nest, and the young Cuckoo which is hatched from it is brought up by the foster-parent, generally at the expense of the legitimate offspring. The large Channel- bill (Scythrops Nffva-Hollandice) is said to possess the same curious habit, but many species of this group build nests for themselves in the ordinary manner. The second family of the Scansores is that of the Pidda, and Fig. 225. — Scansores. A, Foot of Woodpecker (Picus) ; B, Head of Love-bird (Agapomis). comprises the Woodpeckers and Wry-necks. These birds feed chiefly upon insects, and the tongue is extensible, barbed at the point, and covered with a viscid secretion, so as to enable them to catch their prey by suddenly darting it out. The bill is strong and wedge-shaped, and the claws crooked. The tail- feathers terminate in points, and are unusually hard and stiff, assisting the bird in running up the trunks of trees. The next family is that of the Parrots (Psittadda), the largest group of the Scansores, comprising over three hundred species. The bill in the Parrots is large and strong, and the upper mandible is considerably longer than the lower and is hooked at its extremity (fig. 225, B). The bill is used as a kind of third foot in climbing. At the base of the upper mandible is a "cere," in which the nostrils are pierced. The tongue is soft and fleshy. The feet are especially adapted for SCANSORES. 521 climbing, some, however, of the Parrots moving about actively on the ground. The colours of the plumage are generally ex- tremely bright and gaudy; and they live for the most part upon fruits. The Psittacidce are distributed throughout the tropics, and in the southern hemisphere as far south as the 52d parallel. They are monogamous, and make their nests in holes in the rocks. Their natural voice is harsh and grating. The true Parrots (Psittacus) are mostly inhabitants of tropical America, Fig. 226. — Psittacidae. Purple-capped Lory (Lorius douiicella}. and their prevailing colour is green. The Cockatoos (Plyctolo- phus], the Love-birds (Agapornis], and the Lorikeets (Tricho- glossus) belong to the Australian province. The Lories (Lorius) inhabit the East (fig. 226). The true Macaws (Araince) are exclusively American ; and the true Parrakeets (Pezoporince) are exclusively confined to the eastern hemisphere, being especially characteristic of Australia. In the next family of the Scansores are the Toucans (Rham- phastidce), characterised by having a bill which is always very 522 MANUAL OF ZOOLOGY. large, longer than the head, and sometimes of comparatively gigantic size. The mandibles are, however, to a very great extent hollowed out into air-cells, so that the weight of the bill is much less than would be anticipated from its size. The tongue is very long, notched at its side, or feathered with deli- cate lateral processes. The Toucans live chiefly upon fruits. and are all confined to the hotter regions of South America, frequenting the forests in considerable flocks. The Trogons have short and weak feet, a short triangular bill, the gape bordered with strong bristles, and short wings. The plumage is soft and loose, and generally of the most gor- geous description. They inhabit the most retired recesses of the forests of the intertropical regions of both hemispheres, and show many decided points of affinity to the Goat-suckers. ORDER VI. INSESSORES. — The sixth order of Birds is that of the Inses sores, or Perchers — often spoken of as the Passer es, or " Passerine" Birds. They are defined by Owen as follows : — " Legs slender, short, with three toes before and one behind, the two external toes united by a very short membrane" (fig. 227, A, B). "The Perchers form the largest and by far the most nume- rous order of birds, but are the least easily recognisable by dis- tinctive characters common to the whole group. Their feet, being more especially adapted to the delicate labours of nidi- fication, have neither the webbed structure of those of the Swimmers, nor the robust strength and destructive talons which characterise the feet of the Birds of Rapine, nor yet the ex- tended toes which enable the Wader to walk safely over marshy soils and tread lightly on the floating leaves of aquatic plants; but the toes are slender, flexible, and moderately elongated, with long, pointed, and slightly-curved claws. " The Perchers in general have the females smaller and less brilliantly coloured than the males ; they always live in pairs, build in trees, and display the greatest art in the construction of their nests. The young are excluded in a blind and naked state, and wholly dependent for subsistence during a certain period on parental care. The brain arrives in this order at its greatest proportionate size ; the organ of voice here attains its greatest complexity, and all the characteristics of the bird, as power of flight, melody of voice, and beauty of plumage, are enjoyed in the highest perfection by one or other of the groups of this extensive and varied order." The structure of the feet, then, gives the definition of the order, but the minor subdivisions are founded on the nature of the beak ; this organ varying in form according to the INSESSORES. 523 nature of the food, " which may be small or young birds, car- rion, insects, fruit, seeds, vegetable juices, or of a mixed kind" (Owen). In accordance with the form of the beak, the Insessores have been divided into four great sections or sub-orders, known as the Conirostres, Dentirostres, Tenuirostres, and Fissirostres. Sub-order i. Conirostres. — In this section of the Insessores the beak is strong and on the whole conical, broad at the base and tapering with considerable rapidity to the apex (fig. 227, C). The upper mandible is not markedly toothed at its lower margin. Good examples of the Conirostral type of beak are to be found in the common Sparrow, Hawfinch, or Bullfinch. Fig. 227.— Insessores. A, Foot of Yellow Wagtail ; B, Foot of Water-ouzel ; C, Conirostral beak (Hawfinch) ; D, Dentirostral beak (Shrike,) ; E, Tenuirostral beak (Humming-bird) ; F, Fissirostral (Swift). The greater number of the Conirostres are omnivorous ; the remainder are granivorous, or feed on seeds and grains. The sub-order includes the families of the Horn-bills {Bucerid&}, the Starlings (Stumida), the Crows (Corvidcz), the Cross-bills (Loxiada\ and the Finches and Larks (Fringillida). In the Horn-bills the Conirostral shape of the beak is masked, partly by its being of very great size, and partly by the fact that above the upper mandible is placed a hollow appendage 524 MANUAL OF ZOOLOGY. like a kind of helmet. Both the beak and the appendage above it are rendered ligh't by the presence of numerous air- cells. The Horn-bills are exclusively confined to the warm countries of the eastern hemisphere, and are the largest of all the Insessorial birds, sometimes attaining the size of a goose. They live on fruits, and make their nests in the holes of trees. The best-known species is the Rhinoceros Bird (Buceros Rhino- ceros] of India and the Indian Archipelago. The family of the Corvidce, or Crows, is an extremely exten- sive one, and includes a large number of very dissimilar-look- ing birds, all characterised by their long, strong, and com- pressed beaks, the tip of the upper mandible being slightly hooked and more or less notched. In this family are the Jays (Garrulina)') the true Crows or Corvince (comprising the Rooks, Carrion-crows, Ravens, Jackdaws, Magpie, Chough, &c.), and the Birds of Paradise (Paradisticfa). These last differ considerably from the ordinary Corvtda, but can hardly be separated as a distinct family. They are amongst the most beautiful of all birds, and are entirely confined to New Guinea and the neighbouring islands. They feed upon insects and fruit, and are largely destroyed for the sake of their feathers. The natives who capture them usually cut off their legs ; hence the notion formerly prevailed that the Birds of Paradise were destitute of these limbs. It is only the males which possess the brilliant plumage, the females being soberly dressed ; and in accordance with this fact, it is stated that the Birds of Para- dise are polygamous, being in this respect an exception to almost the entire order of the Insessores* "They are char- acterised by extraordinary developments of plumage, which are unequalled in any other family of birds. In several species large tufts of delicate, bright-coloured feathers spring from each side of the body, forming trains, fans, or shields ; and the middle feathers of the tail are often elongated into wires, twisted into fantastic shapes, or adorned with the most brilliant metallic tints. In another set of species, the accessory plumes spring from the head, the back, or the shoulders ; whilst the intensity of colour and of metallic lustre displayed by their plumage, is not to be equalled by any other birds, except, per- haps, the Humming-birds, and is not surpassed by these" (Wallace). The family of the Starlings (Sturnidce) is not separated from that of the Crows by any important characters. Besides our common Starlings,, it includes a number of other more or less * The Humming-birds are thought to he polygamous, and this is cer- tainly the case with the Whydah Finch ( Vidtta). INSESSORES. 525 singular birds, of which the Bower-birds of Australia are per- haps the most peculiar. These curious birds have the habit of building very elaborate bowers, often very beautifully con- structed and of considerable size, in which they amuse them- selves and apparently make love to one another. These bowers are wholly independent of their nests, which they construct elsewhere. The last family of the Conirostres is that of the Fringillida, comprising the Finches, Linnets, and Larks. In these birds the bill is stout and conical, with a shark apex, but not having the upper mandible toothed. The toes are adapted for perch- ing, and are provided with long and curved claws, that of the hinder toe being usually longer than the rest. They are almost all monogamous, and they build more or less elaborate nests. In this family are the true Finches (Fringilla), the Sparrows (Pyrgita], the Lin- nets and Goldfinches (Car- duelis), the Whydah Finches ( Vidna), the Grosbeaks (Coc- cothraustes), the Bullfinches (Pyrrkula], and many others, but their numbers are so great that any further notice of them is impossible here. It may be mentioned, however, Fig. 228.— Head of the common Bullfinch that the Finches of the Old jSr^iT^^ showingthl World are represented in the tropical parts of America by the Tanagers (TanagrincR), remark- able for their brilliant colours. The only remaining members of the Conirostres which require notice are the Cross-bills (Loxiada], which are some- times placed with the Finches, and sometimes considered as a separate family. In these birds the structure of the beak is so peculiar that its Conirostral character is completely masked, and it has been looked upon as a deformity. Both mandibles, namely, cross one another towards the tip, giving the entire bill a most remarkable appearance. In point of fact, however, instead of being a deformity, the bill of the Cross-bills is a beautiful natural adaptation, enabling the bird with the greatest facility to tear in pieces the hard fir-cones, on the seeds of which it feeds. Sub-order 2. Dentirostres. — The birds in this section are characterised by the fact that the upper mandible is provided with a distinct notch in its lower margin near the tip (fig. 227, D). 526 MANUAL OF ZOOLOGY. They all feed chiefly upon insects. This sub-order includes the Shrikes (Laniidce), the Fly-catchers (Musticapida), the Thrushes (Merulida), the Tits (Parina), and the Warblers (Sylviadtz). The Musricapidce, including the numerous species of Fly- catcher, are the most insectivorous of the Dentirostres. The gape is wide and bordered with bristles, and the legs are short and weak. They are mostly sedentary, catching their prey from a fixed point. The Shrikes are highly predacious birds, which in many respects make a close approach to the true Birds of Prey. They feed, however, mostly upon worms and insects, and only occasionally destroy small birds or mice. The great family of the Thrushes (Merulidcz) comprises not only the true Thrushes, Field-fares, and Blackbirds, but a number of exotic forms, of which the most familiar are the Orioles, so well known for their brilliant plumage and their beautifully-constructed nests. In the Sylviada, amongst other forms, are the Wag- tails (MotacUlina] and the Pipits (Anthus\ the Titmice, Robins, Hedge-sparrow, Stone-chat, Redstarts, and other well-known British birds. The Titmice (Parince] are often placed in the sub-order of the Conirostres. The Nightingale also belongs to this family. Sub-order 3. Tenuirostres. — The members of this sub-order are characterised by the possession of a long and slender beak, gradually tapering to a point (fig. 227, E). The toes are very long and slender, the hind-toe or hallux especially so. Most of the Tenuirostral birds live upon insects, and some of these present a near resemblance in many of their characters to the Dentirostres, but it is asserted that some live partially or wholly on the juices of flowers. The chief families of the Tenuirostres are the Creepers {Ccrtkida}, the Honey-eaters (Meliphagid(z\ the Humming- birds (Trochilidce\ the Sun-birds (Promeropida), and the Hoopoes (Upupidce), of which only the Creepers and Hum- ming birds need any further notice. The family Certhidcz includes several familiar British birds, such as the little brown Creeper (Certhia familiaris), the Nuthatch (Sitta Europcea), and the Wrens (Troglodytes}. With these are a number of exotic forms, of which the singular Lyre-birds of Australia are the most remarkable. The family of the Trochilida, or Humming-birds, includes the most fragile and brightly coloured of all the birds, some not weighing more than twenty grains when alive, and many exhibiting the most brilliant play of metallic colours. The INSESSORES. 527 Humming-birds are pre-eminently South American, but extend northwards as far even as the southern portions of Canada. The bill (fig. 227, E) is always very long and slender, as are the toes also. The tongue is bifid and tubular, and appears to be used either to catch insects within the corollas of flowers, or to suck up the juices of the flowers themselves. The plu- mage of the males is always brilliant, with metallic reflections, that of the female generally sombre. The legs are short and weak, but the wings are proportionately very long, and the flight is exceedingly rapid. The Sun-birds represent in the Old World the Humming- birds of the western hemisphere, and the Australian Honey- eaters show also many points of resemblance to the Tro- chilidcE. Sub-order 4. Fissirostres. — In this sub-order of the Inses sores the beak is short but remarkably wide in its gape (fig. 227, F), and the opening of the bill is fenced in by a number of bristles (vibrissa). This arrangement is in accordance with the habits of the Fissirostres, the typical members of which live upon insects and take their prey upon the wing. The most typical Fissirostral birds, in fact, such as the Swallows and Goat- suckers, fly about with their mouths widely opened ; and the insects which they catch in this way are prevented from escap- ing, partly by the bristles which border the gape, and partly by a viscid saliva which covers the tongue and inside of the mouth. The typical Fissirostres, characterised by this structure of the beak, comprise three families — the Swallows and Martins (Hirvndinida), the Swifts (Cypselidce), and the Goat-suckers {Caprimulgida). These three families differ in many important respects irom one another, but it would be inconvenient to separate them here. The Swifts, especially, are remarkable for the peculiarity that whilst the hallux is present, it is turned forwards along with the three anterior toes. The Goat-suckers, again, hunt their prey by night, and they are provided with the large eyes and thick soft plumage of all nocturnal birds. Besides the above, there remain the two families of the King- fishers and Bee-eaters, which are generally placed amongst the Fissirostres, though in very many respects the arrangement appears to be an unnatural one. These families are charac- terised by their stronger and longer bills, and by having the external toe nearly as long as the middle one, to which it is united nearly as far as the penultimate joint. In consequence of this peculiar conformation of the toes, these families were united by Cuvier into a single group under the name of Syndactyli. 528 MANUAL OF ZOOLOGY. The Caprimiilgida are intermediate between the Owls and the Passerine Birds. Their plumage is lax and soft, and they have a hawking flight. The eyes and ears are large, the feet short and weak, and the gape of enormous size and bordered by vibrissae. Amongst the more remarkable members of the family may be mentioned the Whip-poor-will (Antrostomus vociferus) of North America, the More-pork (Podargus Cuvieri) of Australia, and the extraordinary Guacharo Bird (Steatornis Caripensis) of the valley of Caripe in the West Indies. The Bee-eaters (Meropidce) live upon insects, chiefly upon various species of bees and wasps : but the King-fishers live upon small fish, which they capture by dashing into the water. The common King-fisher (Alcedo ispida] is a somewhat rare native of Britain, and is perhaps the most beautiful of British birds. Some exotic King-fishers are of large size, and one of the most remarkable of them is the Laughing Jackass (Dacelo gigas) of Australia, so called from its extraordinary song, re- sembling a prolonged hysterical laugh. A very beautiful species is the Belted King-fisher (Ceryle alcyon) of North America. The Bee-eaters are found chiefly in the warmer regions of the Old World, and their place is taken in America by the Mot- mots (Momotus}. CHAPTER LXX. RAPTORES AND SAURUR&. ORDER VII. RAPTURES. — All the members of this order are characterised by the shape of the bill, which is "strong, curved, sharp-edged, and sharp-pointed, often armed with a lateral tooth " (Owen). The upper mandible is the longest (fig. 229, B), and is strongly hooked at the tip. The body is very muscular ; the legs are robust, short, with three toes in front and one behind, all armed with long, curved, crooked claws or talons (fig. 229, A) ; the wings are commonly pointed, and of considerable size, and the flight is usually rapid and powerful. The Birds of Rapine are monogamous, and the female is larger than the male. They build their nests generally in lofty and inaccessible situations, and rarely lay more than four eggs, from which the young are liberated in a naked and helpless condition. The order Raptorcs is divided into two great sections — the Nocturnal Birds of Prey, which hunt by night, and have the RAPTORES. 529 eyes directed forwards ; and the Diurnal Raptores, which catch their prey by day, and have the eyes directed laterally. The section of the Nocturnal Raptores includes the single family of the Strigitke, or Owls. In these birds the eyes are Fig. 229. — A, Foot of the Peregrine Falcon ; B, Head of Buzzard. large, and are directed forwards. The plumage is exceedingly loose and soft, so that their flight (even when they are of large size) is almost noiseless; and it is generally spotted or barred with different shades of grey, brown, or yellow. The beak is short, strongly hooked, furnished with bristles at its base, and having the nostrils pierced in a membranous " cere " at the base of the upper mandible. The cranial bones are highly pneumatic, and the head is therefore of large size. The feathers of the face usually form an incomplete or complete " disc " or circle round each eye (fig. 230, B). and a circle of plumes is likewise placed Fig. 230.— A, Foot of tawny Owl (Ulula stridula) ; B, Head of white Owl (Strix JJammea) . round each external meatus auditorius. Besides this auricular circle of feathers, the external meatus of the ear is likewise protected by a fold of skin. The legs are short and strong, and are furnished with four toes, all armed with strong crooked 2 L 53O MANUAL OF ZOOLOGY. talons. The outer toe can be turned backwards, so that the foot has some resemblance to that of the Scansores. The tarso- metatarsus is densely feathered (fig. 230, A), and the plumes sometimes extend to the extremities of the toes. The oeso- phagus is not dilated into a crop ; and the indigestible portions of the food are rejected by regurgitation from the stomach in the form of small pellets. The Owls hunt their prey in the twilight or on moonlight nights, and they live mostly upon field-mice and small birds, though they will also eat insects or frogs. The section of the Diurnal Raptores includes the two groups of the Accipitrince. (Falcons, Hawks and Eagles), and the Vul- turidce, or Vultures. The eyes in this section are much smaller than in the preceding, and are placed laterally ; and the plu- Fig. 231. — Head of Vulture (Neophron percnopterus). mage is not soft. As regards their power of flight, they show a decided advance upon the Nocturnal Birds of Prey. The wings are long and pointed; the sternal keel and pectoral muscles are greatly developed ; and many of the members of this section exhibit a more rapid power of locomotion than is seen in any other division of the animal kingdom. The bill is long and strong, with a large " cere " at the base of the upper mandible, in which the nostrils are pierced. The tarso-meta- tarsus and toes are usually covered by scales, and are rarely feathered. Lastly, the oesophagus is dilated into a capacious crop, the gizzard is thin, the intestinal caeca are rudimentary, and the intestinal canal is generally short and wide. In the Accipitrince or Falconida (fig. 229, B) the head and RAPTORES. 531 neck are always clothed with feathers, and the eyes are more or less sunk in the head, and provided with a superciliary ridge or eyebrow. It is to a great extent to the presence of this ,ridge that many of these birds owe their fearless and bold expression. In this family are the Falcons, Hawks, Buzzards, Kites, Harriers, and Eagles, most of which are so well known that any description is unnecessary. In the Vulturida (fig. 231) the eyes are destitute of an eye- brow, and the head and neck are frequently naked, or covered only by a short down. In this family are the Bearded Vul- tures, the true Vultures, and the Condor. The Bearded Vulture, or Lammergeyer (Gypa'ttos barbatus). is the largest of European birds, measuring from nine to ten feet from the tip of one wing to that of the other. This power- ful and rapacious bird inhabits the mountain-ranges of the south of Europe and the west of Asia, and feeds chiefly on goats, lambs, and deer, which it kills by precipitating down steep declivities. It is distinguished from the true Vultures by the fact that the head and neck are feathered. The true Vultures have the head, and generally the neck also, naked, or covered with down. They are filthy and dis- gusting birds, which live almost entirely upon carrion, a pecu- liarity which renders them of great service in hot climates. The Secretary Vultures (Serpentarius) are distinguished -by Fig. 232. — Archczopteryx macrura, showing tail and tail-feathers, with detached bones. their very long and slender legs, unfeathered tarso-metatarsus, and long wings armed with blunt spines. They are found in 532 MANUAL OF ZOOLOGY; Africa and the Philippine Islands, and live upon Serpents and other Reptiles. The last member of this section is the gigantic Condor (Sarcorhampus gryphus}. This enormous bird has a stretch of wing of over ten feet, and is usually seen soaring in majestic circles at a great elevation in the air, rising, it is said, to a height of over twenty thousand feet. It inhabits the lofty mountain-ranges of the Andes, and lays its eggs at a height of from ten to fifteen thousand feet. It differs from the Vultures of the Old World chiefly in possessing a large fleshy protuber- ance or caruncle above the base of the beak. ORDER VIII. SAURUR^E. — This order includes only the extinct bird, the Archczopteryx macrura (fig. 232), a single specimen of which — and that but a fragmentary one — has been discovered in the Lithographic Slates of Solenhofen (Upper Oolites). This extraordinary bird appears to have been about as big as a Rook ; but it differs from all known birds in having two free claws belonging to the wing, and in having a long lizard-like tail, longer than the body, and composed of separate vertebrae. The tail was destitute of any ploughshare-bone, and each vertebra carried a single pair of quills. The metacarpal bones, also, were not anchylosed together as they are in all other known birds, living or extinct. CHAPTER LXXI. DISTRIBUTION OF A VES IN TIME. As regards the geological distribution of Birds, there are many reasons why we should be cautious in reasoning upon merely negative evidence, and more than ordinarily careful not to infer the non-existence of birds during any particular geological epoch, simply because we can find no positive evidence for their presence. As Sir Charles Lyell has well remarked, " the powers of flight possessed by most birds would ensure them against perishing by numerous casualties to which quadrupeds are exposed during floods;" and "if they chance to be drowned, or to die when swimming on water, it will scarcely ever happen that they will be submerged so as to become preserved in sedimentary deposits/' since, from the lightness of the bones, the carcass would remain long afloat, and would be liable to be devoured by predaceous animals. As, with a few utterly trivial exceptions, all the deposits in which fossils are found DISTRIBUTION OF AVES IN TIME. 533 have been laid down in water, and more especially as they are for the most part marine, these considerations put forward by Sir Charles Lyell afford obvious ground against the anticipa- tion that the remains of birds should be either of frequent occurrence or of a perfect character in any of the fossiliferous rocks. In accordance with these considerations, as a matter of fact, most of the known remains of birds are either frag- mentary or belong to forms which were organised to live a terrestrial life, and were not adapted for flight. The earliest remains which have been generally referred to birds are in the form of footprints impressed upon certain sandstones in the valley of the Connecticut River in the United States. These sandstones are almost certainly Triassic ;' Fig. 233. — Footprint supposed to belong to a Bird. Triassic Sandstones of Connecticut. and if the ornithic character of these footprints be admitted, then Birds date their existence from the commencement of the Mesozoic period, and, for anything we know to the contrary, may have existed during the Palaeozoic epoch. The evidence as to the ornithic character of the footprints in the American Trias is as follows : — Firstly r, The tracks are, beyond all question, those of a biped — that is to say, of an animal which walked upon two legs. No living animals walk habitually upon two legs except Man and Birds, and therefore there is a prima fade presumption that the authors of these prints were birds. Secondly, The impressions are mostly tridactylous — that is to 534 MANUAL OF ZOOLOGY. say, formed by an animal with three toes on each foot, as is the case in many Waders and most Cursorial birds (fig. 233). Thirdly >, The impressions of the toes show the same numeri- cal progression in the number of phalanges as exists in living birds — that is to say, the innermost of the anterior toes has three phalanges, the middle one has four, and the outermost toe has five phalanges. Taking this evidence collectively, it would have seemed, till lately, tolerably certain that these impressions were formed by Birds. We must not, however, lose sight of the possibility that these impressions may have been formed by Reptiles more bird-like in their characters than any of the living forms with which we are acquainted. The recent researches of Huxley, Cope, and others, go to show that the Dinosaurian Reptiles possessed the power of walking temporarily or per- manently on the hind-legs, and many curious affinities to the true Birds have been pointed out. It is therefore by no means impossible that these footprints of the Connecticut valley are truly Reptilian.