IIBSi? PAUL JL I'AV'- L, TEXT-BOOK OF Z O O L O G Y FOR SCHOOLS AND COLLEGES BY H. ALLEYM MCHOLSOX, M.D., D.Sc., M.A., PH.D., F.K.8.E., F.G.S., ETC., PROFESSOR OF NATURAL HISTORY AND BOTANY IN UNIVERSITY COLLEGE, TORONTO? FORMERLY LECTURER ON NATURAL HISTORY IN THE MEDICAL SCHOOL OF EDIN- BURGH; AUTHOR OF "MANUAL OF ZOOLOGY FOR THE USE OF STUDENTS," "TEXT-BOOK OF GEOLOGY," "INTRODUCTORY TEXT-BOOK OF ZOOLOGY," "GEOLOGY OF CUMBERLAND AND WESTMORELAND," ETC., ETC. NEW YOKE: D. APPLETON AND COMPANY, 1, 3, AND 5 BOND STREET. 1884. ENTEBED, according to Act of Congress, in the year 1871, by D. APPLETON & CO., In the Office of the Librarian of Congress, at Washington. EDUCA2IOU A) 52. PREFACE. Ix bringing out a Text-book of Natural History, intended mainly for the use of schools, there are a few remarks which it may be as well to make by way of preface, if only to ex- plain the principles upon which the work has been written. In the first place, more space has been devoted, compara- tively speaking, to the Invertebrate Animals than has usually been the case in introductory works, upon the belief that any practical Zoological work likely to be undertaken by young students will certainly be in connection with these rather than with the Vertebrate Animals. Secondly, the Author has devoted considerable space to a discussion of the principles of Zoological classification, be- lieving that it is of paramount importance that the student should have a clear idea of the principles upon which the Animal Kingdom has been systematically divided. At the same time, the introductory portion of the work is more especially intended for the teacher ; and there is much in it that the learner may perhaps hardly understand till he has arrived at some clear idea of Natural History as a whole. Thirdly, while the Author trusts that the style of the work will be found clear and intelligible, he does not believe in the existence of any royal road to learning in Natural History, any more than in any other department of human knowledge. If Natural History is ever to be taught in M577G42 iv PREFACE. schools, with any satisfaction to the teacher, or any profit to the learner, it must be taught as systematically and as un- flinchingly as Mathematics and Greek have been taught for many generations. The Author is one of those who believe that the time is now approaching, if it be not already here, when the Natural Sciences will take their true place in school education, as second to no other branch of knowledge, either as regards their intrinsic value and interest, or regarded mere- ly as a means of developing the mental powers. Acting upon this belief, the Author has, therefore, treated his subject in a purely scientific spirit ; and, while avoiding as much as pos- sible the use of technicalities, he has not endeavored to lend his subject any false glitter or embellishment ; firmly believ- ing that there is even a certain mental training involved in the recognition that a strictly scientific description is not without its own charms and beauties. While the use of tech- nical terms has been as far as possible restricted, it is believed that an explanation of every unavoidable term will be found in the glossary, or is appended in the text. Lastly, the illustrations, with few exceptions, have been drawn on the wood by the Author, and he has thought it wise to wholly eschew the use of pictorial illustrations, as unneces- sary in a scientific work, however elementary it may be. TABLE OF CONTENTS. INTRODUCTION. Definition of Biology and Zoology — Characters of dead and unorganized bodies — Characters of living and organized bodies — Differences between animals and plants — Principles of Zoological classification— The great Physiological Functions— Homology and Analogy- General Divisions of the Animal Kingdom— Invertebrata and Vertebrata, . Pages 1-24 CHAPTER I. General characters of the Protozoa— Classification of the Protozoa— Gregarinidas, . p. 25-28 CHAPTER II. General characters and orders of the Ehizopoda— Anatomy of the Amoebea— Foraminifera— Affinities — Distribution of the Foraminifera in Space and in Time — Radiolaria — Acan- thoinetra3— Polycystina— Thallassicollida— Spongida— Structure of a Sponge— Reproduc- tion of Spongilla— Distribution of Sponges in space, p. 29^4 CHAPTER III. General characters of the Infusoria — Anatomy of Paramcecium — Structure of Epistylis — Orders of Infusoria— Distribution of Infusoria in space — Tabular view of the divisions of the Protozoa, p. 45-49 CHAPTER IV. General characters of the Ccelenterata — Divisions of the Ccelenterata — General characters of the Hydrozoa— General terminology of the Hydrozoa, p. 50-56 CHAPTER V. Divisions of the Hydrozoa — Hydroida — Hydrida — Anatomy of Hydra — Corynida — Repro- duction in the Corynida and in the Hydroid Zoophytes generally— Alternation of gen- erations— Sertularida — Campanularida, p. 57-69 CHAPTER VI. Siphonophora or Oceanic Hydrozoa— Calycophorida>— Physophoridae, . . p. 70-73 CHAPTER VII. Discophora or Medusidse— Structure of Naked-eyed Medusae— Their nature, . p. 74-7T vi TABLE OF CONTENTS. CHAPTER VIII. Lucernarida— Hidden-eyed Medusae— Development of Lucernarida— Bhizostomidae— Grap- tolitidae, ' . Pages 78-83 CHAPTER IX. General characters of the Actinozoa — Zoantharia — Anatomy of a Sea- Anemone — Zoantharia Sclerodermata— Scleroderinic and Sclerobasic Corals— Coral-reefs— Zoantharia Sclero- basica — Alcyonaria — Gorgonidae — Red Coral — Rugose Corals — Ctenophora — Anatomy of Pleurobrachia— Tabular view of the divisions of the Ccelenterata, . . . p. 84-94 CHAPTER X. General characters of the Annuloida — General characters of the Echinodermata — Divisions of the Echinodermata— Echinoidea— Anatomy of Echinus— Asteroidea— Ophiuroidea— Crinoidea— Cystoidea and Blastoidea— Holothuroidea, p. 95-10T CHAPTER XI. General characters of the Scolecida — Divisions of the Scolecida — Tseniada — Development of a Tape-worm — Cystic worms — Trematoda — Turbellaria — Acanthocephala — Gordiacea — Nematoda— Rotifera— Tabular view of the divisions of the Annuloida, . p. 108-117 CHAPTER XII. General characters of the Annulosa — Characters of the Anarthropoda — Gephyrea — Annelida —Divisions of the Annelida— Hirudinea— Oligochaeta— Tubicola— Errantia, p. 118-125 CHAPTER XIII. General characters of the Arthropoda— Divisions of the Arthropoda, . . . p. 12C, 127 CHAPTER XIV. General characters of the Crustacea — Decapoda — Macrura — Anomura — Brachyura — Isopoda — Merostomata— Trilobita— Cladocera, Copepoda, and Ostracoda— Cirripedia— Appendix of the remaining orders of Crustaceans, ........ p. 128-138 CHAPTER XV. General characters of the Arachnida— Podosomata— Acarina— Pedipalpi— Araneida, p. 189-143 CHAPTER XVI. General characters of the Myriapoda— Centipedes— Millipedes . . . . p. 144, 145 CHAPTER XVII. General characters and anatomy of Insects— Metamorphoses of Insects, . . p. 146-152 CHAPTER XVIII. Orders of Insects— Anoplura— Mallophaga— Thysanura— Hemiptera— Orthoptera— ^"europ- tera — Aphaniptera — Diptera — Lepidoptera — Hymenoptera — Strepsiptera — Coleoptera — Tabular view of the divisions of the sub-kingdom Annulosa, . . . p. 153-163 TABLE OF CONTENTS. vii CHAPTER XIX. General characters of the Mollusca — Primary divisions of the Mollusca, . Pages 164-1 6T CHAPTER XX. Molluscoida— General characters of the Polyzoa— General characters of the Tunicata— Gen- eral characters of the Brachiopoda, p. 168-175 CHAPTER XXI. Classes of the Mollusca Proper— General characters of the Lamellibranchiata— General char- acters of the Gasteropoda— Nudibranchiata— Heteropoda— Air-breathing Gasteropods— Pteropoda, p. 176-186 CHAPTER XXII. General characters of the Cephalopoda — Reproductive process hi the Cuttle-fishes — Shell of the Cephalopoda — Dibranchiata — Tetrabranchiata — Orthocerata — Ammonites — Tabular view of the main divisions of the Mollusca, p. 187-194 CHAPTER XXIII. General characters of the Vertebrata — Skeleton of Vertebrates — Structure of a Vertebra — Vertebral column — Limbs of Vertebrates — Digestive system — Circulatory system — Re- spiratory system— Nervous system— Reproduction— Primary divisions— Ichthyopsida— Sauropsida— Mammalia, p. 195-205 CHAPTER XXIV. General characters of the Fishes— Scales— Endoskeleton— Limbs— Tail— Digestive system— Circulation— Respiration— Nervous system— Organs of hearing and smell— Reproduc- tion, ....... .p. 206-213 CHAPTER XXV. Orders of Fishes— Pharyngobranchii— Marsipobranchii— Teleostei— Sub-orders of the Tele- ostei — Ganoidei — Elasmobranchii — Sub-orders of the Elasmobranchii — Dipnoi, p. 214-224 CHAPTER XXVI. General characters of the Amphibia — Orders of the Amphibia — Ophiomorpha — Urodela — Anoura— Labyrinthodoutia, p. 225-233 CHAPTER XXVII. General characters of the Reptilia— Circulatory and Respiratory systems— Divisions, p. 234-237 CHAPTER XXVIII. Orders of Reptilia— Chelonia— Ophidia— Lacertilia— Crocodffia— Ichthyopterygia— Saurop- terygia— Pterosauria, p. 238-252 CHAPTER XXIX. General characters of the Class Aves— Feathers— Vertebral column— Anterior extremity and pectoral arch — posterior extremity and pelvic arch — Digestive system — Respira- viii TABLE OF CONTENTS. tion— Circulatory system— Nervous system — Organs of the Senses— Migrations of Birds, Pages 253-264 CHAPTER XXX. Divisions of Aves — Natatores — Grallatores — Cursores — Easores — Scansores — Insessores Eaptores — Saururae, p. 265-279 CHAPTER XXXI. General characters of the Class Mammalia— Skeleton— Teeth— Dental formula— Digestive system — Heart — Lungs — Nervous system — Integumentary appendages — Development —Primary divisions, p. 280-287 CHAPTER XXXII. Orders of Mammalia— Monotremata—Marsupialia— Edentata— Sirenia— Cetacea— Ungulata — Hyracoidea — Proboscidea-^Carnivora — Rodentia — Cheiroptera — Insectivora — Quad- rumana— Birnana, . p. 288-320 LIST OF ILLUSTEATIO^S. 1. Diagram representing Transverse Sections of the Invertebrata and Vertebrata, . 16 2. Gregarina of the Earth-worm, ..... 28 3. Morphology of Ehizopoda, . . . . . .30 4. Morphology of Foraminifera, ..... 34 5. Nummulites Icevigatus, ....... 38 6. AcantJiometra and Haliomma, ..... 39 7. Morphology of Thalassicollida, . . . . . .40 8. Diagrammatic Section of Fresh- water Sponge, ... 41 9. Morphology and Eeproduction of Spongida, . . . .42 10. Paramozcium, ........ 46 11. Vaginicola, Stentor, and Vorticella, ... . . .48 12. Diagram of Sea-anemone, . .. ^ . ... 51 13. Morphology of Hydrozoa, ... ... . .53 14. Tubularia indivisa, • . • «, ., • • • 61 15. Morphology of Corynida, » .62 16. Eeproductive Processes of Hydrozoa,, » ... 63 17. Morphology of Sertularida, . . ~ . . . . . .67 18. Gonophore of one of the Campanularida, .... 68 19. DipJiyes appendiculata, . . . . , . . .71 20. Portuguese Man-of-War and Velella^ .... 73 21. Naked-eyed Medusao, . . . . . . .75 22. Lucernaria auricula, . . . . . . . 78 23. Development of Lucernarida, ... . . . .79 24. Generative Zooid of one of the Lucernarida, ... 81 25. Transverse Sections of Actinozoa and Hydrozoa, . . .85 26. Morphology of Actinidce, ...... 86 27. Structure of Coral-reefs, ....... 89 28. Pennatula phospfiorea, ...... 91 29. Morphology of Corals, . . . . . . .92 30. Plewdbrachia pileus, ....... 93 31. Morphology of EcJiinoidea, . . * . . . 97 32. Cidaris papillata, ....... 98 x LIST OF ILLUSTRATIONS. FIG. FAGE 33. Cribella oculata, . . . . . . . . 100 34. Morphology of OpMuroidea, . . . . . . 102 35. Comatula rosaeea, . . . . . . . 103 36. Khizocrinus Lofotensis, ...... 104 37. Cystidean, ......... 105 38. Holothurian, ........ 106 39. Morphology of Tceniada, . .• . . . . 109 40. Morphology of Trematoda, . . . . . 112 41. Morphology of Turbellaria, . . . . .113 42. Free Nematodes, . . . . . . , 115 43. Morphology of Botifera, . . . . . . .116 44. Diagram of an Annulose Animal, . . . . . 118 45. Syrinx nudus, . . . . . . . .119 46. Section of an Annelide, . . . . . . 120 47. Morphology of Hirudinea, . . - ; . . .122 48. Morphology of Tubicola, . « . . . ... 123 49. Morphology of Errant Annelides, , . , V . 124 50. Lobster, « . .. . . . , . 130 51. Spiny Spider-crab, . " . .. . i - ; * •' .132 52. Morphology of Isopoda, . . ^ , . . 133 53. King-crab, . . . . . . . ..- . 134 54. Pterygotus Anglicw, . . • . * , ••'. 134 55. Morphology of Trilobites, . . . . , .135 56. Fresh-water Entomostraca, . . . , .. » f 136 57. Morphology of Cirripedia^ .. . . , .. . .137 57i. Morphology of Podosomata and Acarina, . . . . 141 58. Scorpion, . .- . . - . .- . .142 59. Theridion riparium, . . . . . ; . 143 60. Scolopendra, . . . . . ... .145 61. Millipede, .• 145 62. External Anatomy of Insect, . . . - . . . . 147 63. Digestive Apparatus of Beetle, . . . . 148 64. Metamorphosis of Magpie-moth, . . .. . . 151 65. ApUsfdba:, 154 66. Cockroach, . . . . .... . 155 67. Migratory Locust, . . . . ... 156 68. Aphis-lion, . . . ... : -. . 157 69. Termes bellicosus, '.-..- .. .... 157 70. Tipula oleracea, . ,.• . . . ' -, < -• ,- . 158 71. Larva, Pupa, and Imago of Cabbage-butterfly, . . . 159 72. Gooseberry Saw-fly, „ . «, . • . . 161 73. Myrmica rufa, , . . .* . . . 162 74. Cockchafer, . .- . . . . . .163 75. Diagram of a Mollusk, .. . «. . . - . . 164 76. Morphology of Polyzoa, . . .. «. . . . 169 77. Flustra, ValTceria, and LopTiopus, ..... 170 78. Morphology of Tunicata^ ...... 172 LIST OF ILLUSTRATIONS. xj FIO. PAGE 79. Lingitla anatina, ....... 175 80. Anatomy of a Bivalve Mollusk, . . . . .177 81. Shells of Lamellibranchiata, ..... 178 82. Ampullaria canaliculata, . . . . , .181 83. Tongue of Whelk, 182 84. Shells of Gasteropoda, 183 85. Doris JoJimtoni, ....... 184 86. Carinaria cymbium, . . . . . . .184 87. Limax Sowerbyi, . . . . . . . 185 88. Morphology of Pteropoda, . . . . . .180 89. Sepiola Atlantica, . . . . . . .187 90. Paper Nautilus, . . . . . . . .191 91. Pearly Nautilus, . . . . . . .193 92. Orthoceras, . . . . . . . .193 93. Diagram of Invertebrata, and Vertebrata, .... 196 94. Lumbar Vertebra of Whale, and Diagram of Thoracic Vertebra, . 198 95. Skeleton of Beaver, ....... 199 96. Fore-limb of Chimpanzee, . . . . . .200 97. Hind-limb of Chimpanzee, ...... 200 98. Digestive System of a Mammal, ..... 202 99. Blood-corpuscles of Vertebrata, ..... 203 100. Scales of Fishes, ........ 207 101. Skeleton of Perch, ....... 208 102. Outline of a Fish, 209 103. Tails of Fishes, ' . ' 210 104. Diagram of the Circulation of a Fish, . . . . .211 105. Diagram of the Lancelot, . . . . . . 215 106 Lamprey, . . . . . . .217 107. Ganoid Fishes, : .' . . . . . 221 108. Cephalaspis Lyellii, . . . . . . .222 109. White Shark and Chimcera, ' 222 110. Lepidosiren annectens, ....... 224 111. Siphonops annulatus, ...... 227 112. Axolotl, • . . .228 113. Great Water-newt, ....... 229 114. Tree-frog, . . ' * 230 115. Development of the Common Frog, .... 231 116. Skull of a Python, . 235 117. Diagram of the Circulation of a Reptile, .... 237 118. Skeleton of a Tortoise, * . . . . . . 239 119. Hawk's-bill Turtle, . 240 120. Naja Haje, .241 121. Eye and Head of Viper, . . . . . . 243 122. Slow-worm, ........ 246 123. Scincus officinalis, ....... 247 124. Crocodilus vulgaris, . . . . . . . 248 125. Ichthyosaurus, ....... 249 xii LIST OF ILLUSTRATIONS. FIG. PAGE 126. Plesiosaurus, . . . . . . . .250 127. Pterodactyle, ; . 251 1'28. Shoulder-girdle and Fore-limb of Penguin, . . . . 256 129. Hind-limb of the Loon, 257 130. Digestive System of the Fowl, 259 131. Penguin, . ....... 266 132. Common Heron, . . . . . . . .268 133. Apteryx Australia, . . . . . . .270 134. Eock -pigeon, ........ 272 135. Purple-capped Lory, ...... 274 136. Heads and Feet of Insessores, ...... 275 137. Foot of Peregrine Falcon and Head of Buzzard, . . . 277 138. Foot and Head of Owl, . . . . • . • . 278 139. ArcTioBopteryx macrura, .' . . .- . : . -• 279 140. Lower Jaw of Chimpanzee, . . . i . 283 141. Diagram of the Circulation in a Mammal, . . « • « 285 142. OrnithorTiynchus, . . . . . . .289 143. Pkascolarctos cinereus, , , . • . . 290 144. Chlamyphorus truncatus, . . • . . . .292 145. Dugong, . .' . . . . . . •. 294 146. DelpJiinus del/phis, . . > . . '» . 296 147. Feet of Ungulata, . . . . . \ . 297 148. Head of Two-horned Khinoceros, . . . . . 298 149. Stomach of Sheep, . . . . . .300 150. Head of Cervus elapfius, . . . . . .302 151. Head of Strepsiceros Koodoo, . . . » . 303 152. Skull of Indian Elephant, .' .- . . . .305 153. Feet of Carnivora, . . . . . . . 306 154. Greenland Seal, . . . . . . . .307 155. Skull of Beaver, . . . . . 310 156. Hamster, . . . . . 0 .310 157. Skeleton of a Bat, - •. . . . . . 312 158. European Mole, ........ 314 159. Cercocebw sabceus, ....... 317 160. Skulls of Orang and European Adult, . . . .318 ZOOLOGY. INTRODUCTION. 1. DEFINITION OF BIOLOGY AND ZOOLOGY. ALL natural objects may be roughly divided into three groups constituting the so-called Mineral, Animal, and Vegeta- ble kingdoms. The objects comprised in the mineral kingdom are all devoid of life, and they exhibit the following characters : a. Their chemical composition is simple. They consist of either a single element, as is the case, for instance, with native gold ; or, if combined, they are almost always in nature in the form of simple compounds, composed of no more than two or three elements — as, for example, common salt, limestone, plas- ter of Paris, and many others, b. Mineral bodies are, when unmixed, composed of similar particles, which have no definite relations to one another, or, in other words, they are homo- geneous, c. The form of mineral bodies is either altogether indefinite, when they are said to be " amorphous ; " or, if they have a definite shape, they are crystalline, in which case they are usually bounded by plane surfaces and straight lines, d. When mineral bodies increase in size, as crystals may do, the increase is produced simply by the addition of particles from the outside (technically called '" accretion "). e. Mineral bodies exhibit no phenomena which are not purely physical and chem- ical, and they show no tendency to periodic changes of any kind. All the bodies which exhibit these characteristics properly belong to the mineral kingdom, and fall to be treated of by the sciences of Geology, Mineralogy, Chemistry, and Physics. It 2 INTRODUCTION. should be borne in mind, however, that, in the case of what are called " fossils " or " petrifactions," we have mineral bodies which owe their existence and characters to living beings which existed at former periods in the history of the earth. For this reason, fossils, though composed of mineral matter, can hardly be said properly to belong to the mineral kingdom. On the other hand, the objects which belong to the animal and vegetable kingdoms differ from those which are comprised in the mineral kingdom in the following points : a. They are composed of few chemical elements, of which carbon, hydro- gen, oxygen, and nitrogen, are the most important ; and these elements are combined to form complex organic compounds, which always contain a large proportion of water, are very un- stable, and are prone to spontaneous decomposition. #. They are composed of diverse or heterogeneous parts, which have usually more or less definite relations to one another. These heterogeneous but related parts are termed " organs," and the objects possessing them are said to be " organized." Some of the lowest forms of animals have bodies composed of so uni- form a substance that they cannot be said to be organized, as they exhibit no definite organs. This exception, however, does not affect the general value of this distinction, c. They are always more or less definite in shape, presenting concave and convex surfaces, and being bounded by curved lines, d. When they increase in size, or " grow," they do so, not by the addi- tion of particles from the outside, but by the reception of foreign matter into their interior and its assimilation there (technically called "intussusception"). e. They invariably pass through certain periodic changes in a definite and dis- coverable order ; these changes constituting life. They are subject to the same physical and chemical laws as those which govern dead matter, but the living body is the seat of some- thing in virtue of which it can override the physical laws which enslave mere dead matter. The living body, so long as it is a living body, is the seat of energy, and can overcome the primary law of the inertia of matter. It has certain relations with the outer world other than the merely passive ones of dead matter. 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 inde- pendent motion — a power possessed by nothing that is dead. In the higher animals the relations of the living body to dead nature become still further complicated, and their mastery over the physical forces becomes more and more pronounced, INTRODUCTION. 3 till in man, whose complex organization is wielded by an un- dying intelligence, we have a being in whose hands the dead matter of the universe is obedient as plastic wax. f. If our observation be continued for a sufficient length of time, we always discover that every living body has the power, by more or less complex process, of reproducing its like. That is to say, it has the power, directly or indirectly, of giving origin to minute germs, which can be developed under proper con- ditions into the likeness of the parent, g. Lastly, all living beings alike appear to be primitively composed of a substance which is more or less closely allied to albumen or white-of-egg, and which has been termed "protoplasm." Vital phenomena can apparently be manifested by no other form of matter, and protoplasm bears to life the same relation that a conductor does to the electric current. It is the necessary vehicle and medium through which life is brought into relation with the outer world. It does not, however, follow from this, as has been assumed, 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 they are manifested. All the objects, then, which fulfil these conditions, are said to be alive ; and they all belong either to the animal or to the vegetable kingdom.* The study of living objects of all kinds, irrespective of which kingdom they belong to, is conveniently called by the general name of Biology (Gr. Mos, life; and logos, discourse). As all living objects, however, may be re- ferred to one or other of these two kingdoms, so Biology may be divided into the two sciences of Botany, which treats of plants, and Zoology (Gr. zoon, animal ; logos, discourse), which treats of animals. The term Natural History, again, is gen- erally understood nowadays as being equivalent to Zoology alone, though originally it was applied to the study of all natural objects indiscriminately. 2. DIFFERENCES BETWEEN ANIMALS AND PLANTS. It now becomes necessary to inquire into the differences which subsist between animals and plants, and which enable us to separate the kindred sciences of Zoology and Botany. It might have been thought that nothing could be easier than to 4 * As will be mentioned immediately, it has been proposed to form an intermediate king- dom between the animal and vegetable kingdoms for the reception of organisms which cannot certainly be stated to be either plants or animals. There does not appear, however, to be any necessity for this in the mean while. 4 INTRODUCTION. determine the animal or vegetable nature of any given or- ganism ; and such, indeed, was the almost universal belief of older observers. In point of fact, however, no hard-and-fast line can be drawn, in the present state of our knowledge, be- tween the animal and vegetable kingdoms, and it is often a matter of extreme difficulty, or even wholly impossible, to decide positively whether we are dealing with an animal or a plant. So deeply has this difficulty been felt of late, that a most able zoologist — Dr. Ernst Haeckel — has proposed to form an intermediate kingdom, which he calls the Regnum Prolisticum, and in which he proposes to place all organisms of a doubtful character. Even such a cautious observer as Professor Rolleston, while questioning the propriety of this step, is forced to come to the conclusion that " there are or- ganisms which at one period of their life exhibit an aggregate of phenomena such as to justify us in speaking of them as ani- mals, while at another they appear to be as distinctly vege- table." In the case of the higher members of the two king- doms there is no difficulty in arriving at a decision. The higher animals are readily separated from the higher plants by the possession of a distinct nervous system, of locomotive 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 voluntary changes of place, and are not provided with any definite internal cavity, their food being wholly fluid or gaseous. The lower animals (Protozoa) cannot, however, be separated in many cases from the lower plants (Protophytd) by these distinctions, since many of the former have no digestive cavity, and are destitute of a nervous system, and many of the latter possess the power of active locomotion. In determin- ing, therefore, the nature of these ambiguous organisms, the following are the chief points to be attended to : Firstly, as to mere form or external configuration, no certain rules can be laid down for separating animals and plants. Many of the lower plants, either in their earlier stages of existence or when grown up, are exactly similar in form to some of the lower animals. This is the case, for ex- ample, in some of the Algce, which closely resemble some of the Infusorian animalcules. Many undoubted animals, again, are rooted to solid objects in their adult state, and are so plant-like in appearance as to be always popularly regarded as vegetables. This is the case with many of the so-called hydroid zoophytes, such as the sea-firs, and also with the much more highly organized sea-mats (Flustrd), all of which are usually regarded as sea-weeds by seaside visitors. This is also, but less strikingly, the case with the corals and sea-anemones, of which the latter are often spoken of as " sea-flowers." Secondly, no decided distinction can be drawn between animals and INTRODUCTION. 5 plants as to their minute internal structure. Both alike consist essen- tially of minute solid particles (molecules or granules), of cells, or of fibres. Thirdly, as regards chemical composition, there are some decided, though not universal, differences between plants and animals. As a general rule, it may be stated that plants exhibit a decided predominance of what are known to chemists as " ternary compounds " — that is to say, compounds which, like sugar, starch, and cellulose, are composed of the three elements, carbon, hydrogen, and oxygen. They are, comparatively speaking, poorly supplied with " quaternary " compounds, which contain the fourth element, nitrogen, in addition to the three first mentioned (e. g., gluten and legumin). Animals, on the other hand, are rich in quaternary nitrogenized compounds, such as albumen or fibrine. Still in both kingdoms we find nitrogenized and non-nitrogenized compounds, and it is only in the proportion which these bear to one another in the organism that animals differ in any way from plants. The most characteristic of all vegetable compounds is the one known as cellulose, very nearly allied in its chemical composition to ordinary starch. As a general rule it may be stated that the presence of an external envelope of cellulose in any organism raises a strong presumption as to its vegetable nature. Still cellulose is not exclusively confined to plants, as was at one time believed. It is now well known that the outer covering of the so-called sea-squirts or Ascidian Mollusks contains a large quantity of cellulose (as much as 60 per cent, in some cases) ; and recent researches seem to prove that this substance is present also in some of the lower forms of animal life (coccospheres). Another highly characteristic vegetable prod- uct is chlorophyll, the green coloring-matter of plants. Any organism which exhibits chlorophyll in any quantity as a proper element of its tissues is most probably vegetable. In this case also, however, the presence of chlorophyll cannot be regarded as a certain test, since it occurs regularly in some undoubted animals (e. g., Stentor among the Infusoria, and the Hydra viridis, or green fresh-water polype, among the Cozlenterata). Fourthly, as regards locomotive power, or the ability to effect changes of place at will, the results of observation are singularly at variance with our preconceived notions. Before the invention of the microscope, no instances of independent voluntary movements were known in plants, if we except the voluntary opening and closure of flowers and their turning toward the sun, the drooping of the leaves of sensitive plants under irritation, and some other phenomena of a like nature. Now, however, we know of many plants which are endowed, either when young or throughout life, with the power of effecting voluntary movements apparently as spontaneous and independent as those exhibited by the lower animals. In some cases the movements are brought about by means of little vibrating hairs or cilia with which a part or the whole of the surface is furnished. In other cases the movements seem to be certainly not produced by cilia, but their exact cause is obscure (e. g., in the Diatomacece and Desmidice, two of the lower orders of plants, all of which are microscopic in size). When it is added that many animals are permanently fixed and rooted to solid objects in their fully-grown condition, it will be seen that no absolute distinction can be drawn between animals and plants merely on the ground of the presence or absence of independent locomotive power. FiftJdy, we have shortly to consider one of the most reliable of all the tests by which an animal may be separated from a plant — namely, the nature of the food, and the products which are formed out of the food within the body. 6 INTRODUCTION. The differences between animals and plants in this respect may be roughly stated as follows : 1. Plants live upon purely dead or inorganic substances, such as water, carbonic acid, and ammonia — and they have the power of making out of these true organic substances, such as starch, cellulose, sugar, etc. Plants, therefore, take as food very simple bodies, and manufacture them into much more complex substances, so that plants are the great producers in nature. 2. Plants in the process of digestion break up carbonic acid into the two elements of which it is composed — namely, carbon and oxygen, keeping the carbon and setting free the oxygen. As carbonic acid occurs always in the air in small quantities, the result of this is that plants remove carbonic acid from the atmosphere and give out oxygen. 3. Animals, on the other hand, have no power of living on dead or in- organic matters, such as water, carbonic acid, and ammonia. They have no power of converting these into the complex organic substances "of which their bodies are composed. On the contrary, animals require to be supplied with ready-made organic compounds if their existence is to be maintained. These they can only get in the first place from plants, and therefore ani- mals are all dependent upon 'plants for food either directly or indirectly. Animals, therefore, differ from plants in requiring as food complex organic bodies which they ultimately reduce to very much simpler inorganic bodies. While plants, then, are the great manufacturers in nature, animals are the great consumers. Another distinction arising from the nature of their food is, that while plants decompose carbonic acid, keeping the carbon and setting free the oxygen, animals absorb oxygen and give out carbonic acid, so that their reaction upon the atmosphere is the reverse of that of plants. As regards these general distinctions between plants and animals, there are three points which should be remembered : 1. That, even if universally true, these distinctions can often not be ap- plied in practice to the ambiguous microscopic organisms about which alcne any doubt can be entertained. 2. These general laws are certainly not of universal application in the case of plants. Some fungi are known which in the matter of food are ani- mals— that is to say, they cannot live upon inorganic materials alone, but require ready-made organic products for their support. 3. Recent researches have rendered it not unlikely that some of the lower animals have the power of acting as plants, and of manufacturing organic compounds out of inorganic materials. 3. CLASSIFICATION. By the term classification is understood the arrangement of a number of dissimilar objects of any kind into larger or smaller groups according as they exhibit more or less likeness to one another. The number of different animals is so enor- mous that it was long ago perceived that some classification of them, or method of arranging them into groups, was abso- lutely indispensable. Without some such arrangement it would have been utterly impossible to have ever acquired a clear notion of the animal kingdom as a whole. In the older INTRODUCTION. 7 arrangements, animals were grouped in accordance with some particular character, which might or might not be a really essential one ; and the result was that these classifications were "artificial," and not "natural," as they are when all the characters are taken into consideration. To take a familiar example of this : when we speak of " quadrupeds," we really do so in consequence of our having, consciously or uncon- sciously, formed something like a rough classification of the animal kingdom. We have a dim idea that all animals with four legs belong together somehow, and form a single group. Our classification, however, is founded upon a single character only — the possession, namely, of four legs ; and it is, there- fore, a purely artificial arrangement. It will, however, be practically good or bad, just as this single character expresses a genuine and fundamental distinction, or is of a merely trivial and superficial nature. The instance here chosen will serve to illustrate either case. If we insist upon the fact that all the four legs must be externally visible, unmistakable legs, never fewer in number than four, then our classification is a very bad one, in fact entirely " artificial." In this case our group of "quadrupeds" will comprise only the ordinary four-legged mammals, such as oxen, sheep, horses, and such-like — together with the very dissimilar groups of the four-legged reptiles and amphibians, such as tortoises, lizards, crocodiles, frogs, and newts. Now, these different animals have certainly much in common, but we are not justified in placing them together simply upon the ground that they have four conspicuous legs, unless we are willing to put in a vast number of other animals as well. We must, in fact, put in a great number of animals which are not quadrupeds in the sense that they have four legs, but which agree with those that have four legs in the other fundamental and essential points of their 'structure. In this way we may arrive at a very genuine and natural classification by making some concessions. We must allow, for instance, that two of the legs or limbs, ceasing to be fit for walking, may be converted into organs of flight, or wings. This will let in the birds. We must allow, again, that all the limbs may be converted into fins. This admits most of the fishes. We must further grant that two of the legs may be altogether absent while the remaining two are converted into swimming- paddles. This will bring in the whales and dolphins. Lastly — and this is the greatest admission of all — we must allow the total absence of all the limbs, provided the animal only show those other essential characters which are invariably 8 INTRODUCTION. found to go along with the possession of four legs in the regu- lar quadrupeds. This will bring in the snakes and some of the fishes. So that, paradoxical as it may seem, it is in one sense scientifically correct to speak of a snake as a quadruped, though in reality it has no legs at all. In other words, there is no reason why a snake should not some day be found with four legs, and in point of fact some snakes show rudiments of these appendages. Making these allowances, and some more of a similar nature, we may ultimately succeed in converting our division of Quadrupeds into a strictly scientific group, comprising the Mammals, the Birds, the Reptiles, the Amphi- bia, and the Fishes. In fact, our group of Quadrupeds now agrees exactly with the great and natural division of the Ver- tebrata or vertebrate animals. It is true that all vertebrate animals have not got four limbs, or not obviously so, but they never have more than four under any circumstances ; and a closer examination soon shows us that they agree with one another in many other characters which are of much greater importance than the characters of the limbs alone. We have arrived, then, at the grand principle of all good classification — namely, that we should group together those objects only which are united by essential and fundamental points of similarity, and that in so doing we should ignore all mere superficial resemblances. The question now arises, What are these essential and fundamental points in the case of animals ? If for the moment we look at animals simply as so many machines, we shall not find much difficulty in answering this question. Let us suppose ourselves placed in a gigantic workshop full of an immense number of complicated and curi- ously-constructed machines of different sorts, and asked to put them in order — to put those of one kind in one place, and those of another kind in a different place. How should we proceed to act ? Supposing, in the first place, that all the machines were at a stand-still, all that could be done would be to examine carefully the external form and internal struct- ure of each, and to do our best to pick out some peculiarity which would distinguish some from all the others. In this way, if our mechanical knowledge were sufficiently extensive, we should no doubt ultimately succeed in classing all our ma- chines into something like a rough natural arrangement. We should, for instance, have those made on the principle of the lever in one place, those on the principle of the inclined plane in another, and those on the principle of the pulley in a third. INTRODUCTION. 