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CLOWES AND SONS, STAMFORD STREET AND CHARING CROSS. 5'9 0 t /p I t JO THE EDITOR’S PREFACE, >l> 1 The distinguished position occupied by Professor Agassiz, from his numerous and important works on Natural Science, especially his Recherches sur les Poissons Fossiles,^^ renders any eulogium on the contributions of so eminent a naturalist to zoological literature unnecessary. The ^‘Principles of Zoology,” of which the present volume forms the first part, was designed by Professor Agassiz, in conjunction with Mr. Gould, as a text-book for the use of higher schools and colleges, for which it is undoubtedly T^ell adapted, as the style is simple, the arrangement clear, and the range of subjects important and comprehensive : it is, moreover, well suited for imparting to the general reader a sound knowledge of Physiology and the Philosophy of Natural History. In introducing the present edition of this work to the English public, the Editor desires to state that he has endeavoured still farther to increase its value, by large additions to several of the chapters. In doing so, he has availed himself of the treatises of Cuvier, Carus, and Meckel, on Comparative Ana- tomy ; and those of Tiedeman, Muller, Valentin, and Wagner, on Physiology. Prom Dr. Willis’s excellent translation of the Elements of tlie latter profound author much additional matter has been derived. The additions from Wagner are duly acknowledged in the body of the work ; those by the Editor are indicated by his 776934 IV PREFACE. initials, and both are enclosed in brackets, so that the reader may readily distinguish between MM. Agassiz and Gould’s text, and the additions made thereto. The number and excellence of the wood-cuts form an im- portant feature in this edition. With the exception of those belonging to the chapters on Embryology, and the Meta- morphoses of Animals, they are nearly aU additional, by which the original number is more than doubled : the American edition having only 1/0 wood-cuts, whilst the present con- tains 390. The beautiful drawings illustrative of human Osteology were engraved by Branston for the valuable Manual on the Bones by John F. South, Esq. ; those illustrating the chapters on Circulation, Respiration, Secretion, and the De- velopment of the Chick, are chiefly from Wagner’s leones PhysiologiccB,^ and were engraved for the English translation of that author’s Elements of Physiology; the other figures are selected from various sources, references to which are given in the Table of illustrations. It has been the study of the Authors and of the Editor to exclude as much as possible a technical phraseology from the following pages ; but as the use of scientific terms could not altogether be dispensed with, the Editor has given an interpretation of them in a copious Glossarial Index. Cheitenhamy October ^ 1851. T. W. PREFACE. The design of this work is to furnish an epitome of the leading principles of the science of Zoology, according to the present state of knowledge, so illustrated as to be intelligible to the young student. No similar treatise exists in this country, and indeed some of the topics have not been touched upon in the language, except in a strictly technical form, and in scattered articles. On this account, some of the chapters, such as those on Embryology and Metamorphosis, may at first seem too abstruse for the beginner. But so essential have these sub- jects now become to a correct interpretation of philosophical zoology, that the study of them will hereafter be indis- pensable. They furnish a key to many phenomena which have heretofore been locked in mystery. The illustrations have been drawn from the best authorities ; some of them are merely hypothetical outlines, which convey a more definite idea than if drawn from nature ; others have been left imperfect, except as to the parts especially in ques- tion ; a large proportion of them, however, are complete and original. Popular names have been employed as far as pos- sible, and Definitions of those least hkely to be understood, will be found in the Glossary. The principles of Zoology developed by Professor Agassiz in his published works have been generally adopted in this, and the results of many new researches have been added. VI PBEEACE. The Authors gratefully acknowledge the aid they have re- ceived in preparing the illustrations and working out the details from Mr. E. Desor, for many years an associate of Pro- fessor Agassiz ; from Count Pourtales and E.C. Cabot, Esq.; and also from Professor Asa Gray, by valuable suggestions in the revision of the letter-press. The present volume is devoted to Comparative Physiology as the basis of classification ; the second will comprise Sys- tematic Zoology, in which the principles of classification will be applied, and the principal groups of animals briefiy charac- terised. Should our aim be attained, this work will produce more enlarged ideas of man’s relations to Nature, and more ex- alted conceptions of the plan of Creation and its Great Author. Boston, June 1, 1848. TABLE OE CONTENTS INTRODUCTION Page xix CHAPTER FIRST. The Sphere and fundamental Principles of Zoology • 1 CHAPTER SECOND. General Properties of Organized Bodies ... 9 SECTION I. Organized and Unorganized Bodies ... . . 9 SECTION IL Elementary Structure of Organized Bodies . . . , '10 SECTION III. Differences between Animals and Plants . . . ; .20 CHAPTER THIRD Organs and Functions of Animal Life 28 SECTION I. Of the Nervous System and General Sensation . . . .28 Structure of the primary Fibres of Nerves, 29 — Termination of the primary Fibres, 34 — The Cerebro- spinal system of Man^ The Cerebrum, 40 — The Cerebellum, 41 — The Optic Lobes, 42 — The Spinal Cord, 42 — Nervous system of Fishes, 44 — Amphibia, 45 — Scaly Reptiles, 45 — Birds, 45 — Mammaha, 46 — Cerebra.? Nerves, 49 — Nervous system of Articulata, 54 — Conchifera, 55 — Gasteropoda, 55 — Cephalopoda, 56 — Radiata, 57. SECTION IL Of the Special Senses 58 1. Of Sight, 58 — The Eye, 58— Dioptrics of the Human Eye, 60 — 2. Of Hearing, 70 — Comparative Anatomy of the Organ of Hearing, 70 — 80 — 3. Of Smell, 80 — The Nose, 80 — 4 Of Taste, 81—5. Of Touch, 82—6. The Voice, 83. vm TABLE OF CONTEITTS. CHAPTER FOURTH. Of Intelligence and Instinct Perception 86 86 CHAPTER FIFTH. Of Motion 91 SECTION I. Apparatus of Motion 91 Voluntary and Involuntary Muscles, 92 — Microscopic Anatomy of Muscular Fibre, 90 — 94 — Ciliary Motions, 95 — Skeleton of Polyps, 100 — Echinidae, 101 — Astefiadae, 102 — Crinoideae, 103 — Mollusca, 104 — Articulata, 105 — Vertebrata, 106. SECTION 11. Organs of Locomotion .109 Skeleton of Man, 111 — Composition of the Bones in Fishes; 113 — Reptiles, 113 — Birds, 113 — Mammals, 113 — Analysis of Bones, 114 — Microscopic Structure of Bones, 115 — The Head, 116 — The Orbits, 123 — The Trunk, 126 — The Cervical Vertebrae, 127 — The Dorsal Vertebrae, 129 — Tlie Lumbar Vertebrae, 130 — The Sacrum, 131 — The Coccyx, 131 — The Vertebrae, 131 — Comparative Table of the number of the Vertebrae, 134 — The Thorax, 135— The Pelvic Arch, 136 — The Thigh, 138 — The Leg, 139 — The Foot, 139 — The Tarsus, 140 — The Meta- tarsus, 140 — Toes, 140 — The Scapular arch, 141 — The Scapula» 142 — The Clavicle, 143 — The Humerus, 143 — The Hand, 146 — The Carpus, 146 — The Metacarpus, 146 — The Phalanges, 147 — 1. Plan of the Organs of Locomotion in the Vertebrata, 148 — 2. Of Standing, and the Modes of Progression, 152 — Walking, 154 — Running, 155 — Leaping, 155 — Climbing, 155 — Flight, 156 — Swimming, 157. CHAPTER SIXTH. Nutrition 159 SECTION I. Of Digestion 160 The Polypifera, 160 — The Infusoria, 161 — The Acalephae, 162 — The Echinoderms, 163 — The Bryozooan Polypifera, 165 — The Tunicated Mollusca, 166 — The Conchifera, 166 — The Gastero- poda, 167 — The Cephalopoda, 171 — The Annelida, 172 — The Crustacea, 173 — The Arachnida, 174 — Insects, 174 — The Ver- tebrata, 178 — Organs of Mastication, 185 — Insalivation, 191 — Prehension, 193. TABLE or COISTTEISTTS. IX CHAPTER SEVENTH. Of the Blood and Circulation 194 Blood globules in Man, 194 — Mammalia, 196 — Birds, Keptiles, and Fishes, 197, 198 — Blood vessels, 199 — Heart, 200 — Circu- lation of the Blood in Mammals and Birds, 202 — Reptiles, 203 — Fishes, 204 — Crustacea, Mollusca, and Insecta, 205 — Capillary Vessels, 207 — Circulation of the Blood in the Web of the Frog^s foot, 208 — 212 — Circulation in the Lungs of the Triton, 213. CHAPTER EIGHTH. Of Respiration 216 The Echinoderms, 27 — The Tunicata, 218 — The Conchifera, 219 — The Gasteropoda, 219 — The Pteropoda, 220 — The Cephalo- poda, 220— The Crustacea, 220 — The Annelida, 220 — Fishes, 221 — Insects, 223 — Air-breathing Vertebrata, 225 — Develop- ment of the Lungs,. 226 — 231 — Respiration in Gases other than Atmospheric Air, 234. CHAPTER NINTH. Of the Secretions 241 Endosmose and Exosmose, 243 — Structure of Glands, 246 — Ele- mentary parts of Glands, 263 — Origin of Glands, 265 — Dis- tribution of the Vessels in Glands, 269. CHAPTER TENTH. Embryology .... .... 272 SECTION I. Of the Egg 27] Form of the Egg, 272 — Formation of the Egg, 273. SECTION 11. Development of the Young within the Egg .... 278 Development of Fishes, 280 — 289 — Development of the Chick, 290 — Structure of the. Egg as just laid, 290 — Detachment of the Ovum from the Ovary, and completion of its formation in the Oviduct, 292 — Earliest Period in the Development of the Chick, from the first appearance of the Embryo to the first traces of Cir- culation, 295 — Second Period of the Development of the Chick, to the Evolution of the Second Circulation, 308 — Third Period in the history of the Development of the Incubated Egg : from the commencement of the Circulation in the Allantois to the Ex- clusion of the Embryo, 324 — Birth of the Chick, 333 — Phy- sical and Chemical changes in the Egg during Incubation, 334. SECTION III Zoological Importance of Embryology 336 X TABLE OE CONTENTS. CHAPTER ELEVENTH. Peculiar Modes of Reproduction ..... 339 SECTION I. Gemmiparous and Fissiparous Reproduction .... 339 SECTION II. Alternate and Equivocal Reproduction 348 SECTION III. Consequences of Alternate Generation . . . . . 348 CHAPTER TWELFTH. Metamorphoses of Animals 353 CHAPTER THIRTEENTH. Geographical Distribution of Animals . . . 363 SECTION I. General Laws of Distribution 363 SECTION II. Distribution of the Faunas 369 1. Arctic Fauna, 371 — 2. Temperate Faunas, 373 — Tropical Faunas, 377. SECTION III. Conclusions .380 CHAPTER FOURTEENTH. Geological Succession of Animals ; or, their Distribution IN Time 390 SECTION I. Structure of the Earth^s Crust ....... 3^0 SECTION II. Ages of Nature 396 The Palaeozoic Age, 397 — The Secondary Age, 402 — The Tertiary Age, 414 — The Modern Epoch, 415 — Conclusion, 417. List of the most important Authors who may be consulted in reference to the Subjects treated in this Work . . . 419 Glossarial Index 421 EXPLANATION OF THE FIGURES, Frontispiece. — The diagram opposite the title-page is intended to pre- sent, at one view, the distribution of the principal types of animals, and the order of their successive appearance in the layers of the earth’s crust. The four Ages of Nature, mentioned at page 190, are represented by four zones, each of which is subdivided by circles of different shades, indicat- ing the number of formations of which it is composed. The whole disc is divided by radiating lines into four segments, to include the four great departments of the animal kingdom ; the Vertebrata are placed in the upper compartment, the Articulata at the left, the Mollusca at the right, and the Radiata below, as being the lowest in rank. Each of these compartments is again subdivided to include the different classes belonging to it, which are named at the outer circle. At the centre is placed a figure representing the primitive egg, wdth its germinative vesicle and germinative dot (§ 436), indicative of the universal origin of all animals, and the epoch of life when all are apparently alike. Surrounding this, at the point from which each department radiates, are placed the symbols of the several de- partments, as explained on page 337. The zones are traversed by rays which represent the principal types of animals ; their origin and termi- nation indicate the age at which they first appeared or disappeared ; all those which reach the circumference being still in existence. The width of the ray indicates the greater or less prevalence of the type at dif- ferent geological ages. Thus, in the class of Crustaceans, the Trilobites commence in the earliest strata, and disappear with the carboniferous formation. The Ammonites also appeared in the Silurian formation, and became extinct with the deposition of the Cretaceous rocks. The Belemnites appear in the lower Oolitic beds ; many new forms commence in the Tertiary; a great number of types make their appearance only in the Modern age ; while only a few have continued from the Silurian, through every period to the present. Thus, the Crinoids were very nu- merous in the Primary Age, and are but slightly developed in the Tertiary and Modern Age. It is seen, at a glance, that the animal kingdom is much more diversified in the latter, than in the earher ages. Below the circle is a section, intended to show more distinctly the re- lative position of the ten principal formations of stratified rocks (§ 648), composing the four great geological ages ; the numerals corresponding to those on the ray leading to Man, in the circular figure. See also figure 376. EXPLANATION OE THE EIOTJEES. xii The Chart of Zoological Regions, page 370, is intended to shovr the limits of the several Faunas of the American Continent, corresponding to the climatal regions. As the higher regions of the mountains cor- respond in temperature to the climate of higher latitudes, it will be seen that the northern temperate fauna extends, along the mountains of Mexico and Central America, much farther towards the Equator, than it does on the lower levels. In the same manner, the southern warm fauna extends northward, along the Andes. Fig. 1 Tissue of the house leek- Agassiz 2 Pith of the elder . Ibid. 3 Microscopic structure of carti- lage . . . Schwann 4 Branchial cartilage of the larva of a frog . . Ibid. 5 Evolution of cellular tissue. Ibid. 6 Evolution of muscular fibre. Ibid. 7 Evolution 'Of nervous fibre. Ibid. 8 Nucleated cells from the granula- tions of the umbilical cord. Breschet 9 Primary fibres of a human nerve . . . Wagner 10 Branch of a nerve distributed to a muscle of the eye . Ibid. 11 Primary fibres of the olfactory nerve in man . Valentin 12 Terminal plexus of the auditory nerve (pike) . . Wagner 13 Terminal plexus from the ciliary ligament (duck) . Valentin 14 Terminal fibres (central) from the yellow substance of the ce- rebellum . . Wagner 15 Abdominal ganglion of the sym- pathetic nerve . . Ibid. 16 Primary fibres of the intercostal nerve of the sparrow . Ibid. 17 Thin slice from the cervical ganglion of the calf. Valentin 18 Primary fibres and ganglionic glo- bules of the human brain. Ibid. 19 The nervous system of Man. [Milne Edwards 20 A section of the human brain, shewing likewise the point of union of the cerebral nerves therewith . . Ibid 21 The brain and spinal cord of the Cyprinus aihurnus. Cams Fig. 21*A portion of the spinal cord shew- ing the double union of the nerves . . Edwards 22 The brain of the eel seen from above . . . Cams 23 The brain of the eel seen from below . . . Ibid. 24 The brain of the tortoise seen from above . . Bojanus 25 The brain of the tortoise seen from below . . Ibid. 26 The brain of the turkey seen from above . . . Carus 27 The brain of the pigeon seen from below . . Ibid. 28 The brain and spinal cord of the rat ... Ibid. 29 The brain of the hare . Ibid. 30 The brain of the common cat. Ibid. 31 The brain and spinal cord of the racoon . . Ibid. 32 The brain of a monkey laid open .... Ibid. 33 The brain of a monkey seen from below . . Ibid. 34 The nervous system of the gar- den beetle . . . Ibid. 35 The nervous system of Pa- ludina vivipara . Cuvier 36 The nervous system of the star- fish . . Tiedeman 37 Section of the globe of the eye . . . Agassiz 38 Diagram shewing the effect of the eye on rays of light. Wagner 39 Diagram shewing the effect of the eye on rays of light. W agner 40 Ditto ditto . . Ibid. 41 Ditto ditto . . Ibid. { 42 Ditto ditto . . Ibid, EXPLAIfATION or THE EiaFHES. XUl Fig. 43 Optical diagram . Wagner 44 Compound eyes of insects and Crustacea . . . Miiller 45 Vertical section of the organ of hearing in man . Edwards 46 Malleus or hammer-bone of the internal ear . . South. 47 Incus or anvil bone ditto. Ibid. 48 Stapes or stirrup ditto. Ibid. 49 Chain of bones in situ. Ibid. 50 Relative situation of the tympa- num and labyrinth. Soemmering 51 Views of the labyrinth. Ibid. 52 Ditto of the cochlea. Ibid. 53 Ditto of the semicircular canals. [Ibid. 54 Ditto ditto ditto. Ibid. 55 The cochlea, base and apex. Ibid. 56 The spiral laminae of the cochlea . . . Ibid. 57 The external shell of the cochlea removed . . . Ibid. 58 Horizontal section of the coch- lea ... South 59 Front view of the human larynx. 60 The larynx of the merganser {Mergus Merganser) . 60 A muscular fasciculus of the ox. [Wagner 61 The structure of human muscle. [Ibid. 62 Muscular fibre, after Skey. Skey 63 Muscles from the back of the rattle-snake . Wagner 64 Muscular fibres from the inver- tebrata . . . Ibid. 65 Muscular fibres from the eso- phagus . . . Skey 66 Streaked muscles of the Scolo- pend/ra Afra . . Wagner 67 Cilia arising from the epithelial cylinders . . . Ibid. ^8 Epithelial cells producing cilia. [Ibid. 69, 70 Litharaea Websteri. Sow’^erby 71 The test of an echinus. Edwards 72 Apiocrinus rotunda . Miller 73 Encrinus moniliformis . Ibid. 74 Cyprceacdssis rufa. Stutchbury Fig. 75 Astacus Vectensis, from Isle of Wight . . Mantell 75* External skeleton of Dasypus sexcinctus. 76 The muscular system of the perch . . . Carus 77 The muscular system of the Falco nisus . . . Ibid. 78 The skeleton of man. Cheselden 79 The human cranium . South 80 — 83 The temporal bones. Ibid. 84 The calvaria of the human skull . . . Ibid. 85 The temporal bones . Ibid. 86 and 87 External and internal views of ditto ; Ibid. 88 and 89 Anterior and posterior faces of petrous portion. Ibid. 90, 90* External and internal views of the occipital bone. Ibid. 91 The sphenoid and ethmoid. Ibid. 92 The superior and inferior max- illaries . . . Ibid. 93 Internal view of the superior maxillary . . . Ibid. 94 The partition of the nostrils. Ibid. 95 A vertical section of the or- bits, nostrils, and palate. Ibid. 96 The lateralboundary of ditto. Ibid. 97 The orbits . . . Ibid. 98 and 99 Views of the internal structure of the nose . Ibid. 100,101 The internal and external sur- face of the superior maxilla. Ibid. 102 The osseous roof of the mouth . . . Ibid. 103, 104 External and internal sur- faces of the superior maxilla, [Ibid. 105 The dorsal vertebrae. Ibid. 106, 107 The cervical ditto. Ibid. 108 and 109 The atlas . Ibid. 110 The axis . . . Ibid. 111 The seventh cervical vertebra. [Ibid. 112, 113 The dorsal vertebrae. Ibid. 114 The mode of articulation of the dorsal vertebrae . Ibid. 115, 116 Lumbar vertebrae. Ibid. 117 The fifth lumbar vertebra. Ibid, XIV EXPLANATION OF THE FIOUBES. Fig. 118, 119, 120 Diiferent views of the sacrum . . South 121 The front view of the spinal column . . . Ibid. 1 22 The back view of ditto. Ibid. 123 The lateral view of ditto. Ibid. 124 The thorax . . Ibid. 125, 126 Views of the male and female pelvis . . Ibid. 127, 128 The ossa innominata. Ibid. 129, 130 The outlet of the pelvis [Ibid. 131 The acetabulum . . Ibid. 132 The position of the pelvis, the axis .... Ibid. 133, 134 The anterior and posterior view of the femur. Ibid. 137 The tibia, fibula and patella. [Ibid. 138 The tarsus, metatarsus and toes .... Ibid. 139 Tibio-tarsal articulation. Ibid. 140, 141 The two rows of tarsal bones . . . Ibid. 142 The metatarsus. . . Ibid. 143 The toes . . Ibid. 144 The scapular arch. . Ibid. 145, 146, 147 Ditferent views of the scapula . . Ibid. 148 The clavicle . . . Ibid. 149, 150 Front and back view of the humerus . . Ibid. 151, 152 The condyles of ditto. [Ibid. 153 The radius and ulna. Ibid. 154 The carpus, metacarpus and phalanges . . . Ibid. 155, 156 The two rows of carpal bones . . . Ibid. 157, 158 The upper and lower sur- faces of the carpal bones Ibid. 158* The metacarpus . Ibid. 159 The phalanges of the thumb and fingers . . Ibid. 160 The anterior extremity of the stag . . . Agassiz 161 Ditto of the lion . Ibid. 162 Ditto of the whale . Ibid. 163 Ditto of the bat . Ibid. 164 Ditto of the bird . . Ibid. Fig. 165 The anterior extremity of the sloth . . [Agassiz 166 Ditto of the turtle . Ibid. 167 Ditto of the mole , Ibid. 168 Ditto of a fish . . Ibid. 169 The skeleton of the camel. [Edwards 170 The fresh-water polyp {Hydra viridis) . . . Ibid. 1 71 Leucophrys patula . Ehrenberg 172 Eosphora najas . Ibid. 173 A vertical section oiRliizostoma Cuvieri . Eysenhardt 174 Anatomy of the sea urchin, E chinus esculentus. Delle Chiaje 175 Plumatella repens . Edv^ards 176 The anatomy of the common oyster ( Ostrea edulis) . Poli 177 The anatomy of the sea-hare (^Aplysia Camelus) . Cuvier 178 The anatomy of the leech (^Hiru- do medicinalis) . Carus 179 The digestive organs of a beetle . . Edwards 180 The thoracic and abdominal vis- cera of a monkey . Ibid. 1 8 1, 182 The gastric glands from the stomach of man. Wagner 183 Magnified diagram of these glands . . . Ibid. 184 Other forms of glands of this class . . . Ibid. 185 Stomach of the plover (VaneU lus cristatus). . . Ibid. 186, 187, 188 Gastric glands of birds . . . Ibid. 189 The chyliferous vessels and glands . . Edwards 190 The jaws of an urchin {Echi- narachnius parma). Agassiz 191 The jaws of an urchin {Echi- nus granulatus) . Ibid. 192 The jaws of a cuttle fish. Ibid. 193, 194 The dental organs of Nerita and Patella . Wright 195 The anatomy of the mouth of a beetle . . Edwards 196 Ditto of the bee . , Ibid. 197 Ditto of the bug . . Ibid. 198 Ditto lancets of ditto . Ibid. EXPLANATION OF THE FIGmES. XV Fig. 199 The anatomy of the mouth of the butterfly . Edwards 200 The jaws of the snapping tur- tle (Emysaurus serpentina), [Agassiz 201 The head of a whale, shewing the whale-bone . . Ibid. 202 The head of an ant-eater. [Ibid. 203 The head of an alligator. Ibid. 204 The head of a skate-fish {My- liobatis)f shewing palate teeth. [Ibid. 205 The skull of the horse. 206 The skull of a squirrel. 207 The skull of a tiger. 208 Globules of the blood of man. [Wagner 209 Ditto of the common goat (Ca- pra domestica) . . Ibid. 210 Blood and lymph globules of the pigeon (Columba domes- tica) . . . Ibid. 211 Blood globules of the Proteus anyuinus . . Ibid. 212 Blood and lymph globules of the Triton cristatus . Ibid. 213 Blood globules of the Rana esculenta , . . Ibid. 214 Blood and lymph glgbules of the Cobitis fossilis . . Ibid. 215 Blood globules of the A mmocetes branchialis . . Ibid. 216 Vein laid open to shew the valves . . Cloquet 217 Diagram of the course of the blood in mammals and birds. [Edwards 218 Diagram of an ideal section of the human heart . Ibid. 219 Diagram of the circulation in reptiles. . . . Ibid. 220 Diagram ot the circulation in fishes . . . Ibid. 221 The heart and vascular system of the Doris . . Ibid. 222 The vascular system of the lobster . . . Ibid. 223 The organs of circulation in a nenropterous insect Ibid. Capillary vessels of the intestinal villus of a hare . Wagner Circulation of the blood in the inter-digital membrane of the hind foot of a frog, magnified three diameters . Ibid. The same, magnified forty- five diameters . . . Ibid. The same, magnified one hun- dred and ten diameters. Ibid. A venous branch, magnified three hundred and fifty times. Ibid. V iew in outline of a vein, mag- nified six hundred times. Ibid. A portion of the lung of a living triton, drawn under the micro- scope, magnified one hundred and fifty times . . Ibid. Capillary circulation in the lung .... Ibid. The anatomy of the Holothuria tubulosa . Delle Chiaje The branchiae of the Arenicola, [Edwards The respiratory apparatus of the t^epa cinerea. Leon Dufour Lungs, heart, and principal blood- vessels of man . Edwards Lung of the triton, magnified. [Wagner Lung of thetriton, injected. Ibid. Lung of the frog, magnified. Ibid. Lung of the tortoise ditto. Ibid. Lung of the serpent ditto. Ibid. Terminal vesicles of the human lung .... Ibid. Portion of the lung of a hog. Ibid. Portion of the human lung mag- nified two hundred times. Ibid. Rudiment of the lung from the embryo of a fowl . Ibid. Rudimentary lung from the em- bryo of a sheep . Muller Termination of the bronchi of the embryo of a hog. Rathke Diagram of experiment to illus- trate Endosmose and Exosmose. Glands from the auditory pas- sage of the human subject. [Wagner Fig. 224 I 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 XVI EXPLANATION OF THE FIOTJEES. Fig. 249 Sudoriparous glands from the palm of the hand. Wagner 250 Do. do. . . Gurlt 251 Thin layer of the scalp mag- nified . . . Ibid. 252 The salivary glands of insects [Ramdohr and Succow 253 Glands of insects . Ibid. 254 Do. do. . Ibid. 255 Harderian gland of the Pe- lecanus onocrotalus. Wagner 256 Cowper’s gland of the hedge- hog {Erinaceus) . Ibid. 257 Parotid gland of a new-born infant . . . Weber 258 Kidney and supra-renal capsule of an infant . . Wagner 259 Portions of do. magnified. Ibid. 260 Do. magnified 60 diameters. Ibid. 261 Termination of one of the tubuli magnified 250 times . Ibid. 262 Kidney of the porpoise {Delphi- nus phoccetia) . . Muller 263 Lobules of the human liver. [Wagner 264 A branch of the hepatic vein and liver lobules . . Ibid. 265 Superficial lobules of the liver. [Kiernan 266 The intra-lobular plexus of biliary vessels . . Ibid. 267 A transverse section of the lobes of the liver . Ibid. 268 A view, magnified 40 times, of the liver of a newt. Wagner 269 — 272 Show the development of the liver . . Muller 273 Ramifications of the bronchi from the embryonic Falco tin- nunculus . . Wagner 274, 276 Rudimentary form of the parotid gland . . Muller 277 Lobules of the parotid gland. Ibid. 278 Development of the liver in the Falco tinnunculus Wagner 279, 280 Malpighian bodies from the kidney of the Triton and Strix aluco . . Huschke 281 The egg of a skate-fish {Mylio- hatis). . . . Agassiz Fig. 282 The ova of a fresh-water polyp {Hydra) . . Agassiz 283 The egg of an insect — the snow-flea {Podurella). Ibid. 284 The primary ova of a bird magnified . . Wagner 285 The eggs of the Pyrula. Agassiz 286 The ovarial sacs of a Monoculus. [Ibid. 287 Ideal section of a fowPs egg. [Baer 288 Cell layer of the germ. Agassiz 289 Separation of the cell layer in- to three laminae . . Ibid. 290 Embryo of a crab, showing the incipient rings . . Ibid. 291 Embryo of a vertebrate animal, showing the dorsal furrow.Ibid. 292 — 294 Sections of the embryo, shoving the formation of the dorsal canal . . Ibid. 295 Section showing the position of the embryo of a vertebrate animal in its relation to the yolk . . . Ibid. 296 Section showing the same in an articulate animal . Ibid. 297 — 308 Sections showing the suc- cessive stages of development of the white-fish magnified. [Ibid. 309 The young white-fish just es- caped from the egg, with the yolk not yet fully taken in. Ihid. 310 — 311 Sections of the embryo of a bird, showing the formation of the allantois : e, embryo ; x^Xj membrane arising to form the amnios ; a, the allantois ; y, the yolk. 312 The same fully developed ; the allantois (o) is further deve- loped and bent upwards ; the upper part of the yolk (c?, d) is nearly separated from the yolk sphere, and is to become the intestine ; the heart {h) is already distinct and connected by threads with the blood layer of the body. JCXPliAJirATiyjy OP THE EIGITRES. XVU Fig. ^ Fig. 313, 314 Sections of the egg of a 334 mammal ; the thick vitelline membrane or chorion ; y, the 335 yolk ; s, the germinative spot ; g, the germinative vesicle ; 336 the empty space between the vitelline sphere and cho- 337 rion. 315 Shows the first indication of 338 the germ dividing into layers, the serous (s) and the mu- 339- cous (m). , 316 The mucous layer (m) expands 343 over nearly half the yolk, and 344, becomes covered with many little fringes. 346 317 The embryo (c) is seen sur- rounded by the amnios (5), and 347 covered by the large allantois (a) ; py e, fringes of the cho- 348 rion ; p, m, fringes of the ma- 349- trix 318 One of the chalazae of a jack- daw's egg pulled straight. 355 [Wagner 319 Vitellus of a hen^s egg. Ibid. 356 320 The yolk of a jackdaw's egg. [Ibid. 357 321 Section of a yolk almost ripe included in its calyx . Ibid. 358 322 The ovary of a fowl . Ibid. 323, 324 The vitellus twelve hours j 359 after incubation . Ibid. 1 360 325 Magnified view of the blasto- ‘ 361 derma . . Ibid. 326 Ideal sections . . Baer 362 327 Yolk after eighteen hours’ in- cubation . . Wagner 363 328 The pellucid area magnified. 364 [Ibid. 329 Ideal sections of 327, 328. Ibid. 365 330 Yolk after twenty-four hours' incubation . . . Ibid. 331 Magnified view of the pellucid 366 area .... Ibid. 332 Ideal sections of 329 — 331. [Ibid. 333 Yolk of the natural size after thirty-six hours' incubation. [Ibid. Magnified view of the pellucid area of the vitellus Wagner Ideal sections of the embryo. [Ibid. Incubated vitellus of the jack- daw's egg . . Ibid. Anterior extremity of an em- bryo .... Ibid, Ideal section of an embryo. [Ibid. —342 Views of embryos mag- nified . . . [Ibid. Ideal section of ditto . Ibid. 345 Outlines of embrj^os of the fowl .... Ibid. View of the vitellus magnified. [Ibid. View of the embryo of the yolk ... . . Ibid. Yolk of the hen's egg . Ibid. —354 Views of embryos in dif- ferent stages of development. [Ibid. Embryo of a lizard (JLacerta agilis) . . . Ibid. Vorticella, showing its reproduc- tion by buds . Agassiz Vorticella, showing its repro- duction by division . Ibid. Polyps, showing the same phe- nomenon . . . Ibid. A chain of Salpce . Ibid. An individual Salpa . Ibid. Cercaria, or early form of the Distoma . . Steenstrup Distoma, with its two suckers. [Ibid. Nurse of the Cercaria . Ibid. The same magnified, showing the included young . Ibid. Grand nurses of the Cercaria, including the young nurses. [Ibid. Stages of development of the Acalephae (Medusa) : a, the. embryo in its first stage, much magnified ; h, summit, show- ing the mouth ; c, /, g, ten- tacules shooting forth ; e, embryo adhering, and forming h Xviii EXPLANATION OP THE PIGUKES. Fig. a pedicle ; t, separation into segments; c?, a segment become free; form of the adult. [Sars 367 Portion of a horny sheathed polyp {Campanularia) : a, cup, which bears tentaculae; h, the female cell, containing eggs ; c, the cells in which the young are nursed, and from which they issue . Steenstrup 368 The young of the same, with its ciliated margin, magnified. 369 Transformations of the canker worm {Geometra vernalis) : «, the canker worm ; 6, its crysalis; c, female moth; d, male moth. . Agassiz 370 Metamorphoses of the Duck- barnacle {Anatifd)i a, eggs magnified; &, the animal as it escapes from the egg ; c, the stem and eye appearing, and the shell enclosing them ; animal removed from the shell, and further magnified ; e, /, the mature barnacle af- fixed by its pedicle . Ibid. 371 Metamorphoses of a star-fish {Eckinaster sanguinolentus), showing the changes of the yolk, e ; the formation of the pedicle, p ; and’ the gradual change into the pentagonal and rayed form . . Ibid. 372 Comatula, a West Indian spe- cies, in its early stage attached Mj \ item , . Agassiz Fig. 373 The same, detached and swim- ming free . . . Ibid. 374 Longitudinal section of the stur- geon, to show its cartilaginous vertebral column . Ibid. 375 Amphioxus, natural size, show- ing its imperfect organiza- tion .... Ibid. 376 Section of the earth’s crust, showing the relative position of the rocks composing it. [Agassiz 377 Fossils of the Palaeozoic age. [Murchison. 378 Homalonotus delphinocephalus^ [Konig 379 Pterichthys . . Miller 380 Coccosteus cuspidatus . Ibid. 381 The Flora of the coal period. [Richardson 382 Foot-prints of birds . Ibid. 383 Plesiosaurus rugosus . Owen 384 Pterodactylus crassirostris. [Goldfuss 385 Jaw of the Thylacotherium^ magnified. . Richardson 386 Fossils, shells, and Hemicidaris from the oolitic rocks. [Phillips 387, 388 Fossil shells from the greensand strata of the Isle of Wight . . . Mantel! 389 Fossil shells, and Mammalian remains, from the locustrine tertiary strata of the Isle of Wight, to illustrate the fauna of that period . . Ibid. 390 Tlie Megatherium. [Pander and D’ Alton INTRODUCTION. Etert art and science has a language of technical terms peculiar to itself. With those terms the student must make himself familiarly acquainted at the outset ; and first of all, he will desire to know the names of the objects about which he is to be engaged. The names of objects in Natural History are double, that is to say, they are composed of two terms. Thus, we speak of the white-bear, the black-bear, the hen-hawk, the sparrow- hawk ; or, in strictly scientific terms, we have Felis leo, the Hon ; Felis tigris, the tiger; Felis catus, the cat ; Canis lupus, the wolf ; Canis vulpes, the fox ; Canis familiaris, the dog, &c. They are always in the Latin form, and consequently the adjective name is placed last. The first is called the generic name ; the second is called the trivial, or specific name. These two terms are inseparably associated with every ob- ject of which we treat. It is very important, therefore, to have a clear idea of what is meant by the terms genus and species; and although the most common of all others, they are not the easiest to be clearly understood. The Genus is founded upon some of the minor peculiarities of anatomical structure, such ^s the number, disposition, or proportions of the teeth, claws, fins, &c., and usually includes several kinds. Thus, the lion, tiger, leopard, cat, &c., agree in the structure of their feet, claws, and teeth, and they belong to the genus Felis ; while the dog, fox, jackall, wolf, &c., have another and a different peculiarity of the feet, claws, and teeth, and are arranged in the genus Canis, The species is founded upon less important distinctions, such as colour, size, proportions, sculpture, &c. Thus we have different kinds, or species, of duck, different species of squirrel, different species of monkey, &e., varying from each XX INTEODrCTION. other in some trivial circumstance, while those of each group agree in all their general structure. The specific name is the lowest term to which we descend, if we except certain peculi- arities, generally induced by some modification of native habits, such as are seen in domestic animals. These are called vari- etiesy and seldom endure beyond the causes which occasion them. Several genera which have certain traits in common are combined to form a family. Thus, the alewives, herrings, shad, &c., form a family called CLiJPEinJE, among fishes ; the crows, black-birds, jays, &c., form the family Coryid^, among birds. Famihes are combined to form orders, and orders form classes, and finally, classes are combined to form the four primary divisions of the animal kingdom, namely, the departments. For each of these groups, whether larger or smaller, we in- voluntarily picture in our minds an image, made up of the traits which characterize the group. This ideal image is called a TYPE, a term which there will be frequent occasion to em- ploy, in our general remarks on the animal kingdom. This image may correspond to some one member of the group ; but it is rare that any one species embodies all our ideas of the class, family, or genus to which it belongs. Thus, we have a general idea of a bird ; but this idea does not corre- spond to any particular bird, or any particular character of a bird. It is not precisely an ostrich, an owl, a hen, or a sparrow ; it is not because it has wings, or feathers, or two legs ; or be- cause it has the power of flight, or builds nests. Any, or all of these characters would not fully represent our idea of a bird ; and yet every one has a distinct ideal notion of a bird, a fish, a quadruped, &c. It is common, hoY^ver, to speak of the animal which embodies most fully the characters of a group, as the type of that group. Thus, we might perhaps regard an eagle as the type of a bird, the duck as the type of a swimming-bird, and the mallard as the type of a duck. As we must necessarily make frequent allusions to animals, with reference to their systematic arrangement, it seems re- quisite to give a sketch of their classification in as popular terms as may be, before entering fully upon that subject, and with particular reference to the diagram fronting the title- page. IFTEODTJCTION. XXT The Animal Kingdom consists of four great divisions which we call Depaetmeis^ts, namely, I. The department of Vertebrata. II. The department of Articulata. III. The department of Mollusca. IV. The department of Radiata. I. The department of Veetebeata includes all animals which have an internal skeleton, with a back-bone for its axis. It is divided into four classes. 1 . Mammals (animals which nurse their young) . 2. Birds. 3. Reptiles. 4. Fishes. The class of Mammals is subdivided into three orders. a. Beasts of prey {Carnivora), h. Those which feed on vegetables {Herbivora). c. Animals of the whale kind {Cetaceans). The class of Biebs is divided into four orders. a. Birds of prey {Incessores) . b. Climbers {Scansores). c. Waders {Grallatores) . d. Swimmers {Nat at ores). The class of Reptiles is divided into five orders. a. Large reptiles with hollow teeth, most of which are now extinct {Rhizodords). b. Lizards {Lacertans). c. Snakes {Ophidians). d. Turtles {Chelonians) . e. Frogs {Batrachians). The class of Fishes is divided into four orders : a. Those with enamelled scales, like the gar-pike Lepidosteus {Ganoids). b. Those with the skin like shagreen, as the sharks and skates {Placoids). c. Those which have the edge of the scales toothed, and usually with some bony rays to the fins, as the perch {Ctenoids). d. Those whose scales are entire, and whose fin rays are soft, hke the salmon {Cycloids). XXll lOTRODUCTIOlS^. II. Department of Articulata. Animals whose body is composed of rings or joints. It embraces three classes. 1. Insects. 2. Crustaceans, bke the crab, lobster, &c. 3. Worms. The class of Iksects includes three orders. a. Those which have jaws for dividing their food {Man- ducata), fig. 195. h. Those with a trunk for sucking fluids, like the but- terfly {Suctorid)^ fig. 199. c. Those destitute of wings, like fleas {Apterd), The class of Crustaceans may be divided as follows : — a. Those furnished with a shield, like the crab and lob- ster (Malacostracd), h. Such as are not thus protected {Entomostracd) , c. An extinct race, intermediate between these two (Trilobites), fig. 378. The class of Worms comprises three orders : a. Those which have thread-hke gills about the head {Tubulibranchiatd) . b. Those whose giUs are placed along the sides {Bor- sibranchiatd), c. Those which have no exterior gills, Hke the earth- worm {Abranchiatd) , III. The department of Mollusca is divided into three classes, namely : 1. Those which have arms about the head, hke the cuttle-fish {Cephalopoda), 2. Those which creep* on a flattened disc or foot, like snails {Gasteropoda). 3. Those which have no distinct head, and are enclosed in a bivalve shell, hke the clams {Acephald). The Cephalopoda may be divided into — a. The cuttle-fishes, properly so caUed {Teuthideans) . b. Those having a shell, divided by sinuous partitions into numerous chambers {Ammonites), c. Those having a chambered shell with simple partitions {Nautilus) . INTEODUCTION. xxm The Gasteropoda contains three orders : a. The land-snails which breathe air {Pulmonata), b. The aquatic snails which breathe water {Branchiferd), c. Those which have wing-like appendages about the head, for swimming [Ptero^oda) , The class of Acephala contains three orders : a. Those having shells of two valves (bivalves), like the clam (Lamellibmnchiata) , b. Those having two unequal valves, and furnished with peculifr arms {Brachiopoda) , c. Those living in chains or clusters, like the Salpa, or upon plant-like stems, like the Flustra. — Bryozoa, IV. The department of Eadiata is divided into three classes : 1. Sea-urchins, bearing spines upon the surface {Echi- nodermata) . 2. Jelly-fishes {Acalephd), 3. Polyps, fixed like plants, and with a series of flexible arms around the mouth. The Echitoderms are divided into four orders : a. Sea-slugs, like the biche-le-mar (Holothurians) , b. Sea-urchins {Echini), fig. 71. c. Free star-fishes {Asteriadcc), fig. 36. d. Star-fishes mostly attached by a stem {Crinoidce), figs. 69, 70. The Acalepha includes the following orders : a. The Medusae, or common jelly-fishes {Biscophori), ^73. ... b. Those provided with aerial vesicles {Siphon ophori). c. Those furnished with vibrating hairs, by which they move {Ctenophori). The class of Polyps includes three orders : a. Fresh-water polyps, and similar marine forms {Hy- droids), fig. 170. b. Marine polyps, like the sea-anemone and corairpolyp {Actinoids) . c. A still lower form, allied to the mollusca by their shell {Bhizopods), XXIV INTEODUCTION. In addition to these, there are numberless kinds of micro- scopic animalcules, commonly called infusory animals (Infu- soria), from their being found specially abundant in water infused with vegetable matter. Indeed, a great many that were formerly supposed to be animals are now known to be vegetables. Others are ascertained to be crabs, moUusks, worms, &c. in their earliest stages of development. In general, however, they are exceedingly minute, exhibiting the simplest forms of animal life, and are now grouped together, under the title of Protozoa. But, as they are still very imperfectly understood, notwithstandir% the beautiful researches already published on this subject, and as most of them are likely to be finally distributed among vegetables and various classes of the animal kingdom, we have not assigned any special place to them. PHYSIOIOGICAL ZOOLOGY, CHAPTER FIRST. THE SPHERE AND FUNDAMENTAL PRINCIPLES OF ZOOLOGY. § 1 . Zoology is that department of Natural History which relates to Animals. § 2. The enumeration and naming of the animals which are found on the globe, the description of their forms, and the investigation of their habits and modes of life, are the principal, but not the only objects of this science. Ani- mals are worthy of our regard not only in respect to the variety and elegance of their forms, and their adaptation to the supply of our wants ; but the Animal Kingdom, as a whole, has also a still higher signification. It is the exhi- bition of the divine thought, as it is carried out in one de- partment of that grand whole which we call Nature ; and considered as such, it teaches us the most important lessons. § 3. Man, in virtue of his twofold constitution, the spiritual and the material, is qualified to comprehend Nature. Having been made in the spiritual image of God, he is competent to rise to the conception of His plan and purpose in the works of Creation. Having also a material body, like that of ani- mals, he is prepared to understand the mechanism of organs, and to appreciate the necessities of matter, as weU as the in- fluence which it exerts over the intellectual element, through- out the whole domain of Nature. § 4. The spirit and preparation we bring to the study of Nature, is not a matter of indifference. When we w^ould study with profit a work of literature, we first endeavour to make ourselves acquainted with the genius of the author ; 2 SPHEBE AKD EUNDAMENTAL and in order to know what end he had in view, we must have regard to his previous labours, and to the circumstances under which the work was executed. Without this, although we may perhaps enjoy the perfection of the whole, and admire the beauty of its details, yet the spirit which pervades it will escape us, and many passages may even remain unintelligible. § 5. So, in the study of Nature, we may be astonished at the infinite variety of her products, and may even study some portion of her works with enthusiasm, and nevertheless re- main strangers to the spirit of the whole, ignorant of the plan on which it is based ; and may fail to acquire a proper con- ception of the varied affinities which combine beings together, so as to make of them that vast picture, in which each animal, each plant, each group, each class, has its place, and from which nothing could be removed without destroying the proper meaning of the whole. § 6. Besides the beings which inhabit the earth at the pre- sent time, this picture also embraces the extinct races which are now known to us by their fossil remains only. These are of very great importance, since they furnish us with the means of ascertaining the changes and modifications which the Ani- mal Kingdom has undergone in the successive creations which have taken place since the first appearance of living beings. § 7. It is but a short time since it was not difficult for a man to possess himself of the whole domain of positive know- ledge in Zoology. A century ago, the number of known animals did not exceed 8000 ; that is to say, in the whole Animal Kingdom, fewer species were then known than are now contained in many private collections of certain famihes of insects alone. At the present day, the number of living species which have been satisfactorily made out and described, is more than 50,000.* The fossils already described exceed * The number of vertebrate animals may be estimated at 20,000. About 1500 species of mammals are pretty precisely known, and the number may probably be carried to about 2000. The number of Bbds well known is 4 or 5000 species, and the probable number is 6000. The Reptiles, like the Mammals, number about 1500 described species, and will probably reach the number of 2000. The Fishes are more numerous ; there are from 5 to 6000 species in the museums of Europe, and the number may probably amount to 8 or 10,000. The number of Mobusks already in collections, probably reaches 8 or PEIIS-CIPLES OE ZOOLOGY. 3 6000 species ; and if we consider that wherever any one stra- tum of the earth has been well explored, the number of spe- cies discovered has not fallen below that of the living species which now inhabit any particular locality of equal extent, and then bear in mind that there is a great number of geological strata, we may anticipate the day when the ascertained fossil species will far exceed the living species.* § 8. These numbers, far from discouraging, should, on the contrary, encourage those who study Natural History. Each new species is, in some respects, a radiating point which throws additional light on all around it ; so that as the picture is en- larged, it at the same time becomes more intelligible to those who are competent to seize its prominent traits. § 9. To give a detailed account of each and all of these animals, and to show them relations to each other, is the task of the Naturahst. The number and extent of the volumes already published upon the various departments of Natural History show, that only a mere outline of so vast a domain could be given in an elementary work hke the present, and tliat none but those who make it their special study can be expected to survey its individual parts. 10,000. There are collections of marine shells, bivalve and univalve, which amount to 5 or 6000 ; and collections of land and fluviatile shells, which count as many as 2000. The total number of mollusks would there- fore probably exceed 15,000 species. Among the articulated animals it is difficult to estimate the number of species. There are collections of coleopterous insects which number 20 to 25,000 species ; and it is quite probable, that by uniting the principal collections of insects, 60 or 80,000 species might now be counted ; for the whole department of articulata, comprising the Crustacea, the cirrhipeda, the insects, the red-blooded worms, the intestinal worms, and the infuso- ria, as far as they belong to this department, the number would already amount to 100,000; and we might safely compute the probable number of species actually existing at double that sum. Add to these about 10,000 for radiata, echini, star-fishes, medusae, and polypi, and we have about 250,000 species of living animals ; and sup- posing the number of fossil species only to equal them, we have, at a very moderate computation, half a million of species. * In a separate work, entitled Nomenclator Zoologicus^' by L. Agas- siz, the principles of nomenclature are discussed, and a list of the names of genera and families proposed by authors is given. To this work those are referred who may desire to become more familiar with nomenclature, and to know in detail the genera and families in each class of the Animal Kingdom. B 2 4 SPHEEE AND FUNDAMENTAL § 10. Every well-educated person, however, is expected to have a general acquaintance with the great natural phenomena constantly displayed before his eyes. A general knowledge of man and the subordinate animals, embracing their structure, races, habits, distribution, mutual relations, &c., is calculated not only to conduce essentially to our happiness, but is a study which it would be inexcusable to neglect. This general know- ledge, which is given by the science of Zoology, it is the pur- pose of the present work to afford. § 1 1 . A sketch of this nature should render prominent the more general features of animal life, and delineate the arrange- ment of the species according to their most natural relations and their rank in the scale of being ; and thus give a pano- rama, as it were, of the entire Animal Kingdom. To accom- plish this, we are at once involved in the question, what is it that gives an animal precedence in rank ? § 12, In one sense, all animals are equally perfect. Each species has its definite sphere of action, whether more or less extended, — its own pecuhar office in the economy of nature ; and is perfectly adapted to fulfil all the purposes of its crea- tion, beyond the possibility of improvement. In this sense, every animal is perfect. But there is a wide difference among them, in respect to their organization. In some it is very simple, and very hmited in its operation ; in others, extremely complicated, and capable of exercising a great variety of func- tions. § 13. In this physiological point of view, an animal may be said to be more perfect in proportion as its relations with the external world are more varied ; in other words, the more numerous its functions are. Thus, a quadruped, or a bird, which has the five senses fully developed, and which has, moreover, the faculty of readily transporting itself from place to place, is more perfect than a snail, whose senses are very obtuse, and whose motion is very sluggish. § 14. In like manner, each of the organs, wffien separately considered, is found to have every degree of complication, and, consequently, every degree of nicety in the performance of its function. Thus, the eye-spots of the star-fish and jelly- fish are probably endowed with the faculty of perceiving light, without the power of distinguishing objects. The keen eye of the bird, on the contrary, discerns minute objects PETNCIPLES OF ZOLOOGT. 5 at a great distance, and when compared with the eye of a fly, is found to be not only more complicated, but constructed on an entirely different plan. It is the same with every other organ. § 15. We understand the faculties of animals, and appre- ciate their value, just in proportion as we become acquainted with the instruments which execute them. The study of the functions or uses of organs therefore requires an examination of their structure ; Anatomy and Physiology must never be disjoined, and ought to precede the systematic distribution of animals into classes, famihes, genera, and species. § 16. In this general view of organization, we must ever bear in mind the necessity of carefully distinguishing be- tween affinities and analogies, a fundamental principle re- cognized even by Aristotle, the founder of scientific Zoology. Affinity or homology is the relation between organs or parts of the body which are constructed on the same plan, how- ever much they vary in form, or serve for different uses. Ana- logy, on the contrary, indicates the similarity of purposes or functions performed by organs of different structure. § 1 7. Thus, there is an analogy between the wing of a bird and that of a butterfly, since both of them serve for flight. But there is no afiinity between them, since, as we shall here- after see, they differ totally in their anatomical relations. On the other hand, there is an afiinity between the bird’s wing and the hand of a monkey, since, although they serve for dif- ferent purposes, the one for climbing, and the other for flight, yet they are constructed on the same plan. Accordingly, the bird is more nearly allied to the monkey than to the butterfly, though it has the faculty of flight in common with the latter. Affinities, and not analogies, therefore, must guide us in the arrangement of animals. § 18. Our investigations should not be limited to adult animals, but should also be directed to the changes which they undergo during the whole course of their development. Otherwise, we shall be liable to exaggerate the importance of certain peculiarities of structure which have a predominant character in the full-grown animal, but which are shaded off, and vanish, as we revert to the earlier periods of life. § 19. Thus, for example, by regarding only adult indivi- duals, we might be induced to divide aU animals into two 6 SPHEEE AKD EUNDAMENTAL groups, according to their mode of respiration ; uniting in one group all those which breathe by gills, and, in the other, those which breathe by lungs ; but this distinction loses its importance, when we consider that various animals, as, for example, frogs, which respire by lungs in the adult state, have only gills when young : hence it is evident that the respiratory organs cannot be taken as a satisfactory basis for fundamental classification. They are, as we shall see, subordinate to a more important organism, namely, the ner- vous system. § 20. Again, we ave a means of appreciating the relative grade of animals by the comparative study of their develop- ment. It is evident that the caterpillar, in becoming a butter- fly, passes from a lower to a higher state ; clearly, therefore, animals resembhng the caterpillar, as, for instance, worms, occupy a lower rank than insects. There is no animal which does not undergo a series of changes similar to those of the caterpillar or the chicken ; only, in many of them, the most important ones occur before birth, during what is called the embryonic period. § 21. The life of the chicken has not just commenced when it issues from the egg ; for, if we break the shell some days previous to the time of hatching, we find in it a hving animal, which, although imperfect, is nevertheless a chicken ; it has been developed from a hen’s egg, and we know that, should it continue to live, it will infallibly display all the character- istics of the parent bird. Now, if there existed in nature an adult bird, as imperfectly organized as the chicken on the day before it was hatched, we should assign to it an inferior rank. § 22. In studying the embryonic states of the mollusks or worms, we observe in them points of resemblance to many animals of a lower grade, to which they afterwards become entirely dissimilar; for example, the myriads of minute aquatic animals embraced under the name of Infusoria, whose organ- ization is generally very simple, remind us of the embryonic forms of other animals. We shall have occasion to show that the Infusoria are not to be considered as a distinct class of animals, but that among them there are found members of all the lower classes of animals, as mollusks, crustaceans, polyps, and even vegetable organisms.^ 3 And are grouped in the families Desmidice and Diatomacea, — Ed. PRINCIPLES OF ZOOLOGY. 7 § 23. Not less striking are the relations that exist between animals and the regions they inhabit. Every animal has its home. Animals of the cold regions are not the same as those of temperate climates ; and these latter, in their turn, differ fiDm those of tropical regions. Certainly, no one will main- tain it to be the efect of accident that the monkeys, the most perfect of all brute animals, are found only in hot countries ; or that it is by chance that the white bear and reindeer in- hal)it only cold regions. 4 24. Nor is it by chance that the largest of all animals, of every class, as the whales, the aquatic birds, and the sea- turtles, dwell in the water rather than on the land ; and while this element affords freedom of motion to the largest, so is it also the home of the smallest of living things. § 25. In the study of zoology we must not confine our re- searches to animals now in existence. There are buried, in the crust of the earth, the remains of a great number of animals belonging to species which do not exist at the pre- sent day ; many of these remains present forms so extraor- dinary, that it is almost impossible to trace their connection with any animals now living. In general, they bear a striking analogy to the embryonic forms of existing species ; for ex- ample, the curious fossils known under the name of Tri- lobites (Fig. 378) have a shape so singular, that it might well be doubted to what group of articulated animals they belong ; but if we compare them with the embryo crab, we find so remarkable a resemblance, that we hesitate not to refer them to the crustaceans. We shall also see that some of the fishes of ancient epochs present shapes entirely peculiar to them- selves (Fig. 379), resembling in a striking manner* the em- bryonic forms of some of our common fishes. A determina- tion of the successive appearance of animals, in the order of time^ is therefore of much importance in assisting us to deter- mine their relative zoological rank. § 26. Besides the distinctions derived from the varied struc- ture of organs, there is another less subject to rigid analysis, but no less decisive, to be drawn from the immaterial principle, with which every animal is endowed. It is this vital principle which determines the constancy of species, from generation to generation, and which is the source of all the varied exhibi- tions of instinct and intelligence which we see displayed, from 8 rmiTDAMENTAL PBINCIPLES OE ZOOLOGY. the simple impulse in the polyps to receive the food which is brought within their reach through the higher manifestations^ as observed in the cunning fox, the sagacious elephant, the faithful dog, and the exalted intellect of man, which is capable of indefinite expansion. § 27. Such are some of the general aspects in which ve shall contemplate the animal creation. Two points of view should never be lost sight of, or disconnected, namely, the animal in respect to its own organism, and the animal in its relations to creation as a whole. By adopting too exclushely either of these points of view, we are in danger of falling either into gross materialism, or into a vague pantheism. He who beholds nothing in Nature besides organs and tieir functions, may persuade himself that the animal is merely a combination of chemical and mechanical actions and reactions, and thus becomes a materialist. § 28. On the contrary, he who considers only the manifes- tations of intelligence and of creative will, without taking into account the means by which they are executed, and the phy- sical laws, by virtue of which all beings preserve their charac- teristics, will be very likely to confound the Creator with the creature. § 29. It is only by a simultaneous contemplation of matter and mind, that Natural History rises to its true character and dignity, and attains its noblest end, namely, the indication throughout the whole of creation of a plan fully matured in the beginning, and invariably pursued ; the work of a God infinitely wise, regulating Nature according to the immutable laws which He has himself imposed on her. CHAPTER SECOND. GENERAL PROPERTIES OF ORGANIZED BODIES. SECTION I. ORGANIZED AND DNORGANIZED BODIES. § 30. Nateral History, in its broadest sense, embraces the study of all the bodies which compose the crust of the earth, or which are dispersed over its surface. § 31. These bodies may be divided into two great groups ; inorganic bodies (minerals and rocks), and living or organic bodies (vegetables and animals). These two groups have nothing in common, save the universal properties of matter, such as weight, colour, &c. They differ at the same time in form, structure, composition, and mode of existence. § 32. The distinctive characteristic of inorganic bodies is rest; while that of organic bodies is independent motion, LIEE. The rock or the crystal, once formed, never change ; their constituent parts or molecules invariably preserve the position which they have once taken in respect to each other. Organized bodies, on the contrary, are continually in action. The sap circulates in the tree, the blood flows through the animal, and in both there is, besides, the inces- sant movement of growth, decomposition, and renovation. § 33. Their mode of formation is also entirely different. Unorganized bodies are either simple, or made up of elements unlike themselves ; and when a mineral is enlarged, it is simply by the outward addition of particles constituted like itself. Organized bodies are not formed in this manner. They always, and necessarily, are derived from beings similar to themselves ; and once formed, they always increase inter- stitially by the successive assimilation of new particles derived from various sources. § 34. Finally, organized bodies are limited in their dura- tion. Animals and plants are constantly losing some of their parts by decomposition during life, which at length cease to 10 ELEMENTARY STRUCTURE OE ORGANIZED BODIES. be supplied, and they die, after having lived their appointed period. Inorganic bodies, on the contrary, contain within themselves no principle of destruction ; and unless subjected to some foreign influence, would never change. The lime- stone and granite of our mountains remain just as they were formed in ancient geological epochs ; while numberless gene- rations of plants and animals have lived and perished upon theii’ surface. SECTION II. ELEMENTARY STRUCTURE OF ORGANIZED BODIES. § 35. The exercise of the functions of life, which is the es- sential characteristic of organized bodies (§ 32), requires a degree of flexibihty of the organs. This is secured by means of a certain quantity of watery fluid, which penetrates all parts of the body, and forms one of its principal constituents. § 36. AU hving bodies, without exception, are made up of tissues so constructed as to be permeable by liquids. There is no part of the body, no organ, however hard and compact it may appear, which has not this peculiar structure. It exists in the bones of animals, as well as in their flesh and fat ; in the wood, however sohd, as well as in the bark and flowers of plants. It is to this general structure that the term or(/anism is now applied. Hence the collective name of organized beings^ which includes both the animal and the vegetable kingdoms. § 37. The vegetable tissues, and most organic structures, when examined by the microscope, in their early states of growth, are found to be composed of hollow vesicles or cells. The natural form of the cells is that of a sphere or of an ellipsoid, as may be easily seen in many plants ; for example, in the tissue of the house-leek (Fig. 1). The intervals which sometimes separate them from each other are called intercellular spaces (m). When the cellules are very numerous, and * Formerly, animals and plants were said to be organized because they are furnished with definite parts, called organs, which execute particular functions. Thus, animals have a stomach, a heart, lungs, &c. ; plants ELEMENTARY STRIJCTIJEE OE ORGANIZED BODIES. 11 crowd each other, their outlines become angular, and the intercellular spaces disappear, as seen in figure 2, which repre- sents the pith of the elder. They then have the form of a honey-comb, whence they have derived their name of cellules. § 38. All organic tissues, whe- ther animal or vegetable, originate from cells. The cell is to the or- ganized body what the primary form of the crystal is to the secondary in minerals. As a general fact, it may be stated that animal cells are smaller than vegetable cells, but they alike contain a central dot or vesicle, called the nucleus. Hence -such cells are called nucleated cells (Figs. 3 and 48). Sometimes the nucleus itself contains a still smaller dot, called the nucleolus, % 39. The elementary structure of vegetables may be ob- served in every part of a plant, and its cellular character has been long known. But with the animal tissues there is far greater difficulty. Their variations are so great, and their transformations so diverse, that after the embryonic period, it is sometimes impossible, even by the closest examination, to detect their original cellular structure. § 40. Several kinds of tissues have been designated in the animal structure ; but their difierences are not always well marked, and they pass into each other by insensible shades. Their modifications are still the subject of investigation, and we refer only to the most important distinctions. § 41. 1st. The areolar tissue consists of a network of deli- cate fibres intricately interwoven, so as to leave numberless communicating interstices filled with fluid. It is interposed, in layers of various thickness, between all parts of the body, and frequently accompanied by clusters of fat cells. The fibrous and the serous membranes are mere modifications of this tissue. have leaves, petals, stamens, pistils, roots, &c., all of which are indispen- sable to the maintenance of life, and the perpetuation of the species. Since the discovery of the fundamental identity of structure of animal and vege- table tissues, a common denomination for this uniformity of texture has been justly preferred ; and the existence of vital tissues is now regarded as the basis of organization. 12 ELEMENTAET STRUCTURE OF ORGANIZED BODIES. §42. 2ndly. The cartilaginous tissue is composed of nucleated cells, the intercellular spaces being filled with a more compact substance, called the hyaline matter. § 43, 3dly. The osseous or hony tissue, which differs from the cartilaginous tissue, in having the meshes filled with salts of lime, instead of hyaline substance, whence its compact and solid appearance. It contains besides minute, rounded, or star- like points, improperly called bone-corpuscles, which are found to be cavities or canals, sometimes radiated and branched. § 44. 4thly. The muscular tissue, which forms the flesh of animals, is composed of bundles of parallel i^bres, which pos- sess the peculiar property of contracting or shortening them- selves, under the influence of the nerves, the muscles under the control of the will, are commonly crossed by very fine lines or wrinkles, but not so in the involuntary muscles. Every one is sufficiently familiar with this tissue, in the form of lean meat. § 45. 5thly, the nervous tissue is of different kinds. In the nerves proper, it is composed of very delicate fibres, which return back at their extremities, and form loops, as shown in figures 12 and 13, representing the primary fibres of the au- ditory nerve from the auditory sac of the pike. The same fibrous structure is found in the white portion of the brain. But the grey substance of the brain is composed of very mi- nute granulations, interspersed with clusters of large cells, as seen in fig. 14. § 46. The tissues above enumerated differ from each other more widely, in proportion as they are examined in animals of a higher rank. As we descend in the scale of being, the differences become gradually effaced. The soft body of a snail is much more uniform in its composition than the body of a bird, or a quadruped. Indeed, multitudes of animals are known to be composed of nothing but cells in contact with each other. Such is the case with the polyps ; yet they con- tract, secrete, absorb, and reproduce ; and most of the Infuso- ria move freely, by means of little fringes on their surface, arising from modified cells. § 47. A no less remarkable uniformity of structure is to be observed in the higher animals, in the earlier periods of their existence, before the body has arrived at its definite form. The head of the adult salmon, for instance, contains not only all the tissues we have mentioned — namely, bone, cartilage. ELEMENTAEY STEUCTUEE OF OEGANIZED BODIES. 13 muscle, nerve, brain, and membranes, but also blood-vessels, glands, pigments, &c. If we examine it during the embryonic state, while it is yet in the egg, we shall find that the whole head is made up of cells which differ merely in their dimen- sions ; those at the top of the head being very small, those surrounding the eye a little larger, and those beneath still larger. It is only at a later period, after still further deve- lopment, that these cellules become transformed, some of them into bone, others into blood, others into flesh, &c. § 48. Again, the growth of the body, the introduction of various tissues, the change of form and structure, proceed in such a manner as to give rise to several cavities, variously combined among themselves, and each containing, at the end of these transformations, peculiar organs, or peculiar systems of organs. [§ 49. All organic tissues,” says Dr. Schwaitn, how- ever different they may be, have one common principle of development as their basis — viz., the formation of cells ;* that is to say, nature never unites molecules immediately into a fibre, a tube, and so forth, but she always, in the first in- stance, forms a round cell, or changes, where it is requisite, cells into the various primary tissues in which they present themselves in the adult state. The formation of the elementary cells takes place, in the main points, in all the tissues accord- ing to the same laws ; the farther formation and transforma- tion of the cells is different in the different tissues. [§ 50. “ The primary phenomena of cells are the follow- ing : — there is first a structureless substance present (cyto- blastema), which is either contained in pre-existing cells, or exists on the outside of these. Within this, cell-nuclei gene- rally first arise — round or oval, spherical or fiat corpuscles — which usually include one or two small dark points (nuclear- corpuscules). Around these cell-nuclei the cells are produced, and in such wise that they at first closely surround the nuclei. The cells expand by growth, and indeed by intussusception, and the same thing very commonly happens, for a certain period, in regard to the nuclei. When the cells have attained a certain stage of development, the nuclei generally disappear. With reference to the place at which the new cells arise in * These observations have been confirmed by Wagner, Valentin, KoUi- ker, Schleiden, Mohl, Nageli, and others. — Ed. 14 ELEMENTARY STRUCTURE OF ORGANIZED BODIES. any tissue, the law is, that they constantly appear where the nutritive fluid penetrates the tissue most immediately ; there- fore it is that the formation of new cells in the unorganized tissues only takes place at the points where they are in con- tact with the organized matter ; in the completely organized tissues, again, where the blood is distributed to the whole of the texture, new cells are produced in the entire thickness of the tissue. [§ 51. The process by which the cells evolve themselves into the elementary formations of the individual tissues is very multifarious. The most remarkable differences are the following : — 1 . The elongation of the cell into a fibre, which probably takes place in consequence of one or more parts of the ceU-wall increasing in a greater degree than the others. 2. The division into so many isolated fibres, of a cell elon- gated in different directions. 3. The blending of several simple or primary cells into one secondary cell. [§ 52. ‘‘ Cartilage. — The cartilages are distinguished among aU the tissues of the human body, by containing the largest quantity of cytoblastema, which is also extremely consistent (fig. 3). The quantity of cytoblastema, however, differs greatly in different cartilages. It is, for instance, much smaller than usual in the branchial cartilages of the larva of the frog (fig. 4). Here the ceUs maybe observed flattening one another as soon as they touch. The first formation, and subse- Fig. 3.— Cartilage; the q^^ent growth of cartilage, take place in tafaf that cytoblastema is first pro- earthy deposit, from the duced, in which cells then form, whilst, at foetus of the sow. the same time, fresh cytoblastema arises, within which, again, cells are evolved as before, and so the process goes on. As the cartilage is without vessels at first, the formation of new cells only proceeds on the superficies of the substance, or, at all events, in its vicinity ; in the situation, therefore, where the cartilage is in immediate contact with the nutritive matter. The production and growth of the cells of cartilage are exhibited in figure 4 . In the cyto- blastema, on the surface of the cartilage at a, or between the new-formed cells at 5, new cell- nuclei are arising. Around ELEMENTABT STKUCTUBE OE OEGANIZED BODIES. 15 Fig. 4 represents the branchial these, cells will by and by be formed, as at c and d, which still surround the nucleus intimately, and are very thin in the walls. These cells expand by growth, and their walls, at the same time, become thicker. The nuclei also grow in a very slight degree for a while. The cells now contain a clear fluid, then a granular precipitate, which generally first forms it- self around the nucleus, as at e, figure 4, for example. In the old cells young cells occasion- ally arise. By and by cavities or canals are formed in the car- tilages in a way which has not yet been investigated with suffi- cient care, through which these vessels also take their course. If, after this epochs any new cartilage of a very young larva of cells are produced, we may pre- frog. The lower edge of the sume that their evolution takes Preparation is the natural limit of place, not only from the sur- face of the cartilage, but also around these vascular cavities and canals ; and, perhaps, it is from this circumstance that, after ossification, the cells are found dispo’sed in laminae, partly concentric around the cavity of the medullary canal, partly parallel with the surface of the cartilage. In the pro- cess of ossification, the earth is first deposited in the cytoblas- tema of the cartilage. The cells of the cartilage, at the same time, suffer a remarkable change, which seems to consist in their becoming elongated in different directions into hollow processes or canals, and thus acquiring a stellated appearance (stellated cells). The nuclei of the cells, during this process, are absorbed. At length, and finally, the cells themselves, and the canals proceeding from thfem, appear to become filled with calcareous earth. [§ 53. Cellulab Tissue. — The cytobiastema of the cellular tissue is a structureless, gelatinous looking, transparent sub- stance, uot unlike the vitreous humour of the eye. Within this arise small round granular-looking cells, furnished with nuclei (fig. 5 a.) Here, too, the nucleus appears to be the part first formed, the cell being developed around it. As the 16 ELEMENTARY STRUCTURE OE ORGANIZED BODIES. i cellular tissue contains blood-vessels, the evolution of new cells also proceeds through the entire substance of the tissue. The cells grow, but scarcely attain to twice the diameter of the nuclei they enclose ; at a very early period, however, they begin to length- en out in two opposite direc- tions into fibres (figure 5 b). The fibres then stretch on either hand into seve- ral branches (c, d), and these, in their turn, di- vide into still smaller fibres. This fibrillation of the branch- es, however, by and by proceeds backwards, to- wards the stem of the fibre aris- ing immediately from the body of the cell ; so that at a later period, instead of a single fibre, a bundle of isolated fibres is seen proceeding from either side of the body of the cell (fig. 5 e). Finally, the body of the cell itself also splits into fibres, and then, instead of a cell, we have a bundle of separate fibres, to which the nucleus of the former cell still continues attached. This process con- sists, therefore, in a kind of splitting up of a single cell into a multitude of hollow fibres. At a subsequent period, the nucleus is taken away, so that the fibres alone remain, and compose the filaments of the cellular tissue, as we find them in adults. It would appear, however, that they must suffer a chemical change, in addition to the changes in form, inasmuch as the cellular tissue at first affords no proper gelatine. [§ 54. ‘‘ Muscle. — The researches of Valentin have shown that the muscles are composed of globules arranged in rows, like strings of beads, which then unite into a fibre, — the pi4- Fig. 5. — Various stages in the evolution of the ceU lular tissue of the foetus of the sow; the stages are in the order of the letters of reference; c and d are mere varieties. ELEMENTARY STRUCTURE OE ORGANIZED BODIES. 