* The size and other characters of the above-mentioned impressions vary much, and they have certainly been pro- duced by several different animals. In the largest hitherto dis- covered, each footprint is twenty-two inches long, and twelve inches wide, showing that the feet were four times as large as those of the African Ostrich. The animal, therefore, which produced these impressions — whether Avian or Reptilian — must have been of gigantic size. The first unmistakable remains of a bird have been found in the Solenhofen Slates of Bavaria, of the age of the Upper Oolites. A single unique specimen, consisting of bones and feathers, but unfortunately without the skull, is all that has hitherto been discovered ; and it has been named the ArcJm- opteryx macrnra. The characters .of this singular and aberrant bird, which alone constitutes the order Saururce, have been already given, and need not be repeated here. Other doubtful remains of birds have been alleged to occur in the Mesozoic series, but many of these certainly belong in reality to Pterodactyles. In the Cretaceous rocks, however, of the United States, occur the bones of several Wading Birds (Graculavus, Hesperornis, Laornis, Telmatornis, and Pal o — o' * i — i' 4 — 4 The praemolars and molars agree with the incisors in growing from permanent pulps, in which respect the Wombat differs from all the other Marsupials, and agrees with the herbivorous Rodents, with those Edentata which have teeth, and with the extinct Toxodon (Owen). The Wombat is a nocturnal animal, and feeds chiefly upon roots and grass. b. Poephaga. — In this section are the Kangaroos (Macropo- didce) and the Kangaroo-rats or Potoroos (Hypsiprymnus), all strictly phytophagous. The Kangaroos are distinguished by the disproportionate length of the hind-limbs and dispropor- tionate development of the posterior portion of the body as compared with the fore-limbs and fore part of the body. The hind-legs are exceedingly long and strong, and the feet are much elongated — the whole sole being applied to the ground. The hind-feet have four toes each, of which the central one is by far the largest, and the two inner toes are very small, and are united by a common integument. The tail is also extremely long and strong, and by the assistance of this organ 56° MANUAL OF ZOOLOGY. and the powerful hind -limbs the Kangaroos are enabled to effect extraordinarily long and continuous leaps. In fact, leap- ing is the ordinary mode of progression in the typical Kan- garoos ; and when walking upon all fours their locomotion is slow and ungraceful. The anterior extremity of the body is very diminutive as compared with the posterior, and the fore- limbs are quite small, but have five well-developed toes armed Fig. 238. — Koala or Kangaroo-bear (Phascolarctos cine reus) — after Gould. with strong nails. The head is small, with large ears, and the dental formula is — i — i 4—4 — 1> o— o There are therefore six upper incisors, two lower incisors, and no functional canines (though rudimentary upper canines are present in the young of some of the Kangaroos, at any rate). The stomach is complex, and sacculated. The Kan- garoos are all herbivorous, and mostly live, either scattered or gregariously, on the great grassy plains of Australia. The "Tree-kangaroos," however (constituting the genus Dendro- lagus), live mostly in trees • and, in adaptation to this mode of life, the fore-legs are nearly as long and strong as the hind-legs, the tail is not used as a support, and the claws are long, curved, and pointed. They are natives of New Guinea. The " Rock MARSUPIALIA. 561 Kangaroos " form the genus Fetrogale, and inhabit the moun- tainous regions of North-western Australia. The Kangaroo-rats (Hypsiprymnus) differ from the true Kan- garoos chiefly in their smaller size, and in the presence of well- developed upper canines (fig. 239, B), and in having scaly tails. They are diminutive nocturnal animals, and they live mostly upon roots. c. Carpophaga. — Intermediate between the Kangaroos and the typical members of the present section (the Phalangers) is the Fig. 239. — A, Dentition of a carnivorous Marsupial (Thylacinus) , showing the long and pointed canines and the trenchant molars and praemolars. B, Dentition of a herbivorous Marsupial (Hypsiprymnus), showing the flat-crowned molars. (After Owen.) c Canine teeth ; it Incisors. Phascolarctos — the " native sloth " or " bear " of the Australian colonists and the "koala" of the natives (fig. 238). This curi- ous animal is about two feet in length, having a stout body, covered with a dense bluish-grey fur. The tail is wanting ; and the feet are furnished with strong curved claws, which enable the animal to pass the greater part of its existence in trees. In this it is greatly assisted by the fact that all the feet are pre- hensile, the hallux being opposable, and the digits of the fore- limb divided into two sets, the thumb and index-finger being 2 N 562 MANUAL OF ZOOLOGY. opposable to the other fingers. The koala is a slow animal which feeds on the foliage of the trees in which it spends its existence. The typical group of the carpophagous Marsupials is that of the Phalangistidce. or Phalangers, so called because the second and third digits of the hind-feet are joined together almost to their extremities. The family includes a number of small Marsupials, fitted for an arboreal existence, to which end the hallux is opposable and nail-less, whilst the four remaining toes of the hind-feet have long curved claws. The tail, too, is generally very long, and its tip is usually prehensile. The Phalangers are all small nocturnal animals which live upon fruits and other vegetable food. The best known of them is the Australian Opossum (Phalangista vulpina), which must not be confounded with the true or American Opossums, which belong to another section of the Marsupialia. The Phalangers, namely, are distinguished from the Opossums properly so called, amongst other characters, by their dentition, the canine teeth being always very small and functionally useless in the lower jaw, and sometimes in the upper jaw as well. The Pha- langista vtdpina is nocturnal and arboreal in its habits, and its flesh is esteemed a great delicacy by the native Australians, with whom opossum-hunting is a favourite pursuit. The flying Phalangers or Petauri are closely allied to the true Phalangers, but differ in not having a prehensile tail, and in having a fold of skin extending on each side between the sides of the body and the fore and hind limbs. By the help of these lateral membranes the Petauri can take extensive leaps from tree to tree; but though called " flying" Phalangers, they have no power of flight properly so called. ' They are beautiful little animals, nocturnal in their habits, and having the body clothed with a soft and delicate fur. d. Entomophaga. — In this section the jaws are always furnished with canine teeth, but these are not of very large size, and the animals composing the section are therefore not highly predacious, but " prey, for the most part, on the smaller and weaker classes of invertebrate animals." In this section are the Bandicoots (Peramdid] incisor teeth, ( -), small canines, and 7 — -^ molars. Several species of Tapir are known, of which the most fami- liar is the American Tapir (T. Americanus), which inhabits the vast forests of South America. It is a large animal, some- thing like a pig in shape, but brownish black in colour, and having a mane. It is nocturnal in its habits, and is strictly phytophagous. The proboscis is employed in conveying the 584 MANUAL OF ZOOLOGY. food to the mouth, and the nostrils are placed at its extremity. It attains altogether a total length of from five to six feet. Another species, with longer hair (T. villosus], inhabits the Andes, and a still larger species (T. Malay anus) is found in Sumatra and Malacca. In this last, there is no mane, and the general colour is black ; but the back, rump, and sides of the belly are white. Fam. 3. Palceotkeridtf. — This family includes certain ex- tinct Ungulates from the Eocene and Miocene Tertiary. They are characterised by the possession of three toes to all the feet, by having canines, and by the fact that the lower molars have a doubly crescentic form. The canines are longer than the other teeth, and the dental formula is — . ._./OT W 3—3 i— i 4—4 3—3 The chief, if not the only, genus in this family is Palaotherium itself. Several species of this genus are known, varying in size Fig. 251. — Outline of Paleeotherium magnum, restored after Cuvier. Upper Eocene. from a sheep up to a horse. From the size and form of the nasal bones it is deduced, with great probability, that the Palaeo- there possessed a short movable proboscis or trunk (fig. 251). All the known species of Palaotherium are Eocene or Miocene, and the genus attained its maximum in the former period. Fam. 4. Solidungula or Equida. — This family comprises the Horses, Asses, and Zebras, characterised by the fact that the feet have only a single perfect toe each, enclosed in a single UNGULATA. 585 broad hoof, without supplementary hoofs (fig. 249, A).* There is a discontinuous series of teeth in each jaw ; and in the males, canines are present, but these are wanting in the females. The dental formula is — Q 3—3 i — i 3—3 3—3 The skin is covered with hair, and the neck is furnished with a mane. The family Equidce is divided by Dr Gray into two sections or genera : Equus, comprising the Horse ; and Asinus, com- prising the Asses and . Zebras. Many authorities, however, place all the existing forms under the single genus Equus. The genus Equus is distinguished by the fact that the animal is not banded, and has no dorsal line ; both the fore and hind legs have warts, and the tail is hairy throughout. The genus appears to contain no more than one well-marked species, as far as living forms are concerned — namely, the Equus caballus. From this single species appear to have descended all the innumerable varieties of horses which are employed by man. The native country of the horse appears to have been Central Asia, but all the known wild individuals of the present day appear to be descendants of domestic breeds. The genus Asinus is characterised by the fact that there is always a distinct dorsal line, and the body is more or less banded ; the fore-legs alone have warts, and the tail has a tuft of long hairs at its extremity. The Ass is probably a native of Asia (where the wild Ass is at present a native), and there appears to be little doubt but that the common Ass is merely the domesticated form of the wild Ass (Equus onager). An- other well-known species is the mule-like " Djiggetai" (Asinus hemionus) of Central Asia. The striped members of this sec- tion are known as Zebras and Quaggas, and are natives of the southern parts of Africa. SECTION B. ARTIODACTYLA. — In this section of the Ungu- lates the number of the toes is even — either two or four — and the third toe in each foot forms a symmetrical pair with the fourth (fig. 249, B, C). The dorso-lumbar vertebrae are nine- teen in number, and there is no third trochanter on the femur. If true horns are present, these are always in pairs, and are supported by bony horn-cores. The antlers of the Deer are also paired, but they are not to be regarded as true horns. The stomach is always more or less complex, or is divided into * In the extinct Hipparion there are two rudimentary lateral toes ; and in the still more ancient Anchitherium these toes touch the ground. 586 MANUAL OF ZOOLOGY. separate compartments, and the caecum is comparatively small and simple. The section Artiodactyla comprises the Hippopotamus, the Pigs, and the whole group of the Ruminants, including Oxen, Sheep, Goats, Antelopes, Camels, Llamas, Giraffes, Deer, &c. Besides these there is an extensive series of fossil forms com- mencing in the Eocene or Lower Tertiary period, and in many respects filling up the gaps between the living forms. OMNIVORA. i. Hippopotamidcz. — This group contains only the single genus Hippopotamus, characterised by the massive, heavy body, the short blunt muzzle, the large head, and the presence of teeth of three kinds in both jaws. The incisors are , the 2 2 canines extremely large, , and the molars, T- — ?. or - i— i 7—7 6—6, with crowns adapted for grinding vegetable substances. The upper canines are short, but the lower canines are in the form of enormous tusks, with a chisel-shaped edge. The feet are massive, and are terminated by four hoofed toes each. The eyes and ears are small, and the skin is extremely thick, and is furnished with few hairs. The tail is very short. Several extinct species of Hippopotamus are known, but there is only one familiar living form, the Hippopotamus amphibius or River-horse, and this is confined to the African continent. It is an enormously bulky and unwieldy animal, reaching a length of eleven or twelve feet. It is nocturnal in its habits, living upon grass and small shrubs, and it swims and dives with great facility. It is found in tolerable abundance in the rivers of Abyssinia, and occurs plentifully in South Africa. A much smaller form (the so-called Hippopotamus or Chce- ropsis Liberiensis) occurs on the west coast of Africa, but it is exceedingly rare, and comparatively little is known about it. It possesses, however, only two lower incisors instead of four. 2. Suida. — The group of the Suida, comprising the Pigs, Hogs, and Peccaries, is very closely allied to the preceding ; but the feet have only two functional toes, the other two toes being much shorter, and hardly touching the ground. All the three kinds of teeth are present, but they vary a good deal. The canines always are very large, and in the males they usu- ally constitute formidable tusks projecting from the sides of the mouth. The incisors are variable, but the lower ones are UNGULATA. 587 always inclined forwards. The molars vary from three to seven on each side of the mouth (- — - or -), The stom- 3 — 3 7 — 7 ach is mostly slightly divided, and is not nearly so complex as in the Ruminants. The snout is truncated and cylindrical, fitted for turning up the ground, and is capable of consider- able movement. The skin is more or less abundantly covered with hair, and the tail is very short, or represented only by a tubercle. Of the true Swine, the best known and most important is the Wild Boar (Stts scrofa), from which it is probable that most of our domestic varieties of swine have sprung. The Wild Boar formerly inhabited this country, and is still abundant in many of the forests of Europe. It is often hynted, and the size and sharpness of its canines render it a tolerably formidable adver- sary, as is also its congener, the Indian Hog (Sits Indicus}. Another curious form, closely related to the Wild Boar, is the Babyroussa (Sus Babyrusscf), which inhabits the Malayan Peninsula, and some of the islands of the Indian Archipelago. It is remarkable for the great size and backward curvature of the upper canines. The upper canines pierce the upper lip in the males, and their alveoli are directed upwards. The legs are very long and slender ; hence the name " Hog-deer " some- times applied to it. The African Wart-hogs, forming the genus Phawch&rus, are distinguished by having a fleshy wart under each eye. They inhabit Abyssinia, the Guinea coast, and other parts of Africa. The American Peccaries (Dicotyles] represent the Swine of the Old World. They are singular for having only three toes on the hind-feet, the outer of the two supplemental hoofs being wanting. The canines are not exserted, there is no tail, and there is a glandular pouch on the loins secreting a fetid fluid. They are exclusively confined to America, and the commonest species is the Collared Peccary (Dicotyles torquatus}. They are not at all unlike small pigs either in their appearance or in their habits, and they are gregarious, generally occurring in small flocks. Forming a kind of transition between the Swine and the true Ruminants, is the extinct group of the Anoplotheridcz, from the Lower Tertiary Rocks. The Anoplotheria were slender in form, with long tails, and feet terminated by two hoofed toes each, sometimes with small accessory hoofs. The dentition consisted of six incisors in each jaw, small canines not larger than the incisors, and seven molars on each side, there being no interval or diastema between the molars and the canines. 588 MANUAL OF ZOOLOGY. RUMINANTIA. The last section of the Artiodactyle Ungulates is the great and natural group of the Ruminantia, or Ruminant animals. This section comprises the Oxen, Sheep, Antelopes, Giraffes, Deer, Camels, &c., and is distinguished by the following char- acters : — The foot is what is called " cloven," consisting of a symmetri- cal pair of toes encased in hoofs, and looking as if produced by the splitting into two equal parts of a single hoof. In addi- tion to these functional toes, there are mostly two smaller supplementary hoofs, placed at the back of the foot. The metacarpal bones of the two functional toes of the fore-limb, and the metatarsal bones of the same toes of the hind-limb, coalesce to form a single bone, known as the " canon-bone." The stomach is complex, and is divided into several compart- ments, this being in accordance with their mode of eating. They all, namely, ruminate or " chew the cud " — that is to say, they first swallow their food in an unmasticated or partially- masticated condition, and then bring it up again, after a longer or shorter time, in order to chew it thoroughly. This process of rumination is so characteristic of this group, that it will be necessary to describe the structure of the stomach, as showing the mechanism by which this singular process is effected. The stomach (fig. 252) is divided into four compartments, which are usually so distinct from one another that they have generally been spoken of as so many separate stomachs. The gullet opens at a point situated between the first and second of these cavities or "stomachs." Of these the largest lies on the left side, and is called the "rumen " or "paunch" (fig. 252, r). This is a cavity of very large capacity, having its interior furnished with numerous hard papillae or warts. It is the chamber into which the food is first received when it is swallowed, and here it is moistened and allowed to soak for some time. The second stomach, placed to the right of the paunch, is much smaller, and is known as the " reticulum " or " honeycomb-bag " (h). Its inner surface is reticulated, or is divided by ridges into a number of hexagonal or .many-sided cells, somewhat resem- bling the cells of a honeycomb. The reticulum is small and globular, and it receives the food after it has lain a sufficient time in the paunch. The function of the reticulum is to com- press the partially-masticated food into little balls or pellets, which are then returned to the mouth by a reversed action of UNGULATA. 589 the muscles of the oesophagus. After having been thoroughly chewed and prepared for digestion, the food is swallowed for the second time. On this occasion, however, the triturated food passes on into the third cavity (/), which is variously known as the " psalterium," " omasum," or (Scottice) the " many- plies." The vernacular and the first of these technical names both refer to the fact that the inner lining of this cavity is thrown into a number of longitudinal folds, which are so close as to resemble the leaves of a book. The psalterium opens by a wide aperture into the fourth and last cavity, the " abo- masum " (a), both appearing to be divisions of the pyloric portion of the stomach. The mucous membrane of the abo- masum is thrown into a few longitudinal folds, and it secretes the true acid gastric juice. It terminates, of course, in the Fig. 252. — Stomach of a Sheep, o Gullet ; r Rumen or Paunch ; h Honeycomb- bag or Reticulwn ', p Manyplies or Psalterium ,' a Fourth Stomach or Abomasum. commencement of the small intestine — i.e., the duodenum. The intestinal canal of Ruminants, as in most animals which live exclusively upon a vegetable diet, is of great relative length. The dentition of the Ruminants presents peculiarities almost as great and as distinctive as those to be derived from the digestive system. In the typical Ruminants (e.g., Oxen, Sheep, Antelopes) there are no incisor teeth in the upper jaw, their place being taken by a callous pad of hardened gum, against which the lower incisors impinge (fig. 253). There are also no upper canine teeth, and the only teeth in the upper jaw are six molars on each side. In the front of the lower jaw is a continuous and uninterrupted series of eight teeth, of which the central six are incisors, and the two outer ones are 590 MANUAL OF ZOOLOGY. regarded by Owen as being canines. Upon this view, canine teeth are present in the lower jaw of the typical Ruminants, and they are only remarkable for being placed in the same series as the incisors, which they altogether resemble in shape, size, and direction. Behind this continuous series of eight teeth in the lower jaw, there is a vacant space, which is fol- lowed behind by six molars on each side. The prsemolars and molars have their grinding-surfaces marked with two double crescents, the convexities of which are turned inwards in the upper, and outwards in the lower teeth. Fig. 253. — Skull of a hornless Sheep (after Owen), i Incisors ; c Canines ; m Molars and Praemolars. The dental formula, then, for a typical Ruminant animal, is — . o — o o — o i. • — ' f. — I — I ; pm 3—3 m 3—3 - 32. 