9 Still our classification would most certainly be imperfect, and in some cases altogether incorrect. In some instances the parts of the machine would be so complex as to be utterly in- comprehensible, and in many cases our ignorance of what each was intended to effect would be an insuperable bar to our arriving at any arrangement. Suppose now, however, that all the machines were suddenly set in motion, so that we could see not only the manner in which they were constructed and the materials of which they were composed, but could also see what they could do — could see, in fact, for what work each is intended. The task of arrangement now becomes im- mensely easier. Our previous classification, founded simply upon the structure of the machines, is now supplemented and rectified by our knowledge of what each is able to effect. One machine is found performing one set of actions, another a different set ; and in this way not only is our classification rendered much easier, but we now get an insight into the meaning and nature of many points of structure which were formerly obscure. To make this illustration fully meet the case of the natu- ralist who deals with living beings only, we have simply to suppose that the machines to be examined are reasonably per- fect in their parts and fit for work, and that our imaginary workshop is supplied with a reasonable amount of light, not very brilliant, perhaps, and striking upon some objects more sharply than on others, but still upon the whole moderately steady and uniform. Far worse, however, is the case of the naturalist who has to deal with the remains of extinct gen- erations of animals and plants, whose work lies among those relics of a by-gone world which are known as " fossils " or " petrifactions " — objects in many cases more wonderful and more perplexing and more beautiful than the most ornate and elaborate productions of human skill. In his case the work- shop is a vast and gloomy vault or charnel-house, with no in- ternal source of light, and but fitfully illuminated by uncer- tain gleams from the world without. And what is worse than this, his machines are mutilated and defaced, in many cases wanting their most important parts, in all cases destitute of life and motion, and usually very unlike any thing visible at the present day. Nevertheless it is almost incredible with what certainty and precision a mere fragment of a fossil, a single tooth or bone, can be referred by a skilled wrorker in this field of science to its proper place in the animal kingdom — with what exactitude the missing parts can be restored — 10 INTRODUCTION. and what splendid generalizations can be drawn from what at first sight would appear to be the most fragmentary evidence. This imaginary illustration exactly expresses the points which are to be regarded as essential and fundamental in clas- sifying and arranging animals. We have to look, namely, firstly, to the plan upon which each animal is constructed ; secondly, to the manner in which it discharges its vital func- tions. These are the two points of view from which every organism may be regarded — in their nature quite distinct, and indeed sometimes apparently opposite. From the one point of view we have to look solely to the laws, form, and arrange- ment of the structures of the organism. This constitutes what is technically called " Morphology," or the science of form (from the Greek words, morphe, form ; and logos, a discourse). From the second point of view, we are concerned simply with the functions discharged by the different parts of the organ- ism, and this constitutes what is known as " Physiology." It is most important to remember that there are no other points in which it is possible for one animal to differ from another. If two animals are different, they must differ in one or other or in both of these points. Either they differ morphologically, in being constructed upon altogether different plans ; or they differ physiologically, in performing a different amount of vital work in a different manner, and with different instru- ments ; or they differ both morphologically and physiologi- cally. Philosophical classification, therefore, insomuch as it depends entirely upon a due appreciation of what are the real differences between different animals, is nothing more than an attempt to express formally the facts and laws of Mor- phology and Physiology. Examining next into the nature and extent of the morpho- logical or structural differences between different animals, we find that these are much less and much fewer than might have been thought. By one not previously acquainted with the subject, it might readily be supposed that every kind of ani- mal was constructed upon a type or plan peculiar to itself and not shared by any other. We should certainly suppose, for example, that animals so different as a lobster and a butterfly were built upon different types or plans of structure. When we come, however, to examine the question, we find that this is not the case. The lobster and the butterfly are constructed upon the same structural plan or morphological type. What is still more remarkable, we find that all known animals, in spite of their immense differences in external appearance, are INTRODUCTION. H really constructed upon no more than some half-dozen primary plans of structure or morphological types. These types are all different from one another, but there is no animal yet known to us, living or extinct, which cannot be referred to one or other of these six plans. These plans, then, give us the primary basis for a classification of the animal kingdom — all the animals formed upon one plan being grouped together so as to form a single division. The animal kingdom, therefore, is primarily divided into six great sections corresponding to the six morphological types, and these sections are known to naturalists under the name of the " sub-kingdoms." Each of these sub-kingdoms has its special name, and it is the object of the present work to describe the leading characters and more important examples of each. We have to understand, then, that all the animals belong- ing to each sub-kingdom agree with one another in their mor- phological type, or, in other words, in the plan upon which they are constructed ; and the question now arises how they can be separated from each other. If they agree morphologi- cally, there is only one other way in which they can differ, and that is physiologically r, in the manner in which they dis- charge their vital functions. Consequently, all animals which agree with one another in their plan of structure, and which are therefore placed in the same sub-kingdom, are separated from one another solely by their physiological perfection. In other words, as machines, they are constructed of the same fundamental parts, but they do their work in a different way and with different instruments. Returning to our old illustration, suppose we had sepa- rated from the mass of machines before us all those which were intended to mark the lapse of time, and had in this way assembled a large collection of hour-glasses, watches, time- pieces, and clocks, and suppose that we wanted to arrange these more minutely, we should soon discover that each of these different time-keepers was formed upon a principle pe- culiar to itself. The hour-glasses, as the most simple, would form one division ; the timepieces and clocks, possessing pen- dulums, would form another ; and the watches would form a third. These, as being constructed upon different plans, would constitute three distinct groups, which we should call classes or sub-kingdoms according to the value we might see fit to place upon the differences between them. But we must fur- ther suppose that we wished to divide one of these groups — say the watches — into still smaller groups. If they were all 12 INTRODUCTION. standing, we should probably find this a matter of very great difficulty. The moment, however, that they commenced to go — or, in other words, to perform their own peculiar func- tion— we should soon see that some would be different to the others. Some, for instance, would strike the hours, and these would have to be laid aside in a group by themselves. And we should further discover that, in accordance with the difference in the function, there would be an equivalent dif- ference in the structure, of these two groups. The striking watches would be formed upon the same fundamental type as those which did not strike ; but, in addition to the broad and general details of structure in which all were the same, the striking watches would have a special apparatus or structure fitted for striking the hours. The non-striking watches would be destitute of this apparatus, so that the physiological or functional difference between the two groups would thus en- tail a corresponding difference in structure. It is just the same with animals. Tf we take a lobster, a butterfly, a scorpion, and a spider, we find that, dissimilar as they are in external appearance, they are all constructed upon the same fundamental plan. They agree in morphological type, and they belong to the same sub-kingdom. They lead different lives, however — they are placed under different con- ditions— and they discharge different functions in the general economy of Nature. They differ, therefore, physiologically ; and, as every physiological difference implies a corresponding structural difference, they differ structurally as well. But they differ structurally only because they differ physiologi- cally, and in all the really essential details of their structure they are the same. The lobster is aquatic in its habits, and has therefore gills, or organs adapted for breathing air dis- solved in water. The butterfly is aerial, and has respiratory organs adapted for breathing air directly, and not through the medium of water. They differ, then, physiologically, and therefore, necessarily, in the corresponding structure. Both, however, have distinct organs set apart and dedicated to the function of respiration. This is an essential and fundamental point in their structure, and in this they both agree with one another, and differ from a large number of animals in which there are no distinct breathing-organs. It is only by the com- bined effect of a number of these physiological differences, taken collectively, that the lobster and the butterfly come ulti- mately to be so strikingly distinct from one another It is now possible to comprehend fully the principles upon INTRODUCTION. 13 which a naturalist proceeds in framing a classification of the animal kingdom. His great primary divisions are founded up- on differences in the smaller and fundamental details of struct- ure. His smaller divisions are based upon the less important physiological differences with their corresponding structural distinctions. Of course, in carrying out this programme of a truly philosophical and natural classification, the naturalist works to a great extent in the dark, and is liable to many sources of error. It is by no means always easy to deter- mine what points of structure are essential and fundamental, and what are only caused by physiological differences. Such, too, is the constitution of the human mind, that different ob- servers place different values upon the same structures ; points which some look upon as of essential value are regarded by others as of a merely superficial nature. Nevertheless there can be no doubt that the progress of Natural History as a science has been strictly conterminous with the development of these great principles of classification. In the present work an outline is given of the morpho- logical differences between all the larger groups of the animal kingdom, but it may be as well here to say a few words upon the subject of Physiology. As already remarked, Physiology treats of all the functions exercised by living bodies, or dis- charged by the various definite parts or organs of which most animals are composed. All these various functions come un- der three great heads : 1. Functions of Nutrition, comprising all those functions by means of which an animal is able to live, grow, and maintain its existence as an individual. 2. Func- tions of Reproduction, comprising all the functions by which fresh individuals are produced and the perpetuation of the species insured. 3. A series of functions which are known by the somewhat misleading name of the Functions of Rela- tion or of Correlation. Under this term are included all those functions by means of which external objects are brought into relation with the organism, and by which it, in turn, reacts upon the outer world. The functions of nutrition and repro- duction are often spoken of collectively as the functions of " organic " or u vegetative " life, as being common to animals and plants alike. The functions of relation, again, are often called the functions of " animal " life, as being most highly developed in animals. These functions, however, though more highly characteristic of animals, are not peculiar to them, bir'- are manifested to a greater or less extent by various plants. As regards animals, all alike, whatever their structure may 14 INTRODUCTION. be, perform the three great physiological functions — that is to say, they all nourish themselves, reproduce their like, directly or indirectly, and have certain relations with the external world. When we come, however, to compare animals together physio- logically, it is soon seen that the functions of relation stand in quite a different position to that occupied by the functions of nutrition and reproduction. As far as these last are con- cerned, there can be no difference in the amount or perfection of the function discharged by the organism. The simplest and most degraded of animals — say a sponge — nourishes it- self as perfectly, as far as the result to itself is concerned, as does the highest of animals. Nutrition can do no more than maintain the body of any animal in a healthy and vigorous condition. This is the highest possible perfection of the func- tion, and it is attained as fully and perfectly by the sponge as it is by man himself. The same holds good of reproduction. While the functions of nutrition and reproduction are thus, as regards their essence and results, the same in all animals, it must be remembered that there are enormous differences in the manner in which the functions are discharged. The result attained is in all cases the same, but it may be arrived at in the most different ways and with the most different apparatus. As regards the functions of relation, on the other hand, we have every possible grade of perfection exhibited as we as- cend from the lowest members of the animal kingdom to the highest. So numerous, in fact, are the changes in these func- tions, and so great the additions which are made in the higher organisms, that it may be doubted if there exists any common element by which a comparison can be drawn on this head be- tween the higher and lower animals. It may reasonably be doubted whether in this respect a horse or a dog has any thing in common with a sponge. Instead of giving here a general sketch of each of the great physiological functions as a whole, it may be as well to accom- pany the morphological account of each primary division of animals with a short account of the manner in which the vital functions are carried out in the same. In this way a clearer view will be obtained of the gradual rise in physiological per- fection in passing from the bottom to the summit of the ani- mal series. HOMOLOGY AND ANALOGY. — In connection with the mor- phological and physiological differences between animals, a . short explanation may be given of the meaning of the terms Homology and Analogy, which are in constant use in zoologi- INTRODUCTION. 15 cal works. When organs in different animals agree with one another in their plan of structure, they are said to be " homolo- gous," no matter what may be the functions which they perform. For example, the arm of a man, the fore-leg of a horse, the wing of a bird, and the swimming-paddle of a dolphin or whale, are all composed essentially of the same structural elements, and they are therefore said to be homologous, though they are fitted for altogether different functions. On the other hand, when organs in different animals per- form the same functions, they are said to be " analogous," whatever their fundamental structure may be. Thus the wing of a bat, the wing of a bird, and the wing of an insect, all serve for flight, and they are therefore " analogous " organs. They are all, however, constructed upon different plans, and they are, therefore, not "homologous." At the same time, however, it is to be remembered that there are plenty of cases in which organs in different animals are not only constructed upon the same plan, but also perform the same function, so that they are both homologous and analogous. GENERAL DIVISIONS OF THE ANIMAL KINGDOM. As already stated, the entire animal kingdom may be di- vided into some half-dozen primary plans of structure or mor- phological types, to one or other of which every known animal is referable. These primary types are known to naturalists as the sub-kingdoms, under the following names : Protozoa, Coe- lenterata, Annuloida, Annulosa, Mollusca, and Vertebrata. The characters and minor subdivisions of these sub-kingdoms form the subject of the remainder of this work. In the mean while, it is sufficient to state that Ihe first five of these are often grouped together under the collective name of the Inverte- brata, or " invertebrate animals." The Invertebrata, compris- ing the Protozoa, Ccelenterata, Annuloida, Annulosa, and Mollusca, are collectively distinguished by the following points among others : The body, if divided transversely, or cut in two, shows only a single tube containing all the vital organs (Fig. 1, A). These organs, in the higher Invertebrata, consist of an alimentary or digestive cavity, a circulatory or " haemal " system, and a nervous or " neural " system. The side of the body on which the " haemal " or blood-vasculai system is placed is called the " haemal aspect ; '' while the side of the body on which the main masses of the nervous system are situated is called the "neural aspect." When there is 16 INTRODUCTION. any skeleton, this is external (forming an " exo-skeleton "), and it is really nothing more than a hardening of the skin. The limbs, when present, are turned toward the neural aspect of the body. In the Vertebrate, on the other hand, the body, if trans- versely divided, exhibits two tubes. In one (Fig. 1, B) is placed the main mass of the nervous system (the brain and spinal FIG. 1. — Diagrams representing transverse sections of one of the higher Invertebrata, A — and one of the Vertebrata, B. a Wall of the body ; b Alimentary canal ; c Haemal or blood-vascular system ; n Nervous system ; n' Cerebro-spinal axis, or brain and spinal cord of the Vertebrata, enclosed in a separate tube : ch Noto-chord or chorda dorsalis. (Slightly altered from Huxley.) cord). In the other tube are the alimentary canal, the haemal or blood-vascular system, and certain other portions of the nervous system, which are known as the " sympathetic " sys- tem of nerves, and which correspond to, or are homologous with, the entire nervous system of the Invertebrata. Further, in the Vertebrata there is always an internal skeleton (or endo-skeleton), the central stem of which is usually consti- tuted by a true backbone or " vertebral column." When this is not present, there is always a structure which will be after- ward described as the " noto-chord " or " chorda dorsalis." Lastly, the limbs of the Vertebrata^ when present, are never more than four in number, and they are always turned away from the neural aspect of the body — away, that is, from the side on which the main masses of the nervous system are placed. Subjoined is a short tabular view of the main existing divisions of the Animal Kingdom, the characters and smaller divisions of which will be considered- hereafter at length : INTRODUCTION. 17 INVERTEBRATE ANIMALS. SUB-KINGDOM L— PROTOZOA. Animal simple or forming colonies, usually very minute ; the body com- posed of the structureless, jelly-like, albuminous substance called "sarcode;" not divided into regular segments ; having no nervous system ; no regular circulatory system ; usually no mouth ; no definite body-cavity, or at most but a short gullet. CLASS A. GREGARINID.E — Minute Protozoa which inhabit the interior of insects and other animals, and which have not the power of throwing out prolongations of their substance (pseudopodia). No mouth. CLASS B. RHIZOPODA (Root-footed Protozoa). — Protozoa which are simple or compound, and have the power of throwing out and retracting pro- longations of the body-substance (the so-called "pseudopodia " ). No mouth, in most, if not hi all. Order 1. Monera. — Ex. Protogenes. Order 2. Amcebea.—Ex. Proteus Animalcule (Amoeba). Order 3. Foraminifera. — Ex. Lagena, Nodosaria, Globigerina. Order 4. * Radiolaria. — Ex. Thalassicolla, Polycystina. Order 5. Spongida. — Ex. Fresh-water Sponge (Spongilla), Venus's Flower-Basket (Euplectella). CLASS C. INFUSORIA (Infusorian Animalcules). — Protozoa with a mouth and short gullet ; destitute of the power of emitting pseudopodia ; furnished with vibratile cilia or contractile filaments ; the body usually composed of three distinct layers. Order 1. Ciliata. — Ex. Bell-animalcule (Vorticella), Paramcecium. Order 2. Flagellaia. — Ex. Peranema. Order 3. Suctoria. — Ex. Podophyra. SUB-KINGDOM II.—C Modeeria fomnosa ; c Polyxe- nia Alderi (after Gosse). 76 INVERTEBRATE ANIMALS. may be taken as a good example, the general structure is briefly as follows : The hydrosoma is perfectly free and is oceanic, being found swimming near the surface in the open ocean. The body is composed of a thick, transparent, gelatinous disk or swimming-bell (the nectocalyx), by the pulsations of which the animal is driven through the water. From the under surface or roof of this bell-shaped disk is suspended a single polypi te (the manubrium), which bears to the disk the same relative position as the clapper does to an ordinary hand- bell. The distal end of the central polypite is furnished with a mouth, the lips of which are often prolonged into four longer or shorter lobes or processes. The mouth opens into a digestive sac, occupying the axis of the polypite ; and from the upper end of this proceed four radiating canals, which run in the substance of the disk to its margin, where they are united by a single circular vessel, the whole system con- stituting the so-called " gastro-vascular " canals. The margin of the bell is narrowed by a kind of shelf, which runs round the whole circumference, leaving a central aperture, and which is known as the " veil." From the margin of the disk hang more or less numerous tentacles, which are hollow processes of the ectoderm and endoderm, and which communicate with the circular vessel of the canal-system. Also round the cir- cumference of the swimming-bell are disposed certain " margi- nal bodies," which are doubtless organs of sense. Some of these marginal bodies consist of little rounded sacs or " vesi- cles," filled with a transparent fluid, and containing mineral particles, apparently of carbonate of lime. These are probably rudimentary organs of hearing. Others of the marginal bodies are in the form of little masses of coloring-matter or pigment, often of a strikingly bright color, enclosed in distinct cavities. These are known as the " pigment-spots " or " eye-specks," and they are believed to be rudimentary organs of vision. They are placed in a conspicuous and unprotected position on the margin of the disk, and hence these organisms were termed " naked-eyed " Medusae, by Edward Forbes. The reproductive organs are mostly developed in the course of the radiating gastro-vascular canals, but are sometimes situated in the walls of the central polypite. The above is the essential structure of any of the ordinary naked-eyed Medusm ; and it is hardly necessary to remark that it is exactly similar to what has been formerly described as distinguishing the undoubted free- swimming reproductive buds of the fixed Hydrozoa. The probabilities, therefore, as before said, are in favor of the belief DISCOPHORA. 77 that the entire group of the Discophora will have to be ulti- mately done away with. The naked-eyed Medusce are all exceedingly elegant and attractive, when examined in a living condition, resembling little bells of the most transparent glass, adorned here and there with the most brilliant colors. They occur, in their proper localities and at proper seasons, in enormous numbers, and they constitute one of the staple articles of diet to the Greenland whale. They are mostly phosphorescent, or capa- ble of giving out light at night, and they appear to be one of the principal sources of the luminosity of the sea. It does not seem, however, that they phosphoresce unless disturbed or irritated in some way. CHAPTER VIII. SUB-CLASSES LUCERNARIDA AND GRAPTOLITID^E. THE last remaining group of the living Hydrozoa is that of the I/ucernarida (Lat. lucerna, a lamp), under which name are included a considerable number of forms, differing from one another to a great extent in exter- nal appearance. It will be sufficient here to describe one or two typical forms. One group of the Lucernarida is represented by Lucernaria itself (Fig. 22), which occurs not uncommonly in temperate seas. In Lucernaria we have a cup-shaped body, of a more or less gelatinous consistence, usually found attached by its smaller extremity to sea-weeds, this end of the body being developed into a small sucker. Like the Hydra, however, Lucernaria is not fixed, but can detach itself at will, and can even swim freely by means of the alternate contraction and expansion of the cup-shaped body (or " umbrella," as it is termed). Round the margin of the cup are tufts of short tentacular processes, and in its centre is fixed a single polypite, furnished with a four- FiG.22.-Two specimens of LU- lobed mouth. The essential elements cemaria auricula attached of reproduction are developed within ?ohnPSton).°fSea"Weed(after the body of Lucernaria itself, and it does not give off any generative buds, as so commonly occurs in other forms. LUCERNARIDA AND GRAPTOLITIDJ3. 79 Another type of the Lucernarida is represented by the organisms formerly termed " hidden - eyed " Medusas^ and familiarly known as sea-nettles or sea-blubbers. Every sea- side visitor is familiar with the great circular disks of jelly which are left upon the sands by the retreating tide during the summer months ; and many must have noticed on a calm day the large, transparent disks of these same creatures slowly flapping their way through the water. Not a few, too, must have learned by painful experience that some of these singular organisms have the power of stinging most severely, if in- cautiously handled. The forms included under the old name of " covered-eyed " Medusw differ considerably from one an- other in their nature, and even in their structure, though they all present, in spite of their much greater size, a decided re- semblance to the naked-eyed Medusm already described. Some of the covered-eyed Medusae produce eggs which are developed into organisms resembling themselves ; but most of them are now known to be nothing more than the free-swimming re- productive buds of minute rooted Hydrozoa. It will be suf- ficient here to describe shortly the life-history of one of the more remarkable forms of this section. If we commence with the young form of one of these sin- FIG. 23.— Development of Lucernarida (Chrysaora). a Ciliated embryo; b Hydra-tuba; c Hydra-tuba beginning to divide by transverse cleavage ; d The cleavage still further advanced ; e A form in which the cleavage has proceeded still further, and a fresh circle of tentacles has been produced near the base ; / Free-swimming, generative zooid, pro- duced by fission from the Hydra-tuba. gular animals, we find that the egg gives origin to a little microscopic ciliated body, which swims about freely by means of the cilia with which its surface is covered (Fig. 23, a). 80 INVERTEBRATE ANIMALS. This little body, on finding a suitable locality, fixes itself by one end, and develops a mouth and tentacles at the other, when it is known as a "Hydra-tuba" (Fig. 23, #), from its resemblance in shape to the fresh-water polype or Hydra. The Hydra-tuba is only about half an inch in height, and it possesses the power of forming large colonies by gemmation, while it is incapable of developing the essential elements of reproduction. Under certain circumstances, however, repro- ductive zoftids are produced by the following singular process : The Hydra-tuba becomes elongated, and exhibits a number of transverse grooves (Fig. 23, c). These grooves go on get- ting deeper and deeper, and become lobed at their margins, till the whole organism assumes the aspect of a pile of saucers placed one above the other (Fig. 23, d). The tentacles now disappear, and a fresh circle is formed close to the base of the Hydra-tuba (Fig. 23, e). Finally, all the saucer-like segments above the new circle of tentacles drop off one by one, and pre- sent themselves in the form of independent, free-swimming Medusae, (Fig. 23,/). These reproductive zooids or Medusae eat voraciously, and increase rapidly in size, becoming not only comparatively, but often actually, gigantic. Thus, in one case the reproductive zoo'id has been known to attain a size of seven feet across, with tentacles fifty feet in length, though the fixed organism from which it was produced, wras no more than half an inch in height. These gigantic repro- ductive bodies live an independent life until they are able to produce ova and sperm-cells, when they die. The fertilized egg, however, develops itself, not into the monstrous organism by which it was produced, but into the little fixed sexless Hydra-tuba, from which the generative bud was detached. We have, then, here another instance of the so-called " alterna- tion of generations." It is now known, then, that most of the great sea-blubbers which abound around our coasts in summer are really the detached reproductive buds of minute fixed Hydrozoa ; and it may be as well to mention the leading features in their struct- ure, and the points by which they may be distinguished from the smaller or naked-eyed Medusae, to which they have a de- cided superficial likeness. In the commonest forms of these zooids (such as the familiar sea-blubbers, Aurelia and Cyaned)^ the body consists of a great bell-shaped gelatinous disk or " umbrella," from the roof of which is suspended a single polypite, the lips of which are extended into lobed processes, often extending far below the margin of the disk (Fig. 24). LUCERNARIDA AND GRAPTOLITDLE. 81 The digestive cavity of the polypite gives out from its upper extremity a series of radiating gas tro- vascular canals, which proceed toward the margin of the umbrella. These radiating canals are never less than eight in number, and on their way to the margin of the disk they break up into a great number of smaller vessels, which unite with one another to form a complicated net-work. At the margin of the bell they all FIG. 24.— Generative zooid of one of the Lucernarida (Clirysaora hysoscclla). (After Gosse.) open into a circular vessel, which in turn sends processes into a series of marginal tentacles, which are often of extraordinary length. Besides the tentacles, the margin of the umbrella is provided with a number of marginal bodies, each of which consists of a little collection of pigment or " eye-speck," and a little sac filled with fluid and containing mineral particles. Each of these marginal bodies is covered and concealed from view by a kind of hood derived from the ectoderm. Hence the name of "hidden-eyed" Medusae applied to these forms, in contradistinction to the " naked-eyed " Medusas, in which the eye-specks are exposed to view. The reproductive organs are usually of some bright color, and " form a conspicuous cross shining through the thickness of the disk." 82 INVERTEBRATE ANIMALS. From the above description it will be evident that there is considerable resemblance between the so-called " hidden-eyed" Medusae, or the reproductive zoOids of many of i\^Q Lucernarida, and the medusiform gonophores of so many of the Hydrozoa, as well as the true Discophora or naked-eyed Medusae. The differences, however, between them are these: The swimming- disk of the naked-eyed Medusae and of any medusiform gono- phore is furnished at its mouth with an internal shelf or veil ; the radiating gastro-vascular canals are very rarely more than four in number, and, should they subdivide (as in rare cases they do), they do not form an intricate net-work; lastly, the marginal bodies are simply placed in an uncovered situation on the margin of the disk. In the reproductive zooids of the Lucernarida or hidden-eyed Medusae, on the other hand, the swimming-disk or umbrella is destitute of any marginal shelf or veil ; the radiating gastro-vascular canals are never less than eight in number, and they split up into numerous branches, which unite to form an intricate net- work ; lastly, the marginal bodies are concealed from view by a kind of hood. There still remains another family of the Lucernarida (viz., Rhizostomidoe) in which the reproductive process is carried on in the same way as in the forms we have just described, but the structure of the reproductive zooids is somewhat different. In these, as in Rhizostoma, the generative zob'id is much like those just mentioned ; but the umbrella is destitute of marginal tentacles ; and, in place of a single central polypite, there hangs from the under surface of the umbrella a com- plex tree-like mass, the branches of which end in, and are covered by, small polypites and club-shaped tentacles. The umbrella itself does not exhibit any difference as compared with those already described, but the ova are produced in a genital cavity which is placed on the under surface of the umbrella. SUB-CLASS GRAPTOLITID.E. — Before leaving the Hydrozoa, it will be as well to notice very briefly a group of extinct organisms which certainly belong to this class, and which probably find their nearest allies in the Sertularians. The Graptolitidce are without a single living representative, and their anti- quity is, indeed, very high, since it is doubtful if they ever pass above the group of rocks known to geologists as the Silurian formation. The most typical forms of the group agree with the living Sertularians in having a horny polypary, and in having the polypites protected by little horny cups or hydrothecae, all springing from a common flesh or cocnosarc. The typical Graptolites, however, differ from all known Sertularians in the fact that the hydrosoma was not fixed to any solid object, but was permanently free. LUCERNARIDA AND GRAPTOLITID.E. 83 Most of them, also, exhibit a very anomalous and remarkable structure, termed the " solid axis." This is a peculiar fibrous rod, which no doubt served to strengthen the polypary, and which is often prolonged beyond one or both ends of the polypary in a naked state. There is also good evidence that the reproductive process in the Graptolites was carried on in a manner somewhat similar to what is seen in the living Sertularians — namely, by means of reproductive buds enclosed in horny capsules. Graptolites most usually present themselves as beautiful silvery impressions, covering the sur- face of the black shales of various parts of the Silurian system. CHAPTER IX. ACTINOZOA. THE second great class of the Coelenterata is that of the Actinozoa, comprising the sea-anemones and their allies, the corals, the sea-pens, the sea-shrubs, and various other organ- isms. They are all defined as Ccelenterate animals in which there is a distinct digestive sac which opens below into the general cavity of the body, but is nevertheless separated from the body-walls by an intervening space, which is divided into a number of vertical compartments by a series of partitions or " mesenteries" to the faces of which the reproductive organs are attached. The Actinozoa (Fig. 12), therefore, differ fun- damentally from the Hydrozoa in this, that whereas in the latter the digestive cavity is identical with the body-cavity, in the former there is a distinct digestive sac, which opens truly into the body-cavity, but is nevertheless separated from it by an intervening space. The result of this is, that while the body of a Hydrozodn exhibits on transverse section a single tube only, formed by the walls of the combined diges- tive and somatic cavity, the body of an Actinozodn exhibits two concentric tubes, one formed by the digestive sac and the other by the general walls of the body (Fig. 25, A). Further, in the Actinozoa the reproductive organs are always internal, and are never in the form of external processes of the body- wall as in the Hydrozoa. In their minute structure the tissues in the Actinozoa dif- fer little from those of the Hydrozoa. The body is essen- tially composed of two fundamental layers — an ectoderm and endoderm ; but there are often well-developed layers of mus- cular fibres, somewhat obscuring this simplicity of structure. Thread-cells are most commonly present in abundance. Cilia are very generally developed, especially in the endoderm lining ACTINOZOA. 85 the body-cavity, where they serve to maintain a circulation of the contained fluids. The only digestive apparatus consists of a tubular or sac-like stomach, which opens inferiorly directly into the body-cavity (Fig. 12, a), and communicates FIG. 25.— A. Transverse section of an Actinosoon. a Digestive sac; b Outer- wall of the body or ectoderm ; 6' Endoderm ; m Mesenteries, connecting the stomach with the body- walls, and dividing the space between the two into a number of vertical chambers. B. Transverse section of the body of a Hydrozoon, showing the single tube formed by the walls of the body. with the outer world through the mouth. A nervous system has not been shown to exist in any of the Actinozoa except the Ctenophora, and in none are there any traces of a circula- tory system. Distinct reproductive organs are always present, and true sexual reproduction occurs in all the members of the class. In a great many forms, however, of the Actinozoa we have composite organisms or colonies, produced by a process of " continuous " gemmation or fission, the zoOids thus origi- nated remaining attached to one another. In these cases — as in most of the corals — the separate beings or zo5ids thus produced are termed " polypes," the term " polypite " being restricted to the Hydrozoa. In the simple Actinozoa, how- ever, such as the sea-anemones, the term " polype " is applied to the entire organism, as consisting of no more than a single alimentary region. It follows from this, that the entire body of any Actinozoon may be composed of a single polype, or of several such produced by budding or cleavage, and united to one another by a common connecting structure or ccenosarc. Most of the Actinozoa are permanently fixed, like the corals ; some, like the sea-anemones, possess a limited amount of locomotive power ; and one order, the Ctenophora, is com- posed of highly-active free-swimming organisms. Some of them are unprovided with hard structures or supports of any kind, as the sea-anemones and Ctenophora ; but a great many 5 86 INVERTEBRATE ANIMALS. secrete a calcareous or horny skeleton or framework which is known as the " coral " or " corallum." The Actinozoa are divided into four orders^-viz., the Zoan- tharia, the Alcyonaria, the Hugosa, and the Ctenophora. OEDER I. ZOANTHAEIA (Gr. zoon, animal anthos, flower). — The Zoantharia comprise those Actinozoa in which the polypes are furnished with smooth, simple, usually numerous tentacles, which, like the mesenteries, are in multiples of five or six. The Zoantharia are divided into three groups, dis- tinguished from one another by the presence or absence of a coral, and by its structure when present. The first of these groups is termed Zoantharia malacoder- mata, or " soft-skinned " Zoantharia, because the polypes are either wholly destitute of a coral, or, if there is one, it consists merely of little scattered needles or spicules of carbonate of lime. Generally, too, the organism is simple, and consists of FIG. 26.— Morphology ofActinidce. a Actinia rosea ; & Arachnactis albida (after Gosse).. no more than a single polype. The best known of the mem- bers of this group are the beautiful sea-anemones or animal- flowers (Actinidce), which occur so plentifully on every coast (Fig. 26, a). It will be as well to describe the structure of a sea-anemone somewhat in detail, as in this way a clear notion may be obtained of the general anatomy of the Actinozoa. The body of an ordinary sea-anemone (Fig. 26, a) is a truncated cone or short cylinder, termed the " column," and is of a soft, leathery consistence. The two ends of the column are termed ACTINOZOA. 87 respectively the " base " and the " disk," the former constitut- ing a kind of sucker, by means of which the animal can attach itself at will, while the mouth is placed in the centre of the latter. The mouth is surrounded by a flat space, destitute of appendages, and the circumference of the disk is in turn sur- rounded by numerous simple tubular tentacles, arranged in alternating rows. The tentacles consist of both ectoderm and endoderm, enclosing a tube which communicates with the body-cavity. By the muscular contraction of the walls of the column, the fluid contained in the body-chambers can be forced into the tentacles, which can be thus protruded a great length, while they can also be usually retracted. In some cases the tentacles are furnished with perforations at their extremities. The mouth (see Fig. 12, a) leads directly into the stomach, which is a wide, membranous tube, opening by a wide aperture into the body-cavity below, and extending about half-way be- tween the mouth and the base. The wide space between the stomach and body-walls is subdivided into a number of sepa- rate compartments by radiating vertical plates, which are called the " mesenteries," and to the faces of which the re- productive organs are attached, in the form of reddish bands, containing either ova or sperm- cells. Below the stomach, attached to the free edges of the mesenteries, are a series of singularly twisted threads or cords (Fig. 12, c), which are filled with thread-cells, and are termed "craspeda." The function of these is not well understood ; but it is believed that in some cases they can be emitted through apertures, which are occasionally found in the walls of the column. The sea-anemones are mostly to be found between tide-marks, in rock-pools, or on ledges of stone, adhering by means of the expanded base. They are not, however, permanently fixed, but can change their place at will. In the nearly allied llyanthus and Arachnactis (Fig. 26, I) the base is tapering, and it appears that the animal spends the greater part of its existence in an unattached, free condition. The true sea- anemones, as already said, are all simple, each consisting of a single polype ; but there are closely-related forms (such as Zoanthus) in which the organism is compound, consisting of numerous polypes united by a creeping, fleshy trunk or cceno- sarc. The second group of the Zoantharia is termed that of the Zoantharia sclerodermata, from the nature of the skeleton or coral. In this group are all the so-called "reef-building" corals, which are the makers of the well-known " coral-reefs." 