17 mary muscular fibre. The fibre thus evolved cylinder, in the cavity of which, cell-nuclei lie another (fig. 6, a). From this it is probable that the globules which compose the fibre were hollow, — were cells, — and that the nuclei, included in the cyhnder, are the nuclei belonging to these primary cells. The earlier IS a near hollow to one a z ,6 0 i V-v/ li 0 Oi' w D' — te M. Fig. 6. a, b, c. Different stages in the evolution of muscular fibre ; d, a muscular bundle imper- fectly developed, standing on its edge. process of evolution must therefore have been as follows : — the globules or primary cells arranged themselves in a row, or coalesced into a cylinder, and then the septa, by which this cylinder must have been divided, underwent absorption. The nuclei are flat, and lie within the cylinder, not in its axis, but on its walls. This cylinder, rounded and closed at its ends, — this secondary muscular cell, grows continually, like a simple cell, but only in the direction of its length, for it either gains nothing in point of breadth, or it becomes actually thinner. The growth lengthwise, however, does not proceed from the ends only, but through the entire extent of the cylinder, as is obvious, from the fact of the nuclei, which at first lay close to one another, getting more and more distant, and even themselves elongating often in no inconsiderable degree. In this way, the muscular bundle a, (fig. 6) is changed into the bundle b. At this period, the deposition of a new substance upon the inner surface of the parietes of the cylinder, or cellular membrane of the secondary muscular cell, takes place, by which its wall is thickened (compare the fibre c with the fibre b, fig. 6). That the thickening of the wall here, is no thickening of the cell- membrane itself, as is in the case of cartilage, appears from this, that the nuclei are not forced inwards, toAvards the hollow of the cylinder, but outwards, and continue lying in front of the secondary deposition, as is seen in d (fig. 6). The secon- dary deposition in question, goes on until the cylinder is com- pletely filled. The deposited substance changes into very 18 ELEMENTABY STRUCTUBE OF ORGANIZED BODIES. delicate fibres, which run in the direction of the length of the cylinder. These are the primary muscular fibres ; together they constitute a bundle, and this is the primary muscular fasciculus, which is inclosed externally by a peculiar struc- tureless wall — the cell-membrane of the secondary muscular cell. A process, in all respects analogous, occurs, according to Meyen, in the cells of the liber, or inner bark of vegetables. Here, too, simple cells arise, which arrange themselves in rows, and by coalescing at the points where the cellular parietes are in contact, subsequent absorption of the septa being produced, change into a secondary cell, the wall of which increases in thickness by means of secondary deposition ; the only thing wanting in the resemblance is, that this thickening should take place by means of longitudinal filaments. [§ 55. Nerve. — The nerves appear to be formed after the same manner as the muscles, viz. by the fusion of a number of primary cells arranged in rows into a secondary cell. The primary nervous cell, however, has not yet been seen with perfect precision, by reason of the difficulty of distinguishing nervous cells, whilst yet in their primary state, from the in- different cells out of which entire organs are evolved. When first a nerve can be distinguished as such, it presents itself as a pale cord, with a coarse longitudinal fibrillation, and in this cord a multitude of nuclei are apparent (fig. 7, a). It is easy to detach individual filaments from a cord of this kind, as the figure just referred to shows, in the interiors of which many nuclei are included, similar to those of the primitive muscular fasciculus, but at a greater dis- tance from one an- other. The filaments are pale, granulated, and (as appears by their farther develop- muscle, a secondary deposit takes place upon the inner aspect of the walls of of nerve ; a and 6, of a very young foetal sow ; c and d, nervous vagus, from the cranium of a foetal calf. ment) hollow. At this period, as in ELEMENTAET STEUCTUEE OE OEGANIZEE BODIES. 19 the fibrils, or upon the inner aspect of the cell-membrane of the secondary nervous cell. This secondary deposit is a fatty white-coloured substance, and it is through this that the nerve acquires its opacity (fig. 7, b) . Superiorly, the fibril is still pale ; inferiorly, the deposition of the white substance has occurred, and its effect, in rendering the fibril dark, is ob- vious. With the advance of the secondary deposit, the fibrils become so thick, that the double outline of their parietes comes into view, and they acquire a tubular appearance (fig. 7, c). On the occurrence of this secondary deposit, the nuclei of the cells are generally absorbed ; yet a few may still be found to remain for some time longer, when they are observed lying outwardly between the deposited substance and the cell-mem- brane (fig. 7 c), as in the muscles. The remaining cavity of the secondary nervous ceU appears to be filled with a pretty consistent substance, the band of Remak, and discovered by him. In the adult a nerve consequently consists, 1st, of an outer pale thin cell-membrane — the membrane of the original constituent cells, which becomes visible, when the white sub- stance is destroyed by degrees (ex. gr. fig* 7, d) ; 2nd, of a white fatty substance, deposited on the inner aspect of the cell-membrane, and of greater or less thickness ; 3rd, of a substance which is frequently firm or consistent, included within the cells, the band of Remak.* [§ 56. From this resume ^ it would appear that the universal elementary form of every tissue is the cell, which is preceded by the kucletjs as medi- ate, and the ntjcleoltjs as immediate products of the formative power. Cells and nuclei seem to stand in mutual and relative opposition; so that generally, perhaps invariably, the one is evolved at the expense of the other (fig. 8). After these transition stages are accom- plished, the tissue attains individuality according to the general character and place it occupies in the system*. Dur- ing this last stage the more distant * Dr. Schwann, in Professor Wagner’s Physiology, p. 222. c 2 Fig. 8. — Cells from the granulations of the umbi- lical cord of the calf. They hear a striking resem- blance to the cellular tis- sue of vegetables ; nuclei are seen included in the several cells. After Bres- chet and Gluge (Ann. des Sc.]S!at.i.V\\\. pi. 6, fig. 5). 20 DIFFERENCES BETWEEN ANIMALS AND PLANTS. organic parts enlarge, as is distinctly seen in tlie cells of the epithelium, in the muscular fibres, and in the primary fibrous fasciculi of the nerves ; whilst mere nuclei, as the blood, lymph, or pus-globule, remain, or suffer diminution in the course of farther development.]* SECTIOI^ III. DIFFERENCES BETWEEN ANIMALS AND PLANTS. § 57. At first sight, nothing would appear more widely different than animals and plants. What is there in common, for instance, between an oak and the bird which seeks shelter amidst its foliage ? § 58. The difference, indeed, is usually so obvious, that the question would be superfluous, if applied only to the higher forms of the two kingdoms ; but as we descend to the simpler and therefore lower forms, the distinctions become so few, and so feebly characterized, that it is at length difiicult to pronounce whether the object we have before us is an animal or a plant. Thus, the sponges have so great a resemblance to some polyps, that they have generally been included in the animal, although in reality they belong to the vegetable kingdom. f § 59. Animals and plants differ in the relative predomi- nance of their component elements, oxygen, carbon, hydrogen, and nitrogen. In vegetables, only a small proportion of nitro- gen is found, while this element enters largely into the com- position of animal tissues. § 60. Another pecufiarity of the animal kingdom is the presence of large, distinctly limited cavities, for the lodgment of certain organs ; such is the skull and the chest in the higher animals, the branchial chamber in fishes, and the abdomen or general cavity of the body, which exists in all animals, with- out exception, for the reception of the digestive organs. § 61. The well-defined and compact forms of the organs lodged in these cavities is a peculiarity belonging to animals only. In plants, the organs designed for special purposes are never embodied into one mass, but are distributed over various parts of the individual ; thus the leaves, which answer to the * Wagner’s Physiology, p. 221. t The animahty of sponges is maintained by some of our most dis* Ungniblied naturalists. — Ed. DIFFEUENCES BETWEEN ANIMALS AND PLANTS. 21 lungs of animals, instead of being condensed into one organ, are developed on the stem and branches ; nor is there any organ corresponding to the brain, the heart, the liver, or the stomach. § 62. Moreover, the presence of a proper digestive cavity involves marked differences between the two kingdoms, in respect to ahmentation, or the use of food. In plants, the fluids absorbed by the roots are carried to every part of the plant, before they arrive at the leaves ; in animals, on the contrary, the food is at once received into the digestive cavity, where it is elaborated ; and it is only after it has been dis- solved and prepared, that it is introduced into the other parts of the body. The food of animals consists of organized substances, while that of vegetables is derived from inorganic elements ; vegetables produce albumen, sugar, starch, &c., whilst animals consume them. § 63. Plants commence their development from a single point, the seed, and, in like manner, all animals are developed from the egg. But the animal germ is the result of successive transformations of the yolk, while nothing similar takes place in the plant. The subsequent development of individuals is for the most part different in the two kingdoms. No hmit is usually placed to the increase of plants ; trees put out new branches and new roots as long as they live. Animals, on the contrary, have a limited size and figure ; and these once attained, the subsequent changes are accomplished without any increase of volume or essential alteration of form ; while the appearance of most vegetables is repeatedly modified, in a notable manner, by the development of new branches. Some of the lowest animals, however, as the polyps, increase in a somewhat analogous manner. § 64. In the effects they produce upon the air, by respira- tion, there is an important difference. Animals consume the oxygen, and give out carbonic acid gas, which is destructive to animal hfe ; while plants, by respiration, which they, in most instances, perform by means of the leaves, reverse the process, and furnish oxygen, which is essential to the life of animals. If an animal be confined in a small portion of air, or water conr taining air, this soon becomes so vitiated by respiration as to be unfit to sustain life ; but if living plants are enclosed with the animal at the same time, the air is maintained pure, and 22 DirFEEEKCES BETWEEN ANIMALS AND PLANTS. no difficulty is experienced. The practical effect of this com- pensation, in the economy of nature, is obviously most im- portant ; vegetation restoring to the atmosphere what is con- sumed by animal respiration, combustion, &c., and vice versa. § 65. But there are two properties which, more than all others, distinguish the animal from the plant, namely, the power of moving itself or its parts at will, and the power of perceiving objects and the influences produced by them ; in other words, voluntary motion and sensation. § 66. All animals are susceptible* of pleasure and pain. Plants have also a certain sensibility. They wither and fade under a burning sun, or when deprived of moisture ; and they die when subjected to too great a degree of cold, or to the action of poisons. But they have no consciousness, and there- fore suffer no pain ; while animals under similar circum- stances endure it. Hence they have been called animate beings, in opposition to plants, which are inanimate beings, [§ 67. If we take a general view of the animal and vegeta- ble kingdoms, we find that each kingdom may be grouped into three divisions. IN THE ANIMAL. 1. Zoophyta. 2. Mollusca and Articulata. 3. Vertebrata. [§ 68. The first great division of the animal series compre- hends the zoophytes ; their bodies have a circular or radiated form like some of the lowest vegetables, and are composed of a simple organic tissue, which is soft, pulpy, more or less trans- parent, and possessed of irritability and contractibihty, although muscular fibres have not been observed in many groups of this division. They manifest a high degree of sensibility, although distinct nerves and gangha have been only discovered in the acalephae and echinodermata. In these classes the gan- glia form so many centres of life, and each segment of the body has its own special ganglion. Through this simple con- dition of the nervous system many zoophytes possess the power of reproduction by scission or slips, and by buds or gemmules, after the manner of plants. The most inferior forms have no distinct organ except a digestive cavity, which IN THE YEGETABLE. 1. Acotyledons. 2. Monocotyledons. 3. Dicotyledons. DTFl'EEENCES BETWEEi^ ANIMALS AND PLANTS. 23 is sometimes furnished with small coeca ; they have no per- ceptible blood-vessels nor special organs for respiration and reproduction ; they are all aquatic, and are analogous to the lowest division of the vegetable series, the acotyledonous or cellular plants, both in form, consistence, and chemical com- position. [§ 69. The acotyledons all possess a soft, pulpy tissue of the most simple organisation, deprived of fibres. The repro- ductive organs are altogether absent, or are united on the same individual ; they have no medullary substance, and are merely expansions of simple cells, in which no special organs are de- veloped for any of the functions. [I 70. The second division of the animal series comprehends all those in which we find the nervous system disposed in cords in a body more or less symmetrical, extending from the head to the posterior extremity, under the intestinal canal. In all the classes of this great section the nervous trunks lie on the ventral surface of the body, and are provided at intervals with a number of ganglia, from which leashes of fila- ments emanate to supply the different organs. The nervous centre we call the brain, is formed in them of a double gan- glion, situated above the esophagous ; from it two branches arise to unite in ganglia situated below that tube, thus em- bracing the esophagous like a necklace or collar : from this nervous circle filaments proceed to be distributed to the different organs of the body. In all the mollusca, the nervous system preserves this general character ; but among the articulata, as Crustacea, insects, and annelides, each ring of the body pos- sesses a ganglion, which distributes filaments to the organs contained therein. The number of ganglia in the series cor- responds to the segments comprised in the length of the body, the whole being connected together by a double cord, emanating from the lateral parts of the esophagean gan- glion. From this disposition of the nervous system, life is not confined to a single centre (as in the vertebrata), each ganglion presiding, as it were, over the vital manifestations of the organs proper to the individual segments : it is thus they can reproduce many important parts that may have been removed, or lost by accident, as the claws of the crab and lobster, &c. f§ 71. The nutritive functions of the mollusca and articulata 24 DiriTEBENCES BETWEEN ANIMALS AND PLANTS. are under the empire of a ganglionic cord, similar to the sympathetic nerve in man. These two great classes never present an internal articulated skeleton ; their muscles are attached to the skin, which is more or less indurated. The Crustacea and moUusca have a heart and blood-vessels, for propeUing and circulating their nutritive fluids, with branchiae for aquatic and pulmonary sacs for aeriform respiration. In ^ the arachnida, insects, and annelides, the circulation is carried on by a pulsating dorsal vessel, and respiration is accomplished by sacs, branchiae, or trachiae, that ramify, like blood-vessels, through every part of the body : their jaws move on a hori- zontal plane, and many of them are provided with a proboscis or a suctorial apparatus. They possess the senses of vision, and even those of smell and hearing ; touch and taste, being refined modifications of sensibility, are enjoyed in a greater or less degree by all animals. The reproductive organs in the acephalous mollusca (as the oyster) are united in the same in- dividual : they are separate, however, in the gasteropoda (as the snail) and cephalopoda (as the cuttle-fish), as weU as in the Crustacea and insects. [§ 72. This division of the animal series is analogous to the monocotyledonous plants. The marrow or pith is inter- woven with their vegetable fibres, as the nervous system is disseminated by ganglia through the bodies of the inver- tebrata ; there is no osseous skeleton in the one, nor is there any true wood in the other, but in both the circumference is more solid than the centre. We see among some families of this section (as the grasses, lilies, and palms, &c., the same as among insects, Crustacea, and annelides), the integument more or less indurated, and in some families containing a quantity of silicious particles, just as the external skeleton of insects is composed of peculiar animal substances, termed chitine and coccine, and consolidated by minute proportions of the jjhos- phates of lime, magnesia, and iron ; or that of Crustacea, which is hardened with nearly half its weight of the carbonate of lime, and a considerable proportion of the phosphate, with traces of magnesia, iron, and soda. The knotty-jointed stems of many grasses represent the articulated bodies of worms, Crustacea, and myriapods. Many families of this division produce seed only once in their lives, like some worms and insects which cease to exist after having deposited their ova. Their leaves are DIFFEEENCES BETWEEN ANIMALS AND PLANTS. 25 simple, and their nerves are, in general, parallel : their flowers possess only three stamens, or their multiples ((i or 9), and they are often incomplete in many of their parts. None of these endogenous vegetables grow by layers, but by a swelling out of their internal structure, just as the horny or calca- reous envelope of insects and Crustacea is periodically shed to allow of a general increase from within. Among some classes and families of both kingdoms there are many groups which are aquatic in their habits. [§ 73. The third great division of the animal kingdom, called vertebrata, comprehends all those animals provided with two distinct nervous systems ; the one formed of a series of gan- glia extending through the body, and called the ganglionic or sympathetic system, which presides over the functions of internal life or nutrition. The other, consecrated to exter- nal life or relation, is composed of the brain, spinal cord, and nerves, the principal centres of which are enclosed in the cranium and the canal of the vertebral column ; they all possess an internal framework or skeleton, the several jointed pieces of which are moveable on each other. The most perfect possess five senses ; four of these occupying the cavity of the cranium, and there are never more than four members disposed in pairs. They have all a heart with red blood, and respire by lungs, or branchise, and the sexes are separate. They are usually parted into two great groups, the vertebrata with cold blood and feeble respiration, fishes and reptiles, and the vertebrata with warm blood and a com- plete respiration, birds and mammals. The nervous system, in this division of the series, attains its greatest development, presenting the most perfect centralisation, from which the most noble faculties emanate. [§ 74. We compare with this group of animals the dicotyle- donous vegetables, or those whose embryo possesses two coty- ledons or seed lobes. The form of their reproductive organs is always the most perfect, being composed of the number five and its multiples. Their trunks or stems grow by the addition of concentric layers or rings of wood made to their outer surface. Being thus exogenous, they display more or less solidity internally, like the osseous skeleton of the verte- brata. The central marrow or pith is enclosed in a sheath (analagous to the spinal canal) extending through the entire 26 DIFFERENCES BETWEEN ANIMALS AND PLANTS. length of the plant from the collar of the root to the terminal flowers of the stem and branches. This division comprehends the most highly developed families of the vegetable series in which the manifestations of life display themselves in their fullest perfection. Here we meet with all the most vivacious plants, aU the large trees, and all tliose which manifest the most marked irritabihty, as the sensitive plant, &c. &c. [§ 75. In resume we observe in animals and plants certain functions that are analogous, and contain organic traits that are different in each kingdom. The following table will enable the student to understand these analogies and dif- ferences : — IN THE TEGETABLE. 1. The roots are external, and are implanted in the earth, and all the special vital organs are situated externally. 2. Nourishment surrounds the vegetable, which it ab- sorbs by the external organs (the roots, leaves, &c.) 3. The sap ascends and de- scends by the agency of the vessels, aided by absorption and exhalation, through the influence of light and heat. 4. The leaves are the aerating organs or lungs of plants, and are usually of a green colour, and situated externally. 5. The vegetable absorbs carbonic acid gas, retains the carbon, and exhales the oxy- gen through the influence of the solar rays. IN THE ANIMAL. 1 . The absorbent vessels or internal roots penetrate the membranes of the digestive canal, and the vital organs are concealed internally. 2. The animal is compelled to search for its pasture, or its prey, and absorbs the juices by internal organs. 3 . The blood (whether white or red) circulates by means of one or more hearts, or by the contractility of the vessels themselves. 4. The respiratory organs of animals are sacs, tracheae, branchiae or lungs, and are usually placed internally, and tinged of a red colour, from the blood that circulates through them. 5. The animal absorbs the oxygen of the atmosphere, or that contained in the water, and exhales carbonic acid. I DIFFEEEIS^CES BETWEEN ANIMALS AND PLANTS. 27 IN THE YEGETABLE. 6. The vegetable is a comr- pound of many plants that are divisible and capable of mul- tiplication by buds, sbps, suckers, or seeds. 7. The plant has a circular or radiated form, both sexes being often united on the same individual. 8. The reproQUctive organs in the vegetable fall every year. 9. Fructification is the great end of vegetable existence, by the development of the fiower and fruit. 10. The movements in the vegetable are involuntary, de- pending on a state of turges- cence in the vessels, or in a degree of irritability peculiar to their tissues. 11. The vegetable is en- dowed with an organic sensi- bility without consciousness. 12. Vegetables possess de- fensive or protective weapons, and many have poisonous or- gans. IN THE ANIMAL. 6. Animals, some polyps and moUusca excepted, form a whole that is indivisible, being composed of central organs, as the brain, spinal cord, heart, &c. 7. Animals have mostly a binary form, each half being the counterpart of the other : the sexes are usually separate, although they are united in the inferior classes of mol- lusca and radiata. 8. In the animal they are permanent during life. 9. Sensibility and conscious- ness are the highest conditions of animal life, through the ope- ration of the brain and nerves. 10. The motions of animals are voluntary, depending on the energy of their muscular system, regulated by the will acting through the nerves. Some movements belong to the involuntary class . 1 1 . The nervous system con- fers on animals sensibility, accompanied with conscious- ness. 12. Animals, in addition, are furnished with offensive in- struments for seizing and des- troying prey ; some have a venomous, and others an elec- trical apparatus to accomphsh the same end, — T. W.] CHAPTER THIRD. ORGANS AND FUNCTIONS OF ANIMAL LIFE. SECTION 1. OF THE NEEYOTJS SYSTEM AND GENEEAL SENSATION, § 76. Life, in animals, is manifested by two kinds of functions, viz. : First, the functions of animal life, or those of relation, which include sensation and voluntary motion ; those which enable us to approach, and perceive our fellow- beings and the objects around us, and bring us into relation with them : Second, the functions of vegetable life, which are nutrition in its widest sense, and reproduction ;* those in- deed, which are essential to the maintenance and perpetuation of life. § 77. The two distinguishing characteristics of animals, namely, sensation and motion (§ 65), depend upon special systems of organs, wanting in plants, and which are called the nervous and muscular systems. The nervous system, therefore, is the grand characteristic of the animal body. It is the centre from which all the commands of the will issue, and to which all sensations tend. § 78. Greatly as the form, the arrangement, and the volume of the nervous system vary in different animals, they may all be reduced to four principal types, which correspond, more- over, to the four great divisions of the animal kingdom. In the vertebrate animals, namely, fishes, reptiles, birds. This distinction is the more important, inasmuch as the organs of animal life, and those of vegetative life, spring from very distinct layers of the embryonic membrane. The first are developed from the upper layer, and the second from the lower layer of the germ of the animal. See Chapter on Embryology, NEHTOUS SYSTEM AND GENEEAL SENSATION. 29 and mammals, the nervous system is composed of two prin- cipal masses, the spinal cord (fig. 19), which runs along the back, and the brain (fig. 20), contained within the skull.* The volume of the brain is proportionally larger, as the animal occupies a more elevated rank in the scale of life. Man, who stands at the head of creation, is in this respect also the most highly endowed being. § 79. With the brain and spinal cord the nerves are con- nected, which are distributed, in the form of branching threads, through every part of the body. The branches which unite with the brain are nine pairs, called the cerebral nerves, and are destined chiefiyforthe organs of sense located in the head. Those which join the spinal cord are also in pairs, one pair for each vertebra or joint of the back. The number of pairs varies, therefore, in difterent classes and families, according to the number of vertebrae. Each spinal nerve is double, being composed of two threads, which at their junction with the cord are separate, and afterwards accompany each other throughout their whole course. The anterior thread transmits the commands of the will, which induce motion ; the pos- terior receives and conveys impressions to the brain, to pro- duce sensation. STEirCTUEE or THE PEIMAET EIBEES OE NEEVES. [§ 80. Whoever would acquire a knowledge of the minute anatomy of the nervous system, had better begin by examining one of the peripheral nerves. Let a piece of one of the trunks or branches of a nerve, that can easily be dissected out, be chosen, and laid upon a glass plate : here let the nervous bundles be separated or teazed out by the aid of a needle in either hand, until free spaces of the glass plate appear ; let the preparation now have a drop of serum or of albumen added to it, and then be covered with a piece of thin glass. Under a magnifying power of from three to four hundred diameters, numbers of transparent cylindrical, straight, or slightly sinuous filaments will* be perceived as the chief structure, * The brain is composed of several distinct parts, which vary greatly, in their relative proportions, in different animals, as will appear hereafter. They are : 1. The medulla oblongata; 2. Cerebellum; 3. Optic lobes; 4. Cerebral hemispheres ; 5. Olfactory lobes ; 6. The Pituitary body ; 7. The Pineal body. See figures 19, 20. The spinal cord is composed of four nervous columns. 30 NERVOUS SYSTEM AND GENERAL SENSATION. having a mean diameter of from 1 -200th to 1 -300th of a line, and always proceeding distinct from one another, never anas- tomosing. These are the primitive eibres of the nerve (figs. 9, et seq.) If these fibres have under- gone little or no change, each is se- verally seen to be bounded by a dou- ble contour — an appearance which must be viewed as the optical expres- sion of a transpa- rent covering or membrane. The middle space is completely trans- parent. When the nerve has suffered change from pres- sure, imbibition of In the middle clear Fig. 9. — A, Primary fibres of a human body. B, primary fibres (more highly magnified) of the brain. water, or the like, the appearance is altered space granular or grumous particles or masses are perceived, which, under pressure, escape from the divided ends of the primitive fibres (fig. 9, A, to the right). Other changes, but more difficult of apprehension, also take place in the lateral contours of the fibres, which are made up of the double lines. To observe the primitive fibres of nerves in their normal situation, the best subject is the delicate flat muscle of some small animal — one of the muscles of the eye of the common sparrow, for example (fig. 10) — which must be gently pressed between two plates of glass. Here, in the middle trunk (iar^ea^*e65^eri.tiary sands of Bracklesham Bay, THE SKELETON OF ECHINODEEMS. 101 showing the skeleton of one of these lithophytes. The natu- ral size of the polypary is seen at fig. 69, and a magnified view of one of the cells, with its rays, is given in fig. 70.] In the echinoderms, the test is brittle, and intimately united with the soft parts. It is composed of numerous little plat-es, sometimes consolidated and immoveable, as in the sea-urchins, or combined, so as to allow of various motions, as in the star- fishes (fig. 36), and in the sea-lilies (figs. 72 and 73), which use th^ir arms both for crawling and swimming. Fig. 71. — The test of an Echinus. On the right side are seen the spines and tubular suckers : on the left side, those parts have been re- moved, to show the surface of the test, composed of the ambulacral areae, with the small plates, and poriferous avenues at their margins, and the interambulacral areae, composed of the large polygonal plates. The plates of both areae being covered with tubercles, for supporting spines. [In the ECHINID-®, or sea urchins, the test is of a spherical or pentagonal form, constructed of many series of calcareous polygonal plates articulated together, and divided into two groups, of which five form the ambulacral areae, and five the interambulacral areae, each area being composed of two columns of plates (fig. 71 and 174, e). The ambulacral alternate with the interambulacral areae, and they are separated from each other by ten rows of small perforated plates, through the holes of which numerous tubular retractile suckers pass : the 102 THE SKELETON OE ECHINOHEEMS. mouth occupies the base of the test ; the opening is of a cir- cular or decagonal form, in which a complicated mechanism of five jaws and five teeth, with their muscles, are lodged (figs. 190 and 191). The anus in this group opens at the vertex of the test ; the opening is surrounded by a circle of ten plates, five of whieh are perforated to give passage to ducts from the genital organs, and called ovarial plates, and five are per- forated for lodging the eyes, and called ocular plates. The sur- face of the ambalacral and interambulacral plates is covered with tubercles of various sizes, in general raised upon prooSinent eminences, the tubercles having a round smooth head, to which a spine with a concave base is fitted and moved by muscles ; the entire surface of the test and spines is covered by an or- ganised skin ; the skeleton therefore is enclosed in mem- branes, participating in the life and growth of the animal, and forming an integral part of the urchin. In the ASTEEiAn^, or sea stars (figs. 36 and 373), a similar complicated skeleton exists, with this difference, that the ambu- lacral and interambulacral arese, instead of being united to form a hollow case, are stretched out into rays, at the ex- THE SKELETON OE MOLLUSCA. 103 tremity of which the eyes are situated, corresponding to their position in the echinidee ; the summits of the arese being ana- logous to the extremities of the rays bent up towards the anal pole. In the CEiNOiDEJa, or sea hlies, which may be likened to sea-stars supported upon many jointed columns, the skeleton is very complicated, being composed of many thousand separate pieces, beautifully and nicely fitted to each other. Fig. 72 represents the pear encrinite {Apiocrinus rotunda)^ from the Bradford clay ; and fig. 73, the lily encrinite {Encrinus mo- niliformis), from the Muschelkalk. These stalked echinoderms attained a great generic development in the palaeozoic rocks, entire strata being sometimes composed of their broken skeletons ; their forms are less numerous in the triasic and oolitic periods ; a few only are found in the chalk, and one rare species lives in the warm regions of our present seas. —T. W.] Fig. 74. — Cyj)rcBacdssis rufa; a, mature, b, immature state of the same shell. § 220. In the mollusca, the solid parts are secreted by the skin, most frequently in the form of a calcareous shell of one, two, or many pieces, serving for the protection of the soft 104 THE SKELETON OF MOLLUSCA. parts which they cover. These shells are generally so con- structed as to afford complete protection to the animal within their cavities. In a few, the shell is too small for this pur- pose ; in others it exists only at a v^y early period, and is lost as the animal is developed, so that at last there is no other covering than a slimy skin. In some the tegumentary membrane becomes so thick and firm as to have the consistence of elastic leather, or it is gelatinous or transparent; and what is very curious, these tissues may be the same as those of woody fibre, as, for example, in the ascidia. In general the solid parts do not aid in locomotion, so that the moUusca are mostly slug- gish in their movements. It is only in a few rare cases that the shell becomes a true lever, as in the scallops (Pecten), which use the valves thereof to propel themselves in swimming. [The shells of a great majority of the gasteropoda are uni- valve, and rolled obliquely, in consequence of the unequal de- velopment of the body of the animal. They consequently form a helix or oblique spiral ; sometimes the coil is towards the right, but in general it is towards the left side. Some univalve shells have a patelloid form, and are symmetrical, without being spiral ; and there are various intermediate groups, by which these forms blend into each other. Some of the shells vary very much in form at different stages of their growth, as shown in the beautiful Cypraacdssis rufa, from the coral reefs of the South Pacific. Fig. 74, a, is the mature form of that shell, with its greatly developed right lip ; and b, the young, or immature form of the same. — T. W.] § 221 . The muscles of moUusca either form a flat disc under the body, or large bundles across its mass, or they are distributed in the skin, so as to dilate and contract it, or are arranged about the mouth and tentacles, which they put in motion. However varied in their disposition, the muscles always form very considerable masses, in proportion to the size of the body, and have a soft and mucous appearance, such as is not seen in the contractile fibres of the other divisions of the animal kingdom. This peculiar aspect no doubt arises from the nu- merous small cavities extending between the muscles, and the secretion of mucus which takes place in them. § 222. In the articulated animals (fig. 34), the solid parts are external, in the form of rings, generally of a horny structure, but sometimes calcareous, and successively fitting into each other at their edges. The tail of a lobster gives a good idea of this THE SKELETOT^ OF AETICULATA. 105 structure. The rings differ in the several classes of this divi- sion, merely as to volume, form, solidity, number of pieces, and the degree of motion which one has upon another. In some groups they are consolidated, so as to form a shield or carapace, such as is seen in the crabs. In others, they are membranous, and the body is capable of assuming various forms, as in the leeches and worms generally. Fig. 75 is a beautiful fossil Astacus, from the lower greensand, which exhi- bits the character of the skeleton of the Crustacea. Fig. 75. — Astacus Vecte7isis, from the lower greensand, Isle of Wight. § 223. A variety of appendages are attached to these rings, such as jointed legs (fig. 34), or, in place of them, stiff bristles, oars fringed with silken threads, wings either firm or mem- branous (fig. 369), antennse, moveable pieces which perform the office of jaws (fig. 195), &c. But, however diversified this solid apparatus may be, it is universally the case that the rings, to which every segment of the body may be referred, as to a type, combine to form but a single internal cavity, in which all the organs are enclosed, the nervous system, as well as the organs of w^egetative life (§ 76). § 224. The muscles which move all these parts have this peculiarity, that they are enclosed within the more solid frame- work, and are not external to it, as in the vertebrata ; and also that the muscular bundles, which are very considerable in number, have the form of ribbons, or fleshy strips, with pa- rallel fibres of remarkable whiteness. § 225. The vertebrated, hke the articulated animals, have 106 THE SKELETON OE YEETEBEATA. solid parts at the surface, as the hairs and horns of mammals, the coat of mail of the armadillo (fig. 75*), the feathers and claws of birds, the buck- lers and scales of rep- tiles and fishes, &c. But they have, besides this, along the interior of the whole body, a sohd framework, not found in the invertebrata, well known as the Skele- ton. Fig. 75*.— External skeleton of tlie Dasypiis § 226. Theskeletonis sexcmctus. composed of a series of separate bones, called vertebrae, united to each other by liga- ments. Each vertebra has a solid centre with several branches, two of which ascend and form an arch above, and two descend, forming an arch below the body of the vertebra. The upper arches form a continuous cavity along the region of the trunk, which encloses the spinal cord, and in the head receives the brain (§85 and § 89). The lower arches form another cavity, similar to the superior one, for containing the organs of nutrition and reproduction ; the branches generally meet below, and when disjoined, the deficiency is supplied by fleshy walls. Every part of the skeleton may be reduced to this fundamental type, the vertebra, as will be shown when treating specially of the vertebrate animals; so that, between the pieces composing the head, the trunk, and the tail, we have only difierences in the de- gree of development of the body of the vertebra, or of its branches, and not in reality different plans of organization. § 227. The muscles which move this solid framework of the vertebrata are disposed around the vertebrae, as is well exem- plified among fishes, where there is a band of muscles for each vertebra (fig. 76). In proportion as limbs are developed, this intimate relation between the muscles and the vertebrae dimi- nishes. The muscles are unequally distributed, and are con- centrated about the limbs, where the greatest amount of muscular force is required. For this reason the largest masses of flesh, in the higher vertebrata, are found about the shoulders and hips (fig. 7 7) ; while in fishes they are concen- trated about the base of the tail, the part on which they princi- pally depend for motion. MUSCULAR SYSTEM OF FISHES. 107 [Fig. 76 represent the Muscles of the Peroh,^a, inferior half of the great lateral muscular mass ; a\ the superior half; h and c, points where these masses divide for the passage of the rays of the pectoral and ventral fins; de,i\\Q middle inferior longitudinal muscles;/, the middle superior- q muscles for moving the ventral fin ; h, the muscles special to the pectoral fin ; h h, the particular muscles of the dorsal fin ; i, the muscles of the anal fin; /t, the muscles of the caudal tail fin; I l\ the muscles com- mon to the jav»^s ; the muscles of the operculum and the first inter- costal of the cranium ; /3, attachment of the latero-superior muscles of the occiput ; the lateral line between the muscular masses ; the great lateral nerve has been removed, and the superior muscular mass pushed upwards. — Cuvier , Histoire des Poissons. [Fig. 77— Muscular system of -Birds.— Tbe muscles of the Falco msus : 1, the great complexus ; 1 a, its tendon ; 1 b, its superior head • 1 c, its inferior head ; 2, the small complexus ; 3, the lateral flexor of the’ head ; 4, the long flexor of the head ; 5, the great extensor of the neck • 6, the descending cervical; 7,7’, the demi-spinal muscles of the neck and back ; 8, the superior flexor of the head ; 9, the inferior, or long flexor of the head; 10, 10, the anterior and posterior inter - transverse muscles of the neck; 11, the elevator of the coccyx; 12, the depressor of the coccyx; 13, the cruri-coccygean ; 14, the pubi-coccygean ; 15, the eschio-coccygean ; 16, the quadratus ; 17, the external obhque of the abdo- men ; 18, the trapezium; 19, the great serratus; 20, the great pectoral • 21, the latissimus dorsi ; 22, the deltoid ; 23, the subscapular • 24 the coraco-brachialis ; 25, the biceps brachialis ; 26, the supinator ; 27 the long anconaeus ; 28, the short anconseus ; 29, the small anconmus • 3o’ the anterior extensor of the skin of the wing ; 30 a, the portion which goes to the carpus ; 30 b, the portion which goes to the radius ; 31, the posterior extensor of the skin of the wing, divided 32, the long extensor of the metacarpus ; 33, the short extensor of the metacarpus ; 34 cr, the com- mon flexor of the thumb and second Anger ; 34 b, the extensor of the 108 MUSCULAR SYSTEM OE BIRDS. second and third phalanx of the second toe ; 34 c, the short flexor of the thumb ; 35, the radial flexor of the metacarpus ; 36, the ulnar flexor of the metacarpus ; 37, the great glu- teus ; 38, the first adductor of the thigh ; 39, the sartorius; 40,thelarge muscle of the thigh ; 41, the small muscle of the thigh, the tendon of which passes upon the knee, and joins the flexor of the toes ; 42, the common extensor of the leg, the vastus ejcternus and internus ; 43, the first anterior flexor of the leg ; 44, the third flexor of the leg, the semimembranosus ; 45, the fourth flexor, or semi-tendinosus ; 46, the gastrocnemius ; 47, the internal part of this muscle ; 48, the pyra- midal muscle which opens the jaws; 49, the temporal ; 50, the long liga- ment of the lower jaw ; 51, the cu- taneous muscle of the head ; 52, the anterior masseter ; 53, the coniform muscle of the hyoid bone ; 54, the « anterior tibial ; 55, the posterior tibial ; 56, the extensor of the toe ; 57, the flexor of the toe; 58, the long head of the common flexor of the toes ; 59, the tendon of the ex- tensor of the toes ; 60, the abductor •of the internal toes ; 61, the perfo- rated flexor of the three toes ; 62, the fibular muscle ; 63, the abductor of the little toe ; 64, the abductor of the great toe ; a, the pharynx ; h, the trachea ; c, the hyoid ; d, the ear ; e, the humerus ; the radius ; g, the ulna ; h, the thumb ; 2, the tibia ; Ar, the metatarsus ; Z, the great toe ; m, the internal toe ; w, the median toe ; o, the external toe. — CaruSjAnatomie Co7nporee. — T. W. ] 77. — Muscular system of the Falco nisus. or LOCOMOTIOT^. 109 SECTION II. OF LOCOMOTIOIf. § 228. of the most curious and important applications of this apparatus of bones and muscles is for locomotion. By this is understood the movementwhich an animal makes in pass- ing from place to place, in the pursuit of pleasure, sustenance, or safety, in distinction from those motions which are performed equally well while stationary, such as the acts of respiration, mastication, &c. § 229. The means which nature has brought into action to effect locomotion, under all the various circumstances in which animals are placed, are very diversified ; and the study of their adaptation to the necessities of animals is highly interesting in a mechanical, as well as in a zoological point of view. Two general plans may be noticed, under which these varieties may be arranged. Either the whole body is equally concerned in effecting locomotion, or only some of its parts are employed for that purpose. § 230. The medusae (fig. 173) swim by contracting their umbrella-shaped bodies upon the water below, and its resist- ance urges them forwards. Other animals are provided with a sac or syphon, which they may fill with water, and suddenly force out, producing a jet, which is resisted by the surround- ing water, and the animal is thus propelled. The Holothuria (fig. 232), the cuttle-fishes, the salpae, &c. move in this way. § 231. Others contract small portions of their body in suc- cession, which being thereby rendered firmer, serve as points of resistance, against which the animal may strive in urging the body onwards. The earth-worm, whose body is composed of a series of rings united by muscles, and shutting more or less into each other, has only to close up the rings, at one or more points, to form a sort of fulcrum, against which the rest of the body exerts itself in extending forwards. § 232. Some have, at the extremities of the body, a disc, or some other organ, for maintaining a firm hold, each extremity acting in turn as a fixed point. Thus the leech (fig. 178) has a disc, or sucker, at its tail (o), by which it fixes itself ; the body is then elongated by the contraction of the muscular fibres which encircle the animal ; the mouth {a) is next fixed by a similar sucker, and by the contraction of muscles running lengthwise the body is shortened, and the tail, losing its hold, is 110 or LOCOMOTIOIS'. brought forwards to repeat the same process. Most of the hi* valved mollusca, such as the clams, move from place to place in a similar way. A fleshy organ, called the foot, is thrust forward, and its extremity fixed in the mud, or to some firm object, when it contracts, and thus draws along the body and the shell en- closing it. Snails, and many similar animals (fig. 35), have the fleshy under-surface of theirbody («, b) composed of an infinitude of very short muscles, which, by successive contractions — so mi- nute, indeed, as scarcely to be detected — enable them to glide smoothly and silently along, without any apparent muscular effort. § 233. In the majority of animals, however, locomotion is effected by means of organs specially designed for the purpose. The most simple are the minute hair-like cilia, fringing the body of most of the microscopic infusory animalcules (fig. 171), and which, by their incessant vibrations, cause rapid move- ments. The sea-urchins (fig. 174) and star-fishes (fig. 36) have little thread-hke tubes issuing from every side of the body, fur- nished with a sucker at the end. By attaching these to some fixed object, they are enabled to draw or roll themselves along ; but their progress is always slow. Insects are distinguished for the number and great perfection of their organs of motion: they have at least three pairs of legs (fig. 34), and usually two pairs of wings (fig, 369), but those that have numerous feet, like the centipedes, are not distinguished for agility. The Crustacea generally have at least five pairs of legs, which are used for both swimming and crawling. The worms are much less active ; some of them have only short bristles at their sides ; some of the marine species use their gills for paddles. § 234. Among the vertebrata, we find the greatest diversity in the organs of locomotion, and the modes of their application, as well as the greatest perfection, in whatever element they may be employed. The saihng of the eagle, the bounding of the antelope, the swimming of the shark, are not equalled by any movements of insects. This superiority is due to the internal skeleton, which, while it endows the Ji\.in;h.lwit]': great force, gives to the motions, at the same time, a nice di^gree of precision. [§ 235. Before entering upon the study of the various mo- tions of the vertebrate animals, and the means by which these are performed, it is important to put the student in posses- sion of a standard by which he wiU be enabled to compare the form of the osseous elements and the modifications they undergo in fishes, reptiles, birds, and mammals. With this view we THE SKELETON. Ill proceed to give an outline of the structure of the Skeleton of Man (fig. 78), and the uses of its several parts. This bony frame- work is formed of 249 separate pieces, articulated together in Fig. 78. — The Skeleton of Man, 112 THE SKELETO^r. various ways, and divided into the Head, Teunk, and Extee- MiTTES. Some of the bones are single, and disposed on the median line of the body, in which case they are always formed of two halves, the counterpart of each other ; the great ma- jority, however, consist of pairs. The following table exhibits the ^stribution of the bones. CO o O rClaviculae Scapulae Ossa humeri Ulnae Radii Ossa carpi Ossa metacarpi Phalanges digitorum manus Ossa sesamoidea Ossa femoris Patellae I'ibiae Fibulae Ossa tarsi Ossa metatarsi Phalanges digitorum pedis , Ossa sesamoidea 1 2 1 2 8 1 1 2 2 2 2 2 2 1 1 32 1 24 24 2 2 1 1 2 2 2 2 2 16 10 28 4 2 2 2 2 14 10 28 4 COHPOSITIOIS- OE BONES. 113 [§ 236. The internal skeleton of the vertebrata is formed, for the most part, of bone, a substance which is peculiar to this primary division of the animal kingdom. It consists of an organic gelatinous matter, hardened by inorganic earthy particles distributed regularly throughout the animal tissue. The relative proportion of the organic to the inorganic matter varies in the different classes of the vertebrata; the bones of fishes have the least, those of birds the greatest proportion of inorganic elements, whilst reptiles and mammals occupy an intermediate position; the mammals, however, especially the active preda- cious genera, having a larger proportion than the reptiles. From a series of experiments recently made, and conducted with great care, by Bibra,* on thoroughly dried bones of fishes, rep- tiles, birds, and mammals, the following results were obtained. [§ 237. EISHES. Organic . . . Inorganic SALMON. Salmo solar. 60.62 39.38 CARP. Cyprinus carpio, 40.40 59.60 COD. Gadus morrhua. 34.30 65.70 1000 1000 1000 EEPTILES. Organic . . . Inorganic . FROG. Rana esculenta. 35.50 64.50 . SNAKE. Coluber natrix. 31.04 68.96 LIZARD. Lacerta dgilis. 46.67 53.33 1000 1000 1000 MAMMALS. DOLl IIN. Delphinus ^fl/pMs. Organic 35.90 Inorganic . . 64.10 ox.f WILD CAT.f MAN.f Bos taurus. Felis catus. Homo. 31.00 27.77 31.03 69.00 72.23 68.97 1000 1000 iOOO 1000 BIEDS. Organic . Inorganic . GOOSE.f Anser. 67.09 TURKEY.'!* Meleagris qallo-pato. 30.49 69.51 HAWK.f Faleo gallinarius. 26.72 73.28 1000 1000 1000 * Chemische Untersuchungen iiber die Knochen u. Ziihne des Mens- Chen u. der Wirbelthiere, 1844. t From the femur. i il4 ANALYSIS or BONES. [§ 238. The chemical composition of the inorganic consti- tuents of bone in the four clafsses, is shewn in the following table. ANALYSIS OF BONES. Hawk. Man. Tortoise. Cod. Phosphate of Lime with a trace of Fluate ' 64.39 59.63 52.66 57.29 Carbonate of Lime 7.33 12.53 4.90 Phosphate of Magnesia 0.94 1.32 0.82 2.40 Sulphate, Carbonate, and Chlorate of Soda 0.92 0.69 0.90 1.10 Glutin and Chondrin 25.73 29.70 31.75 32,31 Oil 0.99 1.33 1.34 2.00 1000 1000 1000 1000 [§ 239. The piimitive basis of bone, is a subtransparent glairy fluid, resembling mucus in its chemical composition, and containing a multitude of minute corpuscles. When it passes into the stage of cartilage, a number of elliptical nucleated cells make their appearance ; in proportion as the cells increase in size and number, the cartilage hardens, and at the point where ossification is about to commence, they ar- range themselves in linear rows. In the long bones the cell rows are parallel to the axis of the bone, and in the flat bones, they run in rays from the centre to the periphery. The nucleated cells are the agents by which the earthy parti- cles are arranged in order ; and in bone, as in teeth, there may be discerned in this predetermined arrangement, the same re- lation to the acquisition of power and resistance with the great- est economy in the building material, as in the disposition of the beams and columns of a work of human architecture.* [§ 240. The intimate structure of bone can only be studied by the aid of the microscope ; for this purpose, very thin sections of the bones of fishes, reptiles, birds, and mammals, should be prepared and mounted on glass slides in Canada balsam, and covered with very thin glass ; by this means a series of comparative observations may be made. If we take a transverse section of one of the long bones of man, the femur, for example, and examine it with a power of about two hundred linear, we observe that it is traversed by a num- ber of canals called Haversian, which transmit blood-vessels f * Professor Owen’s Comparative Anatomy of Fishes contains ample details on this subject. MICROSCOPIC STRUCTURE OE BONES. 115 tlirougli the substance of the bone ; around each of these canals a series of bony laminae are concentrically arranged, as if they resulted from rings of growth, and reminding us of a transvere section of the branch of a dicotyledonous tree. Between the laminae a number of peculiar spider-like bodies are arranged likewise in a concentric manner ; they have an irregular oval form, with jagged edges, and send out from their circumference a number of small branching tubes, which anastomose freely with the tubes from other cells, forming thereby a complete network of tubes and reservoirs, which traverse the osseous tissue in all directions. The sides of the spider-like bodies lying nearest the Haversian canals, send their small tubes to open into them, by which nutritive fluids passing through the canals are absorbed and trans- mitted through the osseous tissue, so that it is possible to inject the spider-like bodies and the whole system of tubes, by forcing fluids into any of the canals. The spider-like bodies have received different names, as osseous corpuscles, calcigerous cells,* lacunae, or bone cells, according as the observer consi- dered them to be sohd or hollow. The spider-like bodies or bone-cells in man, measure, on an average, about 1-1400 to 1 -2400th of an inch in their long diameter, and about from 1 -4000th to 1 -8000th of an inch in their shortest diameter. The structure between the bone cells has been shewn by Mr. Tomes* to consist of a cellular basis, in which the granular earthy matter of bone is deposited. The granules vary from 1 -6000th to the 1-1 4,000th of an inch in size, and are best shewn in a bone which has been long subjected to the action of boiling water or steam. The microscope, there- fore, enables us to demonstrate that bone is composed of — 1st, granular earthy matter, distributed throughout the cellular tissue ; — 2nd, bone cells and branching tubes, traversing the osseous structure; the former being the hardening material ; the latter for the distribution of nourishment through its substance. This view of the function of the bone cells and tubes is supported by the fact, that there is a constant relation between the size of the bone cell and that of the blood cor- puscle of the same animal, thus : In birds, a transverse section of the femur shews that the Haversian canals are more numerous and smaller, and that Cyclopaedia of Anatomy and Physiology. Art. Osseous Tissue, p. 848. I 2 116 MICROSCOPIC STRrCTIJRE OP BONE. fewer radiating tubes proceed from the bone cells ; in the os- trich the bone cells are from l-1300th to l-2200th of an inch in their long diameter, and from 1 -5425th to l-9600th in their shortest. In reptiles the Haversian canals are few in number, but large in size, and in the same section we observe the canals and the bone cells arranged both vertically and longi- tudinally. The bone cells in the turtle measure 1-3 75th of an inch in length ; in the amphibia, as the siren, they measure 1 -290th of an inch in length. Fishes present considerable variety in the intimate structure of the osseous tissue ; their bone cells have a singular quadrate form ; the ramifying tubes are few in number, and of considerable size, and anastomose freely with the tubes from neighbouring cells, forming thereby a well marked trellis* work in the osseous substance. The specimen before me, a thin section of the scale of an osseous fish, shews this anastomosis most distinctly. The size of the bone cells has been found to bear a remarkable relation to that of the blood corpuscle in the different classes of the ver- tebrata.* [§ 241. The Head is composed of two parts, the cranium, or skull, and the face. The cranium (fig. 79) is a bony case of an oval form, occupying the upper ^nd back part of the head ; it lodges the brain (§ 80), and protects it from injury, and in two of its bones is situated the organ of hearing. The walls are formed of the frontal bone (3), which forms the forehead ; the two parietal bones (1) occupy the sides and roof of the skull ; the two temporal (2) form the walls of the temporal region ; and the occipital (4) is situated at the posterior and inferior part. These bones are firmly united to each other by sutures, the character of which varies in dif- ferent parts of the cranium, and their evident intention being to afford the best kind of mechanism for resisting external violence. Thus, a blow upon the vertex tends to separate the parietal bones from each other and from the frontal, and to force their lower borders outwards ; but this accident is admi- rably provided against by the different kinds of sutures which unite the parietal to the frontal, occipital, and temporal bones, thus a serrated suture locks them together above, to the occi- * For much valuable information on this subject, consult Mr. John Quekett’s papers in the Trans, of the Microscopic Soc. London, vol. ii. part 2. BONES OE THE SKULL. 117 pital behind, and to the frontal before, whilst the temporal bones form the buttresses of this arch, overlapping in a sphced manner the lower border of the parietals, to prevent that portion being thrust outwards. The same mechanical provision prevents the temporal bones from being driven inwards by blows given on the tem- poral region. Fig 80 shews the Fron- to-temporal portion of the frontal bone (os frontis), bounded below by the frontal prominences (1,1), and above by the suture by which it is connected with the parietals. 4, 4, are the temporal arches ; 5, 5, the temporal fossae, in which the temporal muscles are lodged; 10, 10, the superciliary arches ; 11, 11, the supra-orbital holes through which the nerves of that name pass. Fig. 80. 118 BONES or THE SKTJLL. Fig. 81. Fig. 81 is the in- ternal surface of the same bone, shewing the broad and shallow de- pressions (17 and 18) produced by the con- volutions of the ante- rior lobes of the cere- brum and the internal crest (19 and 20), which gives attachment to the dura mater. Fig. 82 represents the external surface of the parietals (ossa pa- rietalia). At its upper (6), anterior (5), and posterior borders (7), are seen the serrated 5 edges of the suture, and at its lower border (8), the bevelled edge, which is overlapped by (he temporal bone. Fig. 83 is the inter- nal surface of the same bone, and at the lower anterior angle is shewn the canal (12) for lodg- ing the middle artery of the dura mater, which is here seen to groove the bone with its numerous branches (b). On the internal sur- face of the parietal bones (fig.- 84) we ob- serve the longitudinal groove, sulcus longi- fMdinalis (1, 1, 1), for the longitudinal sinus BONES or THE SKULL. 119 Fig. 84. of the brain, and a number of little pits (2, 2, 2, 2), more or less deep, in which the glan dulse pacchionse are situated : there are also the impressiones digitatse (3, 3, 3, 3), and emi- nentise ma- millares, (4, 4, 4, 4), produced by the con- volutions of the brain ; the groov- ings for the meningeal arteries are seen at 5, 5, 5, 5, and the parietal holes at 6, 6. [§ 244. The tempo- rals (ossa temporiim), fig. 85, are of an irre- gular form, and consist of three portions, the squa- mous (I), the mammillary (II), and the petrous (HI.) Fig. 86, represents the ex- Fig. 86. ternal surface of the squam- ous portion (a), with the root of zygomotic process (2), and the glenoid cavity for the head of the lower jaw. (6). The internal surface of the same portion (fig. 87) exhi- bits the bevelled edge that overlaps the parietals, and the depressions (b) for receiving the convolutions of the cerebrum. External surface 120 BONES or THE SKULL. Fig. 87. Figs. 88 and 89 represent the anterior and posterior surfaces of the petrous portion of the temporal bone in which the in- ternal ear is situated. These parts, consisting of the tym- panum and its ossicles, the labyrinth with the vestibule, semicircular canals, and coch- lea, have been already de- scribed in our section on the internal ear. § 150 to^ 154. [§ 245. Fig. 90 shews the external surface of the occi- pital bone (o5 occipitis), with its arched protuberances (10), for giving attachment to the muscles of the neck, and the large aperture {foramen magnum) (13) serving for the passage of the spinal cord. The basal portion is seen at (14) ; at each side of the foramen magnum are seen the condyles (16, 16), by which the skull rests upon the first vertebra of the neck, and moves backwards and for- wards thereon. Fig. 90* represents the in- ternal surface of the os occi- pitis, which behind the fora- men magnum (13), is divided into four cavities by a crucial ridge (23, 23,24, 24). To the vertical spine, above the trans- verse portion, is attached the falx cerebri, and to that below, the falx cerebelli, whilst to the transverse ridge the tentorium is attached : the cavities above the transverse spine (21, 21) are for lodging the posterior lobes of the cerebrum, and those below (22, 22), for the cere- bellum; the upper surface of the basal process (14) is hol- lowed out to receive the medulla oblongata. Posterior face. EONES OF THE SKULL. 121 The nead is almost in equilibrium on the condyles (16, 16), but that portion situated in front of the joint is heavier than that placed behind it, hence it overweighs the latter : this ne- cessitates the presence of more powerful muscles in the pos- terior region of the neck, to maintain the head erect upon the spinal column; when these become relaxed, as in sleep, the head falls forward upon the chest. [§ 246. The sphe- noid and ethmoid bones. Fig. 91 (1, 2), are wedged between the cranial bones at the base of the skull, and may be said to be common to the cra- nium and the face. [§ 247. The face is formed by the union of fourteen different shaped bones, which form five large cavi- ties for lodging the organs of vision, smell, and taste. All the bones of the face, the lower jaw excepted, are completely im- moveable, and firmly united to each other Fig. 90. Fig. 90*. 122 BONES or THE SKULL. and to the bones of the skull ; the principal of these are the superior maxillaries, Fig. 92 (2), forming nearly the whole of the upper jaw, and which are connected with the frontal bone in such a manner as to contribute to the formation of the orbits (4) and the nasal cavities (fig. 93,6); they form the anterior part of the roof of the mouth, and unite with the malar bones (1), to constitute the prominence of the cheeks ; behind they unite with the palate bones. In the interior of the nasal fossae are found two spongy bones (figs. 94 and 95), curiously folded, upon which the mucous membrane of the nose Fig. 92. is spread. It is through the horizontal cribriform plate of the ethmoid bone, which separates the nasal cavity from that of the skuU, that the olfactory nerves proceed into the nasal fossae BOIS^ES OE THE SKULL. 123 (13;; this plate, being pierced with numerous holes for their transit ; the cavity of the nose is further increased by commu- Fig. 94. Fig. 95. Partition of Nostrils. Transverse vertical section of Orbits, Nostrils, and Palate. nications established between it and the sinuses existing in the frontal and superior max- Fig. 96. illary bones, and which are lined „ //i ) by a continuation of the nasal membrane. Fig. 96 shews the lateral boun- dary of the nose, and the passages leading to and from the frontal and maxillary sinuses. [§ 248. Fig. 97. The debits (10) are two deep conical cavities, with their base directed outwards ; they are destined protect the eyes. Thereof of the or- bit is formed by a thin plate of the frontal bone (fig. 81, 18) ; the floor chiefly by the superior max- illary (11), the internal wall by the ethmoid and lachrymal (3,4) ; the latter bone is grooved for the passage of the nasal duct (1 1), which conveys the tears into the nose ; the external VJIl Lateral boundary. to lodge and 124 BOXES OF THE SKULL. wall is formed by the malar (6) and a part of the sphenoid bones ; the latter bounds the apex of the orbital cone ; in it are pierced holes for the passsage of the optic and other nerves appertaining to the organ of vision. The Qrbit contains the muscles that move the eye-ball, and in its upper and outer region, the lachrymal gland. Fig. 99. [§ 249. The greater part of the nose is form- ed by cartilages, so that in the skull the anterior opening of the nasal cavity (fig. 98, 29) is very large, and the osseous portion of the nose formed by the two small nasal bones (fig. 99, 2), makes an inconsiderable promi- nence. The nasal ca- Posterior boundary, vity is divided by a vertical partition into two fossae, as seen in fig. 99, 5 and 28, which shews the posterior boundary of the nose ; superiorly it is hoUowed out of the ethmoid bone, the interior of which is full of cells ; and its floor is formed by the superior maxiUary. Anterior boundary. Fig. 101. [§ 250. The superior maxil- lary bones (figs, 100 and 101) contain the teeth ofthe upper jaw; in infancy this bone is compos- ed of several ele- ments, one of which, called the intermaxillary, I remainsas a per- manently dis- tinct bone in monkeys and other quadrupeds, whilst in man it is early sol- dered to the superior maxillary. Fig. 100 shews the internal. BONES OP THE SKULL. 125 Pig. 102. and fig. ]01 the external surface of the superior maxillary, with the sixteen teeth, four incisors, two canine, and ten molars in situ. Fig. 102 exhibits the palate plates of the superior maxillary (2), and the palatine bones (3), together with ^ the arch formed by the sixteen teeth j (1, 1)^ [§251. The lower jaw, in the adult, is composed of a single bone ; in the infant, it consists of two branches united along the median line ; and this separation is permanent in a great many animals, whilst in reptiles and fishes each branch consists of seyeral distinct bones united together. In man the lower jaw (figs. 1 03 and 1 04) has some resemblance to a horse shoe ( with the branches bent up- wards at an obtuse angle ; it contains sixteen teeth, and is articulated to the glenoid cavity of the tem- poral bone by a prominent condyle (12) ; in front of the condyle rises a second eminence, called the coro- noid process (14), serying for the attachment of the tem- poral muscle. The eleyatory muscles of the lower jaw are all attached near its angle (3), they conse- quently act at a short dis- tance from the fulcrum, the condyle (12), whilst the resistance is situated at a distance from the power; the masseter and ptery- goid muscles are fixed to the inside as well as to the out- side of the lower jaw ; they are fleshy and powerful. Internal surface, for the purpose of raising the jaw with force, for crushing External surface. Rg. 104. 126 BONES or THE TEUNK. and dividing the substances introduced between the teeth. The mechanical disadvantage arising from having the power thus placed so near the fulcrum, is compensated by the greater rapidity of motion which such an arrangement permits, whilst sufficient vital power is given to the elevatory muscles to admit of the sacrifice of lever power. When a hard body is introduced between the teeth, requiring an unusual force to break it, we instinctively carry the body far back in the mouth, in order to bring it more immediately under the power of the lever. The motions of the jaws of quadrupeds will he treated of more in detail, when the anatomical structure of the rumi- nants, carnivora, and rodents is under special investigation. The Tetjnk. [§ 252. The most essential part of the skeleton is the verte- bral column, of which the skull may be considered an expan- sion, consisting, as it does, of three vertebra, the elements of which have undergone great development, to encompass and enclose the three primary divisions of the brain. The osseous appears to follow the cerebro-spinal system, in the various phases of its development, and may be regarded as a satellite moving round the primary nervous centres. The vertebral column occupies the middle line of the body, forming the central axis, which sustains all the other parts of the skeleton. It is composed in man of thirty-three vertebrae, arranged into those of the neck, back, loins, sacrum, and coccyx. [§ 253. A vertebra (fig. 105) is one of the segHients of Fig. 105. the internal skeleton constituting this axis, and forming canals OEKYICAL VEETEBEJE. 127 for protecting the central trunks of the nervous and vascular systems, and to which, likewise, sometimes, appendages are attached. A typical vertebra consists of a centre {centrum), and ten processes {apophyses). From the upper part of the centrum rise two neur apophyses, which form an arch for enclosing the spinal cord and brain. These are sur- mounted by a spine, called the neural spine. From the sides of the centrum two transverse processes, or par apophyses, pro- ject, which sometimes carry ribs, or pleur apophyses. From the under side of the centrum two processes descend to enclose the vascular trunks, in the same manner as the neurapophyses en- close the spinal cord, they are called hcBmapophyses ; from them descends a single hcemal spine. The vertebral elements un- dergo various phases of development in. the different classes, and in different regions of the spinal column of the same animal ; it is therefore only by taking a philosophical view of their structural development in the animal series that we obtain a knowledge of the beautiful law which produces such endless variety out of a few simple elements. [§ 254. The ceevical veetebe^ (figs. 106 and 107) are smaller than the others. We ob- serve in them a deviation from the typical form existing in the dorsal region, fig. 105 ; the transverse pro- cesses, fig. 107 {g, g), par apophyses, and pleur apophyses, are rudi- mentary, and soldered together, forming a hole (8), through which the vertebral artery passes to the brain ; the hcEma- pophyses are absent. This explanation of the structure of the transverse processes of the cervical vertebrae is beautifully illustrated in the neck of struthious birds. In all mammals we find seven cervical vertebrae. The first vertebra of the neck, the atlas (figs. 108 and 109), supports the skull ; it is more moveable than the others, and differs considerably from the. typical form; the centrum (^) is much reduced to receive a toothlike process, rising from the centrum of the second ver- tebra (fig. 110, k) ; around this pivot the atlas revolves, and 106. Fig. 107. 1:^8 CEBVICAL VEBTEBB^. the lateral movements of the head are accomplished thereby, whilst the upward and downward movements are performed by Fig. 108. Fig. 109. the play of the condyles of the occipital bone (fig. 90, 16) on the broad concave articular surfaces of the atlas (fig. 108, 2). Fig. 108 shews the superior, and fig. 109 the inferior surface of this vertebra. A firm ligament is stretched across the ring, dividing it into two apertures ; the anterior hole ( 1 ) receives the tooth- like process of the axis, the posterior hole (6) gives passage to the spinal cord. The essential element of a vertebra is the centrum^ the next in constancy are the two neurapophyses, the other elements undergo various phases of development. We rarely find all the elements present in one vertebra; some are absent, others are rudimentary, and others expand into disproportionate dimensions, in order to accomplish some destined end. A typical vertebra with all its elements, presents four channels disposed around the centrum; we find this typical vertebra in the thorax of mammals, birds, and lizards. Let us take, for example, the third, fourth, or fifth dorsal vertebra of man (fig. 105) : the centrum («, h) is broad, solid, and slightly biconcave ; from its posterior part arise the two neur apophyses (fig. 105, 7), which arch over and enclose the spinal cord (6), and terminate in the neural spine (5) ; the two transverse ox par apophyses are seen at (4, 4) ; to the sides of the centrum the dorsal ribs or two pleur apophyses are attached (fig. 1 2Ay,\hohcemapophyses are represented by the sternal cartilages, which are united to the distal extremity of the ribs ; the hcemal element is a broad flat bone, forming one of the segments of the sternum ; these five elements unite to form one of the large hoops of the thoracic cage (fig. 124), for enclosing and protecting the heart and the great trunks of the vascular system ; the lateral channels giving transit to the nerves and blood-vessels. DORSAL VERTEBRA. 