3—3 ' 3—3 ' 3—3 The departures from this typical formula occur in the Camelidce, the M'oschidcz, and in some of the Deer. Most of the Deer con- form in their dentition to the above formula, but a few forms ( o— o> 4—4 3—3 The fore-feet are tetradactylous, the hind-feet tridactylous, and all the toes have rounded hoof-like nails, with the ex- ception of the inner toes of the hind-feet, which have an obliquely- curved nail. There are no clavicles. The nose and ears are short, and the tail is represented by a mere tubercle. The placenta is deciduate and zonary, whereas in the Ungulates it is non-deciduate. Several species of Hyrax are known, but they resemble one another in all essential particulars. They are all gregarious little animals, living in holes of the rocks, and capable of domestication. One species is said to be arboreal in its 6oo MANUAL OF ZOOLOGY. habits. The " coney " of Scripture is believed to be the Hyrax Syriacus, which occurs in the rocky parts of Syria and Pales- tine. Another species — the Hyrax Capensis, or " Klipdas " — occurs commonly in South Africa, and is known by the colo- nists as the " badger." ORDER VIII. PROBOSCIDEA. — The eighth order of Mammals is that of the Proboscidea, comprising no other living animals except the Elephants, but including also the extinct Mastodon and Deinotherium. The order is characterised by the total absence of canine Fig. 256. — Skull of the Indian Elephant (Elephas Indictis], i Tusk-like upper in- cisors ; m Lower jaw, with molars, but without incisors ; n Nostrils, placed at the end of the proboscis. (After Owen.) teeth ; the molar teeth are few in number, large, and trans- versely ridged or tuberculate ; incisors are always present, and grow from persistent pulps, constituting long tusks (fig. 256). In living Elephants there are two of these tusk-like incisors in the upper jaw, and the lower jaw is without incisor teeth. In the Deinotherium this is reversed, there being two tusk-like lower incisors and no upper incisors. In the Mastodons, the incisors are usually developed in the upper jaw, and form tusks, as in the Elephants, but sometimes there are both upper and lower PROBOSCIDEA. 6OI incisors, and both are tusk-like. The nose is prolonged into a cylindrical trunk, movable in every direction, highly sensitive, and terminating in a finger-like prehensile lobe (fig. 256). The nostrils are placed at the extremity of the proboscis. The feet are furnished with five toes each, but these are only partially indicated externally by the divisions of the hoof. The feet are furnished with a thick pad of integument, forming the palms of the hand and the soles of the feet. There are no clavicles. The testes are abdominal throughout life. There are two teats, and these are placed upon the chest. The placenta is de- ciduate and zonary. The recent Elephants are exclusively confined to the tropical regions of the Old World, in the forests of which they live in herds. Only two living species are known — the Asiatic Elephant (Elephas Indtcus) and the African Elephant (£. Africanus}. There can be no doubt, however, but that the Mammoth (Elephas primigenius) existed in Europe within the human period. In both the living Elephants the " tusks " are formed by an enormous development of the two upper incisors. The milk- tusks are shed early, and never attain any very great size. The permanent tusks grow throughout the life of the animal, and often reach six or seven feet in length, and from fifty to seventy pounds in weight. In the Indian Elephant, and its variety the Ceylon Elephant, the males alone have well-developed tusks, but both sexes have tusks in the African species, those of the males being the largest. The lower incisors are absent, and there are no other teeth in the jaws except the large molars, which are one or two in number on each side of each jaw. The molar teeth are of very large size, and are composed of a number of transverse plates of enamel united together by dentine. In the Indian Elephant the transverse ridges of enamel are narrow and undulating, whilst in the African Elephant they enclose lozenge-shaped intervals. The Indian Elephant is the only species which is now caught and domes- ticated, and as it will not breed in captivity, the demand for it is supplied entirely by the capture of adult wild individuals, which are taken chiefly by the assistance of those which have been already tamed. The Indian Elephant is distinguished by its concave forehead, its small ears, and the characters of the. molars. Its skull is pyramidal, and it has five hoofs on the fore-feet, and only four on the hind-feet. Its colour is gene- rally pale brown. (The so-called "White Elephants" are merely albinos.) The African Elephant, on the other hand, has a strongly convex forehead and great flapping ears. Its 6O2 MANUAL OF ZOOLOGY. colour is darker, its skull is rounded, and it has four hoofs on the fore-feet, and only three on the hind-feet. The African Elephant is chiefly hunted for the sake of its ivory, and there is too much reason to believe that the pursuit will ultimately end in the destruction of these fine animals. A great deal, however, of the ivory of commerce comes from Siberia, and is really derived from the tusks of the now extinct Mammoth, which formerly inhabited the north of Asia in great numbers. The Elephants are all phytophagous, living almost entirely on the foliage of shrubs and trees, which they strip off by means of the prehensile trunk. As the tusks prevent the animal from drinking in the ordinary manner, the water is sucked up by the trunk, which is then inserted into the mouth, into which it empties its contents. Many species of fossil Elephants are known, but the most familiar of them is the Mammoth (Elephas primigenius)* This Fig. 257. — Third milk molar of the left side of the upper jaw of Mastodon A rver- nensis, showing the grinding surface. Pliocene. (After Lyell.) enormous animal is now wholly extinct, but it formerly abounded in the northern parts of Asia and over the whole of Europe. It occurred also in Britain, and unquestionably existed in the earlier portion of the human period, its remains having been found in a great number of instances in connec- tion with human implements. From its great abundance in Siberia, it might have been safely inferred that the Mammoth was able to endure a much colder climate than either of the living species. This inference, however, has been rendered a certainty by the discovery of the body of more than one Mammoth embedded in the frozen soil of Siberia. These specimens had been so perfectly preserved that even micro- CARNIVORA. 60. scopical sections of some of the tissues could be made ; and in one case even the eyes were preserved. From these speci- mens we know that the body of the Mammoth was covered with long woolly hair. Closely allied to the true Elephants are the Mastodons, characterised -by the fact that the crowns of the molar teeth have nipple-shaped tubercles placed in pairs (fig. 257). Generally speaking, the two upper incisors formed long curved tusks, as in the Elephants, but in some cases there were two lower incisors as well. The various species of Mastodon all belong to the later Tertiary and Post-tertiary periods. The last of the Proboscidea is a remarkable extinct animal, the Deinotherium. This extraordinary animal has hitherto only been found in Miocene de- posits, and little is known of it except its enormous skull. Mo- lars and prsemolars were present in each jaw, and the upper jaw was destitute of canines and in- cisors. In the lower jaw were two very large tusk-like incisors, which were riot directed forwards as in the true Elephants, but were bent abruptly downwards (fig. 2 5 8). The animal must have attained an enormous size, and it is probable that the curved tusks were used either in digging up roots or in mooring the animal to the banks of rivers, for it was probably aquatic or semi-aquatic in its habits. It is placed by De Blainville in the Sirenia, being regarded as a Dugong with tusk-like lower incisors. Fig. 258. — Skull of Deinotherium gigauteum. CHAPTER LXXIX. CARNIVORA. ORDER IX. CARNIVORA. — The ninth order of Mammals is that of the Carnivora, comprising the Fern, or Beasts of Prey, along with the old order of the Pinnipedia, or Seals and Wal- ruses, these latter being now universally regarded as merely a group of the Carnivora modified to lead an aquatic life. 604 MANUAL OF ZOOLOGY. The Carnivora are distinguished by always possessing two sets of teeth, which are simply covered by enamel, and are always of three kinds — incisors, canines, and molars — differ- ing from one another in shape and size. The incisors are generally 3~3 (except in some seals) ; the canines are always O \) — , and are invariably much larger and longer than the in- cisors. The praemolars and molars are mostly furnished with cutting or trenchant edges ; but they graduate from a cutting to a tuberculate form, as the diet is strictly carnivorous, or becomes more or less miscellaneous. In the typical Carnivores, (such as the Lion and Tiger), the last tooth but one in the Fig. 259. — Feet of Carnivora (after Owen). A, Plantigrada, Foot of Bear ; B, Pinnigrada, Hind-feet of Seal ; C, Digitigrada, Foot of Lion. upper jaw and the last tooth in the lower jaw are known as the " carnassial " teeth, having a sharp cutting edge adapted for dividing flesh, and generally a more or less developed tuberculated heel or process. A varying number, however, of the molars and prgemolars may be " tuberculate," their crowns being adapted for bruising rather than cutting. As a general rule, the shorter the jaw, and the fewer the prsemolars and molars, the more carnivorous is the animal. The jaws are so articulated as to admit of vertical but not of horizontal move- ments ; the zygomatic arches are greatly developed to give room for the powerful muscles of the jaws ; and the orbits are not separated from the temporal fossae. The intestine is com- paratively short. CARNIVORA. 605 In all the Carnivora the clavicles are either altogether want- ing, or are quite rudimentary. The toes are provided with sharp curved claws. The teats are abdominal ; and the pla- centa is deciduate and zonular. The order Carnivora is divided into three very natural sec- tions : — Section I. Pinnigrada or Pinnipedia. — This section com- prises the Seals and Walruses, in which the fore and hind limbs are short, and are expanded into broad webbed swim- ming-paddles (fig. 259, B). The hind-feet are placed very far back, nearly in a line with the axis of the body, and they are more or less tied down to the tail by the integuments. Section II. Plantigrada. — This section comprises the Bears and their allies, in which the whole, or nearly the whole, of the foot is applied to the ground, so that the animal walks upon the soles of the feet (fig. 259, A). Section III. Digitigrada. — This section comprises the Lions, Tigers, Cats, Dogs, &c., in which the heel of the foot is raised entirely off the ground, and the animal walks upon the tips of the toes (fig. 259, C). SECTION I. PINNIGRADA or PINNIPEDIA. — This section of the Carnivora comprises the amphibious Seals and Walruses, which differ from the typical Carnivores merely in points con- nected with their semi-aquatic mode of life. The body in these forms is elongated and somewhat fish - like in shape, covered with a short dense fur or harsh hairs, and terminated behind by a short conical tail. All the four limbs are present, but are very short, and the five toes of each foot are united together by the skin, so that the feet form powerful swimming- paddles. The hind-feet are of large size, and are placed far back, their axis nearly coinciding with that of the body (figs. 259, 260). From this circumstance, and from the fact that the integument often extends between the hind-legs and the sides of the short tail, the hinder end of the body forms an admir- able swimming apparatus, similar in its action to the horizontal tail-fin of the Cetacea and Sirenia. The tips of the toes are furnished with strong claws, but their powers of terrestrial loco- motion are very limited. On land, in fact, the Seals can only drag themselves along laboriously, chiefly by the contractions of the abdominal muscles. The ears are of small size, and are mostly only indicated by small apertures, which the animal has the power of closing when under water. The bones are light and spongy, and beneath the skin is a layer of fat or blubber. The dentition varies, but teeth of three kinds are always present, in the young animal at any rate. The canines 606 MANUAL OF ZOOLOGY. are always long and pointed, and the molars are generally furnished with sharp cutting edges. The section Pinnigrada includes the two families of the Seals (Phocida) and Walruses (Trichecidee). The Seals are distinguished by having incisor teeth in both jaws, and by the fact that the canine teeth are not disproportionately developed. They form a very numerous family, of which species are found in almost every sea out of the limits of the tropics. They abound, however, especially in the seas of the Arctic and Antarctic regions. They live for the most part upon fish, and when awake, spend the greater part of their time in the water, only coming on land to bask and sleep in the sun and to suckle their young. They appear to be universally polygamous. The body is covered with a short fur, interspersed with long bristly Fig. 260.— The Greenland Seal (Phoca Groenlaitdica), hairs ; and the lips are furnished with long whiskers, which act as organs of touch. The Seals are very largely captured for the sake of their blubber. The only common British Seal is the Phoca vitulina, which occurs not uncommonly on the northern shores of Scotland. It is yellowish-grey in colour, and measures from three to five feet in length. Other Seals attain a much greater length — the Great Seal measuring from eight to, ten feet, and the Bottle- nosed Seal reaching a length of from twenty to twenty-five feet. The only Seals which possess external ears constitute the genus Otaria, and are almost exclusively confined to the seas of the southern hemisphere. The second family of the Pinnigrade Carnivores is that of the Trichedda -, comprising only the Walrus or Morse (Triche- CARNIVORA. 607 cus rosmarus}. The chief peculiarity by which the Walrus is distinguished from the true Seals is found in the dentition. According to Owen, there are six incisors in the upper jaw and four in the lower ; but these are only present in the young animal, and soon disappear, with the exception of the outer- most pair of upper incisors. The upper canines are enor- mously developed, growing from persistent pulps, and consti- tuting two large pointed tusks, which attain a length of over fifteen inches (fig. 261). The direction of the tusks is down- wards and slightly outwards, and they project considerably below the chin. The adult animal has usually three simple Fig. 261. — Skull of the Walrus (Trichecus rosmarus, after Owen). i Tusk-like upper canines. molars with flat crowns behind the tusks in the upper jaw ; and four similar teeth on each side of the lower jaw ; but the first of these has been regarded as a lower canine. The upper lip has many pellucid bristles as large as a straw in thickness. In the adult the incisors are obsolete, except the lateral pair in the upper jaw. Unlike the Seals, the Walrus is not Poly- gamous. Except as regards its dentition, the Walrus agrees in all essential respects with the Seals. It is a large and heavy animal, attaining a length of from ten to fifteen feet or up- wards. The body is covered with short brownish or yellowish 608 MANUAL OF ZOOLOGY. hair, and the face bears many long stiff bristles. There are no external ears. The chief use of the tusk-like canines appears to be that of assisting the unwieldy animal to get out of the water upon the ice ; but they doubtless serve as weapons of offence and defence as well. The Walrus is hunted by whalers, both for its blubber, which yields an excellent oil, and for the ivory of the tusks. It is found, living in herds, in the Arctic seas, being especially abundant at Spitzbergen and Nova Zembla. SECTION II. PLANTIGRADA. — The Carnivorous animals be- longing to this section apply the whole or the greater part of the sole of the foot to the ground (fig. 259, A); and the por- tion of the sole so employed is destitute of hairs in most instances (the sole is hairy in the Polar Bear). From the structure of the foot, the Plantigrada have great power of rear- ing themselves up on the hind-feet. They approach the In- sectivora in their comparatively slow movements and their nocturnal habits, and in possessing no caecum. They mostly hybernate, and their feet are always pentadactylous. The typical family of the Plantigrade Carnivora is that of the Ursida or Bears, in which the entire sole of the foot is applied to the ground in walking. The Ursidce are much less purely carnivorous than the majority of the order, and in accordance with their omnivorous habits, the teeth do not exhibit the typical carnivorous characters. The incisors and canines have the ordinary carnivorous form, but the " carnassial " or sectorial molar has a tuberculate crown instead of a sharp cutting edge. The dental formula is — .3—3 T— T 4—4 2—2 '3=^ T-i' ^4-4' -3=3 -42- The claws are formed for digging, large, strong, and curved, but are not retractile. The tongue is smooth ; the ears small, erect, and rounded ; the tail short ; the nose forms a movable truncated snout ; and the pupil is circular. As shown by their smooth tongues and tuberculate molars, the Bears are not peculiarly or strictly carnivorous. They eat flesh when they can obtain it, but a great part of their food is of a vegetable nature. The Bears are very generally distributed over the globe, Australia alone having no representative of the family. The common Brown Bear (Ursus Arctos) was at one time an inhabitant of Britain, and also existed over the whole of Europe. At the present day the Brown Bear is only found in the great CARNIVORA. 609 forests of the north of Europe and in Asia. It feeds on roots, fruits, honey, insects, and, when it can obtain them, upon other Mammals. It attains a great age, and hybernates during the winter months. Very nearly allied to the Brown Bear is the Black Bear of America ( Ursus Americanus). Both are of some commercial value, being hunted for the sake of their skins, fat, and tongues. A much larger American species is the Grizzly bear (Ursus fer ox), found in many parts of the Ameri- can continent. It is about twice as large as the ordinary Bear, but it is said to subsist to a great extent upon vegetable food, such as acorns. The most remarkable, however, of the bears is the great White Bear ( Thalassarctos maritimus), which is exclusively a native of the Arctic regions. It is a very large and powerful animal, the fur of which is quite white. The paws are very long, and the soles of the feet are covered with coarse hair, giving the animal a firm foothold upon the ice. The Polar Bear differs from the other Ursidce in being exclu- sively carnivorous, since vegetable food would be wholly unattainable. It is as much at home in the water as on land, and lives chiefly upon seals and fish, and upon the carcases of Cetaceans. Other well-known Bears are the Syrian Bear ( Ursus Syria- cus) of Mount Lebanon, the Sloth Bear (Prochilus labiatus] of India, and the Malayan Bear (Helarctos Malay anus) of Borneo and Sumatra. It is a singular fact that the bones of a bear — Ursus spelceus or Cave Bear — have been found, in Britain and in many parts of Europe, along with the bones of other Carnivora, such as the Cave Lion and Cave Hysena, The Ursus spelaus was a larger and more powerful animal than even the Polar Bear, and there can be no doubt that it existed in the earlier portion of the human period. Nearly allied to the true Bears are several small animals, of which the Raco'ons (Procyon), the Coati (Nasua\ the Wah (Ailurus), and the Kinkajou (Ccrcoleptes) are the best known. The Racoons are natives of tropical and northern America, and have a decided external resemblance to the Bears. They have tolerably long tails, however, and sharp muzzles. The commonest species is the Procyon lotor of North America, which derives its specific name from its habit of washing its food before eating it. The place of the Racoon is taken in India by the Wah (Ailurus fulgens), which inhabits northern Hindo- stan. It is about the size of a large domestic cat, and is very prettily coloured, being chestnut brown above, and black in- feriorly, with a white face and ears. The Kinkajous (Cerco- 2 Q 6lO MANUAL OF ZOOLOGY. leptes] are inhabitants of South America, and, as is the case with so many of the animals of this continent, they are adapted for an arboreal life, to which end their tails are prehensile. The Coatis (Nasua) are very closely allied to the Racoons, and are exclusively confined to the American continent. All the above-mentioned little animals (with the exception of the Wah) present a singularly close resemblance to the Lemurs of the Old World, and appear to be their representatives in the western hemisphere. In the genus Paradoxurus of the Indian Archipelago, the tail is capable of being rolled up, but its ex- tremity is not prehensile. The " Benturongs " (Arctictis] have a long, hairy, and prehensile tail. They are nocturnal animals which are found in India, and are in some respects inter- mediate between the Racoons and the Civets. The only remaining family of the Plantigrada is that of the Melidcz or Badgers, characterised by their elongated bodies and short legs, and by the fact that the carnassial tooth has a partly cutting edge, and is not wholly tuberculate as in the Bears. The common Badger (Meles taxus), which may be regarded as the type of this group, occurs in Britain, and is one of the most inoffensive of animals. It is nocturnal in its habits, and is a very miscellaneous feeder, not refusing anything edible which may come in its way, though living mainly on roots and fruits. The Badger burrows with great ease, and can bite very severely. The European Badger is represented in the United States and Canada by the " Siffleur " (Meles Labradoricus), and in the hilly parts of India by the Indian Badger (M. collaris). The Glutton (Gulo lusais}, often called the Wolverine, is of common occurrence in the northern parts of Europe, Asia, and America. It is from two to three feet in length, and though doubtless a tolerably voracious animal, it is certainly not so much so as to deserve the name of Glutton. The Grison (Gulo vittatus] is a closely-allied species, which is found in South America. The Ratels or Honey-badgers (Mellivora) are much like the common Badger in their habits and appear- ance, but they get their name from their fondness for honey. They are natives of southern and eastern Africa. SECTION III. DIGITIGRADA. — In this section of the Carnivora the heel is raised above the ground, with the whole or the greater part of the metacarpus and metatarsus, so that the animals walk more or less completely on the tips of the toes (fig. 259, C). No absolute line, however, of demarcation can be drawn between the Plantigrade and Digitigrade sections of the Carnivora, since many forms (e.g., Mustdidcz and Viverrida) CARNIVORA. 6 I I exhibit transitional characters, and it has even been proposed to place these in a separate section, under the name of Semi- plantigrada. The first family of the Digitigrada is that of the Mustdida or Weasels, including a number of small Carnivores, with short legs, elongated worm-like bodies, and a peculiar gliding mode of progression (hence the name of Vermiformes, sometimes applied to the group). Amongst the best known of the Mus~ telidce. are the common Weasel (Mustela vulgaris], the Pole-cat ( Mustela putorius), and the Ferret (Mustela furo), the last being supposed to be only an albino variety of one of the Pole-cats. It is really an African species, but has been long domesticated in Europe. Many of the Mustelidce are of great commer- cial importance, furnishing beautiful and highly-valued furs. Amongst these are the Ermine (Mustela erminea), and the Sable (Mustela zibellind). It is asserted, however, that most of the Sable of commerce is derived from the Black Mink (Puto- rius nigrescent) and the Pine Marten (Mustela Americana) of the United States and Canada. Almost all the Weasels have a very disagreeable odour, pro- duced by the secretion of greatly-developed and modified sebaceous glands, placed in the neighbourhood of the anus, and known as the anal glands. In this respect, however, the nearly-allied genus Mephitis, comprising the American Skunk, \^> facile princeps. The Skunk is a pretty little animal, with a long bushy tail, and when unmolested it is perfectly harmless. If pursued or irritated, however, it has the power of ejecting the secretion of the anal glands to a greater or less distance with considerable force. The odour of this secretion is so powerful and persistent that no amount of washing will remove it from a garment, and its characters are said to be of the most intensely disagreeable description. Also belonging to the family of the MustelidcE, and very nearly allied to the Weasels, are the Otters (Lutra), distin- guished by the possession of webbed feet adapted for swim- ming. The body is long, the legs short, and the tail long, stout, and horizontally flattened. The common Otter (Lutra vulgaris) is a native of Britain, frequenting the banks of streams and lakes. It lives upon fish, and is highly destructive to Salmon. A closely-allied form is the American Otter (Lutra Canadensis). In the Sea Otters (Enhydra) the tail is very short. They are found on both sides of the North Pacific, and yield a very valuable fur. The second family of the Semi-plantigrade Carnivores is that of the Viverridcz, the Civets and Genettes. They are all of 6l2 MANUAL OF ZOOLOGY. moderate size, with sharp muzzles and long tails, and more or less striped, or banded, or spotted. The carnassial molar is trenchant ; the canines are long, sharp, and pointed ; and the tongue is roughened by numerous prickly papillae. The claws are semi-retractile, and the pupils can contract, on exposure to light, till they resemble a mere line. In most of their charac- ters, therefore, the Civets are much more highly carnivorous than are any of the preceding families, and' they approach in many respects very close to the typical group of the Digitigrada (viz., the Felidce], having especially very close affinities with the Hyaenas. All the species of the family are furnished with anal glands, which secrete the peculiar fatty substance known as " civet." The true Civet-cat is the Viverra dvetta, a native of Africa. It is a small nocturnal animal, which climbs trees with facility, and feeds chiefly upon small mammals, reptiles, and birds, but also upon roots and fruits. It furnishes the greater part of the " civet " of commerce, which was formerly in great repute both as a perfume and as a medicinal agent. It is a pomade-like substance with a strong musky odour, and is secreted by a deep double pouch beneath the anus. The Genette ( Viverra genetta) is very closely related to the preceding, and is a native of Africa and southern Europe, being not uncommonly do- mesticated and kept like a cat. The anal pouch in the Ge- nette is much reduced in size, and has hardly any perceptible secretion. Another nearly-allied species is the Ichneumon (Herpestes\ which is kept as a domestic animal in Egypt, and lives upon Snakes, Lizards, the eggs of the Crocodile, and small Mammals. Forming a transition between the Viverridcz and the Fdida is the family of the Hycenidce, distinguished by the fact that, alone of all the Carnivora, both pairs of feet have only four toes each. The hind-legs are shorter than the fore-legs, so that the trunk sinks towards the hind-quarters, and the tail is short. The tongue is rough and prickly. The head is extremely broad, the muzzle rounded, and the muscles of the jaw extremely powerful and well developed. The claws are non- retractile. All the molars are trenchant except the last upper molar, which is tuberculate. The upper carnassial has a small internal tubercle, and the lower carnassial is wholly trenchant. There is a deep glandular pouch beneath the anus. • .