88 INVERTEBRATE ANIMALS. The members of this group all possess the power of secreting carbonate of lime within their tissues, so as to form a more or less continuous skeleton or corallum. Froni the fact that this corallum is secreted by the inner layer of the polypes, and is therefore truly within the body, it is said to be " sclero- dermic," in opposition to the kind of coral produced by other forms (such as the red coral), where the skeleton is secreted by the outer layer of the polypes, and is therefore outside them. In this latter case the coral is said to be " sclerobasic." (For illustrations of these different kinds of corals, see Fig. 29.) In the typical form of sclerodermic coral, the skeleton is in the form of a conical cup, the upper part of which is hol- low. The lower part is divided into a series of compartments by vertical plates, which are called the " septa," and which correspond to the mesenteries of the living animal. Some- times the space contained within the walls of the cup cr " corallite" is broken up by horizontal plates called "tabulas;" but, when these are present, there are generally no septa. In the form of coral just described we have a single corallite, produced by one polype, and this simple condition may be maintained throughout life. In the great majority of cases, however, the polypes bud, so as to form a colony, all bound together by a common flesh or ccenosarc. When such a colony, therefore, produces a sclerodermic coral, in place of a single corallite, we have a composite skeleton composed of a number of little cups or corallites, each of which was produced by one polype, and all of which are united by means of a common calcareous basis secreted by the ccenosarc (Fig. 29, a). In accordance with their mode of formation, an ordinary compound sclerodermic coral may be distinguished from a sclerobasic coral by the fact that it would show a number of little cups in which the polypes were contained, whereas these cups would be absent in the latter. In accordance, also, with the fundamental character of the order Zoantharia, the corals of the present group always show septa which are some mul- tiple of five or six. When it is understood that compound corals, such as we have been speaking of, are produced by the combined efforts of a number of polypes, essentially the same in structure as our ordinary sea-anemones, it is readily intelligible that under favorable circumstances large masses of coral may be produced in this way. When these masses attain such a size as to be of geographical importance, they are spoken of as " coral-reefs," and the phe- nomena exhibited by these are of such interest as to demand some notice. The coral-producing polypes require for their existence that the average ACTINOZOA. 89 temperature of the sea shall not be less during winter than 66° ; and coral- reefs are, therefore, not found in temperate seas. Keefs, however, abound in all the seas not far removed from the equator, being found chiefly on the east coast of Africa and the shores of Madagascar, in the Red Sea and Persian Gulf, throughout the Indian Ocean and the whole of the Pacific Archipelago, around the West-Indian Islands, and on the coast of Florida. The headquarters, however, of the reef-building corals may be 'said to be around the islands and continents of the Pacific Ocean, where they often form masses of coral many hundreds of miles in length. According to Darwin, coal-reefs may be divided into three principal forms — viz., Fringing- reefs, Barrier-reefs, and Atolls, distinguished by the following charac- ters: 1. Fringing-reefs (Fig. 27, 1). — These are reefs, usually of a moderate size, which may either surround islands or skirt the shores of continents. These shore-reefs are not separated from the land by any very deep channel, and the sea on their outward margins is not of any great depth. 2. Barrier-reefs (Fig. 27, 2). — These, like the preceding, may either encircle islands or skirt continents. They are distinguished from fring- ing-reefs by the fact that they usually occur at much greater distances from the land, that there intervenes a channel of deep water between them and the shore, and soundings taken close to their seaward margin indicate great depths. FIG. 27.— Structure of Coral-reefs. 1. Fringing-reef; 2. Barrier-reef; 8. Atoll; a Sea- level ; & Coral-reef; c Primitive land ; d Portion of sea within the reef, forming a chan- nel or lagoon. As an example of this class of reefs may be taken the great barrier-reef on the northeast coast of Australia, the structure of which is on a gigantic scale. This reef runs, with a few trifling interruptions, for a distance of more than a thousand miles, with an average breadth of thirty miles, and an area of 90 INVERTEBKATE ANIMALS. thirty-three thousand square miles. Its average distance from the shore is between twenty and thirty miles, the depth of the inner channel is from ten to sixty fathoms, and the sea outside is " profoundly deep " (in some places over eighteen hundred feet). 3. Atolls (Fig. 27, 3). — These are oval or 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. They agree in all particulars with those barrier-reefs which surround islands, except that there is no central island in the lagoon which they enclose. The last group of the Zoantharia comprises composite or- ganisms in which the ccenosarc is supported upon a central axis or sclerobasic skeleton. These Zoantharia sclerobasica require no notice, except simply to remark that they are dis- tinguished from other sclerobasic corals (such as the Gor~ gonidce) by the fact that each polype possesses tentacles which are a multiple of six in number. ORDER II. ALCYONARIA. — The second great order of living Actinozoa is distinguished by the fact that the polypes are furnished with fringed tentacles, and that these, as well as the mesenteries and somatic chambers, are always some mul- tiple of four. With one doubtful exception, all the Al- cyonaria are composite, their polypes being connected to- gether by a ccenosarc. The body-cavities of the polypes are connected with a system of canals which are excavated in the ccenosarc, and communicate freely with one another, so that a free circulation of nutrient fluids is thus kept up. The struct- ure of the polypes of the Alcyonaria is, in all essential anatomical features, the same as in the sea-anemones, the number of the mesenteries and tentacles being the chief dis- tinction. Of the various different organisms included under this order, one of the best known is the " Dead-men's-fingers," or Alcyo- niurrij which occurs commonly in most seas. It forms spongy- looking masses of a yellow or orange color, attached to shells and other marine objects. The whole mass is covered with little star-shaped apertures, through which the delicate pol- ypes can be protruded and retracted at will. Another well- known member of this order — the type of another family — is the " sea-rod " ( Virgularia mirabilis), which occurs not very rarely in shallow seas. Virgularia occurs in the form of a long rod-shaped body of a light flesh-color, supported upon a cal- careous rod, somewhat like a knitting-needle, which is covered by the ccenosarc. From the ccenosarc are given out lateral ACTINOZOA. 91 processes, each of which bears numer- ous polypes. Closely allied to Virgu- laria is the " CockVcomb" Pennatula (Fig. 28) ; but in this the lower end of the coenosarc is naked and fleshy, and the polype -bearing fringes are considerably longer, giving the whole organism very much the appearance of a feather. Another family of the Alcyonaria, is represented by the so-called " Or- gan-pipe corals," of which Tubipora musica is a well-known example. In this there is a well-developed sclero- dermic coral consisting of numerous cylindrical tubes, which are not di- vided by vertical partitions (septa), but which are connected by strong transverse plates. The coral is bright red in color, and the polypes are usually bright green. The best known, however, of the Alcyonaria is the family Gforgonidce, represented by the sea-shrubs, fan- FiG.28.-Pennatuiid^TheCock'8- corals, and the red coral of commerce. comb (Pennatula phospko- A few of the members of this family live in temperate waters, but they attain their maximum in point of size and numbers in the seas of the tropics. In all the Gorgonidce the organism consists of a composite structure made up of numerous polypes united by a common flesh or coenosarc (Fig. 29, #), the whole supported by a central branched axis or coral. The coral varies* in composition, be- ing sometimes calcareous — as in red coral — sometimes horny, and sometimes partly horny and partly calcareous, as in Isis (Fig. 29). In all cases, however, the corallum differs alto- gether from the sclerodermic corallum, which has been de- scribed as so characteristic of the reef-building corals. The coral in the present instance is always what is called " sclero- basic " — that is to say, it always forms an internal axis, covered by the coenosarc with the polypes produced therefrom. It is, therefore, outside the polypes, and bears to the coenosarc the same relation that the trunk of a tree bears to its investing bark. This is well shown in Fig. 29, #, where there is repre- sented one of these sclerobasic corals in which the corallum 92 INVERTEBRATE ANIMALS. consists of alternate horny and calcareous joints. The pol- ypes of all the GorgonidoB agree, of course, with their order in having eight tentacles each, and by this they are distin- guished from the few Zoantharia in which there is a sclero- basic coral. FIG. 29.— Sclerodermic and Sclerobasic Corals, a Portion of branch of Dendrophyllia nigrescens, a sclerodermic coral (after Dana) ; b Longitudinal section of Isis Mppuris, a sclerobasic coral, exhibiting the external bark or coenosarc, with its imbedded polypes, supported by the internal axis or skeleton (after Jones). The best known of the Gorgonidce is the Corallium rubrum, or " red coral " of commerce, which is largely imported from the Mediterranean. In this species there is a bright-red, finely-grooved, calcareous coral, usually more or less repeatedly branched. The coral is invested by a bright-red coenosarc or bark, which is studded with numerous little apertures. The polypes can be protruded from these openings at will, and are milk-white in color, with eight fringed tentacles each. The entire ccenosarc is excavated into a number of communicating canals, with which the cavities of the polypes are connected, the whole system being filled with a nutritive fluid known as the "milk." ORDER III. HUGOS A (Lat. rugosus, wrinkled). — This order merely requires mention, as all its members are extinct, and are therefore only known to us by their hard parts or skele- ACTINOZOA. 93 tons. They agree with the Zoantharia sclerodermata in having a well-developed sclerodermic corallum, but differ from them in the fact that the septa are always some multiple of four / and there are generally transverse plates or tabulae combined with the vertical plates or septa. On the other hand, they agree with the Alcyonaria in having their parts in multiples of four, but differ from them in having a well- developed sclerodermic corrallum in which septa are present. ORDER IV. CTENOPHORA (Gr. Jcteis, a comb; phero, I carry). — The fourth and last order of the Actinozoa is that of the Ctenophora, comprising a number of free-swimming oceanic creatures, very different in appearance from any of the forms which we have hitherto been considering. They are all trans- parent, gelatinous, glassy-looking creatures, which are found near the surface in the open ocean, swimming rapidly by means of bands of cilia. The cilia are arranged in a series of trans- verse ridges, whioh are disposed in longitudinal bands, the whole constituting locomotive organs which are known as " ctenophores." In none are there any traces of a corallum or skeleton, and thread-cells are asserted to be universally present. FIG. 30.— Ctenophora. Pltwrobraclda pileus. As the type of the order, we may take one of the commoner forms, which is known by the name of Pleurobrachia or Cy- dippe (Fig. 30). The body of Pleurobrachia is transparent, colorless, gelatinous, and melon-shaped, and exhibits two poles, at one of which is placed the mouth. The globe-like body is 94 INVERTEBRATE ANIMALS. divided into a number of crescentic lobes by eight ciliated bands or ctenophores, which proceed from near the mouth to near the opposite pole of the body. Besides the cilia there are two very long and flexible tentacular processes, which are fringed on one side by smaller secondary branches. The ten- tacles arise each from a kind of sac, one placed on each side of the body, and they can be instantaneously and completely retracted within these sacs at the will of the animal. Ihe mouth of Pleurobrachia opens into a spindle-shaped digestive sac or stomach, which in turn opens below into a wider and shorter cavity termed the " funnel ; " from this there proceed in the axis of the body two small canals, which open at the opposite pole of the body. The funnel communicates with a complicated system of canals, which are ciliated internally, and are filled with a nutrient fluid. In the angle between the two canals which run from the base of the funnel to the sur- face is a little vesicle or sac, believed to be a rudimentary organ of hearing, and placed upon this is a- little mass which is generally believed to be of a nervous nature. If this is correct, this is the first indication which we have hitherto en- countered of a genuine nervous system. The reproductive organs are developed in the walls of the canal-system. The only other form of the Ctenophora which deserves mention is the "Venus's girdle" (Cesium Veneris), which agrees in essentials with Pleurobrachia^ but is greatly enlon- gated in a direction at right angles to the alimentary canal, till we have a ribbon-shaped body produced, four or five feet in length and two or three inches high. Cestum is not un- common in the Mediterranean, and has the power of phospho- rescence, appearing at night as a moving and twisting band of flame. SUB - KINGD OM III.— ANNUL OIDA. CHAPTER X. ECHINODERMATA. THE third primary division of the animal kingdom is known by the name of Annuloida, and includes two groups of organ- isms which are extremely unlike one another in appearance, and are termed respectively the Echinodermata and the Sco- lecida. In the former we have the sea-urchins, star-fishes, and their allies, formerly classed in the old sub-kingdom Radiata ; in the latter are a number of internal parasites, with some minute aquatic creatures, all formerly referred elsewhere. Dif- ferent as are these two groups in appearance and habits, they are nevertheless united by the following peculiarities : * They possess a distinct alimentary canal, usually communicating with the outer world by two apertures (a mouth and a vent), but in any case completely shut off from the general cavity of the body. In all there is a distinct nervous system ; and in all there is a peculiar system of canals termed the " water-vascu- lar " or " aquiferous " vessels, which usually communicate with the exterior of the body. It should be mentioned that many naturalists dissent from this grouping together of the Echinodermata and Scolecida into a single sub-kingdom, Annuloida. Many other arrangements have been proposed, most of which present some special advantages and some dis- advantages. In the mean while, in the confessedly uncertain state of this department of Natural History, it has been thought well to adhere to the arrangement proposed by Prof. Huxley, an arrangement with many obvious drawbacks, and at best but provisional. * Some of the internal parasites of this sub-kingdom have no alimentary canal at all , but this does not affect the value of the above definition. 90 INVERTEBRATE ANIMALS. CLASS I. — ECHINODEEMATA. The members of this class are popularly known as sea- urchins, star-fishes, brittle-stars, feather-stars, sea-cucumbers, etc., and derive their name of Echinodermata (Gr. echinos, a hedgehog ; and derma, skin) from the generally prickly nature of their integuments. In all, the skin is possessed of the power of secreting carbonate of lime, but in very different degrees. In the sea-urchins this goes so far that the body becomes en- closed in an immovable box, composed of numerous calcareous plates firmly jointed together. In the star-fishes and their allies the skin is rendered prickly by grains, tubercles, or spines of calcareous matter, and the body is either destitute of regular plates or is only partially enclosed by them. In the sea-cucumbers, again, the calcareous matter is mostly only present in the form of minute grains scattered in the skin. When adult, they all show a more or less distinctly radiate structure, which is most conspicuous in the star-shaped star- fishes and sand-stars, but can be detected in all the members of the class. When young, however, they almost always ex- hibit what is called " bilateral symmetry " — that is to say, they show similar parts on the two sides of the body. In all Echino- derms there is a water-vascular system of tubes, which is termed the "ambulacral system," which generally communi- cates with the exterior, and which in most cases is used in locomotion. An alimentary canal is always present, and is always completely shut off from the general cavity of the body. A vascular or circulatory system is sometimes present. There are always distinct organs of reproduction, which are almost always placed in different individuals, so that the sexes are distinct. The nervous system is in the form of a ring sur- rounding the gullet and sending branches in a radiating man- ner to different parts of the body. The Echinodermata are divided into seven orders, as fol- lows: 1. Echinoidea (Sea-urchins). 2. Asteroidea (Star-fishes). 3. Ophiuroidea (Sand-stars and Brittle-stars). 4. Crinoidea (Feather-stars). 5. Cystoidea (extinct). 6. JBlastoidea (extinct). 7. Holothuroidea (Sea-cucumbers). This is by no means a true arrangement of these orders, but it is convenient to consider them in this sequence. ECHINODEKMATA. 97 ORDER I. ECHISTOIDEA.— The animals included in this order vary from the shape of a sphere or globe to that of a disk, and they are all commonly known as " sea-urchins " or " sea-eggs." They are all characterized by the fact that the body is encased in a " test" or "shell" (Fig. 31, 2) composed of numerous cal- careous plates mostly immovably jointed together so as to form a kind of box. The intestine is convoluted, and there is a distinct vent, or anal aperture. The test of a sea-urchin, as just said, consists of many cal- careous plates accurately fitted together, and united by their edges. In all living forms the test is composed of ten zones of plates, each zone consisting of a double row. In five of these zones (1 a, 2 a) the plates are of large size, and are per- FIG. 31.— Morphology of Echinoidea. 1. Portion of the test of a sea-urchin (Galwites) enlarged, showing the ambulacral areas (6) and interambulacral areas (a). 2. Test of the same, viewed from above: a Interambulacra ; b Ambulacra. 8. Genital disk of a sea-urchin (Hemicidaris) enlarged: c Ocular plate; d Genital plate : e Anal aperture : /Madrcporiform tubercle. 4. Spine of the same. (After Forbes.) forated by no apertures. These are termed the "interambu- lacral areas." In the other five zones (1 5, 2 t>) the plates are of small size, and are perforated by little apertures for the emission of delicate locomotive suctorial tubes (the so-called "ambularcal tube-feet"). These zones are therefore called the " ambulacral areas." Besides these main rows of plates which collectively make up the greater part of the test, there are other plates placed in the leathery skin round the mouth and vent. The most important of these form a kind of disk, which is placed at the summit of the shell. This disk (Fig. 31,3) is composed of two sets of plates — one called the "geni- 98 INVERTEBRATE ANIMALS. tal plates," perforated for the ducts of the reproductive organs; the other set smaller, and each carrying a little " eye," hence their name of " ocular plates." One of the genital plates is also larger than the others, and carries a spongy mass which is called the " madreporiform tubercle," and which protects the entrance of the water-vascular or ambulacral system. The whole of the test is covered with numerous tubercles of dif- ferent sizes, which carry longer or shorter spines (Fig. 32). The spines are jointed to the tubercles by a sort of " ball-and- FIG. 32.— Cidaris papillata (after Gossc). socket " or " universal " joint, and they are completely under the control of the animal, so as to be used both in locomotion and apparently as defensive weapons. In most common species the spines are short, but in many tropical forms they attain a very great length. Besides the spines, the outer surface of the test is furnished with curious little bodies called " pedi- cellariae," which were long believed to be parasitic. They consist of two or three blades mounted upon a flexible stalk and constantly employed in snapping together like the beak of a bird. They occur in many other Echinodermata^ and their use is obscure. Locomotion is effected in the sea-urchins by a curious system of contractile tubes which are known as the "ambu- lacral tubes " or " tube-feet," and which are appendages of the water-vascular system. The following is essentially the arrangement of the whole aquiferous system. From the madreporiform tubercle on the largest of the genital plates ECHINODERMATA. 99 there proceeds a membranous canal by which the outer water is conducted to a central tube, which forms a ring round the gullet. The tubercle is spongy, and is perforated with little holes, and its function is probably to act as a filter, and prevent foreign particles gaining access to the interior. From the " circular canal " round the gullet proceed five " radiating canals " which take their course toward the summit of the shell, underneath the ambulacral areas. In its course each radiating canal gives off numerous short lateral tubes — the ambulacral tubes or tube-feet — which gain the exterior of the shell by passing through the apertures in the ambulacral plates of the shell, and which terminate in little sucking- disks. The tube-feet can be distended with water by means of a series of little muscular bladders placed at their bases, and they can thus be thrust far out beyond the shell, into which they can be again withdrawn at the will of the animal. However long the spines may be, the animal can protrude the tube-feet to a still greater length ; and by the combined action of the little suckers at their extremities locomotion is effected with moderate rapidity, considering the bulk of the body. The digestive system in the Echinus consists of a mouth armed with a curious apparatus of calcareous teeth, which opens into a gullet, which in turn conducts to a distinct stomach. From the stomach there proceeds a long and con- voluted intestine, which is attached to the interior of the shell by a delicate membrane or " mesentery," and terminates in a distinct vent. The surface of the mesentery, as well as that of the lining membrane of the shell, is richly ciliated, and thus serves to distribute the fluids of the body-cavity to all parts of the body. In this way, also, respiration is subserved, though it is probable that the chief agent in this function is to be found in certain specialized portions of the ambulacral system. The circulatory system consists in its central portion of two rings placed round the opposite ends of the alimentary canal, and united by an intermediate muscular cavity or heart. The nervous system consists of a gangliated cord placed round the gullet, and sending five radiating branches along the ambulacral areas. The sexes are distinct, but in both the re- productive organs are in the form of five membranous sacs placed in a radiating manner in the interambulacral areas, and opening at the genital plates. The embryo of the Echinus is at first a little free-swimming ciliated organism, and it passes through an extraordinary development, which can only be 100 INVERTEBRATE ANIMALS. alluded to here. In its later stages it was originally described as a distinct animal under the name of " Pluteus^ In this state the larva is a curious, easel-shaped body, with a distinct alimentary canal and an internal calcareous skeleton, and ex- hibiting distinct bilateral symmetry. The remarkable point, however, about its further development is, that the young Echinus is developed out of only a portion of the Pluteus, and the greater part of the latter, including the skeleton, is cast away as useless. The majority of the sea-urchins are found at moderate depths in the sea, especially in the neighborhood of oyster- banks. Others spend their existence buried in the sand ; and one species excavates holes for itself in the solid rock, ap- parently by some mechanical action. OKDER II. ASTEROIDEA (Gr. aster, star; eidos, form). — As the structure of the sea-urchins may be taken as embody- ing the most important anatomical peculiarities of the Echino- dermata, and as this has been described at some length, it will not be necessary to do more than briefly indicate the more important characteristics of the remaining orders. In the present order are included all the true star-fishes, the sand- stars and brittle-stars being generally regarded as a distinct FIG. SS.—Cribetta oculata (after Forbes). group. The body in all the Asteroidea is more or less ob- viously star-shaped (Fig. 33), consisting of a central disk sur- rounded by five or more lobes or arms, which radiate from the ECHINODERMATA. 101 body, are hollow, and contain prolongations from the stomach. The body is not enclosed in an immovable box or test, as in the sea-urchins, but the integument is of a leathery nature, and is richly furnished with calcareous plates, tubercles, and spines. The true star-fishes are distinguished from the nearly allied brittle-stars ( Ophiuroidea) by the fact that the arms are direct prolongations of the body, that they contain prolonga- tions of the stomach, and that they are deeply grooved on their under surfaces for the radiating vessels of the water- vascular system, which are further protected by a sort of in- ternal skeleton. The upper surface of the body and arms is richly furnished with calcareous matter, in the form of prickles, tubercles, spines, and pedicellarias, these last being peculiarly- modified spines. The upper surface, also, exhibits the madre- poriform tubercle in the form of a concentrically-striated disk placed at the angle between two of the rays, and also the aperture of the anus, when this is present. The mouth is placed in the centre of the lower surface, and is not furnished with teeth. It leads by a short gullet into a stomach which usually terminates on the upper surface by an anal aperture ; but this is occasionally wanting. From the stomach in all the Asteroidea proceeds a series of much-branched membra- nous sacs, two of which are prolonged into each ray. The water-vascular or ambulacral system is in most essential re- spects identical in structure with that of the sea-urchins, making due allowance for the different shape of the body. The nervous system consists of a gangliated ring surrounding the mouth and sending branches along each of the arms. The reproductive organs, like the nervous system, exhibit a radiate condition, being arranged in pairs in each ray. The star-fishes are found on all shores, but many forms are properly inhabitants of deep water. They 'differ much in the general shape of the body. In the common cross-fish ( Ur aster rubens) the disk is small, and is furnished with long, finger-like rays, which are properly five in number. In the Cribettce (Fig. 33) the general shape is much the same. In the sun-stars (Solaster) the disk is large and well marked, the rays are from twelve to fifteen in number, and they are shorter than the diameter of the disk. In the cushion-stars (Goniaster) the body is in the form of a five-angled disk, more or less flattened on both sides, the rays being only marked out by the ambula- cral grooves upon the lower surface. OKDEK HI. OPHIUROIDEA (Gr. ophis, snake; our a, tail; ei- 102 INVERTEBRATE ANIMALS. dosy form). — In this order we have only the common sand-stars ( Ophiurd) and brittle-stars ( Ophiocoma), all closely allied to the true star-fishes in external appearance, especially in their strikingly radiate form. The body in the Ophiuridce consists of a circular central disk covered with small calcareous plates, and giving off five long, slender, snake-like arms (Fig. 34, «, b), which may be simple or branched, but which do not contain any prolongations from the stomach, nor have their under surfaces excavated into grooves for the protrusion of ambu- lacral tube-feet. The arms, in fact, are not prolongations or lobes derived from the body itself, but are special appendages added for purposes of locomotion and prehension. The arms Fio. 84.— Ophiuroidea. a Ophiivra texturata, the common sand-star; I Ophiocoma neylecta, the gray brittle-star (after Forbes). are very much longer than the diameter of the disk, and are protected by four rows of calcareous plates — one above, one below, and one on each side. In the centre of each arm is a row of calcareous pieces which form a kind of internal axis ECHINODERMATA. 103 or skeleton, below which is placed the radiating ambulacral vessel. All the internal organs are contained within the disk, and none of them pass into the arms except the nerve-cords and ambulacral vessels. The mouth is placed in the centre of the under surface of the disk, and opens into a globular, simple stomach, which is not furnished with an anal aperture, all indigestible particles being got rid of through the mouth. In various points of their anatomy the Ophiuroidea differ considerably from the true star-fishes, to which they are most nearly related, but these differences do not require further notice. The habits of the brittle-stars and sand-stars are various, but many of them may be found in rock-pools or under stones at low water on most shores. FIG. 35. — Comatula rosacea. a Free adult ; & Fixed young (after Forbes). ORDER IV. CRINOIDEA (Gr. Jcrinos, a lily ; eidos, form). — Tn this order are comprised Echinodermata, in which the body is fixed, during the whole or a portion of the existence of the animal, to submarine objects by means of a jointed flexible stalk or column. The Crinoidea were formerly very 104 INVERTEBRATE ANIMALS. numerous, both individually and in types, but they are rep- resented at the present day by no more than three or four living forms, of which one only (the feather-star) is at all of common occurrence. The body in the Crinoids con- sists of a central disk or cup formed of calcareous plates, and protecting the body of the animal. From the mar- gins of this cup spring five or more arms -which are ar- ranged in a radiating manner, so as to form a more or less feathery crown. In one of our living forms, the animal, when full grown, is free ; but in all other living genera, and in the great majority of fossil forms, the body was attached throughout life to the sea- bottom by means of a jointed stalk attached to the lower surface of the cup (Fig. 36), thus somewhat resembling a lily. The commonest living spe- cies is the rosy feather-star ( Comatula rosacea\ which occurs not very rarely on European coasts (Fig. 35). This beautiful animal consists of a central body or disk, from which proceed five ra- diating arms, which divide almost directly after their FIG. B&.—iikisocrinus lofotmsis, a living origin into two secondary stalked Crinoid (after Wyville Thomson), KrnnOV,p>q on fhnf nltirrm+^lv four times the natural size, a Stem ; b D es> sc imateiy Cup; cc Arms. there are produced ten long and slender rays. Each arm is furnished on both sides with a number of little jointed lateral processes or " pinnae," so as to assume a feather-like appearance, from which its popular name is derived. The digestive system is furnished with both a mouth and a vent ; ECHINODERMATA. 105 the water-vascular or ambulacral system appears to take no part in locomotion, and the reproductive organs are lodged in the lateral processes of the arms. The most remarkable point, however, about the Comatula is the manner in which it de- velops itself. When fully grown (Fig. 35, a) it presents no small superficial resemblance to some of the Ophiuroidea. When young (Fig. 35, b) the Comatula is so different in ap- pearance from the adult, that it was originally described as a distinct animal. It consists now of a little cup-shaped disk with ten radiating arms above, produced by the splitting into two of five primary rays, and furnished inferiorly with a little flexible column or stalk composed of a number of calcareous joints. By this jointed stem the body is at this period of life fixed to sea-weeds or other submarine objects. When sufficiently mature, however, the body drops off its stalk, and then only requires to grow in size to become a fully-developed Comatula. The stalked condition which we have just seen to consti- tute a merely temporary stage in the life-history of the Coma- tula is, on the other hand, the permanent state of parts in almost all the " stone-lilies " and other fossil Crinoidea, and in two or three living forms. Of these recent species, one of the most remarkable is one which has been recently discovered in the Atlantic and North Seas, and which has been described under the name of Mhizocrinus lofotensis. This curious species (Fig. 36) consists of a little thread-like, jointed stem support- ing a calcareous cup, from which proceed five branched and jointed arms ; and the stalked condition is here permanently re- tained during life. ORDERS V. AND VI. CTSTOIDEA AND BLASTOIDEA. — These orders merely require to be mentioned here, as all the forms in- cluded in them are extinct, and are unrep- resented at the present day by living spe- cies. In both, the body is enclosed in a kind of box formed by jointed calcareous plates (Fig. 37), and it was in most cases permanently fixed to the sea-bottom by a jointed stalk or column. The arms, which form so conspicuous a feature in the true Crinoidea, were either absent or very rudimentary. Both orders are most closely allied to the Crinoidea, and they constitute probably FIG. 37.— Cystoidea. EcMnosphwrites. 106 INVERTEBRATE ANIMALS. the least highly-developed sections of the whole class of the Echinodermata. ORDER VII. HOLOTHUROIDEA. — In this order are comprised the highest of the Ediinodermata, all very different in out- ward appearance from any of the forms we have hitherto con- sidered. They are commonly known as sea-cucumbers, or tre- pangs, but they are mostly rare and inconspicuous animals at the best. They are all more or less worm-shaped or snail-like in form, and they are either altogether destitute of calcareous matter in the skin, or with rare exceptions have only scattered grains and spines of this material. As a rule, the skin is simply leathery, and is endowed with wonderful contractility by means of powerful longitudinal and transverse muscles. In consequence of this, they can, in many cases, eject all or almost all their internal organs, and can sometimes divide their bodies into several parts when- injured or alarmed. Loco- motion is effected by alternate extension or contraction of their worm-like bodies, by anchor-shaped spicules of lime contained in the skin, or by rows of ambulacral tube-feet, like those of the sea-urchins, protruded through the integument. Some- times the tube-feet are scattered over the whole surface of the body, and sometimes they are altogether absent. There is always a mouth at one extremity of the body, and a distinct vent at the other. The mouth is situated anteriorly, and is surrounded by a circlet of feathery tentacles (Fig. 38), which FIG. 3S.— Holothuroidea. Thyone papillosa (after Forbes). are believed to be modified tube-feet. The water-vascular or ambulacral system is sometimes quite rudimentary, but in other cases it much resembles that of the sea-urchins, except that the madreporiform tubercle is not placed on the outside of the body, but hangs down freely in the interior of the body. In most of the Holothuroidea there are appended to the ter- mination of the intestinal canal two much-branched tubes, ECHINODERMATA. 107 which are filled with sea-water from without, and are believed to exercise a respiratory function, hence the name of " respi- ratory tree " often applied to them. The ordinary species of Holothurians, as already said, are all rare, and are mostly only to be obtained by dredging in tolerably deep water. Some of the tropical forms attain a large size, and some are largely searched after to be sold in the Chinese market, being regarded in that country as a delicacye CHAPTER XL CLASS II — SCOLECIDA. IN the second class of the sub-kingdom Annuloida are in- cluded a number of organisms which are, in many cases, very unlike one another in external appearance, but which, never- theless, agree in one or two structural points of importance. The most important of these are the possession of a system of water- vascular ves^sels^the absence of a vascular system, and the possession of a nervous system composed of no more than one or two nervous masses or ganglia. The points by which the Scolecida are distinguished from the Echinodermata are, the absence of calcareous matter in the skin, the absence of any traces of a radiate arrangement of their parts, especially of the nervous system, the constant absence of any blood- circulatory apparatus, and the course of their development. The Scolecida (Gr. skolex, a worm) are often vermiform in shape, but many of them exhibit no worm-like characters, and one whole order is entirely microscopic. A great many of the Scolecida are internal parasites in other animals, and these are often collectively spoken of as JEJntozoa (Gr. entos, within ; zoon, an animal). These parasitic forms subsist by an imbibition of the juices of their host through their delicate integument. They have, therefore, no necessity for acquiring food for themselves ; and we find, in consequence, that many of them are wholly destitute of an alimentary canal, and that in all the organs of " relation " are very rudi- mentary. The /Scolecida are divided into the following seven groups or orders : 1. Tceniada (Tape- worms). 2. Trematoda (Flukes). 3. Turbellaria (Ribbon-worms and Planarians). SCOLECIDA. 109 4. Acanthocephala (Thorn-headed worms). 5. G-ordiacea (Hair-worms). 6. Nematoda (Round-worms and Thread- worms). 7. Rotifer a (Wheel-animalcules). ORDER I. T^EOTADA (Gr. tainia, a ribbon). — In this order are comprised the ribbon-shaped Tape-worms (Fig. 39, 5) and FIG. 39. — Morphology of Taeniada. 1. Ovum containing the embryo in its leathery case; 2. A bladder-worm (Cysticercus longicollis), magnified ; 3. Head of the adult Tomia soliwm, enlarged, showing the suckers and crown of booklets ; 4. A single generative joint, enlarged to show the branched ovary (o), the generative pore (a), and the water- vascular canals (6) ; 5. Fragment of Toenia solium, showing the generative joints and the alternate arrangement of the generative pores. the bladder-worms or cystic worms (Fig. 39, 2). These were formerly described as distinct groups ; but it is now known that the latter are merely the young forms of the former. The peculiarity which distinguishes the development of the Tceni- ada, and which led to the cystic worms being described as distinct animals, is that the different stages of growth are always found inhabiting different animals or " hosts." If the fully-grown tape- worm is found in one animal, then its young form or cystic worm will always be found in another. Many animals are infested by tape-worms ; but all the leading points of interest in the order will be brought out by a consideration of the commonest of the three tape-worms to which man is subject — namely, the common tape-worm, or Tcenia solium. 