129 Fig. 110 is the axis or second vertebra of the neck, with the round tooth-like process {k) rising from Fig. no its centrum (1) ; from the extremity of this process two strong ligaments pass obhquely outwards, to be attached to the occipital bone ; (2) is the articular surface, which plays on a like process of the atlas (fig. 109, 3). The seventh vertebra (fig. Ill) differs from the other cervical, in being larger, processes (4, 4) single, with a hole in each for the transmission of the vertebral veins ; constituting a transition to the typical form met with in the middle re- gion of the thorax. [§ 255. The dorsal yertebr^ (figs. 112 and 113) diminish in size from the first to the fourth or fifth, from which they increase to the twelfth, which is the largest of all. The centrum (1, a, 5,) is longest in the antero-posterior direction ; the parapophyses (4, 4,) are short and stout, and the neurapo having the transverse Fig. 111. Fig. 112. Fig. 113. physes (6) broad, and inclined to form a complete osseous tile- like case for protecting the spinal cord ; the neural spine (5) is long, and direct- ed obliquely downwards, terminating in a tubercle for muscular attachment. The number of the dorsal vertebrae corresponds with the number of the ribs, which in man amounts to twelve pair. Fig. 114 shews the articulation of the xth, xith, and xiith dorsal vertebrae, and the changes of form which the centrum and K 130 LUMBAR YERTEBR^. apophyses present, when Fig. 114. and the pleur apophyses are absent. compared with the fourth and fifth ; (figs. 112 and 113) parapophy- ses and pleur apophyses are short, and the hcemapophyses have disap- peared. We here see a transition form, for blending with the ver- tebrae of the loins. [§ 256. The lumbar verte- bra (figs. 115 and 116) are of a larger size than those in the dor- sal region ; they are five in num- ber, and have the long diameter of the centrum in the trans- verse direction ; the neural spine presents a considerable surface for the tendinous attachment of the muscles of the back and loins ; iho^parapophyses are short. Fig. 115. Fig. 116. Fig. 1 1 7 represents the fifth lumbar vertebra, which differs from the others in having the under surface of its centrum oblique, so that the anterior is deeper than the posterior part, whereby it is better adapted for articulating with the sa- crum, and affording us another example of a phase of transi- tion from one form to another. SACEUM Am) COCCYX. 131 [§ 257. The Saceum (fig. 118) is of a triangular shape, its base (1) facing upwards and forwards ; its apex, which is Fig. 117. Fig. 118 truncated (2), also facing forwards. It is concave before (5), from above downwards, and irregularly convex behind (fig. 120, a) in the same direction. Fig. 119. Fig. 120. In the young subject it consists of five verte- brae, which in the adult become soldered into a single bone. In mammals it is much narrower than in man, and forms in them a straight line with the spine ; the separate pieces thereof remaining permanently united by ligaments. In animals which sometimes hold themselves erect, as monkeys, bears, sloths, and many rodents, it is proportionally larger than in other mammals. On the concave anterior surface of the sacrum we observe holes (4) for the passage of the nerves ; and on its posterior surface (fig. 120), similar apertures (11, 11, 11) for the same purpose are seen. Fig. 119 is a profile of this bone. [§ 258. The Coccyx consists of four small bones, which re- tain only a rudimentary centrum, and are soldered together in man (fig. 119, 2.) These bones are, in fact, the rudiment of an organ, the tail, which attains great importance and dimensions in some animals, as shown in the comparative table (§ 260). [§ 259. The Yeetebe^ are firmly united together by pro-- cesses of bone (fig. 1 1 4 — 1 1 6, 2 and 3) that lock into each other. Between every two vertebrae, an elastic fibro- cartilaginous cushion K 2 132 SPINAL COLUMN. is interposed, converted into Fig. 121. By this arrangement the chain of bones is a strong elastic central axis, more or less move- Fig. 122. hie in different animals, ac- cording to the general struc- ture and habits of each. Fig. 121 exhibits a front view of the spinal column of man. It is of a pyramidal form, the base of the pyramid rests upon the sacrum, and the apex supports the skull. We observe, likewise, that the diameter of the bodies of the vertebrae differs in different regions, being broad in the neck, narrow in the back, and broad again in the loins. Fig. 122 represents a pos- terior view of the spinal co- lumn. The different forms of the neurapophysesy in the cer- vical, dorsal, and lumbar re- gions, are here shewn. They are observed to project back- wards and a httle downwards in the neck; they lieobhquely downwards in the back, and stand backwards in the loins. On each side of the neural spines, a groove is seen formed by a junction of the arches of all the vertebrae ; bounded internally by the neural spines, and externally by the para- pophyses ; in this groove the muscles are lodged that im- part motion to the column. Fig. 123 is a lateral view of the spinal column, which presents anteriorly two con- vex, and one concave surface. SPINAL COLUMN. 133 The upper convexity is formed by the lower cervical and the upper dorsal vertebrae, and the lower convexity by the lum- Fig. 123. vertebrae ; whilst the central conca- vity is formed by the middle dorsal ver- tebrae. Behind the centra we see the lateral holes for giving transit to the spinal nerves, and formed by the junction of the notches in the neur apophyses. The direc- tion of the neurapophyses and parapophy- ses is likewise well seen in this figure. [§ 260. The following table* shows the number of the vertebrae in the different regions of the spinal column, in a few familiar examples from mammals, birds, reptiles, and fishes. It is important to note, that the number seven prevails in the cervical vertebrae of all mammals, whether we study these bones in the rudi- mentary condition in which they exist in whales, or in the enormous development they attain in the neck of the giraffe. The increased number of the bones in the same region, in birds, is a compensa- tion for the want of anterior prehensile members, the neck, in birds, being used as an arm. The number of the dorsal vertebrae ranges from 7 to 320 ; the lum- bar, from 2 to 9 ; and the coccygeal, from ... 4 to 115. The table might have been ' greatly extended ; but those who wish for further information on this interesting branch of comparative osteology, are re- ferred to the great work from which it is extracted : — Cuvier, Le9ons D’Anatomie Comparee, tom. i. 134 NUMBER or THE TERTEBRa:. COMPARATIVE TABLE OF THE NUMBER OF THE VERTEBRiE. MAMMALIA. Cervi- . cal. Dorsal. ! Lumbar. Sacral. Coccy- geal. Total. Man 7 12 5 5 4 33 Long-tailed Monkey . . 7 12 7 3 31 60 Lion 7 13 7 3 26 56 Long-tailed Opossum . . 7 16 6 2 36 64 Long-tailed Ant-eater . . 7 16 3 6 40 72 Elephant 7 20 3 4 27 61 Giraffe 7 14 5 4 18 48 Whale 7 15 9 1 27 59 BIRDS. Vulture 15 7 13 6 41 Swallow 13 7 10 7 37 Turkey 14 7 15 6 42 Ostrieh 18 9 — 19 9 55 Crane 17 10 — 15 6 48 Swan 23 11 — 16 8 58 REPTILES. Tortoise 9 10 3 20 42 Monitor (Lizard) 6 21 2 2 115 146 Python (Boa) — 320 — — 102 422 Rattle- Snake — 171 — — 36 207 Land Salamander .... 1 14 — 1 26 44 Axolote 2 18 — — 42 62 FISHES. Perch __ 21 __ 21 42 Mackerel 15 16 31 Trichiurus — 60 — — 100 160 Salmon — 34 — — 22 56 Cod .. — 19 , — — 34 53 Conger Eel — 60 — — 102 162 Electric Eel — j — 236 Shark — 95 — 1 270 365 BONES OP THE THOBAX. 135 [§ 261. The Thoeax is formed by the twelve dorsal ver- tebrae, the ribs, and sternum ; the vertebrae have their elements well developed in this region, to form an osseous cage for pro- tecting the heart, lungs, and great bloodvessels (fig. 1 24). The ribs, 0^ pleura- jrig. 124. vophyses, are attached by a head to the cen- trum, and by a tubercle to the parapophyses ; the hcemapo- physes, or car- tilages, are un- ossified, and removed to the distal end of the ribs; they unite before with the AcemaZbones,or sternum, which is here placed in the median line. The hcemal elements play an important part in the eco- nomy of many animals. In birds and tortoises, the sternum is widely expanded, its deep keel afibrding a large surface for the attachment of the pectoral muscles in birds (fig. 77), and for the same muscles in the mole and the bat among mammals. In man, only seven of the twelve ribs form a complete hoop, as the hcemapophyses of the five inferior ribs are united together, and the hcemal ele- ments of these are wanting. In crocodiles, the hcemapophyses, or sternal ribs, are ossified ; and similar ossified apophyses are continued along the fore part of the abdomen to the pubis. Rudiments of these abdominal ribs are seen in the transverse tendinous intersections of the rectus abdominis muscles in THE PELYIC AECH. 13t) man and other mammals ; which attain their culminating point in the reptilian type of structure, where they exist under the form of true abdominal ribs. [§ 262. The extremities are united to the trunk by two girdles of bone, composed in the upper of the scapular, and in the lower of the pelvic arches. The scapular arch presents many modifications, to adapt the anterior members as instru- ments for prehension and locomotion. The pelvic arch is of a more uniform structure, as the posterior extremities form in- struments of locomotion alone. § 263. The Pelyic arch (fig. 125) is composed of three pair of bones, which are separate in infancy, but soldered together in the adult. One of these hones, the ilium («), is firmly YW 1?7. Fig. 128. I THE PELYIC AECH. 137 united to the sacrum, and another, the pubis, joins its fellow from the opposite side, forming the crown of the arch, whilst the ischium is wedged in between them ; these three bones form the ossa innominatum of the human anatomist. Figs. 127 and 128 represent these haunch bones, (i) is the ilium (ii), the ischium, and (iii) the pubis. The broad ihac bones form the brim of the pelvis (fig. 125), they afford sup- port to the viscera of the abdomen, and give attachment by both their surfaces to the large and powerful muscles by which the thigh is moved, and the trunk retained erect upon the lower extremities. The brim of the pelvis (a, a, a, a) differs in the two sexes. In the male (fig. 126), the greatest diameter is in the antero-posterior ; in the female (fig. 125), in the trans- verse direction. A comparative view of the outlet {b, b, b, b) (figs. 129 and 130) in a male and female pelvis, shews this opening to be of a diamond form, having the angles before, behind, and on the sides. In the male (fig. 130), the outlet is Fig. 129. Outlet. Fig. 130. small; in the female (fig. 129), it is large. The greatest diameter is from the sacrum to the pubis in the female, in con- sequence of the sacrum being less curved than in the male. The space comprised between the brim and the outlet is called the true pelvis, in which the pelvic viscera are lodged. On each side of the pubic arch a large oval hole (obturator foramen), is formed by the ischium and pubis. It 131. gives passage to blood vessels and nerves, and is partly closed by a ligament. On each side of the obturator hole, but some- what behind that opening, is the cup- shaped cavity for receiving the head of the thigh bone (acetabulum) (fig. 131, c), formed by the junction of the ihum (i). 138 THE THIGH BOHE. the ischium (ii), and pubis (iii). The continuity of the mar- gin is interrupted at the under and fore part, by a notch (/), which is filled up with ligament. Opposite the notch is a cavity (g), to which the round hgament of the femur is attached. The axis of the pelvis is so placed that the weight of the trunk Fig. 132. Fig. 133. Fig. J34. does not rest on the outlet, but upon the tu- berosities of the ischia (fig 132, a). The open- ing of the outlet, there- fore, points downwards and backwards, and that of the brim for- wards and upwards. [§ 264. The Thigh is composed of a single bone, the femur (figs. 133 and 134). It con- sists of a head, neck, trochanters, body, and condyles. The round head (1) has a pit for the insertion of the round ligament (2), which is accurately adapted to the ace- tabulum and retained therein by ligaments and atmospheric pressure. The neck (3) connects the head with the shaft or body. At the point where it joins the latter, we observe two BONES OF THE LEO. 139 large projections. The larger (5) is called the great, and the smaller (7) the lesser trochanter, which serve for the attach- ment of the principal motory muscles of the thigh. The body (9 9) is arched before, and slightly concave behind, where we observe a rough projecting line (linea aspera) (10), which like- wise affords a firm surface for the attachment of the muscles of the thigh. The lower end of the body expands into two large condyles (12, 13), of which the inner (13) is longer and larger. Fig. 134 represents a front view, and fig. 133 a back view of the femur. The condyles move upon the head of the tibia only in one plane. The knee joint is, there- fore, apure hinge, its motions being restricted by lateral and crucial ligaments, whilst the round head of the femur forms, with the acetabulum, a ball and socket joint, and executes thereby movements in all directions. [§ 265. The Leg (fig. 137) consists of two bones, the tibia (ii) and fibula (iii). The tibia has a broad head, on which the condyles of the femur play ; to its upper surface is attached, by a ligament, a small round bone, the patella (i), or knee-pan, which protects the joint in front, and changes the direction of the tendons descending from the thigh to be inserted into the tibia, and thereby enabling them to act more advantageously upon the leg. The fibula (iii) is a slender bone placed at the external side of the tibia. It affords attachment to muscles, and assists in the formation of the ankle joint. The latter joint, however, being formed chiefly by the lower end of the tibia; that bone supporting the entire weight of the body. [§ 266. The Foot consists of the Tarsus, Metatarsus, and Toes. Fig. 138 shews these parts of the foot. A is the tarsus, B the Fiir. 138. Fig. 137. 140 BONES or THE EOOT. metatarsus, c the phalanges of the toes. The Taestjs con- sists of seven bones arranged in two rows. In the first row Eig. 139. (fig. 139) is the astragalus (i), os navicular e (ii), os calcis (iii). The articulation with the leg is formed by the astragalus, which projects above the rest, and fits into the |j space between the tibia and the fibula. The astragalus (i) rests upon the heel bone, os calcis, (iii), which projects backwards, and is connected before with the navi- cular bone (ii). The second row (Fig. 140) consists of three Fig. 140. Fig. 141. wedge-shaped ^ V bones, 055^ CM- neiformia (it, Y, vi), and the cuboid bone, os cuboides (yii). The con- cave posterior surfaces (i, i, i, i) articulate with the first row of the tarsal bones and the convex an- terior surfaces (fig. 141, 2, 2, 2, 2) with the metatarsal bones. [§ 267. The METATAESHS consists of five bones (fig. 142), of which the first, or that of the great toe, is the shortest and largest, and that of the second he longest. The bases (a) have flat articular surfaces to join them with the tarsus, and heads (c) or articular sur- faces for the phalanges ; the middle part is the body (b), which is convex above and broad beneath. [§ 268. The toes consist of fourteen bones (fig. 143), of which there are but two rows ir i Under surface. Fig. 142. Bases. THE SCAPULAR ARCH. 141 Under surface. to the great toe (i), and three to the other toes (ii, iii, lY, y) ; their division is similar to that of the fingers, into base, body, and head, but they are much shorter Eig. 143. and flatter. The foot of man is distin- guished from the corresponding part in the quadrumana by its ca- pability of being planted flat upon the ground, and the strength of the base thus afforded ; the paral- lelism and magnitude of the great toe, the advanced position of the astragalus, the backward < extension of the heel, the fixed condition of the tarsus, the strength of the metatarsal bones and those of the phalanges, form the distinctive differences between the foot of man and that of monkeys : when we notice an ourang or chimpanse attempting to walk erect, the foot is seen resting on its outer side, the heel scarcely projecting, and they can only sustain the erect position by supporting their hands upon some body. [§ 268*. The internal side of the foot is constructed as an arch, for lodging and protecting the blood vessels, nerves, and tendons of the toes ; this arch likewise forms a spring by which sudden shocks are diminished, the elasticity of the tarsal and meta- tarsal articulations contributing to this end ; the jar being broken thereby before.it is transmitted to the limb. This pro- vision is still further developed in the feet of certain animals, like the cats, which bound after their prey ; in addition to the elasticity of the tarsus and metatarsus, their feet are sup- phed with elastic pads, to break the shocks occasioned by their springing habits. [§ 269. The Scapular, like the pelvic arch, consists of three pair of bones, the scapula, the coracoid and the clavicle, which are the homologues of the ilium, the ischium, and the pubis ; early in life, in man, the coracoid becomes soldered to the scapula, and is described as a process of the latter bone, but it exists as a distinct element of the scapular arch in rep- tiles and birds, and in the ornythorhyncus among the mono- trematous mammalia. Fig. 144 shews the right half of the scapular arch of man in 142 BONES OF THE SHOULHEE. Fio*. 144. situ. The clavicle (1) is seen resting its internal head upon the first bone of the sternum, and having its external end attached byhgaments y to the acromion process of the scapula ; the clavi- cle maintains the shoulder at a fixed distance from the trunk. [§ 270. The scapula is a large flat bone, situ- ated on the upper and external part of the back. It is of a triangular form, and at its upper and external angle expands to form a shallow cavity, called Fig. 145. Fig. 146. Fig. 147. U the glenoid cavity (4), in which the head of the humerus is received ; on the upper part of the body a prominent ridge of bone rises (13), which passes upwards and out- wards, and terminates in the acromion process (14), which is expanded over the top of the joint, forming the bony piojection of the shoulder. The coracoid process (16) is attached by a thick root to the anterior and upper part of the neck of the hone (5), and curves forwards and out- BONES OP THE AEM. 143 wards before the glenoid cavity ; the scapula is articulated by the smooth face of the acromion process (15), to the clavicle ; and affords an extensive attachment to the muscles of the shoulder and those belonging to the arm and fore-arm ; this bone is present in all animals possessing anterior members, although its form undergoes many changes in birds and rep- tiles. Fig. 145 represents the posterior view. Fig. 146, the anterior view. Fig. 147, a profile of the scapula. [§ 271. The clayicle, so called from its resemblance to Fig. 148. an ancient key, is divided into a body, two extremities, two arti- cular surfaces, and two processes. Its shape is that of a small Itahc /, placed horizontally ; its inner or sternal extremity (1) is very large, and irregularly cylindri- cal ; upon its point is a large articular surface (2), by which it joins with the interarticular car- tilage placed between it and the sternum ; the round arched body expands and forms the scapular extremity (4), having on its under surface a tuber (5), for the attachment of liga- ments, and upon the outer extremity a plain articular sur- face (6), by which it is united to the acromion process of the scapula. The principal use of this bone is to keep the shoulders apart, and complete the resistance of the scapular arch in those animals, as the quadrumana and rodents, that use their anterior members as prehensile instruments, and in the bats and birds, whose anterior members are organs of fiight ; as the down-stroke of the wing tends to force the humerus inwards ; in birds, likewise, the coracoid bone appears as a distinct element of the arch. [§ 272. The htjmekhs (fig. 149) is the homologue of the femur, and, like it, is formed of a head, neck, body, and con- dyles. The large round head (1) is received into the shallow glenoid cavity (fig. 147, 4), by which great freedom of motion in all directions is obtained ; the neck (5) is short and thick, and the body (6) appears as if the upper part were twisted out- wards, and the lower part inwards, the outer side of the body presenting a rough surface (9) for the attachment of muscles. The lower extremity of the shaft is enlarged to form a pulley-hke surface, upon which the ulna moves in one plane ; the outer 144 BONES OE THE AEM. Fig. 149, condyle (13) projects but little, whilst the inner condyle (14) forms a considerable promi- nence which projects inwards ; the condyles afford an exten- sive surface for the attach- ment of the muscles of the fore-arm ; behind the inner condyle is a deep fossa (19), for receiving the olecranon pro- cess of the ulna, and above the condyles, on the front of the bone, is a pit (18) for receiving the coronoid pro- cess of the same. Fig. 149 gives a front view, fig. 150 a back view of the humerus ; fig. 151, the round head and tubercles (3, 4) ; fig. 152, the lower surface of the con- dyles, (15) is the surface on which the head of the radius plays, (16) receives the sig- moid cavity of the ulna, and (17) is a groove for the pas- sage of the ulnar nerve. [§ 273. The fore-arm con- sists (fig. 153) of two bones, the Radius and the Ulna, which are the homologues of the tibia and the fibula. These bones lie nearly pa- rallel to each other, the ra- dius (1) on the outer, and the Fig. 15i. Fig. 152. ulna (11) on the inner side of the arm; they are united hy hgaments, and by a fibrous membrane stretched across the interspace between them ; they have, however, a considera- ble range of motion upon each other and upon the humerus. The flexion and extension of the forearm is performed by the ulna (1), which forms, with the humerus, a true hinge joint. At its upper part we observe the olecanon process (fig. 153), which locks into a cavity (fig. 150, 19) on the posterior BONES OF THE FORE-ABM. 145 surface of the humerus ; which acting as a stop, renders exten- sion beyond the straight line impossible. The hand is attached to the lower end of the radius ; and as that part was pig. 153. designed to perform pronation and supination, a pecuhar mechanical provision was necessary for these important motions. The round head of the ra- dius (fig. 153, ii) is bound by a firm annular liga- ment to the ulna (i), and the concavity on its sur- face is received in a corresponding convexity on the outer condyle of the humerus. Hence both bones move upon the humerus, in acts of flexion and extension, whilst the radius rolls upon the ulna, carrying with it the hand in pronation and supination, separate sets of muscles being as- signed to each class of movements. It is only among the higher mammals that any motion is permitted between the bones of the fore-arm. These motions ' are most important in man ; for without them the hand would be incapable of a vast variety of movements so necessary to the full develop- ment of the purposes for which that instrument was designed. When the free motions between /ill} the bones of the fore-arm are impaired by injury Fig. 154. 146 BOI^ES OF THE CAEPUS. or disease, we learn the amount of importance they confer upon the hand. [§ 2/4. The HAra consists of the Caepus, Metacaeptjs, and Phalahoes; of these, part of the carpus (fig. 154 a), with the radius, form the wrist joint ; the metacarpus (b) forms the palm of the hand, and the phalanges (c) the fingers. [§ 275. The Caepus consists of eight bones, forming an IV. Upper surface. Lower surface. 1 V . there are, in the first row (figs. 155, 156), on the outside the os scaphoides (i), on its inner side the os lunare (ii), next it the os cuneiforme (m), and on the front of that bone the os pisiforme (iy) : in the second row (figs. 157, 158), on the outside is the os trapezium (y), next to it the os trape- zoides (yi), to its inner side, the os mag- num (yii), and next to Fig. 157. Fig. 158. V VI VII VIll VIII VII VI V that the os unciforme (yiii). Of these bones the first row is articulated above with the radius, and the interarticular car- tilage at the extremity of the ulna, and below with the second row ; the second row articulates above with the first row, and below with the bases of the metacarpal bones. [§ 276. The Meta caepus consists of five bones (fig. 158*), each of which is divided into its upper part, or basis (a) ; middle or body, corpus (b) ; and lower part or head, caput (c), which forms the knuckle, and projects when the fingers are bent. Upon the bases are articular surfaces for the carpal bones. [§ 277. The thumb and fingers of each hand consist of four- teen pieces, or phalanges (fig. 159) ; of these twelve belong to the fingers, and are disposed in three rows, those of the middle finger (iii) being longest, and of the little finger (y) shortest ; BONES OF THE META.CAEPTTS AND PHALANCES. 147 Fig. 158.* Bases. Front. whilst the thumb (i) has but two, its middle phalanx being de- ficient, but they are strong- er than those of the fin- gers. [§ 277. The PHALANGES consist of base (fig. 159) (1), body (2), and head (3) ; they taper from the base, or upper part of the head, the intermediate part or body being rounded be- hind, and flat before, with two projecting lateral edges for giving attachment to the sheaths of the ten- dons. [§ 278. In reviewing the structure of the upper ex- tremity, we have seen that it consists of a series of levers joined together, and diminishing progressively in length. Thus, the arm is longer than the fore-arm ; the lat- ter is longer than the hand ; and each joint of the fingers is short- er than the one which it succeeds. By this admi- rable arrangement the nu- merous joints in the hand permit that useful instru- ment to vary its motions in a thousand chfFerent ways, to adapt it to the various bo- dies it is designed to handle, grasp, and touch; whilst the long levers formed by the arm and fore-arm allow the hand to be rapidly changed to a con- siderable distance in all directions. It is principally by the movements of the humerus upon the scapula, that the direction of the limb is given ; the flexion and extension of the fore-arm L 2 148 OEGAFS or L0C0M0TI055’ regulating the length ; whilst the multiplied movements of the thumb and fingers perform the special acts which the hand was designed so admirably to execute. The quadrumana, like man, have the thumb opposable to the other fingers. It is this, in fact, which forms the true character of the hand. But the bones of the thumb in man are more lengthened and powerful, in propor- tion to the other fingers, than in monkeys, whose hand does not equal his in perfection ; for monkeys can neither seize minute objects with that precision, nor grasp and support large ones with that firmness which is so essential to the dextrous performance of the multitudinous purposes for which the hand of man was designed. — T. W.] 1. Plak op the OnoAHS op Locomotiot^. § 279. The organs of progression in vertebrated animals never exceed four in number, and to them the term limbs is more particularly applied. The study of these organs, as characteristic of the different groups of vertebrate animals, is most interesting, especially when prosecuted with a view to trace them all back to one fundamental plan, and to observe the modifications, oftentimes very slight, by which a very sim- ple organ is adapted to every variety of movement. No part of the animal structure more fully illustrates the unity of de- sign, or the skill of the Intellect, which has so adapted a single organ to such multiplied ends. On this account we shall illustrate the subject somewhat in detail. § 280. It is easy to see, that the wing which is to sustain the bird in the air (fig. 164), must be different from the leg of the stag (fig. 160), which is to serve for running, or the fin of the fish (fig. 168) that swims. But, notwithstanding their dis- similarity, the wing of the bird, the leg of the stag, and the shoulder fin of the fish, may still be traced to the same plan of structure ; and if we examine their skeletons, we find the same fundamental parts. § 281. In the arm of man (fig. 78), the shoulder-blade is fiat and triangular ; the bone of the arm is cylindrical, and enlarged at its extremities ; the bones of the fore-arm are nearly the same length as the humerus, but more slender ; the hand is composed of the eight small bones of the carpus, arranged in two rows, five metacarpal bones, which are elon- gated, and succeed those of the wrist ; five fingers of unequal length, one of which, the thumb, is opposed to the four others. IN VEETEBRATED ANIMALS. 149 § 282. In the stag (fig. 160), the hones of the fore-arm (c, d,) are rather longer than that of the arm (5), and the radius no longer turns upon the ulna, pig. igq. but is blended with it ; the metacarpal or cannon-bone (/), is greatly deve- loped; and being quite as long as the fore-arm, it is apt to be mistaken for it. The fingers (g) are reduced to two, each of which is surrounded by a hoof, at its extremity. § 283. In the arm of the lion (fig. 161), the arm bone (b) is stouter, the carpal bones (e) are less numerous, and the fingers (/) are short, and armed with strong, retrac- tile claws (ff). In the whale (fig. 162), the bones of the arm (6) and fore-arm (c, d,) are much shortened, and very massive ; the hand is broad, the fingers (g) strong, and distant from each other. In the bat (fig. 163), the thumb, which is represented by a small hook, is entirely free, but the fingers L-cdf Fi?. 161 Fig. 162. Fig. 163. Fig. ]64. are elongated in a disproportionate manner, and the skin is stretched across them, so as to serve the purpose of a wing. 150 ORGANS or LOCOMOTION In birds, the pigeon, for example (fig. 164), there are but two fingers (^), which are soldered, and destitute of nails ; and the thumb is rudimentary. § 284. The arm of the turtle (fig. 166) ispecuhar in having. Fig. 165 besides the shoulder-blade («), the coracoid bone and the cla- vicle; the arm-bone (Z>) is twisted outwards, as well as the bones of the fore-arm (c, d), so that the elbow, instead of being be- hind, is turned forwards ; the fingers (^) are long, and widely separated. In the sloth (fig. 16.5), the bones of the arm (b) and fore-arm (c, d) are very greatly elongated, and at the same time very slender; the hand is hkewise very long, and the fingers (ff) are terminated by enormous non-retractile nails. The arm of the mole (fig. 167) is still more extraordinary. The shoulder- blade («), which is usually a broad and flat bone, becomes very narrow ; the arm-bone (b), on the contrary, is contracted so much as to seem nearly square, the elbow projects backwards, and the hand (e, f, g) is excessively large and stout. § 285. In fishes, the form and arrangement of the bones is so pecuhar, that it is often difficult to trace their correspondence to all the parts found in other animals ; nevertheless, the bones of the fore-arm (c, d) are readily recognized. In the cod (fig. 168), Fig. 168. there are two flat and broad bones, one of which, the ulna (cT), pre- sents a long point, anteri- IN YEETEBEATED ANIMALS. 151 orly. The bones of the carpus {e) are represented by four nearly square little bones ; but in these, again, there are considerable variation in dilferent fishes, and in some genera they are much more irregular in form. The fingers are but imperfectly represented by the rays of the fin {g), which are composed of an infinitude of minute bones, articulated with each other. As to the humerus and shoulder, their analogies are variously interpreted by different anatomists. § 286. The form of the members is so admirably adapted to the especial offices which they are designed to perform, that by a single inspection of the bones of the arm, as represented in the preceding sketches, one might infer the uses to which they are to be put. The arm of man, with its radius turning upon the ulna, the delicate and pliable fingers, and the thumb op- posed to them, bespeak an organ for the purpose of handling. The slender and long arm of the sloth, with his monstrous claws, would be extremely inconvenient for walking on the ground, but appropriate for seizing upon the branches of trees, on which these animals live. The short fingers, armed with re- tractile nails, indicate the lion, at first glance, to be a carnivo- rous animal. The arm of the stag, with his very long cannon- bone, and that of the horse also, with its single finger en- veloped in a hoof, are organs especially adapted for running. The very slender, and greatly elongated fingers of the bat are admirably contrived for the expansion of a wing, without in- creasing the weight of the body. The firm and solid arm of the bird indicates a more sustained flight. The short arm of the whale, with his spreading fingers, resembles a strong oar. The enormous hand of the mole, with its long elbow, is con- structed for the difficult and prolonged efforts requisite in bur- rowing. The twisted arm of the tortoise can be applied to no other movement than creeping ; and, finally, the arm of the fish, completely enveloped in muscles (fig. 76), presents, ex- ternally, a mere delicate balancer, the pectoral fin. § 287. The posterior members are identical in their struc- ture with the anterior. The bones of which they are com- posed are, 1. The pelvis (figs. 125 and 169), which corre- sponds to the shoulder blade ; 2. The thigh bone, or femur, which is a simple bone like the humerus ; 3. The bones of the leg, the tibia and fibula, which, like the radius and ulna, some- times coalesce into one bone ; and lastly, the bones of the foot. 152 THE MODES OF PROGRESSIOI?'. which are divided, like those of the hand, into three parts, the tarsus, metatarsus, and toes. Their modifications are generally less marked than in the arm, inasmuch as there is less diversity of function ; for in all animals, without exception, the poste- rior extremities are used exclusively for support or locomotion. § 288. The anterior extremity of the vertebrata, however varied in form, whether it be an arm, a wing, or a fin, is com- posed of essentially the same parts, and constructed upon the same general plan. This affinity does not extend to the in- vertebrata, for although in many instances their limbs bear a certain resemblance to those of the vertebrata, and are even used for similar purposes, yet they have no real affinity. Thus the leg of an insect (fig. 34), and that of a camel (fig. 169), the wing of a butterfly, and the wing of a bat, are quite similar in form, position, and use ; but in the bat (fig. 1 63) and the camel (fig. 169), the organ has an internal bony support, which is a part of the skeleton ; while the leg of the insect has merely a horny covering, proceeding from one of the rings of the body, and the wing of the butterfly is merely a fold of the skin ; showing that the limbs of the articulata are constructed upon a different plan. It is by ascertaining and regarding these real affinities, or the fundamental differences existing between similar organs, that the true natural grouping of ani- mals is to be attained. 2. Oe STANDIKa, Ai^D THE MODES OF PrOGRESSIOIS-. § 289. Sta^^dikg, or the natural attitude of an animal, de- pends on the form and functions of the limbs. Most of the terrestrial mammals, and the reptiles, both of which employ all four limbs in walking, have the back-bone horizontal, and resting at the same time upon both the anterior and posterior extremities. Birds, whose anterior limbs are intended for a purpose very different from the posterior, stand upon the latter, when at rest, although the back-bone is still very nearly hori- zontal. Man alone is designed to stand upright, with his head supported on the summit of the vertebral column. Some monkeys can rise erect upon their hind legs ; but this is evi- dently a constrained posture, and not their habitual attitude. § 290. In standing, it is requisite that the limbs should be so disposed that the centre of gravity may fall within the space included by the feet. If the centre of gravity be with- THE MODES OE PEOGEESSION. 153 out these limits, the animal falls to that side towards which the centre of gravity inclines. On this account, the albatros, and some other aquatic birds which have their feet placed very far back, cannot use them for walking. § 291. The more numerous and the more widely separated the points of support are, the firmer an animal stands. On this account, quadrupeds are less liable to lose their balance than birds. If an animal has four legs it is not necessary that they should have a broad base. Thus we see that most quadrupeds have slender legs touching the ground by only a small surface (fig. 169). Broad feet would interfere with each other, and only increase the weight of the limbs, without adding to their stability. Birds are furnished with long toes, which as they spread out, subserve the purpose of tripods. V Oy cervical vertebrae ; v d, dorsal vertebrae ; v I, lumbar vertebrae ; v s, the sacrum ; v g, caudal vertebrae ; c, the ribs ; o, scapula ; h, the humerus; c (ly the carpus ; m c, the metacarpus ; p h, the phalanges; cw, the radius and ulna ; / e, the femur ; r o, the patella ; t i, the tibia ; t a, the tarsus ; rn ty the metatarsus. 154 THE MODES OF PEOGEESSION. Moreover, the muscles of the toes are so disposed that the weight of the bird causes them to contract firmly, hence birds are enabled to sleep standing, in perfect security, upon their perch, and without effort. § 292. In quadrupeds, the joints at the junction of the limbs with the body bend freely in one direction only, that is, to- wards the centre of gravity ; so that if one limb yields, the tendency to fall is counteracted by the resistance of the limbs at the other extremity of the body. The same antagonism is observed in the joints of the separate limbs, which are flexed alternately in opposite directions. Thus the thigh bends forwards, and the leg backwards ; while the arm bends back- wards, and the fore-arm forwards. Different terms have been employed to express the various modes of progression, accord- ing to the rapidity or the succession in which the limbs are advanced. § 293. Peogeessioh is a forward movement of the body, effected by successively bending and extending the limbs. Walkiivg is the ordinary and natural gait, and other paces are only occasionally employed. When walking is accom- plished by two limbs only, as in man, the body is inclined forwards, carrying the centre of gravity in that direction, and whilst one leg sustains the body, the other is thrown for- wards to prevent it from falling, and to sustain it in turn. For this reason, walking has been defined to be a continual falling forwards, interrupted by the projection of the leg. § 294. The throwing forwards of the leg, which would re- quire a very considerable effort were the muscles obliged to sustain the weight of the limbs also, is facilitated by a very peculiar arrangement ; that is, the joints are perfectly closed up, so that the external pressure of the atmosphere is sufficient of itself to maintain the limbs in place, without the assistance of the muscles. This may be proved by experiment. If we cut away all the muscles around the hip-joint, the thigh-bone still adheres firmly to the pelvis, bat the moment a hole is pierced, so as to admit air into the socket, it separates. § 295. In ordinary walking, the advancing leg touches the ground before the other is raised ; so that there is a moment when the body rests on both limbs. It is only when the speed is very much accelerated, that the two actions become simultaneous. The walking of quadrupeds is a similar process. THE MODES OE PROOEESSIOIS-. 155 but with this difference, that the body always rests on two legs at least. The limbs are raised in a determinate order, usually in such a manner that the hind-leg of one side succeeds the fore-leg of the opposite side. Some animals, as the giraffe, the lama, and the bear, raise both legs of one side at the same mo- ment. This is called ambling ox pacing, § 296. consists of the same successions of motion as walking, so accelerated that there is a moment between two steps when none of the limbs touch the ground ; in the horse and dog, and in most mammals, a distinction is made between the walk, the trot, the canter, and the gallop, all of which have different positions or measures. The trot has but two measures. The animal raises a leg on each side, in a cross direction ; that is, the right fore leg with the left hind leg, and so on. The canter has three measures. After advancing the two fore legs, one after the other, the animal raises and brings forward the two hind legs, simultaneously. When this movement is greatly urged, there are but two measures ; the fore legs are raised together, as well as the hind legs, it is then termed a gallop. § 297. Leapi^^^g consists in a bending of all the limbs, fol- lowed by a sudden extension of them, which throws the body forwards with so much force as to raise it from the ground, for an instant, to strike it again at a certain distance in ad- vance. For this purpose, the animal always crouches before leaping. Most animals make only an occasional use of this mode of progression, when some obstacle is to be surmounted ; but in a few instances, this is the habitual mode. As the hind legs are especially used in leaping, we observe that all leaping animals have the posterior members very much more robust than the anterior ; as frogs, kangaroos, jerboas, and hares. Leaping is also common among certain birds, especially among sparrows, thrushes, &c. Finally, there is also a large number of leaping insects, such as fleas, grasshoppers and crickets, in which we find the posterior pair of legs much more developed than the others. § 298. Climbikg is merely walking upon an inclined or upright surface. It is usually accomplished by means of sharp nails ; and hence many carnivorous animals climb with great facihty, such as the cat tribe, hzards, &c., many birds, the woodpeckers and parrots, &c., have the toes arranged in two 156 THE MODES OF PE0GEESSI01S-. divisions, so as to grasp branches like a forceps. Others hke the bears employ their arms for this purpose ; monkeys use their hands and tails ; and parrots their beaks. Lastly, there are some whose natural mode of progression is climbing ; such as the long-armed sloths, which, when placed upon the ground, move very awkwardly ; yet their structure is by no means defective, for in their accustomed movements upon trees, they use their limbs with very great adroitness. § 299. Most quadrupeds can both walk, trot, gallop, and leap ; birds walk and leap ; lizards neither leap nor gallop, but only walk and run, and some of them with great rapidity. No insect either trots or gallops, but many of them leap. Yet their leaping is not always the effect of the muscular force of their legs, as with the flea and grasshopper ; but some of them leap by means of a spring, in the form of a hook, attached to the tail, which they bend beneath the body, and which, when let loose, propels them to a great distance, as in the FodurellcB. Others leap by means of a spring, attached beneath the breast, which strikes against the abdomen when the body is bent ; as the spring-beetles {Elaters) . § 300. Flight is accomplished by the simultaneous action of the two anterior limbs, the wings, as leaping is by that of the two hinder limbs. The wings being expanded, strike and compress the air, which thus becomes a momentary support, upon which the body of the bird rests. But as this support very soon yields, owing to the slight density of the air, it follows that the bird must make greater and more rapid efforts to compensate for this disadvantage. Hence it requires a much greater expenditure of strength to fly than to walk ; and therefore, we find the great mass of muscles in birds concentrated about the breast (fig. 77). To facilitate its flight, the bird, after each stroke of the wings, brings them against the body, so as to present as little re- sisting surface to the air as possible, and for the same end all birds have the anterior part of the body very slender. § 301. Some quadrupeds, as the flying squirrel, Galeopithe^ cus [and flying lizard, Draco vola/ns\ have a fold of the skin at the sides, which in some extends to the legs, thereby enabling them to leap from branch to branch with more facihty. But this is not flight, properly speaking, since none of the peculiar operations of this act are performed. There are also some THE MODES OE PROGEESSIOH. 157 fishes, whose pectoral fins are so extended as to enable them to dart from the water, and sustain themselves for a short time in the air ; and hence they are called flying fishes. But this is not truly flight. § 302. Swimming is the mode of locomotion employed by the greater number of aquatic animals. Swimming has this in common with flight, that the medium in which it is performed being also the support of the body, readily yields to the impulse of the fins. But water being much more dense than air, and the body of most aquatic animals being nearly the same weight as the water it displaces, it follows, that in swimming, very little effort is requisite to keep the body from sinking. The whole power of the muscles is consequently employed in progression, and hence swimming requires much less muscular force than flying. § 303. Swimming is accomplished by means of various organs, designated under the general term fins^ although, in an anatomical point of view, these represent very diSerent parts. In whales, it is the anterior extremities, and the tail, which are transformed into fins. In fishes, the pectoral fins, which represent the arms, and the ventral fins, which repre-- sent the legs, are employed for swimming, but they are not the principal organs ; for it is by the tail, or caudal fin, that progression is principally effected. Hence the swimming of a fish is precisely that of a boat under the sole guidance of the scuUing-oar. In the same manner as a succession of strokes, alternately right and left, propels the boat straight forwards, so the fish advances by striking alternately right and left with its tail. To advance obliquely, it has only to strike in the opposite direction. Whales, on the contrary, swim by a vertical movement of the tail ; and it is the same with a few fishes also, such as the rays and the soles. The air-blad- der facilitates the rising and sinking of the fish, by enabling it to vary the specific weight of its body. § 304. Most land animals swim with more or less ease, by simply employing the ordinary motions of walking or leaping. Those which frequent the water, like the beaver, or which feed on marine animals, as the otter, the duck, and other palmi- pedes, have webbed feet, the toes being united by membranes, which, when expanded, act as paddles. § 305. There is also a large number of invertebrate animals. 158 THE MODES OF PEOOEESSION. in which swimming is the principal, or the only mode of pro- gression. Lobsters swim by means of a vertical motion of their tail. Other Crustacea have a pair of legs fashioned like oars ; as the posterior legs in sea crabs, for example. Many insects, likewise, swim with their legs, which are abundantly fringed with hairs, to give them surface ; as the httle water boatmen {Gyrinus, Dytiscus), whose mazy dances on the sum- mer streams every one must have observed. The cuttle-fish uses its long arms as oars, and some star-fishes {Comatula, Eu7'yale), use their rays with great adroitness. Finally, there are some insects which have their hmbs constructed for run- ning on the surface of water, as the water spiders {Ranatra, Hydrometra) . § 306. A large number of animals have the faculty of mo- ving both in the air and on the land, as is the case with most birds, and a large proportion of insects. Others move with equal facility, and by the same members, on land and in water, as some aquatic birds and most reptiles. The latter have received the name amphibia on this account. There are some which walk, fly, and swim, as ducks and water-hens ; but they do not excel in either mode of progression. § 307- However different the movements of the limbs may appear to us, according to the element in which they are per- formed, we see that they are the effect of the same mechanism. The contraction of the same set of muscles, causes the leg of the stag to bend in leaping, the wing of the bird to flap in flying, the arm of the mole to strike outwards in digging, and the fin of the whale to row in swimming. CHAPTER SIXTH. NUTRITION. § 308. The second class of functions are those which relate to nutrition and the perpetuation of the species ; the functions of vegetative or organic life. § 309. The increase of the volume of the body requires additional materials. There is also an incessant waste of par- ticles, which, having become unfit for further use, require to be carried out of the system. Every contraction of a muscle ex- pends the energy of some particles, whose place must be sup- plied by others. These supplies are derived from every natural source, the animal, vegetable, and mineral kingdoms ; and are received under every variety of solid, liquid, and gaseous form. Thus, there is a perpetual interchange of substance between the animal body and the world around. The conversion of these supplies into a suitable material, its distribution to all parts, and the assimilation and appropriation of it to the growth and sustenance of the body, is called Nutbition, in the widest sense of the term. § 310. In early life, during the period of growth, the amount of substances received is greater than that which is lost. At a later period, when growth is completed, an equilibrium be- tween the matters received and those rejected is established. At a still later period, the equilibrium is again disturbed, more is rejected than is retained, decrepitude begins, and at last the organism becomes exhausted, the functions cease, and death ensues. §311. The solids and fluids taken into the body as food are subjected to a process called Digestion, by which the solid portions are reduced to a fluid state, the nutritive particles separated from the excrementitious, and the whole prepared to become blood, bone, muscle, &c. The residue is afterwards expelled, together with those particles of the body which re- quire to be renewed, and those which have been derived from the blood by several processes, termed Secretions. Matters in a gaseous form are also received and expelled with the air we 160 ISUTETTION. Dreathe, by a process called Respiration. The nutritive fluids are conveyed to every part of the body by currents, usually confined in vessels, and which, as they return, bring l)ack the particles which are to be either renovated or expelled. This circuit is termed the Circulation. The function of Nutrition, therefore, combines several distinct processes. SECTION I. OP PIGESTIOIf. § 312. Digestio^^, or the process by which the nutritive parts of food are elaborated and prepared to become blood, is effected in certain cavities, the stomach and intestines, or alu mentary canal. This canal is more or less complicated in the various classes of animals ; but there is no animal, however low its organization, which is destitute of a digestive sac. [§ 313. In the Hydraform Polypipeea, as in the common fresh-water polype {Hydra viridis), the body consists of a diges- tive sac, with a row of simple tentacula disposed around the mouth, fig. 170. When the polype is watching for its prey it remains expanded, with its tentacula widely spread in all directions, to seize a passing victim. No sooner does a larve, or worm, or crustacean, impinge upon one of these organs, than it is arrested in its course as if by some ma- gical influence : it appears fixed to the almost invisible thread, and in spite of its efibrts, is unable to escape. The prey, seized in this manner, and repre- sented in fig. 1 70, is conveyed into the sto- mach (a), which has the appearance of a delicate film, stretched over the contained animal. If we watch attentively the pro- cess of digestion, we observe the outhne of the included victim gradually becom- ing more indistinct : soon are the soft parts dissolved, and reduced to a fluid mass; and if any hard parts remain, as the shells of Cypris or Baphnia, these are expelled through the oral aperture. It is impossible to say by what process the nutritive product of The Hydra viridis. POLYPS AIS^D II^PrSORIA. 161 digestion enters the system of the hydra, as no vessels have been discovered in them ; that the colour of the granular parenchyma depends in some measure on the nature of the food is satisfactorily shown ; thus, when a polype feeds upon red larvse, or upon black planarise, the granules acquire a similar hue, although the fluid in which they float remains colourless ; these granules move about in the parenchyma of the animal, and give the appearance of globules of blood un- dulating at large through the general tissue of the polype. Should the Hydra be made to fast for a considerable time, the granules lose their colour, and become almost transparent, in a manner similar to that by which the blood-globules of frogs lose their redness during the winter months, when de- prived of nourishment. [§ 314. The researches of Ehrenberg have demonstrated that the Iotusoria admit of a natural division into two groups, founded on the degree of development of their diges- tive organs ; the one group comprehends those in the interior of whose bodies numerous cellular globules are seen, into which alimentary matters pass : from the many gastric cavities pos- sessed by these animalcules they are called Poltgastrica (fig. 171). In the second group we find a more perfect organization ; the mouth is large, opening into an esophagus and stomach, in which are found gastric teeth, a distinct intestine, and anus ; around the head are numerous ball-shaped bodies, furnished with cilia, which perform motions resembling those of a revolv- ing wheel. The group is therefore called Rotirera (fig. 172). The structure of the digestive organs of many of the inferior forms of polygastrica is still involved in much obscurity ; but in the higher forms, as in Leucophrys patula (fig. 171), these organsbecome visible when the animalcule has been fed with minute particles of carmine diffused through the water. The bodyis covered with long cilia, which form a circle round the mouth, their vibrations causing currents of water to flow therein, together with the minute particles on which Leucophrys subsists ; the intestine is seen taking a winding course through the body, having appended to its walls numerous globular cells, many 171.— Leucophrys of which are distended with colouring patula. 162 ORGANS OE DIGESTION. matter, and forming a natural injection of the gastric cavi- ties ; the anus opens at *, from which egesta are often seen exuding. [§ 314. The Eosphora najas is tyjhcal of the rotifera. The body (fig. ] 72) is enclosed in a double elastic tunic, into which the muscles are inserted ; its anterior part is truncated, and furnished with globular bodies armed with vibratile ciha; this rotatory apparatus is moved by muscles inserted into the base of the ciliiferous organs ; the eyes are seen at a, a, h ; the pharynx (c) is large and capacious, and the stomach {d) is provided with a triturating apparatus, which in many allied genera is armed with jaws. The intestine terminates in the anus at d; the ovary, with many ova, is seen at /. The posterior extremity of the body is fur- nished with a pair of forceps, by which the rotiferae attach themselves at pleasure. [§315. The digestive organs in the Aca- LEPHiE present many phases of develop- Fig. 172. — Eosphora ment ; in some, their pendant arms are traversed by tubes, through which aliments pass to reach the gastric cavity. The most remarkable structure of this class exists in the Rhizostoma Cuvieri, of which a longi- tudinal section is seen in fig. 1 73 ; the gastric cavity (6), sur- rounded by four respiratory chambers, occupies the upper part of the disc ; the peduncle, hanging from the centre of the disc, divides into eight arms, four of which are seen terminating in spongy expansions, and perforated with numerous apertures, leading into a common channel (c) ; these vessels traverse the centre of the tentacula; in the middle and upper part of each of the arms are numerous fimbriated folds, in which ves- sels ramify that likewise open into the central canals ; these, uniting two and two, enter the gastric cavity by four principal trunks. The walls of the stomach are divided by dehcate septee from the four ovarial sacs (d), which open externally by distinct apertures {a, a) ; from the periphery of the stomach sixteen vessels radiate, which divide and anastomose as they proceed towards the margin of the disc, where they form a net- ACALEPH^ AND ECHINODEEMS. 163 work of vessels, in which the blood is exposed to the oxygen- ating influence of the water, whilst the rhizostome floats like a gigantic animalcule through the sea. The aliments gain ad- mission to the stomach 5 only through these ab- sorbent tubes, which re- mind us of a type of structure so common in plants ; in the Medusa aurita the mouth is large and patent, and can be closed by a sphincter muscle ; the stomach is divided by septae ; in these cavities fishes are sometimes found, in dif- ferent states of digestion. The ciliograde tribe, as in the Beroe pileuSy have a digestive tube, passing straight through the body; from thewalls 173.-Rhizobtoma Cuvieri. of which numerous vessels take their origin, to traverse the structure of this most elegant acalephe, the marvels of whose organization can only be understood after patient observation with the microscope. [§ 316. The Echinodeems afford a striking illustration of the law of progressive development, in the structure of their skeleton, and internal organs. In the Asterias the mouth is surrounded by tubular tentacula, and protected by fasciculi of spines ; the short esophagus leads into a capacious stomach, occupying the central disc, provided with a mucous lining, and covered by a muscular layer ; from the stomach branches proceed into each ray ; around these canals a number of ceecal processes cluster, regarded as rudimentary glands : in Ophiura and Euryale the ceecal processes are absent. In Comatula, which connects the sea-stars with the urchins, the stomach occupies the central disc, and leads into a long intestine, which makes two turns around that organ. The mouth forms a large opening at one side of the under surface, and the intestine terminates in a prominent aperture, at the opposite side. In M 2 164 OEGAKS OF DIGESTIOif. the urchins the mouth is for the most part armed with jaws and teeth, and the oral and anal openings, gradually becoming more separate, occupy distinct positions on the shell; ’m Echinus and Cidaris, the mouth is found at the under pole, and the anus at the upper pole of their globular shells. Fig. 1 74 shows the structure of a common urchin (Echinus esculentus) ; the test Fig. 174. — The anatomy of the Echinus esculentus. ts divided near its equator, and the small section is raised to shew the mouth from above ; A is the lantern, with the pyramids and teeth ; the esophagus {m) is long and dehcate, and continuous with the stomach {n) ; the first convolution of the intestine is seen at o, and the second at q, r; the rectum (5) terminates in the centre of the opening formed by the circle of ovarial plates, and surrounded by the branching ECHINODERMS AT^D BRTOZOOA. 165 ovaries {t), which open by canals passing through each of the five ovarial plates. The auricles surrounding the mouth (^) give attachment to the lantern ; the ambulacral avenues (c) give passage to tubular feet ; the simple spines {a) arming the shell are moved by muscles ; the small trident spines, or pedicellariee (6), move like forceps, and the long tubular feet (c) are protruded by the injection of a fluid ; an oblong vesi- cle (/) opens near the mouth ; the intestine is retained in sitit by a delicate mesentery (^), on which blood-vessels ramify ; currents of water flow constantly through the shell, their course being directed by the vibratile cilia covering the lining mem- brane of the test; the net-work of blood-vessels ramifying upon these membranes is therefore bathed by the sea-water, and maintained in a state of oxygenation, so that the whole in- terior of the shell of urchins is a great respiratory chamber. In the Holothuria (fig. 232) the long and uniform intestinal canal makes several convolutions before terminating in the cloaca; around the mouth are numerous csecal salivary ves- sels ; a mesentery retains the intestine, and affords an ex- tensive surface for the ramification of blood-vessels ; the re- spiratory tubes are distinct from the general cavity of the body, and form an arborescent organ like a rudimentary lung. [§ 317. In the Brtozooan Poltpieera, as the Pluma- tella (fig. 175), the digestive organs present a much higher phase of development than in the hydraform group, and mani- fest an approach to the type of the tunicated mollusca. The mouth is surrounded by a circle of ciliated tentacula, the vibra- tions of which cause currents of water to flow towards the oral aperture ; the possession of ciliated tentacula forming one of the distinctive features of this group. The mouth, situated in the centre of the tentacular circle, leads into a long saccu- lated stomach, the walls of which are studded with glandular specks, or biliary follicles. From about the middle of the stomach the intestine proceeds, and ascending close to its walls, opens by a rectum near the mouth (c), in such a position that the excrementitious matter ejected therefrom is at once carried away by the currents sweeping round this region ; the in- testinal canal is Attached to the sac by muscular bands, and. floats freely in the visceral cavity. The tegumentary sheath is an organic portion of the polype, and, after enclosing 166 ORGANS OF DIGESTION. the internal organs, is reflected over the aperture of the cell, and becomes continuous with the tentacular circle. In con- sequence of this union be- tween the pu- lype and its cell, it follows, that when the animal retires therein, that portion of the tunic (c) pushed out- wards by the exit of the po- lype, is drawn inwards on its retreat by a process of in- vagination, so that the flex- ible extremity of the cell is at the same time a sheath for the body, a support to the tentacula, and a door for closing it. In fig. 17o, muscular bands are seen passing from the inner membrane of the cell to the body of the polype, by which the retraction of the animal and the invagination of the superior part of the cell is effected. At a, we see the natural size of the polypedom of Plumatella; at b and c, the cells and polyps magnified and protruded in search of prey ; at d, the polype withdrawn into its cell, and the orifice closed by the retraction (c) of the integument. [§318. In the Tunicated Mollusca the digestive organs are very simple. At the bottom of the cavity formed by the muscular mantle is found the mouth, a simple absorbent tube, opening into the stomach ; that organ is surrounded by the follicles of the liver, the ducts from which enter its cavity; the short intestine terminates near the ventral aperture of the muscular sac. [§319. In the Conchifera, as in the oysler (O^trea edulisj fig. 176), the mouth, surrounded by four labial plates (r), opens into an oval stomach {a) ; the intestine (d, f) makes Fig. 175. — Plumatella repens. — a, natural size ; h, the same magnified. CONCHIFEEOUS MOLLUSCA. 167 tvo turns through the body, terminating in the rectum (^’), at the posterior border of the shell ; the liver (i) is very laige, surrounding the digestive tube, and the biliary ducts open into the stomach, as in the tun cata ; the large branchial leaflets {h, k) f)r respiration are covered by the mantle (/); in them we find the cells for lodging the ova ; the adductor nuscle (g, h) serves f)r closing the valves cf the shell, and at iis internal side is seen tlie heart (i). [§ 320. The Gas- rEEOPODA possess more perfect organs of prehension than the preceding class ; here we find not only complicated tubes for absorbing, but likewise organs for mastication and de- glutition. Some gasteropoda (Buccinum Mur ex Voluta) are furnished with a singular and powerful organ, the proboscis, which they can protrude at pleasure to a considerable dis- tance from the mouth. In the Buccinum (whelk) it is in the form of a hollow tube, surrounded by muscular fibres ; on laying open this sheath we find a bifid cartilaginous tongue, provided with sharp, silicious recurved teeth, and sending out two long processes behind, into which numerous powerful muscles are inserted ; on the right side of the tongue is the opening of the esophagus. The proboscis, in a state of re- pose, is lodged in a distinct cavity, into which it is retracted by numerous longitudinal muscles, having a close analogy in their arrangement with the fleshy columns in the heart of the mammalia. At the point where the esophagus diverges from the proboscis, in Paludina vivipara (fig. 35), it is surrounded by two salivary glands, which insert their ducts at this part ; these glands are always considerably developed in this class ; 168 ORGANS OF DIGESTION. the esophagus now runs a short course, and near the stc;- mach dilates into a small crop, opening into a round mem- branous stomach, surrounded or imbedded in the substance of the liver ; the length of the intestine is considerably less than that of the esophagus ; it describes a turn, di- lates into a ^\ide colon, and terminates on the right s;de, under the open mantle ; the liver is of considerable size, occu- pying the spiral turns of the shell, and, as in the preceding classes, pours its secretion by numerous ducts into the sto- mach. The digestive organs of other gasteropoda are fomed after the same type. The Patella (or limpet) feeds on marine vegetables, and is always found in situations where they are most abundant. It is deprived of a proboscis, but the mouth is armed with % long, slender, convoluted tongue, studded with rows of sharps silicious recurved teeth (fig. 194), by which it exercises a filing process on its vegetable food. The wide sacculated esopha gus opens into a large stomach of a lengthened form, sur rounded by the liver ; the long convoluted intestinal canai makes several turns through the structure of this organ, and finally opens into a dilated rectum ; the long salivary vessels empty themselves into the esophagus. The Helix (snail) and Limax (slug) have large lips, which may be regarded as the rudiments of a proboscis ; the upper jaw of the garden snail (Helix aspera) is furnished with sharp teeth, which perforate and file down the leaves of plants. The short esophagus, having passed through the nervous collar, di- lates into a large membranous stomach, contracted in the centre, into the posterior half of which the biliary ducts enter ; the in- testine, having made a turn through the liver, passes up along the right side of the body, and opens by a small orifice at the margin of the respiratory sac. In the Fleur o-branchus the digestive organs are remarkable for their complex structure, and for the resemblance the stomach bears to the compound stomach of ruminating quadrupeds. The esophagus is dilated into a membranous bag, or paunch, into which the biliary ducts open ; to this succeeds a globular muscular organ, analogous to the second or honeycomb sto- mach of ruminants ; this leads to a membranous organ, provided internally with longitudinal folds of the lining membrane, the analogue of the leafiet, or manyplies, and, lastly, into a fourth. GASTEROPODOTJS MOLLUSCA. 169 or true chylific membranous stomach ; the second chamber is traversed by a muscular gutter, leading from the first to the third stomach. The digestive organs of Aplysia Camelus fsea hare, fig. 177) are not less singular, being not only equally complex, but in addi- tion, having the inter- nal membrane of the second stomach, or giz- zard, armed with carti- laginous bodies. The pharynx {a) is large and muscular ; the straight esophagus {b) having traversed the nervous collar (m), soon dilates into an ample membra- nous crop (o, o), turned into a semilunar form. This leads into a strong muscular gizzard (p), internally armed with rhomboidal semi-cartila- ginous plates, their ac- tion being analogous to the teeth found in the stomach of the lobster, and, like them, perform- ing a similar bruising function. This muscu- lo-cartilaginous organ opens into a third chy lific stomach {q), the in- ternal surface of which is furnished with sharp recurved horny spines, most numerous around the pyloric orifice ; into this region of the canal the ducts from the liver {u, u), and the termination of a glandular ceecal appendage, the pancreas, pour their secretions. It is extremely interesting, in a physiological point of view, to study Fig. 177. — The anatomy of the Aplysia Camelus. 1/0 ORGAIS'S OF DIQESTIOTs^. the development of the glandular organs connected with the assimilating functions. In Holothuria we have seen salivary vessels developed in the form of a series of blind processes surrounding the mouth. In the mollusca these organs are glandular, and extend through nearly half the body in Aplysia {s, v) ; the liver in the mollusca is likewise glandular, whilst in the articulated animals it is composed of a series of con- voluted vessels. A rudimentary pancreas exists in some mollusca, which, like the salivary vessels, in Holothuria^ assumes the form of a long blind secreting sac. The intes- tinal canal (s) in Pleuro-hranchus and Aplysia presents nothing very remarkable ; it makes several turns through the structure of th liver, terminating in the rectum {t), which opens near the branchial, or respiratory aperture {d) ; the ovary (v), the oviduct (v’) and its appendage (y) occupy the posterior part of the body, surrounded by the testes (w) and the epididymus {x) ; ascending from the latter is seen the common generative canal (z, z) ; the heart, consisting of an auricle (/3) and a ventricle (S'), is placed near the branchiae (b) ; the principal artery {t) runs forwards to supply the dif- ferent organs situated at the anterior part of the body ; the gastric artery (tt) and the hepatic (tt’) artery are given off from the root of the principal trunk. In Bulla lignaria the plates lining the muscular sto- mach, or gizzard, acquire the consistence of shell ; they are moved by powerful muscles, and perform the part of stomach jaws. Among the gasteropodous mollusca the liver is a very voluminous organ, divided into many lobes, and very distinct from the intestine ; thus, in the garden snail, whelk, &c., it occupies the several turns of the shell, embracing the convolutions of the intestine, and pouring its secretion, by distinct ducts, into the cavity of the stomach. In the slug and sea-hare it occupies a great portion of the muscular sac, common to the general visceral cavity. The liver of the Boris is remarkable, from the circumstance of possessing, besides ducts for pouring the biliary secretion into the sto- mach, a particular canal running in a direct course from the liver to the anus, and conveying a portion of the bile out of the system, without traversing the intestinal tube. This anatomical fact clearly proves that a portion of the bile is CEPHALOPODOUS MOLLUSCA. 171 excrementitious ; and that the liver is partly an eliminating organ, destined to separate impure carbonaceous materials from the blood. [§ 321. In the Cephalopoda the mouth is situated in the centre of the tentacular circle, and armed with two horny jaws, resembling the bill of a parrot, imbedded in the flesh, and moved by powerful muscles. In the interior of the mouth is a moveable cartilaginous tongue ; the pharynx, lodged at the anterior part of the cephalic cartilage, is very large and muscular ; the long and straight esophagus is surrounded by the nervous collar ; the stomach, like that of Aplysia^ presents three enlargements, forming a crop, a gizzard, and a true digestive stomach. The crop is a dilata- tion of the esophagus, leading into the second globular sto- mach ; it is very muscular, and communicates by a narrow opening with the third, or true digestive cavity, remarkable for possessing a singular spiral valve, formed by a fold of the lining membrane winding round its inner surface ; a modi- fication of structure w^hich we shall find repeated in some cartilaginous fishes, with which the cephalopoda are closely connected in many points of organization. Into this third chamber the ducts from the liver and pancreas pour their several secretions. The short intestinal canal, commencing at the pyloric orifice of the third stomach, ascends in front of the liver, and terminates in a valvular opening within the funnel, situated at the under part of the neck. The liver in the whole of this class is very large, and its copious secretion is poured by two ducts, along with the vessel, from the follicular pancreas into the third stomach, their orifices being provided with a valvular apparatus ; the salivary glands, four in number, insert their superior pair of ducts into the pharynx, and their inferior pair into the esophagus. The naked cephalopods, as the cuttle-fish, have a peculiar black, inky fluid, prepared by the glandular lining membrane of a particular bag, provided with a duct opening into the funnel. This fluid is secreted in great abundance, and being very miscible with water, forms a black cloud when injected into the sea ; and by means of this singular provision these naked, defenceless animals are enabled to elude the pursuit of their numerous enemies. The inky fluid, abounding in 172 ORGANS OF DIGESTION. carbon, may probably be the excrementitous portion of the biliary secretion, eliminated from the system by a distinct organ, and thus made to serve a double use ; it may, in fact, be analogous to that portion of the bile which is carried di- rectly out of the body by a separate canal in the Boris, [§ 322. In the Annelida the digestive tube passes straight through the body. The mouth is provided with jaws, and the glands of the intestine are in the form of lateral caecal appen- dages. The circulation is carried on hy arteries and veins ; their blood is red, and their respiratory organs are in the form of branchiae, or internal air sacs. Fig. 178. — The anatomy of the Himdo medicinalis. [§ 323. The Leech {Hirudo medicinalis^ fig. 178) has a trian- gular-shaped mouth («), armed with three small teeth, a pharynx, composed of numerous muscles (c) ; the action of which is seen when the animal is engaged in sucking ; the pharynx opens into a very large capacious sacculated stomach, with mem- branous parietes, united by small folds to the enveloping elastic tunic. The stomach is divided into numerous separate cham- bers {fyf,ff<,f)i by transverse processes of the lining mem- brane, communicating with each other by central oval open- ings ; it extends through about three parts of the entire length of the body, where it enters the intestine {m) by a valvular funnel-shaped opening ; this tube passes between the two pos- terior ceecal appendages of the stomach, and terminates in a small aperture (?