-- There are two well-known species of Hysena, and the whole group is exclusively confined to the Old World. The best- known species is the Striped Hyaena (Hycena striatd), which is found in North Africa, Asia Minor, Arabia, and Persia. It is CARNIVORA. 6 1 3 an ill-conditioned ferocious beast, but will not attack man unless provoked. The Spotted Hyaena (H. crocuta) occurs solely in Africa, being especially abundant in Cape Colony. If the so-called Aardvvolf (Proteles) is to be placed amongst the Hyaenas, as is generally done, then the characters to be drawn from the feet are not invariable; since this singular animal has the fore-feet furnished with five toes, whilst the hind-feet are tetradactylous (as is the case in the Dogs). It is a nocturnal burrowing animal, and is found in South Africa. The singular " Hunting Dog" (Lycaon pictus], again, of South Africa, agrees with the Hysenas in being tetradactylous, but has no mane, and approaches the Dogs in its dentition and osteology. An extinct Hyaena, considerably larger than either of the living forms, formerly existed in Britain and in various parts of Europe. It is known as the Cave Hyaena (H. spelcea], its remains having been principally found in caves. The next family is that of the Canidcz, comprising the Dogs, Wolves, Foxes, and Jackals. The members of this family are characterised by having pointed muzzles, smooth tongues, and non-retractile claws. The fore-feet have five toes each, the hind-feet have only four. The molar teeth are - 7—7': sometimes —~* and of these, two or three on each side are tuberculate. The carnassial has a tolerably large heel or process. ; The true Dogs (/. 3—3 The clavicles are imperfect. The fore-legs are furnished with five toes, and are considerably shorter than the hind-legs, which have only four toes. The two orbits communicate by an aperture in the septum. Generally there is a short erect tail. The common Hare (Lepus timidus) is dispersed over the whole of Europe, but is not met with in Sweden and Norway, its place there being taken by the Mountain-hare (white in winter), which occurs commonly in Scotland. As a rule, the Hares occur in temperate regions, but some are found in Africa, and one species (Lepus glarialis) is a native of the Arctic regions, whilst the common American Hare (L. Americanus) RODENTIA. 619 extends from Canada to Mexico. The Rabbit is also a native of temperate regions, but appears to thrive, to a more than average extent, in Australia. In the Calling Hares or Pikas (Lagomys), the legs do not differ much in size, there is no visible tail, and the clavicles are nearly complete. They are found in Russia, Siberia, and North America. Fam. 2. CavidcE. — As examples of this family maybe taken the Capybara (Hydrochcerus capybara) and the Guinea-pig (Ancemd). In this family the body is covered with hair, without spines, and the tail is rudimentary. The Capybara is the largest of living Rodents, attaining a length of three or four feet. It is a South American form, leading a semi-aquatic life, to which end the feet are incompletely webbed. It is a harmless stupid animal, and is not unlike a small pig in appear- ance. The Cavia apercea is likewise a South American animal, and is believed to be the parent stock of the Guinea-pigs so often kept as domestic pets in Europe. To the same group as the Capybara belong the Agoutis (Dasyprocta) and the Pacas (Cailogenys\ all of which have eight rootless molars in each jaw, whilst the two former have four toes to the fore-feet, and three toes on the hind-feet. The various species of Agouti are found in South America and the West Indies, whilst the Pacas are exclusively South American. In this family, also, are usually placed the Chinchillas (Chinchilla} of Chili and Peru. Fam. 3. Hystricidce. — In this family are the well-known Por- cupines, distinguished from the other Rodents by the fact that the body is covered with long spines or " quills," mixed with bristly hairs. They have four molars on each side of each jaw, and they possess imperfect clavicles. The true Porcupines (Hystrioc] have non-prehensile tails, which are mostly furnished with long hollow spines, but some- times with scales and bristles. They are found in both the Old and New World, but the American species differ in several respects from those of the eastern hemisphere. They are mostly inhabitants of hot climates, with the exception of the common Porcupine (H. cristata), which occurs in southern Europe and in the north of Africa. In the genus Atherura of Asia and the Indian Archipelago, the tail is terminated by a bundle of flat- tened horny strips. In the genus Erethizon, represented by the Canada Porcupine (E. dorsatum) of North America, the quills are short, and are half hidden in the hair. The nearly-allied genus Cercolabes is South American, and it is distinguished from the preceding by the possession of a long prehensile tail. In fact, Cercolabes, like so many of the 62O MANUAL OF ZOOLOGY. inhabitants of this wonderful continent, is adapted for an arbo- real life, instead of being confined to the ground. Fam. 4. Castorida. — The best-known example of this family is the Beaver (Castor fiber). The distinctive peculiarities of the family are the possession of distinct clavicles, the posses- sion of five toes to each foot, and the fact that the hinder feet are mostly webbed, adapting the animal to a semi-aquatic life. The Beaver is a large Rodent, attaining a length of from two and a half to three feet. Naturally it is a social animal, living in societies, and this is still the case in America ; but in northern Europe and Asia, where the animal has been much 'hunted, it leads a solitary life. When living in social commu- :nities the beavers build dams across the rivers, as well as habi- tations for themselves, by gnawing across the branches of trees or shrubs, and weaving them together, the whole being after- wards plastered with mud. In this last operation the tail, which is flattened and scaly, is employed very much as a mason uses his trowel. There is no doubt but that the Beaver shows ex- traordinary ingenuity in these and similar operations ; but there can be equally little doubt as to the greatly-exaggerated stories which have been set afloat in this connection. The Beaver is hunted chiefly for the sake of the skin, but also for the sub- stance known as castor eum. This is a fatty substance, secreted by peculiar glands, and employed as a therapeutic agent. There are two other members of the Castoridce which are likewise largely captured for the sake of their skins. One of these is the Musquash (Fiber Zibethicus\ which inhabits North America, and the other is the Coypu (Myopotamus coy pus), which inhabits burrows in the banks of rivers in Chili. In the Musquash the hind-feet are not completely webbed, and the tail is moderate in size, and covered with short hairs and small rounded scales. In the Coypu the hind-feet are webbed, but the tail is long, rounded, and furnished with scales and scat- tered hairs. Fam. 5. Muridce. — The fifth family of Rodents is that of the MuridcB) comprising the Rats, Mice, and Lemmings. In this family the tail is long, always thinly haired, sometimes naked and scaly. The lower incisors are narrow and pointed, and there are complete clavicles. The hind-feet are furnished with five toes, the fore-feet with four, together with a rudi- mentary pollex. The Rats (Mus rattus and Mus decumanus\ the common Mouse (Mus musculus\ the Field-mouse (Mus sylvaticus), and the Harvest-mouse (Musmessorius), are all well-known examples of this family, and are too familiar to require any description. RODENTIA. 621 The three first are also common in North America. Closely allied to the true Rats are the Hamsters (Cricetus, fig. 265), and the Voles (Arvicola); the latter represented by many species in both Europe and America. A less familiar example of this family. is the Lemming (Myodes lemmus). This curious little Rodent is found inhabiting the mountainous regions of Norway and Sweden. It is chiefly re- markable for migrating at certain periods, generally towards the approach of winter, in immense multitudes and in a straight line, apparently in obedience to some blind mechanical im- pulse. In these journeys the Lemmings march in parallel columns, and nothing will induce them to deviate from the straight line of march. Fam. 6. Dipodidcz. — The sixth family of the Rodents, which is sufficiently important to need notice, is that of the Dipodid i— i' 2— 2' 3—3 The six lower incisors are split into narrow strips, like the teeth of a comb. The Galeopithed live chiefly upon small birds and insects, but also partially upon fruits. They are nocturnal animals, arboreal in their habits, and they sleep head down- wards, suspended by their prehensile tails. CHAPTER LXXXI-II. QUADRUMANA. ORDER XIII. QUADRUMANA. — The thirteenth order of Mam- mals is that of the Quadrumana, comprising the Apes, Mon- keys, Baboons, Lemurs, &c., characterised by the following points : — The hallux (innermost toe of the hind-limb) is separated from the other toes, and is opposable to them, so that the hind-feet become prehensile hands. The pollex (innermost toe of the fore-limbs) may be wanting, but when present, it 630 MANUAL OF ZOOLOGY. also is usually opposable to the other digits, so that the animal becomes truly quadrumanous, or four-handed. The incisor teeth generally are - — , and the molars ^7^ with broad and tuberculate crowns. Perfect clavicles are pre- sent. The teats are two in number, and are pectoral in posi- tion, and the placenta is discoidal and deciduate. The Quadrumana are divided by Owen into three very natural groups, separated from one another by their anatomical characters and by their geographical distribution as follows : — Section A. Strepsirhina. — The members of this section are Fig. 270. — Green Monkey or Guenon (Cercocebus sabceus) — after Cuvier. characterised by the nostrils being curved or twisted, whilst the second digit of the hind-limb has a claw. This section includes the true Lemurs and a number of allied forms. It is chiefly referable to Madagascar as its geographical centre ; but it spreads westwards into Africa, and eastwards into the Indian Archipelago. Section B. Platyrhina. — This section includes those Quad- rumana in which the nostrils are placed far apart ; the thumbs of the fore-feet are either wanting, or, if present, are not oppos- able to the other digits ; and the tail is generally prehensile. QUADRUMANA. 631 The Platyrhine Monkeys are exclusively confined to South America. Section C. Catarhina. — In this section the nostrils are ob- lique, and placed close together. The thumb of the fore-limb (pollex), with one exception, is present, and is always oppos- able to the other digits. The Catarhine Monkeys are restricted entirely to the Old World, and, with the single exception of a Monkey which inhabits the rock of Gibraltar, they are exclu- sively confined to Africa and Asia. It is in the Catarhine sec- tion of the Quadrumana that we have the highest group of the Monkeys — that, namely, of the Anthropoid or Tail-less Apes. STREPSIRHINA. This section of the Quadrumana, as before said, is charac- terised by the possession of twisted or curved nostrils, placed at the end of the snout. The incisor teeth are generally much modified, and are in number ^^ as a rule ; the lower O O -5 <2 incisors are produced and slanting; the prsemolars are^- 2 2 3~ .3 or- - and the molars are tuberculate. The second disrit 2 2' of the hind-limb has a claw, and both fore and hind feet have five toes each, ail the thumbs being generably opposable. In the true Lemurs, all the digits, except the second toe of the hind-feet, are furnished with nails. This section is often called that of the Prosimm, and it in- cludes several families, of which the Aye-Ayes, Loris, and true Lemurs are the most important. In many works the Galeo- pithecus is also placed in this section. The family of the Aye- Ayes (Cheiromyda) includes only a single animal, the Cheiromys Madagascariensis. In appearance the Aye- Aye is not very unlike a large. Squirrel, having a hairy body and a long bushy tail. There are no canines, and the molars are separated by a wide interval from the incisors. The incisors are ploughshare-shaped, and grow from permanent pulps, as in the Rodents. The fore-feet have five toes, armed with strong claws, but the. pollex is scarcely opposable to the other digits. The middle-finger is about as long as the ring- finger, but only about half as thick, its last two joints being hairless. The hind-feet have also five toes, of which the hallux is opposable, and the second digit is furnished with a long claw. As far as is yet known, the Cheiromys is entirely con- fined to Madagascar. 632 MANUAL OF ZOOLOGY. In the Nycticebidcz are the Loris and the Slow Lemurs, in which there is no tail, or but a rudimentary one ; the ears are short and rounded, and the eyes are large, and are placed close together. The species of this family are all of small size, and are exclusively confined to the eastern portion of the Old World, occurring in Java, Ceylon, the southern parts of Asia, and other localities in the same geographical area. They are nocturnal in their habits, living mostly on trees, and feeding upon insects; and from the slowness with which some of them progress, they are sometimes spoken of as " Slow Lemurs." The best-known species are the Slender Loris (L. gracilis) of Ceylon, and the Nycticebus tardigradus of the East Indies. The largest and most important of the families of the Strep- sirhina is that of the Lemuridce or true Lemurs. In this family the muzzle is elongated, the feet are all furnished with oppos- able thumbs, and the nails on all the toes are flat, with the exception of the second toe of the hind-foot, in which there is a long and pointed claw. The body is covered with a soft fur, and the tail is usually of considerable length, and is covered with hair. They are easily domesticated ; and though capable of biting pretty severely, their disposition is gentle and docile. They are mostly about the size of cats, and not unlike them in appearance, being often termed " Madagascar cats " by sailors. They are found almost exclusively in the great forests of Madagascar, moving about amongst the trees with great activity, by means of their prehensile tails. They appear to fill in Madagascar the place occupied by the higher Quad- rumana upon the adjoining continent of Africa. The largest species is the Indri, which has very long hind-legs, and stands as much as three feet in height. PLATYRHINA. The section of the Platyrhine Monkeys is exclusively con- fined to South America, and one of its leading characters is to be found in the almost universal possession of a prehensile tail; this being an adaptive character by which they are suited to the arboreal life which so many of the South Ameri- can Mammals are forced to lead.- There are neither cheek- pouches nor natal callosities, and there is an additional prse- molar, and sometimes a molar less than in man and the Old World Monkeys. The nostrils are simple, wide apart, and placed nearly at the extremity of the snout. The praemolars are - — - 3 — 3 in number, and have blunt tubercles. The thumbs of the fore- QUADRUMANA. 633 hands are either wanting altogether, or, if present, are not opposable, though versatile. The Platyrhine Monkeys are divided into the two sections of the Hapalidce. and Cebida. Fam. i. HapalidcB. — In this family the number of teeth is the same as in the Old World Monkeys and in Man, but there is an additional praemolar on each side of each jaw, and a molar less. According to Owen, the dental formula of the Marmoset is — = 32. 2 — 2 I — I 3 — 3 2—2 The molars, however, are tuberculate, and though the num- ber of teeth is the same as in the Catarhine Monkeys, in their other characters the Marmosets are genuine Platyrhines. The hind-feet have an opposable hallux with a flat nail, but all the other toes are unguiculate, and the pollex is hardly opposable. The tail is long, but is not prehensile. The Hapalidcz are all small monkeys, mostly about as big as Squirrels, and they are exclusively South American, occur- ring especially in Brazil. The best-known species is the common Marmoset (Hapale penicillata), but several species are domesticated and kept as pets. Fam. 2. CebidcR. — In this family are all the typical Platyrhine Monkeys, in which the dentition differs from that of the Hap- alidce in having an additional molar, so that the molars are the same as in the Catarhina and in Man, but the praemolars are more numerous. The dental formula is — fc; ,1=1; ^3=3 3-3 2—2 i— i 3-3 3—3 There .are neither cheek-pouches nor " callosities ;" and the face is usually more or less naked, though sometimes whis- kered. The tail is long, and is mostly prehensile ; though in rare instances it is non-prehensile, and has its extremity clothed with hairs. The thumb of the fore-hand may be wanting, and, if present, is not opposable. All the fingers are furnished with flat nails. Their diet is miscellaneous, consisting partly of in- sects and partly of fruit. The Cebidcz are exclusively confined to the warmer parts of South America, in the vast forests of which they are met with in large troops, climbing amongst the trees. The Spider Monkeys (Ateles), the Howling Monkeys (Mycetes\ the Ca- puchin Monkey (Cebus\ and the Squirrel Monkey (Calltihrix), may serve as typical examples of this section of the Qiiadru- 634 MANUAL OF ZOOLOGY. mana. In Ateles the tail is long, slender, and powerfully pre- hensile ; and the limbs are very long and slender. The pollex is absent, or is quite rudimentary. In Mycetes there is a bony drum which is formed by a convexity of the os hyoides and communicates with the larynx. The voice is thus rendered extraordinarily resonant. The pollex is not opposable, but is placed on a line with the other fingers. CATARHINA. The third and highest section of the Quadrumana is that of the Catarhina or Old World Monkeys. In this section the nostrils are oblique, and are placed close together, and the septum narium is narrow. The thumbs of all the feet are opposable, so that the animal is strictly quadrumanous. In Colobus alone the anterior thumbs (pollex) are wanting. The dental formula is the same as in man, viz. : — 2 2 I 1 2 2 3 7 I- -; €- -; pm - - ; m* — - = 3*. 2 — 2 I 1 2 2 3 3 The incisors, however, are projecting and prominent, and the canines — especially in the males — are large and pointed. Moreover, the teeth form an uneven series, interrupted by a diastema or interval. The tail is never prehensile, and is sometimes absent. Cheek -pouches* are' often present, and the skin covering the tubera ischii is almost always callous and destitute of hair, constituting the so-called "natal callosities." With the single exception of a Monkey which inhabits the Rock of Gibraltar, all the Catarhina are natives of Africa and Asia. There are three well-marked groups or tribes of the Cata- rhine Monkeys. In the first of these the tail is long, and there are both cheek-pouches and natal callosities. In this tribe is the genus Semnopithecus, all the species of which are natives of Asia and its islands. One of the best-known species is the Sacred Monkey of the Hindoos (Semnopithecus entellus). Closely allied to the Semnopitheci is the genus Colobus, in which alone, of all the Catarhine Monkeys, the pollex is either altogether absent or totally rudimentary. Closely allied to Semnopithecus, also, is the Proboscis Monkey or Kahau (Presbytis nasalis), distinguished by its elongated proboscidiform nose, short pollex, and long tail. Here also come the little Guenons (Cercocebus and Ccrcopithecus, fig. 270). Also referable to this * The cheek-pouches are sacs or cavities in the cheeks, which open into the mouth, and serve to hold any superfluous food. QUADRUMANA. 635 division is the genus Macacus or Inuus (comprising the Ma- caques), which includes most of the Monkeys which are ordi- narily brought to this country. It is a Macaque which occurs at the Rock of Gibraltar, and is the only wild Monkey which is found in Europe at the present day. Most of the Macaques are Asiatic, and a good example is the Wanderoo (M. Silenus) of India. The second tribe of the Catarhine Monkeys is that of the Baboons (Cynocephalus and Papto). In these forms the tail is mostly short, and is often quite rudimentary. The head is large, and the muzzle is greatly prolonged, having the nostrils at its extremity. The facial angle is about 30°, and the whole head has much the aspect of that of a large dog. The natal callo- sities are generally large and conspicuous, and usually of some bright colour. The Baboons are large strong animals, ex- tremely unattractive in outward appearance, and of great ferocity. More than any other of the Monkeys, they employ the fore-limbs in terrestrial progression, running upon all-fours with the greatest ease. They are mainly inhabitants of Africa, and one of them, the Mandrill (Cynocephalus Maimon\ attains very nearly the height of a man. The best-known species are the Chacma (Cynocephalus porcarius\ the Derrias (C. Hama- dryas), the Common Baboon (C,papio), and the Mandrill. The Derrias is found in Arabia and Abyssinia, and occurs both embalmed and sculptured upon ancient monuments in Egypt and Nubia. The Mandrill is rendered probably without ex- ception the most disgustingly hideous of living beings by the possession of a large blood-red natal callosities and of enormous cheek-protuberances striped with brilliant colours in alternate ribs. The third family of the Catarhine Monkeys is that of the Anthropomorphous or Anthropoid Apes, so called from their making a nearer approach in anatomical structure to man than is the case with any other Mammal. The members of this family are Apes in which there is no tail, and cheek-pouches are absent, whilst in some cases there are also no natal callo- sities. The hind-legs are short — shorter than the fore-limbs — and the animal can progress in an erect or semi-erect position. At the same time, the thumbs of the hind-feet (hallux) are opposable to the other digits, so that the hind- feet are prehensile hands. The spine shows a single curve, and articulates with the back part of the skull. The canine teeth of the males are long, strong, and pointed, but this is not the case with the females. The structure, therefore, of the canine teeth is to be regarded in the light of a sexual 636 MANUAL OF ZOOLOGY. peculiarity, and not as having any connection with the nature of the food. In this tribe are the Gibbons (Hylobates\ the Orang-outang (Simla satyrus], the Chimpanzee, and the Gorilla. The Gibbons form the genus Hylobates, and they belong to southern Asia and the Indian Archipelago. The anterior limbs are extremely long, and the hands nearly or quite reach the ground when the animal stands in an erect posture. There is no tail, but there are natal callosities. The body is covered with a thick fur. One of the best known of the Gibbons is the Siamang (Hylobates syndactylus\ which has been sometimes regarded as making a nearer approach to man than any other of the Monkeys. It is a native of Sumatra. It is the largest of the Gibbons, and derives its specific name from the fact that the index and middle toes of the hind-foot are united to one another by skin as far as the nail joint. Another well- known species is the common Gibbon (.H. lar\ Fig. 271. — A, Skull of the Orang-outang. B, Skull of an adult European. In the Orang or " Mias " (Simla satyrus] there are neither cheek-pouches nor natal callosities, and the hips are covered with hair. As in the Gibbons, the arms are excessively long, reaching considerably below the knee when the animal stands in an erect posture. The hind-legs are very short, and there is no tail. When full grown the Orang stands about four feet high. It never progresses with the help of a stick, or walks erect at all, except along the branches of trees, supporting itself by a higher branch, or when attacked. When young, the head of the Orang is not very different from that of an average European child ; but, as the animal grows, the facial bones BIMANA. 