6 110 INVERTEBRATE ANIMALS. The common tape-worm is found inhabiting the intestines of man, one only being generally present in the same individual. In shape (Fig. 39, 5) it is an extremely elongated, flattened, tape-like body, many feet in length, and composed of a num- ber of flattened joints (Fig. 39, 4) all loosely united to one another. At one extremity the joints become much smaller and narrower, till ultimately a point is reached where the organism is firmly fixed to the mucous membrane of the in- testine by means of a minute rounded head (Fig. 39, 3). The organs by which attachment is effected are, in this spe- cies, a crown of recurved hooks and four suckers. The head is in reality the true animal, and all the long, jointed, tape- like body which follows this, is really produced by a process of budding from the head. The head contains no repro- ductive organs, and is not furnished with a mouth or diges- tive organs of any kind, its nutrition being entirely effected by imbibition of the nutritive fluids elaborated by its host. A nervous system, in the form of one or two ganglia, sending filaments backward, is said to be present ; but there is some doubt on this point. The water-vascular system (Fig. 39, 4) consists of two long vessels which run down each side of the body and communicate at each articulation by a transverse vessel, the whole opening in the last joint into a contractile vesicle. Each joint is sexually perfect, or hermaphrodite, containing both male and female reproductive organs (Fig. 39, 4), which open on the surface by a small raised aperture, the "generative pore." Almost the whole of each of the mature joints is filled up by a much-branched ovary. As the head is the true animal, and the numerous joints are only pro- duced by budding, it follows that the entire organism is to be regarded as a kind of colony, constituted by a single sexless zoo"id or " nurse," and numerous sexual zooids, produced by budding from the former. The process of development — that is to say, the process by which this composite organism, commonly known as the tape-worm, is produced — is a very remarkable one, and is briefly as follows: Each generative segment or joint, as al- ready said, is hermaphrodite, and contains innumerable ova. These eggs, however, cannot be developed within the body of the animal infested by the tape-worm itself, but they are compelled to gain access to the body of some different species of animal, if development is to proceed. To secure this end, the mature joints of the colony break off, and are expelled from the alimentary canal of the host. The joints thus ex- SCOLECIDA. HI pelled die and decompose, and their contained eggs are thus set free. Each egg (Fig. 39, 1) is covered with a little leathery capsule which protects it from injury, and contains a minute embryo in its interior. If this microscopically small egg be swallowed — as in many ways it easily may be — by another warm-blooded animal (in this particular case by the pig), then a fresh series of changes ensues. The leathery case of the ovum is dissolved in the stomach of the new host, and the embryo is set free, when it bores its way through the walls of the stomach by means of little siliceous hooks with which it is provided. Having reached a suitable locality, the young tape-worm proceeds to surround itself with a kind of cyst, and it develops from its hinder end a kind of bladder filled with fluid (Fig. 39, 2). It is now a bladder-worm, or cystic worm, and as such would formerly have been regarded as a distinct animal. In the particular case of the Tcenia solium which we are now considering, the cystic worm is found imbedded in the muscles of the pig, and it constitutes in that animal the disease known as the measles. In this cystic stage the young tape-woim rnay remain for an ap- parently indefinite period, being quite incapable of develop- ing eggs, though sometimes fresh bladder-worms may be produced by a process of budding. For its further develop- ment it is necessary that it should now be introduced into the alimentary canal of man. If a portion of measly pork be eaten with these cystic worms imbedded in it, then the young tape-worm is liberated from its cyst: it fixes itself by means of its suckers and booklets to the mucous mem- brane of the intestine, and its caudal bladder drops off. It is now converted into the head of the adult tape-worm. It finally commences to throw out buds from its hinder extremity, and in these buds or joints the reproductive elements are pro- duced, so that ultimately we get the long, flattened jointed colony with which we started. This extraordinary series of phenomena is now known to occur in other cases, but space will not admit our dwelling upon these. Another of the tape-worms of man (the Tcenia mediocanellatd) is developed in the same way from the measles of the ox. The tape-worm of the cat is the mature form of the bladder- worm of mice, and the tape- worm of the fox is derived from the cystic worm of hares and rabbits. Lastly, man is not only liable to be infested with the tape-worms derived from the cystic worms of other animals, but may be attacked by the cystic or immature forms of the tape-worms 112 INVERTEBRATE ANIMALS. of other animals. Thus the disease known as " hydatids " in the human subject is caused by the presence in his tissues of the cystic worms which are ultimately developed into the tape- worm of the dog. ORDER II. TREMATODA (Gr. trema, a pore or sucker). — The " suctorial " worms, or " flukes," as the members of this order are commonly called, are all internal parasites, inhabit- ing various situations in different animals, but especially af- fecting birds and fishes. They are all more or less flattened and rounded in shape, and are furnished with one or more suckers, by which they adhere. They are distinguished from the Tceniada by always possessing an alimentary canal, which is often much branched (Fig. 40, 1), is simply hollowed out FIG. 40.— Trematoda. 1. Distoma hepaticum, the "liver-fluke," showing the branched alimentary canal : 2. Anterior extremity of Distoma lanceolatum, enlarged ; a An- terior sucker ; b Posterior sucker ; o Generative pore ; d Gullet ; e e Bifurcating aliment- ary canal (after Owen). of the tissues of the body, and is never provided with a dis- tinct anus. The best known of the Trematoda is the common liver-fluke (Distoma hepaticum, Fig. 40, 1), which inhabits the gall-bladder or ducts of the liver in sheep, and is the cause of the disease known as the rot. In form it is ovate, flat- tened on the two sides, and presenting two suckers, of which the anterior is perforated by the aperture of the mouth. A branched water-vascular system is present, and opens pos- teriorly by a small aperture. The alimentary canal bifurcates shortly behind the mouth, the two divisions thus produced being much branched, and terminating posteriorly in blind extremities. In Distoma lanceolatum (Fig. 40, 2) the intes- tine is divided into two branches, but these are simple tubes, and are not branched. SCOLECIDA. 113 OKDER HI. TURBELLARIA. — The animals included in this order differ altogether from the Trematoda and Tceniada in being- almost all aquatic in their habits and being all non- parasitic. They never possess sucking-disks or booklets, and their integument is always furnished with vibrating cilia. A water-vascular system is always present, but it appears some- times not to communicate with the exterior. The alimentary canal is sometimes simply hollowed out of the tissues and destitute of an anus, as in the Trematoda, or at other times suspended in a free space (body-cavity) and furnished with an anus. It may be simple or much branched. The best known of the members of this order are certain little jelly-like, soft-bodied, ovate, or elliptical creatures, which are commonly found in fresh water or on the sea-shore, and are known as Planarians. The skin in these curious little ani- mals (Fig. 41, 1, 2) is richly furnished with cilia, and also contains numerous cells which have been compared to the FIG. 41. — Turbellaria. 1. Planaria torva: m Mouth; (7 Nerve-ganglion ; e Eyes; ov Ovary; t Spermarium ; gn Genital opening: 2. Planaria, lactea, showing the branched intestine: 3. Larva of one of the marine Turbellarians : 4. Pilidium, the larva of one of the Nemertidm. "nettle-cells" of the Ccelenterata. The intestine may be either straight or branched, but always terminates behind in blind pouches, and is never provided with an anus. The water-vascular system communicates with the exterior. The nervous system consists of two ganglia, placed in front of the mouth, and united by a cord. There are generally rudimen- tary eyes or pigment-spots, which vary in number from two to sixteen. The remaining members of the Turbellaria are known as ribbon-worms (Nemertidve), and are not uncommonly found on the sea-shore. They differ from the Planarida in beinpf 114 INVERTEBRATE ANIMALS. worm-like in shape, by the fact that the alimentary canal is furnished with a distinct anus, and by the absence of an ex- ternal opening to the water- vascular system of the adult, in some cases at any rate. Their development sometimes shows phenomena very similar to what occurs in the Echinodermata, the larva (Fig. 41, 4) being a free-swimming, ciliated organ- ism, of which only a portion is employed in producing the adult animal, the remainder being cast off as useless. OEDER IV. ACANTHOCEPHALA (Gr. aJcantha, thorn ; Tee- phale, head). — The "thorn-headed worms" included in this order are all internal parasites. They are worm-like in shape, marked with transverse wrinkles, and destitute of any mouth or alimentary canal. The anterior extremity of the body forms a kind of proboscis or snout, which is armed with recurved hooks, and has placed at its base a single nervous ganglion. Beneath the skin is a net-work of canals, containing a clear fluid, and believed to represent the water-vascular system. The thorn-headed worms include some of the most formidable parasites with which we are as yet acquainted, the best known being the various forms of JSchinorhynchus, which are found inhabiting the alimentary canal in many mammals, birds, and fishes, but not as yet in man. ORDER V. 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 beetles and grasshoppers. They possess a mouth and alimentary canal. The sexes are distinct, and they leave the bodies of the insects which they infest to breed, subsequently deposit- ing their eggs in long chains either in water or in some moist situation. In form the Gordiacea are singularly like hairs, and they often attain a length very many times greater than that of the insect in which they live. ORDER VI. NEMATODA (Gr. nema, a thread). — In this order are the " round-worms " and " thread-worms," both of which are parasitic, together with a number of worms which lead a permanently free existence. All the Nematoda (Fig. 42) are elongated and cylindrical or thread-like in shape. They possess a distinct mouth, and an alimentary canal which is freely suspended in an abdominal cavity, and which termi- nates in a distinct anus. They possess a system of canals which are believed to represent the water-vascular system ; SCOLECIDA. 115 and the nervous system is in the form of a gangliated cord surrounding the gullet, and sending filaments backward. Among the best known of the parasitic Nematodes are the common round-worm (Ascaris lumbricoides) and the thread- worm ( Oxyuris) of the human subject, both of which inhabit the alimentary canal, and the guinea- worm (Filarid), which spends a portion of its existence in the cellular tissue of man, especially of the legs, and which attains a length of several feet. More dan- gerous than any of these is the Trichina, which spends its immature stages encysted in the muscles of some such animal as the pig, and only attains maturity and becomes capable of producing eggs, when in- troduced into the alimentary canal of some other warm-blooded verte- brate animal. When this takes place, a train of symptoms are originated which sometimes re- semble rheumatic fever, and appear to be very generally fatal. Of the free Nematode worms, which are never parasitic at any time of their lives, about two hun- dred species have been described, most of which inhabit fresh water or the shores of the sea. One of the most familiar is the so-called " vinegar - eel " (Anguillula acetL Fig. 42, A). FIG. 42. — Nomatoda. A. Vinegar-eel OBDEE Vin. ROOTERA (Lat. rota, wheel; jero, I carry). — The living in stagnant water. Rotifera, or "wheel-animalcules," derive their popular name from the fact that the anterior end of the body is furnished with one or two circlets of cilia (Fig. 43) which, when in motion, vibrate so rapidly as to produce the illusory impression of a quickly-rotating toothed wheel. The Rotifera are almost all aquatic, and are mostly inhabitants of fresh water. They are all microscopic in size, none attaining a greater length than one-thirty-sixth of an inch. In the females there is a distinct mouth, intestinal canal, and 116 INVERTEBRATE ANIMALS. anus. A nervous system is also present, consisting of gan- glia placed near the anterior extremity of the body and send- ing filaments backward. There is, finally, a well-developed water-vascular system. Most of the Hotifera are free-swimming, active little ani- mals (Fig. 43, A), but some are permanently fixed, as in Melicerta (Fig. 43, B), or in the crown-animalcule Stephano- ceros). They are usually simple, but they are sometimes com- posite, forming colonies. As a rule, the male and female Hotifera differ greatly from one another, the males being smaller than the females, devoid of any masticatory or diges- FIG. 43. — Botifera. A. Diagrammatic representation of Uydatina senta (generalized from Pritchard) : a Depression in the ciliated disk leading to the digestive canal ; & Mouth ; c Pharyngeal bulb with masticatory apparatus ; d Stomach ; e Cloaca ; / Contractile bladder ; g ff Eespiratory or water-vascular tubes ; Ji Nerve-ganglion, giving filament to ciliated pit (£) ; o Ovary. B. Melicerta ringens (after Gosse). tive apparatus, and more or less closely resembling the young forms of the species. The males, in fact, merely lead a tran- sient existence, and die as soon as they have succeeded in fertilizing the females. The body in most cases is very dis- tinctly ringed or annulated (Fig. 43, A), but is not composed of distinct rings separated by partitions. The integument is usually provided with bundles of muscular fibres taking a longitudinal and transverse direction. In the free forms the SCOLECIDA. 117 anterior ciliated disk acts somewhat like the propeller of a screw-steamer in driving the organism through the water — in all cases it has the action of producing currents in the water by which particles of food are brought to the mouth. The posterior end of the body is usually developed in the free forms into a kind of tail or foot (Fig. 43, A), which may take the shape of a kind of pincers or of a little suctorial disk. As regards their internal anatomy, in the females of almost all the Rotifera there is a well-developed alimentary canal, which is completely shut off from the general cavity of the body. The mouth (Fig. 43, A b) opens into a dilated cham- ber (c), which contains a complicated apparatus of horny teeth. This in turn opens into a capacious stomach (c?), con- tinued into an intestine which terminates by a chamber known as the "cloaca" (e), which forms the common outlet for the water-vascular and generative systems. In both sexes there is a well-developed water-vascular system consisting of a con- tractile chamber or bladder (/"), opening into the cloaca, and giving origin to two complicated tubes which are known as the "respiratory tubes" (g and e^8' domen with eggs. The ordinary Termites are all sterile fe- males, incapable of laying eggs, and they are divided into two ;i;t.4-;nA+ OQfo ™. "castes," both destitute of wings, and differ- distinct sets or ing1 in the armature of the head. The one caste includes the FIG. 69.— Termites (Termes bellicovus); a King, before the wings are cast off; Z> Queen, with the abdomen distended with eggs ; c Worker ; d Soldier. so-called " workers," who perform all the ordinary work of the colony, while the " soldiers " have greatly-developed jaws, and are simply occupied in defending the nest against all enemies. 8 158 INVERTEBRATE ANIMALS. SECTION III. HOLOMETABOLA. — Metamorphosis complete ; the larva, pupa, and imago, differing greatly from one an- other in external appearance. The larva worm-like, and the pupa quiescent. ORDER VII. APHANTPTERA (Gr. aphanos, inconspicuous ; pteron, wing). — In this order are only the Fleas (Pulicidce), in which the mouth is suctorial, the metamorphosis is complete, and the wings are rudimentary, being represented by four minute scales placed on the last two segments of the thorax. The larva of the common flea is a footless grub, which in about twelve days spins a cocoon for itself, and becomes a quiescent pupa, from which the imago emerges in about a fortnight more. ORDER VIII. DIPTERA (Gr. dis, twice ; pteron, wing). — The insects of this order, as implied by its name, have only a single pair of wings — namely, the anterior pair. The poste- rior wings are rudimentary, and are represented by two FIG. 70.— Diptera. Crane-fly (Tipula oleracea). clubbed filaments called " balancers " or " poisers " (Fig. 70). The mouth in the Diptera is suctorial. ORDERS OF INSECTS. 159 The Diptera constitute one of the largest orders of insects ; the House-flies and Flesh-flies (Musca), the Gnats ( Cltleoo), the Crane-flies (Tipula), the Forest-flies (Hippobosca), and the Gad-flies (Tabanidce), constituting good examples. ORDER IX. LEPIDOPTERA (Gr. lepis, scale ; pferon, wing). — This well-known and most beautiful of all the orders of in- sects comprises the Butterflies and Moths, the former being active by day (diurnal), and the latter mostly toward twilight (crepuscular), or at night (nocturnal). In all the Lepidoptera the mouth of the adult insect is purely suctorial, and is pro- vided with a spiral trunk fitted for imbibing the juices of flowers. The wings are four in number, and are covered more or less completely with modified hairs or scales, which are pretty objects under the microscope, and from which the wings derive their beautiful colors. The larvae of the Lepidoptera (Fig. 71) are generally known as caterpillars. They are worm- like, provided with masticatory organs fitted for dividing solid FIG. 71.— Large white Cabbage-butterfly (Pontia brasvicce). a Larva or caterpillar; & Pupa or chrysalis; c Imago or perfect insect. substances, possessing false legs in addition to the three pairs proper to the adult, and having attached to the under lip a tubular organ or spinneret, by which silken threads can be manufactured. The butterflies or diurnal Lepidoptera are characterized by being active during the daytime, by keeping their wings most- 160 INVERTEBRATE ANIMALS. ly erect when at rest (Fig. 71, c), by having club-shaped an- tennae, and by having a chrysalis (#), which is almost always naked and angular, and is generally attached to some solid object by silken threads variously disposed. The Moths are mostly active during the night-time, when they are said to be nocturnal. Many of them, however, are " crepuscular " — that is to say, they are active during the hours of twilight ; and a few come out in broad daylight and in the brightest sunshine. The pupaa, or chrysalides, are never an- gular, as in the case of the butterflies. Apart from the destruction committed by the Caterpillars of some of the Lepidoptera, the only members of the order which are of importance to man are the various species of Bombyx, from which silk is derived. Several species are cul- tivated for this purpose, but by far the most valuable is the common Silk-moth (Bombyx Mori\ which owes its name to the fact that the larva feeds upon the leaves of the common Mulberry (Morus nigra). It is hardly necessary to say that raw silk is derived from the " cocoon," or silken case in which the caterpillar enwraps itself before becoming a chrysalis. Most of the raw silk is derived from France, Italy, China, and the East Indies. ORDER X. HYMENOPTERA (Gr. humen, membrane ; pteron, wing). — In this order all the four wings are present, as a rule, and they are all membranous in texture, with few nervures (Fig. 72). The mouth is always furnished with biting-jaws or mandibles, but often is adapted for suction as well. The fe- males have the extremity of the abdomen furnished with an instrument connected with the process of laying eggs (ovi- positor) ; and in very many cases this becomes the powerful defensive weapon known as the sting. The metamorphosis is complete. The Hymenoptera form a very extensive order, comprising the Bees (ApidcB), the Wasps ( Vespidce), the Ants (Formi- cidce), the Saw-flies (Tenthredimdce, Fig. 72), and the Ich- neumons. The Bees and Wasps are well known as forming social communities, though solitary members of both are not uncommon. In both groups these organized communities con- sist of a vast number of undeveloped females, or " neuters " — the so-called " workers " — presided over by a single fertile fe- male, or " queen," or containing several such. The males are only produced at certain seasons, and they constitute the so- called " drones " of a hive of bees. The workers discharge all ORDERS OF INSECTS. 161 the duties necessary for the preservation of the colony, such as procuring food, building the nest, and feeding the young. As there is only one set, or " caste," of neuters, the duty of FIG. 72. — Gooseberry Saw-fly (Tenthredo grossulari<%\ larva, pupa, and imago. 1 defending the nest falls to the lot of all the workers, and is not delegated to a special class of soldiers. The queen is the founder of the colony, and her sole function, after starting the community, is to lay eggs. The drones, or .males, do no work, as a rule, and they either die, or are killed by the workers, as soon as the female is fertilized. The Ants likewise form communities, consisting of males, females, and neuters. The males and females, like those of the very different "White Ants," or Termites, are winged (Fig. 73, a), and are produced in great numbers at particular times of the year. They then quit the nest and pair, after which the fecundated females lose their wings and form fresh societies. The workers (Fig. 73, b) are sometimes all of one kind, but they are often divided into two, or even three, distinct classes or "castes." The Ants exhibit many most extraordinary and interesting instincts and habits, of which 162 INVERTEBRATE ANIMALS. FIG. 73.— The Bed Ant (Myrmica rvfa). a Winged male; 6 "Wingless female. Magnified. their custom of "milking" the little Plant-lice has been al- ready mentioned. Another very singular habit of some Ants may be just alluded to — their habit, namely, of capturing the pupae of other species of Ants and bringing them up as slaves. The relations, however, between the masters and slaves vary a good deal in different cases. In the case, for instance, of the Russet Ant (Formica rufescens) the masters are so entire- ly dependent upon their slaves that they cannot even feed themselves, and the only work which they perform unassisted is the capturing of fresh slaves. In the Blood-red Ant (For- mica sanguined) , on the other hand, the slaves are much fewer in number, and the masters are much less dependent upon their good offices. In all cases, the slaves exhibit the greatest devotion to their masters, and are invariably taken the greatest care of by their captors. ORDER XL STREPSIPTERA (Gr. strepho, 1 twist ; pteron, wing). — This is an extremely small order of insects, which merely requires to be mentioned. It includes only certain minute parasites, which are found on bees and other Ily- menoptera. The females are destitute of wings or feet, and are merely soft, worm-like grubs. The males are active, and possess a single pair of large membranous wings. Unlike the Diptera, it is the posterior pair of wings which is present, and the anterior pair is quite rudimentary, and is only represented by curious twisted filaments, from which the name of the order is derived. ORDER XII. COLEOPTERA (Gr. Jcoleos, a sheath ; pteron, wing). — The twelfth and last order of insects is that of the Coleoptera, including the well-known insects familiar to every ORDERS OF INSECTS. 163 one under the name of " beetles." The leading peculiarity of the Coleoptera is to be found in the fact, that though all the four wings are present, only the posterior pair are mem- branous, and perform the function of wings. The anterior pair of wings are no longer capable of being used in flight, but are hardened by the deposition of chitine, and constitute pro- FIG. 74.— Coleoptera. The common Cockchafer (Melolontha vulgaris), with the elytra closed, and in flight. tective cases, which cover the hind-wings, and are known as " elytra " (Gr. elutron, a sheath). The mouth in all the beetles is masticatory, and is furnished with biting and chewing jaws. The larvae of the beetles are all worm-like grubs, with masticatory mouths, and they all pass through a complete meta- morphosis, generally requiring a protracted period for its com- pletion. The known number of different kinds of beetles can- not be estimated with any certainty, but it is probably little short of 50,000 species, and this estimate has been doubled by some writers. They are, as a general roile, remarkable for their hard, chitinous skin, their glittering, often metallic, colors, and their voracious habits, though many of them feed upon vegetable matters. Of the enormous number of known Beetles, the only one which can be said to be of any decided use to man is the so- called " Blister-beetle," or " Spanish Fly " ( Cantharis vesicar toria). This handsome insect is a native of Southern Europe, especially of Italy, Spain, and France, and lives upon the leaves of the ash, lilac, elder, and poplar. It is largely col- lected and exported for medicinal purposes, as it yields one of the most generally used and efficient of blisters. SUB-KINGDOM V.— MOLLUSCA. CHAPTER XIX. SUB-KINGDOM MOLLUSCA. — The Mollusca (Lat. mollis, soft), as implied by their scientific name, are mostly soft- bodied animals, but their popular name of " shell-fish " ex- presses the fact that their soft body is usually protected by an external skeleton or " shell." All the Mollusca are fur- nished with a distinct alimentary canal, which is completely shut off from the general cavity of the body (Fig. 75, a). There is sometimes no distinct blood-circulatory apparatus ; but, when there is, its central portion (i. e., the heart) is placed upon the dorsal aspect of the body. The chief peculiarity, however, FIG. 75. — Diagram of a Mollusk. a Alimentary canal; h Heart; / Foot; n Cerebral gan- glion; n' Pedal ganglion ; n" Parieto-splanchnic ganglion. of the Mollusca is found in the nature of the nervous system. In the lower forms (Fig. 76, 2 d), the nervous system consists essentially of a single ganglionic mass, giving off filaments in various directions. In the higher Mollusca (Fig. 75, n), the nervous system consists of three scattered ganglia, united to one another by nervous cords. One of these ganglia is placed above the gullet or oesophagus, and is known as the " supra- cesophageal " or " cerebral " ganglion. A second supplies MOLLUSCA. 165 nerves to the great locomotive organ of most Mollusks, the " foot," and is therefore called the " pedal " ganglion. The third is known by the cumbrous name of the " parieto-splanch- nic " ganglion, because it supplies nervous filaments to the walls (parietes) of the body, and also to the internal organs (splanchna). In all the higher Mollusks it is this scattered condition of the nervous masses which distinguishes them so sharply from all other animals. Distinct respiratory organs may or may not be present, and they may be adapted for breathing air directly or through the medium of water. All the higher Mollusca are simple animals, and perpetuate their kind by means of the sexes, but many of the lower forms have the power of producing colonies by continuous gemma- tion, much as we have formerly seen in the Hydroid Zoo- phytes. The digestive system in all the Mollusca consists of a mouth, gullet, stomach, intestine, and anus, with the excep- tion of a few forms in which the intestine ends blindly. In some the month is surrounded by ciliated tentacles (Polyzoa, Fig. 77) ; in others, it is furnished with two long ciliated arms (Brachiopoda) ; in the bivalves (Lamellibranchiata), it is mostly furnished with four membranous processes or " palpi " (Fig. 80, p) ; in others, it is furnished with a complicated toothed organ or " odontophore " ( Gasteropoda, Fig. 83, and Pteropoda) ; and lastly, the Cephalopoda, in addition to an odontophore, possess horny mandibles, forming a kind of beak, very like that of a parrot. The blood is colorless, or nearly so. In the lowest class of the Mollusca (Potyzoa),t\\e circulation is carried on by means of cilia, and there is no distinct heart, nor any definite course of the circulating fluid. In the Sea-squirts (Tunicata), there is a distinct heart, but the structure of -this is very simple, consisting of a mere tube, open at both ends, so that the course of the circulation is periodically reversed. In the higher Mollusca, there is a distinct heart, consisting of two chambers, of which one (the auricle) receives the aerated blood from the gills, while the other (the ventricle) drives it through the body. Respiration is very variously effected among the Mollusca. In the Polyzoa (Fig. 77) respiration is discharged mainly by the crown of ciliated tentacles surrounding the mouth. In the sea-squirts (Fig. 78), respiration is effected by a greatly-devel- oped pharynx, which is perforated by numerous ciliated aper- tures. In the lamp-shells and their allies (^Brachiopoda)^ the 166 INVERTEBRATE ANIMALS. long, ciliated arms, which spring from the sides of the mouth, seem to be the main agents in respiration. In the bivalve- shell-fish, the cuttle-fishes, and most of the univalves, the breathing-organs are in the form of gills or branchiae, adapted for breathing air dissolved in water. In the remainder of the univalves (e. g., snails and slugs), the breathing-organs are adapted for breathing air directly, and have the form of an air-chamber or pulmonary sac, produced by the folding of a portion of the mantle. The air is admitted to the chamber by a round opening, situated on the side of the neck, and capable of being closed at will. The lining membrane of the chamber is richly supplied with blood-vessels, and thus the necessary purification of the blood is carried out. In accordance with the scattered or rudimentary condition of the nervous system, the Mbllusca are not characterized by acuteness of senses, nor by any great power of locomotion. Organs of sight exist in some of the lower and many of the higher Mbllusca, attaining in the cuttle-fishes (Fig. 89) an ex- tremely high type of organization. The common bivalve shell- fish, such as the scallop, possess numerous simple eyes placed along the margins of the mantle, but, in many cases, even these are absent. Locomotion is very variously effected, but seldom with much vigor or activity. The lowest classes of the Mol- lusoa are, in the great majority of instances, fixed when adult. The common univalve shell-fish, such as whelks, snails, slugs, etc., creep about slowly by means of a flattened disk, devel- oped on the under surface of the body, and known as the "foot." Other Univalves and many Bivalves can effect short leaps by means of the foot, but many of the latter are perma- nently fixed to solid objects, or buried in the sand. The mi- nute Mollusca, known as the Pteropoda (Fig. 88), swim freely at the surface of the ocean by means of two fins, formed by a modification of the foot, and attached to the sides of the head. The only Mollusks which enjoy really active powers of loco- motion are the predacious cuttle-fishes, which swim rapidly by means of fins, or by ejecting a jet of water from the cavity of the mantle, and which can also creep about by means of the " arms " placed around the mouth (Fig. 89). The last feature in the Mollusca which requires to be men- tioned is the " shell." The shell is not invariably and univer- sally present in the Mollusca, many being either destitute of a shell altogether, or having one so small that it would not com- monly be recognized as such. In these cases, as in the com- mon slugs, the animal is said to be " naked." In all the Mol- MOLLUSCA. 167 lusca which possess a shell, this is secreted by the integument, or by what is technically called the mantle, and, in all cases, it is composed of carbonate of lime. The methods in which the lime is arranged differ in different cases, but all living shells have an outer covering of animal matter, which is known as the " epidermis." In a great many of the higher Mollusca, such as the whelks, periwinkles, snails, and others, the shell consists of only a single piece, when it is said to be " uni- valve." In many others, such as oysters, mussels, scallops, etc., the shell is composed of two pieces, and is then said to be " bivalve." In a few forms, the shell consists of several pieces, and it is then said to be " multivalve." The more important variations in the shells of the Mollusca will be noticed in speaking of the different classes of the sub-kingdom. In accordance with the nature of the nervous system, the Mollusca are divided into two great divisions, known respec- tively as the Molluscoida and Mollusca proper. In the Mol- luscoida, 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 this division are included the three classes of the Sea-mosses (Polyzod), the Sea-squirts (Tu- nicata), and the Lamp-shells and their allies (Brachiopoda). In the Mollusca proper, the nervous system consists of three principal pairs of ganglia, and there is a well-developed heart, consisting of at least two chambers. Under this head come all the ordinary forms of shell-fish. CHAPTER XX. MOLLUSCOIDA. CLASS I. POLYZOA (Gr. polus, many ; zoon, animal.) — The members of this class are the lowest of all Molhtsca, and they are generally known by the popular names of " Sea- mosses " and " Sea-mats." They are invariably compound, forming associated growths or colonies, each consisting of a number of distinct but similar zoftids, produced by gemmation from a single primordial individual. The colonies thus pro- duced are very generally protected by a horny or chitinous integument, and they are so like the Hydroid Zoophytes that they were long described as such. The only absolute distinc- tion between the two classes is to be found in the internal structure of the zoo'ids of each ; . but they may be generally separated by the fact that the separate cells in a compound Hydroid are all united to one another by means of a common flesh or ccenosarc ; whereas in the Polyzoa the separate cells composing the colony are merely connected externally, but very rarely have any direct communication with each other. The separate beings or zooids which collectively constitute the colony of any Polyzoon are spoken of as " polypides " — the term polypite being only used in connection with the Hydro- zoa, and the term polype being similarly restricted to the Actinozoa. Each polypide in a typical Polyzoon has the following structure (Fig. 76, 2) : The body of the animal is enclosed in a double-walled sac, of which the outer layer is usually chitinous or calcareous, and constitutes a " cell " in which the zo5id is contained. This outer layer is known as the " ectocyst," to distinguish it from the ectoderm of the Ccelenterata. The cell, thus formed, is lined by a much more delicate membra- nous layer, which is known as the " endocyst." This membra- MOLLTJSCOIDA. 109 nous sac, formed by the endocyst, is pierced by two openings. One of these is the mouth, and it is always surrounded by a circle or crescent of hollow ciliated processes or tentacles (Fig. 76, 2, a). These ciliated tentacles serve partly as respi- ratory organs, and partly to set up a current of water by which floating particles of food are brought to the mouth. The mouth and tentacular crown can be partially or com- pletely pulled into the sac by means of a muscle which is fixed to the gullet (2, g). The mouth leads into a gullet, and that FIG. 76. — Morphology of Polyzoa. 1. Fragment of one of the Sea-mats (Flustra truncata\ magnified to show the cefls. 2. Diagram of a single polypide of a PolyzoOn (after Allman) : a Mouth surrounded by the ciliated tentacles ; 6 Alimentary canal ; c Anus ; d Nervoua ganglion; e Investing sac or " ectocyst ;" ff ^Reproductive organs ; g Muscle. 3. BirdV head process. again into a stomach, sometimes with a muscular gizzard be- tween. From the stomach proceeds an intestine of variable length, which terminates by a distinct anus at the upper part of the sac (2, c). On one side of the gullet, between it and the anus, is placed a single nervous ganglion (d). Distinct reproductive organs (ff) are also present, and the whole cav- ity of the sac is filled with fluid. From the above description it will be evident that the typical polypide of a Polyzoon differs from the polypite of a Hydrozoon in having a distinct alimentary canal suspended freely in a body-cavity, and hav- ing both a mouth and vent, in having a distinct nervous sys- tem, and in having the reproductive organs contained within INVERTEBRATE ANIMALS. the body. On the other hand, in the Hydrozoa, there is no alimentary canal distinct from the body-cavity, there is no nervous system, and the reproductive organs are in the form of external processes of the body-wall. FIG. 77. — 1. Fragment of F lustra truncata, one of the Sea-mats, natural size. 2. A single polypide of Valkeria, magnified, showing the circular crown of tentacles. 3. A polypide of Loplwpus crystalUnufi, & fresh-water Polyzoon, highly magnified, showing the horse- shoe shaped crown of tentacles : a Tentacular crown ; & Gullet; c Stomach; S Intestine; eAnus; g Gizzard; k Endocyst; I Ectocyst. The foregoing gives the essential structure of the polypide of any Polyzoon^ but in nature this simplicity is lost. In all cases in nature the primitive polypide possesses the power of producing fresh zo5ids by a process of budding; and these zooids remain attached to one another, so that ultimately there is produced a compound growth or colony. Further, in almost all the Polyzoa^ the outer layer of the polypide is more or less hardened by the deposition in it of chitine or of carbonate of lime. The skeletons thus formed are the parts of the colony which are most familiarly known, and in the case of the com- mon Sea-mats (Fig. 77, 1) they are very well known to sea- side visitors, and are generally regarded as sea-weeds. Exam- ined in its dead state, such a skeleton only shows a number of little horny chambers or cells (Fig. 76, 1), each with a little aperture. When alive, however, each of these cells was ten- anted by a single zooid or polypide, capable of protruding its MOLLUSCOIDA. 