^), at the margin of the posterior disc. The gangliated nervous chain {g) is uniform in its development throughout the body, giving oflP nerves at each ring ; the respiratory vesicles (A) and the lateral vessels (^) encircle the body ; the caeca of the digestive tube are seen at q ; the ANNELIDA AND CRUSTACEA. 173 female genital parts at r, the male organs at s, and the anal sucker at o, [§ 324. In some annelida the mouth is provided with a pro- jectile proboscis, formed of the anterior part of the intestinal canal (fig. 233). This organ can be protruded and inverted like the finger of a glove, and, like the proboscis of predacious mollusca, has a set of muscles consecrated to eifect its move- ments ; in the Nereis it is very complicated, its free extremity being armed with long jaws, like the pincers of Crustacea. The proboscis is regarded by some physiologists as a pharynx, armed with teeth, like those of star-fishes and echini ; and being like them, capable of eversion. The stomach of Nereis is large, and from its posterior part two csecal appendages pro- ject ; its inner surface is armed with two small white teeth ; the intestine passes straight through the body, and terminates in an aperture at the posterior part. In the Arenicola, or sand-worm (fig. 233), we observe an additional complication of structure ; to the short esophagus succeeds a complicated stomach, the first portion of which is simple, and the second very complex ; into the latter division of the organ an immense number of branched appendages open, which appear to be a repetition of the biliary caeca ob- served in the star-fish ; the stomach passes imperceptibly into the intestine, which terminates at the posterior part of the body. In the ApJirodita aculeata, or sea-mouse, a similar arrangement of the internal organs exists. [§ 325. In the Crustacea the digestive organs, when com- pared with those of the annelida, present a greater develop- ment of the organs of mastication. The jaws, which are nume- rous, move horizontally by powerful muscles ; the mouth of the lobster and crab is situated on the under surface of the body, on each side of which we find the first pair of jaws ex- panded into a broad form, and sending out behind long pe- dicles for the insertion of powerful muscles, which have their points of attachment at the internal surface of the dorsal shield ; succeeding these we find a second, third, fourth, fifth, and sixth pair of jaws : they are all, especially the three first pair, provided with sensitive palpi, in which it is probable the sense of taste resides. The esophagus is short, opening into a singularly complicated stomach, extended on a carti- 174 OEGAIS-S or DIGESTIOIf. laginous skeleton, which renders it better adapted for bruising the ahments ; the framework is composed of five semi-osseous pieces, provided internally with five teeth, surrounding the pylorus ; three are large and two are small, being a repetition of the type of organization we have already described in some mollusca ; the several plates of this skeleton are moved by muscles, so as to render it a powerful organ for bruising and fracturing the shells of the smaller mollusca, on which the Crustacea prey ; the calcareous parts of the stomach, like the external shell, are periodically cast off ; the intes- tine forms a straight tube, extending from the pylorus to the tail, and terminating at the under surface of the central plate. [§ 326. In the Aeach^^ida, as the common domestic spider (Tegenaria domestica), the mouth is provided with a pair of mandibles, armed with sharp claws, a venomous apparatus, and maxillae or jaws ; the mandibles are used for seizing, wounding, and retaining prey, whilst with the maxillae they squeeze out and suck the contained juices of their victim. The esophagus is short, of a delicate texture, and opens into four crops, or stomachs ; the tube then continues a straight and narrow canal, soon expanding into a muscular organ, sur- rounded by numerous adipose granules ; this dilatation again contracts, and, before terminating in the rectum, undergoes another swelling ; into this enlargement the biliary vessels ter- minate ; the apparatus for spinning is formed of four hollow , cylinders, the inferior parts of which are perforated like a sieve, their superior apertures communicating with ducts, from ramified vessels, destined for the secretion of the viscous fluid forming the filaments of the web ; these tubes occupy a con- siderable portion of the abdomen, surrounding the termination of the intestine, and their sole function being the secretion of this fluid. [§ 327. In Insects (fig. 179) the digestive organs are ex- ceedingly varied and complicated ; in some the mouth is pro- vided with jaws for bruising (fig. 195), in others with an apparatus for sucking (fig. 196) ; the intestinal canal presents many enlargements, and, in some orders, is extremely con- voluted, terminating at the posterior part of the body ; there are distinct organs for the secretion of the bile and the saliva, and in some a rudimentary pancreas exists. Insects pass ARACHNIDA A^^D INSECTA. 175 through a series of metamorphoses, presenting changes both in their external form and in- ternal structure, peculiar to each successive stage; from the egg is produced a vermi- form animal, the larva; this, after a time, becomes the chry- salis, which finally develops the perfect insect. The jaws of insects (figs. 195 to 199) are’ constructed after the type we have already described in an- nelida, Crustacea, and arach- nida, that is to say, they are placed laterally, and moved by powerful muscles ; we recog- nize two pair, an external pair, or mandibulse (fig. 195, m)y and an internal pair, or maxil- lae (^’) ; the mouth is furnished with a superior lip, or labrum, and an inferior lip, or labium. The development of the jaws is in strict relation with the natural food of the insect. The suctorial apparatus of the hy- menoptera, that of the common bee (fig. 1 96), for example, is very singular; projecting from between the jaws we observe a sucker (/), composed of nume- rous rings ; this organ, called bj Treviranus the fleshy tongue, is situated at the com- mencement of the esophagus, in a horny sheath, formed by a prolongation of the labiee, into which Fig. 179. — Digestive Organs of a Beetle. a, the head which supports the it rrni bp with- the crop and gizzard; d, 1 , , , the chylific stomach ; c, the biliary drawn at pleasure. The canal vessels ; c?, the intestine ; e, secreting of the sucker is very incon- organs the anus. 176 ORaAlS'S OE EiaESTIOK. siderable, opening into a bag situated before the esophagus, into which it leads ; the function of this bag appears, ac- cording to Burmeister, to be simply the rarefaction of its contained air, by which fluids in the proboscis and esopha- gus are pumped up into the first stomach. Insects pro- vided with organs of mastication are deprived of this suck- ing apparatus ; so that the development of maxillae and suc- torial instruments stand in an inverse ratio to one another. Burmeister is of opinion that, in insects deprived of a pro- boscis, the sucking bag is converted into a crop. The digestive organs of coleopterous insects present considerable variety in their structure ; two sections of the order are formed on this difference alone ; to the one section belongs those which have a globular muscular stomach, and short intestinal canal ; to the other, those having a large mem- branous stomach, furnished with caeca, and a long tortuous intestine : the first group are carnivorous, the second phyto- phagous. In Cicindila campestris, a carnivorous beetle, belonging to the first group, the short esophagus is dilated into a large glandular crop, opening into a small muscular giz- zard, furnished internally with horny teeth, to perforate, rub down, and divide the aliments. In this muscular sto- mach we recognize a repetition of the type already described in some mollusca. To this organ, called by Ramdohr the plaited stomach, succeeds a flask-shaped chylific organ, fur- nished with a number of small glandular follicles, for secreting the gastric juice ; at the point where this organ emerges into the pylorus, the ramified biliary vessels enter its cavity by four ducts ; the intestine is short and straight, and de- velops a large muscular colon, soon terminating in an anal aperture. The Melolontha vulgaris (common cockchafer) is an ex- ample of the structure of these organs in the coleoptera, com- prised in the second group. Here we find the entire canal much increased in length and diameter ; in this vegetable- eating insect the glandular organs are more voluminous, and from the sides of the ramified vessels numerous csecal appen- dages are produced. The esophagus is dilated into a membra- nous crop ; the gizzard is merely rudimentary ; the stomach is in the form of a long glandular sac, twisted in a spiral man- I^fSECTA. 177 ner on itself, and receiving at its pyloric extremity the ducts of the highly complicated biliary organs ; the small intestine is short, and the colon has three dilatations in passing to the anal aperture ; the biliary vessels are very numerous, and their secreting surface is much increased by the development of in- numerable small caeca from the sides of the large glandular ves- sels ; these two examples sufficiently prove that in the struc- ture of the digestive organs of carnivorous and phytophagous insects a marked difference exists. In the orthoptera, the grasshopper for example, the esopha- gus is dilated into a crop, opening into a round muscular stomach, the internal surface of which is armed with horny teeth ; the true chylific stomach succeeds this muscular organ, and is abundantly supplied with minute follicular appendages, and the secreting surface of its internal membrane is greatly increased by being thrown into delicate folds. In the neuroptera the stomach and intestinal canal are allied to the preceding ; being nearly all predacious, their masticatory organs are highly developed, and the intestine passes nearly straight through the body. Among the hymenoptera the digestive organs of the hee are the most interesting, as, in addition to the functions of nutri- tion, they form two important products, wax and honey. The sucker (fig. 196), leads into a large bag, situated on the anterior part of the esophagus, with which it communicates ; here the nectar obtained from flowers is converted into honey, which the bee disgorges at pleasure into the cells of the honeycomb. The esophagus terminates in a small gizzard, to which suc- ceeds a large sacculated stomach ; into its pyloric portion the bihary vessels enter ; the diameter of the small intestine is inconsiderable, but that of the colon is very ample, the inter- nal membrane of which has a glandular character, probably intended for the secretion of the wax. In the hemiptera, the common bvg has been examined with great care by Ramdohr ; he found its digestive organs to con- sist of two stomachs, the first being very capacious, and serving as a reservoir for the imbibed juices ; the second being very complicated, and provided with caeca ; to the small intestine succeeds a colon of considerable dimensions, provided with caecal appendages. Connected with the termination of the in- N 178 OEGAi^S OF DIGESTION. testinal canal of hymenopterous insects we find in some genera a venomous apparatus, consisting of a sting, a poison-bag, and secreting glandular organs. In the bee the sting is situated on the last segment of the abdomen, above the opening of the rectum ; its base is surrounded by a small bag, embraced at its superior part by numerous muscles ; two vessels, or caeca, enter this reservoir with their poisonous secretion ; the sting is composed of two portions, the corresponding surfaces of which are grooved in a semilunar manner, so that, when ap- proximated, a channel is formed ; into this the duct of the poi- son-gland opens ; each half being armed with small sharp re- curved teeth, for retaining it in the wound. The sting has a sheath for its reception, and a particular set of muscles, under the control of the will, for effecting its movements. Insects possess salivary vessels opening into different situa- tions ; some pour their secretion into the mouth, others into the commencement of the stomach (fig. 179). When we survey the varied forms which the biliary organs assume in theinvertebrated animals, we may remark that among the articulata, respiring atmospheric air, these organs present an arrangement and structure very different from that observed in the aquatic ar- ticulata and mollusca ; we are thus led to study more particu- larly the relations existing between the function of the liver as a secreting organ, and the respiratory apparatus as an ex- halant system ; the latter rejecting from the economy car- bonaceous matter in a gaseous form, whilst the fiver is con- stantly eliminating from the system secretions abounding in carbon and hydrogen, with other greasy and resinous materials. [§ 328. The vertebrate animals resemble man in the general arrangement and division of the digestive organs (fig. 180) ; their principal difierences depending upon the nature of the food ; the purely carnivorous species having a shorter and simpler apparatus than those which are frugivorous : among the latter the stomach is often a compound organ. In the ro- dents, as the rat, there are two compartments, and in ruminants four distinct cavities, whilst in the carnivora it forms a simple bag, as in man. The intestinal canal bears a constant relation, in its length and development, to the kind of food to be di- gested. In general, the length of the intestine is greatest in the ruminants, varying from fifteen to twenty times the length YEETEBEATA. 179 of the body ; in the sheep its proportionate length is as 28 to I, whilst in the carnivora the proportion is about 4 to 1. In Maxillary gland. Trachea. Parotid gland. Lungs. Heart. Pharynx. Esophagous Liver. Gall bag. Colon. Caecum. Small intestine. Thorax. Aorta. Diaphragm. Stomach. Pancreas. Spleen, Kidneys. Colon. Abdomen. Eectum. Bladder. Fig. 180. — The Digestive Organs of a Monkey. animals living upon a mixed diet of animal and vegetable food, the proportionate length of the intestine occupies an inter- mediate position ; in many rodents and monkeys the propor- tion is about 5 to 1 ; in man about 6 to 1 . It may be stated, as a general rule, that the stomach is simple when the food consists of easily-digested animal substances, and is more comphcated when the harder vegetable substances form the sustenance of the animal ; wherever a plurality of stomachs exist, there is one which is the true digestive cavity, the others subserving the processes of maceration and preparation. [§ 329. Upon minute examination with the microscope, the mucous membrane of the stomach is found to be covered with small glandular foUicles, which open internally ; these aper- tures are surrounded by an abundant vascular network, which- also extends more deeply, and includes the caecal and some- what racemiform follicles. The glands are sometimes simple and N 2 180 OEGANS OE DIGESTIOTf. cylindrical, as in fig. 181, which represents the gastric glands of the pyloric portion of the stomach ; at others they are com- Eig. 181. ;■ llil.lW, Fig. 182. pound. Fig. 182 represents the gastric glands in Man ; at A is a section of the stomach with all its elements, magnified about three diameters ; B represents the same glands, with their racemiform ter- minations distended with fluid, as seen with the microscope, and magnified about twenty diameters ; the contents of these glands are always dark and granular, and the membranous walls are of extreme deli- cacy. Lying between these are other glands of a larger size, and having a much more compound racemiform structure ; they lie separate from each other, and contain a transparent fluid, destined for a purpose different to that secreted by the gastric glands. Fig. 1 83 is an outline and highly magnified view of one of these glands, from the middle part of the human sto- mach ; the excretory duct is composed of three branches, which proceed from a mul- titude of blind cells. Fig. 184 is another gland of the same class, from the vicinity of the pylorus, where they are more com- mon than in other parts of the stomach ; it is viewed under the same magnifying power as fig. 181; this gland is more com- pound in structure, and its contents are more transparent than those of the other gastric glands. Much difference of opi- nion prevails regarding these organs : we havd followed Wagner in our de- scription, as they accord with our own microscopic investigations . * [§ 330. The stomach of birds presents a repetition of the type of structure which ^ we have already seen in insects. In the * The stomach should be examined very soon after death, if correct observations ai*e to be made. GASTRIC GLANDS. 181 common plover {Vanellus ci'istatus^ fig. 185), the esophagus {a) opens into the proventriculus (5), the walls of which are stud- Fig. 183. ded with gastric glands, and the muscular stomach, or gizzard (c), is continued into the duodenum {d) . The gastric glands have their hfind extremities turned towards the pe- riphery, and their orifices open in- to the proventriculus, the granular contents are there voided under the most gentle pressure. These glands are, for the most part, simple ex- ternally ; sometimes they form csecal follicles (fig. 1 86, b) ; they are well-developed in the rasores, where they are racemiform and lobular (c), or divided into many clusters, as in f. The common fowl, or goose, form excellent subjects for study, and they can always be procured in a fresh state. Fig. 187 represents the gastric glands in the glandular layer of the proventricu- lus of the common fowl ; A is the gland of its natural size, and B is a magnified representation of the same, where the caeca appear like clusters of berries attached to a stem. In young birds the cellular structure of these glands is very conspicuous. Fig. 188, at A, are seen the simple gastric glands of a young owl, of the natural size ; and at B, the same magnified, to shew the cellular structure of these organs. The relation in which these glands stand to the secretion of the gastric juice is not yet satisfactorily ascertained ; the microscope shows that the orifices, and inner lining of the glands, are covered with a fine tessellated epithelium, whilst the parenchyma of the gland consists of minute granular corpuscules, about 1 -200th of a line in dia- meter, not always nucleated, but formed of an uniform granular 182 ORaANS OF DI&ESTIOIS'. mass; rather than of elements having a cellular character ; the wall of the gland is formed of a transparent structureless mem- brane. Be- sides these granular cor- puscles an al- buminous fluid exudes fromthewalls of the sto- mach, and mingles with that yielded by the gastric glands ; the gastric juice appears to be loaded with corpuscles, having a pe- culiar acid mixed with it, secreted by an appropri- ate set or glands, from which it is expressed by the contrac- tion of the muscular coat of the stomach, when excited into action by the presence of food. — T. W.] § 331. The result of this process is the reduction of the food to a pulpy fluid called chyme, which varies in its nature with the food. Hence the function of the stomach has been named chymification. With this the function of digestion is complete in many of the invertebrata, and chyme is circulated throughout the body ; this is the case in polyps, acalephse, some worms, and moUusca. In other animals, however, the chyme thus formed is transferred to the intestine, by a pecu- liar movement like that of a worm in creeping, which has accordingly received the name of vermicular or peristaltic motion. Fig. 184. aASTEIC GLAIS^DS. 183 § 332. The form of the small intestine is less variable than that of the stomach. It is a narrow tube with thin walls, coiled Fig. 185. A Fig. 186. B Fig. 186. — B, glands of the proventriculus of different birds ; a, of the peacock (Pavo crista- tus). b, of the Cathar- tes percnopterus. c, of Casuarius galeatus. d, of Falcopygargus. e, of the fowl. /, of the os- trich. — After Home, Lecture on Comp. Anat. ii. pi. 56. in various directions in the vertebrate animals (fig. 180), but more simple in the invertebrata, especially the insects (tig. 179), Its length varies according to the nature of the food, being in general longer in herbivorous than in carnivorous animals. In this portion of the canal, the aliment undergoes its com- plete elaboration, through the agency of certain juices which here mingle with the chyme, such as the bile secreted by the liver, and the pancreatic juice secreted by the pancreas. The result of this elaboration is to produce a complete separation of the truly nutritious parts, in the form of a milky liquid called cAy/c. The process is called chylijication ; and there are great numbers of animals, as insects, crabs, lobsters, some worms, and most of the mollusca, in which the product of 184 OEGAJfS or DIGESTIO:S'. digestion is not further modified by respiration, hut circulates through the body as chyle. Fig. 187. Fig. 188. § 333. The chyle is composed of minute, colourless glo- bules, of a somewhat flattened form. In the vertebrata, it is taken up and carried into the blood by means of very minute vessels, called lymphaticvessels or lacteals, which are distributed everywhere in the walls of the intestine, and communicate with the veins, forming also in their course several glandular masses, as seen on a portion of intestine connected with a vein (fig. 189), and it is not until thus taken up and mingled with the circulating blood that any of our food really becomes a part of the living body. Thus freed of the nutritive portion of the food, the residue of the product of digestion passes on to the large intestine, from whence it is expelled in the form of excrement. § 334. The organs above described constitute the most es- sential for the process of digestion, and are found more or less developed in all but some of the radiated animals ; but there are, in the higher animals, several additional ones for aiding in the reduction of the food to chyme and chyle, which render their digestive apparatus quite complicated. In the first place, hard parts, of a horny or bony texture, are usually placed about OEaANS OF MASTICATION. <185 the mouth of those animals that feed on solid substances, which serve for cutting or bruising the food into small frag- ments before it Fig. 189. is swallowed ; ^orta. Thoracic duct. Lymphatic glands, and, in many of the lower ani- mals, these or- gans are the only hard portions of the body. This process of subdi- viding or chew- ing the food is termed mastica- tion, § 335. Begin- ning with the radiata, we find the apparatus for mastication partaking of the star - like ar- rangement Lymphatic Mesentery, which character- izes those animals. Thus, in the Scutella (fig. 190), we have a pentagon composed of five triangular jaws, converging at their summits towards a central aperture corresponding to the mouth, each one bearing a plate or tooth, like a knife-blade, fitted by one edge into a cleft. The five jaws move towards the centre, and pierce or cut the objects which come between them. In some of the sea-urchins, Echinidce^ this apparatus, which has been called Aristotle’s lantern (fig. 191), consists of Fig. 190. Fig. 191. 186 OEGANS OP PiaESTION. numerous pieces, and is much more complicated. Still, the five fundamental pieces or jaws, each of them bearing a tooth at its point, may be recognized, as in the ScuteLla; only, instead of being placed horizontally, they form an inverted pyramid. § 336. Among the mollusca, a few, like the cuttle-fishes. Fig. 192. Fig. 194. Fig. 193. — The dental organ of Fig. 194. — The dental organ of a the Nerita Ascensionensis. PaUlla, from the Straits of Magellan. have solid jaws closely resembling the beak of a parrot (fig. 192), which move up and down, as in birds. [But a much larger number rasp their food by means of a tongue sometimes coiled like a watch-spring, the surface of which is covered with innumerable tooth-like points, as in the highly mag- nified portions of the dental organ of Nerita (fig. 193) and Patella (fig, 194). The teeth present a great variety of patterns, which are constant in the different genera, and even characterize the species. They consist of variously-co- loured sihcious bodies, generally of hook-like form^ ar- ranged in triple rows upon a musculo-membranoiis band. OEGA]S"S OE MASTICATION^. 187 as in figs. 193 and 194. The central part is called the rachis, and the lateral parts pleurcE. The rachidian teeth sometimes form a row of plates, as in Nerita ; or they have a tile-shaped disposition, with pectinated borders, as in Buc- cinum. The lateral series exhibit an immense variety of forms, some having fringed processes, as in Nerita (hg. 193). By the aid of this singular dental organ the gasteropoda bruise, rasp, or pierce the vegetable or animal substances on which they subsist, and bore through the shells of mollusca, on which they prey. The tongue of the whelk (Buccimim) is fur- nished with upwards of one hundred rows of pectinated teeth, but the number of the dental rows on the lingual ribbon varies in different genera, and at the different periods of life of the individual. The dental organ of the common limpet {Patella vuLgata) is more than twice the length of the animal, and in a state of repose is folded back into the digestive tube. The dental membrane is wide in the mouth, and con- tracted in the esophagus; and after a course of nearly three inches, terminates near the small transverse stomach. The new teeth, like those of rays and sharks, are developed from be- hind, and are brought into use when required, a new series arising with the age of the individual.* — T. W.] § 337. The articulata are ^remarkable, as a class, for the diversity and complication of the apparatus for taking and dividing their food. In some marine worms. Nereis, for ex- ample, the jaws consist of a pair of curved, horny instru- ments, lodged in a sheath. In spiders, they are external, and sometimes mounted on long, jointed stems. Insects which masticate their food have, for the most part, at least two pairs of horny jaws (figs. 195, 196 ni), besides several additional pieces serving for seizing and holding their food. Those living on the fluids extracted either from plants or from the blood of other animals, have the masticatory organs transformed into a trunk or tube for that purpose. This trunk is some- times rolled up in a spiral manner, as in the butterfly (fig. * Loven’s Memoir on the Teeth of Mollusca is nearly all that we pos- sess on this subject. Figures 193 and 194 were drawn by Mr. Etheridge, of the Bristol In- stitution, from specimens dissected and prepared by my friend John W. Wilton, Esq., F.R.C.S., Gloucester. The position of the dental organ of the Patella (fig. 194) on the slide does not permit the left lateral teeth of the specimen to be seen. 188 OEGAIS’S OF DIGESTIOIS’. 199) ; or it is stiff, and folded beneath the chest, as in the squash-bugs (fig. 197), containing several piercers of extreme delicacy (fig. 198), adapted to penetrate the skin of animals or other objects whose juices they extract; or the partsof themouth are prolonged, so as to shield the tongue when thrust ouf in search of food, as in the bees (fig. 196,^', p). The crabs have their Fig. 195. Fig. 196. Fig. 197. Fig. 198. Fig. 199. anterior feet transformed into jaws, and several other pairs of articulated appendages perform exclusively masticatory func- tions. Even in the microscopic rotifera, we find very com- plicated jaws, as seen in the interior of Esophora (fig. 172). But amidst this diversity of apparatus, there is one circum- stance which characterizes all the articulata, namely, the jaws move sideways ; while those of the vertebrata and mol- lusca move up and down, and those of the radiata concen- trically. § 338. In the vertebrata, the jaws form a part of the bony skeleton. In most of them the lower jaw (fig. 103) only is moveable, and is brought up against the upper jaw by means of the temporal and masseter muscles, which perform the principal motions requisite for seizing and masticating food. § 339. The jaws are usually armed with solid cutting in- struments, the Teeth, or else are enveloped in a horny covering, the beak, as in birds and tortoises (fig. 200). In some of the whales, the true teeth remain concealed in the jaw bone, and they have instead, a range of long, flexible, horny plates or fans, fringed at the margin, serving as strainers to separate the minute marine animals on which they feed from the water drawn in with them (fig. 201). A few are entirely destitute of teeth, as the ant-eaters (fig. 202). © OEQA^fS OF MASTICATIOIS'. 189 § 340. Though all the vertebrata possess jaws, it must not be inferred that they all chew their food. Many swallow their prey whole ; as most birds, tortoises, and whales. Even many of those which are furnished with teeth do not masticate their food ; some using them merely for seiz- ing and securing their prey, as the lizards, frogs, crocodiles and the great majority of fishes. In such animals, the teeth are nearly all alike in form and structure, as, for instance, in Fig. 201. Fig. 202. Fig. 204. the alligator (fig. 203) ; the porpoises and many fishes. A few of the latter, some of the rays, for example, have a sort of bony pavement (fig. 204), composed of a peculiar kind of teeth, with which they crush the shells of the mollusca and crabs on which they feed. § 341. The mammals, however, are almost the only verte- brata which can be properly said to masticate their food. Their teeth are well developed, and present great diversity in form, arrangement, and mode of insertion. Three kinds of teeth are usually distinguished in most of these animals, whatever may- be their mode of life ; namely, the cutting teeth, incisors ; the 190 OEGAIS^S OE DIGESTIOI^. tusks, or carnivorous teeth, canines ; and the grinders, molars (fig. 205). The incisors occupy the front of the mouth ; they are the most simple and the least va- ried ; they have a thin cutting summit, and are employed almost Fig. 205.— The skull of a horse. exclusively for seizing food, except in the elephant, in which they assume the form of large tusks. The canines are conical, more prominent than the others, more or less curved, and only two in each jaw; they have but a single root, like the incisors, and in the carni- vora become very formidable weapons. In the herbivora they are wanting, or, when existing, they are usually so enlarged and modified as also to become powerful organs of offence and defence, although useless for mastication, as in the babyroussa. The molars are the most impor- tant for indicating the habits and internal structure of the animal, they are, at the same time, most varied in shape. Among them we find every transition, from those of a sharp and pointed form, as in the cat tribe (fig. Fig. 206. — The skull of a 207), to those with broad and level squirrel. summits, as in the ruminants and rodents (fig. 206) ; still, when most diversified in the same animal, they have one character in common, their roots being never simple, but double or triple, a peculiarity which not only fixes them more firmly, but prevents them from being driven into the jaw in the efforts of mastication. § 342. The harmony of organs, already spoken of, is illus- trated, in the most striking manner, by the study of the teeth of mammals, and especially of their molar teeth. So constantly do they correspond with the structure of other parts of the body, that a single molar is sufficient not only to indicate the mode of life of the animal to which it belongs, and to show whether it fed on flesh or vegetables, or both, but also to de- OEaANS OF INSALIVATIOIS^. 191 Fig. 207. — The skull of a tiger. termine the particular group to which it is related ; thus, those beasts of prey which feed on insects, and which, on that ac- count, have been called in- sectivora, such as the moles and bats, have the molars terminated by several sharp, conical points, so arranged that the elevations of one tooth fit exactly into the de- pressions of the tooth oppo- site to it. In the true car- nivora (fig. 207), on the con- trary, the molars are compressed laterally, so as to have sharp- cutting edges, as in the cats, and shut by the side of each other, like the blades of scissors, thereby dividing the food with great facility. § 343. The same adaptation is observed in the teeth of her- bivorous animals. Those which chew the cud (ruminants), many of the thick-skinned animals (pachydermata), (fig. 205), like the horse and the elephant, and some of the gnawers (ro- dentia), like the squirrel (fig. 206), have the summits of the molars flat, like mill-stones, with more or less prominent ridges, for grinding the grass and leaves on which they sub- sist ; finally, the omnivora, those which feed on both flesh and fruit, like man and the monkeys, have the molars terminating in several rounded tubercles (fig. 102), being thus adapted to the mixed nature of their food. § 344. Again, the mode in which the molars are combined with the canines and incisors furnishes excellent means for cha- racterizing families and genera ; even the internal structure of the teeth is so peculiar in each group, and yet subject to such invariable rules, that it is possible to determine with precision the general structure of an animal, merely by investigating fragments of its teeth under a microscope. § 345. Another process, subsidiary to digestion, is called insalivation. Animals which masticate their food have glands, in the neighbourhood of the mouth, for secreting a fluid called saliva. This fluid mingles with the food as it is chewed, and prepares it also to be more readily swallowed. The sahvary glands are generally wanting, or rudimentary or otherwise modified, in animals which swallow their food without masti- 192 OEGANS OF DIGESTION. cation. After it has been masticated, and mingled with saliva, it is moved backwards by the tongue, and passes down through the esophagus into the stomach ; this act is called deglutition^ or swallowing , % 346. The wisdom and skill of the Creator is strikingly illustrated in the means afforded to every creature for securing its appointed food. Some animals have no ability to move from place to place, but are fixed to the soil, as the oyster, the polype, &c. ; these are dependent for subsistence upon such food as may stray or float near them, and they have the means of securing it only when it comes within their reach. The oyster closes its shell, and thus entraps its prey ; the polype has flexible tentacula (figs. 170 and 175), capable of great ex- tension, which it throws instantly around any minute animal coming in contact with them ; the cuttle-fish has elongated arms about the mouth, furnished with ranges of suckers, by which it secures its victim. § 347. Some are provided with instruments for extracting food from places which would be otherwise inaccessible. Some of the mollusca, with their rasp-like tongue (fig. 1 93 j, perforate the shells of other animals, and thus reach and extract the in- habitant. Insects have various piercers, suckers, or a protrac- tile tongue for the same purpose (figs. 195 to 199). Many of the annelida, the leeches for example (fig. 178), have a sucker, which enables them to produce a vacuum, and thereby dra\ out blood from the perforations they make in other animals. Many infusoria and rotifera are provided with hairs, or cilia, around the mouth (figs. 171, 172), which, by their incessant motion, produce currents that bring within reach the still more minute creatures, or particles, on which they feed. § 348. Among the vertebrata, the herbivora generally em- ploy their lips or their tongue, or both together, for seizing the grass or leaves they feed upon. The carnivora use their jaws, teeth, and especially their claws, which are long, sharp, and moveable, and admirably adapted for the purpose. The wood- peckers have long, bony tongues, barbed at the tip, with which they draw out insects from deep holes and crevices in the bark of trees ; some reptiles also use their tongue to take their prey ; thus, the chameleon obtains flies at a distance of three or four inches, by darting out its tongue, the enlarged end of which is covered with a glutinous substance, to which they adhere. The elephant, whose tusk and short neck prevent him from bringing ORaANS OF DIGESTION. 193 his mouth to the ground, has the nose prolonged into a trunk, which he uses with great dexterity, for bringing food and drink to his mouth. Doubtless the mastodon, once so abun- dant in the pre-Adamite earth, was furnished with a similar organ ; man and the monkeys employ the hand, exclusively, for prehension. § 349. Some animals drink by suction, like the ox ; others by lapping, like the dog. Birds simply fill the beak with water, then, raising the head, allow it to run down into the crop. It is difiicult to say how far aquatic animals require water with their food ; it seems, however, impossible that they should swallow their prey without introducing at the same time some water into their stomach. Of many among the lowest animals, such as the polyps, it is well known that they frequent- ly fill the whole cavity of their body with water, through the mouth, the tentacles, and pores upon the sides, and empty it at intervals through the same openings. And thus the aquatic mollusks introduce water into special cavities of the body, or between their tissues, through various openings, while others pump it into their blood-vessels, through pores at the surface of their body. This is the case with most fishes. Besides the more conspicuous organs above described, there are among the lower animals various microscopic apparatus for securing prey. The lassos of polypi have been already mentioned incidentally. They are minute cells, each containing a thin thread coiled up in its cavity, which may be thrown out by inversion, and extended to a considerable length beyond the sac to which it is attached. Such lassos are grouped in clus- ters upon the tentacles, or scattered upon the sides of the actinia, and of most polypi. They occur also in similar clus- ters upon the tentacles and the disc of jelly-fishes. The net- tling sensation produced by the contact of many of these ani- mals is undoubtedly owing to the lasso cells. Upon most of the smaller animals, they act as a sudden, deadly poison. In echinoderms, such as star-fishes, and sea-urchins, we find other microscopic organs in the form of clasps, placed upon a move- able stalk. The clasps, which may open and shut alternately, are composed of serrated or hooked branches, generally three in number, closing concentrically upon each other. With these weapons, star-fishes not more than two inches in diame- ter, seize and retain shrimps of half that length, notwithstand- ing their efforts to disentangle themselves. o CHAPTER SEVENTH. OF THE BLOOD AND CIRCULATION. § 350. The nutritive portions of the food are poured into the general mass of fluid pervading every part of the body, out of which every tissue is originally constructed, and from time to time renewed. This fluid, in the general accepta- tion of the term, is called blood ; but it differs greatly in its essential constitution : in the different groups of the animal kingdom, in polyps, and medusse, it is merely chyme rm most mollusca and articulata it is chyle; but in vertebrata it is more highly organised, and constitutes what is properly called blood. § 351. The Blood, when examined by the microscope, is found to consist of a transparent fluid, the serum, consisting chiefly of albumen, fibrin, and water, in which float many rounded, somewhat compressed bodies, called blood discs, or globules. These Yary in number with the natural heat of the animal from which the blood is taken. Thus, they are more numerous in birds than in mammals, and more abundant in the latter than in fishes. In man and other mammals they are very small, and nearly circular (figs. 208 and 209) ; they are somewhat larger, and of an oval form, in birds and fishes (figs. 210, 214, 215); and still larger in reptiles (figs. 211, 212, 213). [The blood-globules in man appear distinctly dis- Fig. 208. — Globules of the blood of man, the blood having been ^ drawn from a vein and W beaten, to separate the C fibrin. A, blood glo- bules, seen, a, on the^ flat aspect ; 6, standing on the edge ; *, three-quarter view. B, a congeries of blood-globules, with their flat surfaces in opposition, and forming columns such as are made by a number of coins laid one upon another. C, a blood globule in process* of alteration, such as simple exposure to the air will produce. ' D, a lymph globule, mingled with the proper blood globules. ISLB. The subjects of this and the succeeding figures of blood discs from Wagner’s leones Physiologies, are all magnified to the same extent, viz. about nine hundred diameters. OF THE BLOOD AND CIBCITLATION. 195 coidal (fig. 208, A), and vary between the 300th to the 400th of a line in diameter. They are rarely seen either larger or smaller. That they are flat, disc-like bodies, is discovered by examining them on different sides. At the beginning of an observation, before the drop has spread itself abroad com- pletely, and the globules have come to rest, or at any time when the port-object is inclined a little one way or another, numbers of them are always seen on their edges (A, b), when they appear as long-shaped bodies, bounded by two parallel lines. They are also seen falling, or rolling over (*), and with everything at rest, finally sinking down upon their flat sides («). The blood-discs are severally so pale in colour, and so transpa- rent, that when one lies over another, the undermost is seen distinctly shining through the uppermost {a inferiorly). If quite normal, a delicate semicircular shadow upon the flat sur- face gives the observer the idea that the blood-discs are very shghtly hollowed out, or sunk, in the manner of a concave lens. In a short time, sometimes after the lapse of a few se- conds only, particularly when the diluting medium has not been weU selected, though it also happens from the action of the air, the blood-discs begin to suffer change ; they appear puckered and uneven ; they acquire notched edges, and are stellated ; they seem to be made up of very minute globules, or they look like mulberries or raspberries (C). The blood- discs seem to have a natural tendency to approximate by their flat surfaces, and go to form columns such as are produced by pieces of money piled one upon another (B). [§ 352. It is a matter of interest to compare the blood-cor- Fig. 209. — Blood globules of the com- mon goat {Capra domestica). Fig. 210. — A, blood and lymph globules of the pigeon {Columha domestica). B, a blood- globule, treated with diluted acetic acid ; C, with water, by which the central nucleus be- comes visible. o 2 196 OF THE BLOOD AKD CIRCULATION. puscles of the lower animals with those of man. In the mam- malia they are in all essential Tespects the same as in man, round and discoidal ; for the most part, however, particularly among the ruminants, decidedly smaller (fig. 209). In the monkeys, again, they are very nearly of the same size.* In birds, on the other hand, the blood-corpuscles are very difier- ent, having an elongated oval shape (fig. 210, a), and their broad sides, instead of being depressed, are vaulted or raised (b). They are on an average from 1-1 25th to 1-1 50th of a fine in length, and about half as broad. It is among the amphibia that we meet with the largest blood-corpuscles. They are here, as in birds, oval-shaped, but relatively somewhat broader ; and their surface is rather depressed than vaulted. They are par- ticularly large in the naked amphibia : in the Proteus, for ex- ample, they are from l-30th to l-50th of a line in the long diameter, and are even distinguishable as little points by the Fig. 211. — Blood-glo^'dies of the Proteus anguinus. In the gloh'ile d* the nucleus is seen, and m the globule, d, which has been treated with water, it is still more apparent ; c is a lymph granule. * The blood- corpuscles of the monkeys are in no wise to be distin- guished from those in man. In different human subjects, — men, women, children, negroes, — no difference can be perceived. OF THE BLOOD AKD CIECULATIOH. 197 c km naked eye (fig. 211, ah'). They are, consequently, from eight to ten times larger here than in man. After the Proteus, we observe the largest blood-corpuscles in ^ the land salamanders, where they measure in the long diameter from the 1-5 0th to the l-60th of a line. In the water sala- manders they are still very large, — from the l-7bth to the l-80th of a line in length (fig. 212). In the frog and toad they are from the 1 -80th to the 1-1 00th of a line in length (fig. 213). In the lizards, ser- pents, and tortoises, they are throughout smaller, though still measuring from the 1-1 22d to the l-150th of a line in length In the majority of fishes, and particu- larly in all the bony fishes, the blood-cor- puscles are of a rounded oval (fig. 214), not much long- er than broad, flat- tened, and from the d(^ Fig. 212. — Blood and lymph-globules of the great water-newt {Triton cristatus). a, b, blood-globules ; a*, a blood-globule with eccen- tric nucleus ; c, lymph-granules, d, e, blood- globules in progress of development ; they are surrounded with delicate involucra. Globules of this description are found abundantly in the blood of well-fed animals generally. 1-1 50th to the 1 -200th 213. — A, a, a, a, b, blood-globules of of a line in the long the edible frog {Rana esculenta) ; c, lymph diameter. In the granule. B, blood-globules after the action skates and sharks, acetic acid. again, they are notably larger, and very similar to those of the frog ; they are as much as from the 1-5 0th to the 1-1 00th of a line in the long axis. It is remarkable that in the cyclos- tomes they greatly resemble those of man, being rounded, discoidal, vaulted, slightly bi-concave (fig. 215, a, h), and mea- 198 OF THE BLOOD AND CIECULATION. suring 1 -200th of a line in diameter ; they are, therefore, only somewhat larger than in man. In the invertebral series of animals they are generally irregular, granular, rounded cor- puscles.*] Fig. 214. — Blood and lymph glo- bules of the loach {Cohitis fossilis); fl, G, h, perfect blood-globules ; d, a blood-globule altered by the ac- tion of water, and shewing its nu- cleus ; c, lymph granules. Fig. 215. — Blood-globules of the Ammocetes branchialis ; a, G, 6, perfect blood-globules; c, lymph-globule. The blood-glo- bules are exactly similar in the lamprey {Petromyzon), and un- like those of all other fishes, whe- ther cartilaginous or bony. § 353. The colour of the blood in the vertebrata is bright red ; but in some invertebrata, as the crabs and moUusca, the nutritive fluid is nearly or quite colourless, while in the worms, and some echinoderms, it is variously coloured, yellow, orange, red, violet, lilac, and even green. § 354. The presence of this fluid in every part of the body is one of the essential conditions of animal life. A perpetual current flows from the digestive organs towards the remotest parts of the surface ; and such portions as are not required for nutriment and the secretions, return to the centre of circu- lation, mingled with fluids, which need to be assimilated to the blood, and with particles of the body which are to be expelled, or before returning to the heart are distributed through the liver. The blood is kept in an incessant circula- tion for this purpose. § 355. In the lowest animals, such as the polypi, the nutri- tive fluid is simply the product of digestion, chyme, mingled with water in the common cavity of the viscera, with which it comes in immediate contact, as well as with the whole interior of the body. In the jelly-fishes, Medusce, which occupy a some- what higher rank, a similar liquid is distributed by prolongations of the principal cavity to the different parts of the body (fig. 173). Currents are produced in these, partly by the general * Professor Wagner’s Physiology, p. 233, et seq. OF THE BLOOD AHD CIECULATIOH. 199 movements of the animal, and partly by means of the incessant vibrations of cilia, which overspread the interior. In most of the moUusca and articulata, the blood, chyle, is also in imme- diate contact with the viscera, water being mixed with it in tlie mollusca ; the vessels, if there are any, forming a complete circuit, but not emptying into various cavities which interrupt their course. § 356. In animals of stiU higher organization, as the verte- brata, we find the vital fluid inclosed in an appropriate set of vessels, by which it is successively conveyed throughout the system, to supply nutriment and secretions, and to the respi- ratory organs, where it absorbs oxygen, or, in other words, be- comes oxygenated. § 357. The vessels in which the blood circulates are of two kinds : 1 . The arteries, of a firm, elas- tic structure, which may be distended, or contracted, according to the volume of their contents, and which convey the blood from the centre towards the periphery, distributing it to every point of the body. 2. The veins, of a thin, membranous structure, furnished with- in with valves (fig. 216, v), which aid in sustaining the column of blood, only allowing it to flow from the periphery towards the centre. The arteries con- stantly subdivide into smaller and smaller branches, while the veins com- mencing in minute twigs, are gathered Fig. 21G.— Vem laid open, into branches and larger vessels, to valves, v, v. unite finally into a few trunks near the centre of circulation. § 358. The extremities of the arteries and veins are con- nected by a net-work of extremely dehcate vessels, called capil- lary vessels (figs. 224, 225) ; which pervade every portion of the body, so that almost no point can be pricked without wounding some of them. Their ofiice is to distribute the nu- tritive fluid to the organic cells, where all the important pro- cesses of nutrition are performed, such as the alimentation and growth of all organs and tissues, the elaboration of bile, milk) saliva, and other important products derived from the blood, the removal of effete particles, and the substitution of new ones, and all those changes by which the bright blood of the ar- 200 or THE BLOOD AI^D CIECTJLATIOK. teries becomes the dark blood of the veins ; and again, in the cells of the respiratory organs, which the capillaries supply, the dark venous blood is oxygenated, and restored to the bright scarlet hue of the arterial blood. § 359. Where there are blood-vessels, in the lowest animals, the blood is kept in motion by the occasional contraction of some of the principal vessels, as in the worms. Insects have a large vessel running along the back, furnished with valves so arranged that, when the vessel contracts, the blood can flow only towards the head, and being thence distributed to the body, is returned again into the dorsal vessel (fig. 223), by fissures at its sides. § 360. In all the higher animals there is a central organ, the hearty which forces the blood through the arteries towards the periphery, and receives it again on its return. The Heaet is a hollow muscular organ, of a conical form, which dilates and contract's at regular intervals, independently of the will. It is either a single cavity, or is divided by walls into two, three, or four compartments, as seen in the following diagrams. These modifications are important in their connection with the respi- ratory organs, and indicate the higher or lower rank of an Fig. 217. Lesser circulation. Greater circulation. OF THE BLOOD AND CIKCULATION. 201 animal, as determined by the quality of the blood distributed in those organs. § 361. In mammals and birds the heart is divided, by a vertical partition, into two cavities, each of which is again di- vided into two compartments, one above the other (fig. 217). The two upper cavities are called auricles^ and the lower ones are called ventricles. Reptiles have two auricles and one ventricle (fig. 219) ; fishes have one auricle and one ventricle only (fig. 220). The plan (fig. 217) represents the course of the blood in mammals and birds, in which we have a double circulation ; a lesser one through the lungs, and a greater one through the body. § 362. The auricles do not communicate with each other, in adult animals, nor do the ventricles. The former receive the blood from the body and the respiratory organs through veins, and each auricle sends it into the ventricle beneath, through an opening, guarded by valves to prevent its reflux ; while the ventricles, by their contractions, force the blood through arteries into the lungs, and through the body generally. § 363. The two auricles dilate at the same instant, and also contract simultaneously ; so, also, do the ventricles. These successive contractions and dilatations constitute the pulsations of the heart. The contraction is called systole, and the dilata- tion is called diastole. Each pulsation consists of two move- ments, the diastole, or dilatation of the ventricles, during which the auricles contract, and the systole, or contraction of the ventricles, while the auricles dilate. The frequency of the pulse varies in different animals, and even in the same animal, according to its age, sex, and the degree of health : in adult man, they are commonly about seventy beats per minute. § 364. The course of the blood, in those animals which have four cavities to the heart, is as follows, beginning with the left ventricle (fig. 218, /, ^?). By the contraction of this ventricle, the blood is driven through the main arterial trunk, called the aorta {a), and is distributed by its branches through- out the body ; it is then collected by veins, carried back to the heart, and poured into the right auricle {r, a), which sends it into the right ventricle (r, v). The right ventricle propels it through another set of arteries, the pulmonary arteries (p), to the lungs ; it is there collected by the pulmonary veins, and 202 or THE BLOOD AXD CIRCULATTOJT. conveyed to the left auricle (/, a), by which it is returned to the left ventricle, thus completing the circuit. Sup. vena cava. Pul. art. Aorta {a). Pulmonary arterv ( v) V 1 » . ^ Pulmonary veins (p v). Right auricle (?• a). Tricuspid valve. Inferior vena cava. Right ventricle (r v). Partition. Aorta descending (a). Fig. 218. — Ideal section of the human heait. § 365. Hence the blood, in performing its whole circuit, passes twice through the heart. The first part of this circuit, the passage of the blood through the body, is called the great circulation^ and the second part, the passage of the blood through the lungs, is the lesser or 'pulmonary circulation : this double circuit is said to be ^complete circulation (fig. 217). In this case, the heart may be justly regarded as two hearts conjoined, and, in fact, the whole of the lesser circulation intervenes in the passage of the blood from one side of the heart to the other ; except that during the embryonic period, when there is an opening between the two auricles, which closes as soon as respiration commences. § 366. In reptiles (fig. 219) the venous blood from the body is received into one auricle, and the oxygenated blood from the lungs into the other. These throw their conteuts into the single ventricle below, which propels the mixture in part to the body, and in part to the lungs { but as only the smaller portion of the whole quantity is sent to the lungs in a single circuit, the circulation is said to be incomplete. In the crocodiles, the ventricle has a partition which keeps separate the two kinds of blood received from the auricles ; but .he or THE BLOOD AHD CIECULATIOH. 203 mixture soon takes place by means of a special artery which passes from the pulmonary artery to the aorta. [The reptiles have a heart with one ventricle, and two auricles ; the right auricle receives the impure venous blood from the body, the left auricle receives the pure arterial blood from the lungs, and both pour their contents into the same ventricle, where they are mingled together. This mixed blood is transmitted by the ventricular contractions partly into the lungs and partly into the body ; in the crocodile a partial partition divides the ven- tricle into a right side and a left side, as in birds and mammals. Fig. 219 is apian of the circulation in reptiles; the arrows indicating the course of the blood. Lesser circulation. Single ventricle. Greater circulation Fig. 219. — Circulation in reptiles. [§ 367. In fishes the heart possesses two cavities, an auricle and a ventricle, and only receives and transmits venous blood ; it therefore represents the right side of the heart of birds and mammals. The venous blood returned by the systemic veins is poured into the auricle and ventricle, from whence a highly elastic artery arises, which divides into five pairs of branches ; these branchial arteries distribute the blood throughout the gills; from these organs it is conveyed into a large single vessel. 204 OP THE BLOOD A1^T> CIECULATION. lying along the spine, and byits branches is distributed through- out the body. Fig. 220 is a plan of this type of circulating organ. [§ 368. In the mollusca the heart consists of a ven- tricle and an au- ricle, as in fishes ; Heart. but it differs in this, that it is destined to pro- pel the blood through the sys- Dorsal artery, tem, and not through the gills, as in that class. veins. [Fig.221repre- sents the circula- ting organs of the Boris; the heart Greater circulation. COnsists of a ven- Fig. 220. — Circulation in fishes. tricle (a), from whence arises the aorta (5), which sends branches to all parts of the body ; and a single or double auricle (c), in which the veins {d) of the bran- chial organs {e) terminate, the branchiae being developed in the form of external vascular tufts. The blood purified in these or- gans is conveyed to the heart, and transmitted by arteries through the body ; it is collected by the radicles of the veins, which terminate in a large trunk (f). By this vena cava it is dis- tributed through the gills (e), and from these organs it is re- turned to the heart. In the cephalopoda the circulation through the gills is aided by branchial ventricles, situated at the bases of these organs, but in other respects their circu- latory apparatus resembles that of the mollusca in general. [§ 369. In the Crustacea (fig. 222), the circulation is after the type of the mollusca. The heart {a) consists of a ven- tricle only, from which several arteries arise ; the opthalmic {h), the antennal (c), the hepatic (c?), the superior abdominal (e), and the sternal (/). After having circulated through the body, the blood is collected in certain reservoirs {g g), which take the or THE BLOOD ANB CIECULATION. 205 place of veins ; these venous sinuses swell out at the base, and send a branch to each bran- chia. After having circulated through these organs, the blood is returned to the heart, to perform a similar cir- cuit. [§ 370. In insects (fig. 223) the circulation is main- tained by a dorsal vessel («), which acts the part of a heart : it is divided into seve- ral chambers by valves, which permit the blood to flow only towards the head ; the vessel here appears to cease, and the blood seems to flow in the interspaces of the tissues ; cur- rents of globules form arches in the antennae, wings, legs, and the prolongations of the abdomen ; lateral currents are seen at 6, the direction af their course being indicated by the arrows. The circulation in insects can only be Fig. 222. studied in transparent aquatic larva, as those of the ephemera, in which it forms a beautiful spectacle for the rnicroscopist. The chyle globules enter the dorsal vessel by Fig. 221. — Circulating organs of the Doris. 206 OF THE BLOOD AND CIBCULATION. lateral slits, which are protected by valves. The simplicity of the circulating organs in insects forms a striking contrast to the preceaing classes ; but we shall see, when treating of the function of respiration, that in insects the air is so com- pletely conveyed to all parts of their .bodies, that a simple arrangement suifices for the perfect seration of their blood. [§371. We have seen that the arteries terminate in the veins in the periphery of all the organs ; these two divisions of the vascular system are connected by the capillary vessels. A view of these vessels can only be obtained by sucHtssful minute injections, and the aid of the microscope ; size injections of the skin, and the mucous membranes of the lungs and intestinal canal, exhibit the peripheral capillary system in great variety. The web of the frog’s foot, the fishes’ tail, and the branchiae of the tadpoles* of frogs, and salamanders, shew the splendid spectacle of the vascular system in action. — T. W.] [§ 372. However different the more minute capillary reticu- lations in the various organs appear, they may nevertheless be * Every season of the year is not alike favourable for making observa- tions on the circulation. It is only in the spring that tadpoles are to be had, but they are excellent subjects. They should be rolled up in moist OF THE BLOOI) CIECTJLATIOiT. 207 all reduced to a single fundamental type, a type which is most readily observed in the vascular distribution of the intestinal viUi (tig. 224) : the terminal twig of an artery (h, b) bends round into the terminal twig of a vein {a, a), and the two are repeatedly connected by means of delicate loop-like twigs, these in their turn being formed into meshes by cross or intermedi- ate branches. The fundamental type of the peripheral vascular system is therefore an arterial and a venous branchlet — pro- per capillary vessels, and an in- terposed net-work of fine vas- cular canals — vasa intermedia. A distinct separation between capillaries, and intermediate vessels, as this is perceived in the intestinal villi more especi- ally, is not generally to be ob- served, the two blend or are lost insensibly in one another. The parenchyma, or organic substance lying between the finest vascular subdivisions, forms islets of very various size and figure, according as the meshes of the intercurrent ves- sels are open or closer, and as they are rounded or angular. The intimate structure of every organ, the mode of union and of the grouping of its elementary parts, and the diameter of the Fig. 224. — Vessels of one of the intestinal villi of the hare; after an extremely beautiful diy .prepa- ration by Doellinger. The villus is magnified about 45 times. The vein «, a, is injected with white ; the artery, b b, with red ; between the two a most beautiful rete of capil- laries is apparent. blotting-paper, nearly to the end of the tail, and so laid upon a plate of glass of sutficient size, and placed under the microscope, the wrapper of bibulous paper being kept constantly moist by a few drops of water let fall- on it from time to time. In this way the circulation may be watched for hours, and the tadpole set free at the end of the observation is nothing the worse. Young and still transparent fishes may also be treated in the same 208 01' THE BLOOD AISD CIECULATION. vessels which appertain to it, give rise to the greatest diversity of form in the peripheral vascular system, which has never- theless so determinate a character in each tissue, that an ex- amination with the microscope of the smallest particle of a finely injected preparation enables us to say 'with certainty from what part of the body it was obtained.* [§ 373. When a transparent part of a cold-blooded animal, the web of the frog’s foot, for example, is examined under a Fig. 225. — Membrane between two of the toes of the frog’s [Rana esculenta) hind-foot, with the vessels and their anastomoses, drawn under the lens, and magnified three diameters, a c. Veins, h b, Arteries. way, and are excellent subjects, but they require more delicate handling than tadpoles. The circulation in the allantois of the young embryos of lizards and snakes is also a ver)^ beautiful sight, when these subjects can be had at the proper point of evolution ; they require to be removed from the ova, and observed covered vdth fluid albumen in a watch-glass. In the winter, frogs are the best subjects ; fishes are then much less proper. In the web of the hind foot of the common frog {Rana temporarid), the circulation is perhaps seen to as great advantage as anywhere. All our better microscopes are now provided with a stage adapted for placing the animal, which is best secured by being put into a linen or calico bag, with tapes at each corner to tie it down. * Professor Wagner’s Physiolog}", p. 286. OF THE BLOOD AND CIRCULATION. 209 low magnifying power, the directions of the arterial and ve- nous currents are readily discovered (fig. 225, a a, h b). The anastomoses of both orders of vessels are seen distinctly. Under a higher power (figs. 226 and 227) a net-work of very fine vessels is perceived lying now over, now under the larger branches, and con- nected with these by small twigs. In the larger ves- sels the arterial and venous currents are distinguished, not merely by their opposite directions, but also by the kind of motion appropriate to each : that of the arteries is distinctly jerking or pul- satory, but it gets ever less and less, so as the minuter subdivisions are attained, and in the intermediate and finest vessels of all it be- comes a continuous stream, which has the character ap- propriate to the venous cur- rent. In all the vessels, even in the very finest, a distinct boundary, formed by a sim- ple dark line, is perceptible ; the surrounding paren- chyma, now distinctly cel- lular (fig. 226), now rather granular and fused, though still including individual ramified pigmentary cells within it (fig. 227), is sharply limited ; the vessels never appear as simple channels pierced through its substance and without distinct parietes. Larger vessels (figs. 227 and 228) are ob- viously enough furnished with darker parietes, composed of various layers of fibres. In the most minute vessels there is room for no more than a single row of blood-corpuscles, and even these can only pass by their long diameters through the Fig. 226. — A portion of the web of a frog's foot, exhibiting the included network of vessels, magnified 45 times. The angular unnucleated cells c c, of the parenchyma, lying between the different vessels, are beautifully shown ; a is a deeper-lying venous trunk, with which two smaller capil- lary veins, b b, communicate. The superficial net-work of capillaries is seen admitting but a single series of blood-globules. All the vessels here figured are furnished with distinct parietes. 210 OE THE BLOOD AKD CIECULATIOif. axis of the vessel. The larger vessels admit several blood- corpuscles together, and in the decidedly arterial or venous branches they are observed passing on in all positions — three, four, and five abreast, over and near to one another, but those in the centre of the current always in more rapid motion than those on its outside and in contact with the walls of the vessel. (Figs. 227 and 228.) Occasionally we observe single vessels of larger cahbre running very immediately under the epithehum («), which is made up of tubular cells with nuclei (b, b, b, b), through which the fibrous parietes of the vessel are seen shining (fig. 228). Fig. 227. — Vascular rete and circulation of the web of the hind-foot of Hana temporaria^ magnified 110 times. The individual cells of the paren- chyma are indefinite and obscure. The black spots, some of them star- shaped, are depositions of pigmentary matter. The deep venous trunk, a, composed of three principal branches, 6, 6, i, is covered with a rete of smaller vessels. Mingled with the oval-shaped blood-globules, the smaller and rounder lymph-globules are apparent ; here, under the blood-globules, there, more on the outside of the stream. or THE BLOOD AI^D CIECTJLATIOIS'. 211 [§ 374. A magnifying power of from two to three hundred diameters is required, to make out the particular details of the peripheral circulation. The blood in mass, or in the larger channels, is seen to flow more rapidly than in the smaller. Here the blood-corpuscles advance with great rapidity, espe- cially in the arteries, and with a whirling motion, and form a closely crowded stream in the middle of the vessel, without ever touching its parietes. With a little attention a narrower and clearer but always very distinct space is seen to remain betwixt the great middle current of blood-corpuscles and the bounding walls of the vessel, in which a few of the lymph-corpuscles are moved onwards, but at a vastly slower rate (figs. 228 and 229, «, a). These round lymph-corpuscles swim in smaller numbers in the transparent liquor san- guinis, and glide slowly, and in general smoothly, though sometimes they ad- vance by fits and starts more rapidly, but with in- tervening pauses, and, as a general rule, at least from ten to twelve times more slowly than the corpuscles of the central stream. The clear space filled with li- quor sanguinis and lymph- corpuscles is obvious in all the larger capillary vessels, whether arterial or venous; but it ceases to be apparent in the smaller intermediate vessels, wliich admit but one or two ranks of blood-corpuscles p 2 Fig. 228. — A venous branch from the web of Rana temporaria magnified 350 times, running immediately under the sur- face. The cells of the epidermis, h, &, 6, b, flattened, mostly six-sided, connected like a piece of pavement, and generally provided with nuclei, are seen extended over the vessel. The closely serried co- lumn of blood-globules, some with their edges, others with their broad faces turned to the eye, is distinguished ; in the clear space betwixt the blood-globules and the parietes of the vessel, which ap- pear made up of longitudinally disposed parallel fibres, the round, clear, and more slugglishly moving lymph-globules are ap- parent. The object is represented under a weak light. 212 OF THE BLOOD AND CIRCULATION. (fig. 229). In these vessels the round lymph-corpuscles are seen swimming under, over, and behind the oval course of the vessel. The lymph-glohules, a, a, are (>0iY0(J 2:iven principally conspicuous in the clear space near the a? ^ u fL ° walls of the vessel. main sticking for an instant, and then are suddenly carried on again. Single blood-corpuscles, too, may frequently be observed hurled by a wave, as it were, against angles of the containing vessels, and remain hanging for a brief interval ; at these times they may be seen quivering or oscillating, in spite of the pressure they must undergo ; but their stoppages are never long, they soon fly off again, or, becoming in- volved in the general stream, they are borne onwards. In c-uiicempiating the circulation under these circumstances, a tapeciacle of the most interesting kind is presented to the eye ; or THE BLOOD AKD CIECULATIOif. 213 the little molecules of the blood are seen in ceaseless motion and alive, but altogether without inherent activity, now borne forward as upon gentle waves, and then pushed more im- petuously along ; now advancing in serried ranks, now threading their way in single files, the entire phenomena de- pendent upon the activity of the central organ. In the most minute intermediate vessels of aU, a great degree of repose is Fig. 230. — Portion of the lung of a live Triton drawn under the micro- scope, and magnified 150 times ; a, &, c, streams of venous blood ; c?, a branch of the pulmonary artery. The very delicate capillaries serving as bonds of union between the pulmonary vessels, are seen playing round little islets of the substance of the lung. The clear space between the current of the blood and the walls of the vessels observed in the larger branches is almost entirely wanting here. The lymph granules, therefore, are observed mixed with the general torrent. The arrows indicate the course of the currents. 214 or THE BLOOD AISD CIECHLATIOH. apparent ; single streams are often only recognizable by their bounding parietes ; comprehended within two dark lines, these vessels are usually filled with the liquor sanguinis alone ; it is at intervals only that a blood-corpuscle, more rarely a lymph-corpuscle, from some neighbouring and larger streamlet, detaches itself and makes its way into the canal, which till now had appeared empty ; one corpuscle entering in this way is frequently followed by several others in pretty rapid succession, and then, or without anything of the kind occurring, the vessel for a long time circulates nothing but the limpid plasma. Whether there are any vessels or not that never circulate aught but plasma, refusing, by reason of the smallness of their diameters, at all times to admit the blood-corpuscles, is doubtful. [§ 375. Such is the peripheral systemic circulation in every tissue susceptible of special examination. In the peripheral vessels of every part yet examined, the separation into the quicker stream of blood-corpuscles in the centre, and of the slower one of liquor sanguinis in the circumference above in- dicated, has been observed. But the circulation of the respi- ratory apparatus, whe- ther lungs or gills, offers a most remarkable ex- ception to this rule, so uniform in reference to the circulation at large. The capillaries of the respiratory organ are filled with blood gene- rally, e, hquor san- guinis, with its super- added blood and lymph- corpuscles, — to their Fig. 231. — One of the pulmonary islets very walls (figs. 230 and bounded by capillaries on three sides, by a 231.) It is only in the plasma is to be seen in contact with the parietes. which are much more delicate than those of the systemic circulation, and not. Like them, formed of a series of dark OF THE BLOOD AND CIRCULATION. 215 fibrous layers. The circulation through the lungs of the water newt is a very beautiful object (fig. 230). The pulmonary arteries (d) here expand very speedily into a fine-meshed net-work of intermediate vessels, which in general admit no more than single files of blood-corpuscles playing around very minute islets of the parenchyma of the lung (fig. 231). The vessels always appear with distinct parietes, and terminate partly in capillary veins of the same character as themselves (fig. 230), partly in larger venous trunks. The blood-corpus- cles mixed with lymph-corpuscles (fig. 231, c),as already stated, fill both arteries and veins close to their parietes. The same appearances are presented in the branchial fringes of the larva of the water-newt.]* * Professor Wagner’s Physiology, page 294, et seq. CHAPTER EIGHTH. OF RESPIRATION. * § 376. Foe. the maintenance of its vital properties, the blood must be submitted to the influence of the air. This is true of all animals, whether they live in the atmosphere or in the water. No animal can survive for any considerable period of time without air ; and the higher animals almost instantly die when deprived of it. It is the office of eespieation to bring the blood into communication with the air. [§377. In the lowest classes of animals no special organ is developed for the exposure of the nutritive fluid to the oxygen- ating influence of the air contained in the water in which they live. In them, the general cutaneous surface is a respiratory organ ; such is the case in infusoria, polyps, medusae, and many other invertebrata. Many parts of the cutaneous mem- brane on the exterior of their bodies, or that lining the diges- tive organs, are covered with vibratile cilia, by the motions of which, currents of water are made to flow over these surfaces, and th^^reby oxygenating the nutritive fluids circulating in them. [§ 378- In the echinodermata special organs exist ; the up- per surface of the tegumentary membrane of the Aster ias is covered with innumerable small transparent fleshy tubes, which in the living state are seen advancing and receding through openings in the integument. The interior of these tubes is lined with cilia, and by their vibrations currents of water are made to flow through them into the visceral cavity, into which they open. The peritoneal membrane lining this cavity pre- sents a considerable extent of surface continually in contact with the surrounding medium, and appears to be the principal seat of respiration. Its surface is covered with cilia, by which currents of water made to flow in a determinate direction^ OF RESPIRATION". 