637 become gradually produced, whilst the cranium remains in a tolerably stationary condition ; great bony ridges are developed for the attachment of the muscles of the jaws and face ; the incisors project ; and ultimately the muzzle becomes as pro- nounced and well-marked a feature as in the typical Carnivora (fig. 271, A). The Orangs are inhabitants of Sumatra and Borneo. The genus Troglodytes contains the Chimpanzee (T. mger) and the Gorilla (T. Gorilla). The Chimpanzee is a native of Western Africa, and has the arms much shorter, proportionately, than in the Gibbons and Orangs ; still they are much longer than the hind-limbs, and they reach beneath the knee when the animal stands erect. The ears in the Chimpanzee are large, and the body is covered with dark brown hair. The animal can stand erect, but the natural mode of progression is on all-fours. The hands are naked to the wrist, and the face is also naked, and is much wrinkled. The Chimpanzee lives in society in wooded districts, constructs huts, and can defend itself against even the Elephant. The Gorilla is in most respects the same as the Chimpan- zee, but is much larger, attaining a height of fully five feet. The hind limbs are short, and the ears small. It is an enor- mously strong and ferocious animal, and is found in Lower Guinea and in the interior of equatorial Africa. It possesses a laryngeal sac, has a most appalling voice, and is polygamous. The Gorilla is now generally regarded as the most human of the Anthropoid Apes. CHAPTER LXXXIV. BIMANA. ORDER XIV. BIMANA. — This, the last remaining order of the Mammalia, comprises Man (Homo] alone, and it will therefore require but little notice here, the peculiarities of Man's mental and physical structure properly belonging to other branches of science. Zoologically, Man is distinguished from all other Mammals by his habitually erect posture and bipedal progression. The lower limbs are exclusively devoted to progression and to sup- porting the weight of the body. The anterior limbs are shorter than the posterior, and have nothing whatever to do with pro- 638 MANUAL OF ZOOLOGY. gression. The thumb is opposable,. and the hands are pre- hensile, the fingers being provided with nails. The toes of the hind-limb are also furnished with nails, but the hallux is not opposable to the other digits, and the feet are therefore useless as organs of prehension. The foot is broad and plantigrade, and the whole sole is applied to the ground in walking. The dentition consists of thirty-two teeth, and these form a nearly even and uninterrupted series, without any interval or diastema. The dental formula is — . 2 — 2 i — i 2 — 2 •* — 2 t - -; c \pm- -; ^^—^ = 32. 2 2 I 1 2 2 3 3 The brain is more largely developed and more abundantly furnished with large and deep convolutions than is the case with any other Mammal. The mammae are pectoral, and the placenta is discoidal and deciduate. Man is the only terrestrial mammal in which the body is not provided with a covering of hair. The zoological or anatomical distinctions between Man and the other Mammals are thus seen to be of no very striking nature, and certainly of themselves would not entitle us to consider Man as forming more than a distinct order. When, however, we take into account the vast and illimitable psychical differences, both intellectual and moral — differences which must entail corresponding structural distinctions — between Man and the highest Quadrutnana, it becomes a question whether the group Bimana should not have the value of a distinct sub-kingdom ; whilst there can be little hesitation in giving Man, at any rate, a class to himself. At any rate, man's psychical peculiarities are as much an integral portion, or more, of his totality, as are his physical characters, and, as Dr Pritchard says, — "The sentiments, feelings, sympathies, internal consciousness, and mind, and the habitudes of mind and action thence resulting, are the real and essential character- istics of humanity." CHAPTER LXXXV. DISTRIBUTION OF MAMMALIA IN TIME. As a matter of course, the remains of Mammals are scanty, and occupy but a small space in the geological record, since the greater number of the Mammalia are terrestrial, and the DISTRIBUTION OF MAMMALIA IN TIME. 639 greater number of the stratified fossiliferous deposits are marine. The Mammals, too, are the most highly organised of the entire sub-kingdom of the Vertebrata; and therefore, in obedience to the well-known law of succession, they ought to make their appearance upon the globe at a later period than any of the lower classes of the Vertebraia. Such, in point of fact, is to a great extent the case ; and if the geological record were perfect, the law would doubtless be carried out to its full extent. It is in the upper portion of the Triassic Rocks — that is to say, not long after the commencement of the Mesozoic or Secondary epoch — that Mammals for the first time make their appearance ; three or four species being now known in a zone of rocks which are placed at the summit of the Trias, just where this formation begins to pass into the Lias. The earliest of these — the oldest known of all the Mammals — appears at the upper part of the Upper Trias (Keuper) and also at its very summit (Penarth Beds), and has been described under the name of Microlestes antiquus. The nearest ally of Microlestes amongst existing Mammals would seem to be the Marsupial and Insec- tivorous Myrmecobius, or Banded Ant-eater of Australia. As only the teeth, however, of Microlestes have hitherto been dis- covered, it is impossible to decide positively whether this primeval Mammal was Marsupial or Placental. The next traces of Mammals occur in the Stonesfield Slate (Lower Oolites), and here four species, all of small size, are known to occur. Most of these were Marsupial, but it is possible that one was Placental. They form the genera Amphi- lestes, Amphitherium, Phascolotherium, and Stereognathus. After the Stonesfield Slate another interval succeeds, in which no Mammalian remains have hitherto been found ; but in the fresh- water formation of the Middle Purbeck — at the top, namely, of the Oolitic series — as many as fourteen small Mammals have been discovered. These constitute the genera Plagiaulax, Spalacotherium, Triconodon, and Galestes. Another gap then follows, no Mammal having hitherto been discovered in any portion of the Cretaceous series (with doubtful exceptions). Leaving the Mesozoic and entering upon the Kainozoic period, remains of Mammals are never absent from any of the geological formations. From the base of the Eocene Rocks up to the present day remains of Mammals commonly occur, constantly increasing in number and importance, till we arrive at the fauna now in existence upon the globe. The number of known fossil Mammals is so great, and they exhibit so many peculiarities and divergences from existing forms, that it will be impossible here to do more than simply 640 MANUAL OF ZOOLOGY. point out the leading facts known as to the distribution of each order of Mammals in past time. Order /. Monotretnata. — The Monotremes are not known to be represented at all in past time ; and this need not excite any surprise, seeing that the order is represented at the present day by no more than two genera, both confined to a single geographical region. Upon theoretical grounds, however, it may be expected that we shall ultimately discover that the antiquity of the order Monotremata is extremely high. Order II. Marsupialia. — This is probably the oldest of the Mammalian orders; but owing to the detached and fragmen- tary condition of almost all Mammalian remains — consisting mostly of the ramus of the lower jaw, or of separate teeth — it is not possible to state this with absolute certainty. The Microlestes of the Trias, the oldest, or nearly the oldest, of the Mammals, was probably a Marsupial ; but the evidence upon this point is not conclusive. In the Triassic rocks of America, also, perhaps at a lower horizon than that at which Microlestes occurs in Europe, has been found the jaw of a small Mammal, Fig. 272. — Lower jaw of Dromatherium sylvestre (after Emmons). From rocks, supposed to be of Triassic age, in North Carolina. which is probably Marsupial, and has been named Droma- therium (fig. 272). In the next mammaliferous horizon, however — namely, that of the Stonesfield Slate in the Lower Oolites — there is no doubt but that some of the Mammalian remains, if not all, belong to small Marsupials (fig. 273). From this horizon the two genera Phascolotherium and Amphitherium, are almost certainly refer- able to the Marsupialia; the latter seeming to be most nearly related to the living Myrmecobius, whilst the former finds its nearest living ally in the Opossums of America. The Stereog- nathus of the Stonesfield Slate is in a doubtful position. It may have been Marsupial; but, upon the whole, Professor Owen is inclined to believe that it was placental, hoofed, and herbivorous. With the occurrence of small Marsupials in England within the Oolitic period, it is interesting to notice how the fauna of that time approached in other respects to that now inhabiting Australia. At the present day, Australia is almost wholly DISTRIBUTION OF MAMMALIA IN TIME. 641 tenanted by Marsupials ; upon its land-surface flourish Arau- caricz and Cycadaceous plants, and in its seas swims the Port Jackson Shark (Cestracion Philippi)', whilst the Molluscan genus Trigonia is nowadays exclusively confined to the Aus- tralian coasts. In England, at the time of the deposition of the Stonesfield Slate, we must have had a fauna and flora very closely resembling what we now see in Australia. The small Marsupials, Amphitherium and Phascolotherium, prove that the Mammals were the same in order; cones of Araucarian pines, with tree-ferns and fronds of Cycads, occur throughout the Oolitic series ; spine-bearing fishes, like the Port Jackson Shark, are abundantly represented by genera such as Acrodus and Strophodus ; and, lastly, the genus Trigonia, now exclu- sively Australian, is represented in the Stonesfield Slate by species which differ little from those now existing. Fig. 273. — Oolitic Mammals, natural size, i . Lower jaw and teeth of Phascolotheritnn : 2. of Triconodon ; 3. of A tnphitfteriutn ; 4. of Plagiaulax. In the middle Purbeck beds (Upper Oolite), where fourteen species of Mammals are known to exist, it is probable that all were Marsupial. All the Purbeck Mammalia were of small size, the largest being no bigger than a pole-cat or hedgehog. They form the genera Plagiaulax, Triconodon, and Galestes, of which Plagiatilax is believed to be most nearly allied to the living Kangaroo-rat (Hypsiprymnus] of Australia. In the Tertiary series of rocks Marsupials are of rare occur- rence ; but an Opossum, closely allied to the existing American forms, has been discovered in the Eocene rocks of France (Gypseous series of Montmartre), and has been named the Didelphys gypsorum. The next occurrence of Marsupials is in the later Tertiary (Pliocene) and in the Post-tertiary epoch ; and here they are represented by some very remarkable forms. The remains in question have been found in the bone-caves of Australia — the country in which Marsupials now abound above every other 2 S 642 MANUAL OF ZOOLOGY. part of the globe ; and they show that Australia, at no dis- tant geological period, possessed a Marsupial fauna, much resembling that which it has at present, but comparatively of a much more gigantic size. In the remains from the Australian bone-caves almost all the most characteristic living Marsupials of Australia and Van Diemen's Land are represented ; but the extinct forms are usually of much greater size. We have Wombats, Phalangers, Flying Phalangers, and Kangaroos, with carnivorous Marsupials resembling the recent Thylacinus and Dasyurus. The two most remarkable of these extinct forms are Diprotodon and Thylacoleo. In most essential respects Diprotodon resembled the Kangaroos, the dentition, especially, showing many points of affinity. The hind-limbs, however, of Diprotodon were by no means so disproportionately long as in the Kangaroos. In size Dipro- todon must have many times exceeded the largest of the liv- ing Kangaroos, since the skull measures three feet in length (fig. 274). The affinities of Thylacoleo are disputed. By Fig. *u.-$\n\\Qt Diprotodon Awtraiis. Professor Owen it is regarded as being strictly carnivorous, and as finding its nearest living ally in the Thylacine. The great feature in the dentition is the presence in either jaw of one huge, compressed, and trenchant praemolar. This is regarded by Owen as a " carnassial ; " but Professor Flower, with greater probability, regards it as corresponding to the great cutting prgemolar of the Kangaroo-rats {Hypsiprymnus}, a view which is further borne out by the small size of the canines in Thylacoleo. Upon the whole, therefore, Flower concludes that " Thylacoleo is a highly modified and aberrant form of the type of Marsupials now represented by the Macro- podidce and Phalangisti&K, though not belonging to either of these families as now restricted," and he believes that its diet was of a vegetable nature. Under any view of its habits, Thylacoleo is a very remarkable type of the Marsupials ; and it must have attained a very great size, since the length of the crown of the great prsemolar is not less than two inches and a quarter. Order III. Edentata. — The Edentates, like the Marsupials, are singularly circumscribed at the present day. No member of the order is at the present day indigenous in Europe. Tropical Asia and Africa have the Scaly Ant-eaters or Pangolins ; DISTRIBUTION OF MAMMALIA IN TIME. 643 and in Africa occurs the Edentate genus Orycteropus. South America, however, is the metropolis of the Edentata, the order being there represented by the Sloths, the Armadillos, and the true Ant-eaters. It is also in South America that by far the greater number of extinct Edentates have been found ; and, as in the case of the Australian Marsupials, the fossil forms are gigantic in size compared with their living representatives. Fig. 275. — Megatherium. From the Upper Tertiaries of South America (Pleistocene). The Sloths (Bradypodidce) of the present day were repre- sented in Post-tertiary times by a group of gigantic forms referable to the genera Mylodon, Megalonyx, and Megatherium. Of these, Mylodon attained a length of eleven feet, and Mega- therium (fig. 275) was eighteen feet in length, with bones as massive, or more so, than the Elephant. In the same way the little banded Armadillos of South America were formerly represented by gigantic species, £on- Fig. 276. — Glyptodon clavipes. Pleistocene deposits of South America. stituting the genus Glyptodon. The Glyptodons (fig. 276) dif- fered from the living Armadillos in having no bands in their armour, so that they must have been unable to roll themselves up. It is rare at the present day to meet with any Armadillo over two or three feet in length ; but the length of the Glypto- 644 MANUAL OF ZOOLOGY. don davipes, from the tip of the snout to the end of the tail, was more than nine feet. All these gigantic South American Edentates occur in Post- tertiary deposits. Older, however, than any of these is the Macrotherium. This is a gigantic Edentate, intermediate in some respects between the Pangolins and Orycteropus, and found in certain lacustrine deposits of France, of Miocene age. Order IV. Sirmia. — This order contains only the living Manatees and Dugongs, and is of little geological importance. The Halitkcrium, however, of the Eocene, Miocene, and Plio- cene rocks, is a large form, intermediate between the African Manatee and the Dugong. Order V. Cetacea. — The Cetacea, also, are of little geological importance. Remains of Rorquals have been found in the Pliocene, and some of the ear-bones of the Crag (Pliocene) are probably referable to true Whalebone Whales. The Physe- teridce commence in the Pliocene, the Delphinidce. in the Miocene, and the Ziphioid Whales in the Pliocene. The Ztuglodontida, like the other Cetaceans, are only known from the Tertiary Rocks, but Zeuglodon commences in the Eocene. Order VI. Ungtilata. — The hoofed Mammals are repre- sented in past time by so many extinct forms that it will be wholly impossible here to do more than merely allude to some of the more important genera. The earliest-known Ungulates occur in the Eocene rocks, where the order is represented by very numerous and interest- ing forms, the more important of which are Pliolophus, Palceo- therium, and Anoplotherium. Of the section of the Ungulates comprising the living Horse, Zebra, and Ass (Solidungula), the earliest fossil example is the Anchitherium of the Lower Miocene, and this was succeeded by the Hipparion of the Miocene rocks. This genus differed from the existing Equida in the presence of two small toes with hoofs, one on each side of the single functional toe, which alone remains in living horses ; whilst in Anchitherium the lateral toes were sufficiently developed to touch the ground. In the Pliocene period appear, for the first time, remains of , horses which, like the present form, possessed only a single toe encased in a single hoof. It is interesting to observe that one of the Pliocene horses (Equus curvidens) occurs in South America ; though this continent certainly possessed no native horse at the time of its discovery by the Spaniards. About twenty horses— one of them standing no more than two and a half feet in height — have been described from North America, DISTRIBUTION OF MAMMALIA IN TIME. 645 in which continent no indigenous horse existed at the time of its discovery. Of the Rhinoceridce, a hornless form (Acer other ium) occurs in Miocene and Pliocene strata ; but the best-known fossil species is the two-horned woolly Rhinoceros (J?. tichorhinus}. This curious species occurs in Post-pliocene deposits, and must have ranged over the greater part of Europe. It was adapted to a temperate climate, and, like the Mammoth, possessed a thick covering of mixed wool and hair. This has been demonstrated by the discovery of a frozen carcass in Siberia. Of the Hippopotamidtz, the earliest-known species is the Hippopotamus major of the Pliocene period. This form agreed in all essential respects with the living H. amphibius of Africa, but it must have ranged over the whole of Southern Europe. Hexaprotodon, of the Tertiary deposits of the Siwalik Hills of India, is a sub-genus of Hippopotamus proper, and had six lower incisors. Of the Suida, or Pig tribe, various extinct forms are known from the Eocene and Miocene rocks, where the family is represented by the genera Chczropotamus^ Anthracotherium, Hyopotamus, and Hippohyus. Fig, 277. — The Irish Elk (Megaceros Hibernicus). As regards the past existence of the Ruminants, the Cenida or Stag tribe, is represented, for the first time in the Miocene period, by the genus Dorcatherium. The best-known species, however, of this family is the Megaceros Hibernicus, or so-called Irish Elk (fig. 277), which is not a true Elk, but is intermediate between the Fallow-deer and Reindeer. A fossil Camel (C. 646 MANUAL OF ZOOLOGY. Sivalensis) has been discovered in the Tertiary deposits of the Siwalik Hills of India. Of the Giraffe family — represented at the present day by a single African species — a form has been discovered in the Pliocene rocks of Greece, and has been described under the name of Helladotkerium. Somewhat similar forms have been found in the Pliocene deposits of the Siwalik Hills of India. The earliest-known Antelopes are Miocene, but the largest and most extraordinary fossil examples of this family are two gigantic four-horned Antelopes, which occur in the Pliocene strata of the Siwalik Hills of India, and have been described under the names of Sivatherium and Bramatherium. The Bovidft, or Ox tribe, has hitherto only ^occurred in rocks not older than the Pliocene or Post-pliocene. At this latter period England alone possessed four oxen — viz., the Lithua- nian Aurochs (Bos bison or Bos priscus), the Wild Bull or Urus (Bos primigenius), the Bos antiquus, and a small aboriginal species, the Bos longtfrons, believed by Owen to be " the source of the domesticated cattle of the Celtic races before the Roman invasion." Order VII. Hyracoidea. — This little order, represented at the present day by no more than the single genus Hyrax, is not known to have any fossil representatives. Order VIII. Probosridea. — This order, including no other living forms than the Elephants, came into existence in the Miocene period, where it is represented by all its three sec- tions, Deinotherium, Mastodon, and Elephas. Fig. 278.— Skeleton of Mastodon. The Deinotherium (fig. 278) was a gigantic Miocene Mam- mal, probably something like the living Elephants, but having no incisors in the upper jaw. In place of these, the lower jaw was furnished with two long tusk-like incisors, which were bent downwards. DISTRIBUTION OF MAMMALIA IN TIME. 647 In most essential respects the Mastodons (fig. 278) resemble the Elephants, but the molar teeth were furnished with nipple- shaped eminences. Usually there are two tusk-shaped upper incisors, but sometimes lower incisors are present as well Four Mastodons occur in the Miocene of Europe, and three in that of India. No Elephant has yet been discovered in the Miocene rocks of Europe, but six species are known from Miocene strata in India. In the Pliocene period Europe possessed its Elephants (viz., E. priscus and E. meridionalis] ; but the best known of the extinct Elephants, as well as the most modern, is the Mammoth (E. prhnigenius, fig. 279). The Mammoth enjoyed a very extended geographical distribution, remains of it occur- ring in Britain, continental Europe, Siberia, and throughout a Fig. 279. — Skeleton of the Mammoth (F.lephas primi genius). large portion of North America. There can also be no ques- tion but that the Mammoth existed in the earlier portion of the human period. Order IX. Carnivora. — If the little Microlestes of the Upper Trias be Marsupial, as is most probably the case, then the order Carnivora is comparatively modern, the earliest un- doubted remains having been found in the Eocene rocks. In the Eocene period, however, the families of the Canidce and Felidcz appear to have been already differentiated. The Ur- sidcz, Viverridcz, Mustelidcz, Hycznidcz, and Phocidcz, do not seem to have made their appearance before the Miocene period. In the Pliocene and Post-pliocene periods almost all the existing types of the Carnivora are represented by extinct forms, whilst in the latter the remains of various living species are found associated with other animals which have at the present day entirely passed away. The tribe of the Felidcz is repre- sented in the Miocene period by the large Machairodus, with 648 MANUAL OF ZOOLOGY. sabre-shaped upper canines. Species of this genus must have been as large as a Lion. In the later Pliocene and Post- pliocene deposits occur the remains of a large Lion — the Cave-lion or Felis spelcea — along with which, in Britain and continental Europe, are the bones of a large Hyaena (H. spelcea) and a gigantic Bear (Ursus spelceus}. Remains of Wolves, Foxes, Badgers, Otters, Pole-cats, Weasels, and other Carnivora are also found in various later Tertiary deposits, and in bone-caves. Order X. Rodentia. — No Rodent animal is as yet known to have occurred earlier than the Eocene period. Here are found froms allied to the living Dormouse and Squirrel. In the Miocene rocks occur nume- rous small Rodents. In the Pliocene and Post-pliocene deposits the order is also well represented, the most remark- able form being the Great Bea- ver (Trogontherium, fig. 280), Fig. 28o.