171 ciliated head from the aperture, and of again retiring within it, if alarmed. The skeleton is, in some cases, furnished with curious organs, which are known as " bird's-head processes " (Fig. 76, 3), from their resemblance to the beak of a bird. The parts of this beak keep constantly snapping together, very much like the little pincer-like organs called " pedicella- rias " in the sea-urchins and star-fishes ; but it is difficult to see what service they perform. They continue their movements long after the death of the polypides, and this appears, in some cases, at any rate, to be due to a peculiar system of nerves known as the " colonial " nervous system. In addition, namely, to the single ganglion with which each polypide is furnished, it has been shown that in many forms the zoftids composing the colony are united together by a well-developed nervous system, and are thus brought into organic connection with one another. The vast majority of the Polyzoa are fixed, and thus as- sume a very plant-like appearance. There is one fresh-water species, however (viz., Cristatella), in which the colony can creep about upon a flattened base very like the foot of a slug. In this same form, also, alone of all the Polyzoa, there is not any outer covering or ectocyst to the polypides. The Polyzoa are partly inhabitants of the sea and partly of fresh water, and they are thus divided into two groups which differ from one another very much in anatomical struc- ture. In most of the fresh-water Polyzoa the tentacles are borne upon a crescentic disk or stage (Fig. 77, 3), so that the crown of tentacles assumes the shape of a horseshoe. In almost all the marine forms, on the other hand, the tentacles (Fig. 77, 2) are simply arranged in a circle. All the Polyzoa are hermaphrodite, each polypide being furnished with the reproductive organs proper to the two sexes. The eggs are simply liberated into the body-cavity, where they are fertilized ; but it is uncertain how the fertilized ova escape into the external medium. Besides true sexual reproduction, and besides the power of producing colonies by continuous budding, fresh individuals can be produced in many cases by a process of discontinuous gemmation. CLASS II. TUNIC ATA (Lat. tunica, a cloak). — The mem- bers of this class are not uncommonly called Ascidian Mol- lusks (Gr. askos, a wine-skin) from the resemblance which many of them exhibit in shape to a two-necked leather bottle (Fig. 78, 2). They are popularly known as "Sea-squirts," from their power of .forcibly ejecting water from the orifices 172 INVERTEBRATE ANIMALS. of the bottle. Their scientific name, again, of Tunicata, is derived from the fact that the body is enveloped in a leathery elastic integument, which consists of different layers, and which takes the place of a shell. The outer covering of the animal is of a gristly or leathery consistence, and is known as the " test." It is remarkable for containing a considerable propor- tion of a substance apparently identical with cellulose, which is one of the most characteristic of all vegetable products. The test is lined by a second coat, which is highly muscular, and confers upon the animal its power of contracting itself and squirting out water. Of the two necks which are placed at the anterior end of a simple Ascidian (Fig. 78), one is per- x£ & round mouth; & Shell of the common whelk (Buccinum undatum\ showing the mouth notched for a respiratory siphon. form of the shell in the Gasteropoda (Fig. 84). The coils of the spiral are termed the " whorls," and are usually more or less amalgamated on one side. In most cases, too, the whorls are wound obliquely round a central axis or pillar, increasing gradually in size to the mouth. The last whorl is the largest, and is termed the " body-whorl." The mouth of the shell in many forms is unbrokenly round or " entire'" (Fig. 84, a\ and it is found that most of these shells subsist upon vegetable food, as, for instance, the common periwinkles. In others, again (Fig. 84, #), the mouth of the snell is notched or is pro- duced into a canal, as in the common whelk, and it is found that these live upon animal food, or are " carnivorous." There may be more than one of these canals or tubes, but they do not necessarily indicate the nature of the food, as their func- tion is to protect the respiratory siphons. The Gasteropoda are divided into a good many groups, of which the more important may be briefly noticed, the fore- going applying chiefly to the ordinary forms, which, therefore, need no further description. The remaining members of the 184 INVERTEBRATE ANIMALS. water-breathing Gasteropods are divided into two sections, differing a good deal from the typical forms of the class in many respects. As examples of the first of these may be taken the sea- slugs and sea-lemons (Nudibranchi&ta), specimens of which may at any time be found creeping about on sea-weeds, or at- tached to the under surface of stones at low water. These slug-like animals (Fig. 85) are wholly destitute of a shell when fully grown, but possess an em- bryonic shell when young. When there are any distinct respiratory organs, these are in the form of gills, placed, without any protec- tion, upon the back or sides of the body. The head is furnished with tentacles, which do not ap- pear to be used as organs of touch, but are more probably connected with the sense of smell ; and behind the tentacles are generally two eyes. The nervous system is extremely well developed,, and would lead to the be- lief that the Sea-slugs are among the highest of the Gastero- poda. Locomotion is effected, as in the true Slugs, by creep- ing about on the flattened foot. The last remaining group of the " branchiate " Gasteropods is that of the Heteropoda (Fig. 86), comprising a number of curious forms which are found swimming at the surface of the FIG. 85. — Nudibranchiata. Doris Joihn- stoni, one of the Sea-lemons. FIG. 86. — Heteropoda. Carinaria cambium; p Proboscis and mouth; * Tentacles; g Gills; « Shell; /Foot; d Disk (after Woodward). open sea, instead of creeping about at the bottom of the sea. In order to adapt them for this mode of life, the foot, instead of forming a creeping disk, is modified to form a compressed fin (/). The Heteropoda are to be regarded as the most MOLLUSCA PROPER. 185 highly organized 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, but others have large bodies, and the shell is either small or entirely absent. In Carinaria, which may be taken as a good example of the group, there is a little limpet-shaped shell protecting the gills (b) and heart. The animal swims, back downward, by means of a vertically-flattened ventral fin (/), on one side of which is a little sucking-disk (<#), by which the animal can ad- here at pleasure to floating sea-weed. Carinaria is found in the Mediterranean and other warm seas, and is so transparent that the course of the intestine can be seen along its whole length. The last group of the class is that of the " air-breathing " Gasteropods, so well known as Land-snails, Pond-snails, and Slugs (Fig. 87). All the members of this group are formed to breathe air directly, instead of through the medium of water, and they, therefore, never possess gills or branchias. FIG. SI.—Limax Sowerbyi, one of the slugs (after Woodward). In place of these they have a pulmonary chamber or lung, formed by a folding of the mantle, and having air admitted to it by a round hole on the right side of the neck, which can be opened and closed at will. Though thus adapted for breath- ing air directly, many of the members of this group can only live in damp or moist places, while others habitually live in fresh water. The common Pond-snails are examples of these last. The condition of the shell varies much. Some, such as the common Land-snails, have a well-developed shell within which the animal can completely withdraw itself for protec- tion. Others, such as the common Slugs (Fig. 87), have a rudimentary shell which is completely concealed within the mantle. Others are entirely destitute of a shell. They all agree with the typical Gasteropods in creeping about on a broad, flattened foot. CLASS HI. PTEEOPODA (Gr. pteron, wing ; podes, feet). — 186 INVERTEBRATE ANIMALS. This class is a very small one, and includes a number of minute oceanic Mollusks, which are found swimming near the sur- face in the open ocean, far from land, and often in enormous numbers. The organs of locomotion are two wing-like fins (Fig. 88) attached to the sides of the head, and formed by a FIG. 88.— Pteropoda. a Cleodora pyramidata ; 6 Cuvieria columnella. (After Woodward.) modification of a portion of the foot. The body is usually pro- tected by a symmetrical glassy shell (Fig. 88), consisting of two plates united along their edges, or in other cases forming a spiral. In some, however, there is no shell, and the body is quite naked. The head is rudimentary, and bears the mouth, which is furnished with an odontophore. The heart consists of an auricle and ventricle, and the respiratory organs are extremely rudimentary. The sexes are united in the same individual in all the Pteropoda. The Pteropoda occur, as already said, in the open ocean, and they are found in all seas from the tropics to within the arctic circle, sometimes in such numbers as to discolor the water for many miles. Minute as they are, they constitute in high latitudes one of the staple articles of diet of the whale, and they themselves in turn are probably carnivorous, feed- ing upon small Crustaceans and other diminutive creatures. Though all the living forms are small, geology leads us to be- lieve that formerly there existed comparatively gigantic forms, which appear to be truly referable to this class. CHAPTER XXII. CEPHALOPODA. CLASS IV. CEPHALOPODA. — The last and highest class of the Mollusca is that of the Cephalopoda, comprising the Cuttle-fishes, Calamaries, Squids, and the Pearly Nautilus. They are all inhabitants of the sea, and are all carnivorous ; and they are possessed of considerable powers of locomotion. At the bottom of the sea they can walk about, head downward, by means of the arms (Fig. 89), which surround the mouth, which are usually provided with numerous suckers, and which are really produced by a splitting up of the margin of the foot. It is from the presence of these arms that the class derives its name (Gr. Jcephale, head ; and joocfes, feet). The Cuttle-fishes can also swim rapid- ly, either by means of expansions of the skin constituting fins, or by the forcible expulsion of water from the cavity of the mantle, the reaction of which causes the animal to move in the opposite direction. The majority of the living Cephalo- pods are naked, possessing only an internal skeleton, and this often a rudimentary one ; but the Argonaut (Paper Nautilus) and the an external shell, though Ferent in the two forms. 8d,_Sepioia Atlanta, one of the Cuttle- fishes (after Wood- A Ui.VAJLU.A\_/JJLL/C**l ¥ UUW • IJIAV LM.J.Vy •UUf&VrUCVW Pearly Nautilus are protected by the nature of this is extremely diffe 188 INVERTEBRATE ANIMALS. The body in the Cephalopoda is symmetrical, and is en closed in an integument which may be regarded as a modificaN tion of the mantle of the other Mottusca. Ordinarily there it» a tolerably distinct division of the body into an anterior por- tion, carrying the head, and a posterior portion, in which the internal organs are enclosed. The head (Fig. 89) is very distinct, bearing a pair of large globular eyes, and having the mouth in its centre. The mouth is surrounded by a circle of eight, ten, or more, long muscular processes, or arms, which are generally provided with rows of suckers. Each sucker consists of a cup-shaped cavity, the muscular fibres of which converge to the centre, where there is a little muscular eminence. When the sucker is applied to any surface, the contraction of the radiating muscular fibres de- presses the central eminence so as to produce a vacuum below it, and in this way each sucker acts most efficiently as an ad- hesive organ. The whole of this complex mechanism of suckers is completely under the control of the animal, and the ir- ritability of the suckers is retained even for days after death. In most of the Cuttle-fishes ( Octopoda) there are only eight arms, and these are nearly similar to one another. In others, however (Fig. 89), there are ten processes round the mouth, of which eight are like each other, and constitute the true arms, while two — called tentacles — are much longer than the others, and bear suckers only toward their extremities, which are enlarged and club-shaped. The Paper Nautilus (Fig. 90) has two of the arms webbed at their extremities and secreting a shell ; and the Pearly Nautilus, alone of all living Cephalo- poda, has numerous arms, more than ten in number, and destitute of suckers. The mouth leads into a cavity containing two powerful horny or partially calcareous jaws working vertically, very like the beak of a bird, together with an " odontophore " or " tongue," the hinder part of which is furnished with recurved spines. This cavity leads by a gullet, furnished with salivary glands, into a stomach, from which an intestine is continued to terminate by a distinct anus, which opens on the ventral surface at the base of the so-called " funnel." The funnel is a muscular tube placed on the under surface of the head, and communicating on the one hand with the external medium, and on the other with the cavity of the mantle. In the Naw- tilus alone it is simply formed of two muscular lobes, which are in apposition, but are not united together so as to form a tube. In many cases there is also a special gland, known as CEPHALOPODA. 189 the " ink-bag," for the secretion of an inky fluid, which the animal discharges into the water, so as to enable it to escape when menaced or pursued. The duct of the ink-bag opens at the base of the funnel near the anus, but the Pearly Nautilus and the allied fossil forms are without this means of defence, which the presence of an external shell renders unnecessary. The respiratory organs are in the form of plume-like gills, placed on the sides of the body in a branchial chamber, which opens in front on the under surface of the body. In almost all the living Cephalopoda there are only two gills, one on each side, and hence this section is known as that of the " Dibranchiata" In the Pearly Nautilus alone there are four gills, two on each side, hence the name of " Tetrabranchiata" applied to the order of which this is the only living represent- ative. In the Cuttle-fishes, at the base of each gill is a special contractile cavity, called a " branchial heart," by which the venous blood, returned from the body, is driven through the gills. In addition to these branchial hearts there is a true arterial heart, by which the aerated blood received from the gills is driven through the body. The admission of water to the branchiae is effected by the expansion of the mantle, which allows the entrance of the outer water into the mantle-cavity. The mantle then contracts, and the water is forcibly expelled through the funnel, which is often furnished with a valve, al- lowing the passage of water outward, but preventing its en- trance inward. By a repetition of this process both respira- tion and locomotion are simultaneously effected, for the jets of water^expelled from the funnel by their reaction drive the animal in the opposite direction. In this case, therefore, as in many others, the more active the animal is, the more perfectly is the respiratory process carried on. The nervous system is formed upon essentially the same plan as in the other Mollusca^ but the cerebral ganglia are protected by a cartilage, which is to be regarded as a rudimen- tary skull. This structure, therefore, is a decided approach to the Vertebrate type of organization. The sexes in all the Cephalopoda are in different individ- uals, and the reproductive process in the Cuttle-fishes is at- tended with some singular phenomena. The most remarkable point in this connection is the modification of one of the arms of the male Cuttle-fishes, for the purpose of conveying the male element to the female. The details of the modification vary in different species of Cuttle-fish. In some species one arm is simply so modified as to be 190 INVERTEBRATE ANIMALS. able to transmit the sperm-cells to the female, but it remains permanently attached to the animal. In the Paper Nautilus (Argonaut) the process goes still further. The female of this species (Fig. 90) attains a considerable size, and is protected by an external shell. The male is not more than an inch in length, is devoid of a shell, and has its third left arm meta- morphosed. This arm is developed in a cyst, and is ultimately detached from the body, and deposited by the male within the mantle-cavity of the female. When first discovered in this position, it was described as a worm living parasitically on the Argonaut, under the name of " Hectocotylus " (Gr. hekaton, a hundred ; and kotulos, a cup), from the suckers, or cups, with which it was furnished. Subsequently it was described as the entire male Argonaut ; and it is only recently that it has been proved to be nothing more than one of the arms of the male, detached for the purpose of conveying the sperm-cells to the female. The shell of the Cephalopoda is sometimes external, some- times internal. The internal skeleton is seen in the various Cuttle-fishes, in which it is known as the " cuttle-bone " or " pen." It may be either horny or calcareous, and it is some- times complicated by the addition of a chambered portion. The only living Cephalopods which are provided with an ex- ternal shell are the Paper Nautilus (Argonauta) and the Pearly Nautilus (Nautilus pompilius) ; but not only is the structure of the animal different in each of these, but the nature of the shell itself is entirely different. The shell of the Argonaut (Fig. 90) is coiled into a spiral, but it is not di- vided into chambers, and it is secreted by the webbed extrem- ities of two of the dorsal arms of the female. These arms are bent backward, so as to allow the animal to live in the shell ; but there is no organic connection between the shell and the body of the animal. The shell of the Pearly Nautilus, on the other hand, is secreted by the mantle, and is organically connected to the animal. It is coiled into a spiral (Fig. 91), but it differs from the shell of the Argonaut in being divided into a series of chambers by means of shelly partitions, which are connected together by a tube or " siphuncle," the animal itself living in the last and largest chamber only of the shell. The Cephalopoda are divided into two extremely dis- tinct and natural orders, termed respectively Dibranchiata and Tetrabranchiata, according as they have two or four gills or branchiae. The Dibranchiata comprise the Cuttle-fishes, Squids, Cala- CEPHALOPODA. 191 maries, and Paper Nautilus, and they are characterized by being almost invariably destitute of any external shell ; by never having more than eight or ten arms, which are always furnished with suckers ; by having only two gills, which are provided with " branchial hearts ; " by the possession of an " ink-bag ; " and by the fact that the " funnel " forms a com- plete tube. They are divided into two sections — Octopoda and Decapoda — according as they have only eight arms, or eight arms with two additional longer processes or "tentacles " (Fig. 89). Among the Octopoda are the Paper Nautilus and the Poulpes ( Octopus). The Paper Nautilus is found in the warmer seas of various parts of the world, generally floating at the surface. The two sexes differ, as already said, greatly in external appearance. The female (Fig. 90) inhabits a beau- FIG. 90.— Argonauta argo, the Paper Nautilus, female. The animal is represented in its shell, but the webbed dorsal arms are separated from the shell which they secrete, and •which they ordinarily embrace. tiful one-chambered shell, which is secreted by the webbed ex- tremities of two of the dorsal arms. The shell is not in any way attached to the body of the animal, but the webbed arms are turned backward, and the animal sits in the shell with the 192 INVERTEBRATE ANIMALS. funnel turned toward the keel. It swims by the jets of water emitted from the funnel, and crawls upon the sea-bottom, head downward, carrying its shell on its back. The male Argonaut is only about an inch in length, has no shell, and has all its arms alike, except the one which is metamorphosed into the " hectocotylus." The Poulpes ( Octopi) are universally dis- tributed in the seas of both temperate and tropical regions. They are the " polypi " of Homer and Aristotle, and are vo- racious animals inhabiting rocky shores. The Decapoda are chiefly found in the open sea, often in enormous numbers, and the best known are the Calamaries and Squids. The body is elongated, and is always furnished with lateral fins, with which they swim actively. The shell is internal, and differs considerably in different members of the group. To this section of the Dibranchiata belong the sin- gular fossil forms which are known to the geologist as Belem- nites. These singular forms are known almost solely by their complicated internal skeleton, and they appear to have abound- ed in the seas of the Secondary period. The second order of the Cephalopoda — that of the Tetra- branchiata — comprises forms characterized by being creeping animals, protected by an external, many-chambered shell, the partitions between the chambers being perforated for the pas- sage of a membranous or calcareous tube, termed the " si- phuncle." The arms are more than ten in number, and are devoid of suckers ; the gills 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 fossil forms, the only living member of the Tetrabranchiata with which we are acquainted is the Pearly Nautilus, which has long been known by its beautiful chambered shell. The shell of the Pearly Nautilus (Fig. 91) is coiled into a spiral, and is many-chambered, the chambers being walled off from one an- other by curved shelly partitions or septa, perforated centrally by a foramen which transmits a membranous tube or siphuncle. The animal inhabits only the last and largest chamber of the shell, from which it can protrude its head at will. The func- tion of the chambers of the shell is not very clearly under- stood ; but it appears to be that of reducing the specific grav- ity of the shell to near that of the surrounding water ; since they appear to be filled with some gas apparently secreted by the animal. The siphuncle does not communicate in any way with the chambers of the shell, and its functions are also un- CEPHALOPODA. 193 known, except that it must certainly serve to maintain the vitality of the shell. FIG. 91.— The Pearly Nautilus (Nautilus pompitius). a Mantle ; & Its dorsal fold ; c Hood; o Eye ; t Tentacles ; / Funnel. Of the fossil Tetrabranchiata the most important are the Orthocerata and the Ammonites. The Orthocerata (Fig. 92) played a very important part in the seas of the Palaeozoic or Ancient-life period of the earth's history, in which they ap- parently filled the place now taken by the predacious cuttle- FIG. 92.—Orthocera8 arplorator. 1. Side view of a fragment, showing the edges of the septa. 2. Transverse section of the same, showing the siphuncle (s). (Billings.) fishes. They agreed with the Nautilus in having a many- chambered shell, divided by curved partitions, perforated by a tube or siphuncle. The shell, however, differed from that of the Nautilus in not being curved or coiled up, but in being 194 INVERTEBRATE ANIMALS. straight. In other nearly-allied forms the shell was bent or even partially coiled up, but never so completely as in the true Nautilus. Many of the Orthocerata were of small size, but some of them were colossal, shells having been found of six or seven feet in length, and as thick as the body of a man. The Ammonites, with a number of allied forms of varied shapes and beautiful structure, appear to have taken the place of the Nautilidde, to a great extent, in the seas of the Second- arjr period ; at which time, too, Dibranchiate Cephalopods first made their appearance. The true Ammonites resembled the Nautilus in having a many-chambered shell, which was coiled up into a spiral, but the position of the siphuncle was differ- ent, and the partitions or septa between the various chambers of the shell were wonderfully folded and lobed instead of being simply curved. The numerous beautiful shells allied to the Ammonites cannot be even mentioned here ; but it is to be remembered that they are almost all characteristic of the Secondary period in geology, and that they are hardly known as occurring in the older period (Palaeozoic epoch). VERTEBRATE ANIMALS. CHAPTER XXIII. GENEEAL CHAEACTEES OF THE YEETEBEATA. THE five sub-kingdoms which we have previously consid- ered, namely, the Protozoa, Codenterata, Annuloida, Annu- losa, and Mottusca, were grouped together by Lamarck into one great division, which he termed the Tnvertebrata. The remaining sub-kingdom, that of the Vertebrata, is so well marked and compact a division, and its distinctive characters are so numerous and so important, that this mode of viewing the animal kingdom is, at any rate, a very convenient one. The sub-kingdom Vertebrata includes the five great classes of the Fishes (Pisces), Amphibians, Reptiles, Birds (Aves), and Mammals ; and the name of the sub-kingdom is derived from the very general, though not universal, presence of the bony axis known as the "vertebral column" or backbone. One of the most fundamental of the distinctive characters of Vertebrate animals is to be found in the fact that the main masses of the nervous system (that is to say, the brain and spinal cord) are completely shut off from the general cavity of the body. In all Invertebrate animals (Fig. 93, A), the body may be regarded as a single tube, enclosing all the vis- cera ; and, consequently, when a distinct nervous system and alimentary canal are present, these are in no way shut off from one another. The transverse section, however, of any Vertebrate animal (Fig. 93, B) shows two tubes, one of which contains the great nervous axis (•»') or brain and spinal cord, while the other contains the alimentary canal, the chief circu- latory organs, and certain portions of the nervous system (ri), 196 VERTEBRATE ANIMALS. which are known to anatomists as the " sympathetic " system. Leaving the brain and spinal cord out of sight for a mo- ment, we see that the lower or visceral tube of a Vertebrate animal contains the digestive canal (#), the blood-vascular sys- tem (c), and a system of nervous ganglia (ri). Now, this is FIG. 93. — Diagrams representing transverse sections of one of the higher Invertebrata, A, and one of the Vertebrata, B. a Wall of the body; b Alimentary canal; c Haemal or blood-vascular system ; n Nervous system ; n' Cerebro-spinal axis, or brain and spinal cord, enclosed in a separate tube; ch Notochord, or chorda dorsalis. exactly what is contained within the visceral cavity of any Invertebrate animal ; and it follows from this that it is the " sympathetic " system of Vertebrate animals which is truly comparable with the nervous system of the Invertebrata. The brain and spinal cord, or " cerebro-spinal axis," are to be looked upon as something not represented at all in the Invertebrata. Another peculiarity which is present in all the Vertebrata is, that at an early period of life there is developed, in the low- er wall of the tube which contains the cerebro-spinal axis, a singular structure known as the " notochord " (Gr. notos, back ; chorde, string) (Fig. 93, B, ch). This is a semi-gelatinous rod, tapering at both ends, and extending along the floor of the cerebro-spinal tube. In some cases, the notochord remains permanently in this condition, but, in most cases, it is replaced at maturity by the bony column or backbone, from which the Vertebrata derive their name. The general structure of the vertebral column will be described shortly, and it is sufficient to state here that it consists of a series of more or less com- pletely bony segments or " vertebrae," arranged so as to form a longitudinal axis upon which the spinal cord is supported. It is to be remembered, however, that all Vertebrate animals do not possess a vertebral column. They all possess a noto- chord, but this may remain persistent throughout life, and, in many cases, the development of the spinal column is very im- perfect. GENERAL CHARACTERS OF THE VERTEBRATA. 197 The skeleton of all Vertebrate animals is internal, and the muscles are attached to its several parts. The value of this character is in no way affected by the fact that many Verte- brates, such as the Tortoises, Crocodiles, and others, possess an external skeleton as well. The limbs of Vertebrate ani- mals are always articulated or jointed to the body, and they are always turned away from that side of the body (the " neu- ral " side) upon which the great masses of the nervous system are placed. The limbs may be altogether wanting, or partial ly undeveloped, but there are never more than two pairs, and they always have an internal skeleton for the attachment of the muscles of the limb. A distinct blood-vascular system is present in all Ver^ tebrates, and in all except one — the Lancelet — there is a single contractile cavity or heart, furnished with valvular open- ings. Lastly, the masticatory organs of all Vertebrates are modi- fications of parts of the walls of the head, and are never modified limbs or hard structures developed in the mucous membrane of the digestive tube, as they are in the Inverte- brates. The above are the leading characters which distinguish the Vertebrata as a whole, and, before going on to consider the different classes, it may be as well to give a short and general sketch of the anatomy of the Vertebrates, commencing with their bony framework or skeleton. The skeleton of the Vertebrata may be regarded as con- sisting of the bones which go to form the trunk and head on the one hand, and of those which form the supports for the limbs on the other hand. The bones of the trunk and head may be regarded as essentially composed of a series of bony rings or segments, arranged longitudinally. Anteriorly, these segments are much expanded and also much modified to form the bony case which encloses the brain and which is termed the cranium or skull. Behind the head, the segments enclose a much smaller cavity in which is contained the spinal cord, and they are arranged one behind the other, forming the " ver- tebral column." The segments which form the vertebral column are called " vertebras," and they have the following general structure : Each vertebra (Fig. 94, A) consists of a central portion known as the "body," or "centrum" (c), placed immediately below the spinal cord, and giving origin to certain " processes." The ends of the bodies of the vertebrse are all united together in different ways, so as to give the col- 198 VERTEBRATE ANIMALS. FIG. 94.— A. Vertebra (lumbar) of the whale, c Centrum or body; n Neural arches; 8 Spinous process ; a Articular process ; d Transverse processes. B. Thoracic segment or vertebra, c Centrum of vertebra ; n Neural arches, enclosing the canal for the spinal cord ; e Spinous process ; r Eibs ; p Costal cartilages ; b Breastbone or sternum. (After Owen.) umn great flexibility. - From the back of the body of the ver- tebra proceed two bony arches which unite behind and thus form with the centrum a bony canal in which the spinal cord is contained. For this reason, these arches (n) are called the " neural " arches. From the point where the neural arches unite — that is to say, from the back of the neural canal — pro- ceeds a long process, sometimes cleft at its extremity, termed the "spinous process" (s). Springing also from each neural arch is a second shorter process (a) termed the " articular pro- cess," since by means of these, as well as by the bodies, the vertebrae are jointed or " articulated " together. Also arising from the neural arches at their junction with the body of the vertebra, there may be two lateral processes (d) which are called " transverse processes." This is the ordinary structure of the vertebra of a Mammal, and the names here used are those applied to the parts of the vertebra in human anatomy. In philosophical anatomy, however, these parts have proper technical names which can be employed for them in all animals alike. The nature of this work, however, will not allow of the introduction of these here. In the typical vertebra the segment is completed by a second arch, which is placed in front of or beneath the body of the vertebra, and which is known as the " haemal " arch, as it includes and protects the principal organs of the blood cir- culation (Fig. 94, B). This second arch is often only recog- GENERAL CHARACTERS OF THE VERTEBRATA. 199 nizable with great difficulty, as its parts are generally much modified ; but a good example may be obtained in the human chest. Here, attached to the front of the vertebrae, we find a series of bony arches, known as the ribs (r), followed by a series of cartilaginous pieces of a similar shape, termed the " costal cartilages " (p), the whole united in front by a central bone, known as the breastbone or " sternum " (£). FIG. 95.— Skeleton of the Beaver (Castor fiber), showing the regions of the vertebra column, c Cervical region, or region of the neck ; d Dorsal region, or region of the back ; b Lumbar region, or region of the loins ; s Sacrum ; t Caudal region, or region of the tail. As a general rule, among the higher Vertebrates, the fol- lowing regions may be recognized in the vertebral column : Firstly, the cervical region (Fig. 95, c), comprising a variable number of vertebras, which constitute the neck, and immedi- ately follow the head. Secondly, the cervical region is suc- ceeded by a variable number of vertebrae which usually carry ribs, and are known as the dorsal vertebrae (d\ or vertebrae of the back. Thirdly, come certain vertebrae which constitute the lumbar region (0), or the region of the loins. Fourthly, there usually follows a series of vertebrae which are immova- bly united together to form a single bone, which is termed the sacrum (s). Lastly, there comes a variable series of vertebras 200 VERTEBRATE ANIMALS. which are usually free and movable upon one another, and which constitute the caudal region, or the region of the tail (t). The nature of the bones which enter into the composition of the limbs varies somewhat in different Vertebrates in ac- cordance with their mode of life ; but in all the higher mem- bers of the sub-kingdom the limbs are built upon a general FIG. 96.— Fore-limb of the Chimpanzee, c Collar- FIG. 97.— Hind-limb of the Chimpan bone, or clavicle ; « Shoulder-blade, or scapu- la ; b Bone of the upper arm, or humerus ; r Badius ; u Ulna ; d Bones of the wrist, or car- pus ; m Bones of the root of the hand, or me- tacarpus ; p Bones of the digits, or phalanges. zee. i Innominate bone ; / Thigh- bone, or femur ; t Tibia ; s Fibula ; r Bones of the ankle, or tarsus ; m Metatarsus ; p Phalanges. and easily-recognizable type. The fore-limb consists generally of the following parts : 1. A series of bones uniting the limb to the trunk, the two most important being the shoulder blade (scapula) and the collar-bone (clavicle) (Fig. 96, s and c), 2. The bone which forms the upper portion of the limb proper, and which is known as the humerus (b). 3. Two bones which form the lower portion of the limb (e. g., the forearm in man), GENERAL CHARACTERS OF THE VERTEBRATA. 201 and which are known as the radius and ulna (r and u\ of which the former is the bone mainly concerned in carrying the hand or fore-foot. 4. A number of small bones, which form the wrist, and are termed the carpus (d). 5. The cylindrical bones (usually five in number) which form the root of the hand, and are known as the metacarpus (m). 6. The bones which form the fingers proper, and which are known as the phalanges (p). Essentially the same parts can be traced in the hind-limb of a typical Vertebrate animal, but they are known by differ- ent names. The bones which unite the limb to the trunk are usually more or less completely united together, constituting a single mass, known as the innominate bone (Fig. 97, i). This is followed by a long, cylindrical bone, which forms the upper portion of the hind-limb, and is known as the " thigh- bone," or femur (/*). Following this are the two bones of the shank, corresponding to the radius and ulna of the fore- limb, and known as the tibia and fibula (t and s). Of these, the tibia (t) corresponds to the radius, and is mainly con- cerned in carrying the foot. Next comes a series of small bones, which form the ankle, and are known as the tarsus (r). This is succeeded by a series of cylindrical bones (usually five in number), which form the root of the foot, and which are termed the metatarsus (m). Finally, the metatarsus is succeeded by the bones of the toes, which in this case are again termed the phalanges (p). In both limbs the usual number of pha- langes to each toe or " digit " is three. The digestive system of the Vertebrata does not require a lengthened notice. The mouth is usually furnished with teeth, which have for their chief function the reduction of the food to a condition in which it can be digested. In some animals, however, such as the snakes, the teeth are only used to hold the prey, and not for mastication ; and in others, such as the turtles and birds, the jaws are not furnished with any teeth at all. The food is also usually subjected in the mouth to the action of a special fluid — the saliva — which acts chemically as well as mechanically upon the food, and which is secreted by special glands, known as the " salivary glands." From the mouth the food passes through a muscular tube — the gullet, or oesophagus (Fig. 98, g) — to the proper digestive cavity, or stomach (s). Here it is subjected to the action of a special digestive fluid — the " gastric juice " — and is converted into a thick, pasty fluid, which is called chyme. From the stomach the chyme passes into a long, convoluted, muscular tube, which 202 VERTEBRATE ANIMALS. is called the " small intestine " (sm). Here it is subjected to the action of two other digestive fluids, called the " bile " and " pancreatic juice," as well as to the fluids secreted by the intestine itself. The bile is secreted by a large gland, which is known as the " liver," while the pancreatic juice is produced by another, termed the " pancreas," both pouring their secre- tion into the upper part of the small intestine. By the combined action of these digestive fluids the chyme is ultimately converted into a milky fluid, which is called chyle, when it is fit to be taken up into the blood- vessels. The small intestine finally opens into a tube of larger diameter, which is called the " large intestine " (Zm), and this opens on the surface of the body by an anal aperture. In the large intestine the last remain- ing portions of the food which can be rendered useful are absorbed into the blood, the indigestible portions being ultimately got rid of as use- less. The fluid products of diges- tion (chyle) are chiefly absorbed from the intestinal canal by a set of special vessels, which are present in all Vertebrates, and which are called the lacteals (Lat. lac, milk) from the milky fluid they contain. These lacteals combine to form a large . *^ by which their contents are Small in- ultimately added to the circulating £<£ Wood. Part of the products of di- final ^portion, called the "rec- gestion are absorbed by the veins which ramify on the intestinal canal, and which ultimately unite to form a great vessel, called the " vena portse," which goes to the liver. The materials, how- ever, which are taken up in this way also ultimately reach the circulating blood. In this way, therefore, fresh matter is being constantly added to the blood to replace the waste caused by the performance of the vital functions. The blood is thus formed out of the materials which are taken into the alimentary canal as food ; and in all the Verte- brata (with one exception) it is of a red color, when viewed in GENERAL CHARACTERS OF THE VERTEBRATA. 203 mass. This is due to the presence in it of numerous micro- scopical particles, which are known as the " blood-corpuscles," the fluid itself being colorless. In Fig. 99 are represented FIG. 99.