217 and thus the stratum in contact with the vascular membrane IS incessantly renewed, and respiration thereby maintained. [In the Echinidce (fig. 1 74), the space comprised between the viscera and the test is filled with water, which is drawn into and rejected from the body by five pairs of mem- branous respiratory tubes, collected into ten tuft-like organs, situated around the circumference of the oral aperture, and opening internally by two perforated pits, as in Asterias, The water thus introduced into the interior of the test flows along the membrane, covering its surface, and over the peritoneal layer, investing the digestive organs and tubular feet and ovaria by the action of cilia, so that the in- terior of the test of the Echinus is in- cessantly tra- versed by re- spiratory cur- rents, whilst the blood, circulating through the coriaceous in- tegument, is in like man- ner aerated by currents flow- ing over its surface by the vibrations of cilia. In the Ho- lothuria (fig. 232), the re- spiratory function is limited to a pair of or- gans formed after a type which attains pjg 232. — The anatomy of the Holothuria tnhulom^ 218 or EESPIEATIOJT. its full development, among the air-breathing vertebrata, in- stead of entering the general visceral cavity by tubes, and flowing over the surface of the peritoneum by the motions of cilia, as in the Asteriadce and Echinidce ; the water is inspired through a single chamber, called the cloaca ( g, fig. 232) ; and by the contraction of its muscular walls flows into two tubular branched organs {i, k), attached by a process of the peritoneum to the walls of the body ; upon the membra- nous lining of these organs, which divide and subdivide, like a tree, into branches, terminating in tuft-like cells (m) ; the blood-vessels ramify like the pulmonary vessels on the bron- chial tubes in the air-breathing vertebrata, which they further resemble in the rythmic movements of dilatation and contrac- tion, which take place three times in a minute in the Holo- thuria tuhulosa (fig. 232), the water, after each inspiration, re- maining about twenty seconds in the body. [§ 379. The respiratory organs, in all the other classes of the animal series, may be grouped into three principal forms ; branchise, tracheae, lungs. The plan manifested in the structure of these organs is to fold up, into the smallest possible space, a large extent of membranous surface, upon which a net- work of blood-vessels may be spread. It is impossible to imagine a more perfect fulfilment of these conditions than is accomplished in the structure of the branchiae and lungs, whereby the whole circulating fluid of the body is made to traverse a vascular net- work, and is brought thereby into mediate or immediate con- tact with the air of the atmosphere, or that held in solution in the water : as a general rule, it may be stated that branchiae are adapted for aquatic, and lungs for aerial respiration. [§ 380. Most of the mollusca respire by branchiae. In the Tunicata they occupy the interior of a cavity which is tra- versed by currents of water, entering at one orifice and escaping at another, and caused by the vibrations of cilia. In the Salpce the branchia has the form of a tube, formed by a fold of the internal membrane, disposed transversely in spiral turns, which gives an annulated appearance to the cavity, and has caused it to be likened to the tracheae of insects. The su- perior border of this membrane is provided with an infinity of small vessels, running parallel with each other ; in other genera the branchia forms a more continuous lining of the respiratory OF KESPIRATION. 219 sac ; the inhaled currents are made to traverse the body by the cilia, encircling the afferent aperture, and developed on the surface of the branchial membrane. In the CoNCHiFEEA the mantle presents two orifices, the one for the entrance and the other for the exit of the water from the branchial cavity. In the oyster (fig. 176), the bran- chiae form four leaflets (Ji, k), attached by their contiguous .upper margins, and free below ; they consist of innumerable elongated filaments, covered by a delicate membrane, on which a rete of capillary blood-vessels is spread ; vibratile cilia are developed on the surface of this membrane, as well as on that of the branchial cavity, by which currents of water are made to traverse the respiratory organs in a determinate direction ; in the conchifera, burrowing in rocks, sand and mud, the branchiae are greatly elongated, and the mantle is prolonged into tubes, for conducting water into the palleal cavity. The vibratile cilia are of large size in Mytilus and Anodon, covering the entire surface of the branchial filaments, and lining aU parts of the respiratory cavity ; a small portion of the branchiae, detached from the hving animal, is seen to row itself, like an animalcule, through the water, by the motion of its cilia. Nearly all the Gasteeopoda respire by branchiae, which, in most of the naked marine species, are in the form of tufts, fans, or combs, variously disposed on the surface of the body, and in the testaceous kinds are concealed under a fold of the mantle. In the Boris (fig. 221) the branchiae (e) form elegant ramose tufts, disposed around the anal opening ; in Thethys they are composed of two dorsal rows of alternately tufted and crested organs. In Aplysia (fig. 177) they occupy the right side of the body, and are protected by a delicate peUucid shell. In the numerous pecteni-branchiate gasteropods, as the Paludina (fig. 35), inhabiting univalve turbinated shells, the branchiae {g) are placed under an extended fold of the mantle, and in many of the carnivorous genera the water is con- ducted into the branchial chamber, through a muscular si- phuncle, lodged in a canal of the shell, and flowing over the surface of the filamentary gills, by the vibrations of the cilia, is discharged through an opening in the palleal cavity, carrying with it the excreted materials from the glands and intestinal canal. 220 OF SESPIEATIOIS'. [In the Pteropoda, as the Clio and Hyalea^ the branchiae resemble membranous expansions, like fins, or lamellae, on the surface of the body. In the Cephalopoda they form two or four organs, lodged in a distinct chamber, into which the water is inspired, and expelled through a funnel-like tube, situated on the under side of the neck. [§ 381 . The CRTJSTACEA present various phases of branchial development ; in the lowest forms, no special organ exists; the tegumentary membrane forming a general aerating surface. In the bran- chiopods, the last joints of the feet are flattened and covered with a vascular membrane, adapted for respiration ; these organs having a continual oscillating movement. In the Squilla, the bran- chiae are limited to the abdominal members ; whilst in the decapoda, as the crab and lobster (fig. 222), they are formed like those of mollusca and fishes, and lodged in separate cavities under the thoracic shield ; the renewal of the water being effected by the motion of distinct appendages. In those Crustacea, as the land crabs, which live for a time on shore, the branchiae are kept moist by the membrane lining, the cavities being disposed in folds, to serve as reservoirs for water ; and sometimes it presents a spongy texture for the same end. [§ 382. The marine A^hvelida respire by bran- chiae variously disposed, on different parts of their bodies ; in those living in tubes, as Serpula and S^hella, they resemble the tentacula of polyps, and form plumelike coloured organs, sometimes with a spiral winding. When fully expanded in the water, they are adorned with the most beautiful colours. In the Amphitrite they are pectinated; in Terehell(B they resemble small trees planted round the neck. In the genera which swim freely through the water, they are disposed in longitudinal lines ; in the Arenicola (fig. 233), they form a series of tufts, Fi 033 _ iiA bloodvessels. In Eunices, they have a Bralichf^ of pectinated form, and in Aphrodita they are placed the Arenicola. on scales along the back. In the Hirudo (fig. OF EESPIEATION. 221 178) a senes of vesicles lined with mucous membrane, and richly supplied with blood vessels, are regarded as respirating sacs. [§ 383. Fishes respire by branchiae, or gills, for the sup- port and protection of which a complicated framework of bones, cartilages, ligaments, and muscles is provided ; the form and arrangement of this apparatus varies in the diiferent families and genera. It may, however, be classified into — 1st. The lingual bone and branchiostegous rays ; 2nd. The bran- chial arches ; 3rd. The opercula or gill covers. The gills are for the most part attached to the branchial arches, which extend from the sides of the os hyiodes, back- wards to the cranium. They are, in general, four in number on each side of the head, and are composed of numerous la- mellae, placed closely together, and arranged in a regular series over the whole external convex margin of the branchial arches, like the barbs of a feather, or the teeth of a comb. Every- thing is arranged to afford the greatest possible extent of sur- face for the contact of the water with the mucous membrane on which a rich vascular network is spread. In the common ray, the extent of surface of the mucous membrane of the gills is estimated at 2250 square inches. In osseous fishes, as the pike and perch, the gills adhere by their superior bor- der, and are covered by moveable opercula. In the carti- laginous genera, as the rays and sharks, they are attached by both borders, and there are no opercula ; the water, which in the former enters by the mouth and escapes by the oper- cula, in the latter is expelled by a series of fissures situated at the sides of the neck. In the Hippocampus and Syngnathus, the gills are disposed in the form of tufts along the surface of the branchial arches, resembling the tufted branchiae of gastropoda and annelida. In sucking fishes, as the lamprey, Petromyzon, they are in the form of vesicular sacs, ar- ranged on each side of the neck, into which the water is introduced by a canal coming from the cavity of the mouth, and discharged through the holes situated at the sides of the same region. Most fishes, besides gills, possess a hollow organ analagous to a lung, and called the air-sac, or swim-bladder ; it is situated in the abdominal cavity, lying along the under side of the ver- 222 OP RESPIKATION. tebral column, and, in general, communicating with the pha- rynx, or stomach, by a membranous canal. Numerous blood- vessels and nerves, derived from the eighth pair and the sym- pathetic, are distributed on its walls ; this organ is most de- veloped in those fishes which come frequently to the surface of the water, and are remarkable for their vehement and prolonged muscular movements, as the Lepidosteus of the American rivers. The air-sac in this fish is divided into two chambers, the lining membrane presenting an arrangement of cells like the lung of a reptile ; the duct from this air-sac, surmounted by a rudimentary larynx, opens high up in the throat, and, although a simple membranous tube, is the homo- logue of the trachea of air-breathing vertebrata. In the Lepi- dosiren the air-sac is a double organ, each division being divided into several lobes ; it is situated behind the kidneys, against the ribs, and is internally cellular, like the lung of a serpent ; an- teriorly it opens by a tolerably long, narrow membranous tube into the esophagus ; each division of the air-sac receives a branch of the pulmonary artery, arising from the branchial arteries. For these reasons the air-sac of fishes is regarded as a rudimentary lung, performing an accessory part in the great function of respiration. It is least developed, or even wanting, in those species which live at the bottom, and burrow in sand or mud, as the lampreys, rays, and Fleur onectidce. Many fishes respire by the intestinal canal, the air which they swallow at the surface being employed for that purpose, as it escapes from the intestine loaded with carbonic acid gas. The fact of fishes swallowing air may be seen in the electric eel, and in fishes kept in vases, the water of which has been deprived of its air by their respiration. [§ 384. The higher forms of reptiles, as serpents, lizards, and turtles, breathe by lungs. In the amphibia, one group comprising the frogs and salamanders, respire, during a term of their embryonic development, by vascular tufted gills ; but these organs are subsequently absorbed, as the lungs become developed ; and, during adult life, they breathe air by lungs, respiration being aided by the general surface of their smooth, naked, tegumentary membrane. In another group the gills are persistent through life, and co-exist with the lungs. Such is the case in the Amphiuma, Menohranchits, Proteus, Siren, or EESPIEATION. 223 Axolotl ; all these amphibia, like fishes, have branchial arches attached to the hyoid bone, and situated at the under part of the head; in the Proteus, there are three pairs of branchiae, with ramified filaments, extending in the form of vascular branched organs to a considerable distance beyond the branchial apertures ; the water enters by the mouth and escapes by the inter-branchial spaces. Besides gills, the perennibranchiate amphibia possess lungs resembling the air-sacs of fishes, and which we shall describe in treating of the development of these organs. [§ 385. The second form of respiratory organs, called tra- chece, is met with in myriapoda, insecta, and some arachnida. The tracheae are air-tubes which divide and subdivide, and be- come smaller and smaller in diameter, and penetrate the sub- stance of all the organs ; sometimes they are enlarged into vesicular sacs, of different forms and sizes (fig. 234). These tubes convey atmospheric air to the interior of all the tissues, and, as they are everywhere surrounded by the blood, difiiised through the body of insects, a perfect aeration of that fluid is effected ; the extensive ramification of the tracheae being a compensation for the imperfection of their organs of circula- tion. The large quantity of air contained in the bodies of in- sects impart the necessary lightness and elasticity to them, and the highly oxygenated condition of their circulating fluids imparts energy to the muscular system, and precision and activity to their movements ; to the same cause we must like- wise attribute the high temperature which their bodies so often acquire. Fig. 234 exhibits the respiratory system in the cinerea. The air is admitted by the spiracles, or stig- mata, into two great lateral tubes, which subdivide and ramify through the body ; the tracheae are fined with a soft mucous membrane, and covered externally with a dense, shining, serous coat ; between these is interposed an elastic fibrous tunic, formed of a cartilaginous filament rolled into a spiral form, like the spiral vessels in plants. This admirable struc- ture, affording as it does one of those striking examples of creative wisdom and design, extends through all the ramifi- cations of the tracheae, giving the necessary elasticity and patency to tubes destined to convey air, and to ramify like blood-vessels through all parts of the head, antennae, palpi, legs, tarsi, wings, muscular, nervous and digestive systems ; 224 OF EESPIEATION. the stigmata, or spiracles, are provided with muscles to open and close them, and with valves, processes, and hairs, va- Head. 1st pair of legs 1st segment of the thorax. Origin of the wings. 2d pair of legs. 3d pair of legs. Tracheae. Spiracle. Vesicular air sacs. Fig. 234. — Respiratory apparatus of the Nepa cinerea. nously modified in the different famihes, to protect them from the entrance of foreign bodies. The abdominal segments of the body exhibit rythmic contractions and expansions during respiration, which are well seen in the dragon-fiy, and resem- ble the muscular movements of the thorax and abdomen during the same act in the pulmonated vertebrates. — T. W.] RESPIEATION. 225 § 386. In the lower vertebrata provided with lungs they form a single or- gan ; but in the higher classes they are in pairs, placed in the cavity formed by the ribs, one on each side of the vertebral co- lumn, and en- closing the heart between them (fig. 235). The lungs communi- cate with the atmosphere by means of a tube, composed of car- tilaginous rings, arising at the back part of the mouth, and dividing below, first into a branch for each organ, and then into innumerable branches penetrating their whole mass, and finally terminating in minute cells. This tube is the trachea {t), and its branches are the bronchi. In the higher air-breathing animals the lungs and heart occupy an apartment by themselves, the chest (fig. 124), which is separated from the other contents of the lower arch of the vertebral column by a fleshy partition, called the diai^hragm (fig. 180), passing across the cavity of the body, and arching into the chest. The only access to this apartment from without is by the glottis through the trachea (fig. 235, £), § 386*. The mechanism of respiration by lungs may be compared to the action of a bellows. The cavity of the chest is enlarged by raising the ribs, the arches of which naturally slope somewhat downward, but more especially by the con- traction of the diaphragm, whereby its intrusion into the chest is diminished. This enlargement causes the air to rush in through the trachea, distending the lungs so as to fill the ad- Q Fig. 235. — Lungs, Heart, and principal blood- vessels of Man. a r, right auricle ; v r, right ventricle ; v I, left ventricle ; a, aorta ; v c, vena cava ; a c, carotid arteries ; vj, jugular veins ; a 5, subclavian ar- tery ; V s, subclavian veins ; trachea. 226 EESPIRATIOif. Fig. 236. — Lung^of the water- newt {Triton cristatus) ; A, the natural size ; B, magnified ; a, pulmonary artery ; h, pulmonary vein. Fig. 237. — Portion of the lung of the Triton cristatuSc The ves- sels are injected with fine size and vermilion, and form so dense a net- work that minute islets only of parenchyma remain visible. ditional space. When the dia- phragm is again relaxed, and the ribs are allowed to subside, the cavity is again diminished, and the air expelled. These move- ments are i^cm^diinspiration and expiration. The spongy pulmo- nary substance being thus dis- tended with air, the blood sent from the heart is brought into such contact with it as to allow the re- quisite interchange to take place. [§ 387. The minute anatomy of the lungs, in vertebrate ani- mals, exhibits many interesting varieties. The structure is sim- plest in the naked amphibia, where it is but little more com- plex than in the snails.* In the water-newt, for instance, the lungs present themselves as a pair of simple elongated sacs (fig. 236), attached to an ex- tremely short rudimentary la- rynx, and internally exhibiting no projection ; the air distends the entire hollow internal sac, or cavity. In the frogs the mem- branous surface of the lungs is increased by the development of cells upon their internal aspects (figs. 237 and 238), upon the bottoms of which cells other secon- dary and smaller ones can be per- ceived ; all these pulmonic cells, * The lung presents itself in its very simplest form in the snails and slugs. The contractile respiratory ori- fice here leads to a simple smooth in- ternal cavity lined with a dehcate mucous membrane, upon which the pulmonary vessels are distributed. EESPIEATION. 227 Fig. 238. — Portion of the frog's lung from within, to shew the open parietal cells — figure drawn twice the size of nature. however, are merely parietal, and communicate directly with the middle cavity of the lung, which is filled with atmo- spheric air, and upon the membranous walls of which, as well as upon their bot- toms, the blood-vessels ra- mify, In the turtles (fig. 239) and crocodiles the cel- lular subdivisions increase in number and dechne in size, andthe common cavity is divided by various bands and septa stretching across it, into a number of mutually communicating sacs or pouches; the whole lung thus acquires a more compact or parenchy- matous appearance. In the serpents (fig. 240), in which one only of the two lungs is ever completely evolved, this at the upper part is covered with small parietal cells ; but these gradually become smaller and smaller, less and less distinct, and finally disappear entirely, so that the lower part of the lung is completely vesicular and unvascular. [§ 388. In the class of birds we observe, in the same interesting manner, the general type of the lung preserved, but the sur- face of contact is greatly in- creased by means of parie- tal cells, which are repeated again and again. This mo- dification is made necessary Fig. 239. — A, several cells from the lung of a Tortoise. A portion of one of these cells is exhibited in B, magnified five hundred times — part of the septum, a, a, which divides this cell from those next to it, c and d, is seen. The ves- sels are injected with sizejand vermilion, and form such thick masses, that the islets of pulmonic parenchyma betwixt them almost disappear. by the larger quantity of blood which is here transmitted to q2 228 EESPIEATIOIii . the respiratory system, and the consequent augmented amount of respiratory process, by which a larger extent of membranous surface became indispensable. The bronchi in birds are continued into the lungs, where they divide into membranous tubes, which permeate their sub- stance; the deeper tubes stand like organ-pipes, and open into the superficial tubes ; and all are covered with small parietal cells, upon which vessels are dis- tributed ; the cells form very elegant, delicate microscopic reticulations, and generally present themselves as six- sided spaces. [§389. The lungs of man and the mammalia are form- ed after another and a differ- ent type ; the trachea here divides and subdivides, like the branches of a tree, into finer and finer branches, which at first contain carti- lages in their constitution, but which by and by become membranous, and finally end in blind sacculi, or rather in hollow berry or bud-like and clustered vesicles (figs. 241 and 242). The pulmo- nic cells of man and the mammalia, consequently, are not parietal, but termi- nal ; they vary from the 6th to the 18th of a line in magnitude, the majority of them measuring between the 8th to the 10th of a line in diameter. Fig, 240. — A piece from that part of the Serpent’s lung which is most scan- tily supplied with vessels, magnified four hundred times. The vessels here form a very beautiful rete, with wide meshes ; they have been successfully injected with fine size and vermilion. Fig. 241. — Terminal vesicles of the human lung, hanging to a branch of the bronchi as berries hang to their stalk, and distinct from one another. The figure is half a plan, and the mag- nifying power used very high. EESPIEATION. 229 Fig. 242 — A, portion of the lung of a hog. The terminal vesicles are filled with mer- cury, and of the natural size. B, the same part seen under a simple lens. Delicate arcuate fibres, of the nature of elastic tissue, sur- round these terminal vesicles, and hold them distended, whilst the vessels spread freely over their sur- face (fig. 242). [§ 390. The development of the lungs is extremely interesting. In the embryo of the bird and mammal they first appear in the shape of a simple, and then of a double projec- tion from the esophagus (fig. 244, a), which soon divides more distinctly into two, becomes separated from this part, and is finally supported upon a pedicle — the future trachea (fig. 244, b). In birds these little sacs are then drawn out into hollow tubes, which pass over into the paral- lel pipes above described (§ 387). In the mammalia they divide, after the man- ner of branch- es, into twigs and minute vesicles (figs. 241 and 242), which advance in develop- ment, and be- come the future terminal cells (fig. 242, E). [§ 391. The capillary vas- Fig. 243.— Small portion of lung from the body of cular net- work ^ examined shortly after death, under a magnify- r iV 1 ing power of 200 times. The vessels, 6, &, &c., still 01 tne blood, include very minute islets of paren- as already chyma between them ; the semicircular fibres, a, a, c, stated, exhi- surround the smallest terminal cells of the lungs. 230 EESPIEATIOIS". Fig. 244. — a, Rudiment of the lung in the embryo of the fowl of the fourth day ; &, the lung in the embryo of the sixth day. Both figures twice the size of nature. bits a peculiar structure, which may be studied very readily in the lungs of the live newt (fig. 230), or in preparations of the same part that have been finely injected. From the whole extent of the pulmonary artery a vast number of very small arteries arise, the orifices of which give the inner surface of its principal branches the appearance of a regularly per- forated sieve ; these minute ves- sels form a very close irregular hexagonal intermediate net-work, without resolving themselves into branches and twigs like a tree, and so forming a capillary rete. Yet single larger vessels (fig. ' 230, d) proceed from the pulmonary artery to reach some more remote part of the lung. The pulmonary vein, like the pul- monary artery, is partly perforated at every point in its course for the reception of smaller vessels, and is partly formed by larger venous trunks, which collect and bring the blood from greater distances (fig. 230, c). The islets of the thin and indistinctly cellular pa- renchyma, are often of a di- ameter inferior to that of the ves- Fig. 245. — The greater part of the right lung of a foetal sheep, an inch and a half long, seen under the microscope (af- ter Muller, De Gland, secern, struct, penit. T. xvii. f. 7). Fig 246. — Termination of one of the branchings of the bronchi from the lung of a very young embryo of the hog after Rathke (fig. viii. T. xviii.) sels which surround them ; this is the case in the tortoise, for ex- ample (fig. 239), and appears to be the case in man also (figs. 241, 242). It is remarkable that even in the more conspicuous branches of the pulmonary vas- cular system, the layer of trans- parent lymph in immediate con- tact with the walls of the vessels EESPIRATION. 231 should either be wanting, or of the greatest delicacy ; and that no lymph -corpuscles should be visible swimming in it apart from the general current, but that they should be observed mingled with the common stream (fig. 230 «, c).]* [§ 392. The organs which serve in man and the various classes of animals for respiration, and the mechanical part of the function of these organs, have now been described. The very essence of respiration, however, consists in this : that the air of the atmosphere brought into contact with the blood within the lungs effects certain changes in that fluid which are indispensable to the maintenance of life. The air^ it is true, does not come into direct contact with the blood even in the lungs, but is separated from it by the parietes of the pulmo- nary cells and the walls of the blood-vessels. The air, how- ever, readily penetrates these moist tissues, for it combines with the watery fluid which permeates them, and so makes its way even immediately to the blood. f As the lungs contain air at all times, the influence which the elastic fluid exerts upon the blood, and the changes which the blood undergoes, are not connected with the alternate assumption and rejection of so much air. These are but means to an end : the proper respiratory process, or that process for which inspiration and expiration are instituted, goes on incessantly. Inspiration and expiration are merely provisions for changing the air, which must be renewed at intervals, longer or shorter, if the object of respiration is to be attained. — Before entering on the peculiar chemical processes occurring in respiration, it is proper to inquire into the changes which, 1st, the air^ and 2nd, the bloody experience in its course. [§ 393. The earliest accurate researches into the nature of respiration, were instituted with a view to determine the changes which the air experienced in passing through the lungs, and our infoimation upon this part of the function * Professor WagnePs Physiology, pp. 358, et seq, t The penetration of the moist parietes of the air-cells and blood- vessels is a general physical phenomenon, and independent of any peculiar power or property inherent in the lungs ; any moist animal membrane without or within the living body is gradually penetrated by the air of the atmosphere and other ^ases; (§ 413). The extensive subdivision which the blood undergoes in the minute vessels of the lungs is obviously calculated greatly to assist the operation of the air. 232 HESPIEATIOI^. may be said to be pretty full. The air of the atmosphere consists of a mixture of nitrogen and oxygen, with a shght addition of carbonic acid and of hydrogen gases : 100 parts of atmospheric air consist, according to the latest analyses, very constantly of 79 parts of nitrogen, and 2 1 of oxygen ; the admixtures of carbonic acid and hydrogen, on the contrary, are extremely variable in amount; the carbonic acid has been ascertained to vary between 0,0003 and 1,0 per cent. ; the hydrogen may amount to about 1 per cent. The air that is expired yields very nearly the same quantity of nitrogen as the air that is inspired; but it contains less oxygen, and a larger quantity of carbonic acid, and also of hydrogen ; it likewise contains some volatile organic matters. The quantities of oxygen and carbonic acid, in the air, have altered relatively during respiration, in suchwise that the volume of the oxygen which has disappeared is rather greater than that of the carbonic acid which has made its appearance. Sir Humphrey Dary breathed during one minute, making 19 inspirations in the time, 161 cubic inches of air, which in 100 parts consisted of 72,7 nitrogen, 26.3 oxygen, and 1,0 carbonic acid; and during this time he expired 152 cubic inches of air, of which 100 parts contained 73.4 nitrogen, 15,1 oxygen, and 11,5 carbonic acid. In this ex- periment, consequently, if we disregard the disappearance of 9 cubic inches of air and a slight increase of nitrogen, it appears that from the respired air 1 1,2 per cent of oxygen had vanished, and 10,5 per cent, of carbonic acid had appeared. In the experiments of Allen and Pepys, 100 parts of expired air were found to consist of 79 nitrogen, 13 oxygen, and 8 carbonic acid; supposing, therefore, the air which was breathed to have been of the normal constitution, 8 per cent, of oxygen had disap- peared, and rather more than 8 per cent, of carbonic acid had been evolved. Like results w^ere come to by Dulong, Des- pretz, Lavoisier, and Seguin. In the quantity of the absorbed oxygen and of the added carbonic acid, however, the state- ments of the different observers differ. Davy, for example, found that the quantity of the added carbonic acid amounted to from 3,95 to 4,5 per cent. ; in the particular experiment quoted above, it was as much as 10,5 percent. Allen and Pepys state it at from 8 to 8,5 per cent. ; Berthollet at from 5,53 to 13 per cent. ; Menzies at 5 per cent. ; Prout at from CHAllfGES TK THE AIR. 233 3,3 to 4,6 per cent. ; Murray at from 6,2 to 6,5 per cent. ; Fyfe at 8,5 per cent., and Irvine at 10 per cent. The mean of the whole of these observations is about 5,8 per cent. If we presume that errors had crept into some of these experi- ments, it is still obvious that the quantity of carbonic acid eliminated by different individuals, and at different times, is not always the same. Prout, whose skill in observation inclines us to place the most implicit reliance on his results, found by direct experiment that the time when the smallest quantity of carbonic acid was produced, was shortly after midnight ; it increased towards morning, and rose continually towards mid- day, when it attained its maximum ; in the afternoon it declined again, and sank continually through the course of the evening, until it reached its minimum about midnight. The formation of carbonic acid, therefore, experiences regular fluctuations in accordance with the times of the day. Prout observed, farther, that a larger quantity of carbonic acid was produced in states of mental tranquillity, during gentle exer- cise and with a low state of the barometer ; and that, on the contrary, less was formed under the influence of active exer- tion, depression of mind, and the use of spirituous liquors. The estimates which we have of the absolute quantity of car- bonic acid eliminated during a given time also vary greatly. According to Lavoisier and Seguin, the quantity formed in twenty-four hours amounts to 8,534 grains French ; according to Davy, it is 17,811 grains English; according to Allen and Pepys, it is 18,612 grains English. But these quantities Berzelius has shown are far too great with reference to the quantity of food consumed in the same interval of time.* * Berzelius observes {Thierchemie^ 3tte Auf, S. 124), that upwards of six pounds of solid aliment daily would be required to replace this loss of carbonic acid, even were the whole of the carbon of the food to he elimi- nated by the lungs in the shape of carbonic acid, and none to pass olf with the foeces, the bile, the urine, &c., which, however, is very far from being the case. The above quantities must, therefore, be looked upon as exag- gerated, though the observations themselves may be perfectly correct ; the error, probably, lies in the reckoning ; during the short period that such experiments last — one or two minutes — inspiration and expiration are almost certainly forced or exaggerated ; the air is more rapidly changed, and more carbonic acid is eliminated than during ordinary^ respiratiou. The indications afforded by two minutes, under such circumstances, ap- plied to the whole of the twenty-four hours, obviously raise the general result far above the proper standard. 234 RESPIEATIOjr. The quantity of water contained in the expired air amounts^ taking the mean of the estimates of a great number of ob- servers, to about 8,000 grains, or one pound in the four-and- twenty hours.* RESPIRATION IN GASES OTHER THAN ATMOSPHERIC AIR. [§ 394. With a view of o*btaining still more precise informa- tion regarding the changes induced in air by its assumption into the lungs, experiments have been instituted on the respi- ration of different kinds of gas. These experiments, however, * See Muller’s Physiology j by Baly, vol. i. p. 330. The statements in the text refer particularly to man ; but they also apply very closely to animals which breathe by lungs, with this difference, that in cold- blooded animals the quantities of oxygen absorbed, and of carbonic acid eliminated, are relatively smaller. Dulong found, no matter what animal he made the experiment upon, that there was rather more oxygen ab- sorbed than carbonic acid evolved. The excess in graminivorous animals amounts to one-tenth ; in carnivorous creatures, it was from one-fifth to one-half more than the carbonic acid, Despretz observed the same thing. Allen and Pepys, on the other hand, found the quantity of oxygen that disappeared, and of carbonic acid that was generated, to be equal. The oxygen which disappears is used up in the combustion of hydrogen, the product of which is watery vapour. Treviranus and Muller instituted comparative experiments upon the respiration of some of the lower animals, and the quantity of carbonic acid formed in a given time, con- trasted with the weight of the animal, from which it appears that mammals, for every one hundred grains of their weight, produce 0.52 of cubic inch of carbonic acid in one hundred minutes ; that birds, consi- dered in the same way, produce 0.97 of a cubic inch ; that amphibia (the frog), still considered in the same way, produce 0.05 of a cubic inch. The respiratory process performed by the medium of water is precisely the same as that which goes on with the direct contact of air : the air dis- solved in the water comes into contact with the blood which circulates through the gills, and oxygen disappears, and carbonic acid appears as usual. Water, in general, contains from five to five and a quarter per cent, of its bulk of air dissolved in it — this air, however, having a somewhat greater relative proportion of oxygen than the air of the atmosphere, oxygen being somewhat more soluble in water than nitrogen. We have very admirable researches on the respiration of fishes by A. von Humboldt and Provencal. The water in which the fishes were put in these experi- ments contained 20,3 per cent, of air, which, in one hundred parts, con- sisted of 29,8 oxygen, 66,2 nitrogen, and 4,0 carbonic acid. After having been used for respiration, the water still contained 17,6 per cent, of air, which consisted, in one hundred parts, of 2,3 oxygen, 63,9 nitrogen, and 33,8 carbonic acid. Here, therefore, oxygen was also absorbed, and carbonic acid evolved. KESPIEATION or NITEOOEN. 235 almost necessarily extended to the consideration of the effects which breathing different gases produced upon the organism, as well as to the changes which the gases suffered in the process. We shall therefore here consider the two together. During healthy respiration, the atmospheric air that supplies the lungs is constantly changed. If this renewal of the air is not provided for, but the same air is breathed over and over again, the circumstances attending respiration are altered. In the same proportion, for example, as the oxygenous con- tents of the air diminish, and the carbonaceous contents in- crease, less and less oxygen is absorbed, less and less carbonic acid is evolved ; and when the air comes to have a certain proportion of carbonic acid mixed with it, which, from the experiments of Allen and Pepys, appears to be ten per cent., no more carbonic acid is formed, and the elastic fluid no longer suffices for respiration, although it still contains some- thing like ten per cent, of oxygen. A little oxygen, indeed, continues to disappear, but the respiration becomes laborious, and cannot be carried on without imminent risk of suffocation to any of the higher animals. This is the source of the oppressive sensation experienced when many persons, crowded together in a limited space, continue to breathe the same atmosphere. In pure oxygen gas respiration goes on as readily as in atmospheric air, but a feeling of uneasiness and of exhaustion is soon ex- perienced. The changes produced in the gas are of the same nature as when the common atmospheric air is breathed — oxygen disappears, and carbonic acid is engendered; the quantity of the latter, according to Allen and Pepys, being, however, greater than under ordinary respiration — it amounts, instead of eight per cent., to between eleven and twelve per cent. The same experimenters also found that nitrogen gas was evolved during the respiration of oxygen gas. Nitrous oxyde gas (consisting of sixty-four nitrogen, thirty-six oxygen), like oxygen, will support life for a time, but it produces a pe- culiar intoxicating effect upon the economy. A portion of the gas is dissolved by the blood, which assumes a purple red colour ; and the face and hands, in consequence of this change, acquire a livid and cadaverous hue. Nitrogen and traces of carbonic acid are found in the expired nitrous oxyde gas. Pure nitrogen, although it can be taken readily into the lungs, and is not at all poisonous, is quite incompetent to support 236 EESPIRATION. life ; small animals immersed in it, therefore, soon die as- phyxiated. Pure hydrogen, too, can be breathed, but will not support life ; it is either without effect on the economy, or exerts a soporific influence. The experiments of many in- quirers, however, have shown that cold-blooded animals, such as frogs, can exist for hours in pure nitrogen and hydrogen ; they become asphyxiated at length, and are apparently dead ; but if not kept too long immersed in the gases, they recover when brought into contact with the air of the atmosphere. All observers, too, are agreed that these animals eliminate car- bonic acid when confined in nitrogen and hydrogen. In a mix- ture of four parts hydrogen and one part (volume) oxygen, animals were found by Allen and Pepys to become sleepy, without any prejudicial effect upon the health appearing to ensue. Oxygen disappeared, and carbonic acid was evolved precisely as when atmospheric air was breathed ; at the same time, however, nitrogen made its appearance, and in such quan- tity, too, that in the course of an hour the volume eliminated equalled, and even exceeded by a half, the volume of the animal which was the subject of experiment. Other gases are true poisons to the economy — carburetted, phosphuretted, sulphuretted, arseniuretted hydrogen, &c. Air that contained no more than 1-1 500th of its bulk of sulphuretted hydrogen was sufficient to prove fatal to a bird ; 1 -800th destroyed a dog, 1 -250th killed a horse. Some gases inspired in a state of purity, or but little diluted, induce spasm and complete closure of the glottis, and consequent death ; more largely diluted, they excite violent cough. To this list belong chlorine, the vapour of iodine, nitric oxyde, ammoniacal gas, fluoboric and fluosilicious gas, and the greater number of the strong acid vapours, such as those of nitric acid, sulphuric and sul- phurous acid, succinic acid, &c. The greater number of the particulars related in the preceding paragraph have been made known to us through the admirable researches of Sir Humphrey Davy.]* § 395. The vivifying power of the air upon the blood is due to its oxygen. If an animal be confined for a time in a closed vessel, and the contained air be afterwards examined, a considerable portion of its oxygen will have disappeared, and another gas of a very different character, namely, carbonic * Dr. Julius Vogel, in Wagner’s Physiology, p. 366. BESPIEATION. 237 acid gas, will have taken its place. The essential office of respiration is to supply oxygen to the blood, at the same time that carbon is removed from it. § 396. An immediately obvious effect of respiration in the red-blooded animals is a change of colour ; the blood, in passing through the respiratory organs, being changed from a very dark purple to a bright scarlet. In the great circulation the scarlet blood occupies the arteries, and is usually called red blood, in contradistinction to the venous blood, which is called black blood. In the lesser or pulmonary circulation, on the contrary, the arteries carry the dark, and the veins the red blood. § 396*. The quantity of oxygen consumed by various ani- mals in a given time has been accurately ascertained by expe- riment. It has been found, for instance, that a common- sized man consumes, on an average, about one hundred and fifty cubic feet in twenty-four hours ; and as the oxygen con- stitutes but twenty-one per cent, of the atmosphere, it follows that he inhales, during a day, about seven hundred cubic feet of atmospheric air. In birds, the respiration is still more active, while in reptiles and fishes it is much more sluggish. § 397. The energy and activity of an animal is somewhat dependent on the activity of its respiration. Thus the toad, whose movements are very sluggish, respires much more slowly than mammals, birds, and even insects ; and it has been ascer- tained that a butterfly, notwithstanding its comparatively diminutive size, consumes more oxygen than a toad. § 398. The circulation and respiration have a reciprocal influence upon each other. If the heart be powerful, or if violent exercise demand a more rapid supply of blood to repair the consequent waste, respiration must be propor- tionally accelerated to supply air to the greater amount of blood sent to the lungs. Hence the panting occasioned by running or other unusual efforts of the muscles. On the other hand, if respiration be hurried, the blood being ren- dered more stimulant by greater oxygenation, causes an ac- celeration of the circulation. The quantity of air consumed varies therefore with the proportion of the blood which is sent to the lungs. § 3^9. The proper temperature of an animal, or what is termed animal heat, depends on the combined activity of 238 rvESPIEATION. the respiratory and circulating systems, and is in direct pro- portion to it. In many animals the heat is maintained at a uniform temperature, whatever may be the variations of the surrounding medium. Thus birds maintain a temperature of about 108° Fahrenheit ; and in a large proportion of mammals it is generally from 95° to 105°. These bear the general de- signation of warm-blooded animals, § 400. Reptiles, fishes, and most of the invertebrate animals, have not this power of maintaining a uniform temperature. The heat of their body is always as low as from 35° to 50°, but varies perceptibly with the surrounding medium, being, however, often a httle above it when the external temperature is very low, though some may be frozen without the loss of hfe. For this reason they are denominated cold-blooded animals ; and aU animals which have such a structure of the heart, that only a part of the blood which enters it is sent to the respira- tory organs (§ 366), are among them. § 401. The production of animal heat is obviously con- nected with the respiratory process. The oxygen of the respired air is diminished, and carbonic acid takes its place. The carbonic acid is formed in the body by the combination of the oxygen of the air with the carbon of the blood. The chemical combination attending this function is, therefore, essentially the same as that of combustion. It is thus easy to understand how the natural heat of an animal is greater, in proportion as respiration is more active. How far nutri- tion in general, and more particularly assimilation, by which the liquid parts are fixed and solidified, is connected with the maintenance of the proper temperature of animals, and the uniform distribution through the body, has not yet been satis- factorily ascertained. § 402. Some of the higher warm-blooded animals do not maintain their elevated temperature during the whole year ; but pass the winter in a sort of lethargy, called hibeknation, or the hibernating sleep. The marmot, the bear, the bat, the crocodile, and most reptiles, furnish examples. During this state the animal takes no food ; and as it respires only after very prolonged intervals, its heat is diminished, and its vital functions generally are much reduced. The structural cause of hibernation is not ascertained ; but the phenomena at- tending it fuUy illustrate the laws already stated (§397 — 401). EESPIEATIOIS-. 239 § 403. There is another point of view in which respiration should be considered, namely, with reference to the buoyancy of animals, or their power of rising in the atmosphere, and their ability to hve at different depths in the water, under a di- minished or increased pressure. The organs of respiration of birds and insects are remarkably adapted for the purpose of admit- ting at will a greater quantity of air into their body, birds being provided with large pouches extending from the lungs into the abdominal cavity and into the bones of the wing ; insects have their whole body penetrated by air-tubes, the ramifications of their tracheae, which are enlarged at intervals into wider cells, whilst most of the aquatic animals are provided with minute, almost microscopic tubes, penetrating from the surface into the substance, or the cavities of the body for admitting water into the interior, by which they thus adapt their whole system to pressures which would otherwise crush them These tubes may with propriety be called water-tubes. In fishes, they penetrate through the bones of the head and shoulder, through skin and scales, and communicate with the blood vessels and heart, into which they pour water ; in moUusca they are more numerous in the fleshy parts, as, for example, in the foot, which they help to distend, and communicate with the main cavity of the body, supplying it also with liquid ; in echino- derms they pass through the skin, and even through the hard shell, whilst in polyps they perforate the walls of the general cavity of the body, which they constantly fill with water. § 404. In order fully to appreciate the homologies between the various respiratory apparatus observed in different animals, it is necessary to resort to a strict comparison of the fundamen- tal connections of these organs with the whole system of or- ganization, rather than to the consideration of their special adaptation to the elements in which they live. In vertebrata, for instance, there are two sets of distinct respiratory organs, more or less developed at different periods of life, or in dif- ferent groups. All vertebrata, at first, have gills arising from the sides of the head, and directly supplied with blood from the heart ; but these gills are the essential organs of respira- tion only in fishes and some reptiles, and gradually disappear in the higher reptiles, as well as in birds and mammalia, towards the close of their embryonic life (§ 489). Again, all ver- tebrata have lungs opening: in or near the head ; but the lungs 240 RESPIRATIOIS'. are fully developed only in mammalia, birds, and the higher reptiles, in proportion as the branchial respiration is reduced; whilst in fishes the air-bladder constitutes a rudimentary lung. § 405. In the articulata, there are also two sorts of respiratory organs ; aerial, called tracheae in insects, and lungs in spiders; and aquatic, called gills in Crustacea and worms. But the tracheae and lungs open separately upon the two sides of the body (air never being admitted through the mouth or nostrils in the articulata) ; the gills are placed in pairs ; those which are like the tracheae occupying a smilar position, so that there are nearly as many pairs of tracheae and gills as there are seg- ments in these animals. The different respiratory organs in the articulata are in reality mere modifications of the same appa- ratus, as their mode of formation and successive metamor- phoses distinctly show, and cannot be compared with either the lungs or gills of the vertebrata; they are special organs not found in other classes, though they perform the same func- tions. The same may be said of the gills and lungs of mol- lusca,- which are essentially alike in structure, the lungs of snails and slugs being only a modification of the gills of aquatic moUusca ; but these two kinds of organs differ again in their structure and relations from the tracheae and gills of ar- ticulata, as much as from the lungs and gills of vertebrata. In those radiata which are provided with distinct respiratory organs, such as the echinoderms, we find still another type of structure, their gills forming bunches of fringes around the mouth, or rows of minute vesicles along the radiating seg- ments of the body. CHAPTER NINTH- OF THE SECRETIONS. § 406. Weile, by the process of digestion, a homogeneous fluid is prepared from the food, for supplying new material to the blood, another process is also going on, by which the blood is analyzed, as it were ; some of its constituents being selected and so combined as to form products for useful pur- poses, while other portions of it, which have become useless or injurious to the system, are taken up by difl’erent organs, and expelled in different forms. — This process is termed Seceetion. § 407. The organs by which these operations are performed are much varied, consisting either of flat surfaces or mem- branes, of minute simple sacs, or of dehcate elongated tubes, all hned with minute cells, called epithelium cells, which latter are the real agents in the process. Every surface of the body is covered by them ; and they either discharge their products directly upon the surface, as on the mucous mem- brane, or they unite in clusters, and empty into a common duct, and discharge by a sing e oriflce, as is the case with some of the intestinal glands, and of those from which the perspiration issues from the skin. § 408. In the higher animals, where separate organs for special purposes are multiplied, numerous sacs and tubes are assembled into compact masses called glands. Some of these are of large size, as the salivary glands, the kidneys, and the liver. In these, clusters of sacs open into a common canal, and this canal unites with similar ones, forming larger trunks ; and finally, they all discharge by a single duct, as we find in the salivary glands. § 409. By the organs of secretion two somewhat different purposes are effected, namely, fluids of a peculiar character are selected from the blood for important uses, such as the sahva, tears, milk, &c., some of which differ but httle in their composition from that of the blood itself, and might be 242 OP THE SECRETIONS. retained in the blood with impunity ; or the fluids selected are such as are positively injurious, and cannot remain in the blood without soon destroying life. These latter are usually termed excretions. § 410. As the weight of the body, except during its period of active growth, remains nearly uniform, it follows that it must daily lose as much as it receives ; in other words, the excretions must equal in amount the food and drink taken, with the exception of the small proportion discharged by the alimentary canal. Some of the most important of these outlets will be now indicated. § 411. We have already seen that all animal tissues admit of being traversed by hquids and gases. This mutual trans- mission of fluids from one side of a membrane to the other is termed endosmose and exosmose, or imbibition and transu- dation, and is a mechanical rather than a vital phenomenon, inasmuch as it takes places in dead as well as in living tissues. The blood-vessels, especially the capillaries, share this property. Hence portions of the circulating fluids escape through the walls of the vessels, and pass off at the surface. This super- ficial loss is termed exhalation. It is most active where the blood-vessels most abound, and accordingly is very copious from the air tubes of the lungs, and from the skin. The loss in this way is very considerable, and it has been estimated that, under certain circumstances, the body loses, by exhala- tion, five-eighths of the whole weight of the substances re- ceived into it. § 412. The skin, or outer envelope of the body, is other- wise largely concerned in the losses of the body. Its layers are constantly renewed by the tissues beneath, and the outer dead layers are thrown off. This removal is sometimes gradual and continual, as in man ; in fishes and many moUusca, it comes off in the form of slime, which is, in fact, a collection of cells de- tached from the surface of the skin ; sometimes the loss is pe- riodical, when it is termed moulting. Thus, mammals cast their hair, and the deer their horns, birds their feathers, serpents their skin, crabs their test, and caterpillars their outer en- velope, with the hairs growing from it. § 413. The skin presents such a variety of structure, in the different groups of the animal kingdom, as to furnish excellent distincti\e characters of species, genera, and even or THE SECRETIONS. 243 families, as will hereafter be shown. In the vertebrata it is composed of three very distinct layers of unequal thickness (fig. 250) ; the lower and the thickest layer is the corium, (c, c), or true skin, and is the part which is tanned into leather. Its surface presents numerous papillae, in which the nerves of general sensation terminate ; they also contain a fine net-work of blood-vessels, usually termed the vascular layer. The superficial layer is the epidermis, or cuticle ; the cells of which it is composed are distinct at its inner portion, but become dried and flattened as they are pushed outwards. It is destitute of vessels and nerves, and, consequently, is in- sensible. Between these two layers, and more especially connected with the cuticle, is the rete mucosum, a very thin layer of cells, some of which contain the pigment which gives the complexion to the different races of men and animals. The scales of reptiles, the nails and claws of mammals, and the solid covering of the Crustacea are merely modifications of the epidermis; on the other hand, the feathers of birds, and the scales of fishes, are derived from the vascular layer. [§> 413*. Dutrochet investigated the phenomena called endos- mose and exosmose more carefully than had yet been done, and designated them by these names.* Berzehus has given an excellent con- densed view of the subject : The phe- nomena exhibited by bodies in solu- tion,” he observes, ‘^in traversing c d solid living parts, do not depend solely on the properties which bodies in solu- tion have of diffusing themselves evenly through the fluids which are their men- strua ; the animal membranes and the water contribute their share, inasmuch as the water passes with the dissolved substance, and from this results a phe- nomenon, which in its effects resembles in every respect an absorption. For the sake of illustration, let a, a, fig. 247, be a tube open at both ends, but having a piece of moist bladder tied around its lower . extremity ; let a solution of any salt be now poured into the * Memoires pour servir a FHistoire Anatomique et Physiologique des Vegetaux et Animaux, Paris, 1837. Fig. 247. 4jN/'W\r I. a 244 STEIJCTrEE OE GLAT^ES. tube, and this be plunged into a larger vessel, c, c?, containing water, the tube being immersed till the solution, «, 5, is at the same level, e, e, as the water in the outer vessel, c, d. After a little time it will be found that the fluid in «, a has risen, and got above the level, e, to for example, and that it is continuing to rise, and will go on rising until the two fluids, on the opposite sides of the bladder, are of the same density, so that, if the tube, «, «, be not of sufiicient length, the fluid may even run over, having filled it completely. If the tube, «, a, instead of containing a saline solution, contain water, and the recipient, c, c?, instead of water, contain a saline solution, things being disposed as before, the fluid in a, far from rising, wiU begin to fall, and instead of fall- ing in c, d, it will begin to rise. When the tube and the recipient contain solutions of difierent salts respec- tively, but as nearly as may be of the same density, the level of the fluid in neither wdll be altered perceptibly ; but, after a certain time, the two salts will be discovered mingled to- gether in both the tube and the recipient, or in the fluid on both sides of the bladder. If the densities of the twm sahne solutions have been difierent, the surface of that which is the more dense w^ill rise, that w^hich is less dense will fall ; but it will be found, nevertheless, that from the solution of greatest density a portion will have passed into that of least density ; the penetration has not therefore been all one way, but^ reci- procally from each to the other, only in greatest measure from the less to the more dense fluid. This phenomenon does not take place only when moist animal membranes are the inter- media between the two heterogeneous but miscible fluids ; it also occurs when the interposed body is of an inorganic nature, but thin and porous, and possessed of strength enough to sup- port the increasing column of the denser fluid, such as thin slices of slate, earthenware, &c. In general it may be said that the power producing the phenomenon in question belongs to all bodies which can absorb and retain a fluid in extremely dehcate pores.”* The blood-vessels, especially the capillary vessels, share this property of permeability to liquids ; hence, while the circulation goes on, portions of the circulating fluid, espe- cially its watery parts, escape through the walls of the vessels, and pass off at the surface. This superficial loss, termed exha- * Chimie, 4te. Aufl. B. ix. S. 161. STETJCTTJEE OF OLAISTDS. 245 lation, IS most active where vessels most abound, and accord- ingly most copious from the surface of the lungs. It has been estimated that, under certain circumstances, the human body loses, by exhalation, five-eighths of the whole weight of sub- stances taken into it. [§ 414. Seceetioiv is a more complicated process than ex- halation. It is not a mere mechanical operation, but is ac- complished by means of organs, called glands ; which elaborate peculiar juices, such as the sweat, the tears,the milk, the sahva, the bile, the urine, &c. [§415. At first glance there would seem to be nothing in common between the organs which secrete the tears and that which produces the bile, or between the kidneys and the salivary glands. Still they all have the same elementary structure. Every gland is composed of minute vesicles, or extremely thin membranous sacs, generally too small to be discerned by the naked eye, but easily distinguished by the microscope. Sometimes these vesicles are single, and open separately at the surface ; they are then called crypts or fol- licles, but more frequently they unite to form clusters opening into a common canal, which itself unites with the canals of similar clusters to form trunks of various sizes, such as are found in the salivary glands (figs. 257 and 277), in the mam- mae, or in the liver (figs. 265, 267), which is a very large gland receiving a great quantity of blood from the veins of the alimentary canal [§ 416. Sometimes the canals of the little clusters do not unite, but open separately upon the surface of the body or into its cavities, as in the intestinal glands or those from which the perspiration issues (fig. 250, e). Occasionally the canals themselves combine into bundles composed of a multitude of parallel tubes, as we find in the kidneys, figs. 260 — 262. — T. AY.J § 417. The operation of the glands is one of the most mysterious phenomena of animal hfe. By virtue of the pe- cuhar properties with which they are endowed, they select from the blood, which penetrates to their remotest ramifica- tions, the elements of the special humours they are designed to elaborate. Thus the liver extracts the elements of the bile •; the salivary glands the elements of saliva ; the pancreas those of the pancreatic juice ; and the sodoriferous glands those of the sweat, *^c. 246 STRirCTURE OF GLANDS. § 418. Of the secretions thus formed by the different glands, some are immediately expelled from the body, as the sweat, the urine, &c. ; these are denominated excretions. Others, on the contrary, are destined either to be us^d as food for the young, as the milk ; or to take part in the different functions of the body, as the saliva, the tears, the gastric and pancreatic juices, and the bile, which are properly denominated secretions. Of all the secretions, if we except that from the lungs, the bile is the most important ; and hence a liver, or some analogous organ by which bile is secreted, is found in all animals, while some or all of the other glands are wanting in the lower classes. In the vertebrata the liver is the largest of all the organs of the body. In the mollusca it is no less preponderant. In the gastero- poda, like the snails, it envelops the intestine in its convolu- tions (fig. 177); and in the conchifera, like the clam and oyster (fig. 176), it generally surrounds the stomach. In insects it is in the form of long tubes variously contorted and interlaced (fig. 179). In the radiata this organ is largely developed, especially among the echinoderms. In the star-fishes (fig. 36) it extends into all the recesses of the rays ; and in colour and structure resembles the liver of the mollusca. Even in bryo- zoan polyps (fig. 175) we find brown cells lining the digestive cavity, which probably perform functions similar to those of the liver of higher animals. STBirCTXJRE OF GLANDS. [§ 419. The type or elementary form of every secreting gland is either a simple capsule, an elongated blind sac, or a rounded vesicle, upon the outer aspect of which vessels are ramified, and which on the inside generally exhibits numbers of small cellular projections or depressions, and an outlet through which the secreted matter escapes. Many of the cutaneous and mucous glands, as also the simple glands of the stomachs of birds (fig. 186, B. a, d), and the Lieberkuh- nian glands of the intestines, afford examples in point ; but they soon begin to get more complex, coalescing, dividing, and sending forth new lateral lobules (fig. 185, b. e), and by repetitions of the same process even acquiring a pretty complicated mulberry appearance (fig. 184, B. f). The ventricular glands of mammals are already somewhat more compound (fig. 181, et seq.). The extent of secreting sur- STEXJCTUEE OE GLA.T^DS. 247 face can be increased without any additional external com- plexity, by a capsule or canal extended in length, and at the same time rolled up or convoluted upon itself. We have an example of this kind of gland in the ceruminous glands of the ear (fig. 248, a. b), and in the sudoriparous glands (fig. 249, A. b). We have only to conceive these two forms farther subdivided, ramified, and the several parts connected by means of vessels and cellular tissue, to have a perfect idea of the most complex parenchymatous gland. The skeleton of every gland is the ramified excretory duct, formed in the man- ner already described, to which are attached the secreting blind sacs, vesicles, or tubes, connected together by cellular tissue, and surrounded by net-works of capillary vessels. Fig. 248. — Glands from the meatus auditorius externus of a young fe- male of eighteen. A, section of the skin, seen magnified three diameters ; &, 6, hairs ; c, c, superficially situated sebaceous glands ; a, a, larger and more deeply seated glands, which are coloured yellow, and appear to secrete the cerumen. B, a gland of this kind more highly magnified ; Uj a, the tortuous canal composing the gland and passing over into the excretory duct 6 ; c, a small vessel, with its branches. C, a hair of the auditory passage, penetrating the epidermis at 6?, and at d, contained within its double follicle e, e ; o, a, sebaceous follicles of the hair, with their excretory ducts. 248 STEUCTUEE OF GLANDS. [§ 420. The best picture we possess of the vast variety existing in the structural connection of the several parts of the glandular skele- ton, is in the secreting organs of in- sects, particularly the salivary glands (fig. 25 2) . Here we observe the most elegant and singular forms, having frequently much of the vegetable character in their appearance. The sahvary glands present themselves now as filiform canals (fig. 252, b), now thicker and convoluted, now with a sacculate end (c), here ex- tending into a simple (e) or a double vesicle (m), there branched Fig. 249.— Sudoriparous gland from the palm of the hand of a young person eighteen years of age. A, a gland entire vdth its excretory duct, , magnified forty times ; cz, zz, the convoluted canals forming the gland, and from which two excretory ducts arise, 6, &, which unite to form the single spiral duct, which, at c, passes through the laminae of the epidermis, and opens on the surface at d ; c, c, surrounding fat -cells. B, the same gland more highly magnified. Around the canal of the gland play the vessels^ 6, 6. C, a few fat-globules from the emptied fat-cells. STEIJCTURE OF GLANDS. 249 like the horns of a deer (o), or in the guise of a pair of long shaped canals ending in many smaller saccules, or form- ing a tuft or corymb of blind canals (h), or a cluster of vesicles connected hke a bunch of grapes or berries to a com- mon duct (a, n). " .0 Fig. 250. — Two sudoriparous glands after Gurlt, Magaz. /. d. gesammte Thierheilk, 1835, Tab. 2, fig. 1. a, epidermis ; h, tactile papillae ; c, corium ; d, adipose tissue ; e, sudoriparous glands. Fig. 251. — A thin layer from the scalp of the human subject, a, a, sebaceous glands ; &, a hair with its follicle, c. After Gurlt, Mag. /. d. gesam. ThierheiU kunde, 1835. The varieties in form presented by the seminal organs or testicles are still greater, new inquiries constantly offering new shapes to our notice. From the simple, linear and filiform canal of Julus (fig. 253), to the highly complicated yet beau- tiful appearance, comparable to a leafy tree laden with fruit, which we observe in Silpha obscura (fig. 253, 10), there are forms of every intermediate degree of complexity, but always as varieties of the same elementary type. Even the simple canalicular or sacculate form, presents numerous variations. In one case it is the straight pretty regular canal already indi- cated (1) ; in another the canal is irregular, of different thick- 250 STRUCTURE OF GLA>^DS. nesses in different parts, and tortuous (2) ; in a third it is spirally twisted (3), or is rolled up into a skein simple or double, and with club-shaped ends (4), in every case for the A B C Fig. 252. — Salivary glands of insects, to show the variety in the form and combination of the secreting follicles, from the simple lobular or filiform canal and blind sac to the greatly complicated raceme. A. Part of the salivary gland of Nepa cinerea; After Ramdohr. B. Sahvary vessel of Asida grisea. Alter ^xxccovf^Anat.physiolog. Unters. C. Salivary vessel of Musca deviens. After the same. E. The same of Musca carnaria. After the same. G. The same of Blaps gigas. After the same. H. The same of Cicada ormi. After the same. M. The^ame of Pulex irritans. After Ramdohr. N. The same of Scolopendra Afra. After nature. (All these figures, with the exception of that indicated by N, are more or less magnified.) STEUCTTJEE OF GLANDS. 251 obvious purpose of saving room ; in other instances, still, the organ presents itself in the shape of one or more club-like canals nearly straight (5), or bent at an angle with com- 1. Testis of Julus. 2. Tipula crocata. 3. Ranatra linearis. 4. Harpalus ruficornis. 5. Cercopis spumaria. mencing divisions at the end, or with the end forming a rounded vesicle ; or otherwise two ccecal canals are connected like hooks, or they are finger-shaped, or form tufts of dif- ferent kinds — quiver-hke, star-shaped (6), or hke the flowers of syngenesious plants (7), or they form small saccules in the shape of pannicles (8), or they are clustered like grapes or berries, and attached to styles (9). In this way do the forms of this gland alter in nearly alhed species in the insect world, 252 STEUCTUEE OF GLANDS. SO rich in varied forms.* The peculiar constitution and mode of distribution of the blood of the insect division of the Fig. 253 (continued). 6. 8. 6. Capsus tricolor. 9. Prionus coriarius. 7- Bostrichus capucinus. 10. Silnha obscura 8. Staphylinus maxillosus. * There are few divisions of comparative anatomy so much calcu- lated to set in a clear light the importance of this science in connexion with the study of general morphology, as the sketch just given of the vast variety of form presented by the glandular system. If we would give plans or ideal outlines of the principal forms of the different elements of STKUCTTJKE OE GLAifDS. 253 animal kingdom (§ 370) probably required the singular un- folding of the glandular elements which we observe among its A B Fig. 254. — The glands of insects which secrete the acrid or corroding juice, after Leon Dufour, An^ d. Sc. Nat. T. vii. pi. 19 and 20. A, of Chlaenius velutinus. B, of Brachinus crepitans. C, of Calathus fulvipes. the glandular system in man and the more perfect animals, no better method could be followed than to pursue a single gland through the class of insects. As supplementary to this part of our subject, the elegant forms which the clustered canals and vesicles of others of the special secreting organs of insects exhibit may be referred to in the subjoined figures. 254 STEUCTUEE OE GLAIS'DS. members. The blind extremities of the glands are surrounded immediately by the blood, which is poured freely into all the interstices of the body, and so attract the substances from its mass which the glands of other and higher animals have brought to them by finely divided capillary reticulations, to be subjected to their peculiar elective attractions. [§ 420*. It is infinitely more difficult to form an idea of the glandular skeleton of man and the vertebrata, in the fully formed condition, the composition of this being much ob- scured by the connecting cellular tissue and intermingled net- works of vessels. Still there are cases even here, where, without peculiar difficulty, the two principal types in glandu- lar architecture may be seized. As examples, the Harderian glands of birds generally (fig. 255), and the Cowper’s glands of the hedgehog (fig. 256) may be quoted. Into both struc- tures a quicksilver injection flows readily, and renders the arrangement of their parts perfectly distinct even to the naked eye. The gland of Harder of the pelican (fig. 255) is seen as a considerable lobulated body, each lobe being subdivided into smaller rounded or elongated or angular lobules, which again present themselves as small hollow pannicles or berries, Fig. 255. — A, a Harderian gland of tKe Pelecanus onocrotalus^Wiih. the excretory duct of the natural size injected with mercury. B, a portion of the same slightly magnified. Some vascular ramifications are still appa- rent between the lobules. STETTCTUEE OF GLANDS. 255 attached to the enlarged excretory duct, these, in their turn, having still smaller, rounded blind cells (fig. 255, b) sur- rounded by vascular net-works attached to them, an arrange- ment by which the whole structure acquires a cauliflower appearance. The Gowper’s glands of the hedgehog, on the other hand (fig. 256, a), afford an example of that form in which the ramified excretory duct divides into elongated, pretty even, and slender coeca, which subditide at their ends into finger-shaped processes (fig. 256, b), partly straight, partly sinuous, which are then applied to one another in the form of flat lobules, these, in their turn, being connected by cellular tissue into larger lobes. [§ 421. In man and the higher verte- brata, glands of the simple fol- licular form (as they exist in the Lieberkiihnian glands of the intestines, for example) attain to the highest degree of com- Fig. 256.— A, the Cowper^s gland of the hedge- plexity — ^in the hog, with the excretory duct, «. The coeca composing liver for in- gland are filled in the most beautiful manner stance.Thecom- 'vith the mercury ; the object is not magnified. B, , , , a few of the blind sacs seen slightly magnified, pound glands may be arranged according to their structure into four groups. 1. Compound follicles, the short excretory canal passing without farther ramification at once into pedicu- lated vesicles or racemiform lobules ; or the outwardly simple sac exhibiting internally open cellular projections or shallow pits ; to this head belong the greater number of the larger mucous and cutaneous glands. 2. Glands with tree-like ramifications of their excretory duct, and enlargements of the terminal branches into racemiform or cauliflower-like aggre- gated vesicles, which are visible with the naked eye, and vary in magnitude from the 25th of a line to one line. To this group belong the lachrymal glands, the salivafy glands, and 256 STEUCTTJEE OF GLATOS. the pancreas* The lung of the mammal, with its terminal vesicles attached to the minute ramifications of the bronchi, may serve as a prototype of this form of gland, which is made up of repetitions of the same fundamental structure, as we have seen in the preceding paragraph to be the case with regard to the Harderian gland. 