-J^of Trozontherium Cuvieri. which appears tO have Survived Post-pliocene. into the historical period. Order XL Cheiroptera. — The earliest-known indications of Bats are in the Eocene period, but the order is of no geological importance. Order XII. Insectivora. — The Insectivorous Mammals, like- wise, commenced their existence, so far as is known, in the Eocene period; and they, also, are of little importance from a geological point of view. Order XIII. Quadrumana. — With two not wholly satisfactory exceptions, from the Eocene Tertiary, the earliest-known remains of Quadrumana occur in the Miocene period. Several genera are known, but the most important are Pliopithecus and . Dryopithecus, both of which are European, and both of which belong to the section of the Catarhine Monkeys, which are at present characteristic of the Old World ; the former being most nearly allied to the living Semnopitheci, the latter to the Gib- bons. It is interesting to notice that the American fossil Monkeys — from the later Tertiary deposits of South America — belong to the division of the Quadrumana now peculiar to that continent — to the section, namely, of the Platyrhine Monkeys. GEOGRAPHICAL SUCCESSION OF ORGANIC FORMS. A few words may be said here on a law which may be called the " law of the geographical succession of organic forms/' and DISTRIBUTION OF MAMMALIA IN TIME. 649 which is illustrated more completely by the Mammalia than by any other extinct animals. An examination, namely, of the facts of the geological distribution of Mammals leads to the striking generalisation that " the present distribution of organic forms dates back to a period anterior to the origin of existing species" (Lyell). In other words, though the extinct Mam- mals of the later geological deposits of any given country differ specifically from those now existing in the same country, they are nevertheless referable to the same orders, and are in every respect more closely allied to the present Mammalian fauna than to that of any other country. A few examples will render this perfectly clear. Australia at the present day is an altogether peculiar zoolo- gical province, characterised by the abundance and variety of Marsupials which inhabit it. In the Post-tertiary deposits of Australia, however, we are presented with proofs that Marsu- pials were just as characteristic of Australia during late geolo- gical epochs as they are now. In the Post-pliocene period we know that Australia was occupied by Kangaroos, Kangaroo- rats, Wombats, Phalangers, and Carnivorous Marsupials, in every way representing the living Marsupials in zoological value, but specifically distinct, and generally of gigantic size. In the same way, South America at the present day is espe- cially characterised by a Mammalian fauna, containing many peculiar forms, the Edentata being especially conspicuous, and having a larger representation than in any other region. Simi- lar but distinct forms, however, are found to have existed in South America anterior to the creation of any existing species. Thus, the modern Sloths of South America are represented by the colossal Mylodon, Megalonyx, Scelidotherium, and Megathe- rium. The little armour-plated Armadillos are represented by the equally colossal Glyptodon. The Llamas — representing in South America the Camels of the Old World — are represented by the curious extinct genus Macrauchenia. The Platyrhine Monkeys have their extinct representatives. Fossil Tapirs take the place of the two existing species ; and the Peccaries are represented by at least five extinct species of Dicotyles. Similarly, India is at present the only country in which four- horned Antelopes occur ; and it is in the Siwalik Hills that there have been found the two gigantic four-horned Antelopes which constitute the genera Sivatherium and Bramatherium. In Europe, again, the Mammalian fauna of the later Tertiary periods is much more closely allied to that now characterising the Old World, than to that of the New. We have the Lion, Bear, Wolf, Fox, and other well-known Carnivora. Elephants, 650 MANUAL OF ZOOLOGY. Rhinoceroses, and Hippopotami, then as now, are characteristic Old World forms. The Ruminants are equally characteristic of the eastern hemisphere, though not exclusively confined to it, and they have numerous and varied representatives in later Tertiary deposits. The Giraffe is represented by the Hellado- therium, and the Bactrian Camel by the Merycotherium of the Siberian Drift. The fossil Quadrumana, too, of Europe, all belong to the Catarhine section of the order. It is unnecessary to pursue the subject further, but no law is more firmly established than this : " That with extinct as with existing Mammalia, particular forms were assigned to particular provinces ; and that the same forms were restricted to the same provinces at a former geological period as they are at the present day " (Owen). It is to be borne in mind, however, that the law, as just stated, holds good for the later Tertiary period only, and does not apply, in any manner that admits of being traced, to the earlier geological epochs. TABULAR VIEW OF THE CHIEF SUBDIVISIONS OF THE SUB-KINGDOM VERTEBRATA. SUB-KINGDOM VI.— VERTEBRATA. CLASS I. PISCES. Order i. Pharyngobranchii. 2. Marsipobranchii. 3. Teleostei. 4. Ganoidei. 5. Elasmobranchii. 6. Dipnoi. CLASS II. AMPHIBIA. Order i. Labyrinthodontia. 2. Ophiomorpha. 3. Urodela. 4. Anoura. CLASS III. REPTILIA. Order i. Chelonia. 2. Ophidia. 3. Lacertilia. 4. Crocodilia. 5. Ichthyopterygia. 6. Sauropterygia. 7. Anomodontia. 8. Pterosauria. 9. Deinosauria. TABLE OF VERTEBRATA. 65 I CLASS IV. AVES. Order i. Natatores. 2. Grallatores. 3. Cursores. 4. Rasores. Sub-order a. Gallinacei. b. Columbacei. 5. Scansores. 6. Insessores. Sub-order a. Conirostres. b. Dentirostres. c. Tenuirostres. d. Fissirostres. 7. Raptores. 8. Saururae. CLASS V. MAMMALIA. Division A. Ornithodelphia. Order i. Monotremata. Division B. Didelphia. Order 2. Marsupialia. Division C. Monodelphia. Order 3. Edentata. 4. Sirenia. 5. Cetacea. 6. Ungulata. Section Perissodactyla. a. Multungula. b, Solidungula. Section Artiodactyla. a. Omnivora. b. Ruminantia. 7. Hyracoidea. 8. Proboscidea. 9. Carnivora. a. Pinnigrada. b. Plantigrada. c. Digitigrada. 10. Rodentia. 11. Cheiroptera. 12. Insectivora. 13. Quadrumana. a. Strepsirhina. b. Platyrhina. c. Catarhina. 14. Bimana. 653 GLOSSARY. ABDOMEN (Lat. abdo, I conceal). The posterior cavity of the body, contain- ing the intestines and others of the viscera. In many Invertebrates there is no separation of the body-cavity into thorax and abdomen, and it is only in the higher Annulosa that a distinct abdomen can be said to exist. ABERRANT (Lat. aberro, I wander away). Departing from the regular type. ABNORMAL (Lat. ab, from ; norma, a rule). Irregular ; deviating from the ordinary standard. ABOMASUM. The fourth cavity of the complex stomach of the Ruminants. ABRANCHIATE (Gr. a, without ; bragchia, gills). Destitute of gills or bran- chise. ACALEPH^E (Gr. akalephe, a nettle). Applied formerly to the Jelly-fishes or Sea-nettles, and other Radiate animals, in consequence of their power of stinging, derived from the presence of microscopic cells, called thread- cells," in the integument. ACANTHOCEPHALA (Gr. akantha, a thorn ; kephale, head). A class of para- sitic worms in which the head is armed with spines. ACANTHOMETRINA (Gr. akantha; and metra, the womb). A family of Pro- tozoa, characterised by having radiating siliceous spines. ACANTHOPTERYGII (Gr. akantha, spine ; pterux, wing). A group of bony fishes with spinous rays in the front part of the dorsal fin. ACARINA (Gr. akari, a mite). A division of the Arachnida, of which the Cheese-mite is the type. ACEPHALOUS (Gr. a, without; kephale, head). Not possessing a distinct head. ACETABULA (Lat. acetabulum, a cup). The suckers with which the cephalic processes of many Cephalopoda (Cuttle-fishes) are provided. ACETABULUM. The cup-shaped socket of the hip-joint in Vertebrates. ACRITA (Gr. akrilos, confused). A term sometimes employed as synonymous with Protozoa, or the lowest division of the animal kingdom. ACTINOMERES (Gr. aktin, a ray ; meros, a part). The lobes which are mapped out on the surface of the body of the Ctenophora, by the ctenophores, or comb-like rows of cilia. ACTINOSOMA (Gr. aktin ; and soma, body). Employed to designate the entire body of any Actinozoon, whether this be simple (as in the Sea-anemones), or composed of several zooids (as in most Corals). ACTINOZOA (Gr. aktin; and zoiin, an animal). That division of the Coslen- terata of which the Sea-anemones may be taken as the type. ADELARTHROSOMATA (Gr. adelos, hidden ; arthros, joint ; soma, body). An order of the Arachnida. AGAMIC (Gr. a, without ; gamos, marriage). Applied to all forms of repro- duction in which the sexes are not directly concerned. ALLANTOIDEA. The group of Vertebrata in which the foetus is furnished with an allantois, comprising the Reptiles, Birds, and Mammals. ALLANTOIS (Gr. alias, a sausage). One of the "membranes" of the foetus in certain Vertebrates. 654 GLOSSARY. ALVEOLI (Lat. dim. of alvus, belly). Applied to the sockets of the teeth. AMBULACRA (Lat. ambulacrum, a place for walking). The perforated spaces or "avenues" through which are protruded the tube-feet, by means of which locomotion is effected in the Echinodermata.^ AMBULATORY (Lat. ambulo, I walk). Formed for walking. Applied to a single limb, or to an entire animal. AMETABOLIC (Gr. a, without ; metabole, change). Applied to those insects which do not possess wings when perfect, and which do not, therefore, pass through any marked metamorphosis. AMNION (Gr. amnos, a lamb). One of the fcetal membranes of the higher Vertebrates. AMNIOTA. The group of Vertebrata in which the foetus is furnished with an amnion, comprising the Keptiles, Birds, and Mammals. AM peri ; and plasso, I mould). The intercellular substance or matrix in which the organised structures of a tissue are embedded. PERISOME (Gr. peri; and somai> body). The coriaceous or calcareous integu- ment of the Echinodermata. PERISSODACTYLA (Gr. perissos^ uneven ; daktulos, finger). Applied to those . Hoofed Quadrupeds (Ungulata) in which the feet have an uneven number of toes. PERISTOME (Gx-. peri; andsfoma, mouth). The space which intervenes be- tween the mouth and the margin of the calyx in Vorticella ; also the space between the mouth and. the tentacles in a sea-anemone (Actinia) • also the lip or margin of the mouth oif a univalve shell. PERIVISCERAL (Gr. peri ; and Lat. viscera, the internal organs). Applied to the space surrounding the vis<3era. PETALOID. Shaped like the petal of a flower. PHALANGES (Gr. phalanx, a row). The small bones composing the digits of the higher Vertebrata. Normally each digit has three phalanges. PHAKYNGOBRANCHII (Gr. pharugx, pharynx ; bragchia, gill). The order of Fishes comprising only the Lancelot. PHARYNX. The dilated commencement of the gullet. PHRAGMACONE (Gr. phragma, a partition ; and konos, a cone). The chambered portion of the internal shell of a Bdemnite. PflYLACTOLjEMATA (Gr. phulasso, I guard, and laimos, throat). The division of Polyzoa in which the mouth is provided with the arched valvular process known as the "epistome." PHYLLOCYSTS (Gr. jthullon, leaf ; and kustis, a cyst). The cavities in the in- terior of the " hydrophyllia " of certain of the Oceanic Hydrozoa. PHYLLOPODA (Gr. phullon, leaf ; and pous, foot). An order of Crustacea. PHYOGEMMARIA (Gr. phuo, I produce ; and Lat. gemma, bud). The small gonoblastidia of Velella, one of the Pliysophoridce. PHYSOGRADA (Gr. phusa, bellows or air-bladder ; and Lat. gradior, I walk). GLOSSARY. 675 Applied formerly to the Physophoridce, an order of Oceanic Hydrozoa, in which a " float " is present. PHYSOPHORID^E (Gr. phusa, air-bladder ; and phero, I carry). An order of Oceanic Hydrozoa. PHYTOID (Gr. phuton, a plant ; and eidos, form). Plant-like. PHYTOPHAGOUS (Gr. phuton, a plant ; and phago, I eat). Plant-eating, or herbivorous. PINNATE (Lat. pinna, a feather). Feather-shaped, or possessing lateral pro- cesses. PINNIGRADA (Lat. pinna, a feather; gradior, I walk). The group of Carni- vora, com prising the Seals and Walruses, adapted for an aquatic life. Often called Pinnipedia. PINNULE (Lat. dim. of pinna}. The lateral processes of the arms of Grinoids. PISCES (Lat. piscis, a fish). The class of Vertebrates comprising the Fishes. PLACENTA (Lat. a cake). The "after-birth," or the organ by which a vascu- lar connection is established in the higher Mammalia between the mother and the foetus. PLACENTAL. Possessing a placenta, or connected with the placenta. PLACOID (Gr. plax, a plate; eidos, form). Applied to the irregular bony plates, grains, or spines which are found in the skim of various fishes (Elasmobranchii). PLAGIOSTOMI (Gr. pfaaios, transverse ; stoma, mouth). The Sharks and Ptays, in which the mouth is transverse, and is placed on the under surface of the head. PLANARIDA (Gr. plane, wandering). A sub-order of the Turbellaria. PLANTIGRADE (Lat. planta, the sole of the foot ; gradior, I walk). Applying the sole of the foot to the ground in walking. PLANULA (Lat. 'planus, flat). The oval ciliated embryo of certain of ttie Hydrozoa. PLASTRON. The lower or ventral portion of the bony case of the GJhelonians-. PLATYELMIA (Gr. platus, broad ; and helmins, an intestinal worm). The division of Scolecida comprising the Tape-worms, &c. PLATYRHINA (Gr. platus, broad ; rhines,xiostrils). A group of the Quadrumana. PLEURA (Gr. the side). The serous membrane covering the lung in the air- breathing Vertebrates. PLEURON (Gr. pleuron, a rib). The lateral extensions of the shell of Crustacea. PLUTEUS (Lat. a pent-house). The larval form of the Echinoidea. . PNEUMATIC (Gr. pneuma, air). Filled with air. PNEUMATOCYST (Gr. pneuma, air; and: kusfis, cyst). The air-sac or float of certain of the Oceanic Hydrozoa (Physophoridce). PNEUMATOPHORE (Gr. pneuma, air ; and phero, I carry). The proximal dilatation of the coenosarc in the Physophoridce which surrounds the pneu- matocyst. PNEUMOSKELETON (Gr. pneuma; and skeletos, dry). The hard structures which are connected with the breathing organs (e.g., the shell of Molluscs). PODOPHTHALMATA (Gr. pous, f oot ; and ophthalmos, eye). The division of Crustacea in which the eyes are borne at the end of long foot-stalks. PODOSOMATA (Gr. pous, foot ; soma, body). An order of ' Arachnida. POEPHAGA (Gr. poe, grass ; phago, I eat). A group of the Marsupials. POLLEX (Lat. the thumb). The innermost of the five normal digits of the anterior limb of the higher Vertebrates. In man, the thumb. POLYCYSTINA (Gr. po'us, many ; and kustis, a cyst). An order of Protozoa, with foraminated siliceous shells. POLYGASTRICA (Gr. polus ; and gaster, stomach). The name applied by Ehrenberg to the Infusoria, under the belief that' they possessed many stomachs. POLYPARY. The hard chitinous covering secreted by many of the Hydrozoa. POLYPE (Gr. polus, many ; pous, foot). Restricted to the single individual of a simple Actinozoon, such as a Sea-anemone, or to the separate zooids of a compound Actinozoon. Often applied indiscriminately to any of the Ccelen- lerata, or even to the Polyzoa. • 6;6 GLOSSARY. TOLYPIDE. The separate zooid of a Polyzoon. POLYPIDOM. The dermal system of a colony of a Hydrozoon, or Polyzoon. POLYPITE. The separate zooid of a Hydrozoon. POLYSTOME (Gr. polus, many ; and stoma, mouth). Having many mouths ; applied to the Acinetce amongst the Protozoa. POLYTHALAMOUS (Gr. polus ; and thalamos, chamber). Having many chani bers ; applied to the shells of Fomminifera and Cephalopoda. POLYZOA (Gr. polus ; and zob'n, animal). A division of the Molluscoida, com- prising compound animals, such as the Sea-mat. Sometimes called Bryozoa. POLYZOARIUM. The dermal system of the colony of a Polyzoon (= Polypi - dom). POKCELLANOUS. Of the texture of porcelain. PORIFERA (Lat. porus, a pore ; and/ero, I carry). Sometimes used to desig- nate the JForaminifcra, or the Sponges. POST-ANAL. Situated behind the anus. POST-(ESOPHAGEAL. Situated behind the gullet. POST-ORAL. Situated behind the mouth. PR^E-MAXILL^E. (See Intermaxillse). PR^EMOLARS (Lat. prce, before ; molares, the grinders). The molar teeth of Mammals which succeed the molars of the milk-set of teeth. lu man, the bicuspid teeth. PRjE-(ESOPHAGEAL. Situated in front of the gullet. PR^E-STERNUM. The anterior portion of the breast-bone, corresponding with the manubrium sterni of human anatomy, and extending as far as the point of articulation of the second rib. PRESSIROSTRES (Lat. pressus, compressed; rostrum, beak). A group of the Grallatorial Birds. PROBOSCIDEA (Lat. proboscis, the snout). The order of Mammals comprising the Elephants. PROBOSCIS (Lat. or Gr. the snout). Applied to the spiral trunk of Lepido}>- terous Insects, to the projecting mouth of certain Crinoids, and to the cen- tral polypite in the Medusce. PROCCELOUS (Gr. pro, before ; koilos, hollow). Applied to vertebrae, the bodies of which are hollow or concave in front. PROGLOTTIS (Gr. for the tip of the tongue). The generative segment or joint of a Tape-worm. PRO-LEGS. The false abdominal feet of Caterpillars. PRONATION (Lat. pronus, lying on the face, proue). The act of turning the palm of the hand downwards. PROPODIUM (Gr. pro, before ; pous, foot). The anterior part of the foot in Molluscs. PROSCOLEX (Gr. pro, before ; scolex, worm). The first embryonic stage of u Tape-worm. PROSOBRANCHIATA (Gr. proson, in advance of ; bragchia, a gill). A division of Gasteropodous Molluscs in which the gills are situated in advance of the heart. PROSOMA (Gr. pro, before ; soma, body). The anterior part of the body. PROTHORAX (Gr. pro ; and thorax, chest). The anterior ring of the thorax of insects. PROTOPHYTA (Gr. protos; and phuton, plant). The lowest division of plants. PROTOPLASM (Gr. protos/ &ndplasso, 1 mould). The elementary basis of or- ganised tissues. Sometimes used synonymously for the " sarcoid " of the Protozoa. PROTOPODITE (Gr. protos, first ; and pous, foot). The basal segment of the typical limb of a Crustacean. PROTOZOA (Gr. protos; and zoon, animal). The lowest division of the animal kingdom. PROVENTRICULUS (Lat. pro, in front of ; ventriculus, dim. of venter, belly). The cardiac portion of the stomach of Birds. PROXIMAL (Lat. proximus, next). The slowly-growing, comparatively-fixed extremity of a limb or of an organism. GLOSSARY. 677 PSALTERIUM (Lat. a stringed instrument). The third stomach of Ruminants. (See Omasum.) PSEUDEMBRYO (Gr. pseudos, falsity ; cmbruon, embryo). The larval form of an Echinoderm. PSEUDOBRANCHIA (Gr. pseudos, falsity ; bragchia, gill). A supplementary gill found in certain fishes, which receives arterialised blood only, and does not, therefore, assist in respiration. PSEUDOH^MAL (Gr. pseudos, falsity ; and haima, blood). Applied to the vas- cular system of Annelida. PSEUDO-HEARTS. Certain contractile cavities connected with the atrial system of Brachiopoda, and long considered to be hearts. PSEUDO-NAVICELL^E (Gr. pseudos, false ; and Navicula, a genus of Diatoms). The embryonic forms of the Gregarinidce, so called from their resemblance in shape to the Navicula. PSEUDOPODIA (Gr. pseudos ; and pous, foot). The extensions of the body- substance which are put forth by the Rhizoftoda at will, and which serve for locomotion and prehension. PSEUDOVA (Gr. pseudos ; Lat. ovum, egg). The egg-like bodies from which the young of the viviparous Aphis are produced. PTEROPODA (Gr. pteron, wing; zndpous, foot). A class of the Mollusca which swim by means of fins attached near the head. PTEROSAURIA (Gr. pteron, wing ; saura, lizard). An extinct order of Reptiles. PUBIS (Lat. pubes, hair). The share-bone ; one of the bones which enter into the composition of the pelvic arch of Vertebrates. POLMOGASTEROPODA (= Pulmonifera). PULMONARIA. A division of Arachnida which breathe by means of pulmo- nary sacs. PULMONATE. Possessing lungs. PULMONIFERA (Lat. pulmo, a lung ; and fero, I carry). The division of Mol- lusca which breathe by means of a pulmonary chamber. PUPA (Lat. a doll). The stage of an insect immediately preceding its appear- ance in a perfect condition. In the pupa-stage it is usually quiescent — when it is often called a "chrysalis ; " but it is sometimes active — when it is often called a " nymph." PYLORUS (Gr.' puloros, a gatekeeper). The valvular aperture between the stomach and the intestine. PYRIFORM (Lat. pyrus, a pear; and/orma, form). Pear-shaped. QUADRUMANA (Lat. quatuor, four ; manus, hand). The order of Mammals comprising the Apes, Monkeys, Baboons, Lemurs, &c. RADIATA (Lat. radius, a ray). Formerly applied to a large number of animals which are now placed in separate sub-kingdoms (e.g., the Ccdenterata, the Echinodermata, the Infusoria, &c.) RADIOLARIA (Lat. radius, a ray). A division of Protozoa. RADIUS (Lat. a spoke or ray). The innermost of the two bones of the fore- arm of the higher Vertebrates. It carries the thumb, when present, and corresponds with the tibia of the hind-limb. RAHUS (Lat. a branch). Applied to each half or branch of the lower jaw or mandible of Vertebrates. RAPTORES (Lat. rapto, I plunder). The order of the Birds of Prey. RASORES (Lat. rado, I scratch). The order of the Scratching Birds (Fowls, Pigeons, &c). RATITJE (Lat. rates, a raft). Applied by Huxley to the Cursorial Birds, which do not fly, and have therefore a raft-like sternum without any medium keel. RECTUM (Lat. rectus, straight). The terminal portion of the intestinal canal, opening at the surface of the body at the anus. REPTILIA (Lat. repto, I crawl). The class of the Vertebrata comprising the Tortoises, Snakes, Lizards, Crocodiles, &c. RETICULARIA (Lat. reticulitm,, a net). Employed by Dr Carpenter to desig- 6;8 GLOSSARY'. nate those Protozoa, such as the Foraminifera , in which the pseudopodia run into one another and form a network. RETICULUM (Lat. a net). The second division of the complex stomach of Ruminants, often called the " honeycomb bag." REVERSED. Applied to spiral univalves, in which the direction of the spiral is the reverse of the normal— i.e., sinistral. RHIZOPHAGA (Gr. rhiza, root ; phago, I eat). A group of the Marsupials. RHIZOPODA (Gr, rhiza, a root ; smdpous, foot). The division of Protozoa com- prising all those which are capable of emitting pseudopodia. RHYNCHOLITES (Gr. rhunchos, beak ; and lithos, stone). Beak-shaped fossils, consisting of the mandibles of Cephalopoda. RODENTIA (Lat. rodo, I gnaw). An order of the Mammals ; often called Glires (Lat. glis, a dormouse). ROSTRUM (Lat. rostrum, beak). The " beak " or suctorial organ formed by the appendages of the mouth in certain insects. ROTATORIA (=Rotifera). ' ROTIFERA (Lat. rota, wheel ; and fero, I carry). A class of the Scolecida (Annuloidd) characterised by a ciliated "trochal disc." RUGOSA (Lat. rugosus, wrinkled). An order of Corals. RUMEN (Lat. the throat). The first cavity of the complex stomach of Rumi- nants ; often called the "paunch." RUMINANTIA (Lat. ruminor, I chew the cud). The group of Hoofed Quadru- peds (Ungulata) which " ruminate " or chew the cud. SACRUM. The vertebrae (usually anchylosed) which unite with the haunch- bones (ilia) to form the pelvis. SAND-CANAL (— STONE-CANAL). The tube by which water is conveyed from the exterior to the ambulacral system of the Echinodermata. SARCODE (Gr. sarx, flesh ; eidos, form). The jelly-like substance of which the bodies of the Protozoa are composed. It is an albuminous body containing oil-granules, and is sometimes called "animal protoplasm." SARCOIDS (Gr. sarx; and eidos, form). The separate amoebiform particles which in the aggregate make up the "flesh " of a Sponge. SAURIA (Gr. saura, a lizard). Any lizard-like Reptile is often spoken of as a "Saurian ; " but the term is sometimes restricted to the Crocodiles alone, or to the Crocodiles and Lacertilians. SAUROBATRACHIA (Gr. saura; batrachos, frog). Sometimes applied to the order of the tailed Amphibians (Urodela). SAUROPSIDA (Gr. saura ; and opsis, appearance). The name given by Huxley to the two classes of the Birds and Reptiles collectively. .SAUROPTERYGIA (Gr. saura; pterux, wing). An extinct order of Reptiles, called by Huxley Plesiosauria, from the typical genus Plesiosaurus. SAURUR^: (Gr. saura; oura, tail). The extinct order of Birds comprising only the Archceopteryx. SCANSORES (Lat. scando, I climb). The order of the Climbing Birds (Parrots, Woodpeckers, &c.) SCAPHOGNATHITE (Gr. skaphos, boat ; and gnathos, jaw). The boat-shaped appendage (epipodite) of the second pair of maxillae in the Lobster ; the function of which is to spoon out the water from the branchial chamber. SCAPULA (Lat. for shoulder-blade). The shoulder-blade of the pectoral arch of Vertebrates ; in a restricted sense, the row of plates in the cup of Crlnoids, which give origin to the arms, and are usually called the " axillary radials." SCLERENCHYMA (Gr. skleros, hard; and enchuma, tissue). The calcareous tissue of which a coral is composed. SCLERITES (Gr. skleros). The calcareous spicules which are scattered in the soft tissues of certain Actinozoa. SCLEROBASIC (Gr. skleros, hard ; basis, pedestal). The coral which is produced by the outer surface of the integument in certain Actinozoa (e.g. , Red Coral), and forms a solid axis which is invested by the soft parts of the animal. It is called "foot-secretion " by Mr Dana. GLOSSARY. 