— Blood-corpuscles, magnified, a Man ; & Goose; c Crocodile; d Frog; e Skate. some of the forms of blood-corpuscles which are found in dif- ferent divisions of the Vertebrata. The blood is always distributed through the body by means of a system of closed tubes, which constitute the "blood- vessels," and, with the single exception of the Lancelet, it is always propelled by means of a contractile muscular cavity or " heart." The heart and other circulatory arrangements differ considerably in different classes of the Vertebrata, but these differences will be best considered at a later period. Respira- tion in all the Vertebrata is effected by means of distinct breathing-organs, assisted in many cases by the skin. In the water-breathing Vertebrates, such as fishes, the respiratory organs are in the form of gills or branchiae, which are richly supplied with blood, and are exposed to the influence of water holding oxygen in solution. In the air-breathing Vertebrates, the breathing organs are in the form of lungs. These essen- tially consist of cellular or spongy organs, placed in the cavity of the chest, richly furnished with blood-vessels, and receiving constant supplies of fresh air by means of a tube which opens in the throat and is known as the " windpipe," or trachea. In the higher Vertebrates the heart becomes a double organ, one side being concerned wholly with driving the impure (venous) blood to the lungs, while the other side propels the pure oxy- genated (arterial] blood to all parts of the body. The waste substances of the body — of which the most im- portant are water, carbonic acid, and the peculiar substance called urea — are got rid of by the skin and lungs, but prin- cipally by two glands which are called the kidneys. The ex- cretion of urea from the body, as a general rule, is wholly effected by means of the kidneys alone ; and this is their most important function, as the retention of this substance within the body rapidly causes death. The secretion of the kidneys is sometimes got rid of by means of special canals appropriated 204 VERTEBRATE ANIMALS. to this alone ; but in the lower Vertebrata it is discharged in- to the hinder extremity of the alimentary canal, and is evacu- ated along with the undigested portions of the food. The nervous system varies greatly in its development in the Vertebrata. In the little fish called the Lancelet, the main mass of the nervous system consists of a cord of nervous mat- ter, representing the spinal marrow, but not having in front any enlargement which represents the brain. In all the other Vertebrata the central masses of the nervous system (termed the cerebro-spinal axis) consist of a nervous cord (the spinal cord) contained in the canal formed by the neural arches of the vertebrae, and of an anterior mass of nervous matter, which is protected by the skull, and is termed the encephalon or brain. The size and development, however, of the brain vary enormously in different Vertebrates ; and in the lower forms the brain is little more than an aggregation or collection of nervous masses or " ganglia," which are connected with the special senses, sight, hearing, taste, and smell, special organs for which are present in almost all the Vertebrata. Reproduction in the Vertebrata is always truly sexual, the sexes are always in different individuals, and in no case are compound organisms produced by a process of budding or fis- sion. Most are oviparous, producing eggs from which the young are developed. Some retain the eggs within the body till the young are ready to be hatched, and these are some- times said to be ovo-viviparous. The higher Vertebrates, however, bring forth their young alive, and are said to be viviparous (Latin, vivus, living ; and pario, I bring forth). PRIMARY DIVISIONS OF THE VEBTEBRATA. — The Verte- brata are variously divided into great primary sections b}T dif- ferent writers, and all of these divisions have more or less merit. Here, however, the classification proposed by Prof. Huxley will be followed, and it is not necessary to enter into any consideration of the others. It has also been thought ad- visable to give in this place a brief account of the leading characters which separate these divisions from one another, though it is not to be expected that the learner will be able to appreciate the full value of these characters till he has com- pleted his study of the Vertebrata as a whole. The Vertebrata are divided by Prof. Huxley into the fol- lowing great divisions : I. ICHTHYOPSIDA (Gr. ichtfius, a fish; and opsis, appear- ance).— In this section are included the fishes (Class Pisces), GENERAL CHARACTERS OF THE VERTEBRATA. 205 and the frogs, newts, and their allies (Class Amphibia). They are all characterized by the fact that they possess gills or branchiae, either throughout life or during the earlier stages of their existence ; that they possess nucleated red blood- corpuscles (i. e., blood-corpuscles with a central particle or nucleus. Fig. 99, d, e), and by certain embryonic characters as well. From the temporary or permanent possession of gills, they are often spoken of as the Branchiate Vertebrates. II. SAUROPSIDA (Gr. saura, a lizard; and opsis, appear- ance).— In this division are the birds (Class Aves), and the true reptiles (Class Reptilia). They are characterized by the fact that at no time of their life are they ever provided with gills ; that the skull is jointed to the vertebral column by a single articulating surface (or condyle) ; that the lower jaw is composed of several pieces, and is united to the skull by means of a special bone (called the os quadratum] ; that they possess nucleated red blood-corpuscles (Fig. 99, #, c\ and by certain embryonic characters as well.* III. MAMMALIA (Lat. mamma, the breast). — In this di- vision are all the ordinary quadrupeds ; characterized by the constant absence of gills; by the skull being jointed to the vertebral column by two articulating surfaces (or condyles) ; by the fact that the lower jaw is composed of only two pieces, and is not united to the skull by means of a special bone (the quadrate bone) ; by having non-nucleated red blood-corpuscles (Fig. 99, a) ; and by having special glands — the mammary glands — which secrete a special fluid — the milk — by which the young are nourished for a longer or shorter period after birth. These three primary divisions comprise the five great classes into which the Vertebrata are divided : 1. Fishes (Pisces). 2. Amphibia (Frogs, Newts, etc.). 3. Heptilia (True Reptiles). 4. Aves (Birds). 5. Mammalia. * Recent researches have led to the belief that the appearance of nuclei in the red blood- corpuscles of the Oviparous Vertebrates is due to changes taking place after death, and that these structures are not present during life. 10 ICHTHYOPSIDA. CHAPTER XXIV. CLASS I. PISCES. THE fishes form the lowest class of the Vertebrata, and they may be broadly defined as being Vertebrate animals pro- vided with gills, whereby they are enabled to breathe air dis- solved in water ; the heart, when present, consists of a single auricle and ventricle (with the exception of the mud-fishes) ; and the limbs, when present, are in the form of fins, or expan- sions of the integument. In their external form, fishes are in most cases adapted for rapid locomotion in water, the shape of the body being such as to cause the least possible friction in swimming. To this end, as well as for purposes of defence, the body is generally enveloped in a species of chain-mail formed by overlapping scales, to which bony plates, tubercles, and spines, are some- times added. Valuable characters can sometimes be drawn from the nature of the scales, and with a view to this the integumentary appendages of fishes have been divided by Agassiz as follows (Fig. 100) : 1. Cycloid scales (a), consisting of thin, flexible, horny scales, which are circular or elliptical in shape, and have a smooth outline. These scales occur in most of our common fishes (e. g., the pike). 2. Ctenoid scales (b). These resemble the cycloid scales in being thin, flexible, horny scales, but they are distinguished by having their hinder margins cut into comb-like projections, or fringed with spines. The common perch supplies a good example of these scales. 3. Placoid scales (c). These are detached bony grains, PISCES. 207 tubercles, or plates, scattered through the skin, and sometimes armed with projecting spines. 4. Ganoid scales (y ciliated apertures (Fig. 105). The arrangement and struct- .re of the gills in fishes vary a good deal in different orders, and the leading modifications will be noticed hereafter. In the mean while it will be sufficient to give a short description of the branchial apparatus in one of the bony fishes. In such a fish the gills consist of a single or double series of flat carti- laginous leaflets, covered by mucous membrane, richly supplied with blood, and arranged on bony or cartilaginous arches which are connected with the tongue-bone (hyoid bone) below and with the under surface of the head above. The branchial arches and branchias are suspended in cavities placed on the side of the neck, and in the ordinary bony fishes there is only one such cavity on each side. The water is taken in at the mouth by a process analogous to swallowing, and it gains ad- mission to the branchial chamber by means of a series of clefts or slits which perforate the sides of the pharynx. Having passed over the gills and lost its oxygen, the effete water makes its escape behind by an aperture called the " gill-slit," which is placed on the side of the neck. The opening of the gill-slit is closed in front by a chain of flat bones which con- stitute the " gill-cover," and by a membrane which is sup- ported upon a variable number of slender bony spines. This is the general mechanism of respiration in one of the bony fishes, but different arrangements are found in other cases, which will be subsequently noticed. 212 VERTEBRATE ANIMALS. The heart in fishes may be regarded as essentially a branchial or respiratory heart, being concerned chiefly with driving the venous and impure blood to the gills. It con- sists in almost all cases of two cavities, an auricle and a ventricle (Fig. 104). The auricle (a) receives the venous blood which has passed through all the various parts of the body, and propels it into the ven- tricle (v). From the ventricle pro- ceeds a single great vessel (the "branchial artery"), the base of which is usually developed into a muscular cavity, the "bulbus arte- riosus" (m), which acts as a kind of additional ventricle. By the ventri- cle and bulbus arteriosus the venous blood is driven to the gills, where it is subjected to the action of the wa- ter. The aerated blood is not re- turned to the heart, but is driven from the gills through all parts of the body, the propulsive force neces- sary for this being derived partly from the heart, and partly from the contractions of the muscles between which the blood-vessels pass. The FIG. 104.— Diagram of the circuia- essential peculiarity of the circulation fi* *!&&SS?1E; of fishes consists in this, that the ar- venous system is left light. aAu- terialized blood returned from the ricle, receiving the venous blood „. ,, .. .. , , from the body; « Ventricle; m gills IS propelled through the gen- Bulbus arteriosus; n Branchial i Trac«^la rvf +1-,^ Korlv /cTrcf^rmV Korl artery, carrying the venous blood DOd to the gills (&); c Great systemic vessels) without being sent back to vessel, carrying the pure blood ,11, T j/i f i ^ i to the tissues. the heart. In the JLancelet, alone of all fishes, there is no single heart, and the circulation is effected by means of contractile dila- tations situated upon several of the vessels. In the Mud- fish (Lepidosiren) the heart consists of two auricles and a ventricle. In all cases the blood is cold, or, in other words, has a temperature very little, or not at all, higher than that of the surrounding medium. The blood-corpuscles (Fig. 99, e) are always nucleated, and, except in the Lancelet, are most of them red. While the respiration of all fishes is truly aquatic, most PISCES. OJ3 are, nevertheless, furnished with an organ which doubtless corresponds to (or is homologous with) the lungs of the higher Vertebrata. This is known as the " air " or " swim bladder," and is a sac filled with gas and situated between the alimen- tary canal and the kidneys. In most cases, the sac contains only a single cavity, but, in many instances, it is variously divided by partitions. In most fresh-water fishes, the gases in the swim-bladder are mainly composed of nitrogen, but, in the sea fishes, it is chiefly filled with oxygen. The sac of the swim-bladder is often closed, but, in other cases, it opens into the gullet by means of a duct which corresponds to the wind- pipe. In the great majority of fishes, the functions of the air-bladder are mainly hydrostatic, that is to say, it serves to maintain the necessary agreement between the specific gravity of the fish and that of the surrounding water. In the singu- lar Mud-fish (Lepidosiren), the air-bladder is composed of two distinct sacs, divided into a number of cellular compartments, and opening into the gullet by a tube. In this fish it acts as a respiratory organ, and is, therefore, not only in structure, but also in function, the representative of the lungs of the other Vertebrates. The nervous system of fishes is of an inferior type of or- ganization, the brain being of comparatively small size, and consisting mainly of a collection of ganglia. As regards the or- gans of the senses, two peculiarities deserve notice. In the first place, though fishes possess the essential parts of the organ of hearing, they possess no external ears, and in no -case is there any direct communication between the ear and the outer world. In the second place, the organs of smell consist of a double cavity lined by a mucous membrane folded into numer- ous plaits, into which water is admitted, usually by two dis- tinct apertures or nostrils. Behind, however, the nasal sacs are closed, and they do not communicate by any aperture with the throat, as they do in all the higher Vertebrates. The only exceptions to this rule are the Hag-fishes and their allies (Myxinoids) and the Mud-fish (Lepidosiren). As regards their reproductive system, most fishes are truly oviparous, and the ovaries are familiarly known as the " roe." Some fishes are ovo-viviparous, retaining their eggs within the body till the young are hatched. The male organs of repro- duction are commonly spoken of as the " milt " or " soft roe." CHAPTER XXV. OEDEES OF FISHES. THE number of different kinds of fishes is so enormous that nothing further will be attempted than merely to give an out- line of the leading peculiarities which distinguish the different orders. The classification here adopted is the one proposed by Prof. Huxley, who divides the class Pisces into the follow- ing six orders : 1. Pharyngobranchii. 2. Marsipobranchii. 3. Teleostei. 4. Ganoidei. 5. ElasmobranchiL 6. Dipnoi. OEDEE I. PHAEYNGOBEAKCHII (Gr. pliarugx, the upper part of the gullet, and bragchia, gills). — This order of fishes in- cludes only a single animal, the anomalous Amphioxus, or Lancelot, the organization of which differs in almost all its important points from that of all the other members of the class. In fact, the Lancelet presents us with the lowest type of organization as yet known in the Vertebrata. The Lance- let is an extraordinary little fish, from one and a half to two inches long, which burrows in sand-banks in various seas, but is especially abundant in the Mediterranean. The body is lanceolate in shape, and is provided with a narrow membra- nous border, of the nature of a median fin, which runs along the whole of the dorsal and a portion of the ventral surface, and expands at the tail to form a lancet-shaped caudal fin. There are no true " paired " fins, representing the fore and hind limbs. The mouth is a longitudinal fissure, placed at the front of the head, and completely destitute of jaws, but sur- ORDERS OF FISHES. 215 rounded by a number of cartilaginous filaments. The throat is provided with several leaf-like filaments, which are richly supplied with blood, and are believed to discharge in part the function of gills. The mouth (Fig. 105, m) opens into a dilated chamber, which is believed to represent the pharynx, and is termed the pharyngeal or " branchial " sac. The walls of this chamber (p) are strengthened by numerous cartilagi- FIG. 105. — Diagram of the Lancelet (AmpMoxus lanceolatus). m Mouth with cartilagi- nous filaments ; p Greatly-developed pharynx, or branchial sac, perforated by ciliated apertures; i Intestine; a Anus; h Blood-vessels, with pulsating dilatations in place of a heart ; ch Notochord ; n Spinal cord. nous filaments, between which are a series of transverse slits or clefts, and the whole is covered with a richly-ciliated mu- cous membrane. The function of this sac is clearly respiratory, the water from without being admitted through the mouth, passing through the branchial clefts into the abdominal cavity, and finally escaping by means of an aperture placed on the ventral surface a little in front of the anus. From the hinder end of the branchial sac proceeds the alimentary canal, which has appended to it a sac-like organ, believed to represent the liver, and which terminates behind in a distinct anal aperture. There is no heart, and the circulation is entirely effected by means of several contractile dilatations, developed upon the great blood-vessels (h). The blood itself is colorless. No kidneys have hitherto been discovered, and the reproductive elements are emitted into the abdominal cavity, from which they escape by the pore placed upon the lower surface. There is no skeleton properly so called. The notochord (ch) remains throughout life as a semi-gelatinous rod, enclosed in a membranous sheath, and supporting the spinal cord. There is no skull, and the spinal cord (n) does not expand in front to form a distinct brain. The brain, however, may be said to be represented, as the front portion of the nervous axis gives off nerves to a pair of eyes, and another branch to 216 VERTEBRATE ANIMALS. a ciliated pit, which is believed to be a rudimentary organ of smell. OEDEK II. MARSIPOBEANCHII (Gr. marsipos, a pouch ; brag- chia, gills). — This order includes the Hag-fishes (Myxinidce) and the Lampreys (PetromyzonidvB), and it is defined by the following characters : The body is cylindrical and worm-like, and is destitute of limbs. The skull is cartilaginous, there is no lower jaw, and the notochord remains through life, so that there is no vertebral column. The heart is composed of an auricle and a ventricle, but there is no bulbus arteriosus. The gills are pouch-like, communicating with the throat on the one hand, and opening externally on the other by means of apertures placed on the sides of the neck. The Hag-fish (Myxine) is an eel-like fish, which agrees with the Lampreys in having neither pectoral nor ventral fins, the representatives of the fore and hind limbs. The mouth is of a very remarkable character, and enables the Hag-fish to lead a very peculiar existence. It is generally found imbedded in the interior of some large fish, into which it has penetrated by means of a single serrated and recurved fang attached to the centre of the palate. The mouth itself is destitute of jaws, and forms a sucking disk or cup. Another remarkable peculiarity of the Hag-fishes is found in the structure of the nose. In all fishes, namely, except these and the Mud-fish (Lepidosiren\ the nasal chambers are closed behind, and do not communicate with the cavity of the mouth, as they do in the higher Vertebrates. In the Myxinoids, however, such a communication does exist. The nasal sacs are placed in com- munication with the throat (pharynx) by means of a canal which perforates the palate. A second canal leads from the nasal cavities in front to open by an external aperture (the nostril or "spiracle") on the top of the head behind the mouth. Another peculiarity, which is best considered in the Lam- preys, is to be found in the structure of the respiratory or- gans, from which the name of the order is derived. ^ When viewed externally, instead of the single great " gill-slit," cov- ered by a " gill-cover," as seen in the ordinary bony-fishes, the side of the neck presents seven round holes placed far back in a line on each side. These holes are the external apertures of the gills (Fig. 106, A), which in these fishes are in the form of sacs or pouches, the lining membrane of which is thrown into numerous folds or plaits, over which the branchial ORDERS OF FISHES. 217 vessels ramify (Fig. 106, B). Internally the sacs communi- cate with the cavity of the pharynx, by means of a common respiratory tube into which they all open. It follows from this arrangement that the gill-pouches on the two sides of the neck communicate freely with one another through the phar- ynx. The object of this arrangement is to obviate the ne- cessity for admitting the water to the gills through the mouth, FIG. 106.— A, Lamprey (Petromyzon\ showing the sucking-mouth and the apertures of the gill-sacs. B, Diagram to illustrate the structure of the gills in the Lampreys, a Pharynx ; b Tube leading from the pharynx into one of the gill-sacs ; c One of the gill- sacs, showing the lining membrane thrown into folds ; d External opening of the gill- sac. (In reality the gill-sacs do not open directly into the pharynx, but into a common respiratory tube which communicates with the pharynx ; but this is omitted for the sake of clearness.) as ordinary fishes do. These fishes are in the habit of fixing themselves to foreign objects by means of the suctorial mouth ; and, when in this position, it is, of course, impossible that they can obtain the necessary water of respiration through the mouth. As the gill-sacs, however, on the two sides of the neck communicate freely with one another through the phar- ynx, water can readily pass in and out. The gills are not provided with cilia, but the circulation of water is assisted by a kind of elastic cartilaginous framework upon which the whole respiratory apparatus is supported, and which acts some- what like the ribs of the higher Vertebrates. The nasal cavities of the Lampreys, unlike those of the Myxinoids, are closed behind, and do not communicate with the throat. Some of the Lampreys are permanently inhabit- ants of rivers, but the great sea-lamprey (Petromyzon mari- nus) only quits the salt water and betakes itself to fresh in order to deposit its eggs. ORDER III. TELEOSTEI (Gr. teleios, perfect; and osteon, bone). — The fishes comprised in this order, as implied in their name, have a well-ossified or bony skeleton, and they are com- 218 VERTEBRATE ANIMALS. monly known as the " bony " fishes. In all the Teleostei, the skeleton is bony, the skull is composed of distinct bones, and there is a lower jaw. The vertebral column always consists of more or less completely ossified vertebras; and the two pairs of limbs, when present, are in the form of fins, supported by rays. The gills are free, comb-like or tufted in shape, and always protected by a bony gill-cover. The bulbus arteriosus is not capable of regular contractions, and is separated from the ventricle by only a single valve. The order Teleostei comprises almost all the most familiar fishes, and it will be unnecessary to dilate here upon their structure, as they were taken as the type of the class in de- scribing the fishes generally. It may be as well, however, to recapitulate some of the leading points in the anatomy of the bony fishes. 1. The skeleton is always more or less complete- ly ossified, and does not remain cartilaginous throughout life. The notochord is not permanent, and the vertebral column consists of a number of distinct vertebras. The vertebras, however, are " amphiccelous," or hollow at both ends, so that there is left between each pair a doubly-conical cavity, which is filled with the cartilaginous or semi-gelatinous remains of the notochord. In this way an extraordinary amount of flexi- bility is given to the entire vertebral column. In no fish (ex- cept the Bony Pike, which belongs to another order) is the conversion of the bodies of the vertebras into bone carried further than this. 2. The integument usually develops scales, and these in the great majority of cases are of the forms known as " cy- cloid " and " ctenoid," the former being circular or elliptical horny plates, with plain margins ; while the latter have their hinder margins cut into comb-like projections, or fringed with spines (Fig. 100, a, b). 3. The anterior and posterior limbs are usually, but not always, present, and when developed they are always in the form of tins. These fins may be supported by " spinous rays " or " soft rays," or by both. . The spinous rays are simple un- divided bony spines which taper to a point. The soft rays are doubly divided, splitting up toward their extremities into a number of secondary rays, and being also divided by trans- verse joints into numerous short pieces. 4. Besides the " paired " fins which represent the limbs, there is also a series of unpaired or " median " fins, the rays of which are supported upon a series of dagger-shaped bones, deeply plunged in the flesh in the middle line of the body, OKDERS OF FISHES. 219 and known as the " interspinous " bones (Fig. 101). The me- dian fins are variable in number, but when fully developed they consist of one or two fins on the back (the dorsal fins), one or two on the ventral surface (the anal fins), and one clothing the posterior extremity of the body (the caudal fin, or tail, Fig. 102). In all the Teleostei, the caudal fin has the shape called " homocercal " — that is to say, it consists of two equal lobes — and the vertebral column is not prolonged into the upper lobe (Fig. 103, a}. 5. The heart consists of two cavities, an auricle and a ven- tricle, but the bulbus arteriosus is not rhythmically contractile, and is separated from the ventricle by only a single pair of valves. 6. The respiratory organs are in the form of free, comb- like, or tufted gills, enclosed in two cavities placed on the sides of the neck. Each of these branchial chambers opens externally by a single aperture, the " gill-slit," which is pro- tected by a chain of bones, forming the " gill-cover," and by a membrane supported by bony rays. Internally the branchial chambers communicate with the throat by a series of clefts or fissures, and the water required in respiration is taken in at the mouth by a process analogous to swallowing. 7. The nasal sacs never communicate behind with the throat (pharynx). TABULAR VIEW OF THE MAIN DIVISIONS OF THE TELEOSTEI. SUB-ORDER I. MALACOPTERI. — Usually a complete series of fins, supported by rays, all of which are soft, or many-jointed (with the occasional exception of the first rays in the dorsal and pectoral fins). A swim-bladder is always present, and is always connected with the gullet by a duct. The skin is rarely naked, and is mostly furnished with cycloid scales, but sometimes ganoid scales are present. Among the more important families in this sub-order are the Eels (Mu- rcenidce), Herrings (Clupeidce], Pikes (Esoddce), Carps (Cyprinidce), Salmon and Trout (Salmonidai), and Sheat-fishes (Siluridce). SUB-ORDER II. ANACANTHINI. — Fins entirely supported by soft rays, and never by spinous rays. Ventral fins either wanting, or placed under the throat, beneath or in advance of the pectorals. The two leading families in this sub-order are the Cod, Ling, and Haddock family (Gadidce), and the Flat-fishes (Pleuronectidce\ comprising the Sole, Turbot, Flounder, and others. SUB-ORDER III. ACANTHOPTERI. — Fins with- one or more of the first rays in the form of undivided, inflexible, spinous rays. Scales mostly ctenoid. Swim- bladder without a duct. The leading families in this order are the Wrasses ( Cyclo-labridce\ the Perches (Percidce), the Mackerels (Scomberidce), the Mullets (Mugilidce], and the Gobies (Gobiidce). 220 VERTEBRATE ANIMALS. SUB-ORDER IV. PLECTOGNATHI. — Certain of the bones of the mouth (the maxillary and prae-maxillary bones) immovably connected on each side of the jaw. Integumentary skeleton in the form of ganoid plates, scales, or The chief families in this sub-order are the File-fishes (Balislidce), and the Trunk-fishes ( Ostraciontidce). SUB-ORDER V. LOPHOBRANCHII. — Gills arranged in little tufts on the branchial arches. Integumentary skeleton in the form of ganoid scales. The two families contained in this division are the Sea-horses (Hippocam- pidce), and the Pipe-fishes (Syngnathidce). OEDEK IV. GANOIDEI (Gr. ganos, splendor, or brightness). — The fourth order of fishes is that of the G-anoidei, including few living forms, but having a great and varied development in past geological epochs. The Ganoid fishes are dis- tinguished by the imperfect development of the skeleton, which is mostly cartilaginous throughout life., and by having an integumentary skeleton composed of ganoid scales, plates, or spines (Fig. 100, d). The skull is composed of distinct bones, and there is always a lower jaw. There are usually two pairs of fins (pectoral and ventral), supported by many series of cartilages, and the ventral fins are placed very far back. The first rays in the fins are usually in the form of strong spines. The caudal fin or tail is mostly heterocercal or unsymmetrical (Fig. 103, #). The swim-bladder is always present, is often cellular, and is provided with an air-duct. The gills and gill-covers are essentially the same as in the bony fishes. The heart has one auricle and a ventricle ; and the bulbus arteriosus is rhythmically contractile, is furnished with a distinct coat of muscular fibres, and is furnished with several transverse rows of valves. The best known of the living Ganoids are the Bony Pike (Lepidosteus), the Sturgeon (Sturio), and the Polypterus. Of these, the Bony Pike is found in the rivers and lakes of North America. It is a large fish, attaining a length of several feet, and it has the body entirely covered with an armor of ganoid scales arranged in obliquely transverse rows. The jaws form a long, narrow snout, armed with a double series of teeth, and the tail is heterocercal. The vertebral column is more perfect- ly ossified than in any other fish, the bodies of the vertebras being convex in front and concave behind ( " opisthocoelous "). The Polypterus (Fig. 107, A) inhabits the rivers Nile and Senegal, and is remarkable for the peculiar structure of the dorsal fin, which is broken up into a series of small, detached portions, each composed of a single spine in front, with a soft fin attached to it behind. Some of the species of Polypterus ORDERS OF FISHES. d 221 FIG. 107. — Ganoid Fishes. A, Poli/pterus, a living1 Ganoid. B, Osteolepis, a fossil Ganoid (restored) : a Pectoral fin ; b Ventral fin ; c Anal fin ; d d' Dorsal fins. are stated to possess external gills when young, which they lose when grown up, thus making an approach to the Am- phibia. Many of the fossil Ganoids are more or less closely allied to the living Lepidosteus and Polypterus. Another great group of the Ganoid fishes is represented by the Sturgeons (Sturiom SipJionops annulatus, one of tho Caecilians, much reduced ; & Head of the same ; c Mouth, showing the tongue, teeth, and internal openings of the nostrils ; d Tail of the same. (After Dumeril and Bibron.) ORDER II. URODELA or ICHTHYOMORPHA (Gr. ichthus, a fish, and morphe, shape). — In this order are a number of fish- like Amphibians, of which the Newts and Land-salamanders are the most familiar examples. In all the members of this section, the skin is naked, and never develops any hard struct- ures, and in all there is a well-developed, fish-like tail, which is retained throughout life. The vertebras are sometimes hol- low at both ends (amphiccelous), sometimes hollow behind and convex or rounded in front (opisthocoelous). The ribs are rudimentary and the bones of the forearm (radius and ulna\ and of the shank (tibia and^frw/a), are separate, and are not combined so as to form single bones. The Ichthyomorpha are not unfrequently spoken of as the "Tailed" Amphibians (Urodeld), and they fall into two natu- ral sections, according as the gills are permanently retained throughout life, or are cast off before maturity is attained. The animals belonging to the first section are often called " perennibranchiate," while those belonging to the second are said to be " caducibranchiate." Among the Perennibranchiate forms, in which the gills are permanently retained after the lungs make their appearance, the best-known examples are Axolotl (Fig. 112), the curious Proteus anguinus, and the Mud-eel (Siren). The Axolotls 228 VERTEBRATE ANIMALS. inhabit various of the lakes of the American Continent, the best- known species being the Siredon pisciforme of the Mexican lakes (Fig. 112). It attains a length of a foot or more, and FIG. 112.— The Axolotl (Siredon pisciforme). (After Tegetmeier.) possesses both pairs of limbs, the fore-feet having four toes, the hind-feet five toes. The branchiae are in the form of three long ramified processes on each side of the head ; and the tail is compressed, and fringed by a fin which is prolonged on the back between the shoulders. In a state of nature, the Axolotl is certainly perennibranchiate, and it breeds freely in this condition. It has been shown, however, by Prof. Marsh, of New Haven, that some species, when kept in confinement, lose their gills, and undergo certain other changes, becoming ul- timately converted into a Salamandroid, apparently belonging to the genus Amblystoma. The Proteus is an extraordinary Amphibian which is found inhabiting the waters of caves in Illyria and Dalmatia. It attains a length of about a foot, and is of a pale flesh-color or nearly white. The gills, which are retained throughout life, are of a bright scarlet. Both pairs of limbs are developed, but they are only short and weak, the fore-limbs having three toes each, and the hind-limbs only two. The eyes are extremely small, the animal spending its existence in darkness; and swimming is effected mainly by means of the tail. The Siren, or Mud-eel, is a large lizard-like Amphibian, which is found abundantly in the swamps of South Carolina, and attains the great length of three feet. The ex- ternal branchiae are retained throughout life, and they are the main organs of respiration. The fore-limbs are present, but the hinder pair of limbs is never developed. AMPHIBIA. 229 The " caducibranchiate " section of this order is charac- terized by the fact that both pairs of limbs are always de- veloped, and the branchiae are never retained throughout life. The most familiar examples are the Water-salamanders or Newts (Triton), and the Land-salamanders. The Newts (Fig. 113) are well known as inhabiting pools in many countries, FIG. 113.— The great Water-Newt (Triton cristatm), male. (After Bell.) and the young lead a strictly aquatic life. When the lungs are developed the external gills wholly disappear, and the respiration becomes strictly aerial, though the animals still spend a great part of their time in the water. The larva or young form is at first destitute of limbs, and the fore-limbs are the first to be developed, the reverse of this taking place in the Frogs. In accordance with their mode of life, the tail is compressed and flattened, so as to form an efficient swimming apparatus. The Water-salamanders are all oviparous, and the young are like the tadpoles of the common frog. The Land-salamanders, in both their adult and young state, live upon land, and the tail is rounded and cylindrical. The yeung are not developed in water, but are retained with- in the body of the parent for a longer or shorter period, so that the reproduction becomes ovo-viviparous, or even vivip- arous. The best-known Salamanders occur upon the Con- tinent of Europe, and one species is singular in the fact that it inhabits high mountains. It is important to remember in connection with all these " tailed " Amphibians, that they are wholly distinct from the true Lizards, with which they are often confounded. Many of them are completely lizard-like in form, having a long tail and two pairs of legs ; all, however, at some time or other in their life, respire by means of gills, and this is never the case with any true Lizard. It must be confessed, however, that a 230 VERTEBRATE ANIMALS. near approach to the Lizards is made by the Land-salamanders, the young of which have sometimes lost their gills before birth. ORDER III. ANOURA or THERIOMORPHA (Gr. ther, a beast ; and morphe, shape). — This order is the highest of the Am- phibia, and comprises the Frogs and Toads. It is sometimes known by the name of JBatrachia (Gr. batrachos, a frog), or Anoura (Gr. a, without; our a, a tail), the latter name being derived from the fact that the adults are " tailless." The tailless Amphibia or Theriomorpha are characterized by the fact that while the larva possesses a tail, and is fur- nished with gills, the adult has no tail, and breathes wholly by lungs. Both pairs of limbs are always developed in the full-grown animal, and the hind-limbs are usually considerably longer than the fore-limbs, and generally have the toes webbed, while those of the fore-limbs are free. The skin is FIG. 114.— Anoura. Tree-frog (Hyla leucotcenia), (After Gunther.) soft, and there are rarely any traces of any integumentary skeleton. The spinal column (Fig. 114) is short ; the dorsal vertebrae are very long ; and the ribs are quite rudimentary, their place being taken by greatly-developed transverse pro- cesses. The bodies of the vertebrae are hollow in front and convex behind (proccelous). The bones of the forearm (radius and ulna), and those of the shank (tibia &ud fibula), are united together to form single bones. The upper jaw is usually fur- AMPHIBIA. 231 nished with teeth, and the lower jaw sometimes, but there are no teeth in the Toads. The lungs are well developed, comparatively speaking ; and, as there are no ribs by which the cavity of the chest can be expanded, the air is taken into the lungs by a process nearly akin to that of swallowing. There can be no doubt, also, that the skin plays a very im- portant part in the aeration of the blood, and that the frogs, especially, can carry on their respiration by means of the skin without the assistance of the lungs for a very lengthened period. This, however, should not lead to any credence being given to the often-repeated stories of frogs and toads being found in closed cavities in solid rock, no authenticated instance of such an occurrence being known to science. The ova of the frogs and toads are deposited, in masses or strings, in water, and the young or larvae are familiar to every one as tadpoles. Upon its escape from the egg, the young frog (Fig. FIG. 115.— Development of the common Frog, a Tadpole, viewed from above, showing the external branchiae (Q) ; 6 Side view of a somewhat older specimen, showing the fish-like tail ; c Older specimen, in which the hind-legs have made their appearance ; d Specimen in which all the limbs are present, but the tail has not been wholly absorbed. (After Beii.) 115) presents itself as a little fish-like creature with a broad head, a sac-like belly, and a long, compressed tail with which it swims actively. It breathes by means of gills or branchiae, of which there are two sets, one external, and the other in- ternal ; at first there are no limbs ; but, as development pro- ceeds, the limbs make their appearance — the hind-legs first, and then the fore-legs. The tail, however (Fig. 115), is still retained as an instrument of progression. Ultimately, when 232 VERTEBRATE ANIMALS. the limbs are fully developed, and the gills have given place to lungs, the tail disappears, and the animal now takes to the land as a perfect frog. The development of the Frog is a good illustration of the general zoological law, that the transitory 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 which it breathes by external branchiae, is to a certain extent permanently represented by the perma- nent condition of a perennibranchiate Amphibian, such as the Proteus. The stage at which the external branchiae have dis- appeared, but the tail is still present, and the limbs are de- veloped, is permanently represented in the common tailed Amphibians, such as the Newts. The order Anoura comprises the three families of the Frogs, Toads, and Surinam Toads. The Frogs (Ranidaz) are distinguished by having a tongue which is fixed to the front of the mouth, and can be protruded at will, while the upper jaw is always armed with teeth. The typical Frogs have enormously-developed hind legs, the toes of which are united by membrane, or are " webbed." They swim very power- fully, and can take extensive leaps. The Tree-frogs (Fig. 114), on the other hand, are adapted for a wholly different life, inhabiting trees, among which they climb with great ease by the help of suckers developed upon the ends of the toes. They are mostly found in warm countries, especially in Amer- ica, but one species is European. In the equally familiar Toads (Bufonidce) the structure of the tongue is the same as in the Frogs, but the jaws are not furnished with teeth. In the Surinam Toads (Pipidce) there is no tongue at all, and usually no teeth. ORDER IV. LABYRrNTHODONTiA. — This, the last order of the Amphibia, is not represented by any living forms, and re- quires to be little more than mentioned. The Labyrinthodonts were Amphibia which were mostly of large size, and of which some must have obtained absolutely gigantic dimensions, the skull of one species being three feet in length and two in breadth. They were first known to science simply by their footprints, which were found in certain Secondary sandstones (Trias). These footprints consisted of a series of alternately placed pairs of hand-shaped impressions, the hinder print of each pair being much larger than the fore one. So like were AMPHIBIA. 