3. Glands with a tubular structure ; the secreting canals are here extremely slender, of great length, convoluted, bhnd at the ends, not ramified, or only once or twice divided, not sensibly or but very shghtly enlarged at the extremities, sometimes anastomosing by re- current loops, or connected by cross branches, and from the tenth of a line to half a line in thickness ; to this category belong the kidneys and the testicles especially. The Cowper’s gland of the hedge-hog (fig. 256) may serve as a prototype of the form of which that of the organs just mentioned may be viewed as an extension. 4. Acinous glands. The excretory duct here ramified through the substance of the gland, divides at length into extremely minute branches ; all the branches and twigs are beset with compact lobules, consisting of very small, firm, angular cells, which effect the secretion. To this division belongs the liver of vertebrate animals generally. [§ 422. Compound follicles or glands of the first descrip- tion, are progressive or more complex forms of the rounded or elongated inversion, which we have seen constituting the simple follicle of the mucous membrane and of the skin (§419); no precise line of demarcation can, in fact, be drawn between them and the simple folhcle, or the sudoriparous or ceruminous gland. The large glands of the stomach and intestines may serve as types of this kind of gland (fig. 182), or the numerous glands which are in connection with the skin. All these glands consist of ramifications of the excretory ducts, which swell out into single saccules, that do not combine into true racemes or lobes. The glands which areconnected with the hairs (fig. 248 c, a^ a, and 251, a a) are small follicles, with rough external sur- faces, and internally presenting the appearance of projecting pa- rietal cells. To this division also belong the associated un- branched saccules arranged along the excretory duct like the grains of an ear of barley, which compose the Meibomian glands.* Among animals a multitude of variously formed ♦ Figured by *Muller — De Gland, structura, Tab. v. figs. 1 and 2. STEUCTUBE OP GLANDS. 257 glands of the skin, other than the sudoriparous and sebaceous glands are encountered.* [§ 423. The progressive development of the last form of gland is observed in the lachrymal, salivary and lacteal glands, f in all of which a greater amount of ramification, an increase in the quantity of vesicles and racemes produced, and a greater degree of separation of the individual parts into lobes, are observed. The lachrymal gland of man, of mammals and of birds, exhibits terminal cells, which in the latter class are large and conspicuous ; in man, on the contrary, they are much smaller. The salivary glands of man are formed in the same way (fig. 257). The cells of the terminal vesicles of the parotid may still be readily filled with mercury in young sub- jects ; they are two or three times ^mailer than the finest pulmonary cells, measuring no more than from the 30th to the 60th of a line in di- ameter. The structure of the pan- creas is similar, and the terminal vesicles of this gland are very easily filled with mercury or with air, in birds especially, measuring when thus distended from a 50th to a 30th of a line’ in diameter!! The mammary glands in the ormthorhyn- piece jf the parotid gland of chus are extremely simple, und ex- a new-born infant, filled with hibit the commencement of a series ^ercury and magnified five of evolutions that end with the ^ameters. After Weber, most complicated raceme ; the structure here consists of a con- * To this number belong, for example, the musk bag, and the anal sacs of many animals — the marten, the otter, &c., which exhale a peculiar odour or stench. They are, in fact, extensive involutions of the skin, of simple structure, occupied internally by shallow pits ; these structures might be regarded as simple follicles, which, upon occasion, however, may become more complicated, as they do in the anal sac of the hyaena, for example, which is made up of several racemes clustered together. t On the structure of the glands in general, and of each of those men- tioned in particular, see the work of Muller, and the Elementary Treatises, on Anatomy of E. H. AVeber and of Krause. X The pancreas of fishes has been very commonly quoted as affording an example or type of the successive evolution of glands from the simplest 258 STRUCTURE OF GLANDS. geries of very large unramified coeca but in the higher mam- maha and in man the wide excretory ducts pass over into finer branched canals, upon which the terminal cells form botryoidal clusters; the cells are on an average from 1 -20th to 1-1 5th of a line in diameter. [§ 424. Among the glands having tubular vessel -like secret- Fig. 258. — Kidney and supra-renal gland of the new-born child, of the natural size, a, kidney ; h, supra-renal gland ; c, artery ; d, veins ; e, ureter. Fig. 259. — A, B, por- tions of the kidney repre- sented in fig. 258 injected. A, of the natural size ; the Malpighian bodies, a, ap- pearing as points in the cor- tical substance ; h, the pa- pilla of one of the tubular pjTamids. B, a small por- tion of A, seen under a simple lens and shghtly magnified; a, Malpighian bodies ; 6, tubuli uriniferi. coecal tubes to the most complex form observed in the glandular system Recent inquiries, however, rather lead us to conclude that the bony fishes in general have a pancreas, which is comparable in } It respects to that of the other vertebrate animals ; perhaps the coecal appendages which were so long mistaken for the pancreas have a totally dififerent function. * See Meckel : Ornithorhynchi paradoxi descript. Anatom. Tab. viii. and Owen on the Mammary Gland of the Ornithorhynchus, in Philos, Trans. STETTCTUEE OF GLANDS. 259 ing canals, the KIDNEYS de- serve particu- lar notice. The development Fig. 260.— A still smaller piece of the same kid- ney magnified about sixty di- ameters, and drawn in part as a plan, so that the relations of the tubuli to one another and to the vascular glo- meruli may be distinctly seen and understood, a, a simple ter- minal tubulus uriniferus; &, tubuli, forming loops and return- ing ; c, c, tubuli terminating in hi* furcated points ; e, /, points where the tubuli join, continuing their course to- wards the papil- la ; g, g, g, arte- rial glomerules or convolutions, connected with one another by a general vascular rete ; a larger arterial trunk, which feeds this rete and the con- nected glomeru- li (the Malpighi- an bodies). 260 STKUCTUEE OF GLANDS. Fig. 261 — Termination of one of the tubuli uriniferi from the kidney of an adult, examined soon after death. The cellular structure is con- spicuous. Magnified 250 times. of the kidneys in the vertebrate series is of Special interest. In fishes and amphibia the entire tissue of the kidney con- sists of tortuous canals, which end partly in blind extremi- ties, and partly pass into one another in loops, but which, from their great length and intimate connection, cannot be demonstrated singly. They are not divided into single py- ramids or lobules, a peculiarity that first makes its appearance among birds . Here the highly tortuous uriniferous tubules are furnished with lateral branches, which come off like the tines of a stag’s horn ; in all probabihty they pass over the one into the other by means of loops. In the mammaha the tubuli uriniferi form many pyramids or lobes, each a system by itself (figs. 258 and 259, a). In the cortical sub- stance of the human kidney the tubuli can be traced, al- though with difficulty, wind- ing among the vascular plex- uses or skeins, mostly looped towards the margin of the or- gan, and running into one another (fig. 260, 5, 5), or ending bhndly (a), more rarely slightly enlarged and club-shaped (fig. 261), occa- The entire cortical substance consists of convolutions of the uriniferous tubules, which are found to present a very nearly uniform diameter, and which, on an average, may be from about’ the 50th to the 60th of a line. They unite two and two as they approach the tubular or medullary structure, becoming at the same time somewhat Fig. 262. — A lobe of the kidney of the adult porpoise (Delphinm phocoena). After Muller. sionally also cleft (fig. 260, c). STEirCTUBE or GLANDS. 2^1 thicker, and then they run quite parallel to one another to their termination (fig. 262). [§ 425. Among the whole of the vertebrata, the parts which are the efficient agents of secretion in the hver are so intimately connected into a compact and little lobular organ, by means of the vessels and cellular substance, that it is ex- tremely difficult to form a proper notion of its struc- ture. Perhaps the follow- ing is the true account of the structure of the liver, when fully formed in man and the mammalia: It is easy to obtain convic- tion of the fact, that the ends of the secreting parts of the liver are leaf-like lobules with blunt projec- tions, which, in prepara- tions of the organ, are most apt to remain at- tached to the minute ve- nous twigs (fig. 263, A, «, and 264, a, b, b). These lobules are composed of compact angular and rounded cells (fig. 263, b) . Betwixt the several di- visions of the cells of the individual lobules, the branches of the gall-ducts penetrate (fig. 266), and there form anastomosing retes, which surround sin- gle groups of cells like islets. Some observers describe the final ends of the secreting element of the liver of mammals as hollow acini or vesicles Fig. 263. — A, four lobules from the liver of a human subject forty years of age, magnified twice ; a branch of the hepatic vein, a, receives a more minutely ramified twig from each lobule. B, some Of the cells of which the lobules of the liver are composed, seen under a magnifying power of 200 ; in the greater number the clear nucleus is apparent. Fig. 264. — a, a branch of the hepatic vein with the tributary twigs of which the lobules of the liver are connected, as leaves are with the final branches of a tree. The venous ramuscles {vencs intralohulares) lie in the middle of each lobule, as is seen in the two next succeeding figures which re- present transverse sections of the hepatic lobules magnified. After Kiernan. 262 STRUCTURE OE GLATOS. with thin parietes, from the 40th to the 50th of a line in diameter, and Fig. 265. — Lobules of the liver, superficially si- tuated, divided horizontally ; a, a, intralobular veins ; 6, 6, clefts between the several lobules, in which cellular tissue, minute subdivisions of the hepatic ducts of the vena portae and hepatic artery, are included ; the middle portion of each lobule is here in a state of congestion. After Kiernan. Fig. 266. — The intralobular plexus of bihary ves- sels, as figured by Kiernan — although the injection of these vessels was not so complete as it is here re- presented *, c?, dj two lobules divided across, with the ramifications of the hepatic vein, a, «, the twigs of which perforate their centres ; 5, &, 6, 5, branches of the hepatic duct, as they take their rise from the plexus of biliary vessels, which are here injected, and surround the uninjected portions of the substance of the lobules, o?, d; c, cellular substance between the lobules. capable of being distended by air, introduced into the gall - ducts with which they are connected. For this struc- ture we have the assurance of ana- logy, from what we witness in the constitution of the other glands, the mode of evo- lution of the li- ver itself, and the structure of the organ in the invertebrate se- ries of animals ; in fact, if we turn to the cray- fish and common garden snail, we find the precise structure in ques- tion. In the cray-fish the li- ver consists en- tirely of small pointed caeca, clustered like grapes ; in the snail it is made up of bhnd, rounded, termi- nal vesicles, which may be blown up with STEUCTURE OF GLAIS’ES. 263 air from the biliary ducts. If we farther examine the Iher of the larva of the water-newt (fig. 268, b) we see distinct clusters of csecal ca- nals, or round ter- minal cells, hke is- lets, sirrounded by subdivisions of the hepatic vein ; but these caecal canals, at all eyents, are not thin-walled cells ; they are almost as compact as the acini of the fully formed liver of the highest mamraal. ELEMEiTTAET PARTS OF ELANDS. dinary celular sub- stance, but by and from othe more d9f TVi of three lobules of the liver me pro- across, the centre of each occupied by the per substance of ramifications of the intralobular (the hepatic) glands is lotformed vein, a, a, a. &, 6, &, Branches of the vena by or out of the or- portae which course in the spaces between the ' lobules, surrounding these and constituting the intralobular veins. Numerous ramuscles pene- trate into the interior of the lobules and anasto- mose with the intralobular or hepatic veins. The or less (istinctly rounded and oval interspaces or islets between cellular dements these vessels are filled or possessed by the hi- This aiutomicai truth IS particu- ^ ^ larly evideit in the liver (fig. 263, a). Here the parietes of the acin: consist entirely of compact, irregularly rounded or angular (ells, of about 1 -200th of a line in magnitude. The cells of the liver enclose a distinct clear nucleus and a yellowish-coloured molecular matter in their interior. The cells are hke the stones of a piece of ancient masonry, irregularly ajphed to one another. Externally, where the blood-vessels play around them, fibres of cellular tissue are added. An pithehal covering of flat tessellated cells first makes its ajpearance in the larger branches and trunks of the gall-ciicts. In other cases, as in the glands of the stomach, for instance (§ 329), the substance of the 264 ELEMEFTAET PARTS OF OLANDS glandular parietes consists of rounded dark granules, not ob- viously formed like cells, which appear to be arranged or A Fig. 268. — A, a larva of the water-newt . of the natiral size ; Cf liver; 6, sto- mach ; c, gall- bladdff. thi| larva mag- nifed 40 times. Tie dark co- loired stream- let of blood are sen surround- iig the hepatic Iconics, which cmsist of aggre- gted racemi- frm coeca. The ’^scalar chan- Jels represented re those of the iepatic vein. OBIGIN or THE GLAKHS. 265 packed between a very delicate external envelope turned to- wards the blood-vessels, and an internal epithelial investment. The cellular structure of the parietes of the ventricular glands is, however, very apparent in young birds (fig. 186, b). In other glands, moreover, we recognize the cellular structure with different degrees of distinctness — in the tubuli uriniferi, for example, where the cells have nuclei, but are far from being so compact, and are not nearly so readily isolated as in the hver (fig. 261). It is difficult to say in how far this cel- lular structure, which may be followed to the very ends of the canaliculi, belongs to the innermost layer of the glandular paries, or is connected with the epithelial investment, ap- pertaining to the trunk and larger branches of the excretory duct of every gland. Apparently, however, there are always several layers of flattened cells placed one upon another, over which a structureless membrane is drawn externally, and this is the part that is surrounded immediately by the vascular reticulation. Certain it is, that wherever we find secreting follicles, they consist of a number of more or less distinctly cellular or fibrous layers, which lie as the proper substance of the gland betwixt the external net-work of blood-vessels and the inner wall whence the secreted matter distils away. ORIGIH OF THE GLAISTHS. [§ 427. The greater number of the secreting glands arise from Fig. 269. — Rudiments of the liver formed by evolution from the tractus intestinalis in the embryo of the fowl of the fourth day. After Miiller — De Glands &c. Fig. 270.— Liver and pancreas of an embryo of the fowl at the end of the fourth day, magnified twelve times linear, a, the liver; 6, the pancreas; c, the stomach; d, dy the lungs. 266 OEIGiy OF THE GLAIiTHS. the mucous lamina of the germinal membrane, and, like the salivary glands, the lungs, the liver, the pancreas, are to be regarded as evolutions of this mem- brane, or of the intesti- nal canal. This view is liable to misapprehen- sion, by the process of evolution being conceiv- ed in a purely mechani- cal way. The general plan of the evolution of the secreting glands is as follows. At the place where the gland is to be formed — take the liver or the pancreas as a par- ticular instance (figs. 269, 270,and271,a, 5),arough projection appears upon the intestine. This projection consists of a delicate, finely granular, and pale tissue — the blast emay as it is called, which was in former times looked upon as without structure . By watching this part we see how particular divisions make their appearance within it (fig. 272), which by and by form lobules or club-shaped bodies, and are the elements or ground- work of the future caecal canals, where these are to appear. It is now that a kind of solution of the internal contents of the mass or masses takes place, or rather that distinct walls with double contours are produced. This is to be seen most beautifully displayed in the lungs (fig. 273).* And now appears the Fig. 271. — The same parts in another embryo more highly magnified, to exhibit the undoubtedly cellular and racemose structure of the liver and pancreas. The references are likewise the same. Fig. 272. — The liver more ad- vanced than in the last figure from an embryo of the fowl of the sixth day. It is not only divided into two lobes, but shows minute coeca in its interior. After Muller. * The lungs are to be viewed as the prototype of all secreting glands. OEIGIlSr OP THE GLANDS. 267 true glandular skeleton, as it has been described in speaking of the conformation of the glands. Would we follow this generation of the glands step by step, a gland must be chosen in which the ra- mifications of the excretory duct can be seen amidst the clearer blastema, from the sim- ple rudiment to the term of extreme com- plexity. In young em- bryos of the sheep (fig. 274) we can, by the aid of a simple lens, see the excretory duct of the parotid still simply branched, the seve- ral branches enlarged like buds at their extremities, and but seldom divided. The same thing may be seen in small human embryos (fig. 276). To follow the onward evolution, embryos successively more and more advanced mustbe procured, and, the parotid being re- moved, it is to be examined Fig. 273. — Ramifications of the bronchi from the embryonic Falco tinnunculus^ to show the way in whifcn they sprout as blind canals. Both figures axe magnified about 150 times. with a low power and as an opaque object (fig. 277). The clearer blastema of the gland now appears dark, and the excretory duct, Fig. 274. — Rudiments of the parotid gland in the embryo of a sheep, two inches in length magnified. After Muller. OEIGIN OF THE GLANDS. 2bS Fig. 276, — First appearance of the parotid gland in a human embryo of the seventh week ; magnified twice. wnicn consists of a firmer granular mass, appears white, and in the form of an ele- gant and numerously branched tree. The leaf-like ends now undergo transform- ation into blind vesi- cles, whilst the branch- es and twigs of the tree become hollow, and unite them selves to the excretory duct (fig. 277). The blood- vessels are seen enter- ing the blastema in the shape of dark ramifica- tions (fig. 277), but of much smaller diame- ters than those of the ramified glandular canal. The finest ele- ments of the secreting follicles do not consist properly of cells ; in the liver, for example (fig. 278), they are ex- tremely soft, roundish, granular corpuscles, which give to the larger lobules (a) a racemi- form appearance. It is betwixt these major divisions or lobules that the blood-vessels make their entrance (fig.’ 278, B, a, a), none ever penetrating betwixt the finest ele- ments of all. Fig. 277. — Lobules of the parotid gland wuih the excretory ducts from the embryo of a sheep four inches long, magnified eight times. After Muller. DISTBIBUTION OF VESSELS IN GLANDS. 269 DISTBIBUTION OE THE VESSELS IN GLANDS. [§ 428. Glands in general derive their blood from arteries, and all that is not used for purposes of secretion returns in the usual way through veins and lymphatics into the general current of the circulation. The lymphatics of glands are often very large and conspicuous ; those of the liver are particularly so. Among vertebrate animals the liver receives but a small portion of its blood from an arterial source, and this appears to be exclusively expended upon the gall-bladder, the gall- ducts, and the coats of the larger vascular trunks, though branches of the hepatic artery can also be followed, entering along with the cellular substance of the organ between its several component lobules. The blood from which the bile is prepared is received from the portal vein, which ramifies through the substance of the fiver, and at length anastomoses with the finest subdivisions of the hepatic vein, which spring from the deeper parts, and then fiow round about the clusters of hepatic cells united into coecal-looking lobules (fig. 267) In the two lower classes of vertebrate animals, there is an extension to the kidneys of the same system of circulation which we observe confined to the fiver among the two higher classes. In amphibia and fishes a portion of the blood returning from the hind-legs, tail, abdominal parietes, and A B Fig. 278. — A couple of feathery lobules trom the embryo of the Faho tinnunculus or Hobby, fourteen lines in length ; the substance of the liver is seen composed of large pale granulated particles (cells) ; betwixt the lobules a blood-vessel is seen well filled with blood-discs. 270 DISTRIBUTION OF VESSELS IN GLANDS. Fig. 279. — Malpighian bodies of the kidney of the water-newt ( j!9aZMs. 336 EMBRYOLOGY. SECTION III. ZOOLOGICAL IMPORTANCE OF EMBRYOLOGY. § 500. As a general result of the observations which have been made, up to this time, on the embryology of the various classes of the animal kingdom, especially of the vertebra ta, it may be said, that the organs of the body are successively formed in the order of their organic importance, the most es- sential being always the earliest to appear. In accordance with this law, the organs of vegetative life, the intestines and their appurtenances, make their appearance subsequently to those of animal life, such as the nervous system, the skeleton, &c. ; and these, in turn, are preceded by the more general phenomena belonging to the animal as such. § 501. Thus we have seen that, in the fish, the first changes relate to the segmentation of the yolk and formation of the germ, which is a process common to all classes of animals. It is not until a subsequent period that we trace the dorsal furrow, which indicates that the forming animal will have a double cavity, and consequently belong to the division of the vertebrata ; an indication afterwards fully confirmed by the successive ap- pearance of the brain and the organs of sense. Later still, the intestine is formed, the limbs become evident, and the organs of respiration acquire their definite form, thus enabling us to distinguish with certainty the class to which the animal belongs. Finally, after the egg is hatched, the peculiarities of the teeth, and the shape of the extremities, mark the genus and species. § 502. Hence the embryos of different animals resemble each other more strongly when examined in the earlier stages of their growth. We have already stated that, during almost the whole period of embryonic life, the young fish and the young frog scarcely difier at all : so it is also with the young snake compared with the embryo bird. The embryo of the crab, again, is scarcely to be distinguished from that of the insect ; and if we go still farther back in the history of development, we come to a period when no appreciable differ- ence whatever is to be discovered between the embryos of the various departments. The embryo of the snail, when the ZOOLOaiCAL IMPOETANCE OF EMBETOLOGT. 337 germ begins to show itself, is nearly the same as that of a fish or a crab. All that can be predicted at this period is, that the germ which is unfolding itself will become an animal ; but the class and the group are not yet indicated. § 503. After this account of the history of the develop- ment of the egg, the importance of embryology to the study of zoology cannot be questioned. For evidently, if the for- mation of the organs in the embryo takes place in an order corresponding to their importance, this succession must of itself furnish a criterion of their relative value in classification. Thus, those peculiarities that first appear should be considered of higher value than those that appear later. In this respect, the division of the animal kingdom into four types, the ver- tebrata, the articulata, the moUusca, and the radiata, cor- responds perfectly with the gradations displayed by embry- ology. § 504. This classification, as has been already shown, is founded essentially on the organs of animal life, the nervous system and the parts belonging thereto, as found in the per- fect animal. Now, it results from the above account, that in most animals the organs of animal life are precisely those that are earliest formed in the embryo ; whereas those of vege- tative life, on which is founded the division into classes, orders, and families, such as the heart, the respiratory apparatus, and the jaws, are not distinctly formed until afterwards. There- fore a classification, to be true and natural, must accord with the succession of organs in the embryonic development. This coincidence, while it corroborates the anatomical principles of Cuvier’s classification of the animal kingdom, furnishes u* with new proof that thete is a general plan displayed in every kind of development. § 505. Combining these two points of view, that of Embrj^- ology and that of Anatomy, the four divisions of the animal kingdom may be represented by the four figures which are to be found, at the centre of the diagram, at the beginning of the volume. § 506. The type of Veetebeata, having two cavities, one above the other, the former destined to receive the nervous system, and the latter, which is of a larger size, for the intes- tines, is represented by a double crescent united at the centre, and closing above, as well as below z 338 EMBRYOLOGY. § 507. The type of Articulata, having but one cavity^ grow- ing from below upwards, and the nervous system forming a series of ganghons, placed below the intestine, is represented by a single crescent, with the horns directed upwards. § 508o The type of Molltjsca having also but one cavity, the nervous system being a simple ring around the esophagus, with ganglions above and below, from which threads go off to all parts, is represented by a single crescent with the horns turned down. § 509. Finally, the type of Rabiata, the radiating form of which is seen even in the youngest individuals, is represented by a star. CHAPTER ELEVENTH. PECULIAR MODES OF REPRODUCTION. SECTION I. aEMMIPAROIJS AKD FISSIPAEOUS REPEODUCTIOIS^. §510. We have shown, in the preceding chapter, that ovula- tion, and the development of embryos from eggs is common to all classes of animals, and must be considered as the great process for the reproduction of species. Two other modes of propagation, applying, however, to only a limited number of animals, remain to be mentioned, namely, gemmiparoiis reproduction, or multiplication by means of buds, and Jissi- parous reproduction, or propagation by division, and also some still more extraordinary modifications yet involved in much obscurity. §511. Reproduction by buds occurs among polyps, medusae, and some infusoria. On the stalk, or even on the body of the Hydra (fig. 170), and of many infusoria (fig, 356), there are formed buds, like those of plants. On close examination they are found to contain young animals, at first very imperfectly formed, and communicating at the base with the parent body, from which they derive their nourishment. By degrees the animal is developed ; in most cases the tube by which it is connected with the parent withers away, and the animal is thus de- tached, and becomes independent. Others remain through life united to the parent stalk, and in this respect present a more striking analogy to the buds of plants ; but in polyps, as in trees, budding is only an accessary mode of reproduction, which presupposes a trunk already existing, originally the product of ovulation. § 512. Reproduction by division^ or lissiparous reproduc- Fig. 356. 340 EEPTIODUCTIO?^'. tion, is still more extraordinary ; it takes place only in polyps and some infusoria. A cleft, or fis- sion, at some part of the body takes place, very slight at first, but con- stantly increasing in depth, so as to become a deep furrow, like that observed in the yolk, at the begin- ning of embryonic development ; at the same time the contained organs are divided and become double, and thus two individuals are formed of one, so similar to each other that it is impossible to say which is the parent and which the offspring. The division takes place sometimes vertically, as, for example, in Vorti- cella (fig. 357, c, d), and in some po- lyps (fig. 358, «, 6^) ; and sometimes transversely. In some infusoria, the ParameciaioY instance, this division occurs as often as three or four times in a day. § 513. In consequence of this same faculty many animals are able to reproduce various parts of their bodies when accidentally lost. It is well known that crabs and spiders, on losing a limb, acquire a new one. The same happens with the rays of star-fishes ; the tail of a lizard is also readily reproduced ; salamanders even possess the faculty of reproducing parts of the head, including the eye with all its comphcated structure. Something similar takes place in our own bodies, when a new skin is formed over a wound, or when a broken bone is reunited. § 514. In some of the lower animals this power of repara- tion is carried much farther, and applies to the whole body, so as closely to imitate fissiparous reproduction. If an earth- worm or a fresh-water polype be divided into several pieces, the injury is soon repaired, each fragment speedily becoming a per- fect animal. Something like this reparative faculty is seen in the vegetable as well as in the animal kingdom. A willow- branch, planted in a moist soil, throws out roots below and branches Fig. 357. Fig. 358. ALTEETfATE AND EQUIYOCAL EEPEODUCTION. 341 above ; and thus, after a time, assumes the shape of a perfect tree. § 515. These various modes of reproduction do not exclude each other. All animals which propagate by gemmiparous or fissiparous reproduction also lay eggs. Thus the freshrwater polyps (Hydra) propagate both by eggs and by buds. In Vor~ ticella, according to Ehrenberg, all three modes are found ; it is propagated hy eggs, by buds, and by division. Ovulation, however, is the common mode of reproduction, the other modes, and also alternate reproduction, are only additional means employed hy nature to secure the perpetuation of the species. SECTION II. ALTEENATE AND EQUIYOCAL EEPEODUCTION. § 516. It is a matter of common observation, that individuals of the same species have the same general appearance, by which their peculiar organization is indicated. The transmis- sion of these characteristics, from one generation to the next, is justly considered as one of the great laws of the animal and vegetable kingdoms. It is, indeed, one of the points on which fhe definition of species is generally founded. AYe would, however, adopt the new definition of Dr. S. G. Morton, who defines species to be ‘^primordial organic forms.’’ § 517. But it does not follow that animals must resemble their parents in every condition, and at every epoch of their existence ; on the contrary, as we have seen, this resemblance is very faint in most species at birth, and some undergo com- plete metamorphoses before attaining their final shape, such as the caterpillar and the tadpole, the butterfly and the frog. Nevertheless, we do not hesitate to refer the tadpole and the frog to the same species ; and so with the caterpillar and the butterfly, because we know that there is the same individual observed in different stages of development. § 518. There is also another series of cases in which the offspring not only do not resemble the parent at birth, but moreover remain different during their whole life, so that their relationship is not apparent until a succeeding generation. The son does not resemble the father, but the grandfather ; and in some cases the resemblance reappears only at the fourth or fifth generation, and even later. This singular mode of re- production has received the name of alternate generation. 342 EEPRODITCTIOI^. The phenomena attending it have been of late the object of numerous scientific researches, which are the more deserving of our attention, as they furnish a solution of several problems alike interesting in a zoological and philosophical point of view. § 519. Alternate generation was first observed among the SalpcB, marine mollusca, without shells, belonging to the family tunicata. They are distinguished by the curious pe- culiarity of being united together in considerable numbers, so as to form long chains, which float in the sea (fig. 359), the mouth (m), however, being free in each. The indivi- duals thus joined in floating colonies produce eggs ; but in each animal there is generally but one egg formed, which is developed in the body of the parent, and from which is hatched a little mollusk (fig. 360), which remains solitary, and differs in many respects from the parent. This little animal, on the other hand, does not produce eggs, but propagates by a kind of budding, which gives rise to chains already seen within the body of the parent (a), and these again bring forth solitary individuals, &c. some parasitic worms, alternate generation is accompanied by still more extraordinary phe- nomena, as shown by the late discoveries of Steenstrup, a Danish naturalist. Among the numerous animals inhabiting stagnant pools, in which fresh-water-mollusca (particularly Lymncea and Paludina) are found, there is a small worm, known to naturalists under the name of Cercaria (fig. 361). When examined with a lens, it looks much like a tadpole, with a long tail, a triangular head, and a large sucker {a) in the middle of the body. Various viscera appear within, and among others a very dis- tinctly forked cord (c), embracing the sucker and wliich is thought to be the liver. § 520. In Fig. 361. Fig. 359. ALTEPvlS’ATE AND EQUIYOCAL REPRODUCTION. 343 Fig. 362. Fig. 363. § 521. If we watch these worms, which always abound in company with the mollusks mentioned, we find them after a while attaching themselves, by means of their sucker, to the bodies of these animals. When fixed they soon undergo con- siderable alteration . The tail, which was pre- viously employed for locomotion, is now useless, and falls off, and the animal surrounds itself with a mucous substance, in w^hich it remains nearly motionless, like a caterpillar on its trans- formation into the pupa. If, however, after some time we remove the little animal from its retreat we find it to be no longer a Cercaria, but an intestinal worm called Distoma, with two suckers, having the shape of fig. 362. The Distoma, therefore, is only a particular state of the Cercaria, or rather the Cercaria is only the larva of the Distoma. § 522. What now is the origin of the Cerca- ria ? The following are the results of the latest researches on this point. At certain periods of the year, we find in the viscera of the Lymncea (one of the most common fresh-water mollusks) a quantity of little worms of an elongated form, with a well-marked head, and two posterior pro- jections like limbs (fig. 363). On examining these worms attentively under the microscope we discover that the cavity of their body is filled by a mass of other little worms, which a practised eye easily recognizes as young Cer- carice, the tail and the . ther characteristic fur- cated organ (fig. 364, a) being distinctly visible within it. These little embryos increase in size, distending the worm containing them, and which seemingly has no other office than to protect and forward the development of the young Cercarice. It is, as it were, their living envelope. On this account, it has been called the nurse. § 523. When they have reached a certain size, the young Cercari(B leave the body of the nurse, and move freely in the abdominal cavity of the Lymncea, or escape from it into the Fig. 364. 344 EEPRODUCTIOIS'. water to fix themselves, in their turn, to the body of another mollusk, and begin their transformations anew. § 524. But this is not the*end of the series. The nurses of the Cercaria are themselves the offspring of little Fig. 365. worms of yet another kind. At certain seasons, we find in the viscera of the LymncEa worms some- what like the nurses of the Cercaria in shape (fig. 365), but rather longer, more slender, and having a much more elongated stomach {s). These worms contain, in the hinder part of the body, little em- bryos («), which are the young nurses of figures 363, 364. This generation has received the name of grand-nurses. § 525. Supposing these grand-nurses to be the immediate offspring of the Bistoma (fig. 362), as ^ is probable, we have thus a quadruple series of generation. Four generations and one metamorphosis are re- quired to evolve the perfect animal ; in other words, we find no resemblance to the parent in any of its progeny, until we arrive at the fourth generation or the great-grandson § 526. Among the Aphides, or plant-lice, the number of generations is still greater. The first generation, which is produced from eggs, soon undergoes metamorphoses, and then gives birth to a second generation, which is followed by a third, and so on ; so that it is sometimes the eighth or ninth generation before the perfect animals appear as males and fe- males, the sexes being then for the first time distinct, and the males provided with wings. The females lay eggs which are hatched the following year, to repeat the same succession. Each generation is an additional step towards the perfect state; and as each member of the succession is an incomplete ani- mal, we cannot better explain their office, than by considering them analogous to the larvae of the Cercaria, that is, as nurses.* * There is a certain analogy between the larvae of the plant-louse {^Aphis') and the neuters or working ants and bees. This analogy has given rise to various speculations, and, among others, to the following theory, which is not without interest. The end and aim of all alternate generation, it is said, is to favour the development of the species in its progress towards the perfect state. Among the plant-lice, as among all the nurses, this end is accomplished by means of the body of the nurse. Now a similar end is accomplished by the working ants and altee:n^ate ato equivocal eepeoductiois’. 345 § 527. The development of the Medusce is not less instruct- ive. According to the observations of M. Sars, a Norwegian naturalist, the Medusa brings forth living young, which, after having burst the covering of the egg, swim about freely for some time in the body of the mother. When born, these ani- mals have no resemblance whatever to the perfect Medusa, They are little cylindrical bodies (fig. 366, a)^ much resembling infusoria, and like them covered with minute cilia, by means of which they swim with much activity. § 528. After swimming about freely in the water for some days, the little animal fixes itself by one extremity (fig. 366, c). At the opposite ex- tremity a depression is gra- dually formed, the four cor- ners (5, /') become elongated, and by degrees are trans- formed into tentacles (c). These tentacles rapidly mul- tiply, until the whole of the upper margin is covered with them (jj). Then transverse wrinkles are seen on the body at regular distances, appearing first above and extending down- wards. These wrinkles, which are at first very slight, grow deeper and deeper, and, at the same time, the edge of each segment begins to be serrated, so that the animal presents the appearance of a pine cone, surmounted by a tuft of tentacles (Ji) ; Fig. 366, bees, only, instead of being performed as an organic function, it is turned into an outward activity, which makes them instinctively watch over the new generation, and nurse and take care of it. It is no longer the body of the nurse, but its own instincts, which become the instrument of the development. This seems to receive confirmation from the fact that the working bees, like the nurses of the plant-lice, are barren females. The attributes of their sex, in both, seem to consist only in their solicitude for the welfare of the new generation, of which they are the natural guardians, but not the parents. The task of bringing forth young is con- fided to other individuals, to the queen among the bees, and to the female of the last generation among the plant-lice. Thus the barrenness of the working bees, which seems an anomaly as long as we consider them complete animals, receives a very natural explanation so soon as we regard them merely as nurses. 346 REPEODUCTIO^\ whence the name of Strohila, which was originally given to it, before it was known to be only a transient state of the jelly- fish. The separation constantly goes on, until at last the divi- sions are united by only a very slender axis, resembling a pile of cups placed within each other {i). The divisions are now ready for separation ; the upper ring first disengages it- self, and then the others in succession.* Each segment {d) then continues its development by itself, until it becomes a complete Medusa {k) ; while, according to recent researches, the basis or stalk remains and produces a new colony. § 529. It is thus, by a series of metamorphoses, that the little animal which, on leaving the egg, has the form of the infusoria, passes in succession through all the phases we have described. But the remarkable point in these metamorpho- ses is, that what was at first a single individual is thus trans- formed, by tranverse division, into a number of entirely dis- tinct animals, which is not the case in ordinary metamor- phoses. Moreover, the upper segment does not follow the others in their development. Its office seems to be accom- plished as soon as the other segments begin to be indepen- dent ; being intended merely to favour their development, by securing and preparing the substances necessary to their growth. In this respect it resembles the nurse of the Cer- caria. § 530. The Hydraform-Polyps present phenomena no less numerous and strange. The Campanidaria has a branching, plant-like form, with little cup-shaped cells on the ends and in the axils of the branches, each of which contains a little animal. These cups have not all the same organization. Those at the extre- mity of the branches {a), and which appear first, are furnished with long tentacles, wherewith they seize their food (fig. 367). Those in the axils of the branches, and which appear late, are females (6), and have no such tentacles. Inside of the lat- ter, little spherical bodies are found, -each * These free segments have been described as peculiar animals, under the name of Ephyra. Fig. 367. ALTEEKA.TE AKD EQUIYOCAL EEPEODUCTION. 347 having several spots in the middle ; these are the eggs. Finally, there is a third form, different from the two prece- ding, produced by budding from the female polyp, to which it in some way belongs (c). It is within this that the eggs arrive, after having remained some time within the female. Their office seems to be to complete the incubation, for it is always within them that the eggs are hatched. § 531. The little animal, on becoming free, has not the slightest resemblance to the adult polyp. As in the young Medusa^ the body is cylindrical, and co- T’ig- 368. veredwith delicate cilia (fig. 368) . After having re- mained free for some time, the young animal fixes it- self and assumes adattened form. By degrees alittle swelling rises from the centre, which elongates, and at last forms a stalk. This stalk ramifies, and we soon recognize in it the animal of fig. 367, with the three kinds of buds, which we may consider as three distinct forms of the same animal. § 532. The development of the Cainpanularia presents, in some respects, an analogy to what takes place in the repro- duction of plants, and especially of trees. They should be considered as groups of individuals, and not as single indivi- duals. The seed, which corresponds to the embryo of the polyp, puts forth a little stalk. This stalk soon ramifies by gemmiparous reproduction, that is, by throwing out buds which become branches. But ovulation, or reproduction by means of seeds, does not take place until an advanced period, and requires that the tree should have attained a considerable growth. It then produces flowers with pistils and stamens, that is, males and females, which are commonly united in one flower, but which in some instances are separated, as in the hickories, the elders, the willows, &c. &c.* * Several plants are endowed with organs similar to the third form of the Polyps, as seen in the Campanularia : for example, the liver- wort {Marchantia poly'morphd), which has at the base of the cup a small receptacle, from the bottom of which little disk-like bodies are constantly forming, these, when detached, send out roots, and gradually become complete individuals. Besides that, wo find in some polyps, as in plants, the important peculiarity, that all the individuals are united in a com- mon trunk, which is attached to the soil ; and that all are intimately dependent on each other, as long as they remain united. And if we compare, in this point of view, the various species in which alternate re- 348 EEPEODUCTIOK. SECTION III. CONSEQTJElSrCES OE ALTEEIfATE GEIfEEATIOlS’. § 533. These various examples of alternate generation render it evident, that this phenomenon ought not to be considered as an anomaly in nature ; but as the special plan of develop- ment, leading those animals in which it occurs to the highest degree of perfection of which they are susceptible. Moreover, it has been noticed among all types of the invertebrated animals ; while among the vertebrata it is as yet unknown. It would seem that individual life in the lower animals is not defined within such precise limits as in the higher types, owing, perhaps, to the greater uniformity and independence of their consti- tuent elements, the cells ; and that instead of passing at one stride, as it were, through all the phases of their development, in order to accomphsh it, they must either be born in a new form, as in the case of alternate generation, or undergo meta- morphoses, which are a sort of second birth. § 534. Many analogies may be discovered between alter- nate reproduction and metamorphosis. They are parallel lines leading to the same end, namely, the development of the species. Nor is it rare to see them coexisting in the same animal. Thus, in the Cercaria, we have seen an animal pro- duced from a nurse afterwards transformed into a Distoma, by undergoing a regular metamorphosis. § 535. In each new generation, as in each new metamor- phosis, a real progress is made, and the form which results is more perfect than its predecessor. The nurse that produces the Cercaria is manifestly an inferior state, just as the chry- salis is inferior to the butterfly. production has been observed, we find that the progress displayed in each type consists precisely in the increasing freedom of the individual in its various forms. At first, we have all the generations united in a common trunk, as in the lower polyps and in plants ; then in the Medusa and in some of the hydraform polyps (the Coryne)^ the third generation begins to disen- gage itself. Among some of the intestinal worms (the Distoma), the third generation is enclosed within its nurse, and this in its turn is contained in the body of the grand nurse, while the complete Distoma lives as a parasitic worm in the body of other animals, or even smms freely about in the larva state, as Cercaria. Finally, in the plant-lice, all the genera- tions, the nurses as well as the perfect animals, are separate individuals.. CONSEQUEIS'CES OE ALTEEIS'ATE EEPEOErCTIOI^. 349 § 536. But there is this essential difference between the meta- morphoses of the caterpillar and alternate reproduction, that in the former case, the same individual passes through all the phases of development ; whereas, in the latter, the individual disappears, and makes way for another, which carries out what its predecessors had begun. It would give a correct idea of this difference to suppose that the tadpole, instead of being itself transformed into a frog, should die, having first brought forth young frogs ; or that the chrysalis should, in the same way, produce young butterflies. In either case, the young would still belong to the same species, but the cycle of development, instead of being accomplished in a single individual, would involve two or more acts of generation. § 537. It follows, therefore, that the general practice of deriving the character of a species from the sexual forms alone, namely, the male and the female, is not applicable to all classes of animals ; since there are large numbers whose various phases are represented by distinct individuals, endowed with peculiarities of their own. Thus, while in the stag the species is represented by two individuals only, stag and hind, the Medusa, on the other hand, is represented under the form of three different types of animals ; the first is free, like the in- fusoria; the second is fixed on a stalk, like a polyp ; and the third again is free, consisting in its turn of male and female. In the Distoma also, there are four separate individuals, the grand nurse, the nurse, the larva or Cercaria, and the Distoma, in which the sexes are not separate. Among the Aphides the number is much greater still. § 538. The study of alternate generation, besides making us better acquainted with the organization of animals, greatly simplifies our nomenclature. Thus, in future, instead of enu- merating the Distoma and the Cercaria, or the Strohila, the Ephyra and the Medusa, as distinct animals belonging to dif- ferent classes and families, only the name first given to one of these forms will be retained, and the rest be struck from the pages of zoology, as representing only the transitory phases of the same species. § 539. Alternate generation always pre-supposes several modes of reproduction, of which the primary is invariably by ovulation. Thus we have seen that the polyps, the medusae, the salpae, &c., produce eggs, which are generally hatched within the mother. The subsequent generation, on the con- 350 EEPEODUCTIOJf. trary, is produced in a different manner, as we have shown in the preceding paragraphs ; as among the medusae, by trans- verse division ; among the polyps and the salpse, by buds, &c. § 540. The subsequent generations are moreover not to be regarded in the same light as those which first spring directly from eggs. In fact, they are rather phases of de- velopment than generations properly so called ; they are either without sex, or females whose sex is imperfectly developed. The nurses of the 'Distoma, the Medusa, and iheCampanularia, are barren, and have none of the attributes of maternity, ex- cept that of watching over the development of the species, being themselves incapable of producing young. § 541. Another important result follows from the above observations, namely, that the differences between animals which are produced by alternate generation are less, the earlier the epoch at which we examine them. No two animals can be more unlike, than an adult Medusa (fig. 366, k), and an adult Campanularia (fig. 367) ; they even seem to belong to different classes of the animal king- dom, the former being an acaleph, the latter a polyp. On the other hand, if we compare them when first hatched from the egg, they appear so n\uch alike, that it is with the greatest difficulty they can be distinguished. They are then little infusoria, without any very distinct shape, and moving with the greatest freedom. The larvse of certain intestinal worms, though they belong to a different department, have nearly the same form, at one period of their life. Further still, this resemblance extends to plants. The spores of cer- tain sea- weeds have nearly the same appearance as the young polyp, or the young Medusa ; and what is yet more remark- able, they are also furnished with cilia, and move about in a similar manner. But this is only a transient state. Like the young Campanularia and the young Medusa, the spore of the sea- weed is free only for a short time ; it soon becomes fixed, and from that moment the resemblance ceases. § 542. Are we to conclude, then, from this resemblance of the different types of animals at the outset of life, that there is no real difference between them ; or that the two king- doms, the animal and the vegetable, actually blend because their germs are similar ? On the contrary, we think nothing is better calculated to strengthen the idea of the original sepa- ration of the various groups, as distinct and independent CONSEQUENCES OF ALTEENATE EEPEOUUCTION. 551 types, than the study of their different phases. In fact, a differ- ence so wide as that between the adult Medusa and the adult Campanularia must have existed even in the young ; only it does not show itself in a manner appreciable by our senses ; the character by which they subsequently differ so much, being not yet developed. To deny the reality of na- tural groups, because of these early resemblances, would be to take the resemblance for the reality. It would be the same as saying that the frog and the fish are identical, because at one stage of embryonic life it is impossible, with the means at our command, to distinguish them. § 543. The account we have given above of the develop- ment, the metamorphoses, and the alternate reproduction of the lower animals, is sufficient to undermine the old theory of spontaneous generation, which was proposed to account for the presence of worms in the bodies of animals, for the sudden appearance of myriads of animalcules in stagnant water, and, under other circumstances, rendering their occurrence mysterious. We need only recollect how the Cercaria in- sinuates itself into the skin and the viscera of rnollusca (§ 520, § 521), to understand how admission may be gained to the most inaccessible parts. Such beings occur even in the eye of many animals, especially of fishes ; they are numerous in the eye of the common fresh-water perch of Europe. § 544. As to the larger intestinal worms found in other animals, the mystery of their origin has been entirely solved by recent researches. A single instance will illustrate their history : — At certain periods of the year the sculpins of the Baltic are infested by a particular species of Tcenia, or tape- worm, from which they are free at other seasons. M. Esch- richt found that, at certain seasons, the worms lose a great portion of the long chain of rings of which they are composed. On a careful examination he found that each ring contained several hundred eggs, which, on being freed from their enve- lope, float in the water. As these eggs are innumerable, it is not astonishing that the sculpins should occasionally swallow some of them with their prey. The eggs, being thus intro- duced into the stomach of the fish, find conditions favourable to their development ; and thus the species is propagated, and at the same time transmitted from one generation of the fish to another. The eggs which are not swallowed are probably lost. 352 UEPE0DUCT102^. § 545. Al] animals swallow, in the same manner, with their food, and in the water they drink, numerous eggs of such pa- rasites, any one of which, finding in the intestine of the animal favourable conditions, may be hatched. It is probable that each animal affords the proper conditions for some particular species of worm ; and thus we may explain how it is that most animals have parasites peculiar to themselves. § 546. As respects the infusoria, w^e also know that most of them, the Rotifer a especially, lay eggs. These eggs, which are extremely minute (some of them only 1 -12,000th of an inch in diameter), are scattered everywhere in great profusion, in water, in the air, in mist, and even in snow. Assiduous observers have not only seen the eggs laid, but, moreover, have followed their development, and have seen the young animal forming in the egg, then escaping from it, increasing in size, and, in its turn, laying eggs. They have been able, in some instances, to follow them even to the fifth and sixth generation. § 547. This being the case, it is much more natural to sup- pose that the infusoria* are products of like germs, than to assign to them a spontaneous origin altogether incompatible with what we know of organic development. Their rapid appearance is not at all astonishing, when we reflect that some mushrooms attain a considerable size in a few hours, but yet pass through all the phases of regular growth ; and, indeed, since we have ascertained the different modes of gene- ration among the lower animals, no substantial difficulties any longer exist to the axiom “ omne vivum ex (§ 433). * In this connection it ought to he remembered that a large proportion of the so-called Infusoria are not independent animals, but immature germs, belonging to different classes of the animal kingdom, and that many m.ust be referred to the vegetable kingdom. CHAPTER TWELFTH. METAMORPHOSES OF ANIMALS. § 548. Uneee the name of metamorphoses are included those changes which the body of an animal undergoes after birth, and which are modifications, in various degrees, of its organ- ization, form, and mode of life. Such changes are not pe- culiar to certain classes, as has been so long supposed, but are common to all animals without exception. § 549. Vegetables also undergo metamorphoses, but with this essential difference, that in vegetables the process consists in an addition of new parts to the old ones. A succession of leaves, difiering from those which preceded them, comes on each season ; new branches and roots are added to the old stem, and woody layers to the trunk. In animals the whole body is transformed, in such a manner that all the existing parts contribute to the formation of the modified body. The chrysalis becomes a butterfly ; the frog, after having been herbivorous during its tadpole state, becomes carnivorous, and its stomach is adapted to this new mode of life ; at the same time, instead of breathing by gills, it becomes an air- breathing animal, its tail and gills disappear, lungs and legs are formed, and finally it lives and moves upon the land. § 550. The nature, the duration, and importance of meta- morphoses, and also the epoch at which they take place, are infinitely varied. The most striking changes naturally pre- senting themselves to the mind, when we speak of meta- morphoses, are those occurring in insects. Not merely is there a change of physiognomy and form observable, or an organ more or less formed, but their whole organization is modi- fied. The animal enters into new relations with the external world, while at the same time, new instincts are imparted to it. It has lived in water, and respired by gills ; it is now furnished with tracheae, and breathes air ; it passes by with indifference objects which before were attractive, and its new instincts prompt it to seek conditions which would have been most per- A A 354 METAMORPHOSES OE ANIMALS. nicious during its former period of life. All these changes are brought about without destroying the individuality of the animal. The mosquito, which to-day haunts us with its shrill trumpet, and pierces us for our blood, is the same animal that, a few days ago, lived obscure and unregarded in stagnant water, under the guise of a little worm. § 551. Every one is familiar with the metamorphoses of the silk-worm. On escaping from the egg the little worm or caterpillar grows with great rapidity for twenty days, when it ceases to feed, spins its silken cocoon, casts its skin, and re- mains inclosed in its chrysalis state.* During this period of its existence most extraordinary changes take place. The jaws with which it masticated mulberry leaves are transformed into a coiled tongue, the spinning organs are reduced, the gullet is lengthened and more slender, the stomach, which was nearly as long as the body, is now contracted into a short hag, the intestine, on the contrary, becpmes elongated and narrow ; the dorsal vessel is shortened. The thoracic nervous ganglia approach each other, and unite into a single mass. Antennae and palpi are developed on the head, and simple eyes are exchanged for compound ones. The muscles, which before were uniformly distributed, are now gathered into masses. Tlie limbs are elongated, and wings spring forth from the thorax. More active motions then reappear in the digestive organs, and the animal, bursting the envelop of its chrysalis, issues in the form of a winged moth. § 552. The different external forms w^hich an insect may assume is well illustrated by one which is unfortunately too well known in this country, namely, the canker- worm (fig. 369). Its eggs are laid on posts and fences, or upon the branches of the apple, elm, and other trees. They are hatched about the time the tender leaves of these trees begin to unfold. The caterpillar (a) feeds on the leaves, and attains its full growth at the end of about four weeks, being then not quite an inch in length. It then descends to the ground, and enters the earth to the depth of * In the raising of silk-worms this period is not waited for, hut the animal is killed as soon as it has spun its cocoon. Fig. 369, METAMOEPHOSES OE ANIMALS. 355 four or five inches, and having excavated a sort of cell, is soon changed into a chrysalis or nymph (b). At the usual time in the spring it bursts the skin, and appears in its perfect state, under the form of a moth (d). In this species, however, only the male has wings. The perfect insects soon pair, the female (c) crawls up a tree and having deposited her eggs, dies. § 5.53. Transform- ations no less remark- able are ob- served among the Crustacea. The meta- morphoses in the class cirrhipoda are es- pecially striking. It is now known that the barnacles (Balanus), which have been arranged among tha moUusca, are truly crusta- ceans ; and this result of modern researches has been deduced in the clearest manner from the study of their transformations. Figures 370, a — -/, represent the different phases of develop- ment of the duck-barnacle (Anatifa) . § 554. The Anatifa, \\ke all Crustacea, is reproduced by eggs, specimens of which, magnified ninety diameters, are repre- sented in fig. 370, a. From these eggs little animals issue, which have not the slightest resemblance to the parent. They have an elongated form (b), a pair of tentacles, and four legs, with which they swim freely in the water. § 555. Their freedom, however, is of but short duration. The httle animal soon attaches itself by means of its tentacles, having previously become covered with a transparent shell, through which the outhnes of the body, and also a very distinct eye, are easily distinguished (c). Fig. 370, d, shows the animal taken out of its shell. It is plainly seen that the anterior portion has become considerably enlarged ; subse- quently, the shell becomes completed, and the animal casts its Fig. 370. 356 METAMORPHOSES OE ANIMALS. skin, losing with it both its eyes and its tentacles. On the other hand, a thick membrane lining the interior of the shell, pushes out and forms a stem (e), by means of which the animal fixes itself to immersed bodies, after the loss of its tentacles. This stem gradually enlarges, and the animal soon acquires a definite shape, such as is represented in fig. 370, attached to a piece of floating wood. § 556. There is, consequently, not only a change of organ- ization in the course of the metamorphoses, but also a change of faculties and mode of life. The animal, at first free, be- comes fixed ; and its adhesion is effected by totally different organs at different periods of hfe, first by means of tentacles^ which were temporary organs, and afterwards by means of a fleshy stem, especially developed for that purpose. § 557. The radiata also furnish us with examples of vari- ous metamorphoses, especially among the star-fishes. A small species, living on the coastof New England {Echinaster sanguino- lentus), undergoes the following phases (fig. 371). § 558. If the eggs are ex- » amined by the microscope, each one is found to contain a small, pear-shaped body, which is the embryo (e), surrounded by a transparent envelope. On es- caping from the egg the little animal has an oblong form, with a constriction at the base ; this constriction, becoming deeper and deeper, forms a pedicle, (p), which soon divides into three lobes. The disc also assumes a pentagonal form, with five double series of vesicles ; the first rudiments of the rays, are seen to form in the interior of the pentagon. At the same time the peduncle contracts still more, being at last entirely absorbed into the cavity of the body, and the animal soon acquires its final form (m). § 559. Analogous transformations take place in the Coma- tula. In early life it is fixed to the ground by a stem (fig. 372), but becomes detached at a certain epoch, and then floats freely in the sea (fig. 373). On the other hand, the polypi Fig. 371. METAMORPHOSES OE AHIMALS. 357 Fig. 372. seem to follow a reverse course, many of them becoming per- manently fixed after having been previously free. § 560. The metamorphoses of the mollusca, though less striking, are not less worthy of notice. Thus, the oyster, with which we are fami- liar in its adhering shell, is free when young, like the clam (My a) and most other shell-fishes. Others, which are at first attached or sus- pended to the gills of the mother, afterwards become free, as the Urdo. Some naked gasteropods, the Ac- teon and the Eolis, for example, are born with a shell, which they part with, shortly after leaving the egg. § 561. The study of metamor- phosis is therefore of the utmost importance for understanding the real affinities of animals very dif- ferent in appearance, as is readily shown by the following instances. The butterfly and the earth-worm seem, at the first glance, to have no relation whatever. They differ in their organization no less than in their outward appearance. But on comparing the caterpillar and the worm, these two animals are seen closely to resemble each other. The analogy, however, is only transient ; it lasts only during the larva state of the caterpillar, and is effaced as it passes to the chrysalis and butter- fly conditions. The latter becominga more and more perfect ani- mal, whilst the worm remains in its inferior state. § 562. Similar instances are furnished by animals belong- ing to all the types of fhe animal kingdom. Who would suppose, at the first glance, that a barnacle, or an anatifa, were more nearly allied to the crab than to the oyster ? And, nevertheless, we have seen (§ 553), in tracing back the anatifa Fig. 373. 358 METAMOEPHOSES OE ANIMALS. to its early stages, that it then bears a near resemblance to a little crustacean (fig. 370 c?). It is only when full grown that it assumes its peculiar mollusk-like covering. § 563. Among the cuttle-fishes there are several, the Loligo, for example, which are characterized by the form of their tentacles, the two interior being much longer than the others, and of a different form ; whilst, in others, as the Octopus, they are all equal. But if we compare the young, we find that in both animals the tentacles are all equal, though they differ in number. The inequality in the tentacles being the result of a further development. § 564. Among the radiata, the Peutacrinus and the Co- matula exemphfy the same point. The two are very different when full grown, the latter being a free-swimming star-fish (fig. 373), while the former is attached to the soil, like a polyp. But we have seen (§ 559) that the same is the case with Comatula in its early period ; and that in consequence of a further metamorphosis, it becomes disengaged from its stem, and floats freely in the water. § 565. In the type of thevertebrata,the considerations drawn from metamorphoses acquire still greater importance in re- ference to classification. The sturgeon and the white-fish before mentioned (§ 463) are two very different fishes ; yet, taking into consideration their external form and bearing merely, it might be questioned which of the two should take the highest rank ; whereas, the doubt is very easily resolved by an examination of their anatomical structure. The white- fish has a skeleton, and moreover a vertebral column com- posed of firm bone. The sturgeon (fig. 374), on the con- Fig. 374. trary, has no bone in the vertebral column, except the spines or apophyses of the vertebrae. The middle part, or body of the vertebra, is cartilaginous ; the mouth is transverse, and underneath the head ; and the caudal fin is unequally forked, while, in the white-fish, it is equally forked. METAMORPHOSES OE ANIMALS. 359 § 566. If, however, we observe the young white-fish just after it has issued from the egg (fig. 309), the contrast will be less striking. At this period the vertebrae are cartilaginous, hke those of the sturgeon ; its mouth also is transverse, and its tad undivided ; at that period the white-fish and the stur- geon are therefore much more alike. But this similarity is only transient; as the white-fish grows, its vertebrae become ossified, and its resemblance to the sturgeon is comparatively slight. As the sturgeon has no such transformation of the vertebrae, and is in some sense arrested in its development, while the white-fish undergoes subsequent transformation, we conclude that, compared with the white-fish, it is really in- ferior in rank. § 567. This relative inferiority and superiority strikes us still more, when we compare with our most perfect fishes (the salmon, the cod &c.) some of those worm-like animals, so different from ordinary fishes that they were formerly placed among the worms. The Amphioxus, represented of its natural size (fig. 375), not only has no bony skeleton, but not even a head, properly speaking. Yet the fact that it possesses a dor- Fig* 375 sal cord, extending from one ex- tremity of the body to the other, proves that it belongs to tbe type of tbe vertebrata (§458). But as this peculiar structure is found only at a very early period of embryonic development, in other fisbes, we conclude that the Amphioxus holds the very lowest rank in this class. § 568. Nevertheless, the metamorphoses of animals after birth will, in many instances, present but trifling modifica- tions of the relative rank of animals, compared with those which may be derived from the study of changes previous to that period, as there are many animals which undergo no changes of great importance after their escape from the egg, and occupy nevertheless a high rank in the zoological series, as, for example, birds and mammals. Tbe question is, whether such animals are developed according to different plans, or whether their peculiarity in that respect is merely apparent. To answer this question, let us go back. to the period anterior to birth, and see if some parallel may not be made out between the embryonic changes of these animals, and the metamor- phoses which take place subsequently to birth in others 360 METAMOEPHOSES OF ANIMALS. § 569. We have already shown that embryonic development consists in a series of transformations ; the young animal en- closed in the egg dijffering, at each period of its development, from what it was before. But because these transformations precede birth, and are therefore not generally observed, they are not less important. To be satisfied that these transfor- mations are in every respect similar to those which follow birth, we have only to compare the changes which immedi- ately precede birth with those which immediately follow it, and we shall readily perceive that the latter are simply a con- tinuation of the former, till all are completed. § 570. Let us recur to the development of fishes for illus- tration. The young white-fish, as we have seen (§ 4/1), is far from having acquired its complete development, when born. The vertical fins are not yet separate ; the mouth has not yet its proper position ; the yolk has not yet retreated within the cavity of the body, but hangs below the chest in the form of a large bag. Much, therefore, remains to be changed, before its development is complete. But the fact that it has been born does not prevent its future evolution, which goes on without interruption. § 571. Similar inferences maybe drawn from the develop- ment of the chick. The only difference is, that the young chicken is born in a more mature state, the most important transformations having taken place during the embryonic period, while those to be undergone after birth are less con- siderable, though they complete the process begun in the embryo. Thus we see it, shortly after birth, completely changing its covering, and clothed with feathers instead of down ; still later its crest appears, and its spurs begin to be developed. § 572. In certain mammals, known under the name of marsupials (the opossum and kangaroo), the link between the transformations which take place before birth, and those occurring at a later period, is especially remarkable. These animals are brought into the world so weak and undeveloped, that they have to undergo a second gestation, in a pouch with which the mother is furnished, and in which the young re- main, each one fixed to a teat, until they are entirely developed. Even those animals which are born nearest to the complete states undergo, nevertheless, embryonic transformations. Bu- minants acquire their horns ; and the hon his mane. Most METAMOEPHOSES OE ANIMALS. 