679 ScLERODERjtfic (Gr. sUeros ; and derma, skin). Applied to the corallum which is deposited within the tissues of certain Actinozoa, aud is called " tissue-secretion" by Mr Dana. SCLEROTIC (Gr. skleros, hard). The outer dense fibrous coat of the eye. SCOLECIDA (Gr. skolex, worm). A division of the Annuloida. SCOLEX (Gr. skolex). The embryonic stage of a Tape-worm, formerly known as a "Cystic Worm." SCUTA (Lat. scutum, a shield). Applied to any shield-like plates ; especially to those which are developed in the integument of many Keptiles. SELACHIA or SELACHII (Gr. selachos, a cartilaginous fish, probably a shark). The sub-order of Elasmobranchii, comprising the Sharks and Dog-fishes. SEPIOSTAIRE. The internal shell of the Sepia, commonly known as the " cuttle-bone." SEPTA. Partitions. SERPENTIFORM. .Resembling a serpent in shape. SERTULARIDA (Lat. sertum, a wreath). An order of Hydrozna. SESSILE (Lat. sedo, I sit). Not supported upon a stalk or peduncle ; attached by a base. SET.E (Lat. bristles). Bristles, or long stiff hairs. SETIFEROUS. Supporting bristles. SETIGEROUS (= Setiferous). SETOSE. Bristly. SILICEOUS (Lat. silex, flint). Composed of flint. SINISTRAL (Lat. sinistra, the left hand). Left-handed ; applied to the direc- tion of the spiral in certain shells, which are said to be "reversed." SINUS (Lat. sinus, a bay). A dilated vein or blood-receptacle. SIPHON (Gr. siphon, a tube). Applied to the respiratory tubes in the Mol- lusca ; also to other tubes of different functions. SIPHONOPHORA (Gr. siphon ; and phero, I carry). A division of the Hydrozoa, comprising the Oceanic forms (Calycophoridce and Physophoridce). SIPHONOSTOMATA (Gr. siphon ; and stuma, mouth). The division of Gas- teropodous Molluscs, in which the aperture of the shell is not " entire," but possesses a notch or tube for the emission of the respiratory siphon. SIPHUNCLE (Lat. siphunculus, a little tube). The tube which connects together the various chambers of the shell of certain Cephalopoda (e.y., the Pearly Nautilus). SIPHUNCULOIDEA (Lat. siphunculus, a little siphon). A class of Anarthropoda (Anmdosa). SIRENIA (Gr. seiren, a mermaid). The order of Mammalia comprising the Dugongs and Manatees. SOLIDUNGULA (Lat. solidus, solid; ungula, a hoof). The group of Hoofed Quadrupeds comprising the Horse, Ass, and Zebra, in which each foot has only a single solid hoof. Often called Solipedia. SOMATIC (Gr. soma, body). Connected with the body. SOMATOCYST (Gr. soma ; and kustis, a cyst). A peculiar cavity in the ccenosarc of the Calycophoridce (Hydrozoa). SOMITE (Gr. soma). A single segment in the body of an Articulate animal. SPERMARIUM. The organ in which spermatozoa are produced. SPERMATOPHORES (Gr. sperma, seed ; phero, I carry). The cylindrical cap- sules of the Cephalopoda, which carry the spermatozoa ; sometimes called the "moving filaments of Needham." SPERMATOZOA (Gr. sperma, seed ; and zoon, animal). The microscopic fila- ments which form the essential generative element of the male. SPICULA (Lat. spiculum, a point). Pointed needle-shaped bodies. SPINNERETS. The organ by means of which Spiders and Caterpillars spin threads. SPIRACLES (Lat. spiro, I breathe). The breathing-pores, or apertures of the breathing-tubes (tracheae) of Insects. Also the single nostril of the Hag- fishes, the "blow-hole" of Cetaceans, &c. SPLANCHNOSKELETON (Gr. splagchna, viscera; skeletos, dry). The bard 6 So GLOSSARY. structures occasionally developed in connection with the internal organs or viscera. SPONGE-PARTICLES. (See Sarcoids. ) SPONGIDA (Gr. spoggos, a sponge). The division of Protozoa commonly known as sponges. SPORES (Gr. spora, seed). Germs, usually of plants ; in a restricted sense, the reproductive "gemmules " of certain Sponges. SPOROSACS (Gr. spora, seed; and sakkos, a bag). The simple generative buds of certain ffydrozoa, in which the medusoid structure is not deve- loped. SQUAMATA (Lat. squama, a scale). The division of Reptiles comprising the Ophidia and LacertiHa in which the integument develops horny scales, but there are no dermal ossifications. STATOBLASTS (Gr. statos, stationary ; blastos, bud). Certain reproductive buds developed in the interior of Polyzoa, but not liberated until the death of the parent organism. STEGANOPHTHALMATA (Gr. steganos, covered ; and ophthalmos, the eye). Ap- plied by Edward Forbes to certain Medusce, in which the sense-organs ("marginal bodies") are protected by a sort of hood. The Steganophthal- mata are now separated from the true Medusidce, and placed in a separate division under the name Lucernarida. STELLERIDA (Lat. stella, star). Sometimes employed to designate the order of the Star-fishes. • STELLIFORM. Star-shaped. STEMMATA (Gr. stemma, garland). The simple eyes, or " ocelli," of certain animals, such as Insects, Spiders, and Crustacea. STERNUM (Gr. sternon). The breast-bone. STIGMATA. The breathing- pores in Insects and Arachnida. STOLON (Gr. stolos, a sending forth). Offshoots.— The connecting processes of sarcode, in Foraminifera ; the connectiug tube in the social Ascidiattx ; the processes sent out by the coenosarc of certain Actinozoa. STOMAPODA (Gr. stoma, mouth ; pous, foot). An order of Crustacea. STOMATODE (Gr. stoma). Possessing a mouth. The Infusoria are thus often called the Stomatode Protozoa. STREPSIPTERA (Gr. strepho, I twist ; and ptcron, wing). An order of Insects in which the anterior wings are represented by twisted rudiments. STREPSIRHINA (Gr. strepho, I twist ; rhines, nostrils). A group of the Quad- rumana, often spoken of as Prosimice. STROBILA (Gr. strobilos, a top, or fir-cone). The adult Tape-worm with its generative segments or proglottides ; also applied to one of the stages in the life-history of the Lucernarida. STYLIFORM (Lat. stylus, a pointed instrument ; forma, form). Pointed in shape. SUB-CALCAREOUS. Somewhat calcareous. SUB-CENTRAL. Nearly central, but not quite. SUB-PEDUNCULATE. Supported upon a very short stem. SUB-SESSILE. Nearly sessile, or without a stalk. SUPINATION (Lat. supinus, lying with the face upwards). The act of turning the hand with the palm upwards. SUTURE (Lat. suo, I sew). The line of junction of two parts which are immovably connected together. Applied to the line where the whorls of a univalve shell join one another ; also to the lines made upon the exterior of the shell of a chambered Ceplialopod by the margins of the septa. SWIMMERETS. The limbs of Crustacea, which are adapted for swimming. SYMPHYSIS (Gr. sumphusis, a growing together). Union of two bones in which there is no motion, or but a very limited amount. SYNAPTICUL^E (Gr. sunapto, I fasten together). Transverse props sometimes found in Corals, extending across the loculi like the bars of a grate. SYSTOLE (Gr. sustello, I contract). Applied to the contraction of any contrac- tile cavity, especially the heart. GLOSSARY.. 68 1 TABULA (Lat. tabula, a tablet). Horizontal plates or floors found in some Corals, extending across the cavity of the "theca," from side to side. TACTILE (Lat. tango, I touch). Connected with the sense of touch. T^ENIADA (Gr. tainia, a ribbon). The division of Scolecida comprising the Tape-worms. T.ENIOID (Gr. tainia; and cidos, form). Ribbon- shaped, like a Tape-worm. TARSO-METATAKSUS. The single bone in the leg of Birds produced by the union and anchylosis of the lower and distal portion of the tarsus with the whole of the metatarsus. TARSUS (Gr. tarsos, the flat of the foot). The small bones which form the ankle (or "instep" of man), and which correspond with the wrist (carpus) of the anterior limb. TECTIBRANCHIATA (Lat. tectus, covered ; and Gr. bragchia, gills). A division of Opisthobranchiate Gasteropoda in which the gills are protected by the mantle. TEGUMENTARY (Lat. tegnmentum, a covering). Connected with the integu- ment or skin. TELEOSTEI (Gr. teleios, perfect; osteon, bone). The order of the "Bony" Fishes. TELSON (Gr. telson, a limit). The last joint in the abdomen of Crustacea ; variously regarded as a segment without appendages, or as an azygous appendage. TENUIROSTRES (Lat. tcnuis, slender ; rostrum, beak). A group of the Perch- ing Birds characterised by their slender beaks. TERGUM (Lat. for back). The dorsal arc of the somite of an Arthropod. TERRICOLA (Lat. terra, earth ; and colo, I inhabit). Employed occasionally to designate the Earth-worms (Lumbricidce). TEST (Lat. testa, shell). The shell of Mollusca, which are for this reason sometimes called "Testacea;" also, the calcareous case of Echinoderms ; also, the thick leathery outer tunic in the Tunicata. TESTACEOUS. Provided with a shell or hard covering. TESTIS (Lat. testis, the testicle). The organ in the male animal which pro- duces the generative fluid or semen. TETRABRANCHIATA (Gr. tetra, four; bragchia, gill). The order of Cephalopoda characterised by the possession of four gills. THALASSICOLLIDA (Gr. thalassa, sea; kolla, glue). A division of Protozoa. THECA (Gr. theke, a sheath). A sheath or receptacle. THECOSOMATA (Gr. theke; and soma, body). A division of Pteropodous Molluscs, in which the body is protected by an external shell. THERIOMOKPHA (Gr. ther, beast; rnorphe, shape). Applied by Owen to the order of the Tail-less Amphibians (Anoura). THORAX (Gr. a breastplate). The chest. THREAD-CELLS. (See Cnidse). THYSANURA (Gr. thusanoi, fringes; and oura, tail). An order of Apterous Insects. TIBIA (Lat. a flute). The shin-bone, being the innermost of the two bones of the leg, and corresponding with the radius in the anterior extremity. ToTiPALMATiE (Lat. lotus, whole ; palma, the palm of the hand). A group of "Wading Birds in which the hallux is united to the other toes by mem- brane, so that the feet are completely webbed. TRACHEA (Gr. tracheia, the rough wind-pipe). The tube which conveys air to the lungs in the air-breathing Vertebrates. TRACHEA. The breathing-tubes of Insects and other articulate animals. TRACHEARIA. The division of Arachnidq which breathe by means of tra- cheae. TREMATODA (Gr. trema, a pore). An order of Scolecida. TRICHOCYSTS (Gr. thrix, hair ; and kustis, a cyst). Peculiar cells found in certain Infusoria, and very nearly identical with the "thread-cells" of Coslenterata. TRILOBITA (Gr. treis, three ; lobos, a lobe). An extinct order of Crustaceans. TRITOZOOID (Gr. tritos, third;. soon, animal; and eidos, form). The zooid 682 -GLOSSARY. produced by a deuterozooid ; that is to say, a zooid of the third genera- tion. TROCHAL (Gr. trochos, a wheel). Wheel-shaped; applied to the ciliated disc of the Rotifera. TROCHANTER (Gr. trecho, I turn). A process of the upper part of the thigh- bone (femur) to which are attached the muscles which rotate the limb. There may be two, or even three, trochanters present. TROCHOID (Gr. trochos, a wheel ; and eidos, form). Conical with a flat base ; applied to the shells of Foraminifera and Univalve Molluscs. TROPHI (Gr. trophos, a nourisher). The parts of the mouth in insects whicli are concerned in the acquisition and preparation of food. Often called " instrumenta cibaria." TROPHOSOME (Gr. trepho, I nourish ; and soma, body). Applied collectively to the assemblage of the nutritive zooids of any Hydrozoon. TRUNCATED (Lat. trunco, I shorten). Abruptly cut off ; applied to univalve shells, the apex of which breaks off, so that the shell becomes "decol- lated." TUBICOLA (Lat. tuba, a tube ; and colo, I inhabit). The order of Annelida which construct a tubular case in which they protect themselves. TUBICOLOUS. Inhabiting a tube. TUNICATA (Lat. tunica, a cloak). A class of Molluscoida which are enveloped in a tough leathery case or "test." TURBELLARIA (Lat. turbo, I disturb). An order of Scolecida. TURBINATED (Lat. turbo, a top). Top-shaped ; conical with a round base. ULNA (Gr. olene, the elbow). The outermost of the two bones of the fore- arm, corresponding with theJiMa of the hind-limb. UMBELLATE (Lat. umbella, a parasol). Forming an umbel— i.e., a number of nearly equal radii all proceeding from one point. UMBILICUS (Lat. for navel). The aperture seen at the base of the axis of certain univalve shells, which are then said to be "perforated" or " urn- bilicated." UMBO (Lat. the boss of a shield). The beak of a bivalve shell. UMBRELLA. The contractile disc of one of the Lucernarida. UNCINATE (Lat. uncinus, a hook). Provided with hooks or bent spines. UNGUICULATE (Lat. unguis, nail). Furnished with claws. UNGULATA (Lat. ungula, hoof). The order of Mammals comprising the Hoofed Quadrupeds. UNGULATE. Furnished with expanded nails constituting hoofs. UNILOCULAR (Lat. unus, one ; and loculus, a little purse). Possessing a single cavity or chamber. Applied to the shells of Foraminifera and Mollusca. UNIVALVE (Lat. unus, one ; valvce, folding-doors). A shell composed of a single piece or valve. URODELA (Gr. oura, tail ; ddos, visible). The order of the tailed Amphi- bians (Newts, &c.) URTICATING CELLS (Lat. urtica, a nettle). (See Cnidae). VACUOLES (Lat. vacuus, empty). The little cavities formed in the interior of many of the Protozoa by the presence of little particles of food, usually surrounded by a little water. These are properly called " food-vacuoles," and were supposed to be stomachs by Ehrenberg. Also the clear spaces which are often seen in the tissues of many Ccelenterata. VARICES (Lat. varix, a dilated vein). The ridges or spinose lines which mark the former position of the mouth in certain univalve shells. VASCULAR (Lat. vas, a vessel). Connected with the circulatory system. VELUM (Lat. a sail). The membrane which surrounds and partially closes the mouth of the " disc " of Medusa, or medusiform gonophores. VENTRAL (Lat. venter, the stomach). Relating to the inferior surface of the body. VENTRICLE (Lat. dim. of venter, stomach). Applied to one of the cavities of the heart, which receives blood from the auricle. GLOSSARY. 683 VERMES (Lat. rermis, a worm). Sometimes employed at the present day in the same, or very nearly the same, sense as Annuloida, or as Annuloida plus the Anarthropoda. VERMIFORM (Lat. vermis, worm; and forma, form). "Worm-like. VERTEBRA (Lat. verto, I turn). One of the bony segments of the vertebral column or back-bone. VERTEBRATA (Lat. vertebra, a bone of the back, from vcrtere, to turn). The division of the Animal Kingdom roughly characterised by the possession of a back-bone. VESICLE (Lat. vesica, a bladder). A little sac or cyst. VIBRACULA (Lat. vibro, I shake). Long filamentous appendages found in many Polyzoa. VIBRIONES (Lat. vibro, I shake). The little moving filaments developed in organic infusions. VIPERINA (Lat. vipcra, a viper). A group of the Snakes. VIVIPAROUS (Lat. vivus, alive ; and pario, I bring forth). Bringing forth young alive. WHORL. The spiral turn of a univalve shell. XIPHISTERNUM (Gr. xiphos, sword ; sternon, breast-bone). The inferior or posterior segment of the sternum, corresponding with the " xiphoid carti- lage " of human antimony. XIPHOSURA (Gr. xiphos, a sword ; and oura, tail). An order of Crustacea, comprising the Limuli or King- Crabs, characterised by their long sword- like tails. X YLOPHAGOUS (Gr. xulon, wood ; and phaao, I eat). Eating wood ; applied to certain Mollusca. Zoom (Gr. zoon, animal ; and eidos, like). The more or less completely inde- pendent organisms, produced by gemmation or fission, whether these remain attached to one another or are detached and set free. ZOOPHYTE (Gr. zoon, animal ; phuton, plant). Loosely applied to many plant- like animals, such as Sponges, Corals, Sea-anemones, Sea-mats, &c. ZOOSPORES (Gr. zoon, animal ; and spora, seed). The ciliated locomotive germs of some of the lowest forms of plants (Protophyta). INDEX. AARDV.ARK, 569. A an) wolf. 613. Abdominalia (Cirn'pedia), 233 ; (Fishes), 40P. Abranchiata (Vertebrata), 383. Abyla, 105. Acalepkce, 110. Acanthocephala, 183, 190 ; characters of, 18; distribution of, in space, 18'J ; in time, ib2. Asteroid Polypes, 137. Astomata, 49. Asratidm, 150,152. Astrogonium, 182. Astropecten, 168, 182. Astropectinidie, 168. Astrophydia, 170. Astrophyton, 170. .AteZes, «33, t>3t. Athecata, 93. Atherura, «19. Athorybiad.e, 109. Atkyris, 316. Atlanta, 341. Atlantidce, 338, 341. Atolls, 149, 150. Atrial system (Brachiopodd), 294, 314. Atrium (Tunicata), 308. Xttcbem'a, 591. 4ic/ojwid:e, 512. Aulosteges, 317. Aurelia, 120. Aurelia, 275. Auricula, 341. Auricularia, 178. Auriculidce, 339, 311. Autophagi, 4«6. -dues, 383: general characters of, 480; feathers of. 48! ; vertebral column of, 4S3 ; beq. Av!cula, 327. Avicularia, 302, 304. Aviculidce, 326,327. Avocet, 507. Axinus, 327. Axolotl, 436, 437. Aye-Aye, 631. BABOON, 635. Babyroussa, 587. Bacteria, 3', 38. liactrites, 361. Baculites, 356, 357, 358, 361. Badger, 610. £alct;na, 573, 576. Baltmide, 573, 676. Balcenoptera, 576. Balancers, 269, 284 Balanidie, 226, 229, 231, 232; distribution of, in time, 253. Balanus, 231,232. Ba/earica, 510. Baleen, 513, 574, 575, 5J. Balistide, 412. Bandicoot, 562. Banxring, 628. Barrier-reefs, 148, 150. Barnacles, 229, 231, 232. Jjascanion, 458. Jiathybius, 11, 64. Bathycrinus, 180. atides. 422, 423. Batrachia, 438. Bats, 540, 541, 513, 554, 623, et sea. Bear, 6 8, 609, 648. Beaver, 620. Bee-eaters, 528. Bees, parthenogenesis of, 32,33; communi- ties of, 288 Belemnites, structure of, 352. Bdemnitidce, 35V, 3o7, 3(31. Belemnitella, 358. Belemniteuthis, 358. Belinurus, 254. Bellerophina, 359. Bellerophon, 341, 359. Belodon, 470. Beloptera, 358. Beluga, 417. Benturong, 610. Beroe, 146. Beroidce, 146. Bimana, 654 ; general characters of, 037. Biology, definition of, 1. Bioplasm, 5. Bipes, 461, 462. Bipinnaria. 167. Bird-lice, 278. Birds of Prey, 528. Bird's-head process, 302. Birgus, 249. Bison, 598. Bivalve Shell-fish, 321. Bladder, contractile, of Rotifera, 20n. Blastoidca, 157 ; general characters of, 176 ; distribution of, m time, 181. Blattina *8i>. Blennid2 '. Casteroidce, 620. Casuarius, 513. Catarhina, 631, 631. eatodonttdiF, 573, 577. Cats, 54 », 614, 616. C'a»ta, 619. Cavicnrnia, 531, 595. Cavid.n, 619. Cebidce, 633. C'e&HS, 633. Cecidomyia, 285. Cells, of Polyzoa. 299, 302. Cellulose, in Ascidians, 10, 307. Cement gland, of Cirripedes, 229, 230. Centetes, 628. Centipadeb, 26% 266. Centrocerus, 51 6. Cephalaspis, 408, 417, 428. Cephalobranchiata (see Tubicola). Cephalopoda, 294, 295, 296, 32 » ; general characters of, 344 ; arms of, 344, 345 ; suckers of, 345 ; funnel of, tf> ; hik bag of, 346; mandibles of, 345; digestive system of, 346 ; branchiae of, ib. ; ner- vous system of, 347 ; reproduction of, ib. et seq ; skeleton of, 349; divisions of, ib. ; distribution of, in time, 36>». Cephalophora (Mollusca), 320. Cephaloptera, 423. Cephalothorax, of Crustacea, 22) ; of Ar- achnida, 255. Cephaluna, 227. Cephea, UO. Cerastes, 458. Ceratiocaris, 253. Ceratitcs, 350, 353, 361. 688 INDKX. Ceratodus, 424, 426. Cercocebus, 630, 634. Cercolabes, 619. Cercoleptes, 6i>9 Cercopithecus, 634. Cere, of Birds, 491, 498. Cerianthits, 12s, 14'.. Cerithiadce, 335, 339. Cerithium, 339. Certhia, 526. Certhidce, 526. fervid* 591, 592, 553, 645. fmws, 593. Ceryle, 52 S. Cestidce, 146. Cestoidea (see Tatniada). Cedracion, 422 42 •«. Cestraphori, 422, 429. Cestum, J46. C^acea, 533, 539, 540. 541, 542T 543, 547, 548, 649, 651, 553 ; general characters of, 572 ; groups of, 673 ; distribution of, in time, 644. Cetiosaurus, 471. Cetonia, 292. Choeropotamus, 645. Choeropsis, 5%f<. Chceropus, £63. Chatognatha. 216. ChoKtonotus, Iii9. Chalcidce, 462. Chama, 327. Chameleo, 466. Chameleontidce, 468. Chamidue, 327. Charadriidce, 511. Cheetah, 616. Cheilostomata, 306, 318. Cheiromydce, 631. Cheiromys, 631. Cheironectes, 663. Cheiroptera, 550, 554 ; general characters, 623 ; divisions of, 624 ; distribution of, in time, 648. f'heirothenum, 442. Chelae, 2M ;of King-crab, 241 ; of Scorpion, 256, 261 ; of Book-scorpion, 261. Chelicerse, 25*5, 262. Chelichnus, 453. Vhdifcr, 260. Chelonia, 448 ; general characters of, 449, subdivisions of, 451 ; distribution of, in time, 453. Chdoniidv, 451, 453. Chelonobatrachia, 438 (see Anoura). Chelydidce, 449. Chelydra, 4=)2. Chtmnitzia, 339. Chilognatha, 267. Chilopoda, 266, 267. f.'Aimtera, 420, 42i. Chimoeridce, 420. Chimpanzee, 637. Chinchilla, 61^. Chirutes, 460. 462. (?M(m, 296, 340. Chitonidce, 336, 340. Chlamydosaurus, 465. Chlamyphorus, 567, 568. Chlorophyll in animals, 10. Chol-ripedia\ Cirripedia, 2'26 ; general characters of, 229 ; development of, 230 ; shell of, 229, 231, 232 ; reproduction of. 2"2 : divisions of, 233 ; distribution of. iu time, 253. C-irrostomi, 400 (see Pharyngoltranchii . Civet, 6ll. Cladocera, 226 ; characters of, 236. Clamatores, 515. Clangula, 50(3. Classification, 20. Clausilia, 3tl. Clavatella, 96. Clavellinidce, 311. Cleodora, 342, 343. Clepsine, 209, 216. WwdcB, 343. Climacograpsus, 124. CWo, 343. Cliona, 74. Clitellum, 209. Cloaca, ofEotifera, 210 ; of Instct.a, 271 ; of Tunicata, 308; of Amphibia, 4:31, 433 ; of Reptiles. 446 ; of Birds, 493 ; of Monotremes, 551, 555. Clotho, 458. Clupeidce, 409. Clypeastridce, 163. Clytia, 96. Cnidse, 87. Coati, 609. Cobra, 459. Coccidce, 2T9. Coccoliths, 64. Coccospheres, 64. Coccosteus, 409, 418, 428. Coccothraustes, 525. Coccus, 279. Cochliodus, 422. Cocoon, 275. 'Cwlenterata, 17, 84; characters of, 85 J thread-cells of, 87 J divisions of, 88. Cceloyenys, 619. Coenenchyma, 131. Ccencecium, 300, 302. INDEX. 689 Cocnosarc. 89 ; of Oceanic Hydrozoa, 104 ; of Physalia, 110; of Veldia, llo. Coleoptera, 269, 273 ; mouth of, 270 ; char- acters of, 29J ; sections of, 291. Collosphara, 68, 69. Colobus, 634. Colossochelys, 453. Coluber, 458. Colubrina, 457, 458. Columba, 518. Columbacei, 515, 517. Columbidce, 518. Columella, of Corals, 131 ; of the shells of Gasteropoda, 334. Column, of Actinidve, 128. Columnar -ia, ]34. Colymbidce, 504. Colymbus, 490, 504. Comarocystites, 176. Comatula, 174, 175 ; distribution of, in time, 181. Compsognathus, 479. Conchicolites, 2 1 6. Conchifera, 326 (see Lamell ibranchi- ata). Condylura, 627. Conidw, 335, 339. Conirostres, 523. Conocardium, 328. Conodonts, 427. Conosmilia, 151. Conovulus, 341. Contractile vesicle, of Protozoa, 49 ; of Amoeba, 55 ; of Paramcecium, 78 ; of Vorticella 80 ; of Epistylis, 82. Conularia, 343, 359. CVmws, 339. Coot, 508. Copepoda, 227 ; characters of, 236. Coral, 130 (see Corallum). Corallite, 131. Corallium, 140, 147, 151. Corallum, 130 ; distinctions between dif- ferent coralla. 142. Coral-reefs, 147, e£ se^. Cordylophora, 93, 96 ; gonophores of, 94 ; distribution of, 123. Cornulites, 216. Cortical layer, of Infusoria, 78 ; of JVbc- ttZwca. 83. CorvidcK, 524. Coryne, 94, 96. C'orynida, 93 ; characters of, 93 ; repro- duction of, 94 ; types of, 97, 98 ; de- velopment of, 97 ; distribution of, 123. Corynoides, 123. Coryomorpha, 93, 98. C'ossus, 2&6. Coturnix. 516. Coypu, 620. Cracidce, 517. Crane, 509. Crane-fly, 285. Crania, 313, 317, 319. Craniadce, 315, 317. Craspeda, 129. Crax, 517. Crex, 508. Cribdla, 164, 167. Cricetus, 621. Crinoidea, 156, 157 ; general characters of, 173, e£ seg.; distribution of, in space, 189 ; in time, 181 ; structure of calyx in fossil forms of, ib. Crioceras, 356, 357. Cristatella, 302. Crocodilia, 445, 446, 448 ; general charac- ters of, 468 ; divisions of, 469 ; distribu- tion of, in time, 470. Crocodiliis, 469, 470. Crop of Insects, 271 ; of Birds, 491. Cross-bill, 525. Crossopteryffidce, 415. Crotalidce, 457. Crotalus, 457. Crust, of Crustacea, 219 ; of Trilobites, 238. Crustacea, 219 ; general characters of, 219, 220 ; Morphology of a typical Crus- tacean, 222, et seq. ; divisions of, 225 ; distribution of, in space, 252; in time 252, 253. Cryptochiton, 340. Cryptoniscus, 245. Cryptophialus, 233. Crystalline stylet, 324.. Ctenocyst, 144. Ctenodiscus, 165. Ctenoid scales of Fishes, 386. C'tenophora, 126, 127 ; characters of, 142 ; homologies of, 145 ; divisions of, 146 ; distribution of, 147. Ctenophoral canals, 144, 145. Ctenophores, 143, 144. Ctenostomata, 299, 306. Cuckoo, 520. CuculidcK, 520. Cucullcea, 327. Culex, 285. Culicidce, 284. Cultdlus, 328. Cultirostres, 5C9. Curculio, 292. Curlew, 510. Cursor 'es, 495, 500 ; characters of, 511."' Cuticle, of Amoeba, 54; of Infusoria, 73 ; of Noctiluca, 83. Cuttle-bone, 349, 35ft. Cuttle-fishes, 344, 345, 346, 347, 350. Cyamus. 243. Cyanea,'u8, 120. Cyathaxonia, 131. Cyathaxonido', 151. Cyathophyllida.', 151. Cydadida?, 328. Cyclas, 325, 328. Cycloid scales of Fishes, 386. CydolabridoK, 411. Cydophorus, 341. Cyclophthalmus, 264. Cydopoidea, 221. Cyclops, 235. Cydostoma, 341. C'ydostomata (Polyzoa), 306, 318 ; (Fishes), 402. Cyclostomi (Fishes), 402. CydostomidcK (Gasteropoda), 33P, 341. Cydippe, 142. Cygnidce, 506. Cygnus, 506. Cylichna, 341. Cymothoa, 244. Cynocephalus, 635. Cynomys, 622. Cynthia, 307. 2 X 690 INDEX. Cyprcea, 839. Cyprceidce, 335, 339. Cypridina, 234. Cyprina, 328. CyprinidcK (Mollusca), 327 ; (Fishes), 409. Cypris, 234. Cypselidce, 527. Cyrena, 328. Cyrtta, 316. Cyrtoceras, 356, 358, 361. Cyrtolites, 359. Cysticerci. 187, 188. Cystic Worms, 184, 186, 188. CystiphyllidiK, 151. Cystiphyllum, 14). Cystoidea, 157 ; general characters of, 175 ; distribution of, in time, 182.. Cy there. 234. C'ytherea, 321, 328. Dacelo, 528. Uactylethraj 441. Z>acfy£op(!ertt*,<.393. Dafila,, 576. Dakosaurus,- 471. Dama, 694. Daphnia, 237. ])arwinian iTheory, 41. Dasypodidx, 565, 5ti7. Dasyprocta, 619. Dasypus, 567. Dasyurus, 564. DecapodA (Crustacea), 246 ; distribution of, in time, 254 ; (Cephalopoda), 350, 351. Decollated shells, 297. Deer, 591, 593, 594, Deinosauria (see Dinosauria). Deinotheriumt 6uO, 603, 646. Delphinidce, 577, 579. Delphinula, 340. Ddphinus, 578. Demodex, 260. Dendroccela, 192. Dendrograpsus, 121, 12 1. Dendrolagus, 560. Dendrophyllia, 132. Dendrostyles, 120. Dental formula, 546. DentaUdce, 336, 340. Dentalina, 62. Dentalium, 340; shell of, 333; position of, 340. Dentirostres, 523, 525. Development, 35 ; Retrograde, 37 ; of Gregarinidae, 61; of Foraminifera. 61 ; of Hydra, 92 ; of Corynida, 97 ; of Sertularida, IQI;ofCalyCophoridce, 105 ; of Physophoridce, 108 ; of Medusidoe, 113; of Lucernarida, 116; of Actinidin, 1-29; of Pleurobrachia, 145; of Echino- dermata, 155; of Echinoidea, 157; of Asteroidea, 167; of Ophiuroidea, 169; ofComatula, l75;ofHolothuroidea, 178; of Toeniada, 185; of Trematoda, 190 ; of Nemertida, 193 ; of J canthocephala, 394; of Trichina, 196; of the Guinea- Worm, t'6. ; of Tubicolar Annelides, 211 ; of Errant Annelides, 215 ; of Crustacea, 22') ; of Ichthyophthira. 