233 these prints to the shape of the human hand that the unknown animal which had produced them was christened the " Cheiro therium " (Gr. cheir, hand ; ther, beast). Further researches, however, showed that these footprints were produced by various species of large Amphibians, to which the name of Ldbyrinthodontia was applied, in consequence of the compli- cated microscopic structure of the teeth. These extinct Am- phibians are known to have existed at the time of the Coal, but they are most characteristic of the period known to geolo- gists as the Trias. SAUROPSIDA. CHAPTER XXVII. CLASS III. REPTILIA. WE commence now the second great primary division of the Vertebrata, namely, that of the /Sauropsida, comprising the Reptiles and the Birds. These two classes, though very unlike in external appearance, are united by the following characters : There are never at any period of life gills or bran- chiae adapted for aquatic respiration ; the red corpuscles of the blood are nucleated (Fig. 99, b, c) ; the skull articulates with the vertebral column by means of a single articulating surface or condyle ; each half of the lower jaw is composed of several pieces, and is jointed to the skull, not directly, but by the intervention of a special bone (the so-called " quadrate bone " ). These being the characters by which, among others, Rep- tiles and Birds are collectively distinguished from other Ver- tebrates, it remains to see what are the characters by which the Reptiles are distinguished, as a class, from Birds. In all Reptiles the blood is cold — that is to say, very slightly warm- er than the temperature of the external medium in which they live. The integument secretes scales, with or without bony plates, but in no case do the integumentary appendages take the form of feathers. The heart consists of two auricles, and a ventricle, which in most is partially divided into two cham- bers by an incomplete partition, and in a few is completely divided. In any case, however, more or less of the impure venous blood is mixed with the pure arterial blood which cir- culates over the body. There is no division between the cavi- ties of the thorax and abdomen, and the lungs are not con- nected with air-sacs placed in various parts of the body. The limbs may be wanting, or rudimentary, but in no case are the REPTILIA. 235 fore-limbs constructed upon the type of the " wing " of birds, and in no living Reptile is there the bone which is known in Birds as the " tarso-meta tarsus." The class Reptilia includes the Tortoises and Turtles ( Che- Ionia), the Snakes ( Ophidia], the Lizards (Lacertilia), and the Crocodiles (Crocodilia). With the exception of the Tortoises and Turtles, they are mostly of an elongated cylindrical form, furnished behind with a long tail. The limbs may be alto- gether absent or quite rudimentary, as in the Snakes, but in almost all the higher members of the class there are two pairs of limbs, which may be either adapted for walking or swim- ming, and which in some extinct forms support a flying mem- brane. The internal skeleton is always bony, never cartila- ginous or semi-cartilaginous as in many of the fishes. The skull is joined to the spine by a single articulating surface (or condyle). The lower jaw is complex, each half being com- posed of several pieces united by sutures. In Tortoises and Turtles, however, these separate pieces are amalgamated to- gether, and the two halves are also united, so that the whole lower jaw appears to form a single piece. In most Reptiles, on the other hand, the two halves of the lower jaw (Fig. 116) are only loosely united ; in the Snakes by ligaments and mus- cles, in the Lizards by gristle, and in the Crocodiles by suture. FIG. 116.— Skull of a Serpent (Python), a Quadrate bone ; & Lower jaw, articulating with the movable quadrate bone. In all, the lower jaw is jointed to the skull by means of a special bone, called the " quadrate bone ; " and as this often projects backward, the opening of the mouth is often very extensive, and may even extend backward beyond the base of the skull (Fig. 116, a). Teeth are generally present, but these are used chiefly to hold the prey, and not in biting or chewing 236 VERTEBRATE ANIMALS. the food. Except in the Crocodiles, the teeth are not sunk into distinct sockets, and they are usually replaced as fast as shed. They likewise do not differ from one another sufficient- ly in form or function as to allow of their being divided into different sets, as they can be in the Mammals. Usually the teeth are confined to the jaws proper, but in some cases they are carried by other bones of the mouth. In the Tortoises and Turtles there are no teeth, and the jaws are simply sheathed in horn, so as to constitute a kind of beak, like that of a bird. The integumentary skeleton is in the form of scales, sometimes combined with bony plates. In the Tor- toises and Turtles the integumentary skeleton is so united with the true skeleton as to form a kind of bony case or box, in which the body is enclosed. The digestive system presents little worthy of special no- tice, except that the termination of the intestine (rectum) opens into a cavity called the " cloaca," which receives also the ducts of the urinary and generative organs. It is, however, in the structure of the circulatory and respir- atory organs that the most important characters of the Reptiles are to be looked for. The heart in all Reptiles may be regarded as being, in function^ three-chambered, being composed of two auricles and a single ventricle, imperfectly divided by an in- complete partition. In the Crocodiles alone the heart is, struct- urally, four-chambered, the ventricle being divided into two by a complete partition. Here, however, the same results are brought about as in the other Reptiles, by means of a commu- nication which subsists between the great vessels which spring from the ventricles thus formed. In the ordinary Reptiles the course of the circulation is as follows (Fig. 117) : The impure or venous blood that has circulated through the body is poured by the great veins into the right auricle (a). The pure or arterial blood that has been submitted to the action of the lungs is poured by the pulmonary veins into the left auricle (a1). Both auricles empty their contents into the ventricle, and, as the partition which divides the ventricle is an incom- plete one, it follows that the venous and arterial streams must mix to a greater or less extent in the ventricle. From the ventricle arise the great vessels which carry the blood to the lungs and to all parts of the body, and it follows, as a matter of necessity, that all these parts are supplied with a mixed fluid, consisting partly of impure or venous blood, and partly of pure or arterial blood. In the Crocodiles, in which there are two ventricles completely separated from each other, the REPTILIA. 237 same result is brought about by means of a communication which takes place between the great vessels which spring from the ventricles, in the imme- diate neighborhood of the heart. From this brief description it will be seen that the peculiarity of the circulation in Reptiles con- sists in the fact, that the lungs and all parts of the body are sup- plied with mixed blood ; whereas in the higher Vertebrates the lungs are supplied with pure venous blood, and the various tis- sues of the body with pure arte- rial blood. As regards the structure of the lungs, it is merely to be noted that there is no partition (dia- phragm or midriff) separating the two cavities of the thorax and abdomen, and that the lungs, therefore, often attain a great pro- portionate size, sometimes ex- tending through almost the whole length of the cavity of the trunk. There are also no air-sacs commu- nicating with the lungs, as in the Birds. Lastly, all Reptiles are essen- tially oviparous, some being ovo- viviparous. The egg-shell is usu- ally parchment-like, but in other cases contains more or less cal- careous matter. The class Reptilia is divided into four living and five ex- tinct orders, as follows, but the latter require but brief notice : 1. Chelonia (Tortoises and Turtles). 2. Ophidia (Snakes). 3. Lacertilia (Lizards). 4. Crocodilia (Crocodiles). 5. Ichthyopterygia 1 6. Sauropterygia 7. Pterosauria V Extinct. 8. Anomodontia 9. Deinosauria venous blood from the body ; a' Left auricle, receiving arterial blood from the lungs; v Arterio-venous ventri- cle, containing mixed blood, which is driven by (p) the pulmonary artery to the lungs, and by (0) the aorta to the body. (The venous system is left light, the arterial system is black, and the vessels containing mixed blood are cross-shaded.) CHAPTER XXVIII. DIVISIONS OF REPTILIA. ORDER I. CHELONIA (Gr. chelone, a tortoise). — In this order are included the various Tortoises and Turtles, charac- terized by having the body enclosed in a bony case or box, and by the fact that the jaws are not provided with teeth, but are encased in horn, so as to form a kind of beak. The case in which the body of a Chelonian is protected is composed partly of integumentary plates, and partly of flattened bones belonging to the true skeleton, and it is composed essentially of two pieces, one placed on the back and the other on the lower surface of the body, firmly united together at their edges. The dorsal shield is more or less convex and rounded, and is called the carapace (Fig. 118, ca) ; while the ventral shield is more or less completely flat or concave, and is called the plas- tron. The carapace and plastron, as just said, are united by their edges, but they leave two openings, one in front for the head, and one behind for the tail. The carapace is essentially composed of the flattened and expanded spinous processes of the vertebrae and the greatly-developed ribs, covered by a series of horny plates. These are growths of the integument, and in some cases they constitute the " tortoise-shell " of com- merce. The plastron is also composed partly of bony and partly of horny plates, but opinions differ as to whether the bony plates are to be looked upon as formed by an expanded breastbone, or whether they are merely integumentary, the probabilities being in favor of the latter view. The remaining peculiarities with regard to the skeleton which deserve special mention are : Firstly, that the dorsal vertebrae are immovably connected together, so that this region of the spine is quite inflexible ; secondly, that the heads of the ribs are articulated directly to the bodies of the vertebrae ; and, DIVISIONS OF REPTILIA. 239 thirdly, that the scapular and pelvic arches, supporting respec- tively the fore and hind limbs, are situated within the carapace (Fig. 118, s and p\ so that the shoulder-blade is placed inside the ribs instead of outside, as is usually the case. FIG. 118.— Skeleton of a Tortoise (Emys Ewropaia\ seen from below, the plastron having: been removed, ca Carapace, showing1 the flattened and expanded ribs ; s Scapular arch, carrying the fore-limbs, and placed in the interior of the carapace ; p Pelvic arch, carrying the hind-limbs ; r Kibs. The Chelonia are conveniently divided into groups, accord- ing as the limbs are adapted for swimming (natatory), or for progression on land (terrestrial) ; or, again, enable the animal to lead an amphibious life, sometimes on land and sometimes in the water. Of the strictly aquatic forms the best known are the edible Green Turtle ( Chelonia midas) and the Hawk's- bill Turtle ( Chelonia imbricata). The former is found abun- dantly in many of the seas of warm climates, and is largely imported into Europe as a delicacy. The latter (Fig. 119) is truly a native of warm seas, though an occasional straggler has reached the shores of Britain. It is of comparatively small size — not more than about three feet in length — but is 240 VERTEBRATE ANIMALS. of considerable commercial importance, as it furnishes the " tortoise-shell " of trade, so largely used in various kinds of ornamental work. FIG. 119.— The Hawk-billed Turtle (CJwlonia imbricata). (After Bell.) The Sea-tortoises or Turtles have the carapace much flat- tened, the legs of unequal length, in the form of solid fins or oars, the toes being conjoined, and hardly distinct from one another. The Marsh, Pond, and River Tortoises are generally fur- nished with webbed feet, and lead an amphibious, semi-aquatic existence. The so-called " Soft Tortoises " (Trionycidce] be- long here, and are distinguished by the imperfect condition of the carapace, which is simply covered with a leathery skin. A good example is the Soft-shelled Turtle (T.ferox) of the Southern States. Here also belong the Snapping-turtles, so well known in the person of the common American species (Chetydra serpentina), and the Terrapins (Emydidce), of which many forms are found in all parts of the United States. In the curious little Box-tortoise ( Cistudo Virgined) the plas- tron is composed of two movable portions which can be brought into accurate apposition with the carapace, thus com- pletely protecting the animal within. The Land Tortoises have short legs of nearly equal length, the toes little distinct, and united into a sort of stump, with indistinct, horny claws. Good examples of this group are the DIVISIONS OF REPTILIA. 241 common European Tortoise (Testudo Grceca) and the Indian Tortoise (T. Indica), the last attaining a length of over three feet. ORDER II. OPHIDIA (Gr. ophis, a serpent). — This order in- cludes most of the animals which would commonly be called snakes or serpents, and is characterized by the following pecu- liarities : The body is always more or less elongated, worm- like or cylindrical, and the skin develops horny scales, but never bony plates. There is never any breastbone (sternum), nor pectoral arch, nor fore-limbs ; nor, as a rule, are there any traces of hind-limbs. In a few cases, however, rudimentary hind-limbs can be detected. The ribs are always very numer- ous. The two halves of the lower jaw are composed of several pieces each, and they are united to one another in front only by ligaments and muscles (Fig. 120). Hooked, conical teeth FIG. 120.— The Naja Hqje, a poisonous Snake of Egypt. are always present, but they are never lodged in distinct •sockets, and are only used to hold the prey, and not in masti- cation. The lungs and other paired organs are often not sym- metrical, one of each pair being usually smaller than the other, or altogether absent. 242 VERTEBRATE ANIMALS. The most striking of these characters of the snakes is to be found in the nature of the organs of locomotion. The fore-limbs are invariably altogether wanting, and there is no pectoral arch nor breastbone ; and the hind-limbs are either totally absent or are at best rudimentary and never exhibit any outward evidence of their existence, beyond the occasion- al presence of short, horny claws or spurs. In the entire ab- sence, then, or rudimentary condition of the limbs, the snakes progress by means of the ribs, which are always excessively numerous, and, in the absence of a breastbone, are also ex- tremely movable. Their free ends, in fact, are simply attached by muscular fibres to the scales or " scutes," which cover the lower or abdominal surface of the animal. The number of ribs varies from 50 up to 320 pairs, and, by means of this arrangement, the snakes are able to progress rapidly, walking, as it were, upon the ends of the ribs. Their movements are also much assisted by the extreme flexibility of the whole spine, caused by the cup-and-ball articulation of the bodies of the vertebrae, each of which is concave in front and convex behind (proccelous). Of the other characters of the snakes, a few words may be said as to the tongue, the eye, and the teeth — all important structures in this order. The tongue, in serpents, is probably more an organ of touch than of taste, and consists of two muscular cylinders, which are united toward their bases. The forked organ thus formed can be protruded and retracted at will, being in constant vibration when protruded, and being in great part concealed by a sheath when retracted. The eye of serpents (Fig. 121, A) is not protected by any eyelids, and hence the peculiar stony and unwinking stare for which these reptiles are celebrated. In place of eyelids, the outer layer of the skin is prolonged over the eye as a continuous and transparent film, behind which is a chamber formed by the mucous covering of the eye, into which the tears are dis- charged. The outer membrane is periodically shed along with the rest of the external or epidermic layer of the integument, and is again renewed. The pupil is round in most serpents, but it forms a vertical slit or fissure in the venomous snakes and in the Boas. As regards the teeth, it is to be noticed that the snakes are not in the habit of chewing their prey, but of swallowing- it whole, and the construction of their dental apparatus is in accordance with this peculiarity. The lower jaw, as before said, articulates with the skull by means of a quadrate bone DIVISIONS OF REPTILIA. 243 (Fig. 117), and this in turn is movably jointed to the cranium. The two halves of the lower jaw are also merely united loosely in front by ligaments and muscles. In consequence of this peculiar arrangement of parts, the serpents have the power of opening the mouth to an extraordinary width, and they can perform the most astonishing feats in the way of swallowing. The teeth are simply fitted for seizing and hold- ing the prey, but not in any way for chewing or dividing it. In the harmless snakes, the teeth are in the form of solid cones, which are arranged in rows round the whole of the upper and lower jaws, a double row existing on the palate as well. In the venomous snakes, on the other hand, the ordinary teeth are usually wanting upon the upper jaws, and these bones are themselves much reduced in size. In place of the ordinary teeth, however, the upper jaws carry the so- called "j>oison-fangs " (Fig 121, B). These are a pair of long, FIG. 121.— A, Diagrammatic Section of the Eye of a Viper (after Cloquet). a Eyeball; 6 Optic nerve ; c Chamber into which the tears are poured ; d Epidermic layer covering the eye. B, Head of the common Viper (after Bell), showing the poison-fangs. curved fangs, one on each maxilla or upper jawbone, which, when not in use, are pointed backward, and concealed in a fold of the gum, but can be raised at will by special muscles. Each tooth is perforated by a fine canal or tube, which opens by a distinct aperture at the point of the fang, and is connect- ed with the duct of the " poison-gland." This is a gland, situated under and behind the eye, secreting the poisonous fluid which renders the bites of these snakes dangerous or fatal. When the serpent strikes at any animal, the poison is forced through the poison-fang into the wound, partly by the contractions of the muscular walls of the gland, and partly by the compressive action of the muscles of the jaws. In some other snakes, several of which are not certainly known to be 244 VERTEBRATE ANIMALS. venomous, there are large, grooved fangs placed far back in the mouth upon the upper jaw. Of the non-venomous, harmless snakes, we have an excel- lent instance in the common Ringed Snake (Coluber natrix), which is of frequent occurrence in most parts of Europe. Like all the snakes, it is strictly carnivorous, having a special liking for frogs, which it swallows whole. It often takes to the water, and can swim rapidly and gracefully, though, in this respect, it is excelled by the true venomous water-snakes (Hydrophidce), which are adapted to an aquatic life by having a compressed swimming- tail. A well-known American exam- ple of this group is the common Black Snake (Bascanion constrictor). It attains a length of from three to five feet, but is perfectly harmless so far as man is concerned. Other non- venomous snakes, such as the Boas and Pythons, though des- titute of poison-fangs, are, nevertheless, highly dangerous and destructive animals. Their bite is harmless, and they seize their prey by coiling themselves round it in numerous folds. By gradually tightening these folds, they reduce their victim to the condition of a shapeless bolus, which they finally pro- ceed to swallow whole. In this way, a large Python or Boa will certainly succeed in disposing of an animal as large as a sheep or calf, and it has been asserted that human beings, and even oxen, can also be swallowed by unusually large specimens of this family. The Boas and Pythons have a horny spur on each side of the vent, and the tail is prehensile. Their dental apparatus is extremely powerful, giving them a firm hold for the constric- tion of their prey. They are the largest of all the serpents, attaining a length of thirty to forty feet. The true Boas and Anacondas belong to the New World, but the Pythons are confined to India, Africa, and the Indian Archipelago. The poisonous snakes are represented by the Crotalidce of the New World and the Viperidce of the Old World. The common Rattlesnake ( Crotalus horridus) of the United States has the extremity of the tail furnished with a " rattle " or horny appendage composed of several membranous cells of a pyramidal shape articulated one within the other. Before striking its prey, it throws itself into a coil, and shakes its rattle. Another highly-dangerous species is the Copperhead (Trigonocephalus contortrix). The common European viper (Pelias berus) is hardly fatal to adults, but its bite causes serious inflammation. Highly deadly, however, is the Cobra di Capello or Spectacled Snake (JVaja trijncdians) of India, as DIVISIONS OF EEPTILIA. 245 also is the nearly-allied JVaja haje (Fig. 120) of Africa. Oth- er venomous snakes of evil notoriety are the Death-adder (Acanthophis tort or) of Australia, the Puff-adder ( Viper a in- flatd) of South Africa, the Horned Viper ( Cerastes cornutus] of Egypt, and the Harlequin-snakes (JElaps), but many others are equally dangerous. OEDEK III. LACEETILIA (Lat. lacerta, a lizard). — The third order of reptiles is that of the Lacertilia, comprising all the ani- mals which are properly known as Lizards, together with some snake-like creatures, such as the Blind-worm. They are distin- guished by the following characters : Usually there are two pairs of well-developed limbs, but there may be only one pair, or all the limbs may be rudimentary. In all cases, however, a scapular arch is present. The vertebrae are usually hollow in front (procoelous) , rarely hollow at both ends (amphicoelous). In no living Lacertilian are the teeth lodged in distinct sockets. The eyes are mostly furnished with movable eyelids. As a general rule, the animals included under this head have four well-developed legs, and would, therefore, be popu- larly called " Lizards." Some of them, however, such as the common Blind-worm (Anguis fragilis) of Europe, exhibit no external indications of limbs, and would, therefore, be generally regarded as Snakes. These snake-like Lizards, however, can be distinguished from the true Ophidians by the consolidation of the bones of the head and jaws, and by the fact that the eyes are generally provided with movable eyelids. Dissection also shows that the shoulder-girdle (or scapular arch) is always present in a rudimentary condition. Of the snake-like Lizards, a good example is to be found in the common Blind-worm or Slow-worm of Europe. It is completely serpentiform, without any external indications of limbs (Fig. 122), and it is quite harmless. It is remarkable for the fact that, when alarmed, it stiffens its muscles to such an extent that the tail can readily be broken off, as if it were brittle. This same brittleness exists in the Glass-snake ( Ophi- saurus ventralis) of the Southern States, in which also there are no limbs. In other allied genera, there may be fore-feet alone, or hind-feet may be present, or all four limbs exist in a more or less rudimentary condition. In the true Lizards (Lacerta\ all four limbs are present in a well-developed form ; as seen in the common Green Lizard (J£. viridis) of Europe. The genus Lacerta is represented in America by the Ameivce, of which the Striped Lizard (Ameiva sex-lineatd) of the Southern 246 VERTEBRATE ANIMALS. States may be taken as a good example. Of all living Lizards, the largest are the Monitors ( Varanidoe^) which are exclusively confined to the Old World, and attain sometimes a length of from six to eight feet. Very large, too, are some of the FIG. 122.— Blind-worm (Anguis fragilis). (After BclL) Iguanas which occur in warm regions in various parts of the world, but especially in South America, where they are often eaten. Related to the Iguanas are the singular Lizards known as the Flying Dragons (Draco volans), various species of which inhabit the Indian Archipelago and the East Indies. They are all of small size, living in trees and feeding on in- sects ; and their great peculiarity consists in the fact that cer- tain of the ribs are straightened out, and support a wing-like fold of the skin on each side of the body, by means of which the animal can take very extensive leaps from tree to tree. The Scincoid Lizards form a very large family, represented by numerous species in all parts of the world. The species figured below is a common form in Egypt and Arabia, and was formerly used as a remedy in various diseases. A nearly- allied species is the Blue-tailed Lizard (Scincus fasciatus) of the United States. The Geckos ( GeckotidoB] form a large group of night-lov- ing Lizards, which are found in most parts of the world, and DIVISIONS OF KEPTILIA. 247 chiefly deserve notice from the fact that their eyes are not pro- vided with movable eyelids. The Chameleons, also, cannot be said to possess movable eyelids, for the eye is covered with FIG. 123.— The Skink (ScincuxofficinaUz) a single lid, leaving only a central aperture for the pupil. The common species ( Chameleo Africanus) occurs abundantly in the north of Africa, and has long been known for the changes of color which it has the power of exhibiting. It is a sluggish animal, and catches insects by darting out its long and pro- trusible tongue with extreme rapidity. ORDER IV. CROCODILIA. — The last and highest order of the living Reptiles is that of the Crocodilia, comprising the Crocodiles, Alligators, and Gavials, and characterized by the following peculiarities : The outer or integumentary skeleton consists partly of horny scales developed by the outer layer of the skin, and partly of large bony plates produced by the inner layer of the skin. The bones of the skull and face are firmly united, and the two halves of the lower jaw are joined by a distinct suture. The teeth form a single row in both jaws, and are implanted in distinct and separate sockets. The front ribs of the trunk are double-headed, and there are no collar-bones. The heart consists of four distinct chambers, two auricles and two ventricles, all completely separated from 248 VERTEBRATE ANIMALS. one another. The mixture of arterial and venous blood, how- ever, which is so characteristic of Reptiles, is provided for by a communication between the great vessels which spring from the two ventricles in the immediate neighborhood of the heart. The eyes are protected by movable eyelids, and the ear by a movable earlid. The tongue is large and fleshy, and is im- movably attached to the bottom of the mouth (hence the be- lief of the ancients that the Crocodile had no tongue). Lastly, the Crocodilia agree with the typical Lizards, and differ from the Snakes in having four well-developed limbs. FIG. 124. — Head and fore-part of the body of the common Crocodile (Crocodilus vulgaris). The Crocodilia abound in the fresh waters of hot climates, and are the largest of all living Reptiles, not uncommonly at- taining a length of sixteen feet or upward. The best known of the Crocodilia is the Nilotic Crocodile, which occurs abun- dantly in Egypt, and was described by both Herodotus and Aristotle. The true Crocodiles have the feet completely webbed, the hind-legs bordered by a fringe, and the fourth tooth in the lower jaw received in a notch on the side of the upper jaw. They belong mainly to Africa and Asia, but they are also rep- resented in the West Indies and in South America. The Alligators have the hind-legs simply rounded, and the toes not completely webbed ; while the fourth tooth in the lower jaw fits into a cavity in the palate, and is concealed from view when the mouth is shut. Like the Crocodiles they are essentially aquatic in their habits, and lie dormant during the winter in cold climates and the hot season in warm coun- tries. They are extremely voracious, and live upon fish and small Mammals. The best-known species are the common Alligator (A. Mississippiensis) of the Southern States, the Caiman (A. palpebrosus) of Surinam and Guiana, and the " Jacare1 " (A. sclerops) of South America. The Gavial or Gangetic Crocodile occurs in India, and is DIVISIONS OF REPTILIA. 249 distinguished by its narrow, elongated jaws, forming a kind of beak. It attains a length of more than ten feet. OKDER V. ICHTHYOPTEEYGIA (Gr. ichthus, fish ; pterux, wing). — In this order are included a number of gigantic, fish- like Reptiles, which are all extinct, and are characteristic of the Secondary period of geology, and especially of the forma- tion known as the Lias. The chief characters by which they are distinguished have reference to their purely aquatic life, for there can be no doubt that they were inhabitants of the sea. Thus the body was fish-like, without any distinct neck. The vertebras were hollow at both ends (amphiccelous) , and the spine thus possessed the flexibility and power of motion so characteristic of the true fishes. The limbs also consti- tuted powerful swimming-paddles (Fig. 125), and it is proba- ble that there was a vertical tail-fin. Much has been gathered from various sources as to the habits of the Ichthyosauri, and their history is one of the most interesting chapters in the geological record. That they chiefly kept to open seas may be inferred from their strong and well-developed swimming apparatus ; but the presence of a powerful bony arch supporting the fore-limbs proves that FIG. 125. — Ichthyosaurus communte. they must have occasionally betaken themselves to the land. That they were tenants of stormy waters, or were in the habit of diving in search of 'prey, has been inferred from the fact that the eyeball is protected from pressure by a ring of bony plates. That they possessed great powers of vision, espe- cially in the dusk, seems to be rendered certain from the size of the pupil and the enormous width of the bony cavities (orbits) which contained the eyes. Lastly, that they were carnivorous and predacious in the highest degree is shown by their wide mouths, long jaws, and numerous powerful and pointed teeth. This is also proved by an examination of their petrified droppings, which are known as " coprolites," and which contain in abundance undigested fragments of fishes and other marine animals. 250 VERTEBRATE ANIMALS. ORDER VI. SAUROPTERYGIA (Gr. saura, lizard ; pterux, wing). — The Reptiles belonging to this order agree with the last in being all extinct, and in being confined to the Second- ary period of geology. The best known are the Plesiosauri, which resembled the Ichthyosauri in having all the limbs con- verted into swimming-paddles, but differed in several respects, of which the most obvious is the great elongation of the neck (Fig. 126). The Plesiosauri were gigantic marine Reptiles, FIG. 126.— Plesiosaurus dolichodwrus. chiefly characteristic of the formations known as the Lias and Oolites. As regards the habits of the Plesiosaurus, Dr. Cony- beare concludes : " 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 have occasionally visited the shore, the resemblance of its ex- tremities to those of the Turtle 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 organization which so admirably fits the Ichthyosaurus to cut through the waves." As its breathing-organs are such that it must of ne- cessity have required to obtain air frequently, it may be in- ferred " 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 per- haps have lurked in shoal-water along the coast, concealed among the sea-weed, and, raising its nostrils to a level with the surface from a considerable depth, may have found a se- cure 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." ORDER VII. PTEROSATJRIA (Gr. pteron, wing; saura, lizard). — The Reptiles of this order are all extinct, and, like those of the preceding orders, are exclusively confined to the DIYISIONS OF REPT1LIA. 251 Secondary period of geology. The most familiar examples are the so-called Pterodactyles, and the distinguishing charac- ters of the order have reference to the fact that they were all adapted for an aerial life. They present, in fact, an extraor- dinary combination of the characters of birds and reptiles, and they make also some approach to the Mammalian order of the Bats. In the presence of teeth in distinct sockets, and, as we shall see hereafter, in the structure of the fore-limbs, the Pterodactyles differ altogether from all known birds ; and there can be little doubt as to their being genuine Reptiles. The only living Reptile which has any power of sustaining itself in the air is the little Draco volans, which has been pre- viously mentioned. In this case, however, the animal has no power of true flight, but is simply enabled to take extensive leaps by means of a membranous expansion on each side of the body. In the Bats, again, the power of genuine flight is present ; and this is given by means of a leathery membrane which is supported chiefly by certain of the fingers — which are greatly lengthened — and is attached to the sides of the body and hind-limbs. In the Pterodactyles the power of true flight was present, and this was also conditioned by means of a leathery expand- ed membrane, attached to the hind-limbs, the sides of the body, and the fore-limbs. In this case, however, the chief support of the flying membrane was derived from the outer- most finger of the fore-limb, which was enormously elongated (Fig. 127). That the Pterodactyles passed their existence FIG. 127. — Pterodactylus br&virostris, the skeleton and the animal restored. chiefly in the air, and did not simply leap from tree to tree, is shown by two characters in which they agree with the flying 252 VERTEBRATE ANIMALS. birds. Many of the bones, namely, were " pneumatic " — that is to say, were hollow and were filled with air, thus giving the animal the degree of lightness necessary for flight. Secondly, while the shoulder-girdle has many of the characters of birds, the breastbone (sternum) is furnished with a prominent ridge or keel, serving for the attachment of the great muscles which work the wings. There can be no doubt, therefore, as to the Pterodactyles having enjoyed the power of genuine flight. Many of them attained no great size, but some of them must have been gigantic, the expanse of wing in one species having been calculated at probably about twenty-seven feet from tip to tip. ORDER VIII. ANOMODONTIA (Gr. anomos, irregular ; odous, tooth). — This order comprises a few Reptiles which be- long to the Triassic period of geology, and are distinguished by the fact that the jaws were sheathed in horn, so as to form a kind of beak very like that of the Turtles. In some species there appear to have been no teeth at all ; but in one genus there were two long tusks, one on each side of the upper jaw. The limbs were fitted for walking and not for swimming, and these singular Reptiles must, therefore, have been terrestrial in their habits. ORDER IX. DEINOSAURIA (Gr. demos, terrible; saura, lizard). — In this order are included a number of extinct Rep- tiles, most of which were of gigantic size, and which are con- fined to the Secondary period of geology. They possessed teeth, sunk in distinct sockets, and the limbs were extremely strong, and adapted for progression on land. In some cases the fore-limbs were very much smaller than the hind-limbs, and there is reason to suppose that some of these extraordi- nary animals, though of enormous size, walked habitually upon their hind-legs, like Birds. It is also interesting to note that the gigantic footprints of the Sandstones of the Connecti- cut Valley, formerly regarded as formed by Birds, are now with great probability looked upon as truly the tracks of Dei- nosaurian Reptiles. CHAPTER XXIX. CLASS IV.— AVES. THE fourth class of the Vertebrates is that of the Birds or Aves, which may be shortly defined as being " oviparous Ver- tebrates, with warm blood, a double circulation, and a cover- ing of feathers" (Owen). The other leading characters which separate the Birds from the other Vertebrata are that the red blood-corpuscles are nucleated, the skull articulates with the spine by a single articulating surface (or condyle), the breath- ing-organs are in the form of lungs, which communicate with a variable number of air-sacs scattered through the body, and the fore-limbs are never terminated (in existing birds) by more than two fingers, ending in claws, and are generally modified so as to form " wings " or organs of flight. The feathers, which form such a distinctive character of birds, are formed by a modification of the outer layer of the. skin (epidermis), and from their non-conducting nature they serve to maintain the high temperature of the body which is so characteristic of the class. A typical feather, such as one of the long feathers of the tail or wing, consists of the follow- ing parts : 1. A horny cylindrical tube, which forms the lowest portion of the feather, and is termed the "quill." 2. The " shaft," which forms the central axis of the feather, and which is simply the continuation of the " quill." The under surface of the shaft is always marked by a strong longitudinal groove, and it consists of a horny sheath, filled with a white spongy material, not unlike the pith of a plant. 