361 mammals, at birth, are destitute of teeth, and incapable of using their limbs ; and all are dependent on the mother and the milk secreted by her, until the stomach is capable of digesting other aliment. § 573. If it be thus shown that the transformations which take place in the embryo are of the same nature and of the same importance as those which occur afterwards, the cir- cumstance that some precede and others succeed birth, cannot mark any radical distinction between them. Both are pro- cesses of the life of the individual. Now, as life does not commence at birth, but goes still farther back, it is quite clear that the modifications which supervene during the former period are essentially the same as the later ones ; and hence that metamorphoses, far from being exceptional in the case of insects, are one of the general features of the animal king- dom. § 574. We are therefore perfectly entitled to say that all animals, without exception, undergo metamorphoses. Were it not so, we should be at a loss to conceive why animals of the same division present such wide differences ; and that there should be, as in the class of reptiles, some families that undergo metamorphoses (the frogs, for example), and others in which nothing of the kind is observed after birth (the lizards and tortoises). § 575. It is only by connecting the two kinds of trans- formation— namely, those which take place before, and those after birth, that we are furnished with the means of ascer- taining the relative perfection of an animal ; in other words, these transformations become, under such circumstances, a natural key to the gradation of types. At the same time, they force upon us the conviction that there is an immu- table principle presiding over all these changes, and regulat- ing them in a peculiar manner in each animal. § 576. These considerations are important, not only from their bearing on classification, but not less so from the appli- cation which may be made of them to the study of fossils. If we examine attentively the fishes that have been found in the different strata of the earth, we remark that those of the most ancient deposits have in general preserved only the apophyses of their vertebrae, whilst the vertebrae themselves are wanting. Were the sturgeons to become petrified, they 362 METAMOEPHOSES OE ANIMALS. would be found in a similar state of preservation. As the apophyses are the only bony portions of their vertebral column, they alone would be preserved. Indeed, fossil sturgeons are known, which are precisely in this condition. § 577. From the fact above stated, we may conclude that the oldest fossil fishes did not pass through ail the metamor- phoses which our osseous fishes undergo, and consequently that they were inferior to analogous species of the present epoch, which have bony vertebrae. Similar considerations apply to the fossil Crustacea and to the fossil echinoderms, when compared with their living types ; and it will probably be true of all classes of the animal kingdom, when they are fuUy studied as to their geological succession. CHAPTER THIRTEENTH. GEOGRAPHICAL DISTRIBUTION OF ANIMALS. SECTION I. GENERAL LAWS OF DISTRIBUTION. § 5/8. No animal, excepting man, inhabits every part of the surface of the earth. Each great geographical or climatal re- gion is occupied by some species not found elsewhere ; and each animal dwells within certain limits, beyond which it does not range while left to its natural freedom, and within which it always inclines to return, when removed by accident or design. Man alone is a cosmopolite ; his domain is the whole earth ; for him, and with a view to him, it was created ; his right to it is based upon his organization and his relation to nature, and is maintained by his intelligence and the perfecti- bihty of his social condition. § 579. A group of animals inhabiting any particular region, embracing all the species, both aquatic and terrestrial, is called its Fauna, in the same manner as the plants of a country are called its Flora. To be entitled to this name it is not necessary that none of the animals composing the group should be found in any other region ; it is sufficient that there should be pecuharities in the distribution of the fami- lies, genera, and species, and in the preponderance of cer- tain types over others, sufficiently prominent to impress upon a region well-marked features ; thus, for example, in the islands of the Pacific are found terrestrial animals, altogether peculiar, and not found on the nearest continents. There are numerous animals in New Holland differing from any found on the continent of Asia, or, indeed, on any other part of the earth ; if, however, some species, inhabiting both shores of a sea which separates two terrestrial regions, are found to be ahke, we are not to conclude that those regions have the same Fauna, any more than that the Flora of Lapland and England 364 GEKEEAL LAWS OE LISTEIBUTIOIS'. are alike, because some of tlie sea-weeds found on both their shores are the same. § 580. There is an evident relation between the fauna of any locality and its temperature, although, as we shall here- after see, similar climates are not always inhabited by similar animals. Hence the faunas of the two hemispheres have been distributed into three principal divisions, namely the arctic, the temperate, and the tropical, in the same manner as we have arctic, temperate, and tropical floras ; hence, also, ani- mals dweUing at high elevations upon mountains, where the temperature is much reduced, resemble the animals of colder latitudes, rather than those of the surrounding plains. § 581. In some respects the pecuharities of the fauna of a region depends upon its flora, at least so far as land animals are concerned ; for herbivorous animals will exist only where there is an adequate supply of vegetable food ; but, taking the terrestrial and aquatic animals together, the limitation of a fauna is less intimately dependent on climate than that of a flora. Plants, in truth, are for the most part terrestrial (marine plants being relatively very few) while animals are chiefly aquatic. The ocean is the true home of the animal kingdom ; and while plants, with the exception of the lichens and mosses, become dwarfed or perish under the influence of severe cold, the sea teems with animals of all classes, far beyond the ex- treme limit of flowering plants. § 582. The influence of chmate, in the polar regions, acts merely to induce a greater uniformity in the species of animals. Thus, the same animals inhabit the northern polar regions of the three continents ; the polar bear is the same in Europe, Asia, and America, and so are also a great many birds ; in the tempe- rate regions, on the contrary, the species differ on each of the continents, but they still preserve the same general features ; the t}q)es are the same, but they are represented by different species. In consequence of these general resemblances, the first colonists of New England erroneously applied the names of European species to American animals. Similar differences are observed in distant regions of the same continent, within the same parallels of latitude. The animals of Oregon and of Cahfornia are not the same as those of New England. The difierence, in certain respects, is even greater than between the animals of New England and Europe. In like manner, GENERAL LAWS OE DISTRIBUTION. 365 the animals of temperate Asia differ more from those of Europe than they do from those of America. § 583. Under the torrid zone the animal kingdom, as well as the vegetable, attains its highest development. The animals of the tropics are not only different from those of the tempe- rate zone, but, moreover, they present the greatest variety among themselves. The most gracefully proportioned forms are found by the side of the most grotesque, decked with every combination of brilliant colouring. At the same time, the contrast between the animals of different continents is more marked ; and, in many respects, the animals of the different tropical faunas differ not less from each other than from those of the temperate or frozen zones ; thus, the fauna of Brazil varies as much from that of central Africa as from that of the United States. § 584. This diversity upon different continents cannot de- pend simply on any influence of the climate of the tropics ; if it were so, uniformity ought to be restored in proportion as we recede from the tropics towards the antarctic temperate regions. But, instead of this, the differences continue to in- crease ; — so much so, that no faunas are more in contrast than those of Cape Horn, the Cape of Good Hope, and New Hol- land. Hence other influences must be in operation besides those of climate ; — influences of a higher order, which are in- volved in a general plan, and intimately associated with the development of life on the surface of the earth. § 585. Faunas are more or less distinctly limited, according to the natural features of the earth’s surface. Sometimes two faunas are separated by an extensive chain of mountains, like the Rocky Mountains. Again, a desert may intervene, like the desert of Sahara, which separates the fauna of Central Africa from that of the Atlas and the Moorish coast, the latter of which is merely an appendage to the fauna of Europe. But the sea effects the most complete separation. The depths of the ocean are quite as impassable for marine species as high mountains are for terrestrial animals. It would be quite as difficult for a fish or a mollusk to cross from the coast of Europe to the coast of America, as it would be for a reindeer to pass from the arctic to the antarctic regions, across the torrid zone. Experiments of dredging in very deep water have also taught us that the abyss of the ocean is nearly a desQ . . Not only are no materials found there for sustenance, 366 GEIS^EEAL LAWS OF LISTKIBUTION. but it is doubtful if animals could sustain the pressure of so great a column of water, although many of them are provided with a system of pores (§ 403), whic^ enables them to sustain 9 much greater pressure than terrestrial animals. § 586. When there is no great natural limit, the transition from one fauna to another is made insensibly. Thus, in pass- ing from the arctic to the temperate regions of North America, one species takes the place of another, a third succeeds the second, and so on, until finally the fauna is found to be an entirely new one, without its being always possible to mark the precise limit between the two. § 587. The range of species does not at all depend upon their powers of locomotion ; if it were so, animals which move slowly and with difiiculty would have a narrow range, whilst those which are very active would be widely diffused. Precisely the reverse of this is actually the case. The com- mon oyster extends at least from Cape Cod to the Carohnas ; its range is consequently very great ; much more so than that of some of the fleet animals, as, for instance, the moose. It is even probable that the very inabihty of the oyster to travel, really contributes to its diffusion, inasmuch as having once spread over extensive grounds, their is no chance of its return to a former limitation, being fixed, and consequently unable to choose positions for its eggs, they must be left to the mercy of currents ; while fishes, by depositing their eggs in the bays and inlets of the shore, undisturbed by currents and winds, secure them from too wide a dispersion; § 588. The nature of their food has an important bearing upon the grouping of animals, and upon the extent of their distribution. Carnivorous animals are generally less confined in their range than herbivorous ones ; because their food is almost everywhere to be found. The herbivora, on the othei hand, are restricted to the more limited regions correspond - ing to the different zones of vegetation. The same remark may be made with respect to birds. Birds of prey, like the eagle and vulture, have a much wider range than the granivorous and gallinaceous birds. Still, notwithstanding the facilities they have for change of place, even the birds that wander widest recognize limits which they do not over- pass. The condor of the Cordilleras does not descend into the temperate regions of the United States ; and yet it is not that he fears the cold, since he is frequently known to ascend GEJ^'ERAL LAWS OF DISTETBUTIOIS'. 367 even above the highest summits of the Andes, and disappears from view where the cold is most intense. Nor can it be from lack of prey. § 589. Again, the peculiar configuration of a country some- times determines a peculiar grouping of animals into what may be called local faunas. Such, for example, are the prai- ries of the West, the pampas of South America, the steppes of Asia, the deserts of Africa ; — and for marine animals, the basin of the Caspian. In all these localities, animals are met with which exist only there, and are not found except under those particular conditions. § 590. Finally, to obtain a true picture of the zoological distribution of animals, not the terrestrial types alane, but the marine species must also be included. Notwithstanding the uniform nature of the watery element, the animals which dwell in it are not dispersed at random ; and though the limits of the marine may be less easily defined than those of the terres- trial fauna, still marked differences between the animals of great basins are not less observable. Properly to apprehend how marine animals may be distributed into local faunas, it must be remembered that their residence is not in the high sea, but along the coasts of continents and on soundings. It is on the Banks of Newfoundland, and not in the deep sea, that the great cod-fishery is carried on ; and it is well known that when fishes migrate, they run along the shores. The range of marine species being therefore confined to the vicinity of the shores, their distribution must be subjected to laws similar to those which regulate the terrestrial faunas. As to the fresh-water fishes, not only do the species vary in the dif- ferent zones, but even the different rivers of the same region have species peculiar to them, and not found in neighbouring streams. The gar-pikes, Lepidosteus, of the American rivers, afford a striking example of this kind. § 591. A very influential cause in the distribution of aqua- tic animals is the depth of the water ; so that several zoological zones receding from the shore may be defined according to the depth of water, much in the same manner as we mark dif- ferent zones at different elevations in ascending mountains. The mollusks, and even the fishes found near the shore in shallow water differ, in general, from those living at the depth of twenty or thirty feet, and these again are found to be different from those which are met with at a greater depth. Their colouring. 368 GENERAL LAWS OE EISTRIBUTION. in particular, varies, according to the quantity of light they re- ceive, as has also been shown to be the case with marine plants. § 592. It is sometimes the case that one or more animals are found upon a certain chain of mountains, and not else- where ; as, for instance, the mountain sheep {Ovis montand), upon the Rocky Mountains, or the chamois and the ibex upon the Alps. The same is also the case on some of the wide plains or prairies. This, however, does not entitle such regions to be considered as having an independent fauna, any more than a lake is to be regarded as having a peculiar fauna, ex- clusive of the animals of the surrounding country, merely be- cause some of the species found in the lake may not ascend the rivers emptying into it. It is only when the whole group of animals inhabiting such a region has such peculiarities as to give it a distinct character, when contrasted with animals found in surrounding regions, that it is to be regarded as a separate fauna. Such, for example, is the fauna of the great steppe or plain of Gobi, in Asia ; and such indeed that of the chain of the Rocky Mountains may prove to be, when the animals inhabiting them shaU be better known. § 593. The migration of animals might at first seem to pre- sent a serious difiiculty in determining the character or the limits of a fauna ; but this difiiculty ceases, if we regard the country of an animal to he the place where it makes its habi- tual abode. As to birds, which of all animals wander the farthest, it may be laid down as a rule, that they belong to the zone in which they breed. Thus, the gulls, many of the ducks, mergansers, and divers, belong to the boreal regions, though they pass a portion of the year with us. On the other hand, the swallows and martins, and many of the gallinaceous birds be- long to the temperate faunas, notwithstanding their migration during winter to the confines of the torrid zone. This rule does not apply to the fishes, who annually leave their proper home, and migrate to a distant region merely for the purpose of spawning. The salmon, for example, comes down from the North to spawn on the coasts of Maine, Nova Scotia, and the British isles. § 594. Few of the Mammals, and these mostly of the tribe of rodents, make extensive migrations. Among the most remarkable of these are the Kamtschatka rats. In spring they direct their course westward, in immense troops ; and nSTEIBUTIOJ^f OF THE FAUNAS. 369 after a very long journey return again in autumn to their quar- ters, where their approach is anxiously awaited by the hunters, on account of the fine furs to he obtained from the numerous carnivora which always follow in their train. The migrations of the Lemmings are marked by the devastations they commit along their course, as they come down from the borders of the Frozen Ocean to the valleys of Lapland and Norway ; but their migrations are not periodical. SECTION IL HISTEIBUTION OF THE FAUNAS. § 595. We have stated that all the faunas of the globe may be divided into three groups, corresponding to as many great climatal divisions, namely, the glacial or arctic, the tem- perate, and the tropical faunas. These three divisions apper- tain to both hemispheres, as we recede from the equator to- wards the north or south poles. It will hereafter be shown that the tropical and temperate faunas may be again divided into several zoological provinces, depending on longitude or on the peculiar configuration of the continents. § 596. No continent is better calculated to give a correct idea of distribution into faunas, as determined by climate, than the continent of America ; extending as it does across both hemi- spheres, and embracing all latitudes, so that all climates are represented upon it, as shown by the chart on the following page. § 597. Let a traveller embark at Iceland, which is situated on the borders of the polar circle, with a view to observe, in a zoological aspect, the principal points along the eastern shore of America. The result of his observations will be very much as foUows. Along the coast of Greenland and Iceland, and also along Baffin’s Bay, he will meet with an unvaried fauna composed throughout of the same animals, which are also for the most part identical with those of the arctic shores of Europe. It wiU be nearly the same along the coast of Labrador. § 598. As he approaches Newfoundland, he will see the landscape, and with it the fauna, assuming a somewhat more varied aspect. To the wide and naked or turfy plains of the boreal regions succeed forests, in which he will find various animals dwelling only therein. Here the temperate fauna B B 370 GEOGEAPHICAL DTSTEIBUTION OF A^flMALS, CHART OF ZOOLOGICAL REGIONS. DISTEIBTJTIOIf OE THE EAUHAS. 371 commences. Still the number of species is not yet very considerable ; as be advances southward, along the coasts of Nova Scotia and New England, he finds new species gradually introduced, while those of the colder regions diminish, and at length entirely disappear, some few accidental or periodical visiters excepted, who wander during winter as far south as the Carolinas. § 599. But it is after having passed the boundaries of the United States, among the Antilles, and more especially on the southern continent, along the shores of the Orinoco and the Amazon, that our traveller will be forcibly struck with the astonishing variety of the animals inhabiting the forests, the prairies, the rivers, and the sea-shores, most of which he will also find to be different from those of the northern conti- nent. By this extraordinary richness of new forms, he will become sensible that he is now in the domain of the tropical fauna. § 600. Let him still travel on beyond the equator towards the tropic of Capricorn, and he will again find the scene change as he enters the regions where the sun casts his rays more obliquely, and where the contrast of the Seasons is more marked. The vegetation will be less luxuriant ; the palms will have disappeared to make place for other trees ; the ani- mals will be less varied, and the whole picture will recall to him, in some measure, the scene which he witnessed in the United States. He will again find himself in the temperate region, and this he will trace on, till he arrives at the extremity of the continent, the fauna and the flora becoming more and more impoverished as he approaches Cape Horn. § 601. Finally, we know that there is a continent around the South Pole. Although we have as yet but very imperfect notions respecting the animals of this inhospitable clime, still the few which have already been observed there, present a close analogy to those of the arctic region. It is another glacial fauna, namely, the antarctic. Having thus sketched the general distribution of the faunas, it remains to point out the principal features of each. § 602. I. Aectic Faota. — The predominant feature of the Arctic Fauna is its uniformity. The species are few ; but, on the other hand, the number of individuals is im- mense. We need only refer to the clouds of birds which B B 2 S72 GEOGKAPHICAL DISTElBlTTlcW OE AKIMALS. hover upon the islands and shores of the North ; the shoals of fishes, the salmon, among others, which throng the coasts of Greenland, Iceland, and Hudson’s Bay. There is uni- formity also in the form and colour of these animals. Not a single bird of brilliant plumage is found, and few fishes with varied hues. Their forms are regular, and their tints as dusky as the northern heavens. The most conspicuous animals are the white bear, the moose, the reindeer, the musk-ox, the white fox, the polar hare, the lemming, and various seals ; but the most important are the whales, which, it is to be remarked, rank lowest of all the mammals. Among the birds, may be enumerated some sea-eagles and a few waders, while the great majority are aquatic species, such as gulls, cormorants, divers, petrels, ducks, geese, gannets, &c., all belonging to the lowest orders of birds. Reptiles are altogether wanting. The articulata are represented by numerous marine worms, and by minute crustaceans of the orders isopoda and amphipoda. Insects are rare, and of inferior types. Of the moUusca, there are acephala, particularly tunicata, fewer gasteropods, and very few cephalopods. Among the radiata are a great number of jelly-fishes, particularly the Beroe; and to conclude with the echinoderms, there are several star-fishes and echini, but few holothuriae. The class of polypi is very scantily repre- sented, and those producing stony corals are entirely wanting. § 603. This assemblage of animals is evidently inferior to that of other faunas, especially to those of the tropics. Not that there is a deficiency of animal life ; for if the species are less numerous, there is a compensation in the multitude of individuals, and also in this other very significant fact, that the largest of all animals, the whales, belong to this fauna. § 604. It has already been said (§ 602) that the arctic fauna of the three continents is the same ; its southern limit, how- ever, is not a regular line. It does not correspond precisely with the polar circle, but rather to the isothermal zero, that is, the line where the average temperature of the year is at 32°. of Fahrenheit. The course of this line presents numerous undulations. In general, it may be said to coincide with the northern limit of trees, so that it terminates where forest vegetation succeeds the vast arid plains, the barrens of North America, or the tundras of the Samoyedes. The uniformity of these plains involves a corresponding uniformity of plants and animals. On the North American continent it extends DISTEIJiCTION OJP THE EATJNAS. 373 much farther southward on the eastern shore, than on the western. From the peninsula of Alashka it bends northwards towards the Mackenzie, then descends again towards the Bear Lake, and comes down near to the northern shore of New- foundland. § 605. II. Tempeeate Faotas. — The faunas of the tem- perate regions of the northern hemisphere are much more varied than that of the arctic zone. Instead of consisting mainly of aquatic tribes, we have a considerable number of terrestrial animals of graceful form, animated appearance, and varied colours, though less brilliant than those found in tropi- cal regions. Those parts of the country covered with forests especially swarm with insects, which become the food of other animals : worms, terrestrial and fluviatile moUusca are also abundant. § 606. Still, the climate is not sufficiently warm over the whole extent of this zone to allow the trees to retain their foliage throughout the year. At its northern margin the leaves, excepting those of the pines and spruces, fall, on the ap- proach of the cold season, and vegetation is arrested for a longer or shorter period. Insects retire, and the animals which live upon them no longer find nourishment, and are obliged to migrate to warmer regions, on the borders of the tropics, where, amid the ever-verdant vegetation, they find the means of subsistence. § 607. Some of the herbivorous mammals, the bats, and the reptiles which feed on insects, pass the winter in a state of torpor, from which they awake in spring. Others retire into dens, and live on the provisions they have stored up dur- ing the warm season. The carnivora, the ruminants, and the most active portion of the rodents, are the only animals that do not change either their abode or their habits. The fauna of the temperate zone thus presents an ever-changing picture, which may be considered as one of its most important features, since these changes recur with equal constancy in the Old and .the New World. § 608. Taking the contrast of the vegetation, as a basis, and the consequent changes of habit imposed upon the deni- zens of the forests, the temperate fauna has been divided into two regions ; a northern one, where the trees, except the pines, drop their leaves in winter, and a southern one, where they are evergreen. Now, as the limit of the former, that of 374 GEOGEAPHICAL DISTRIBUTION OE ANIMALS. the deciduous trees, coincides, in general, with the limit of the pines, it may be said that the cold region of the temperate fauna extends as far as the pines. In the United States this coincidence is not so marked as in other regions, inasmuch as the pines along the Atlantic coast extend into Florida, while they do not prevail in the Western States ; but we may con- sider as belonging to the southern portion of the temperate region, that part of the country south of the latitude where the palmetto or cabbage-tree {ChamtErops) commences, namely, all the States to the south of North Carolina ; while the States to the north of this limit belong to the northern portion of the temperate region. § 609. This division into two zones is supported by obser- vations made on the maritime faunas of the Atlantic coast. The line of separation between them, however, being influ- enced by the Gulf Stream, is considerably farther to the north ; — namely, at Cape Cod : although there is also another decided hmitation of the marine animals at a point nearly coinciding with the line of demarcation above-mentioned, namely, at Cape Hatteras. It has been observed, that of one hun- dred and ninety-seven mollusca inhabiting the coast o^ New England, fifty do not pass to the north of Cape Cod, and eighty-three do not pass to the south of it ; only sixty-four being common to both sides of the Cape. A similar limita- tion of the range of Ashes has been noticed by Dr. Storer ; and Dr. Holbrook has found the fishes of South Carolina to be different from those of Florida and the West Indies. In Europe, the northern part of the temperate region extends to the Pyrenees and the Alps ; and its southern portion consists of the basin of the Mediterranean, together with the northern part of Africa, as far as the desert of Sahara. § 610. A peculiar characteristic of the faunas of the tem- perate regions in the northern hemisphere, when contrasted with those of the southern, is the great similarity of the pre- vailing types on both continents. Notwithstanding the im- mense extent of country embraced, the same stamp is every- where exhibited. Generally, the same families, frequently the same genera, represented by different species, are found. There are even a few species of terrestrial animals regarded as identical on the continents of Europe and America ; but their supposed number is constantly diminished, as more accurate observations are made. The predominant types DISTBIBTJTIOK OF THE FAUNAS. 375 among the mammals are the bison, deer, ox, horse, hog, nu- merous rodents, especially squirrels, and hares, nearly all the insectivora, weasels, martens, wolves, foxes, wild cats, &c. On the other hand, there are no edentata and no quadrumana, with the exception of some monkeys on the two slopes of the Atlas and in Japan. Among birds, there is a multitude of climbers, passerine, gallinaceous, and many rapacious fami- lies. Of reptiles, there are lizards and tortoises of small or medium size, serpents, and many batrachians, but no croco- diles. Of fishes, there is the trout family, the cyprinoids, the sturgeons, the pikes, the cod, and especially the great family of herrings and scomberoids, to which latter belong the mackerel and the tunny. All classes of the mollusca are represented ; though the cephalopods are less numerous than in the torrid zone. There is an infinite number of articu- lata of every type, as well as numerous polyps, though the corals proper do not yet appear abundantly. § fill. On each of the two continents of Europe and America, there is a certain number of species extending from, one extreme of the temperate zone to the other. Such, for example, are the deer, the bison, the cougar, the flying- squirrel, numerous birds of prey, several tortoises, and the rattle-snake, in America. In Europe, the brown bear, wolf, swallow, and many birds of prey. Some species have a still wider range, like the ermine, which is found from Behring’s Straits to the Himalaya Mountains — that is to say, from the coldest regions of the arctic zone to the southern confines of the temperate zone. It is the same with the musk-rat, which is found from the mouth of Mackenzie’s River to Florida. The field-mouse has an equal range in Europe. Other species, on the contrary, are limited to one region. The Canadian elk is confined to he northern portion of the fauna ; while the prairie wolf, the fox-squirrel, the Bassai^is, and numerous birds, never leave the southern portion.* * The types which are peculiar to temperate America, and are not found in Europe, are the opossum, several genera of insectivora, among them the shrew-mole {Scalops aquaticus)^ and the star-nose mole {Condylnra cristata), which replaces the My gale of the Old World ; several genera of rodents, especially the musk-rat. Among the types characteristic' of America must also be reckoned the snapping-turtle among the tortoises ; the Menohranchus and Menopoma among the Salamanders ; the Lepidos- tens and Amia among the fishes ; and, finally, the Limulus among the 376 GEOGKAPHICAJi DISTlllliUTlOlS' OP A-KIMALS. § 612. In America, as in the Old World, the temperate fauna is further subdivided into several districts, which may be regarded as so many zoological provinces, in each of which there is a certain number of animals differing from those in the others, though very closely allied to them. Temperate America presents us with a striking example in this respect. We have, on the one hand : — 1st. The fauna of the United States properly so called, on this side of the Rocky Mountains. 2d. ThS fauna of Oregon and California, beyond those mountains. Though there are some animals which traverse the chain of the Rocky Mountains, and are found in the prairies of the Missouri as well as on the banks of the Columbia, as, for example, the Rocky Mountain deer {Antilope furcifer), yet, if we regard the whole assemblage of animals, they are found to differ entirely. Thus, the rodents, part of the ruminants, the insects, and all the mollusks, belong to distinct species. § 613. The faunas or zoological provinces of the Old World corresponding to these are : — 1st. The fauna of Europe, which is very closely related to that of the United States proper. 2d. The fauna of Siberia, separated from the fauna of Europe by the Ural Mountains. 3d. The fauna of the Asiatic table-land, which, from what is as yet known of it, appears to be quite distinct. 4th. The fauna of China and Japan, which is analogous to that of Europe in the birds, and to that of the United States in the reptiles — as it is also in the flora. Lastly, it is in the temperate zone of the northern hemi- sphere that we meet with the most striking examples of those local faunas which have been mentioned above. Such, for example, is the fauna of the Caspian Sea, of the steppes of Tartary, and of the Western prairies. § 614. The faunas of the southern temperate regions differ from those of the tropics as much asr the northern temperate Crustacea. Among the types which are wanting in temperate America, and which are found in Europe, may be cited the horse, the wild boar, and the true mouse. All the species of domestic mice living in America, have been brought from the Old World. BISTEIBUTIOK or THE FAdiVAS. 377 faunas do ; and, like them also, may be distinguished into two provinces, the colder of which embraces Patagonia. But, besides differing from the tropical faunas, they are also quite unhke- each other on the different continents. Instead of that general resemblance, that family likeness, which we have noticed between all the faunas of the temperate zone of the northern hemisphere, we find here the most complete con- trasts. Each of the three continental peninsulas jutting out southerly into the ocean represents, in some sense, a separate world. The animals of South America, beyond the tropic of Capricorn, are, in all respects, different from those at the southern extremity of Africa. The hyenas, wild boars, and rhinoceroses of the Cape of Good Hope have no analogues on the American continent ; and the difference is equally great between the birds, reptiles, fishes, insects and mollusks. Among the most characteristic animals of the southern ex- tremity of America are peculiar species of seals, and especially among aquatic birds, the penguins. § 615. New Holland, with its marsupial mammals, with which are associated insects and mollusks no less singular, furnishes a fauna still more peculiar, and which has no simi- ^ larity to those of any of the adjacent countries. In the seas of that continent, where every thing is so strange, we find the curious shark, with paved teeth and spines on the back (Cestracion Philippii), the only living representative of a family so numerous in former zoological ages. But a most remarkable feature of this fauna is, that the same types pre- vail over the whole continent, in its temperate as well as its tropical portions, the species only being different in different localities. § 616. Tkopical Eaunas. — The tropical faunas are dis- tinguished, on all the continents, by the immense variety of animals which they comprise, not less than by the brilliancy of their dress. All the principal types of animals are represented, and all contain numerous genera and species. We need only refer to the tribe of humming-birds, which numbers not less than three hundred species. It is very im- portant to notice, that here are concentrated the most per- fect, as well as the most singular types of all the classes of the animal kingdom. The tropical region is the only one occu- pied by the quadrumana, the herbivorous bats, the great 378 GEOGRAPHICAL DISTRIBUTION OF ANIMALS. pachydermata, such as the elephant, the hippopotamus, and the tapir, and the whole family of edentata. Here also are found the largest of the cat tribe, the lion, and tiger. Among the birds we may mention the parrots and toucans, as essen- tially tropical ; among the reptiles, the largest crocodiles and gigantic tortoises ; and, finally, among the articulated animals, an immense variety of the most beautiful insects. The ma- rine animals, as a whole, are equally superior to those of other regions : the seas teem with crustaceans and numerous cepha- lopods, together with an infinite variety of gasteropods and acephala. The echinoderms there attain a magnitude and variety elsewhere unknown ; and, lastly, the polyps there display an activity of which the other zones present no example. Whole groups of islands are surrounded with coral reefs formed by those httle animals. § 617. The variety of the tropical fauna is further enriched by the circumstance that each continent furnishes new and peculiar forms. Sometimes whole types are limited to one continent, as the sloth, the toucans, and the humming-birds to America, the girafie and hippopotamus to Africa ; and again, animals of the same group have different characteristics, according as they are found on different continents. Thus, the monkeys of America have fiat and widely-separated nos- trils, thirty-six teeth, and generally a long, prehensile tail. The monkeys of the old world, on the contrary, have nostrils close together, only thirty-two teeth, and not one of them has a prehensile tail. § 618. But these differences, however important they may appear at first glance, are subordinate to more important cha- racters, which establish a certain general affinity between all the faunas of the tropics. Such, for example, is the fact that the quadrumana are limited, on all the continents, to the warmest regions ; and never, or but rarely, penetrate into the temperate zone. This limitation is a natural consequence of the distribution of the palms ; for as these trees, which con- stitute the ruling feature of the fiora of the tropics, furnish, to a great extent, the food of the monkeys on both continents, we have only to trace the limits of the palms, to have a pretty accurate indication of the extent of the tropical faunas on all three continents. DISTEIBUTIOiS^ OP THE PAIJHAS. 379 § 619. Several well-marked faunas may oe distinguished in the tropical part of the American continent, namely : 1st. The fauna of Brazil, characterized by its gigantic reptiles, its monkeys, its edentata, its tapir, its humming-birds, and the astonishing variety of its insects. 2nd. The fauna of the western slope of the Andes, comprising Chili and Peru, is distinguished by its llamas, vicunas, and birds, which differ from those of the basin of the Amazon, as also do the insects and mollusks. 3dly. The fauna of the Antilles and the Gulf of Mexico. This is especially characterized by its marine animals, among which the MamUus is particularly remarkable ; an infinite variety of singular fishes, embracing a large number of plectognaths ; also mollusca, and radiata of peculiar species. It is in this zone that the Pentacrinus caput-meduscB is found, the only representative, in the existing creation, of a family so nume- rous in ancient epochs, the Crinoidea with a jointed stem. The limits of the fauna of Central America cannot yet be well defined, from a want of sufficient knowledge of the* animals inhabiting those regions. § 620. The tropical zone of Africa is distinguished by a striking uniformity in the distribution of the animals, cor- responding to the uniformity of the structure and contour of that continent. Its most characteristic species are spread over the whole extent of the tropics : thus, the giraffe is met with from Upper Egypt to the Cape of Good Hope. The hippopo* tamus is found at the same time in the Nile, the Niger, and Orange River. This wide range is the more significant, as it also relates to herbivorous animals, and thus supposes condi- tions of vegetation very similar over wide countries. Some forms are nevertheless circumscribed within narrow districts ; and there are marked differences between the animals of the eastern and western shores. Among the remarkable species of the African torrid region are the baboons, the African ele- phant, the crocodile of the Nile, a vast number of antelopes, and especially two species of ourang-outang, the chimpanzee and the Engeena, a large and remarkable animal, only recently described. The fishes of the Nile have a tropical character, as well as the animals of Arabia, which are more allied to those of Africa than to those of Asia. § 621. .The tropical fauna of Asia, comprising the two pe- 380 GEOGEAPHICAL DISTETBUTION OE AI^IMALS. ninsulas of India and the isles of Sunda, is not less marked. It is the country of the gibbons, the red ourang, the royal tiger, the gavial, and a multitude of pecuhar birds. Among the fishes, the family of chetodons is most numerously repre- sented. Here also are found those curious spiny fishes, whose intricate gills suggested the name Labyrinthiciy by which they are known. Fishes with tufted gills are more numerous here than in other seas. The insects and mollusks are no less strongly characterized. Among others is the Nautilus, the only living representative of the great family of large chambered- shells, which prevailed so extensively over other types in for- mer geological ages. § 622. The large island of Madagascar has its peculiar fauna, characterized by its makis and its curious rodents. It is also the habitat of the Aya-aya, Polynesia, exclusive of New Holland, furnishes a number of very curious animals, which are not found on the Asiatic continent. Such are the herbivorous bats, and the Galeopithecus, or fiying maki. The Galapago islands, only a few hundred miles from the coast of Peru, have a fauna exclusively their own, among which gigantic land-tortoises are very characteristic. SECTION III. COIfCLTJSIOKS. § 623. Feom the survey we have thus made of the distribution of the Animal Kingdom, it follows : 1st. Each grand division of the globe has animals which are either wholly or for the most part peculiar to it. These groups of animals constitute the faunas of different regions. 2d. The diversity of faunas is not in proportion to the dis- tance which separates them. Very similar faunas are found at great distances apart ; as, for example, the fauna of Europe and that of the United States, which yet are separated by a wide ocean. Others, on the contrary, difiTer considerably, though at comparatively short distances ; as the fauna of the East Indies and the Sunda Islands, and that of New Holland ; or the fauna of Labrador and that of New England. 3d. There is a direct relation between the richness of a fauna and the climate. The tropical faunas contain a much larger number of more perfect animals than those of the tem- perate and polar regions. 4th. There is a no less striking relation between the fauna toj^^oLnsiOi^s. 381 and flora, the limit of the former being oftentimes determined, so far as terrestrial animals are concerned, by the extent of the latter. § 624. Animals are endowed with instincts and faculties corresponding to the physical character of the countries they inhabit, and which would be of no service to them under other circumstances. The monkey, which is a frugivorous animal, is organized for living on the trees from which he obtains his food. The reindeer, on the contrary, whose food consists of lichens, lives in cold regions. The latter would be quite out of place in the torrid zone, and the monkey would perish with hunger in the polar regions. Animals which store up provi- sions are all pecuhar to temperate or cold climates. Their instincts would be uncalled for in tropical regions, where the vegetation presents the herbivora with an abundant supply of food at all times. § 625. However intimately the chmate of a country may be alhed with the peculiar character of its fauna, we are not to conclude that the one is the consequence of the other. The differences observed between animals of different faunas are no more to be ascribed to the influences of climate, than their organization is to the influence of the physical forces of nature. If it were so, we should necessarily find all animals precisely similar, when placed under the same conditions. We shall find, by the study of the different groups in detail, that certain species, though very nearly alike, are nevertheless distinct in two different faunas. Between the animals of the temperate zone of Europe, and those of the United States, there is similarity, but not identity ; and the particulars in which they differ, though apparently trifling, are yet constant. § 626. Fully to appreciate the value of these differences, it is often requisite to know all the species of a genus or of a family. It is not uncommon to find, upon such an examina- tion, that there is the closest resemblance between species dwelling far apart from each other, while species of the same genus, living side by side, are widely different. This may be illustrated by a single example. The Menopoma, Siren, Amphiuma, Axolotl, and the Menobranchus, are batrachians which inhabit the rivers and lakes of the United States and Mexico. They are very similar in external form, yet differ in the fact that some of them have external gills at the sides of the head, in which others are deficient ; that some have five toes, 382 GEOaHAPHICAL DISTRIBUTION OF ANIMALS. while others have only two ; and also in having either two or four legs. Hence we might be tempted to refer them to differ- ent types, did we not know intermediate animals, completing the series, namely, the Proteus and Megalohatrachus, Now the former exists only in the subterranean lakes of Austria, and the latter in Japan. The connection in This case is con- sequently established by means of species which inhabit dis- tant continents. § 627. Neither the distribution of animals therefore, any more than their organization, can be the effect of external in- fluences, We must, on the contrary, see in it the realization of a plan wisely designed, the work of a Supreme Intelligence, who created, at the beginning, each species of animal at the place, and for the place, which it inhabits. To each species has been assigned a limit which it has no disposition to over- pass so long as it remains in a wild state. Only those animals which have been subjected to the yoke of man, or whose subsistence is dependent on man’s social habits, are exceptions to this rule. § 628. As the human race has extended over the surface of the earth, man has more or less modified the animal popula- tion of different regions, either by exterminating certain spe- cies, or by introducing others with which he desires to be more intimately associated, — the domestic animals. Thus, the dog is found wherever we know of the presence of man. The horse, originally from Asia, was introduced into America by the Spaniards ; where it has thriven so well, that it is found wild, in innumerable herds, over the Pampas of South America, and the prairies of the West. In hke manner the domestic ox became wild in South America. Many less wel- come animals have followed man in his peregrinations ; as, for example, the rat and the mouse, as well as a multitude of insects, such as the house-fly, the cock-roach, and others which are attached to certain species of plants, as the white- butterfly, the Hessian-fly, &c. The honey-bee also has been imported from Europe. § 629. Among the species which have disappeared, under the influence of man, we may mention the Dodo, a pecuhar species of bird which once inhabited the Mauritius, some re- mains of which are preserved in the British and Ashmolean Museums ; a large cetacean of the north {Rytina Stelleri), formerly inhabiting the coasts of Behring’s Straits, and which coNCLrsiois^s. 383 has not been seen since 1768. According to all appearances, we must also reckon among these the great stag, the skeleton and horns of which have been found buried in the peat-bogs of Ireland, and those of the Isle of Man. There are also many species of animals whose numbers are daily diminishing, and whose extinction may be foreseen ; as the Canadian deer (Wapiti), the ibex of the Alps, the Lammergeyer, the bison, the beaver, the wild-turkey, &c. § 630. Other causes may also contribute towards dispersing animals beyond their natural hmits. Thus the sea-weeds are carried about by marine currents, and are frequently met with far from shore, thronged with little crustaceans, which are in this manner transported to great distances from the place of their birth. The drift-wood which the Gulf, stream floats from the Gulf of Mexico even to the western shores of Europe, is frequently perforated by the larvae of insects, and may probably serve as depositories for the eggs of fishes, Crustacea and mollusks. It is possible also that aquatic birds may con- tribute in some measure to the diffusion of some species of fishes and mollusks, either by the eggs becoming attached to their feet, or by means of those which they evacuate undi- gested, after having transported them to considerable dis- tances. Still, all these circumstances exercise but a very feeble influence upon the distribution of species in general, and each country, none the less, preserves its peculiar physiog- nomy, so far as its animals are concerned. §631. There is only one way to account for the distribu- tion of animals as we find them, namely, to suppose that they are autochthonoi, that is to say, that they originated like plants, on the soil where they are found. In order to explain the particular distribution of many animals, we are even led to admit that they must have been created at several points of the same zone, an inference which we must make from the distri- bution of aquatic animals, especially that of fishes. If we ex- amine the fishes of the different rivers of the United States, pe- culiar species will be found in each basin, associated with others which are common to several basins. Thus, the Delaware River contains species not found in the Hudson ; but, on the other hand, the pickerel is found in both. Now, if all animals originated at one point, and from a single stock, the pickerel must have passed from the Delaware to the Hudson, or vice 384 aEOGEAPHlt^Afi DISTEIBUTION OE AlflMALS. versa, which it could only have done by passing along the sea-shore, or by leaping over large spaces of terra jirma; that is to say, in both cases it would be necessary to do vio- lence to its organization. Now such a supposition is in direct opposition to‘the immutabihty of the laws of nature. § 632. We shall hereafter see that the same laws of distri- bution are not limited to the actual creation only, but that they have also ruled the creations of former geological epochs, and that the fossil species have lived and died, most of them, at the place where their remains are found. § 633. Even man, although a cosmopolite, is subject, in a certain sense, to this law of limitation. While he is every- where the one identical species, yet several races, marked by certain pecuharities of features, are recognised ; such as the Caucasian, Mongolian, and African races, of which we are hereafter to speak. And it is not a httle remarkable, that the abiding places of these several races correspond very nearly with some of the great zoological regions. Thus we have a northern race, comprising the Samoyedes in Asia, the Laplanders in Europe, and the Esquimaux in America, cor- responding to the Arctic fauna (§ 602), and like it, identical on the three continents, having for its southern limit the region of trees (§ 604). In AMca, we have the Hottentot and Negro races, in the south and central portions respectively, while the people of northern Africa are allied to their neighbours in Europe ; just as we have seen to be the case with the zoolo- gical fauna in general (§ 584). The inhabitants of New Hol- land, like its animals, are the most grotesque and uncouth of all races (§ 615). § 634. The same parallelism holds good elsewhere, though not always in so remarkable a degree. In America, espe- cially, while the aboriginal race is as well distinguished from other races as is its flora, the minor divisions are not so de- cided. Indeed, the facihties, or we might sometimes rather say, necessities, arising from the varied supplies of animal and vegetable food in the several regions, might be expected to involve, with his corresponding customs and modes of life, a difference in the physical constitution of man, which would contribute to augment any primeval differences. It could not, indeed, be expected, that a people constantly sub- jected to cold, like the people of the north, and living almost COI^CLUSIONS. 385 exclusively on fish, which is not to be obtained without great toil and peril, should present the same characteristics, either bodily or mental, as those who idly regale on the spontaneous bounties of tropical vegetation. [§ 635. Many other causes still more intimately connected with the aspect of our globe have also a great influence upon the distribution of the animals and plants living on its surface. The form of continents, the bearing of their shores, the direction and height of mountains, the mean level of great plains, the amount of water circumscribed by land, and form- ing inland lakes or seas, each shows a marked influence upon the general features of vegetation. Small low islands, scat- tered in clusters, are covered with a vegetation entirely dilferent from that of extensive plains under the same lati- tudes. The bearing of the shores, again, modifying the cur- rents of the sea, will also react upon vegetation. Mountain chains will be influential, not only from the height of their slopes and summits, but also from their action upon the prevailing winds. It is obvious, for instance, that a moun- tain chain like the Alps, running east and west, and form- ing a barrier between the colder region northwards and the warmer southwards, will have a tendency to lower the temperature of the northern plains, and to increase that of the southern below or above the mean which such localities would otherwise present ; while the influence of a chain running north and south, like the Rocky Mountains and the Andes, will be quite the reverse, and tend to increase the natural dif- ferences between the eastern and western shores of the conti- nent, laying open the north to southern influences and the south to those of the north, thus rendering its climate ex- cessive, e. its summer warmer and its winter colder. [§ 636. Again, the equalizing influence of a large sheet of water, the temperature of which is less liable to sudden changes than the atmospheric air, is very apparent in the uniformity of coast vegetation over extensive tracts, provided the soil be of the same nature ; and also in the slower transition from one season into another along the shores, the coasts having less extreme temperatures than the main land. The absolute de- gree of temperature of the water acts with equal power ; • as the aquatic plants of the tropical regions, for instance, those 386 GEOGEAPHICAL EISTEIBUTIOK OE AKIMALS. of Guyana, differ as widely from those of Lake Superior as the palms differ from the pine forests. [§ 637. But, however active these physical agents may be, it would be very un philosophical to consider them as the source or origin of the beings upon which they show so exten- sive an influence. Mistaking the circumstantial relation under which they appear for a causal connection, has done great mischief in natural science, and led many to believe they un- derstood the process of creation, because they could account for some of the phenomena under observation. But, however powerful may be the degree of the heat ; be the air ever so dry, or ever so moist ; the light ever so moderate, or ever so bright ; alternating ever so suddenly with darkness, or passing gradually from one condition to the other ; these agents have never been observed to produce anything new, or to call into existence anything that did not exist before. Whether acting isolated or jointly, they have never been known even to modify to any great extent the living beings already existing, unless under the guidance and influence of man, as we observe among domesticated animals and cultivated plants. This latter fact shows, indeed, that the influence of the mind over material phenomena is far greater than that of physical forces, and thus refers our thoughts again and again to a Supreme Intelligence for a cause of all these phenomena, rather than to the so- called natural agents. [§ 638. The physical agents whose influence upon organized beings we have just examined, show a regular progression in their action, agreeing most remarkably with the degrees of latitude on one side, and the elevation above the level of the sea on the other. Hence the difference in the vegetation, as we proceed from tropical regions towards the poles, or as we ascend from the level of the sea to any height along the slopes of a mountain. In both these directions there is a striking agreement in the order of succession of the pheno- mena, so much so, that the natural products of any given lati- tude may be properly compared with those occurring at a given height above the level of the sea ; for instance, the vege- tation of regions near the polar circles, and that of high moun- tains near the limits of perpetual snow under any latitude. The height of this limit, however, varies, of course, with the lati- tude. In Lapland, at 67° north latitude, it is three thousand CO'N’CLTJSIOIS'S. 387 five hundred feet above the level of the sea ; in Norway, at lat. 60^ it is five thousand feet ; in the Alps, at lat. 46®, about eight thousand five hundred ; in the Himalaya, at lat. 30®, over twelve thousand ; in Mexico, at lat. 1 9®, it is fifteen thousand ; and at Quito, under the equator, not less than sixteen thou- sand. At these elevations, in their different respective lati- tudes, without taking the undulations of the isothermal lines into consideration, vegetation shows a most uniform character, so that it may be said that there is a corresponding similarity of climate and vegetation between the successive degrees of latitude and the successive heights above the sea. As a strik- ing example, the fact may be mentioned of the occurrence of identical plants in Lapland in lat. 67°, at a height of about three thousand fe.et and less above the level of the sea, and upon the summit of Mount Washington, in lat. 44®, at a height of not less than six thousand feet ; while below this limit, in the. wooded valleys of the White Mountains, there is not one spe- cies which occurs also about North Cape. [§ 639 . There is, nevertheless, one circumstance which shows that climatic influences alone, however extensive, taking, for instance, into account all the above-mentioned agents together, will not fully account for the geographical distribution of or- ganized beings ; as their various limits do not agree precisely with the outlines indicating the intensity of physical agents upon the surface of the earth. A few examples may serve to illustrate this remark. The limit of forest vegetation round the arctic circle does not coincide with the astronomical limits of the arctic zone ; nor does it agree fully with the isothermal line of 32® of Fahrenheit ; nor is the limit of vegetation in height always strictly in accordance with the temperature, as the Cerastium latifolium and Ranunculus glacialis^ for in- stance, occur in the Alps as high as ten, and even eleven thousand feet above the level of the sea. Again, eastern and western countries within the same continent, or compared from one continent to the other, show such differences under similar climatic circumstances, that we at once feel that some- thing is wanting in our illustrations, when we refer the dis- tribution of animals and plants solely to the agency of climate. But the most striking evidence that climate neither accounts for the resemblance nor the difference of animals and plants in different countries, may be derived from the fact, that the c c 2 388 GEOGEAPHICAL DISTEIBTJTIOIS' OP ANIMALS. development of the animal and vegetable kingdoms differs widely, under the same latitudes, in the northern and in the southern hemispheres, and that there are entire famihes of plants and animals exclusively circumscribed within certain parts of the world ; such are, for instance, the magnolia and cactus in America, the kangaroos in New Holland, the ele- phants and rhinoceros in Asia and Africa, &c., &c. [§ 640. From these facts we may indeed conclude, that there are other influences acting in the distribution of animals and plants besides climate ; or, perhaps, we may better put the proposition in this form : that however intimately con- nected with climate, however apparently dependent upon it, vegetation is, in truth, independent of those influences, at least so far as the causal connection is concerned, and merely adapted to them. This position would at once imply the ex- istence of a power regulating these general phenomena in such *a manner as to make them agree in their mutual connection ; that is to say, we are thus led to consider nature as the work of an intelligent Creator, providing for its preservation under the combined influences of various agents equally his work, which contribute to their more diversified combinations. [§ 641. The geographical distribution of organized beings displays more fully the direct intervention of a Supreme Intelligence in the plan of creation, than any other adapta- tion in the physical world. Generally, the evidence of such an intervention is derived from the benefits, material, intel- lectual, and moral, which man derives from nature around him, and from the mental conviction which consciousness im- parts to him, that there could be no such wonderful order in the universe, without an omnipotent Ordainer of the whole. This evidence, however plain to the Christian, will never be satisfactory to the man of science, in that form. In these studies evidence must rest upon direct observation and induc- tion, just as fully as mathematics claims the right to settle all questions about measurable things. There will be no scien- tific evidence of God’s working in nature, until naturalists have shown that the whole creation is the expression of a thought, and not product of physical agents. Now what stronger evidence of thoughtful adaptation can there be, than the various combinations of similar, though specifically differ ent assemblages of animals and plants repeated all over the CO^fCLUSIOIfS. 389 world, under the most uniform and the most diversified cir- cumstances ? When we meet with pine trees, so remarkable for their peculiarities, both morphological and anatomical, combined with beeches, birches, oaks, maples, &c., as well in North America as in Europe and Northern Asia, under similar circumstances ; when we find, again, representatives of the same family with totally different features, mingling, so to say, under low latitudes with palm trees, and all the luxu- riant vegetation of the tropics ; when we truly behold such scenes, and have penetrated their full meaning as naturalists, then we are placed in a position similar to that of the anti- quarian who visits ancient monuments. He recognizes at once the workings of intelligence in the remains of an an- cient civilization ; he may fail to ascertain their age correctly, he may remain doubtful as to the order in which they were successively constructed, but the character of the whole tells him that they are works of art, and that men, like himself, originated these relics of by-gone ages. So shall the intelli- gent naturalist read at once in the pictures which nature pre- sents to him, the works of a higher Intelligence ; he shall re- cognize in the minute perforated cells of the Coniferce, which differ so wonderfully from those of other plants, the hierogly- phics of a peculiar age ; in their needle-like leaves, the escut- cheon of a peculiar dynasty ; in their repeated appearance under most diversified circumstances, a thoughtful and thought- eliciting adaptation. He beholds, indeed, the works of a being thinking like himself, but he feels at the same time that he stands as much below the Supreme Intelligence, in wisdom, power and goodness, as the works of art are inferior to the wonders of nature. Let naturalists look at the world under such impressions, and evidence will pour in upon us that all creatures are expressions of the thoughts of Him whom we know, love and adore unseen.*] * Lake Superior, by Professor Louis Agassiz, page 104 at seq. CHAPTER FOURTEENTH. GEOLOGICAL SUCCESSION OF ANIMALS ; OR, THEIR DIS- TRIBUTION IN TIME. SECTION I. STRUCTURE OF THE EARTH’ S CRUST. § 642. The records of the Bible, as well as human tra- dition, teach us that man and the animals associated with him were created by the word of God ; “ The Lord made Heaven and earth, the sea, and all that in them is and this truth is confirmed by the revelations of science, which unequivocally indicate the direct interventions of creative power. § 643. But man and the animals which now surround him are not the only kinds which have had a being. The surface of our planet, anterior to their appearance, was not a desert. There are, scattered through the crust of the earth, numerous animal and vegetable remains, which show that the earth had been repeatedly supplied with, and long in- habited by animals and plants altogether different from those now living. § 644. In general, their hard parts are the only relics of them which have been preserved, such as the skeleton and teeth of vertebrata ; the shells of mollusca and radiata ; the shields of crustaceans, and sometimes the wing-cases of insects. Most frequently they have lost their original chemical composition, and are changed into stone ; and hence the name of petrifactions or fossils, under which latter term are comprehended all the organized bodies of former epochs, obtained from the earth’s crust. Others have entirely dis- appeared, leaving only their forms and sculpture impressed upon the rocks. § 645. The study of these remains and of their position in the rocks constitutes Paleontology ; one of the most essen- tial branches of zoology. Their geological distribution, or the order of their successive appearance — namely, the distri- bution of animals in time, is of no less importance than the STRUCTITHE OE THE EARTH’s CRUST. 391 geographical distribution of living animals, their distribution in space, of which we have treated in the preceding chapter. To obtain an idea of the successive creations, and of the stupendous length of time they have required, it is necessary to sketch the principal outlines of geology. § 646. The rocks* which compose the crust of our globe are of two kinds : — 1. The Massive Bocks, called also Plutonic, or Igneous Bocks, which lie beneath all the others, or have sometimes been forced up through them, from beneath. They were once in a melted state, like the lava of the present epoch, and, on cooling at the surface, formed the original crust of the globe, the granite, and later porphyry, basalt, &c. 2. The Sedimentary, or Stratified Bocks, called also Nep- tunic Bocks, which have been deposited in water, in the same manner as modern seas and lakes deposit sand and mud on their shores, or at the bottom, § 647. These sediments have been derived partly from the disintegration of the older rocks, and partly from the decay of plants and animals. The materials being disposed in layers or strata have become, as they hardened, limestones, slates, marls, or grits, according to their chemical and mechanical composition, and contain the remains of the animals and plants which were scattered through the water s.f § 648. The different strata, when undisturbed, are ar- ranged one above the other in a horizontal manner, like the leaves of a book, the lowest being the oldest. In consequence of the commotions which the crust of the globe has under- gone, the strata have been ruptured, and many points of the * Rocks, in a geological sense, include all the materials of the earth, the loose soil and gravel, as well as the firm rock. t Underneath the deepest strata containing fossils, between these and the Plutonic rocks, are generally found very extensive layers of slates without fossils (gneiss, mica-slate, talcose-slate), though stratified and known to the geologist under the name of Metamorphic Rocks (fig. 376, M), being probably sedimentary rocks which have undergone considerable changes. The Plutonic rocks, as well as the metamorphic rocks, are not always con- fined to the lower levels, hut thfey are often seen rising to considerable heights, and forming many of the loftiest peaks of the globe. The former also penetrate, in many cases, like veins, through the whole mass of the stratified and metamorphic layers, and expand at the surface ; as is the case with the trap dykes, and as lava streams actually do nov/ (fig. 376, 2\ L.) 392 GEOLOGICAL SUCCESSION OE ANIMALS. surface have been elevated to great heights, in the form of mountains ; and hence it is that fossils are sometimes found at the summit of the highest mountains, though the rocks con- taining them were originally formed at the bottom of the sea. But even when folded, or partly broken, their relative age may still be determined by an examination of the ends of the up- turned strata, where they appear or crop out in succession, at the surface, or on the slopes of mountains, as seen in the dia- gram (fig. 376). Fig. 376. § 649. The sedimentary rocks are the only ones containing animal and vegetable remains. These are found imbedded in the rock, just as we should find them in the mud now deposited at the bottom of the sea, if laid dry. The strata containing fossils are numerous. The comparison and detailed study of them belongs to geology, of which Palaeontology forms an essential part. A group of strata extending over a certain geographical extent, all of which contain some fossils in com- mon, no matter what may be the chemical character of the rock, whether it be limestone, sand, or clay, is termed a geological Formation, 'Jhus, the coal beds, with the inter- vening slates and grits, and the masses of limestone between which they often he, constitute but one formation, — the car- boniferous formation. § 650. Among the stratified rocks, we distinguish ten prin- cipal formations, each of which indicates an entirely new era in the earth’s history ; while each of the layers com- posing a formation indicates but some partial revolution. Proceeding from below upwards, they are as follows, as STRUCTURE OE THE EARTH’ S CRUST. 393 shewn in the cut, and also in the lower diagram in the frontispiece. 1st. The Lower Silurian. This is a most extensive forma- tion, no less than eight stages of which have been made out by geologists in North America, composed of various lime- stones and sandstones.* * * § 2d. The Upper Silurian. It is also a very extensive forma- tion, since about ten stages of it are found in the State of New York.f 3d. The Devonian, including in North America no less than eleven stages. J It occurs also in Eussia and Scotland, where it was first made out as a distinct formation. 4th. The Carboniferous Formation, consisting of three grand divisions. § ' 5th. The Trias, or Saliferous Formation, contains the richest deposits of salt on the continent of Europe, and comprises three stages, || to one of which the sandstone of the Con- necticut valley belongs. 6th. The Oolitic Formation, only faint traces of Avhich exist on the continent of America. It comprises at least four dis- tinct stages.^ 7th. The Cretaceous, or Chalk Formation, of which three principal stages have been recognized : two of these are feebly represented in the Southern and Middle States of North America. * 1. Potsdam Sandstone; 2. Calciferous Sandstone; 3. Chazy Lime- stone ; 4. Bird’s-eye Limestone ; 5. Black River Limestone ; 6. Trenton Limestone; 7. Utica Slate ; 8. Hudson River Group; beina; all found in the western parts of the United States. t 1. Oneida Conglomerate ; 2. Medina Sandstone ; 3. Clinton Group ; 4. Niagara Group ; 5. Onondaga Salt Group ; 6. Water Limestone ; 7. Pentamerus Limestone ; 8. Delthyris Shaly Limestone ; 9. Encrinal Limestone ; 10. Upper Pentamerus Limestone, X 1. Oriskany Sandstone ; 2. Cauda-Galli Grit ; 3. Onondaga Lime- stone ; 4. Corniferous Limestone ; 5. Marcellus Shale ; 6. Hamilton Group ; 7. Tully Limestone ; 8. Genesee Slate ; 9. Portage Group ; 10. Chemung Group ; 11. Old Red Sandstone. § 1. The Permian, extensively developed in Russia, especially in the government of Perm ; 2. The coal measures, containing the rich deposits of coal in the Old and New World ; 3 The Magnesian Limestone of England. II 1. New Red Sandstone ; 2. Muschelkalk ; 3. Keuper. ^ 1. The Lias ; 2. The Lower Oolite ; 3. The Middle Oolite ; 4. The Upper Oolite. 394 GEOLOGICAL SUCCESSIOI^ OE ANIMALS. 8th. The Lower Tertiary, or Eocene, very abundant in the Southern States of the Union, and to which belong the coarse limestone of Paris, and the London clay in England. 9th. The Upper Tertiary or Miocene, and Pleiocene, found also in the United States, as far north as Martha’s Vineyard, and Nantucket, and very extensive in Southern Europe, as well as in South America. 10th. The Drift, forming the most superficial deposits, and extending over a large portion of the northern countries in - both hemispheres. We have thus more than forty distinct layers already made out, each of which marks a distinct epoch in the earth’s his- tory, indicating a more or less extensive and important change in the condition of its surface. § 651. All the formations are not everywhere found, or are not developed to the same extent, in all places. So it is with the several strata of which they are composed. In other words, the layers of the earth’s crust are not continuous throughout, like the coats of an onion. There is no place on the globe where, if it were possible to bore down to its centre, all the strata would be found. It is easy to understand how this must be so. Since irregularities in the distribution of water upon the solid crust have, necessarily, always existed to a certain extent, portions of the earth’s surface must have been left dry at every epoch of its history, gradually forming large islands and continents, as the changes were multiplied. And since the rocks were formed by the subsidence of sedi- ment in water, no rocks would be formed except in regions covered by water ; they would be thickest at the parts where most sediment was deposited, and gradually thin out to- wards their circumference. We may therefore infer, that all those portions of the earth’s surface which are destitute of a certain formation were dry land, during that epoch of the earth’s history to which such formation relates, excepting, indeed, where the rocks have been subsequently removed by the denuding action of water or other causes. § 652. Each formation represents an immense period of time, during which the earth was inhabited by successive races of animals and plants, whose remains are often found, in their natural position, in the places where they lived and died, not scattered at random, though sometimes mingled to- STEUCTUEE OE THE EAETH’s CEHST. 395 gether by currents of water, or other influences, subsequent to the time of their interment. From the manner in which the remains of various species are found associated in the rock, it is easy to determine whether the animals to which these remains belonged lived in the water, or on land, on the beach or in the depths of the ocean, in a warm or in a cold climate. They will be found associated in just the same way as animals are that live under similar influences at the present day. § 653. In most geological formations, the number of species of animals and plaflts found in any locality of given extent, is not below that of the species now living in an area of equal extent, and of a similar character; for though, in some deposits, the variety of the animals contained may be less, in others it is greater than that on the present surface. Thus, the coarse lime- stone in the neighbourhood of Paris, which is only one stage of the lower tertiary, contains not less than 1200 species of shells; whereas the species now living in the Mediterranean do not amount to half that number. Similar relations may be pointed out in America. Mr. Hall, one of the geologists of the New York Survey, has described, from the Trenton lime- stone (one of the ten stages of the lower Silurian), 170 species of shells, a number almost equal to that of all the species found now living on the coast of Massachusetts. § 654. Nor was the number of individuals less than at present. Whole rocks are entirely formed of animal remains, particularly of corals and shells. So, also, coal is composed of the remains of plants. If we consider the slowness with which corals and shells are formed, we may form some faint notion of the vast series of ages that must have elapsed in order to allow the formation of those rocks, and their regular deposition, under the water, to so great a thickness. If, as all things combine to prove, this deposition took place in a slow and gradual manner in each formation, we must conclude, that the successive species of animals found in them followed each other at long intervals, and are not the work of a single epoch. § 655. It was once believed that animals were successively created in the order of their relative perfection ; so that the most ancient formations contained only animals of the lowest grade, such as the polyps and the echinoderms, to which 396 GEOLOaiCAL SUCCESSION OF ANIMALS. succeeded the moUusca, then the articulated animals, and last of all, the vertebrata. This theory, however, is now untenable ; since fossils belonging to each of the four de- partments have been found in the fossiliferous deposits of every age. Indeed, we shall see that even in the lower Silu- rian formation there exist not only polyps and other radiata, but also numerous mollusca, trilobites (belonging to the arti- culata), and even fishes and reptiles.