227; of Rhizoce- phala, 228; of Cirripedia, 229; of Cope- poda, 235; of Ostracoda, 234; of Phyllo- poda, 237; ofTrilobita, 239 ; of Limulus, 241; of Isopoda, 244; of Amphipoda, 243; of Stomapoda, 245; of Macrura, 246 ; of ylnomwra, 249; of Brachyura, 251; of Myriapoda, 2d6 ; of Insecta, 273, e« se^. ; ofPolyzoa, 305 ; of Tunicata, 310 ; of ttrachiopoda, 315 ; of Lamelli- branchiat'i, 325; of Gasteropoda, 332; of Amphibia, 431, e£ sew. Dextral shells, 297. Dibranchiata (Cephalopoda), 350 ; charac- ters of, i6. ; divisions of. i6. ; distribution of, in time, 361. Dicer as, 327. Dicoryne, 96. Dicotyles, 587, 649. Dicranograpsus, 124. Dictyonema, 12 1. Dicynodon, 474. Dicynodontia, 474. Didelphia, 551, 557. Didelphidie, 557, 5')3. Didelphys, 557, 563, 641 Didunculus, 519. ZJi'dws, 518 Didymograpsus, 124. Diffltiffia, 57. Digitigrada, 605, 610. Dimerasomala, 261. Dimorphodon, 477. Dimyaria, 326. Dinabolus, 317. Dinophis, 460. Dinornis, 535. Dinosauria, 477, 478. Diomedea, 504. Diphydce, 106. Diphyes, 106. Diphyllidia, 341. Diphyozooids, 106. Diplacanthus, 428. Diplodonta, 328. Diplograpsus, 122, 124. Diplostomum, 191. Dipnoi, 424, 428 ; general characters of. 424, e£ seg. Dipodidce, 621. Diprotodon, 642. Diptera, 271, 275 ; mouth of, 271 ; char- acters of, 284. Dipterus, 428. -Dipws, 621. Discina. 317, 319. Discinidce, 315, 3l7. Discophora (Medusce), 90; cliaracters of, 111, eiseg. Discophora (Leeches^— see Hirudinea. Dissepiments of Corals, 134. Distal, 89. Distoma, 190, 191. Distribution, geographical. 43; bathy- metrical, 16. ; geological, 44. Dithyrocaris, 253. Dodo, 518, 519, 536. Dog, 544, 613. Dog-fishes, 422. Dolabella, 341. Doliolum, 309. Dolphins, 538, 542, 549, 578, 644. Dorcatherium 614. Doridce, 336, 3 11. INDEX. 691 Doris, 337, 341. Dormice, 691. Dorsal vessel, of Insects, 272. Dorsibranchiata, 213 (see Errant ia). Draco, 466, 476. Dracunculus, 196. Dreissena, 327. Dromaius, 512, 513. Dromatherium, 640, 615. Dromedary, 591. Dromia, 249. Di-yopithecus, 648. Duck, 498, 506. Duck-mole, 539, 540, 545, 548, 55', 555. 556. Dugong. 539, 552, 570, 571. Dytiscidie, 276. EAGLE, 530. Ecderon, 125. Echidna, 540, 545, 548, 549, 552, 556, 557. Echinidie, 1(5:1 Echinococci, 189. Echinoconid(e, 163. Echinodermata, 154 ; general characters of, 15 i; development of, 156; divisions of, 157; distribution, of, in time, 181, et seq. Echinodon, 467. Echinoidea, 156 ; characters of, 157 ; test of, ib. ; ambulacral system of, 160 ; digestive system of, Itjl ; families of. 163; distribution of, in space, 180 ; in time, 182. Echinoneid(e, 163. Echinorhijnchus, 194. Echinothuridx, 167. Echinozoa, 154 (see Annuloida). Echinus, 159, 161. Echiurus, 284. Ectocyst, 302. Ectoderm, 87, 125. Ectosarc, 54. Edaphodus, 421, 430. Edentata, 541, 548, 550, 552 ; general characters of, 565; distribution of, in time, 642. Edriophthalmata, 226; characters and divisions of, 242. Edwardsia, 128. Elasmobranchii, characters of, 418, 419 ; divisions of, 420 ; position of, in the scale of Fishes, 424 ; distribution of, in time, 430. E/asmodas. 421,430. Eledone, 357. Elephant, 542, 54S, 553. Elephant-shrew, 628. Elephas. 601, 6u2, 616. Elysia, 341. Eiysiadce, 337, 341. Elytra, of Aphrodite, 214 ; of Coleoptera, 26-), 291. Emarginula, 310. Emeu, 513. Emydidce, 452, 453. Emys, 450, 452. Enaliosauria, 472. Enallostega, 63. Encephala (Mollusca), 320, 329. Encrinus, 18 1. Euderon, 125. Endocyst, 302. Endoderm, 87, 125. Endopodite, 223. Endosarc, 5*. Endostyle, 3.j8. Enhydra, 611. Entcmophaga, 562. Entomostega, 63. Entomostraca, 226 ; characters of, 233 ; divisions of, 234. Entosolenia, 61. Entozoa, 183. Eocystites, 182. Eosaurus, 472. Eosphora, 201. Eozoon, 65. Ephemeride, 231. Ephyra, 117* Epidermis (of the shell of Mollusca), 297. Epiinera^ 222. Epipodite, 224. Epipodium, 330 ; of Pteropoda, 342 ; of Cephalopoda, 345. Epistema, 222. Epistome, 303, 306. Epistylis. 81. Epizoa, 2-25 ; characters of, 226. Equidie, 585, C44. Equus, 5b5. 644. Erethizon, 619. Erichthyx, 246. Erinaceidw, 628. Erinaceus, 62 4. Errantia, 207 ; characters of, 212 ; gem- mation of, 214 ; development of, 2l5 ; distribution of, in time, ib. Esocidce, 40^. Estheria, 253. Eudendrium>) 97. Kugereon, 292. Eulima, 339. Eunice, 215. Eunicea. 215; Siiomphalus, 314. Euplectella, 74. Eupsammidie, 152. Euryale, 169. Eurypterida, 241 ; distribution of, in, time, 253. Eurypterus, 253. Eurystomata, 146. Exoccetus, 3y3. Exopodite, 222. Extracrinus, 181. FACIAL Suture of Trilobites, 239. Falconidae, 530. Favositidce, 152. Favospongia, 75. Feathers (structure of), 481. Feather-star, 174. J-Wtdoe, 541, 6 [4, 615. Felis, 615, 616. Fenestella, 318. .Fera, 603. ^t6er, 620. Field-bug, 279. Filar ia, 196. File-fishes, 412. Finches, 525. Finner-whales, 576. Firola, 341. 692 INDEX. Ftrolidw, 338, 341. Fissilinguia, 462. Fission, 26, 28 ; of corals, 136. Fissirostres, 523, 527. Fissurdla, 340. Fissurdlidce, 336, 340. Flagella, 49, 83. Flagellata (Infusoria), 77, 83. Flamingo, 507. Flat-fishes, 388, 410, 422. Hints, origin of, 7 5. Float of Physophoridce, 107. Floscularia, 198, 201. Flukes (Suctorial worms), 189. Flustra, 9, 27, 303. Flying-Dragon, 465. Flying-Lemur, 628. Flying-Phalanger, 622, 629. Flying-Squirrel, 622, 629. Food of animals and plants, 10. Food-vacuoles, 55, 57. Foot, of Rotifera, 191 ; of Lamellibran- chiata, 325 ; of Gasteropoda, 330 ; of Heteropoda, 337 ; of Pteropoda, , 342 ; of Cephalopoda, 345. Foot-jaws, of Lobster, 224 ; of Centipedes, 266. Foraminifera, 3, 27, 50, 58 ; sarcode of, 59 ; pseudopodia of, 60 ; test of, 68, 00 ; unilocular and multilocular,61 ; stolons of, ib. ; classification of, t>2 ; affinities of, ti3 ; distribution of, in space ana time, 65. Forficula, 269. Formiddix, 289. Fowl, 516. Fox, 613, 614. Fox-bats, t>26. Francolinus, 510. Fratercula, 503. Fringilla, 525. Fringillidce, 523, 525. Fringing-reefs, 148. Frog, 439, 442 ; development of, 440. Fulgora, 279. Fulica, 508. Fuligula, 506. Fuligulince, 506. Functions, specialisation of, 14, et seq. Fungidm, 152. Funiculus, of Polyzoa, 304. Funnel, of Ctenophora, 144 ; of Cephalo- poda, 345 ; of Nautilus, 355. Furculum, 487. Fusus, 339. GADID^E, 410. Galeocerdo, 430. Galeodes, 256, 261. Galeopithecidce, 628. Galeopithecus, 628, 631. Galestes, <539, 6il. Gallinacei, 515. Galling, 487. Gallinulce, 5u8. Gallus, 516. Gallyworm, 266. Gammarus, 243. Gampsonyx, 254. Ganasida;, 260. Gannet, 505. Ganodus, 430. Ganoid (Scales of Fishes), 386. Ganoidei, characters of, 412 ; divisions of, 415 ; distribution of, in time, 428. Garrulince, 524. Gasteropoda, 293, 294, 295, 320 ; general characters of, 329 ; foot of, 330 ; odou- tophore of, ib. ; circulatory and respira- tory organs of, 331 ; embryo of, 332 ; shell of, 333 ; divisions of, 335 ; families of, 339 ; distribution of, in time, 359. Gastornis, 535. 6' astrobranchus, 405. Gastrochcena, 329. Gastrodicenidce , 827, 329. Gavial, 468, 470. Gavialis, 470. Gecarcinus, 250. Geckotidie. 465. Geese, 506. Gelasimus, 251. Gemitores, 515, 517. Gemmation, continuous and discontinu- ous, 26 ; internal, 29 ; of Foraminifera, 62 ; of Vorticella, 80 ; of Hydra, 92 ; of medusiform gonophores, 113 ; of corals, 133 ; of Naididw, 210 ; of Errant Annelides, 2i4 ; of Polyzoa, 301 ; of Tunicata, 310. Gemmules, of Spongilla, 73. Generations, alternation of, 29 ; of Sal- pians, 310. Generation, spontaneous, 37. Genette, 612. Geocorisce, 279. Geomelania, 341. Geophilus, 266. Gephyrea, 203, 204. Gerbillus, 621. Gibbon 636. Giraffe, 538, 591, 595, 646. Gizzard, of Insects, 271 ; of Birds, 492. Glabella, 239. Gladius (Cuttle-fishes), 349. 351. Glareola. 511. Glaucus, 34.1. Glires, 617 (see Rodent ia). Globicephalus, 578. Globigerina, 60, 62. Glutton, 610. Glycimeris, 328. Glyptodon, 643, 619. Glyptolepis, 428. Goat, 697. Goat-sucker, 522, 527. Gobiidce, 4 11. Goniaster, 167, 182. Goniatites, 355, 361. Goniodiscus, 182. Goniophyllum, 140. Gonoblastidia, 96. Gonocalyx. 95 ; structure of, ib. ; canals of, ib. Gonophores, 94 ; medusiform, 95, 96, 105, 108, 112, 113, 120. Gonosome, 90. Gouotheca, 101. Gordiacea, 185 ; characters of, 194. Gordius, 194. Gorgonidoe, 141, 142; characters of, 147; distribution of. in time, 152. Gorilla, 637. Gouridce, 518. INDEX. 69. Graculavus, 534. Grallatores, 500 ; characters of, 507. Grantia, 74. Graphularia, 152. Graptolitidce, characters of, 120 ; distribu- tion of, in time, 124. Greenland Whale, 573. Gregarina, 50. Gregarinidce, 50 ; reproduction of, 51. Griffithides, 253. Grison, 610. Gromia, 58. Gromida, 63. Growth, 3, 26 ; correlation of, 19. Gruidce, 509. Grus, 509. Gryllina, 280. Guard, of Belemnite, 353, 358. Guinea-fowl, 516. Guinea-pig, 619. Guinea- worm, 196. Gulo, 610. Guynia, 151. Gymnochroa, 91. Gymnodontidce, 412. Gymnohpmata, 306. Gymnophiona, 434. Gymnophthalmata (Medusidce)-, 95, 110, 120. Gymnosomata, 343. Gymnotus, 408. Gynophores, 108. Gypaetos, 531. Gyrencephala, 550. Gyroceras, 356. Jlfpmatocrya, 384. JI(f,matopus, 511. HfEmatotherma, 384. Hag-fishes, 402, 403, 404, 4C5. Haimeia, 137. Hair-worms, 194. Halcyornis, 535. Halicore, 570, 571. Haliomma, 67. Haliotida, 836, 340. Haliotis. 346. Halitherium, 644. Ilalteres, 269, 284. Ha mites, 360. Hamster, 621. Hapale, 633. Hapalidos, 633, Haplophyllia, 151. Harpa, 339. Haustellata, 226 (see Epizoa). Hawks, 530. Hectocotylus, 347, 351. Hedgehog, 549, 628. Helarctos, 609. Helianthoid Polypes, 127. Hdicidgoch(eta, 210, 216. Ommasirephes, 357. Omnivora (Ungulata], 5: 698 INDEX. Onchuna, 227. Onchus, 429. Oncidiadce, 339, 341. Oncidium, 341. Oniscus, 244. Onychoteuthis, 345, 357. Operculata, 339, 341. Operculum, of JBalanidie, 231, 233 ; of Gas- teropoda, 330 ; of Heteropoda, 337 ; of Fishes, 389, 390. Ophicrinus, 175. Ophidia, 448 ; general characters of, 453, e£ seqr. ; divisions of, 456 ; distribution of, in time, 459. Ophidobatrachia, 434. Ophiocoma, 169, 182. Ophioderma, 182. Ophiolepis, 169, 182. Ophiomorpha, 434. Ophisaurus, 462. Ophiura, 169. Ophiuridea, 170. Ophiuroidea, 156, 157 ; general characters of, 169 ; families of, 170 ; distribution of, in space, 180 ; in time, 182. Opisthobranchiata, 335, 336. Opisthoccelia (Crocodilia), 471. Opossum, 562, 563. Orang-outang, 636. Orbitoidts, 66. OrbitoHtes, 62. Oreaster, 182. Organ of Bojanus, 325. Organ-pipe Coral, 138. Organs of the mouth of Insects, 270,- et seq. Oribatidce, 260. OrnithoJelphla, 551, 555. Ornithorhynchus, 543, 548, 551, 555, £56. Ornithosauria, 476. Orthis, 317. Orthisina, 317. Orthoceras, 356, 358, 360. Orthoceratidce, 358, 360. Orthoptera, 269, 279, 292. Ortonia, 216. Orfyor, 516. Orycteropidce, 569. Orycteropus, 569. Oscula, of Sponges, 70, 76 ; of Tapeworm, 186. Otsteolepis, 415, 428. Ostraciontidrv, 412. Ostracion, 411. Ostracoda, 226 ; characters of, 334 ; dis- tribution of, in time, 253. Ostracostei, 415, 417. Osfrea, 326, 327. Ostreidce, 325, 327. Ostrich, 511, 512. Otaria, 606. Otter, 611. Owdenodon, 475. Ounce, 616. Ovarian vesicles, of Sertularida, 101. Ovibos, 598. Otncte, 597. Ovipositor, 269, 288. Ovis, 597. Ovulum, 339. Owls, 529. Oxen, 591, 597, 646. Oxyuris, 195. PACA, 619. Pachi/dermata, 580. Paddle-fish, 416. Paguridiv, 249. Palceaster, 182. Pal, 29«, 327, 329. PhoJadomya, 328. PAoZas, 32t5, 328. Phorus, 340. Phosphorescence of the Sea, 83. Phragmacone, 296 ; of Spifula, 349, 352 ; of Belemnite, 352. Phraff/noceras, 358. Phryganeidaz, 281. Phylactolcemata, 306. Ph,,lUdia, 841. J'hyilidiadce, 33^?, 341. Phyllirrhoe. 341. Phyllirrhoidce, 336, 341. Phyllium, 19. Phyllocyst, 105. Phyllopoda, 226'; characters of, 237 ; dis- tribution of, in time, 253. Phyllostoma, 6.25. Phyllostomidce, 624, 625. Phyogemmaria, 108. Pkysa, 341. Physalia, 83, 88, 103, 108. Physaliadce, 110. Physalus, 576. Physeter, 577. Physeteridce, 577. Physiology, 13. PJiysophora, 108. Pfiysophoriadce, 109. Physophoridce, 103 ; characters of, 107, eisei?..; tentacles of, 107; reproduction of, 108 ; distribution of, in space, 123. P/iysostomata, 407. Picidce, 519. Pigeons, 518. Pigment-spot, ot Infusoria, 82; of .RoJi- /era, 201. Piieolus, 340. Pileopsis, 340. Pilidium, 192, 193. Pinna, 326, 327. Plnnigrada, 605, 606. Pinnipedia, 605. Pinnoctopus, 357. Ptpa, 439, 441. Pipe-fish, 412. Pipidce, 441. Pirimela, 251. Pisces, 383 ; general 'characters of, 386 ; scales of, i'&. ; skeleton of, 387, e^seg. ; limbs of, 391 ; tail of, 394 ; digestive system of, 397 ; respiratory system of, 3b5 ; heart of, 396 ; swim-bladder of, 398 ; nervous system of, i&. ; reproduc- tive system of, ?6. ; orders of, 400, distribution of, in time, 427, cf *e#. Placenta, 533, 550. Placentalia (Mammalia), 550. Placodus, 475. Placoganoidei, 416, 417, 423. Placoid (scales of Fishes), 386. 700 INDEX. Placoidei, 418. Plaffiaulax, 6.R 641. Plagiostomi, 420 ; characters of, 421. Plan-irida. 191, 192, 2o2 Planorbis. 333, 341. Plantigrada, 605, 608. Planula, 116. Plastron, 449, 450. Plataleadce, 510. Platanista, 578. Platycrinus, 173. Platydmia, 183 ; characters of, 184. Platyrhina, 630, 632. 1'lecotus, 6-25. Plectognathi, 411. Plectropto-us, 485. PlesiosauTia, 473. Plesiosaiirus, 473, 474. Pleura, of Lobster, 222 ; of Trilobite, 239. Pleur acanthus, 429, 430. Pleurobrachia, 142 ; ctenophores of, 143 ; canal-system of, 143, 144 ; development of, 145 ; homologies of, 145. Pleurobrachiadce, 146. Pleurobranchidce, 336, 341. Pleurobranchus, 341. Pleuronectidce, 410, 423. Pleuronema, 83. Pleurotoma, 339. Pleurotomaria, 340. Pliolophus, 644. Pliopithecus, 648. Plotus, 505. Plough-share bone, 484. Plumaster, 182. Plumularia, 101. Pluteus, 156, 157. Plyctolophus, 521. Pueumatic filaments of Physopfioridce, 107. Pueumatocyst, 107. Pneumatophore, 107, 103. Pneumodermon, 343. Podarffus, 528. Podophthalmata, 226 ; characters of, 245. Podosomata, 258. Podura, 270, 278. Poephaga, 569. Polistes. 35. Polyarthra, 201. Polyccelia, 151. Polycystina, 67, 68. Polydesmus, 266. Polygastrica (of Ehrenberg), 78. Polypary, 93, 97, 98. Polype, 127. Polypide, 300. Polypidom, 89. Polypite, 89. Polyplectron, 516. Polypterus, 4 16. Polystome Infusoria, F3. Polythalamia (Foraminifera), 61, 62. Polytrema, 66. Polyxenia, 112. Polyzoa, 293, 294, 295; characters of, 29S ; distinctions from Hydrozoa, 299 ; typi- cal polypide of, 300 ; avicularia of, 301 ; lophophore of, 303 ; nervous system of, 304 ; digestive system of, 303 ; repro- duction of, 304 ; statoblasts of, 305 ; development of. 16. ; relations to Tuni- cata, 311 ; divisions of, 3J6 ; orders of, #>. ; distribution of, in space, 318 ; in time, ib. Polyzoarium, 300. Pontarachna, 260. Pontia, 285. Pontobdella, 209, 216. Porambonites, 317. Porcdlana, 249. Porcellanous shells, 296. Porcellia, 359. Porcupine, 549, 619. Pores of Sponges, 70, 71. Porites, loO. Poritid, 353, 355 ; of Belemnites, 353 ; of Tetra- branchiata, 355, 356 ; of Naut lidae, 356 ; of Ammonitidce. ib. ; of Oi-tkoceras, 357. Si'punculacea, 205. Sipunculoidea, 203. Sipunculus, 204. Kiredon, 436, 437. Siren, 435, 436. Sirenia, 538, 540, 543, 543, 551, 552 ; char- acters of, 570, et seq. ; distribution of, , in time, 644. INDEX. Kirenidre, 436. ,S7«a, 5i6. Sivatherium, 535, 645, 649. Slaters, 245. Slimonia, 253. Sloth, 538, 539. Snakes, 445, 443, 453, 454, 456, 457. Solarium, 34 J. Solaster, 167. Solecurtus, 328. SoZera, 328. Solenidce, 327, 323. Solidungula, 580, 584, 641. Solipedia (see Solidungula). Solitaire. 519. Solpugidce, 261. Somateria, 506. Somatic cavity, of CceJenterata, 86 ; of Hydrozoa, 88 ; of Hydra, 91 ; of Actino- zoa. 125. Somatocyst, 103, 104. Somite, 218 ; of Crustacea, 220 ; of .4>ac7i- mda, 254. Sorex, 628. Soricidce, 627. Soroidea, 63. Spalacotherium, 639. Spar sis pongia, 75. Spatangidte, 163. Spatiformes, 163. Spatularia, 416. Species, definition of, 23 ; origin of, 4). Spermatophores, 347. Sperm-whale, 577. Sphcerogastra, 262. Sphceroma, 244. Rphceronec ide, 106. Sphcerozoum, 68. Sphagodus, 429. Xphargis, 451. Spheniscidce, 502. Spheniscus, 503. Spicula, of Sponges, 70, 73 ; of R>tdlo- laria, 67, 6« ; of ^dmozoct, 132, 137. Spider-monkey, 633. Spiders, 254, 235, 257, 262. Spinax, 419. £p niferites,, 75. Spinnerets of Spiders, 263 ; of Caterpillars, 286. »Sp.:o, 87. Spirialis, 343. Spirifer, 316. Spirifendx, 316, 319. Spiriferina, 31*. Spirorbis, 212, 216. Spirula, 349, 352, 358. Spirulidce, 352, 3)8. Spirulirostra, 358. SpondyJus, 327. Spongida, 69 ; skeleton of, 70, 73 ; sar- coids of; 70, 73 ; aquiferous system of, 71 j reproduction of, 72; classification of, 73; distribution of, in space, 74,; in time, 75 ; affinities of, t'6. ; individu- ality of, 76. Spongilla, 54, 74 ; reproduction of, 74 ; sarcoids of, i&. Spoon-bill, 510. Spoon-worm, 203. Spores, of Sponges, 73. Sporosac, of C'orynid:.i, 94, 95. Spring-tails, 270, 273. SqualidcB, 422. Squalodon, 530. Squamae, of Aphrodite, 214. Squamata (Reptilia), 446. Squamulina, 64. Squids, 344, 350. Squilla, 245. Squirrel, 622. Squirrel Monkey, 633. Staggers, of Sheep, i&9. St'igonolepis, 470. Star-nosed Mole, 627. Statoblasts, 29, 305. Stauria, 151. Stauridfe, 151, 153. Stauridia, 96. Steatoritiis, 528. Strganddictyum, 75. Steganophthalmata (Medusa), 110, 114, 115, 120. Stem-muscle, of Vorticdla, 79. Stemmata (see Ocelli). Stenaster, 182. Steneosaurus, 471. Stcnostomata, 146. Stentor, 10, 82. Stephanoceros. 198, 201. Stephanomiadce, 109. Sterelmintha, 192. Stereognathus, 639, 640. Sternaspis, 204. Sternum, of Crustacea, 222 ; of Aruch- nida, 255 ; of Chelonia, 451 ; of ^4ves, 486; of Mammalia, 540. Stichostega, 63. Stigmata, of Physophorid t>, 107 ; of Leeches, 208 ; of AracJinida, 257 ;* of Insecta, 273. Stolons, of Foraminffera, 61 ; of com- posite -4c. Sylviadcs, 526. Synapta, 179. Synapticulsc, 135. Synaptidw, 180. Syndactyli, 527. Syndendi-ium, 120. Syngnathidce, 412. Syrinx, 204. 2'abanidw, 235. Tabulae, of Corals, 134. Tabulate/,, 134, 152. Tachy petes, 505. Tania, 185, Ib7, 188, 1F9. Tffiniada, If3 ; characters and develop- ment of, 184, ei seg. Talitrus, 243. Taipa, 627. Talpidve, 627 Tamms, 622. Tanagrincv, 525. Tanais, 245. Tank-worms. 196. Tantalinw, 510. Tape-worm, 185, e£ seg. Tapir, 583, 64P. TapiridcK, 583. Tardiprada, 259. Tectibranchiata, 336, 349. Teleosaurus, 471. . Teleostei, characters of, 405, e£ se^. ; sub- divisions of, 407, eiseg. ; distribution of, in time, 427, et seq. Telerpeton, 467. Tellina. 328. Teilinida;, 327, 323. Telmatornis, 534. Telson, of Crustacea, 220 ; of Lobster, 223 ; of Limulus, 241 ; of Scorpion, 261. Tenrec, 628. Tentacles, of Hydra, 91 ; of Tubularia, 98; of CalycophoridcK, 104; of Fhyso- phoridce, Io7 ; of Medusidce, 111 ; of Hydra-tuba, 116; of Actinia, 128; of Alcyonaria, 137 ; of Pleurobracliia, 143 ; of Holothuroidea, 179 ; of Polyzoa, 303; of Tunicata, 308 ; of Cuttle-fishes, 350, 351. Tentaculites, 216, 360. Tenthredinida', '288. Tenuirostres, 523, 526. Terebella, 212; development of, i6. 2'erebratella, 316. Terebratula, 314, 31S, 31fi. Terebratulidce, 315, 3l6, 319. Terebratulina, 315, 316. Teredo, 329. Tergum, of the exoskeleton of Crustacea, 222; of Arachnida, 255. Terricola, 2i)9. Termites, 281 ; communities of, ?&. Terrapin, 452. Tesselata, 163. Test, of Foramiw'fera, 58'; of Echinoiil- /, 157, 158; of Tunicata, 307, 513. Testacella, 296, 341. Testudinidce, 452. Testudo, 453. Tetrabranchiata (Cephalopoda), 349 ; char- acters of, 353 ; divisions, of, 355 ; distri- bution of, in time, 36y. Tetradecapoda, 242. Tetramera, 293. Tetranychus, 259. Tetrao, 516. Tetraonidce, 51 6. Teuthida;, 351, 357, 361. Thalassarachna, 260. Thalassarctos. 609. Thalassemacea, 205. Thalassicolla, 68. T/ialassicollida, 68. j?7ieca, 343. Theca, of sclerodermic corallum, 131. Thecaphora, 98, 103. ThecidcB, 152. ThecididoE, 316. Thecidium, 316. Thecodontia, 470. Thecodontosaurus, 470. Thecosomata, 343. Thelyphonidce, 262. Theriomorpha, 438 (see ^4 noura). Thoracica (Cirripedia), 226, 233. Thread-cells, 85, 87. Thread-worms, 195. Thylacinus, 564, 642. Thylacoleo, 642. Thysanura, 278. Ticks, 259. Tiger. 614, 616. Tipw/a, 284. Tipulidce, 284,385. Toad, 441. Tongue, of Insects, 271; of Gasteropoda, 330 ; of Cephalopoda, 346 ; of Fishes 390 ; of Snakes, 454 ; of Lizards, 46^; of 1 Crocodile, 469 ; of Birds, 491, 498. Tornatella. 340. Tornatellidce, 336, 340. Torpedo, 423. Tortoise Encrinite, 181. Tortoises, 445, 446, 448, 452, 453. Tortrix, 453. Totanus, 511. Totipalmatce, 504. Toucan, 521. Toxoceras, 356, 357. Toxodon, 359. Tracheae, 218; of Arachnida, 257; of Myriapoda, 2G5 ; of Insecta, 272. Trachearia (Arcchnida), 258. Trachiopoda, 316. Trachyderma, 2 16. Trachynema, 113. Trachynemidw, 113, 120. Tragulus, 592. Transformation, 36. INDEX. 705 Trematis, 317. xy_ J>>^ rrematoda, 183; general characters of, 189, 190; development of, 190; habitat of, 191. "inoctopus, 357. .-iurthra, 201. •ichecidce, 606. ,-ichecus, 606, 607. richina, 195. richocysts, 8'2. richoglossus, 521. "ichoptera, 281. 'iconodon, 639, 641. 'ridacna, 328. Tridacnicke, 327, 328. Trigonia (Mollusca).32~; (Mammalia') , 641. Triaoniadw, 326, 327. Trilobita, 238 ; structure of the crust of, 239 ; distribution of, in time, 253. Trimera, 292. Trimerella, 317. TrimerdlidiK, 317. Trmffidce, 510. Trionycidce, 449, 452, 453. Trionyx, 452. 2Vttow, (Mollusca), 339 ; (Amphibia), 438. Tritonia, 341. Tritoniadce, 336, 341. Trociiilidce, 526. Trochoceras, 356, 358. Trochocystites, 182. Trochoid shell, of Foraminifera, 62 ; of Gasteropoda, 333. Trochus, 340. Troglodytes, 526, 637. Trogon, 522. Trogonidai, 520, 522. Trogontherium, 648. Trombididd', 260. Trophi, of Insects, 270. Trophosome, 90. Truncated Shells, 297. Trygon, 423. Tube-feet, of Echinus, 160; of Asteroidea, 165 ; of Ophiuroidea, 169 ; of Crinoidea, 170 ; of Holothuroidea, 178. Tubicola, 207 ; characters of, 210 ; de- velopment of, 211 ; distribution of, in time, 216. Tubifex, 210, 216. TuUporidce, 137, 138, 142. Tubularia, 93, 97. Tubularida, 93 (see Corynida). Tubulosa, 135, 1&2. Tunicata, 294, 295 ; characters of, 306 ; respiratory process of, 308 ; circulation of, 309 ; reproduction of, 310 ; homo- logies of, 16. ; divisions of, 311 ; dis- tribution of, in space, 318 ; in time, z&. Tunics, of Ascidians, 3i>7. Tupaia, 628. Turbellaria, 1?3 ; characters of, 191 ; divisions of, 191. Turbinated Shells, 333. Turbinidffi, 336, 340. Turbinolidai, 152. Twrfeo, 340. Turkey, 516. Turrilepas, 253. Turrilites, 356, 357, 358, 361. Turrildla, 340. Turritellidcc, 330, 34Q. parties, 44S, 452, 453. Ti/lcnchus, 197. Tylodina, 341. Type, morphological, 15. , 529. Umbilicated shell of Gasteropoda, 334. Umbo, 3-22. Umbrella, 341. Umbrella of Lucernarida, 114, 118. Ungulata, 541, 551, 553; characters of, 580 ; divisions of, 581 ; distribution of, in time, 644. LTnio, 327. Unionidce, 326, 327. Univalve Shells, 296, 329, 333. Upupidce, 526. PYia, 503. Uraster, 182. Urnatella, 303. Urodela, 432 ; characters of, 435. t/rsz'dre, 608. ^•«w, 608, 609, 648. Urus,646. VACUOLES, of Protozoa, 55 ; of Infusoria, 77. Vaginicola, 82. Vaginulus, 341. Valkeria, 303. I'aiuata, 340, 359. Vampire-bat. 6i>5. Vanellus, 511. Farawtd«j, 464. Varanus, 464. Veil, of Gonophores, 95 ; of nectocalycesr, 105 ; of naked-eyed Medusae, 111. FeZeMa, 107, 108, 109. Velellidce, 110. Fenenosa (Ophidia), 458. Veneridw, 327, 328 ; distribution of, in time, 359. Venerupis, 328. s, 75. Venus's girdle, 146. Vermts, 155. Vermetus, 333, 340. Verrucidre, 226, 233; distribution of, in time, 253. Verruca, 231. Vertebra, structure of, 337. Vertebrata, 369 ; general characters of, ib., et seq. ; skeleton of, 373, et seq. ; digestive system of, 378 ; blood of, 380 ; respiratory system of, 381 ; nervous system of, 382 ; reproduction of, 883 ; development of, ib.; divisions of, ib.etseq. Vesicle, contractile, of, Protozoa, 49 ; of A mosba, 55 ; of Paramaxium, 78 ; of Epistylis, 81. Vesicles, of Medusa;, 111, 114. Vespidte, 288. Vespertilio, 625. Vesper tilionida;, 624. Vibracula, 302. Vibrios, 37, 197. Vidua, 524, 525. Viperina, 457. Virgularia, 138. Visceral arches, of the embryo of Verte- brates, 372. 2 Y 7o6 [NDEX. Vitrea (Sponges), 73. r/ren-a, til-'. Viverridcv, 612. Vole, 621. Valuta, 339. Volutidte, 335, 339. Vorticdla, 77 ; structure of, 79 ; repro- duction of, 80, 81. Vortidava, 93. Vulpes, 613. 530. WAH, 609. Waldheimia, 316. Walrus, 6u6, 607. Warblers, 526. Wasps, 238. Water-hen, 508. Water- vascular system, of Annuloida, 154 ; of Echinoidea, 160 ; of Asteroidea, 165 ; of Ophturoidea, 169 ; of Crinoidea, 170 ; of Holothuroidea, 177, 179 ; of Scoledda, 184 ; of Taniada, 185 ; of Trematoda, 189 ; of Turbeltaria, 1«1; of Acanthocephala, 194 ; of Nematoda, 196 ; of Eotifera, -200. Weasel, 611. Wefoferia, 152. Whalebone Whales, 515, 573. Whales, 53S, 539, 541, 545, 540, 572, 573. 576, 644. Wolf, 613. Wolverine, 610. Wombat, 559. Wood-pecker, 519. Wrasse, 411. Wry-neck, 519. sYanthidia, 75. Jrtphosura, characters of, 240 ; distribu- tion of, in time, 258. Xylobius, 267. ' ZEBRA, 585. Zeuglodon, 580, 644. Zeuglodontidce, 580, 644. ZipUus, 644. Zoantharia, 127 ; Malacodermata, 127, 141, 147 ; Sclerobasica, 130, 133, 15:2 ; Sderodermata, 134, 135, 142 152. Zoanthidce, 130. Zoanthus, 130. Zoea, 237, 245, 246, 249, 251. Zonites, 359. Zooid, 90. Zoology, definition of, 1. Zootoca, 464. i'RINTED BY BALI.ANTYNE AND COMTANY EDINBURGH AND LONDON t ^ 14 DAY USE RETURN TO DESK FROM WHICH BORROWED BIOLOGY LIBRARY TEL. NO. 642-2532 This book is due on the last date stamped below, or on the date to which renewed. Renewed books are subject to immediate recall. General Library University of California Berkeley 77