3. The " webs," which form the lateral expansions of the feather, and are attached to the sides of the shaft. Each web is composed of a number of small branches, called the " barbs," and 'each barb, in turn, is furnished with a series of smaller fibres called the " bar- bules." As a rule, the barbs are all kept in connection with 12 254 VERTEBRATE ANIMALS. one another by means of the barbules, the ends of which are hooked. Toward the base of the shaft, however, the barbs are usually more or less separate and placed at a distance from one another, constituting what is known as the " down." In the Ostriches and the birds allied to them, all the barbs are disunited and placed at a distance, and they are often not at all unlike hairs in appearance. The feathers of birds not only greatly conduce to the high temperature of the body, but also serve to keep out moisture, to which end there is a peculiar oil-gland at the base of the tail, with the secretion of which the bird anoints its plumage. The skeleton of birds exhibits many points of peculiar interest, mostly in adaptation to an aerial mode of life ; but only some of the more important of these can be noticed here. The entire skeleton is at the same time peculiarly compact and singularly light, the compactness being due to the pres- ence of an unusual quantity of phosphate of lime, and the lightness to the fact that many of the bones are filled with air in place of marrow. The cervical region (neck) of the verte- bral column is unusually long and flexible, since the fore-limbs are useless as organs of prehension, and all these functions have to be performed by the beak. In all birds the neck is, at any rate, sufficiently long to allow of the application of the beak to the tail, so as to permit of the cleaning and oiling of the, whole plumage. The vertebrae which form the back or dorsal region of the spine are generally more or less immov- ably connected together, so as to give a base of resistance to the wings. In the Ostrich, however, and in other birds in which the power of flight is either very limited or is absent, the dorsal vertebrae are more or less movable one upon the other. The vertebrae which follow the dorsal region of the spine are all amalgamated together to form a single bony mass, which is termed the " sacrum," and this, in turn, is united on both sides with the bones which form the pelvic arch, which carries the hind-limbs. The vertebrae of the tail are more or less movable upon one another ; and in almost all living birds, when fully grown, the last joint of the tail (Fig. 129, B, s) is a long, slender, ploughshare-shaped bone, which is really composed of several vertebrae united together. It is usually set on at an angle nearly perpendicular to the axis of the body, and it serves to support the great tail-feathers, which act as a rudder during flight. It also serves to support the oil-gland, which supplies the secretion with which the feathers are lubricated. The skull in birds has its several AVES. 255 bones generally so amalgamated in the adult, that it forms a bony case of a single piece, the lower jaw alone remaining movable. The head is jointed to the spine by no more than a single articulating surface or condyle. The beak, which forms such a conspicuous feature in birds, is composed of two halves, an upper half or "upper mandible," and a "lower mandible." The lower mandible, like the lower jaw of all the Sauropsida, is at first composed of several pieces, but these are all undistinguishably united in the adult, and the two halves of the jaw are also amalgamated together. In no adult bird are teeth ever developed in either mandible; but both mandibles are sheathed in horn, constituting the " beak," and the margins of this sheath are sometimes serrated. The most characteristic points, however, in the skeleton of the birds, are to be found in the structure of the limbs. The cavity of the chest or thorax is bounded behind by the dorsal vertebrae, on the sides by the ribs, and in front by the breast- bone or sternum. The ribs vary in number from seven to eleven pairs, and in most birds each rib gives off a peculiar process (Fig. 128, B), which passes over the rib next in suc- cession behind. In front the ribs are jointed to a series of straight bones, which are called the " sternal ribs," and these, in turn, are movably articulated to the breastbone in front. According to Owen, these sternal ribs are " the centres upon which the respiratory movements hinge." In front the cavity of the chest is completed by an enormously-expanded breast- bone or sternum (Fig. 128, A), which, in most birds of any powers of flight, extends more or less over the abdominal cavity as well. The sternum of all birds which possess the power of flight is characterized by the presence of a prominent ridge or "keel" (Fig. 128, A, J), to which are attached the great muscles (pectoral muscles) which move the wings. As a general rule, the size of this crest or keel gives a tolerably just estimate of the flying powers of the bird to which it be- longed. The keel is, of course, most largely developed in those birds which possess the power of flight in its greatest perfection ; and in those which do not fly, such as the Ostrich, there is no sternal keel at all. The pectoral arch or shoulder- girdle of birds consists of the shoulder-blades (scapulas), the clavicles or collar-bones, and of two bones, which are distinct in birds, and are called the " coracoid bones." The shoulder- blades (s s) are usually long and narrow bones. The coracoid bones (IcJc) correspond with the part of the shoulder-blade which is known in most of the Mammals as the "coracoid 256 VERTEBKATE ANIMALS. FIG. 128. — A, Breastbone, shoulder-girdle, and fore-limb of Penguin (after Owen); & Breast- bone (sternum), with its prominent ridge or keel ; s $ Shoulder-blades (seapulce) ; k k Coracoid bones ; o Furculum or Merry -thought, composed of the united collar-bones (clavicles) ; h Bone of the upper arm or humerus ; r Kadius ; u Ulna, forming together the forearm; q Bones of the wrist or carpus; t Thumb; m Metacarpus; p Phalanges of the fingers. B, Kibs of the Golden Eagle ; a a Bibs giving off processes (b V) ; c c Sternal ribs. process ; " and in birds they are not only separate bones, but they are the strongest bones of the pectoral arch. They are more or less nearly vertical, and they form fixed points for the downward stroke of the wing. The collar-bones or clavi- cles (c) in the great majority of birds are united together in front, so as to form a somewhat V-shaped bone, which is tech- nically called the "furculum," but is familiarly called the " merry-thought." The function of this clavicular arch is to keep the wings asunder during their downward stroke, and the strength of the furculum varies, therefore, with the powers of flight enjoyed by each bird. The bones which form the limb proper, or " wing," are considerably modified to suit the special function of flight, but essentially the same parts are present as in the fore-limb of the Mammals. The upper arm is constituted by a single bone, the humerus (h\ which is gen- erally short and stout, The forearm is composed of two bones, the radius (r) and the ulna (u), of which the ulna is the bigger. These are followed by the small bones, which AVES. 257 form the wrist or carpus (ID-UN'OU-LA (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. SO-MAT'IO (Gr. soma, body). Connected with the body. SO-MAT'O-CYST (Gr. soma ; and Icustis, a cyst). A peculiar cavity in the cceno- sarc of the Calycophorida (Hydrozoa). SO'MITE (Gr. soma}. A single segment in the body of an Articulate animal. SPER-MA RI-TJM. The organ in which spermatozoa are produced. SPER-MAT'O-PHORES (Gr. sperma, seed ; phero, I carry). The cylindrical cap- sules of the Cephalopoda, which carry the spermatozoa ; sometimes called the " moving filaments of Needham." SPER-JIA-TO-ZO A (Gr. sperma, seed ; and zoon, animal). The microscopic fila- ments which form the essential generative element of the male. SPI'CU-LA (Lat. spiculum, a point). Pointed needle-shaped bodies. SPIN'NER-ETS. The organs by means of which Spiders and Caterpillars spin threads. SPI'RA-CLES (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, etc. SPLANOH-STO-SKEI/E-TON (Gr. splagchna, viscera ; skeletos, dry). The hard structures occasionally developed in connection with the internal organs or viscera. SPONGE-PAR'TI-CLES. (See Sarcoids). SPON'GI-DA (Gr. spoggos, a sponge). The division of Protozoa commonly known as sponges. GLOSSARY. 349 SPOKES (Gr. tpora, seed). Germs, usually of plants ; in a restricted sense, the reproductive " gemmules " of certain Sponges. SPO'BO-SACS (Gr. spora, seed ; and sakkos. a bag). The simple generative buds of certain Ifydrozoa, in which the medusoid structure is not developed. SQUA'MA-TA (Lat. squama, a scale). The division of Reptiles comprising the OpJiidia and Lacertilia in which the integument develops horny scales, but there are no dermal ossifications. STAT'O-BLASTS (Gr. statos, stationary ; Uastos, bud). Certain reproductive buds developed in the interior of Polyzoa, but not liberated until the death of the parent organ: sm. STEG-AN-OPH-THAL'MA-TA (Gr. steganos, covered; and opTithalmos, the eye). Applied by Edward Forbes to certain Medusce, in wnich 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. STEL-LEB'I-DA (Lat. stella, star). Sometimes applied to designate the order of the Star-fishes. STEL'LI-FOBM. Star-shaped. STEM'MA-TA (Gr. stemma, garland). The simple eyes, or " ocelli," of certain animals, such as Insects, Spiders, and Crustacea. STEB'NUM (Gr. sternon). The breast-bone. STIG'MA-TA. The breathing-pores in Insects and Arachnida. STO'LON (Gr. stolos, a sending-forth). Off-shoots. — The connecting processes of sarcode, in Foramiwifera ; the connecting tube in the social Ascidians ; the processes sent out by the coenosarc of certain Actinozoa. STO-MAP'O-DA (Gr. stoma, mouth : pous, foot). An order of Crustacea. STOM'A-TODE (Gr. stoma ; eidos,wrm). Possessing a mouth. The Infusoria are thus often called the Stomatode Protozoa. STBEP-SIP'TE-BA (Gr. strep ho, I twist ; and pteron, wing). An order of In- sects in which the anterior wings are represented by twisted rudiments. STBEPS-I-BHI'NA (Gr. strepho, I twist ; rines, nostrils). A group of the Quad- rumana, often spoken of as Prosi/mice. STBOB'I-LA (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. STY'LI-FOBM (Lat. stylus, a pointed instrument ; forma, form). Pointed in shape. SUB-CAL-CA'EE-OTTS. Somewhat calcareous. SUB-CEN'TBAL. Nearly central, but not quite. SUB-PE-DUN'CU-LATE. Supported upon a very short stem. SUB-SES'SILE. Nearly sessile, or without a stalk. SUO-TO'BI-AL. SU-PI-NA'TION (Lat. supinus, lying with the face upward). The act of turn- ing the hand with the palm upward. STJ-PBA-CE-SO-PHAG'E-AL. SU'TUBE (Lat. suo, I sew). The line of junction of two parts which are im- movably 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 Cephalopod by the margins of the septa. SWIM'MEB-ETS. The limbs of Crustacea, which are adapted for swimming. SYM'PHY-SIS (Gr. sumphusis, a growing together). Union of two bones in which there is no motion, or but a very limited amount. SYN-AP-TIO'U-L^: (Gr. sunapto, I fasten together). Transverse props some- times found in Corals, extending across the loculi like the bars of a grate. SYS'TO-LE (Gr. sustello} I contract). Applied to the contraction of any con- tractile cavity, especially the heart. TAB'U-L.E (Lat. tabula, a tablet). Horizontal plates or floors found in some Corals, extending across the cavity of the " theca," from side to side. TAO'TILE (Lat. tango, I touch). Connected with the sense of touch. 16 . 350 GLOSSARY. T^E-NI'A-DA (Gr. tainia, a ribbon). The division ofScoleoida comprising the Tape-worms. TJE'NI-OID (Gr. tainia / and eidos, form). Ribbon-shaped, like a Tape-worm. TAR-SO-MET-A-TAR'SUS. The single bone in the leg of Birds produced by the union and anchylosis of the lower or distal portion of the tarsus with the whole of ihe metatarsus. TAR'SUS (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. TEC-TI-BRAN-CHI-A'TA (Lat. tectus, covered ; and Gr. Iragchia, gills). A divi- sion of OpistJiobrancMate Gasteropoda in which the gills are protected by the mantle. TEG-U-MENT'AR-Y (Lat. tegumentum, a covering). Connected with the integu- ment or skin. TEL-E-OS'TE-I (Gr. teleios, perfect ; osteon, bone). The order of the " Bony " Fishes. TEL' SON (Gr. telson, a limit). The last joint in the abdomen of Crustacea; variously regarded as a segment without appendages, or as an azygos ap- pendage. TEN-U-*-ROS'TRES (Lat. tennis, slender ; rostrum, beak). A group of the Perch- ing Birds characterized by their slender beaks. TERGUM (Lat. for back). The dorsal arc of the somite of an Arthropod. TER-RES'TRI-AL. TER-RIC'O-LA (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 Echinoderma ; also, the thick, leathery, outer tunic in the Tunicata. TES-TA'CEOUS. Provided with a shell or hard covering. TES'TIS (Lat. testis, the testicle). The organ in the male animal which pro- duces the generative fluid or semen. TET-RA-BRAN-CHI-A'TA (Gr. Utra, four ; bragchia, gills). The order of Cephalop- oda, characterized by the possession of four gills. THA-LAS-SI-COL'LI-DA (Gr. thalassa, sea ; kolla, glue). A division of Protozoa. THE'CA (Gr. theke, a sheath). A sheath or receptacle. THE-CO-SOM'A-TA /Gr. ihelce ; and soma, body). A division of Pteropodous Molluscs, in which the body is protected by an external shell. THE-RI-O-MOR'PHA (Gr. therion, beast ; morphe, shape). Applied by Owen to the order of the Tail-less Amphibians (Anoura). THO'RAX (Gr. for a breast-plate). The chest. THREAD-CELLS. (See Cnidse.) THYS-A-NU'RA (Gr. thusanoi, fringes ; and oura, tail). An order of Apterous Insects. TIB'IA (Lat. for a flute). The shin-bone, being the innermost of the two bones of the leg, and corresponding with the radius in the anterior extremity. TO-TI-PAL'MA-TJB (Lat. totus, 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. TRA-CHE'A (Gr. tracheia, the wind-pipe). The tube which conveys air to the lungs in the air-breathing Vertebrates. TRA-CHE'^E. The breathing-tubes of insects and other articulate animals. TRA-CHE-A'RI-A. The division of Arachnida which breathe by means of tra- cheae. TREM-A-TO'DA (Gr. trema, a pore ; eidos, form). An order ofScolecida. TRICH'O-CYSTS (Gr. thrir, hair ; and Tcustis, a cyst). Peculiar cells found in certain Infusoria, and very nearly identical with the " thread-cells " of Ccelenterata. TRI-LOB'I-TA (Gr. treis, three ; lolos, a lobe). An extinct order of Crustaceans. TRIT-O-ZO'OID (Gr. tritos, third ; zoijn, animal ; and eidos, form). The zooid produced by a deuterozooid ; that is to say, a zooid of the third genera- tion. GLOSSARY. 351 TRO'CHAL (Gr. trocJios, a wheel). Wheel-shaped ; applied to the ciliated disc of the Eotifera. TRO-CHAN'TER (Gr. trecho, I run). 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. TRO'CHOID (Gr. trochos, a wheel ; and eidos, form). Conical, with a flat base ; applied to the shells of Foraminiftra and Univalve Molluscs. TRO'PHI (Gr. trophos, a nourisher). The parts of the mouth in insects which are concerned in the acquisition and preparation of food. Often called u instrumenta cibaria." TROPH'O-SOME (Gr. trepho, I nourish ; and soma, bodv). Applied collectively to the assemblage of the nutritive zooids of any Hydrozobn. TRTO'OA-TED (Lat. trunco, I shorten). Abruptly cut off ; applied to univalve shells, the apex of which breaks off, so that the shell becomes " decol- lated." TU-BIC'O-LA (Lat. tuba, a tube ; and cola, I inhabit). The order of Annelida which construct a tubular case in which they protect themselves. TU-BIC'O-LOUS. Inhabiting a tube. TU-BU-LAR'I-DA. TU-NI-CA'TA (Lat. tunica, a cloak). A class of Molluscoida which are envel- oped in a tough, leathery case or " test." TUR-BEL-LA'RI-A (Lat. turbo, I disturb). An order of Scoledda. TUR'BI-NA-TED (Lat. turbo, a top). Top-shaped ; conical, with a round base. UL'NA (Gr. olene, the elbow). The outermost of the two bones of the fore- arm, corresponding with \hzfibula of the hind-limb. UM'BEL-LATE (Lat. umbella, a parasol). Forming an umbel — i. e., a number of nearly equal radii, all proceeding from one point. UM-BIL'I-CUS (Lat. for navel). The aperture seen at the base of the axis of certain univalve shells, which are then said to be "perforated" or " um- bilicated." UM'BO (Lat. for the boss of a shield). The beak of a bivalve shell. UM-BREL'LA. The contractile disc of one of the Lucernarida. UN'CI-NATE (Lat. uncus, a hook). Provided with hooks or bent spines. UN-GUIC'U-LATE (Lat. unguis, nail). Furnished with claws. UN-GU-LA'TA (Lat. ungula, hoof). The order of Mammals comprising the Hoofed Quadrupeds. UN'GU-LATE. Furnished with expanded nails constituting hoofs. U-NI-LOC'U-LAR (Lat. unus, one ; and loculus, a little purse). Possessing a single cavity or chamber. Applied to the shells of Foraminifera and Mol- lusca. U'NI-VALVE (Lat. unus, one ; valvce, folding-doors). A shell composed of a single piece or valve. U-RO-DE'LA (Gr. oura, tail ; delos, visible). The order of the tailed Amphi- bians (Newts, etc.). UR'TI-OA-TING CELLS (Lat. urtica, a nettle). (See Cnidse.) VAO'U-OLES (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. VAR'I-OES (Lat. -varix, a dilated vein). The ridges or spinose lines which mark the former position of the mouth in certain univalve shells. VAS'OU-LAR (Lat. vas, a vessel). Connected with the circulatory system. VE'LUM (Lat. for a sail). The membrane which surrounds and partially closes the mouth of the " disc" of Medusae, or medusiform gonophores. VEN'TRAL (Lat. venter, the stomach). Eelating to the inferior surface of the body. VEN'TRI-CXE (Lat. dim. of venter, stomach). Applied to one of the cavities of the heart, which receives blood from the auricle. 352 GLOSSARY. VEB'MES (Lat. vermis, 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. VER'MI-FORM (Lat. vermis, worm ; snid/orma. form). Worm-like. VER'TE-BRA (Lat. verto, I turn). One of the bony segments of the vertebral column or back-bone. VER-TE-BRA'TA. (Lat. vertebra, a bone of the back, from vertere, to turn). The division of the Animal Kingdom roughly characterized by the posses- sion of a back-bone. VES'I-CLE (Lat. vesica. a bladder). A little sac or cyst. VI-BRAC'U-LA (Lat. Vidro, I shake). Long filamentous appendages found in many Polyzoa. VIB-RI-O'NES (Lat. vibro, I shake). The little moving filaments developed in organic infusions. VIP-E-RI'NA (Lat. vipera, a viper). A group of the Snakes. Vis'cE-RA. VI-VIP'A-ROTJS (Lat. vivus, alive ; and pario, I bring forth). Bringing forth young alive. WHORL. The spiral turn of a univalve shell. XIPH-I-STER'HTJM (Gr. xiphos, sword ; sternon, breast-bone). The inferior or posterior segment of the sternum, corresponding with the " xiphoid carti- lage " of human anatomy. XIPH-O-SU'RA (Gr. xiphos, a sword ; and oura, tail). An order of Crustacea, comprising the Limuli or King-Crabs, characterized by their long sword- like tails. XY-LOPH'A-GOUS (Gr. xulon, wood ; and^Aa^o, I eat). Eating wood ; applied to certain Mollusca. ZO'OID (Gr. zoon, animal ; and eidos, form). The more or less completely in- dependent organisms, produced by gemmation or fission, whether these re- main attached to one another or are detached and set free. ZO'O-PHYTE (Gr. zoon, animal ; phuton* plant). Loosely applied to many plant-like animals, such as Sponges, Corals, Sea-anemones, Sea-mats, etc. ZO'O-SPOKES (Gr. zoon, animal : and spora, seed). The ciliated locomotive germs of some of the lowest forms of plants (Protophyta). QUESTIONS. 1. MENTION some of the characters of living beings. 2. What is understood by " organization ? " 8. Define Biology and Zoology. 4. What characters separate the higher animals from the higher plants ? 5. How does the nutrition of plants differ from that of animals ? 6. What is understood by " classification ? " 7. What is the basis of a natural and scientific classification ? 8. Explain the terms "morphology" and "physiology." 9. What is understood by " sub-kingdoms," and upon what characters are these founded ? 10. What are the great Physiological functions ? Define these. 11. Explain the terms "homology " and "analogy," and give examples. 12. What leading characters separate the Invertebrate from the Verte- brate animals. 13. What are the chief characters of the Protozoa? 14. What is sarcode ? 15. What are cilia, flagella, and pseudopodia? 16. Mention the three great classes of Protozoa. 17. What is the structure of a Gregarina, and where would you expect to find one? 1 8. What structures characterize the Rhizopoda ? 19. Describe an Amoeba. 20. What is the so-called " contractile vesicle ? " 21. What is meant by "fission? " 22. How do the pseudopodia of the Foraminifera differ from those of an Amoeba ? 23. What structures are absent in the Foraminifera, which occur in the Amoeba ? 24. What is the nature of the shell of the Foraminifera ? 25. What differences subsist between a perforated and an imperforate shell ? Between a simple and a compound shell ? 26. Where do Foraminifera mostly occur? 27. What is understood by "Distribution in Space" and "Distribution in Time ? " 28. Mention one or two remarkable fossil Foraminifera. 29. What is Chalk to a great extent composed of? 30. What is the nature of the skeleton of the Radiol"rin / 31. Mention some example of the Radiolaria. 354 QUESTIONS. 32. Of what two essential elements is a Sponge composed ? 33. What is the nature of the " sponge-flesh ? " 34. Describe the circulation of water in a Sponge.. 35. What are the chief variations in the skeleton of Sponges ? 36. Whence are the Sponges of commerce obtained ? 37. How do the Infusorian Animalcules derive their name ? 38. By what leading character are the Infusoria distinguished from tlie other Protozoa ? 39. Why were the Infusoria formerly called Polygastrica ? 40. Describe the Bell-animalcule. 41. What peculiarity of the digestive system characterizes the sub-king- dom Ccdenterata ? 42. Of what is the body of a Coelenterate animal composed ? 43. What is a " thread-cell ? " 44. Into what two classes are the CceJenterata divided, and what charac- ters distinguish these ? Mention examples of each. 45. What is understood by " gemmation ? " How is a compound animal or colony produced ? 46. What is meant by the term " zooid ? " 47. What is scientifically understood by the term " individual ? " 48. Define the terms " polypite," " crenosarc," and " polypary." 49. Give examples of the Hydroid Zoophytes. 50. Describe shortly the structure of the Hydra. 51. What is the method of reproduction in the Hydra ? 52. What peculiarities distinguish the polypary of the Corynida .« 53. Give an example of the Corynida. 54. What two sets of zooids go to form the colony of a Hydroid Zoo- phyte? 55. Define the terms " trophosome " and " gonosome." 56. What is a " gonophore ? " 57. What is a " medusiform gonophore ? " Why is it so called, and whai is its general structure ? 58. Give an example of the Sertularida, and mention the differences which distinguish their polypary from that of the Cofynida. 59. What is a "hydrothcca?" 60. Describe the general structure of the reproductive bud of a Cam- panularian. 61. How do the Oceanic Hydrozoa differ from the Hydroid Zoophytes ? 62. What is a " nectocalyx," and what is its structure ? 63. What is a "bract?" 64. Mention examples of the Oceanic Hydrozoa. 65. What is the " float " or " pneumatophore " of the Physophoridce ? 66. Of what real nature are many of the so-called Medusae or Jelly-fishes ? 67. What is the general structure of a Medusa, and with what structure in the Hydroid Zoophytes does it agree ? 68. From what circumstance is the name " naked-eyed " Medusae derived ? 69. What are the "marginal bodies " of the Medusce? 70. Describe Lucernaria. 71. Of what nature are the great Sea-blubbers ? 72. Describe "Hydra-tuba" and its development. 73. What is the structure of a " Hidden-eyed Medusa " or Sea-blubber, and from what circumstance is the former name derived ? 74. Differences between the naked-eyed and hidden-eyed Medusas ? 75. Describe the generative bud of Khizostoma. QUESTIONS. 355 76. Give the leading characters of the Actinozoa. 77. How does the transverse section of a Hydrozoon differ from that of an Actinozoon ? 78. What is a "polype?" 79. Describe a Sea-anemone. 80. What are the "mesenteries " of a Sea-anemone, and what organs do they carry ? 81. What is a " coral ? " 82. What are the " septa " of a coral, and to what part of the living animal do they correspond ? 83. What are coral-reefs, where do they occur most abundantly, and what are the chief varieties which occur ? 84. How do the Alcyonaria differ numerically from the Zoantharia ? 85. Mention some example of the Alcyonaria. 86. In what Alcyonarian is there a well-developed sclerodermic coral ? 87. Of what nature is the sclerobasic coral of the Gorgonidce? 88. Mention a well-known example of the Gorgonidce. 89. Give the leading characters of the Ctenophora. 90. What is a " ctenophore ? " 91. Is a nervous system present in any of the Actinozoa, except in the Ctenophora ? 92. Mention an example of the Ctenophora. 93. What animals belong to the Echmodermata, and whence is the name of the class derived ? 94. What is understood by " bi-lateral symmetry ? " 95. At what time of life are the Ecliinoderms bi-laterally symmetrical, and what is their condition in this respect when adult ? 96. What is a water-vascular system, what is it called in this class, and what special function does it generally discharge ? 97. What is the arrangement of the nervous system in Echinoderms ? 98. What distinguishes the Sea-urchins from other Echinoderms ? 99. Into how many zones may the test of a living Sea-urchin be divided, and how many rows of plates are contained in each zone? 100. What are the " ambulacral " and " inter-ambulacral areas ? " 101. What plates are always placed at the summit of the shell ? 102. What is the " madreporiform tubercle ? " 103. Describe the general nature of the spines and their function. 104. What are " pedicellariae ? " 105. What are the " tube-feet ? " Describe the general arrangement of the u ambulacral system." 106. What is the structure of the circulatory and nervous organs in the Echinus ? 107. Mention a peculiarity in the development of the Echinus. 108. Give the leading characters of the Star-fishes. 109. What peculiarities distinguish the arms of Star-fishes ? 110. What is the structure of the stomach in Star-fishes ? 111. How do the Brittle-stars resemble the true Star-fishes, and how are they distinguished ? 112. What is the structure of the digestive system in Brittle-stars? 113. What is the essential peculiarity of the "Crinoids? 114. Mention a living Crinoid which is free when adult, and one which is permanently fixed. 115. What is the general shape of the Holothurians, and the nature of their integuments ? 356 QUESTIONS. 116. What is the condition of the ambulacral system, and where is the * madreporiform tubercle " situated ? 117. What is the mouth surrounded by? 118. What is the " respiratory tree " of the Holothurians ? 119. What characters distinguish the Scolecida ? How are they separated from the Echinoderms ? 120. What is meant by the term Entozoa? 121. In what relation do the Bladder-worms stand to the Tape-worms ? 122. What is the structure of an ordinary Tape-worm? 123. Give the structure of the "head" and of a single joint, and state what is the relation of the head to the joints. 124. State shortly the process of development in a Tape-worm. 125. What is the " measles " of the Pig ? 126. What are " hydatids " in man ? 127. What are the characters of the Trcmatode worms? Mention an ex- ample. 128. What is the " rot " of Sheep caused by ? 129. What groups of animals are included in the lurbellaria? 130. Give an example of the Acanthocephala, and state the character from which the name is derived. 131. Where do the Gordiacea spend the earlier part of their existence, and what is their common name ? 132. Mention examples of the Nematode worms. 133. From what do the Wheel-animalcules get their name ? 134. What is the general size of the Rotifers, and where are they found ? 135. What marked differences are there between the males and females ? 136. What are the functions of the ciliated "wheel? " 137. Give the general anatomy of a Rotifer. 138. Give the leading characters of an Annulose animal. 139. Into what great divisions is the sub-kingdom Annulosa divided, and what are the characters of these ? 140. What is the general structure of one of the rings of an An- nelifle ? 141. What is the " pseudohaemal system " of the Annelida, and to what is it believed to correspond ? 142. What are the characters of the Hirudmea* 143. To what does the Medicinal Leech owe its value ? 144. How is locomotion effected in the Leeches ? 145. How are the Oligochceta distinguished? 146. What are the locomotive organs of the Earth-worm ? 147. Of what nature are the breathing-organs of the Tubicola, and where are they placed ? 148. Mention a common Tubicolous Annelide. 149. To what do the Errantia owe their name, and what are their loco- motive organs ? 150. Where are the gills placed in the Errantia? 151. What orders of Annelida possess gills, and which have not ? 152. Give the general characters of Articulate animals. 153. Give the characters of the Crustacea. 154. How many segments go to the body of a Crustacean, and into what distinct regions may these be distributed ? 155. What is understood by the " cephalothorax ? " 156. To what section of Crustacea does the Lobster belong ? 157. What is the "carapace" of the Lobster ? QUESTIONS. 357 158. What is the part generally called the " tail," and what is the so- called " head ? " 159. What are the " antennae," and how many are there hi the Lobster and in Crustacea generally ? 160. What are "foot-jaws," and why are they so called? 161. What are " chelaa ? " 162. Of what nature are the appendages of the abdomen in the Lobster ? 163. What is the last segment of the abdomen called ? 164. Describe the gills of the Lobster. Where are they placed ? 165. Of what nature is the abdomen of the Hermit-crabs ? 166. How are the Crabs distinguished from the Lobsters? 167. By what character does the young Crab approach the Lobster? 168. Give an example of the Isopoda ? 169. What is the character of the appendages of the mouth in the King- Crabs ? 170. What is the structure of a Trilobite ? 171. What is the nature of the shell of the Ostracode Crustaceans ? 172. What change do the Cirripedes undergo in passing from the larval to the adult condition ? 173. What are the two types of the Cirripedes ? Give examples. 174. Give the general characters of the Arachnida? 175. What is the structure of the mandibles of the Spiders ? Of the Scorpions ? 176. To what do the mandibles of the Arachnida correspond? 177. Of what nature are the breathing-organs of the Arachnida? 178. What is the structure of tracheae? Of pulmonary sacs ? 179. What are the organs of vision in the Arachnida ? 180. What are the habits of the Mites ? Give examples. 181. By what structure do the Scorpions inflict wounds ? 182. What is the condition of the abdomen in Scorpions ? In Spiders ? 183. By means of what organs do the Spiders spin webs? 184. What are the general characters of the Myriapoda? 185. What is the general condition of the young Myriapod? 186. What are the distinctions between the Centipedes and Millipedes? 187. What is the number of legs in Pauropus? 188. What are the general characters of Insects? 189. What organs are carried by the head in Insects ? 190. How many segments form the thorax, and what appendages do they always carry ? What appendages do they sometimes carry ? 191. What are " nervures ? " 192. How many rings generally go to the abdomen of Insects ? What appendages (if any) do these support ? 193. What are the chief modifications in the organs of the mouth in Insects ? 194. Describe the digestive system of an Insect? 195. How is the circulation carried on ? 196. Of what nature are the breathing-organs ? 197. Of what nature are the eyes in Insects ? 198. What is understood by the "metamorphosis " of an Insect ? 199. What are the chief differences in the metamorphoses of Insects ? 200. What peculiarity distinguishes the adult state of Insects which undergo no metamorphosis ? 201. What is understood by the terms "larva," "pupa," and "imago ? " 202. What is a " chrysalis ? " A " cocoon ? " 358 QUESTIONS. 203. What are the more important Insects which pass through no meta- morphosis ? 204. 'The chief characters of the Hemiptera ? Give examples. 205. What are " hemelytra ? " 208. The chief characters of the Orthoptcra ? Give examples. 207. The chief characters of the Neuroptera? Give examples. 208. What members compose a colony of White Ants or Termites ? 209. The chief characters of the Aphaniptera ? Give an example. 210. The chief characters of the IHptera? Give examples. 211. The chief characters of the Lepidoptera? 212. Characters of the larvae of Lepidoptera ? 213. What characters distinguish Butterflies and Moths respectively? 214. Chief characters of Hymenoptera ? Give examples. 215. Give some account of the social communities of Bees and Ants ? 216. What is the condition of the wings in Strepsiptcra ? 217. Chief characters of Coleoptera ? Give examples. 218. What are " elytra ? " 219. Mention a useful Beetle. 220. Chief characters of the Mollusca? 221. Condition of nervous system in Mollusks ? Of circulatory system ? Of breathing-organs ? Of digestive system ? 222. Primary divisions of Mollusca, and the characters of these ? 223. Chief characters of the Polyzoa ? 224. Explain the term " polypide ? " 225. How is the polypide of a Polyzobn distinguished from the polypite of a Hydrozoon ? 226. Structure of a single " polypide. " 227. What are " bird's-head processes," and to what may they be com- pared ? 228. What general distinction is there between the fresh-water and marine Polyzoa ? 229. Chief characters of Tunicata ? 230. Nature of the " test ? " 231. Structure of the heart in Tunicata? 232. Distinctions between simple, social, and compound Tunicates ? 233. Chief characters of Brachiopoda ? 234. Nature of the shell, as compared with that of Bivalves ? 235. Structure and nature of the " arms ? " 236. Chief characters of the Lamdlibranchiata ? Give examples. 237. Nature and uses of the " foot ? " 238. Nature, uses, and number of the " adductor muscles ? " 239. What are the " muscular impressions " and the " pallial line ? " 240. Structure and mode of opening, and connection between, the valves ? 241. Structure of the respiratory organs ? 242. Nature and uses of the " respiratory siphons ? " 243. Condition of circulatory system ? Of digestive system ? 244. Condition of young when first hatched ? 245. Chief characters of the Gasteropoda ? Give examples. Why spoken of as " univalves .*" 246. What is the " operculum ? " 247. Compare the Gasteropoda with the Lamellibranchiata as regards the head. 248. What is the nature of the " odontophore ? " QUESTIONS. 359 249. Condition of the heart and breathing-organs ? 250. What divisions of the Gasteropoda may be founded on the nature of the breathing-organs ? 251. Condition of the young water-breathing Gasteropod ? 252. Structure and modifications of the shell in Gasteropods ? 253. What are the two leading conditions of the mouth of the shell ? 254. General characters of the Nudibranchiata ? 255. Nature of the foot in the Heteropoda ? 256. General characters of the air-breathing Gasteropods ? 257. General characters of the Ptcropoda? 258. General characters of the Cephalopoda? 259. Nature of the "arms" and their suckers in the Cuttle-fishes? 260. Structure of the " funnel ? " 261. Nature of the ink-bag ? What living Cephalopod is without an ink- bag? 262. Nature of the breathing-organs ? Of the circulatory organs ? Of the respiratory process ? Of the nervous system ? 263. Peculiarities in the reproductive process in the Cuttle-fishes ? 264. Nature of the internal shell of the Cuttle-fishes ? 265. What two living Cephalopods possess an external shell, and ^vilat are the differences between these ? 266. Characters of the Dibranchiate Cephalopods ? Give examples. 267. Describe the shell of the Argonaut ? 268. Characters of the Tetrabranchiate Cephalopods ? 269. Describe the shell of the Pearly Nautilus ? 270. Mention some fossil forms allied to the Pearly Nautilus ? 271. General characters of the Vertebrata? 272. What is the " notochord ? " 273. General structure of a " vertebra ? " 274. Kegions generally recognizable in the vertebral column ? 275. General structure of the fore-limb ? 276. General structure of the hind-limb ? 277. General structure of the digestive system ? 278. Source of the blood ? Nature of the " blood-corpuscles ? " 279. What Vertebrate animal has no heart ? 280. General nature of the respiratory organs ? 281. What is the difference between a gill and a lung ? 282. General structure of the nervous system ? 283. Define the terms "oviparous," "viviparous," and " ovo- viviparous." 284. Into what primary sections are the Vertebrata divided by Huxley ? 285. What are the five classes of Vertebrates ? 286. General characters of Fishes ? 287. Chief forms of scales ? 288. Nature of the " lateral line ? " 289. Form of the vertebrae of a Fish ? 290. Position and connections of the ribs ? 291. Nature of the " interspinous bones ? " 292. Nature and position of the limbs of Fishes ? 293. Distinction between the " paired " and " median fins ? " 294. Number and names of the median fins ? 295. Difference between homocercal and heterocercal tail ? 296. What are the "rays?" Difference between "soft rays" an, 219. Scorpion, 141, 142. Sea-anemones, 86. Sea-cucumbers, 106. Seals, 306, 307. Sea-mosses, 167, 168. Sea-mouse, 124, 125. Sea-slugs, 184. Sea-spiders, 140. Sea-squirts, 165, 171. Segmental organs of Annelides, 121. Selachii, 223. jSemnopithecufi, 316. Serpvla, 123, 124. Sertularida, 57, 61 ; characters of, 66 ; poly- pites of, 66; reproduction of, 67. Sheep, 303. Shell, of Foraminifera, 84; of Mollwca, 166, of Brachiopoda, 174; of LamelU- branchiata, 178; of Gasteropoda, 182; of Ifeteropoda, 185; of Pteropoda, 186 ; of the Argonaut, 190, 191 ; of Pearly Nautilus, 190, 192. Shrew-mice, 314. Silk-moth, 160. Siluridce, 219. Simla, 318. /Siphonophora, 57 ; characters of, 70. Siphons, of LamellibrancJiiata, 174, 179. Sipunculus, 120. Siren, 227, 228. Sirenia, 287; characters of, 203. Skink, 246, 247. Skunk, 308. Sloths, 292. Slow-worm, 245. Snakes, 201, 235. Snapping-turtle, 240. Snipes, 269. Soft-tortoises, 240. Solaster, 101. Slien, 180. Somatic cavity, of Cml&nterata, 51, 84. Sorex, 314. Soricidce, 314. Spatularia, 221. Sperm-whale, 295. Spfieniscidw, 267. Spider-monkeys, 316. Spiders, 139, 140, 142. Spinneret, of Spiders, 143; of Caterpillars, 159. Spirorbis, 124. Spongida, 29 ; characters of, 36; aquiferous system of, 41; reproduction of, 43; dis- tribution of, in space, 43. Spongilla, 42 ; reproduction of, 43. Spoon-bill, 269. Spoon-worm, 120. Spring-bok, 303. Spring-tails, 153. Squids, 187, 190, 192. Squilla, 138. Squirrel, 311. Star-nosed Mole, 814. Stentor, 5, 48, 49. Stephanoceros, 116. Stomapoda, 138. StrepsirMna, 816. Strepsiptera, 162. Strigidce, 278. Struthio, 270. Sturgeon, 220, 221. Sturio, 220. Sturionidaz. 221. Sub-kingdoms, 11, 15. Suctoria (Infusoria), 49. * Surinam Toad, 232. Swallows, 277. Swifts, 258, 277. Swim-bladder, of Fishes, 218. Swimming-bells, 70, 71. Syngnathidce, 220. Syrinx, 120. 372 INDEX. Tabanidce, 159. Tcenia, 109, 111. Tceniada, 108; characters of; 109; develop- ment of, 110, 111. Talitrus, 138. Talpidce, 314. Tanagers, 276. Tantalince, 269. Tape-worm, 109-111. Tapir, 297. Teleostei, characters of, 217-219; sub-orders of; 219, 220. Tenrec, 315. Tenthredinidw, 160. Termites, 156, 157. Terrapin, 240. Test, of Foraminifera, 34; of Echinoid ea, 97 ; of Tunicata, 172. Testudo, 241. Tetrabranchiata, 189, 192, 193. Tetranychw, 141. Tetrao, 272. Tetraonidte, 272. Thala&ricolla, 39, 40. ThalassicoUida, 39. Theriomorpha, 230. Thick-knee, 269. Thread-cells, 52. Thread-worms, 114. Tfiylacinus, 291. Tkysanura, 153. Ticks, 140, 141. Tiger, 309. Tipula, 158. Tits, 276. Tongue, of Gasteropods, 181 ; of Cuttle-fish- es, 188; of Snakes, 242; of Birds, '25J. Tortoises, 235, 236, 238, 240. Tracheae, 140, 149. Tree-frog, 230, 232. Trematoda, 108; characters of, 112. Trichecus, 307. Trichina, 115. Trigonocephalus, 244. Trilobita, 135. Tringidce, 269. Trionycidce, 240. Triton, 229. TrochiUdce. 276. Troglodytes. 818. Troffonidce, 274. Trophosome, 63. Tube-feet of Echinus, 98, 99. Tubicola, 121, 123. TfoW/w, 123. Tubipora, 91. Tubularia, 61. Tutntlarida (see rori/nida). Tunicata. 165, 167; characters of, 171, 172. Tupaia, 815. Twrbellaria, 108; characters of, 113. Turkey, 272. Turn-stone, 269. Turritella, 183. Turtles, 235, 236, 238, 239. Umbo, 178. Umbrella, of Lucemarida, 78, 80-82. Univalve Shells, 167, 180, 182. Ungulata, 287 ; characters of, 296. Upupince, 276. Uraster, 101. Urodela, 226, 227. Ursidce, 308. Vacuoles, of ^i«?CB&a, 31 ; of Paranuxciwm., Vaginicola, 48, 49. Valkeria, 170. Vampire-bats, 313. Varanidce, 246. Veil, of gonophores, 64, 68 ; of nectocalyces, 71 ; of naked-eyed Medusa, 76. Velella, 72, 73. Venus's Flower-basket, 42. Venus's Girdle, 94. Vermes, 119. Vertebra, structure of, 197, 198. Vertebrata, 195; general characters of, 195; skeleton of, 197-201 ; digestive system of, 201; blood of, 202; respiration of, 203; nervous system of, 204; reproduction of, 204; divisions of, 204. 205. Vesicle, contractile, of Protoeoa, 26. Vespidce, 160. Viperidce, 244. Virgularia, 90. Viverridce, 808. Vorticella, 48, 49. Vulture, 278. Wah, 30a Walrus, 807. Wapiti, 802. Warblers, 276. Wasps, 160. Water-hens, 269. Water-vascular system, 95, 96. Weasel 808. Wolf, 308. Wolverine, 308. Woodcock, 269. Woodpeckers, 273. Wren, 276. Xiphosura, 133. Zoantharia,86', Mala cod ermata, 86; Sole- robasica. 90 ; sclerodermata, 87. Zoanthm, 87. Zooid, 55. Zoology, definition of, 3. THE END. 14 DAY USE RETURN TO DESK FROM WHICH BORROWED This book is due on the last date stamped below, or on the date to which renewed. Renewed books are subject to immediate recall. 7 p*.y iicr r\ 1 1 r utr SES JUL 2 3 I960 III! 1 c RFCD ^ t, u , JUL 1 D nuuu LD 21-50m-6,'59 (A2845slO)476 General Library University of California Berkeley rtt cJbU/6 1 M577042 QL42 N52 1871 Educ. Lib.