* SECTION IL AOES OF NATUEE. § 656. Each formation, as has been before stated (§ 649), contains remains peculiar to itself, which do not extend into the neighbouring deposits above or below it. Still there is a connection between the different formations, more strong in proportion to their proximity to each other. Thus, the animal remains of the chalk, while they differ from those of all other formations, are nevertheless much more nearly re- lated to those of the oolitic formation, which immediately precedes, than to those of the carboniferous formation, which is much more ancient ; and in the same manner, the fossils of the carboniferous group approach more nearly to those of the Silurian formation than to those of the Tertiary. § 657. These relations could not escape the observation of naturalists, and indeed they are of great importance for the true understanding of the development of life at the sur- face of our earth. And, as in the history of man, several grand periods have been established, under the name of Ages^ marked by peculiarities in his social and intellectual condition, and illustrated by contemporaneous monuments, so, in the history of the earth also, are distinguished several great pe- riods, which may be designated as the \2iic\o\x^ Ages of Nature, illustrated in like manner by their monuments, the fossil re- mains, which, by certain general traits stamped upon them, clearly indicate the eras to which they belong. § 658. We distinguish four Ages of Nature, correspond- ing to the great geological divisions, namely : 1st. The Primary or Palceozoic Age, comprising the lower * See an important communication, by Mr. Logan, on the Footprints of Reptiles in the Potsdam sandstone of Lower Canada, Quart. Jour. Geol. Soc. vol. vii. p. 247. — Ed. AGES OF IS-ATITEE. 397 Silurian, the upper Silurian, and the Devonian. During this age there were few air-breathing animals. The fishes were the masters of creation. We may therefore call it the Reign of Fishes, 2d. The Secondary Age, comprising the carboniferous, the trias, the oolitic, and the cretaceous formations. This is the epoch in which air-breathing animals more extensively prevail. The reptiles predominate over the other classes, and we may therefore call it the Reign of Reptiles, 3d. The Tertiary Age, comprising the tertiary formations. During this age, terrestrial mammals, of great size, abound. This is the Reign of Mammals, 4th. The Modern Age, characterized by the appearance of the most perfect of all created beings. This is the Reign of Man, Let us review each of these four Ages of Nature, with re- ference to the diagram at the beginning of the volume. § 659. The Palh:ozoic Age. Reign of Fishes, — The palaeozoic fauna, being the most remote from the present epoch, presents the least resemblance to the animals now existing, as will easily be perceived by a glance at the following sketches (fig. 377). In no other case do we meet with animals of such extraordinary shapes, as in the strata of the palaeozoic age. § 660. We have already stated (§ 655) that there are found, in each formation of the primary age, animal remains of all the four great departments, namely, vertebrata, ardculata, mollusca, and radiata. We have now to examine to what peculiar classes and families of each department these remains belong, with a view to ascertain if any relation between the structure of an animal and the epoch of its first appearance on the earth’s surface may be traced. § 661. As a general result of the inquiries hitherto made, it may be stated that the palaeozoic animals belong, for the most part, to the lower divisions of the different classes. Thus, of the class of echinoderms, we find scarcely any but Crinoids (figs. 72 and 73), which are the least perfect of the class ; of which there are some quite peculiar types from the Trenton limestone and from the Black River limestone. § 662. Of the mollusca, the bivalves or acephala are nu- merous, but for the most part belong to the brachiopoda, that is to say, to the lowest division of the class, including mollusks 398 GEOLOGICAL SFCCESSIOIS’ OF AOTMALS. with unequal valves, having peculiar appendages in the interior. The Leptcena alternata^ found very abundantly in the Trenton limestone, is Fig. 377. one of those 2 ' shells. The only fossils yet found in the Potsdam sand- stone, the old- est of all fossi- liferous depo- sits, belong al- so to this fa- mily (Lingula prima) . Be- sides this, there are also found some bivalves of a less un- common shape (Avicula de- cussata) ; [and in the upper stages of the Silurian group in England we find Orthis or- bicuLaris (1), Terebratula navicida (2), Orthis navicularis^ (3) Pentameus Knightii (4), Atrypa affinis (5), fig. 377.j § 663. The gasteropoda are less abundant ; some of them are of a peculiar shape and structure, as Bucania expansa, Euomphalus hemisphcericus. Those more similar to our common marine snails have all an entire aperture ; those with a canal being of a more recent epoch. § 664. Of the cephalopoda we find some genera not less curious, part of which disappear in the succeeding epochs ; such, in particular, as those of the straight, chambered shells called orthoceratites, some of which are twelve feet in length iOrthoceras ventricosum) . There are also found some of a coiled shape, like the ammonites of the secondary age, but having less complicated partitions (Litiiites giganteus, 7). The true cuttle-fishes, which are the highest of the class, are not AGES OF FATrEE. 399 yet found. On the contrary, the Bryozoa, which have long been considered as polyps, but which, according to all appear- ances, are moUusks of a very low order, are very numerous in this epoch. § 665. The articulata of the palaeozoic age are mostly trilobites, animals which evidently belong to the lower order of the crustaceans (tig. 378). There is an incompleteness and want of development in the form of their body, that strongly re- minds us of the embryo among the crabs. A great many ge- nera have al- Fig. 378. — Homalonotus delphinocephalus. — Konig. ready been dis- covered. The Silurian rocks of Bohemia have yielded up- wards of two hundred species. Homalonotus (tig. 378), one of the family CalymenidcEy will give a general idea of the form of these palaeozoic crustaceans. Some others seem more allied to the crustaceans of the following ages, but are never- theless of a very extraordinary form, as Eurypterus remipes. There are also found, in the Devonian, some very large entomostraca. The class of worms is represented only by Nereis and a few Serpulce, which are marine worms, surrounded by a solid sheath. The class of insects is entirely wanting. § 666. The inferiority of the earliest inhabitants of our earth appears most striking among the vertebrata. There are as yet neither birds nor mammals. The fishes, and a few reptiles whose fossil foot-marks we only know, are the sole representatives of this division of animals. § 667. The fishes of that early period were not like ours. Some of them had the most extraordinary forms, so that they have been often mistaken for quite different animals ; for example, the Pterichthys (fig. 379), with its two winglike appendages, and also the Coccosteiis (fig. 380), of the same deposit, with its large plates covering the head and the ante- rior part of the body. There are also found remains of shark’s spines, as well as palatal bones, the latter of a very peculiar 400 GEOLOGICAL SUCCESSIO^f OF ANIMALS. kind. Even those fishes which have a more regular shape, as the Bipterus, have not horny scales hke our common fishes. Fig. 379. — Pterichthys, from the Devonian rocks of Scotland. — Agass. but are protected by a coat of bony plates, covered with enamel, like the gar pikes {Lepidosteus) of the American rivers. Moreover they all exhibit certain characteristic fea- tures, which are very interesting in a physiological point of view. They all have a broad head, and a tail terminating in two unequal lobes. What is still more curious, the best preserved specimens show no indications of the bodies of the vertebrae, but merely the spinous processes ; from which it must be inferred that the body of the vertebra was cartilaginous, as it is in our sturgeons. § 668. Recurring to what has been stated on that point in Chapter Twelfth, we thence conclude that these ancient fishes were not so fully developed as most of our fishes, being, hke AGES OE NATURE. 401 the sturgeon, arrested, as it were, in their development ; since we have shown that the sturgeon, in its organiza- tion, agrees, in many re- spects, with the cod or salmon in their early age. § 669. Finally, there was, during the palaeozoic age, less variety among the animals of the differ- ent regions of the globe ; and this may be readily explained by the peculiar configuration of the earth at that epoch. Great mountains did not then exist ; there were neither lofty elevations nor deep depressions. The sea co- vered the greater part, if not the whole, of the sur- face of the globe ; and the animals which then exist- ed, and whose remains have been preserved, were all, with the exception or the reptiles which have left their foot-marks on the Potsdam sandstone, aquatic animals, breathing by gills. This wide dis- tribution of the waters im- pressed a very uniform character upon the whole animal kingdom. Between different zones and conti- nents, no such strange ^ ^ . contrasts of the different cuspidatus,--A^^^^^^ types existed as at the present epoch. The same geneni, and often the same species, were found in the seas of America, Europe, Asia, Africa, and New Holland ; from which we must D D 402 GEOLOaiCAL SUCCESSION OF ANIMALS. ♦ This circumstance has caused the coal-measures to be generally referred conclude that the climate was much more uniform than at the present day. Among the aquatic population, no sound was heard. All creation was then silent. § 670. The Second art Age. Reign of Reptiles. — The Secondary age displays a greater variety of animals as well as plants. The fantastic forms of the palaeozoic age disappear, and in their place we see a greater symmetry of shape. The advance is particularly marked in the series of vertebrata. Fishes and a few reptiles are no longer the sole representatives of that department. Reptiles, birds, and mammals succes- sively make their appearance, but reptiles preponderate, par- ticularly in the Oolitic formation ; on which account we have called this age the Reign of Reptiles. ^ § 671. The Carboniferous formation is the most ancient of the Secondary age. Its fauna bears, in various respects, a close analogy to that of the palaeozoic epoch, especially in its Trilobites and mollusca.* Besides these, we meet here h d c g e b a f Fig. 381.— The Flora of the coal period. a Arborescent fern. d Neuropteris. g Araucaria* b Pecopteris. e Lepidodendron. h Casuerina. c Asterophy Hites. / Calamites. AGES OE NATURE. 403 with air-breathing animals, as insects, scorpions, and rep- tiles. At the same time, land-plants first make their ap- pearance, namely, ferns of great size, club-mosses, and other fossil plants. Fig. 381 exhibits some of the most typical forms of the flora of this period. This abundant vegetation corroborates what has been already said concerning the inti- mate connection existing between the animals and the land- plants of all epochs. The class of crustaceans has also improved during the coal period. It is no longer composed exclusively of Trilobites, but the type of horse-shoe crabs also appears, with other gigantic forms. Some of the mollusca, particularly the bivalves, seem also to approach those of the Oolitic period. § 672. In the Trias period, which immediately succeeds the Carboniferous, the fauna of the Secondary age acquires its definitive character ; here the reptiles first appear in con- siderable numbers, consisting of huge crocodilian animals, belonging to a peculiar order, the Rhizodonts {Protosaurus, Notosaurus, and Labyrinthodon). The well-known discoveries of Professor Hitchcock, in the red sandstone of the Con- necticut Valley, have made us acquainted with a great number of birds’ tracks belonging to this epoch, for the most part indi- cating animals of gigantic size. These impressions, which he has designated under the name of Ornithichnites, are some of them eighteen inches in length, and five feet apart, far exceed- ing in size the tracks of the largest ostrich. Other foot-marks of a very peculiar shape, have been found in the red sandstone of Germany (fig. 382), and in Pennsylvania. They were probably made by reptiles, which have been called Cheiro- Fig. 382. — Line of footmarks on a slab of sandstone, from Hildburghausen, in Saxony. to the palaeozoic epoch. But there are reasons which induce us to unite the carboniferous period with the secondary age, especially when we consider that a luxuriant terrestrial vegetation was developed at this epoch ; that here land animals first appear in any considerable number, whereas, in the palaeozoic age, there were chiefly marine animals, breathing by gills, and a few reptiles known only by their foot-marks. I) D 2 404 GEOLOGICAL SLCCESSION OE ANIMALS. therium, from the resemblance of the impressions to a hand. The mollusca, articulata, and radiata approach those of the fauna of the suc- ceeding period. •§ 673. The Oolitic fauna is remarkable for the great number of gigantic rep- tiles it contains. In this formation we find those enormous amphi- bia, known under the name Ichthy- osaurus^ Plesio- saurus, and Me- galosaurus. The first, in particular, the Ichthyosauri, greatly abounded on the coasts of the continents of that period, and their skeletons are so well preserved, that we are ena- bled to study even the minutest de- tails of their struc- ture, which differs essentially from that of the rep- tiles of the pre- sent day. In some respects they form an in- termediate link between fishes and mammals, and may be con- Fig. 383. — Plesiosaurus rugosus. — Owen. AGES OE NATTJEE. 405 sidered as the prototypes of the whales, having, like them, limbs in the form of oars. The Plesiosaurus (fig. 383) agrees, * in many respects, with the Ichthyosaurus in its structure, but is easily distinguished by its long neck, which somewhat resembles the neck of some aquatic birds. A still more Ex- traordinary reptile is the Pterodactylus (fig. 384), with its long fingers, like those of a bat, for the support of wings, by which it was enabled to fly. Fig. 384. — Pterodactylus jsrmsirostris. — Goldfass* § 674. It is also in the upper stages of this formation that we meet with the skeletons of tortoises. Here also we find the remains of several families of insects {Lihellulce, Coleop- ter a. Ichneumons^ ^c.) Finally, in these same stages, the slates of Stonesfield, the first traces of mammals are found, namely, the jaws and teeth of animals belonging to extinct forms of 406 GEOLOGICAL SUCCESSION OE ANIMALS. Marsupialia, and having some resemblance to the opossum (fig. 385). Fig. 385. — Jaw of the Thylacotherium^ from Stonesfield. § 675. The department of mollusca is largely represented in all its classes ; Some of the most common forms are sketched in fig. 386. The peculiar types of the primary age have almost disappeared, and are replaced by a greater variety of new forms. Of the brachiopoda only one type, namely, that of the Terehratula (10), is abundant. Among the other bi- valves there are many peculiar forms, Gryphcea (1 and 2), Cardium (4), Trigonia (5), Goniomya (6), and Gervillia (8). The gasteropoda display a great variety of species, and the genus NerincEa (11) is an abundant form. The Cephalopoda are very numerous, among which the Ammonites (9) are the most prominent. There are also found, for the first time, the representatives of the cuttle-fishes, under the form of Belem- nitesy an extinct type of animals, with an internal chambered shell, protected by a sheath, and terminating in a conical body somewhat similar to the bone of the Sepia, and which is commonly the only preserved part. § 676. The variety is not less remarkable among the radiata. There are to be found representatives of all the classes; even traces of jelly-fishes have been made out in the slates of Solenhofen, in Bavaria. The* polyps were very abundant at that epoch, especially in the upper stages, one of which, from this circumstance, has received the name of Coral-rag. Indeed, there are to be found whole reefs of corals in their natural position, similar to those which are to be seen in the islands of the Pacific. [Among the most remarkable types Fig. 386. — Fossil Mollusca and Kadiata of the Oolitic period, 1. Gryphseadilatata Sow. — Kello way rock and Oxford clay. 2. Gryphsea incurva Sow. Lower lias. 3. Nucleolites clunicularis. Combrash. 4. Cardium truncatum Sow. Lias marl- stone. 5. Trigonia costata Sow. Inferior oolite. 6. Goniomya V scripta Agass. Inferior oolite. 7. Hemicidaris intermedia. Gt. Oolite and Coral rag. 8. Gervillia acuta Sow, Lower oolites. 9. Ammonites Calloviensis Sow. Kello- way rock. 10. Terebratula acuta Sow. Lias marl- stone. 11. Nerineea cingenda Voitz. Lower oolites. 40S GEOLOaiCAL SUCCESSION OE ANIMALS. of the family Asteeid^ the genera Stylina, Montlivaltia^ Thecosmilia, Rhabdophyllia^ Cladophyllia, Goniocora, Isastrea, Thamnastrea ; and of the family Fungidje, the genera Como- seris, Protoseris, are found in the Coral-rag of Wiltshire. In the Great Oolite, besides species of many of these genera, oth ers belonging to Convexastrea, Calamophyllia^ Cladophyllia, Clausastrea, occur. Similar coralbeds exist in the limestones belonging to the Inferior Oohte, from whence the genera Biscocyathus, Trochocyathus, Axosmilia, Thecosmilia, Latomeandra, Anahacia, with numerous species belonging to many of the Coral-rag genera, are found. The echinoderms present a great variety of forms. The crinoids are not quite so numerous as in former ages. Among the most abundant is the Pentacrinus. There are also comatula-hke animals, that is to say, free crinoids {Pterocoma pinnatd). Many star-fishes are hkewise found in the various stages of this formation. Finally, there is an extraordinary variety of urchins, among them Cidaris and Hemicidaris (fig. 386, 7) with large spines, and several other types not found before, as, for example, Pyg aster, Dysaster and Nucleolites (fig. 386, 3).] § 677. The fauna of the Cretaceous period bears the same general characters as the Oolitic, but with a more marked tendency towards existing forms. Thus the Ichthyosauri and Plesiosauri, characterizing the preceding epoch, are suc- ceeded by gigantic hzards, approaching more nearly the rep- tiles of the present day. Among the mollusca, a great num- ber of new forms appear, especially among the cephalopoda, as Ammonites, Crioceras, Scaphites, Ancyloceras, Hamites, ^ Baculites, Turrilites, some of which resemble the gasteropoda in shape, but are nevertheless chambered. The Ammonites themselves are quite as numerous as in the Oolitic period, and are in general much ornamented. The acephala furnish us also with pecuhar types, not found elsewhere, as Magas, Ino- ceramus, Hippurites, and peculiar Spondyli, with long spines. There are also a great variety of gasteropoda, among which some peculiar forms of Pleurotomaria, Rostellaria, and Ptero- ceras, are very characteristic. The radiata are not inferior to the other classes in the novelty and variety of their forms. In figs. 387 and 388, some of the most characteristic fossil shells from the lower greensand strata are represented. AGES OE 2TATTJRE, 409 Fig. 387.— Fossil shells from the lower greensand of the Isle of Wight. 410 GEOLOGICAL STJCCESSIOJI OF ANIMALS. Fig* 388. — Fossil shells from the lower greensand of the Isle of Wight. AGES OF NATUEE. 411 DESCRIPTION OF FIG. 387. 1. Corbis corrugata, from the sand-rock, Athertield: the figure is one- half the size in linear dimensions of the original. 2. Trigonia caudata, from the sand-rock, Atherfield. 3. Gervillia anceps, from the Cracker Rocks, Atherfield ; a denotes the markings of the hinge, which are seen in consequence of the valves being slightly displaced. It is represented half the size linear of the original. These shells are often much larger, and more elongated than in the figure. 4. Venus striato-costata ; a small shell, common in the Cracker Rocks at Atherfield ; the figure is twice the size of the original in linear dimensions. 5. Area Raulini, from the sand-rock, Atherfield. 6. Perna Mulleti, from the lower beds of sand in conjunction with the Wealden, Sandown Bay ; the figure is but half the size of the origi- nal : o, the structure of the hinge ; by comparing this figure with a, No. 3, the difference of the hinge in the genera Perna and Gervillia will be recognized. This large and remarkable shell is highly cha- racteristic of the lower beds of the greensand. 7. Venus parva, from Shanklin Cliff. DESCRIPTION OF FIG. 388. 1. Thetis minor, from the ferruginous sand-rock at the base of Shanklin Cliff. 2. Another view of the same, to show the beaks and hinge-line. 3. Exogyra sinuata, represented one-fourth the natural size ; it is often found much larger. From the greensand at Shanklin, Ventnor, Sandown, &c. 4. Tornatella albensis, from the Cracker Rocks, Atherfield. 5. Terebratula sella ; an abundant shell in the sand at Atherfield. 6. Nucula scapha, from the sand-rock, Atherfield. The three follow ina shells are embedded in a fragment of the Cracker Rock, from Atherfield, 7. Natica rotundata. 8. Pterocera retusa. 0. Rosteilaria Robinaldini. 10. Cerithium turriculatum, from Atherfield. 11. Ancyloceras gigas, from Atherfield. The figure is one-third the size, linear, of the original. This fossil is often found two feet in length, associated with Ammonites equally gigantic. 412 GEOLOaiCAL SUCCESSION OF ANIMALS, Fig. 389. — Fossil shells and Mammalian remains, from the fresh-water strata of the Isle of Wight. AGES OE JS'ATUKE. 413 DESCRIPTION OF FIG. 389. FOSSIL SHELLS AND TEETH OF MAMMALIA, FROM THE FRESH-WA TER EOCENE STRATA OF THE ISLE OF WIGHT. SHELLS. Fig. 1 . — Potomomya gregaria ; from Headon Hill, This shell is described by Mr. Sowerby in Mineral Conchology as Mya gregaria. The genus Potomomya (river mussels) comprises those species which inhabit rivers only, and are not found in estuaries and brackish waters. 2. — Potamides concavus ; Headon Hill. 3. — Melanopsis fusiformis; Headon Hill. 4. brevis ; Headon Hill. 5. — Neritina concava ; Colwell Bay. 6. — Melanopsis carinata ; Colwell Bay. 7. — Helix globosus ; Shalfleet. 8. — Potamides plicatus ; Headon Hill. 9. ventricosus ; Headon Hill. MAMMALIAN REMAINS 10. — Upper canine tooth of Anoplotherium commune ; from Seafield near Ryde. ] 1. — The grinding surface of ojiupper molar Palceotherium medifum; from Binstead. 12. — One side of the lower jaw of Palceothermm minus, with hve teeth ; from Seafield.* 13*. — A tooth of Dichobune cervinum, from Binstead. 13. — The grinding surface of fig. 13*. With the exception of the gigantic snail-shell, fig. 7, the fossil shells here delineated are abundant at Headon Hill, and in the clays and marls at Colwell Bay. The Mammahan remains are of excessive rarity, and have hitherto only been found in the quarries near Ryde, and at Headon Hill. From the latter locality. Dr. Wright recently obtained a fine specimen of the jaw of a Dicodon, a new genus established 1)/ Professor Owen. * See British Fossil Mammals, p. 323. 414 GEOLOaiCAL STJCCESSIOIf OE A:N^IMALS. § 678. Teetiabt Age. Reign of Mammals, — The most significant characteristic of the Tertiary faunas is their great resemblance to those of the present epoch. The animals be- long in general to the same families, and mostly to the same genera, differing only as to species. The specific differences, however, are sometimes so shghtly marked, that a consider- able famiharity with the subject is required, in order readily to detect them. Many of the most abundant types of for- mer epochs have now disappeared. The changes are espe- cially striking among the moUusca, the two great families of Ammonites and Belemnites, which present such an astonish- ing variety in the Oolitic and Cretaceous epochs, being now completely wanting. Changes of no less importance take place among the fishes, which are for the most part covered with horny scales, Hke those of the present epoch, while in earlier ages they were generally covered with enamel. Among the radiata, we see the family of crinoids reduced to a very few species, while, on the other hand, a great number of new star-fishes and sea-urchins make their appearance. There are besides, innumerable remains of a very pecuhar type of animals, almost unknown in the former ages, as well as in the present period. They are little-chambered shells, known to geologists under the name of Nummulites, from their coin-like appearance, and which form in some countries very extensive layers of rocks. § 679. But what is more important, in a philosophical point of view, is, that aquatic animals are no longer predomi- nant in Creation. The great marine or amphibian reptiles give place to numerous mammals of great size. For which reason we have called this age the Reign of Mammals, § 680. The lower stage of this formation is particularly characterized by great pachyderms, among which we may mention the Palceotherium and Anoplotherium, which have acquired such celebrity from the researches of Cuvier. These animals, among others, abound in the tertiary formations of the neighbourhood of Paris, and those of the Hampshire basin. The Palceotheria, of which several species are known, are the most common ; they resemble, in some respects, the tapirs, while the Anoplotheria are more slender animals. In America are found the remains of a most extraordinary animal of gigantic size, the Basilosaurus, a true cetacean. Finally, in these stages, the earliest remains of monkeys have CONCLUSIONS. 415 been detected. In fig. 389 are figured tlie jaw and teeth, of Palceotheria, from the tertiary strata of the Isle of Wight. 10 is the canine tooth of P. commune^ and 1 1 the grinding sur- face of^the molar tooth of P. medium; 12 is one half of the lower jaw of P. minus, diXidi 13 are the molars of a Dichohune, another extinct genus of the Eal^othekid^. The mollusca of the estuary beds of the same locality are figured in this plate. Potomomya gregaria (1), Potamides concavus {2), Mela- nopsis fusiformis (3), M, hrevis (4), Neritina concava (5), Melanopsis carinata (6), Potamides plicatus (8) and P. ven- tricosus (9), Helix globosus (7). § 681. The fauna of the upper stages of the tertiary forma- tion approaches yet more nearly to that of the present epoch. Besides the pachyderms, that were also predominant in the lower stage, we find numbers of carnivorous animals, some of them much surpassing in size the lions and tigers of our day. We meet also gigantic edentata, and rodents of great size. § 682. The distribution of the tertiary fossils reveals to us the important fact, that in this epoch animals of the same species were circumscribed in much narrower limits than befbre. The earth’s surface, highly diversified by mountains and valleys, was divided into numerous basins, which, like the Gulf of Mexico, or the Mediterranean of our day, contained species not found elsewhere. Such was the basin of Paris, that of London, and in the United States, that of South Carolina. § 683. In this limitation of certain types within certain bounds, we distinctly observe another approach to the actual ^ condition of things, in the fact that groups of animals which occur only in particular regions are found to have already existed in the same regions during the Tertiary epoch. Thus the edentata are the predominant animals in the fossil fauna of Brazil as well of its present fauna ; and the marsupialia were formerly as numerous in New Holland as they now are, though they were in general of much larger size. § 684. The Modeen Epoch. Reign of Man, — The present epoch succeeds to, but is not a continuation of, the Tertiary age. These two epochs are separated by a great geological event, traces of which w'e see everywhere around us. The cli- mate of the northern hemisphere, which had been, during the Tertiary epoch, considerably warmer than now, so as to allow of the growth of palm-trees in the temperate zone of our time. 4^6 GEOLOaiCAL SUCCESSION OE ANIMALS. became much colder at the end of this period, causing the polar glaciers to advance south, much beyond their previous limits. It vras this ice, either floating as icebergs, or, as there is still more reason to believe, moving along the ground, like the glaciers of the present day, that, in its movement to- wards the south, rounded and polished the hardest rocks, and deposited the numerous detached fragments brought from dis- tant localities, which we And everywhere scattered about upon the soil, and which are known under the name of erratics^ boulders^ or greyheads. This phase of the earth’s history has been called, by geologists, the Glacial or Drift 'period, and is represented by the second circle of the frontispiece. § 685. After the ice that carried the erratics had melted away, the surface of North America and the North of Europe was covered by the sea, in consequence of the general subsi- dence of the continents. It is not until this period that we find, in the deposits known as the diluvial or Pleistocene formation, incontestable traces of the species of animals now living. § 686. It seems, from the latest researches of geologists, that the animals belonging to this period are exclusively marine ; for, as the northern part of both continents was covered to a great depth with water, and only the summits of the mountains were elevated above it, as islands, there was no place in our latitudes where land or fresh-water animals could exist. They appeared therefore at a later period, after the water had again retreated ; and, as from the nature of their or- ganization, it is impossible that they could have migrated from other countries, we conclude that they were created at a more recent period than our marine animals. § 687. Among the land animals which then made their appearance, there were representatives of aU the genera and species now hving around us, and besides these, many types now extinct, some of them of a gigantic size, such as the Masto- don f the remains of which are found in the uppermost strata of the earth’s surface, and probably the very last large animal which * The gallery of fossil remains in the British Museum contains a fine skeleton of the Mastodon, a splendid specimen of which, disinterred at Newburg, N. Y., is now in the possession of Dr. J. C. Warren, in Boston ; the most complete skeleton which has ever been discovered. It stands nearly twelve feet in height, the tusks are fourteen feet in length and nearly every bone is present, in a state of preservation truly wonderful. CONCLUSIONS. 417 became extinct before the creation of man. In the continent of South America are found, in the drift of that region, the re- mains of another gigantic animal, the Megatherium (fig. 390), which resembles the armadillos of that country, but differs from all other quadrupeds in the colossal dimensions of its skeleton. Fig. 390. — The Megatherium. § 688. It is necessary, therefore, to distinguish two periods in the history of the animals now living ; one in which the marine animals were created, and a second, during which the land and fresh-water animals made their appearance, and at their head Man.* CONCLUSIONS. § 689. From the above sketch it is evident that there is a manifest progress in the succession of beings on the surface of the earth. This progress consists in an increasing similarity to the hving fauna, and among the vertebrata, especially, in their increasing resemblance to Man. § 690. But this connection is not the consequence of a direct lineage between the faunas of different ages. There is nothing like parental descent connecting them. The fishes of the Palaeozoic age are in no respect the ancestors of the reptiles of the Secondary age, nor does Man descend from the mam- mals which preceded him in the Tertiary age. The link by which they are connected is of a higher and immaterial nature ; and their connection is to be sought in the view of the Creator * The former of these phases is indicated in the frontispiece, by a circle, inserted between the upper stage of the Tertiary formation and the Reign of Man properly so called. E E 418 aEOLOaiCAL SUCCESSION OE ANIMALS. himself, whose aim, in forming the earth, in allowing it to un- dergo the successive changes which geology has pointed out, and in creating successively all the different types of animals which have passed away, was to introduce Man upon its sur- face. Man is the end towards which all the animal creation has tended, from the first appearance of the first Palaeozoic fishes. § 691. In the beginning the Creator’s plan was formed, and from it He has never swerved in any particular. The same Being who, in view of man’s moral wants, provided and declared, thou- sands of years in advance, that “ the seed of the woman shall bruise the serpent’s head,” laid up also for him, in the bowels of the earth, those vast stores of granite, marble, coal, salt, and the various metals, the products of its several revolutions ; and thus was an inexhaustible provision made for his necessities, and for the development of his genius, ages in anticipation of his appearance. § 692. To study, in this view, the succession of animals in time, and their distribution in space, is therefore to become ac- quainted with the ideas of God himself. Now, if the succes- sion of created beings on the surface of the globe is the reali- zation of an infinitely wise plan, it foUow^s that there must be a necessary relation between the races of animals and the epoch at which they appear. It is necessary, therefore, in order to comprehend Creation, that we combine the study of extinct species with that of those now living, since one is the natural complement of the other.* A system of zoology will consequently be true, in proportion as it corresponds with the order of succession among animals. * In investigating the “ Ages of Nature’’ much lasting and invaluable information will be derived from an earnest study of the magnificent col- lection of fossil remains contained in the palaeontological department of the British Museum. The arrangement and naming of these monuments of nature, which mark the past revolutions of the earth, are now so far advanced by the great talents and zeal of Messrs. Waterhouse and Wood- ward, the present curators, that it has become a national educational saloon for this branch of natural history. In his visits to the gallery of organic remains, the student will obtain much aid and useful knowledge from Dr. Mantell’s recent work, “ Petrifactions and their Teaching ; or, a Hand-book to the Gallery of Organic Remains of the British Museum.’’ Bohn’s Scientific Library, 1851. — Editor. r 419 LIST OF THE MOST IMPORTANT AUTHORS WHO MAT EE CONSULTED IN BEEERENCE TO THE SUBJECTS TREATED IN THIS WORK. GENERAL ZOOLOGY. Aristotle’s Zoology ; Linnaeus’ System of Nature ; Cuvier’s Animal Kingdom ; Oken’s Zoology ; Humboldt’s Cosmos, and Views of Nature ; Spix, History of Zoological Systems ; Cuvier’s History of the Natural Sciences. ANATOMY AND PHYSIOLOGY. Henle’s General Anatomy ; and most of the larger works on Compara- tive Anatomy, Physiology, and Botany, such as those of Hunter, Cuvier, Meckel, Muller, Burdach, Todd and Bowman, Grant, Owen, Carpenter, Rymer Jones, Hassall, Quain and Sharpey, Bourgery and Jacob, Wagner, Siebold, Milne Edwards, Cams, Schleiden, Burmeister, Lindley, Robert Brown, Dutrochet, Decandolle, A. Gray. On Special Subjects of Anatomy and Physiology may be CONSULTED Schwann, on the Conformity in the Structure and Growth of Animals and Plants. Dumas and Boussingault, on Respiration in Animals and Plants. Valentin, on Tissues ; and Microscopic Anatomy of the Senses. Soemmering, Figures of the Eye and Ear. Kolliker, Theory of the Animal Cell, and Mikroskopische Anatomie. Breschet, on the Structure of the Skin Locomotion; Weber and Duges. Teeth; Fred. Cuvier, Geoff. St. Hilaire, Owen, Nasmyth, Retzius. Blood; Bollinger, Barry. Digestion; Spallanzani, Valentin and Brunner, Dumas and Boussin- gault, Liebig, Matteucci, Beaumont INSTINCT AND INTELLIGENCE. Kirby, Blumenbach, Spurzheim, Combe. E E 2 420 EMBRYOLOGY. D^Alton, Von Baer, Purkinje, Wagner, Wolfe, Rathke, BischofF, Vel- peau, Flourens, Barry, Leidy. PECULIAR MODES OF REPRODUCTION, Ehrenberg, Trembly, Rosel, Sars, Loven, Steenstrup, Van Beneden. METAMORPHOSIS. St. Merian, Rosel, De Geer, Harris, Kirby and Spence, Burmeister, Reaumur. GEOGRAPHICAL DISTRIBUTION. Zimmerman, Milne Edwards, Swainson, A. Wagner, Forbes, Pennant, Richardson, Ritter, Guyot. GEOLOGY. The Works of Murchison, Phillips, Lyell, Mantell, Hugh Miller, Agassiz, D'Archiac, De Beaumont, D’Orbigny, De Verneuil, Cuvier, Brongniart, Deshayes, Morton, Hall, Conrad, Hitchcock, Troost, and the Reports on the various local Geological Surveys. Very many of the papers of the authors above referred to are not pub- lished in separate treatises, but are scattered through the volumes of Sci- entific Periodicals ; such as the Transactions of the Royal Society of London. Annals and Magazine of Natural History. Annales, and Archives, du Museum d’ Hist. Naturelle. Annales des Sciences Naturelles. Wiegmann’s Archiv fiir Naturgeschichte. Muller’s Archiv. Oken^s Isis. Berlin Transactions. Transactions of the American Philosophical Society. Memoirs of the American Academy. Journal of the Academy of Nat. Sciences, Philadelphia. Silliman’s Journal. Journal of Boston Society of Natural History. GENERAL AND GLOSSARIAL INDEX, Note. — The Arabic figures refer, not to the pages, but to the numbered sections ; the Roman numerals indicate the pages of the Introduction. A, a Greek prefix, signifying gene- j rally “ without,” as in Abran- chiata (without gills, ppayxia), which see. Abdo'men (Lat. abdo, I conceal), the posterior and principal cavity of the animal, containing the bowels and many other viscera. The abdomen is distinct from the thorax in crustaceans, spiders and insects, 60. Abranchia'ta (Gr. a , without ; Ppayxict, gills), mollusks devoid of gills, xxii. Acale'pha (Gr. aicaXrjcprj, a nettle), radiates with soft skins, which have the property of stinging like a nettle, xxiii. Acale'phae, digestion in the, 315. Ac'arus (Gr. dicapiy a mite), arach- nides, as the cheese-mite and allied species. Aceph'ala, Aceph'alous (Gr. a, with- out ; KEcbaXri, head), headless ; animals in which a distinct head is never developed, xxii. 662. Acetab'ula (Lat. acetabulum, a shal- low cup), fleshy sucking cups, with which many of the inverte- brate animals are provided. Acetab'ulum, the, in man, 263. Ac'ini (Lat. acinwn, a berry), the secreting parts of glands, which are suspended like grains or small berries to a slender stem. I Acotyl'edons, plants without a dis- tinct cotyledon, 69. Acous'tic (Gr. dicovo, I hear), ap- pertaining to sound, or the organ of hearing. Ac'rita (Gr. dicpiroQ, confused), a term applied to the lowest ani- mals, in which the organs, and especially the nervous system, were supposed to be confusedly blended with the other tissues. Actin'ia (Gr. liktlv, a ray), polyps with many arms radiating from around the mouth. Actino'ceras (Gr. aKviv, a ray ; icepag, a horn), a generic term signifying the radiated disposition of the horns or feelers. Actin'oids, polyps, as the coral- polyps, xxiii. Adipose' (Lat. adeps, fat), fatty. Affinities and analogies, 16. Ages of nature, 656 — 690. Air, changes effected in, by respir- ation, 393. A'lar (Lat. ala, a wing), belonging to a wing. Albu'men (Latin), the white of an egg, 446. Albu'minous, consisting of albumen. Al'iform (Lat. aliformis), shaped like a wing. Aliment'ary canal, the, 312. Alimenta'tion, or nutrition, 62. Allan'tois (Greek), a vesicular organ 422 INDEX. in connection with the intestine, which makes its appearance dur- ing the development of the embryo, 472. Alliga'tor, teeth of the, 340. Allu'^dum (Latin), sand, gravel, &c.. Drought down by rivers. Alternate generation, 518 — 547. Alter'nate reproduction, 516 — 532; consequences of, 533, 547 ; dif- ferences between, and metamor- phosis, 536. Ambula'cra (Lat. ambulacrum, an avenue or place for walking), the perforated series of plates in the shell of the sea- star or sea-urchin. Am'bulatory (Lat. ambulo, I walk), an animal, or a limb for w^alking. Amer'ica, distribution of the faunas of, 596—619. Am'monites, an extinct genus of mollusks, allied to the nautilus, which inhabited a chambered shell, called Ammonite, from its resem- blance to the horns on the statues of Jupiter Ammon, xxii. 675. Amor'phous (Gr. a, without ; /uop0?7, form), bodies devoid of regular form. Amphibious (Gr. dfi^L, two, fStoc, life), having the faculty of living both in water and on land, 306. Amphiox'us, a genus of fishes, pecu- liar structure of the, 567. Am'phipods (Gr. dfKpi, on both sides ; ttovq, a foot), an order of Crustacea which have feet for both walking and swimming. Amphisto'ma (Gr. dfx(pi, on both sides ; arSfia, a mouth), sucto- rial parasitic worms, which have pores like mouths at both ends of the body. Amphiu'ma, a batrachian, 626. Ampul'la (Lat. a bottle), a mem- branous bag, shaped like a leathern bottle, 158. An'aema (Gr. d, without ; alfxa, blood), the name given by Aris- I totle to the animals which have I no red blood, and which he sup- I posed to be without blood. I An'alogue, a part or organ in one I animal which has the same func- tion as another part or organ in a different animal ; see Homo- LOGUE. Anal'ogy, distinguished from affinitv, 16. Anas'tomose (Gr. dva, through ; (jTOfia, mouth), when the mouths of two vessels come into contact and blend together, or when two vessels unite as if such kind of union had taken place. Anat'ifa, or duck barnacle, metamor- phoses of the, 553 — 556. Androg'ynous (Gr. dvrip, a man; yvvr), a woman), the combina- tion of male and female parts in the same individual. Anella'ta (Lat. annellus, a little ring), worms, in which the body seems to be composed of a suc- cession of little rings, character- ised by their red blood. Anel'lide, the anglicised singular of Anellata, An'enterous (Gr. a, without; ivrepov, a bowel), the animalcules of in- fusions which have no intestinal canal. Animal heat, 399. Animal life, organs and functions of, 76—184. Animal and vegetable kingdoms, three great divisions of the, 67. Animal'cule (dim. of animal), a very minute animal. Animals, extinct, 629. Animals, geographical distribution of, 578 — 641 ; general laws, 578 — 594 ; the faunas, 595 — 622 ; conclusions, 623 — 641. Animals, geological succession of, 642—690. Animals, metamorphoses of, 548 — 577. INDEX. 423 Animals and plants, differences be- tween, 57 — 74 ; resume, 75. An'imate, possessed of animal life. Annelida, or Annel'ids, digestive organs of the, 322 — 324 ; respira- tion, 382. Annula'ted (Lat. annulus, a ring), when an animal or part appears to be composed of a succession of rings. Anoplolbe'riura (Gr. dvoTrXog, un- armec ; Orjpiov, beast), an ex- tinct mammal, somewhat resem- bling the pig, but unprovided with tisks or offensive arms, 680. An'ourou's (Gr. a, without ; ovpa, a tail), tul-less. Anten'na ^Lat. a yard-arm), applied to the jointed feelers, or horns, upon tie heads of insects and Crustacea ; and sometimes to the analogois parts which are not jointed in worms and other ani- mals. Anthozo'a (Gr. dvOog, a flower ; ^ujov, m animal), polyps (in- cluding the actinia and allied species', commonly called animal flowers. Antiperis:alt'ic (Gr. dvri, against ; and peHstaltic), when the vermi- cular 3ontractions of a muscular tube follow each other in a direc- tion the reverse of the ordinary one ; see Peristaltic. Ant'lia (Lat. a pump), restrictively applied to the spiral instrument of the mouth of butterflies and allied insects, by which they pump up the juices of plants. Aor'ta (Gr. doprrj, the wind-pipe : and also the name of the great vessel springing from the heart, which is the trunk of the systemic arteries) ; it is exclusively applied in the latter sense in modern anatomy. Aphid^ian, belonging to the aphis. A'phis (Greek), the aphis, or plant- louse, one of the articulata, alter- nate generation of the, 526. Ap'ical (Lat. apea^, the top of a cone), belonging to the pointed end of a cone-shaped body. Ap'odal (Gr. a, without ; -rroda, feet), footless, without feet or locomotive organs ; fishes are so called which have no ventral fins. Apoph'ysis (Greek), a projection from the body of a bone. Apparatus of motion, 205 — 227. Ap'tera (d,without ; TTrepov, awing), wingless insects, xxii. Ap'terous (Gr. a, without ; TTTspov, a wing), wingless species of in- sects or birds. Aquat'ic (Lat. aqua, water), living in water. Aquat'ic animals, water tubes of,403. A'queous, like water. A'queous humour of the eye, 127. Arach'nida (Gr. dpaxvrj, a spider), a class of articulates ; as spiders and allied animals. Arach'nidse, or Arach'nids, digestive organs of the, 326 ; jaws, 337 • respiration, 385. Arach'noid membrane, 85. Arbores'cerit (Lat. arbor, a tree), branched like a tree. Arc'tic (Gr. ^Apfcroc, the Bear, a northern constellation, thus signi- fying northern) fauna, the, 602 —604. Are'olar (Lat. areola, a nipple tissue, 41. Aristotle’s lantern, jaws of the Echi- nidse, so called, 335 Arm of man, 281 ; corresponding organ in other animals, 282 — 286. Ar'teries, 357. Arthro'dial (Gr. dpOpov, a joint) ; it is restricted to that form of joint in which a ball is received into a shallow cup. Articula'ta (Lat. articulus, a joint), a department of the animal king- dom, consisting of animals with 424 INDEX. external jointed skeletons or jointed limbs ; as the leech, the spider, the gnat, xxii. Articula'ta, or Artic'ulates, 70 ; ner- vous system, 115 ; jaws, 337 ; of the trias period, 665, 670. Ascid'ian (Gr. cto-zcoc, a bottle), shell- less acephalous mollusks, shaped like a leathern bottle. Assimila'tion, the change of blood into bone, muscle, &c. 401. Asteria'dae (Gr. aorpov, a star), the family of star-fishes, xxiii. Astre'idae, a family of polyps, found in the Coral-rag, 674. Au'ditory (Lat. audio ^ I hear), per- taining to the sense of hearing. Au'ricle(Lat.«wWe2^/«),a cavity of the heart, shaped like a little ear, 36 J . Australia, fauna of, 615. Autoch'thonoi (Greek), Aborigines, or first inhabitants, theory of, ap- phed to the distribution of ani- mals, 631. Automat'ic (Gr. avrofiarogf self- moving), a movement in a living body without the intervention or excitement of the will. Aves (Latin), birds ; the second class of vertebrate animals, xxi. Axil'la (Lat. arm-pit), apphed to other parts of the animal body which form a similar angle. Ax'olotl, a genus of reptiles, 626. Az'ygos (Gr. a, without ; ^vyog, yoke), single, without fellow. Bac'ulite (Lat. astatf), an extinct genus of mollusks, allied to the nautilus, which inhabited a straight-chambered shell, resem- bling a staff. Bal'anoids (Gr. paXaiwg, an acorn), a family of sessile cirripeds, the shells of which are commonly called acorn shells. Bar'nacle ; see Anatifa. Bas'ilar (Lat. basis, a base), belong- ing to the base of the skull. Bas'ilosaurus, an extinct cetacean, 680. Batra'chians (Gr. jSdrpaxog, a frog), the order of reptiles includi/ig the frog, xxi. Batra'chians, peculiar species nf, 626. Belem'nite (Gr. pkXspvog, g dart), an extinct genus of mollusks ; animals allied to the sepia, and provided with a long, straight, chambered conical shell ii the in- terior of the body, 673. Bi, or Bis, a Latin prefix, signifying twice, as in the following words : Bi'fid, cleft into two parts, Jr forked. Bi'furcate, divided into tvo prongs or forks. I Bi'lateral, having two syjnmetrical sides. Bi'lobed, divided into two lobes. Bip'artite, divided into tw^ parts. Bi'peds (Lat. bis, two, pet, a foot), animals with two feet, as man and birds. I Bird tracks, fossil, 670. Birds, the second division (jf the ani- mal kingdom, xxi. Birds, muscular system Df, 227 ; stomach of, 330. Bis (Latin), two, or twice; used in composition only. 1 Bi'valve, a shell of two part^, closing like a double door, 662. Blas'toderm, the embryonic germ. Blood, the, and circulation,35i) — 375. Blood, the, its constituents, 350 — 351; corpuscles, 352; colour, 353 ; its presence an essential condition of life, 354; circulation, 361 — 375; changes that it under- goes in circulation, 395. Bone, analysis of, 238 ; basis, 239 ; microscopic structure, 240 ; the various bones of the human ske- leton, 235, 241—278. Bot'ryoi'dal (Gr. porpvg, a bunch of grapes), having the form of a bunch of grapes. Bould'ers, 684. INDEX. 425 Brach'ial (Gr. ppaxtov, the arm), belonging to the arm. Brach'iopods (Gr. jipaxiov, the arm ; TTo^a, feet), acephalous mollusks, with two long spiral fleshy arms continued from the side of the mouth, xxiii. Brachyu'ra (Gr. ppayvcy short, ovpa, tail), Crustacea with short tails, as the crabs. Brachyu'rous, short tailed, usually restricted to the Crustacea. Brain, 78; in man, 85 — 88; in fishes, 92; in the amphibia, 93 ; in scaly reptiles, 94 ; in birds, 95 ; in mammalia, 96. Bran'chia (Gr. ppayxi^f the gills of a fish), the respiratory organs which extract oxygen from the air contained in water. Bran'chifers (Gr. j5payxici^ gills ; Lat. /ero, I bear), univalve mol- lusks breathing by gills, xxiii. Bran'chiopods (Gr. jSpayxt-a, gills ; Trod ay feet), Crustacea, in which the feet support the gills. Bron'chi, tubes branching from the windpipe in the lungs. Bron'tes, a genus of the family Tri- lobitidae. Biymzo'a (Gr. fipvovy moss; ^iJjovy animal), a class of highly organ- ized polyps, most of the species of which incrust other animals or bodies like moss, xxiii. 664. Buc'cal (Lat. buccuy mouth or cheeks), belonging to the mouth. C^'cuM and C^'ca (Lat. c(2cusy blind), a blind tube, or produc- tions of a tube, which terminate in closed ends. Calca'reous (Lat. calXy chalk), com- posed of lime. Camel, skeleton of the, 291. Campanula' ria, alternate generation of the, 350—352. Canine' (Lat. canisyd^ dog) teeth, 341. Canker-worm, metamorphoses of the, ' 552. Can'non-bone, the metacarpal bone of the horse and stag, 282, 286. Cap'illary vessels (Lat. capillusy a hair), the minute vessels through which the arteries and veins are united, 358, 371. Carapace', the upper shell of the crab and tortoise, 318. Car'bon (Lat. carbo)y the basis of charcoal and most combustibles. Carboniferous, or coal,formation,650, 669. Car'dia (Gr. Kapdia, the heart or stomach), the opening which ad- mits the food into the stomach ; also the region called the pit of the stomach. Carniv'ora (Lat. carOy flesh ; vorOy I devour), animals which feed on flesh, xxi. Car'pus (Latin), the wrist, 275. Cartilaginous, or gristly, tissue, 42, 52. Cau'dal (Lat. cauday a tail), belong- ing to the tail. Cau'da Equi'na (Lat. horse-tail), the leash of nerves which terminates the spinal marrow in the human subject, and the analogous part in the lower animals. Cell (Lat. cello) y the universal ele- mentary form of every tissue, 56. Cellule', a little cell. Celiular tissue (Lat. celloy a cell), the elastic connecting tissue of the different parts of the body which everywhere forms cells or interspaces containing fluid, 53, 56. Cen'tipede (Lat. centum, a hundred ; peSy a foot), a genus of insects ■with very numerous feet. Cen'trum (Gr. KsvTpov, centre), the body or essential elements of a vertebra, around which the other elements are disposed. Cephal'ic (Gr. KscpaXrj, head), be- longing to the head. Cephal'opods (Gr. KscpaXrjy head ; TTodoy feet), mollusks in which 426 INDEX. long prehensile processes or feet | project from the head, xxii, 663, 673. j Cephal'o-tho'rax (Gr. KscpaXi}, head ; Lat. thorax, chest), the anterior! division of the body in spiders, scorpions, &c., which consists of the head and chest blended to- gether. Cerca'ria, alternate generation exem- plified in the, 520 — 524. Cerca'riee (Gr. KepKog, a tail), ani- malcules whose body is termi- nated by a tail-like appendage. Cerebel'lum, or little brain,inman,87. Cer'ebral nerves, 97—114. Cer'ebrum, or brain, in man, 86. Cestra'cion Phiriipii, a living repre- sentative of the fishes of a former age, 615. Ceta'cea, or Ceta'ceans (Lat. cete, a whale) , marine animals, which nurse their young, like the whale, por- poise, &c., xxi. 304. Chala'za, the albuminous thread by which the yolk of the egg is sus- pended, 446. Chalk formation, 650. Chart of zoological regions, 595 — 622. Chelo'nia (Gr. xfXwi/?/, a turtle), the order of reptiles including the tor- toises and turtles, xxi. Che'le (Gr. a claw), applied to the bifid claws of the Crusta- cea, scorpions, &c. Chick, development of the, first period, 482 — 485; second period, 486 — 492 ; third period, 493 — 497 ; birth, 498 ; physical and chemical changes in the egg du- ring incubation, 499. Chil'ognatha (Gr. ^ 5 yj/aOog, a jaw), the order of many- footed insects, typified by the gaily -worm or julus. Chi'tine (Gr. a coat), the pe- culiar chemical principle which hardens the integument of insects. 1 Chol'edochus (Gr. xoXj), bile ; I Sox£, receptacle), the tube form- ed by the union of the hepatic and cystic ducts. j Cho'rion, from the Greek word sig- nifying the membrane which en- closes the foetus, and applied ge- nerally to the outer covering of the ovum, 475. Cho'roid, one of the coats of the eye, 124. Chrys'alis (Gr. xpurro^, gold), the stage of the butterfly immediately preceding its period of flight, when it is passive, and enclosed in a case, which sometimes glitters like gold. Chyle (Gr. %uXoc, juice), nutrient fluid extracted from digested food by the action of the bile, 333. Chylifica'tion, 332. Chyme (xvfiog, juice), digested food which passes from the sto- mach into the intestines, 331. Chymifica'tion, 331. Cil'ia (Lat. cilium, an eye-lash), mi- croscopic hair-like bodies, which cause, by their vibratile action, currents in the contiguous fluid, or a motion of the body to which they are attached, 216. Cil'iary motions, 211, 216, 217. Cilia' ted, provided with vibratile cilia. Ciliobrachia'ta (Lat. cilium, an eye- lash ; Gr. ppaxiov, the arm), po- lyps, in which the arms are pro- vided with vibratile cilia. Ciliogrades' (Lat. cilium, an eye- lash ; gradior, I walk), acalephae which swim by the action of cilia. Circulation, the, 350 — 375; its course in the mammalia, 364, 365 ; in reptiles, 366 ; in fishes, 367 ; in mollusca, 368 ; in Crus- tacea, 369 ; in insects, 370 ; in cold-blooded animals, 373. Cir'ri (Lat. cirrus, a curl), curled filamentary appendages, as the feet of the barnacles. iij^DEx. 427 Ciriig'erous, supporting cirri. Cirrigrades', moving by cirri. Cir'ripeds, or Cirripe'dia (Lat. cirrus, a curl ; pes, a foot), articulate animals having curled jointed feet, sometimes written cirrhipedia and cirrhopoda. Classes, a subdivision of the animal kingdom, xx ; again divided into orders, xx. Cla'vate (Lat. clavus, a club), club- shaped ; linear at the base, but growing gradually thicker towards the end. Clav'icle, the, or shoulder blade, 271. Climate, insufficient alone to ac- count. for the geographical dis- tribution of animals and plants, 638—641. Climate, the polar, its influence on animals, 582. Climbing, 298. Cloa'ca (Latin, a sink), the cavity common to the termination of the intestinal, urinary, and gene- rative tubes. Clyp'eiform (Lat. clypeus, a shield ; forma, shape), shield-shaped, ap- plied to the large prothorax in beetles. Coal period, flora of the, 669. Coc'costeus, an extinct genus of fishes from the Devonian rocks, 667. Coc'cyx, the, 258. Coch'lea, one of the divisions of the internal ear, 154. Cold-blooded animals, as reptiles, fishes, &c. 400. Coleop'tera (Gr. KoXeog, a sheath n-repov, a wing), the order of in- sects in which the first pair of wings serves as a sheath to defend the second pair, as the common dor-beetle. Columeria (Lat. a small column), used in conchology to signify the central pillar around which a spiral shell is wound. Comat'ula, a genus of the family Crinoidea. Comat'ula, metamorphoses of the, 559. Commis'surae (Lat. committo, I sol- der), belonging to a line or pan by which other parts are con- nected together. Compa'ges (Latin), a system or structure of united parts. Con'chifers (Lat. concha, a shell ; fero, I bear), shell-fish, usually re- stricted to those with bivalve shells. Cor'al rag, a stage of the oolite, 674. Coria'ceous (Lat. corium, hide), when a part has the texture of tough skin, 413. Cor'nea (Lat, corneus, horny), the transparent horny membrane in front of the eye, 123. Cor'neous, horny. Cor'neule (diminutive of cornea), applied to the minute transparent segments which defend the com- pound eyes of insects. Cor'nua (Lat. cornu, a horn), horns or horn-like processes. Cor'puscles (diminutive of corpus, a body), minute bodies. Cotyl'edon (Greek), a seed lobe. Creta'ceous (Lat. creta, chalk), be- longing to chalk. Creta'ceous formation, 650, 675 ; fauna, 675. Crinoid' (Gr. icpiuov, a lily ; sidog, like), belonging to the Echino- derma, which resemble lilies ; the fossils called stone lilies, or encri- nites, are examples, xxiii. Crio'ceras, a genus . of the family Ammonitidae. Cru'ra (Lat. crus, a leg), the legs of an animal, or processes r esem- bling legs. Crusta'cea (Lat. crusta, a crust), the class of articulate animals with a hard skin or crust, which they 1 periodically cast, xxii. 428 IKDEX. Grusta'cea, or Crusta'ceans, digestive organs of the, 325 ; jaws, 337 ; cir- culation, 369; respiration,38 1,405. Crypts, or follicles, 415. Crys'talline-lens, a transparent len- ticular body, situated behind the pupil of the eye, 126. Cte'noids (Gr. ktsviq, a tooth), fishes which have the edge of the scales toothed, xxi. Cte'nophori, soft radiated animals moving by cilia, xxiii. Cuttle-fish, jaws of, 321 ; metamor- phosis of, 563 ; mode of escape, 321 ; mode of swimming, 305. Cu'tis (Lat.), the true skin, the part which is tanned to form leather. Cy'clobranchia'ta (Gr. kvkXoqj round ; ppayxt’Cif gills), molluscous ani- mals which have the gills disposed in a circle. Cy'cloids, fishes with smooth scales, xxi. Dec'apoda (Gr. dsKa, ten ; ttovq, a foot), crustaceous and molluscous animals which have ten feet. Decid'uous, parts which are shed, or do not last the lifetime of the animal. Deflect'ed, bent down. Degluti'tion, 345 Dendrit'ic (Gr. devSpovj a tree), branched like a tree. Departments, primary divisions of the animal kingdom, xxi ; sub- divided into classes, xxi. Der'mal (Gr. deppia^ skin), belonging to the skin. Development of the chick, 48 2 — 499. Devonian formation, 650. Di'aphragm, the partition between the chest and abdomen, 209. Di'astole, the dilatation of the heart, 363. Di'branchia'ta (Gr. twice; jSpay- Xia, gills), cephalopods having two gills. Dicotyl'edons, plants with two seed- lobes, 74. Di'dactyle (Gr. twice; and daKrvXoQj a finger), a limb termi- nated by two fingers. Digestion, 312, 349 ; in the infuso- ria, 314 ; acalepha, 315 ; echino- derma,316 ; polypifera, 317 ; mol- lusca, 318 — 321 ; annelida, 322 — 324 ; Crustacea, 325 ; arachnida, 326; insects, 327; vertebrata, 328 ; microscopic examination, 329 ; the stomach, 330 ; chymi- fication, 331 — 334 ; mastication, 335 — 341 ; harmony of organs, 342 — 344 ; insalivation, 345 ; de- glutition, 346 — 349. Digestive organs ; see Digestion. Digitate' (Lat. digitus, a finger), when a part supports processes like fingers. Dilu'vium (Latin), a deposit from the w'ater of a flood or deluge. Dimidia'te (Lat. dimidium, half ), divided into two halves. Dimy'ary (Gr. twice ; gvov, a muscle), a bivalve whose shell is closed by two muscles. Dip'tera (Gr. dig, twice ; TZTtpov, a wing), insects which have two wings. Dis'coid (Lat. discus, a quoit), quoit- shaped. Discopho'ri, soft radiates, or jelly- fishes, xxiii. Disk (Lat, discus, a quoit), a more or less circular flattened body. Disto'ma (Gr. dig, two; aropa, mouth), the intestinal worms with two pores. Dist'oma, alternate generation ex- emplified in the, 521. Distribution, geographical, of ani- mals, 578—641. Distribution in time of animals, 642 Di'verticulum (from the Latin for a bye-road), apphed to a blind tube branching out from the course of a longer one. Do'do, an extinct bird, 629. Dor'sal (Lat. dorsum, the back), to- w^ards the back. Dor'sal cord, in the germ, 459. iraEX. 429 Dor'sal vessel, in insects, 359. Dorsibranchia'ta (Lat. dorsum^ the | back : Gr. gills), mol- lusks with gills attached to the back, xxii. Drift formation, 650, 684. Duc'tus (Latin), a duct, or tube, which conveys away the secretion of a gland. Duode'num (Lat. duodecimo twelve), the first portion of the small in- testine, which in the human sub- ject equals the breadth of twelve fingers. Du'ra master, 85. E, Ex, a liatin prefix, signifying generally “without,'’ or “from,” as Edentata, Exosmose; which see. Ear, the, 145—161. Earth’s crust, structure of the, 642 —655. Echinas'ter sanguin'olentus, meta- morphoses of the, 557, 558. Ech'ini,an order of Echinoderms,xxiii. Echin'oderms (Gr. a hedge- hog ; dspiJia, skin), the class of radiated animals, most of which have spiny skins, xxiii. Echin’oderms, 661 ; internal organs of the, 316 ; jaws of the, 335. Eden'tata (Lat. ew, without, dens^ a tooth), a class of mammals, in which the teeth are in some degree incomplete ; as in the armadillo. Eden'tulous, from the Latin word for toothless. Egg, the, all animals produced from, 433, 434 ; form, 435 ; formation, 436 — 446 ; development of the young, 447 — 479 ; structure as just laid, 480 ; changes in, during incubation, 499. Elementary structure of organized bodies, 35 ; of tissue, 56. Elytra (Gr. tkvrpov, a sheath), the wing sheaths formed by the mo- dified anterior pair of wings of beetles. I Emar'ginate (Lat. emarginoj to re- I move an edge), when an edge or margin has, as it were, a part bit- ten out. Em'bryo (Latin), the earliest stage of the young animal before birth, 433. Embryol'ogy, 429 — 509 ; the egz. 429 — 446 ; development of the young, 447 — 499 ; zoological im- portance of embryology, 500 — 509. Enal'iosaur (Gr. evaXiog, marine ; aavpng, a lizard), an extinct order of marine gigantic reptiles allied to crocodiles and fishes. Enceph'ala(Gr.62/,in; KetpaXr], head), molluscous animals which have a distinct head. Endog'enous, increasing by inw ird addition, as the palm tree, 72. Endosmose' and exosmose',41 1,413. Entomol'ogy (Gr. evroga, insects ; Xoyo^, a discourse), the depart- ment of natural history which treats of insects. Entomos'tracans (Gr. evroga, in- sect ; oarpaicov, shell), small crus- taceans, many of which are en- closed in an integument, like a bivalve shell, xxii. Entozo'a (Gr. evrog, within ; animal), animals which exist with- in other animals. Eocene' (Gr. the dawn ; Kaivog, recent), the stage of the tertiary period, in which the extremely small proportion of living species indicates the first commencement or dawn of the existing state of animate creation, 650. Epidermal (Gr. eTrideppiig, the cuti- cle), belonging to the cuticle or scarf skin, 413. Epister'nal (Gr. sttl, upon ; (TTepvovy the breast-bone), the piece of the segment of an articulate animal which is immediately above' the middle inferior piece, or sternum. 430 INDEX. Epithe'lium, the thin membrane which covers the mucous mem- branes : it is analogous to the epi- derm of the skin. Epizo'a (Gr. f tti, upon ; ^wov, ani- mal), the class of low organised parasitic crustaceans which live upon other animals. Errat'ics, rolling stones, 684. Eusta'chian tube, the, 146. Exci'to-rno'tory, the function of the nervous system, by which an im- pression is transmitted to a cen- tre, and reflected so as to produce the contraction of a muscle with- out sensation or volition. Exog'enous, increasing by outward addition, as in the case of most trees, 74. Exosmose' (Gr. out of ; o9eo, I expel), the ac.t in which a denser fluid is expelled from a membra- nous sac by the entry of a hghter fluid from without, 411,413*. Exu'vium (Latin, the skin of a ser- pent), the skin which is shed in moulting. Exu'vial, any part which is moulted. Eye, the, 121 — 129; dioptrics of the human, 130 — 134 ; simple, 135 — 140; aggregate, 141; com- pound, 142, 143 ; rudimentary, 144. Eye-lids and eye-lashes, 129- Faq'ette (French), a flat surface with definite boundary, 142. Fa'cial nerve, 1 03. Famihes, a group of the animal kingdom, xx. ; divided into ge- nera, XX. Fas'cicle (Lat. fasciculus), a small bundle. Fau'na (Latin), the animals pecuhar to a country, 579 ; general con- siderations, 579 — 594 ; the arctic, 602—604 ; the temperate, 605 — 615; the tropical, 616 — 622; conclusions, 623 — 641. Fe'mur (Latin), the thigh bone, 264. Fib'ula, the smallest of the two bones of the leg, 265. Fil'iform (LdX.filum, a thread ; for- ma, a shape), thread-shaped, 420. Fishes, the fourth division of the animal kingdom, xxi. Fishes, 667 ; muscular system of, 227 ; jaws, 340; circulation, 367; respiration, 383. Fishes, reign of, 659 — 669. Fissip'arous (Lat. findo, I cleave; pario, 1 produce), the multiplica- tion of a species by the cleavage of the individual into two parts, 510. Fissip'arous and gemmip'eirous repro- duction, 510 — 515. Flabel'liform {hdX. flabellum, a fan), fan-shaped. Flex'ors (Lat. flecto, I bend), the muscles emploved in bending a hmb. Flex'uous, a bending course. Flo'ra (Latin), the plants pecuhar to a country, 579 ; of the coal period, 669 ; of the oohtic period, 671. Flu' viatile (Lat. fluvius, a river), per. taining to rivers. Flying, 300. Foe'tus (Latin), the animal in the womb, after it is perfectly formed. Foha'ceous (Lat. folium, a leaf), shaped or arranged like leaves. Fol'licles(Lat. folliculus,^ small bag), minute secreting bags which com- monly open upon mucous mem- branes, 415, 421. Food, various methods of securing, by different animals, 346 — 349. Foot, the, 266 — 268. Footsteps, fossil, 672. Foraminif era, a class of microscopic radiated animals having many chambered shells, the septan of which are perforated. Formations, geological, 649 — 655. Fossiliferous if^x.fossilis, anything dug out of the earth ;/ero, I bear), applied to the strata which con- tain the remains of animals and INDEX, plants, to which remains geolo- gists now restrict the term fossil. Fossil remains, 25,652 — 682. Frontispiece, explanation of, xi. Func'tion, the office which an organ is designed to perform. Fun'gidae, found in the coral rag, 673. Galapagos islands, fauna of the,622. Gan'glion (Gr. yayyXiov, a knot), a mass of nervous matter forming a centre, from which nervous fibres radiate. Gan'glion'ic cells, 83. Gan'oids, fishes having large bony enamelled scales, mostly fossil, xxi. Gases, respiration in, other than atmospheric air, 394. Gaster'opods (Gr. ya^rep, stomach ; TTovQ, a foot), molluscous animals which have the locomotive organ attached to the under part of the body, xxii. 673. Gas'tric glands, 330. Gas'tric juice, 330. Gemmip'arous (Lat. gemma^ a hud; pario, I bring forth), propagation by the growth of the young like a bud from the parent, 510. Gemmip'arous and fissip'arous repro- duction, 510 — 515. Gemmule' (dim. of gemma) ^ the embryos of radiated animals at that stage when they resemble ciliated monads. Gen'era (Genus, in the singular), a group of the animal kingdom, xix. ; divided into species, ixix. Genera' tion, alternate, 518 — 532; consequences of, 533 — 547 ; spon- taneous, 543. Geograph'ical distribution of ani- mals,578 — 641; ofvegetation,639. Geolog'ical formations, 649. Germ (Lat. germen), the earliest maniffistation of the embryo. Germ, first indication of the, 465. Gesta'tion (Lat. gestatio), the carry- ing of the young before birth, 439, 431 Gla'cial (JL2A,. glades , ice), or Drift period, 684. Glands, structure of, 419—425 ; elementary parts, 426 ; origin,427 ; distribution of the vessels, 428. Globo'se (Lat. globus, di globe), globo- shaped. Glob'ules (diminutive of globe) of chyle, 333. Glossopharyn'geal nerve, 1 04. Glot'tis, the, 180. Grallatores, or wading birds, xxi. Grand-nurses, what, 524. Granules' (dim. of granum, a grain), little grains. Graniv'orous (Lat granum, grain ; voro, 1 devour), birds feeding on grain. Greyheads, or boulders, 684. Gul'let, the, 115, 345. Hand, the, 274—278. Hsemapophy'sis (Gr. aiga, blood ; aTrocpvaic, a process of bone) ; the vertebral elements which de- scend from the centrum, and en- close the blood-vessels in the cartilages of the ribs. Haversian canals, 240. Head, the, 241—251. Hearing, sense of, 145- — 161. Heart, the, 360; circulation of the blood, 361—375. Hemip'tera (Gr.^jLiKTU, half; Tmpov, a wing), the order of insects in wffiich the anterior wdngs are hemelytrous ; see Elytra. Hepat'ic (Lat. hepar, liver), belong- ing to the liver. Herbiv'ora (Lat. herba, grass ; voro, I devour), animals wffiich subsist on grass, xxi. Hermaph'rodite (‘Epjit Mercury ; L40pochV?/, Venus), an individual in which male and female cha- racteristics are combined. Hex'apod (Gr. six ; ttovq, a foot,) animals with six legs, such as true insects. 432 INDEX. Hibernation (Lat. hyems^ winter), the torpid state of animals during winter, 402. Histolog'ical (Gr. tdro^, a tissue ; \oyoQ, discourse), the doctrine of the tissues which enter into the formation of an animal and its different organs, 210. Holothu'rians, soft sea slugs, biche- le-mar, xxiii. Homal'onotus delphinoceph'alus,665 Homoge'neous, uniform in kind. Hom'ologue (Gr. oyoc, like ; Xoyoc, speech), the same organ in dif- ferent animals under every variety of form and function. Homol'ogy, or affinity, 16. Homoptera (Gr. byog, like ; irTspov, a wing), the insects in which the four wings have a similar struc- ture, but restricted in its applica- tion to a section of Hemiptera. Hu'merus, or shoulder-bone,the, 272. Hy'aline (Gr. vaXog, crystal) matter, the pellucid substance which de- termines the spontaneous fission of cells, 42. Ilydat'id (Gr. itbarig, a vesicle), a bladder of albuminous membrane, containing serous fluid ; generally detached ; sometimes with an or- ganised head and neck. Hy'dra (Gr. vbpa, a water-serpent), the modern generic name of fresh- water polyps. Hy'driform, similarly-formed polyps. Hy'drogen (Gr. vbiop, water ; yevvd(o^ I produce ;) a gas which is one of the constituents of water. Hy' droids, fresh-water polyps, xxiii. Hydrozo'a (Gr. vbpa^ water ; animal), the class of Polypi or- ganised like the Hydra. Hymenop'tera (Gr. vyriv, a mem- brane ; TTTspovy 8. wing,) the order of insects, including the bee, wasp, &c. which have four membranous wings. Ichthyosau'rus (ixOvg, a fish; (ravpog, a lizard), an extinct saurian, 673. Ide, idse (Gr. eldog, resemblance), a termination indicating likeness. As Acarus, a mite ; Acaridae, re- sembling the mite. Ig'neous (Lat. ignis, fire) rocks, 646. Iguan'odon, an extinct gigantic rep- tile, resembling in its teeth the iguana, an existing lizard. ll'ium, the, 263. Imbrica'ted (Lat. imbricatus, tiled), scales which lie one upon another like tiles. Inanimate beings, plants, 75. Incesso'res, perching birds, like birds of prey, xxi. Inci'sor (Lat. incido, I cut), or cut- ting teeth, 341. Incuba'tion (Lat. incubatio), hatch- ing of eggs by the mother. Incuba'tion, 442 ; physical and che- mical changes in the egg during, 499. In'cus, or anvil, the, 149. Infuso'ria (Lat. infundo), microscopic animals, inhabiting infusions of ani- mal or vegetable substances, xxiv- Infuso'ria, digestion in the, 314. Inoper'cular, univalve shells which have no operculum or lid. Inorgan'ic, not made up of tissues. Insaliva'tion, 345. In'sects, a class of the Articulates, xxii. In'sects, digestive organs of, 327 ; jaws of, 337 ; circulation, 370 ; respiration, 385. Instinct, 191 — 204. Intelligence and instinct, 185 — 204, Interambula'cra, the imperforate plates which occupy the intervals of the perforated ones, or ambu- lacra in the shells of the Echino- derms ; see Ambulacra. Intersti'tial (Lat. inter stitium), rela- ting to the intervals between parts. Invertebra'ta (Lat. in, used in com- position to signify not, like un ; II^DEX. 433 vertebra, a bone of the back) ani- mals without back bones. I'ris, the coloured part of the eye. Is'opoda (Gr. lcjoq, equal ; ttovq, a foot), an order of crustaceans, in which the feet are alike, and equal. Jaws, of man, 251 ; of other ani- mals, 334 — 344. Jelly-fishes, fossil, 676. Judgment, 188, Kidneys, development of the, 424. La'bium, Latin for a lip ; but ap- plied only to the lower lip in Entomology. La'brum, Latin for a lip, but ap- plied only to the upper lip in Entomology. Lab'yrinth, a part of the internal ear, 150. Labyrin'thodon, an extinct reptile, 672 Lacer'tans, or lizards, xxi. Lac'teals (Lat. lacteus, milky), ves- sels which take up the nutriment. Lamellibranchia'ta (Lat. lamella, a plate ; Gr. /3|Oayxta, gills), aceph- alous mollusca, with gills in the form of membranous plates, xxiii. Lamel'liform (Lat. lamella, thin leaves), shaped like a thin leaf or plate. Lar'va (Lat. a mask), applied to an in- sect in its first active state, which is generally a different form, and as it were masks the ultimate form. Lar'viform, shaped like a larva. Lar'ynx (Gr. Xdpvy^), the organ of voice, situated at the top of the trachea, 180. Laying of eggs, 439. Leaping, 297. Leg, the, 265. Lepidop'tera (Gr. Xfttiq, a scale ; TTTEpov, a wing), the order of in- sects in which the wings are clothed with fine scales, as butter- flies and moths. Life, the distinctive characteristic of organic bodies, 32 ; animal life, 76 ; blood an essential condition of, 354. Lith'ophytes (Gr. XiOog, a stone ; (pvTov, a plant), a stone plant, or coral. Liver, structure of the, in man, 425. Locomotion, 228 — 307 ; plan of the organs of, 279 — 288; standing, and modes of progression, 289 — 307. Lower Silurian formation-, 650. Low'er tertiary formation, 650. Lungs, the, 386* ; their various forms, 387 — 391. Lymphat'ics, 333. Malacol'ogy (Gr. fiaXaKog, soft^ Xoyog, discourse), the history of the soft bodied or molluscous animals, which were termed ma~ lakia by Aristotle. Malacos'tracans, crustaceans, like the lobster, xxii. Mal'leus, the, or hammer, 149. Mamma'lia, or Mam'mals (Lat. mam- ma, a breast), the class of animals which give suck to their young, xxi. Mam'mals, jaws of, 338 ; alone mas- ticate their food, 341 ; circulation of the blood, 364, 365 ; structure of the liver, 425. Mam'mals, reign of, 658, 678. Man, nervous system of, 84 — 91 ; special senses, 120 — 184 ; skeleton of, 235 — 278 ; circulation of the blood in, 364 — 366 ; respiration, 386, 389, 390 ; structure of the liver, 425. Man, reign of, 658, 684 — 686. Mandibula'ta(Lat.m«?26?i^z«Z«, a jaw), the insects which have mouths provided with jaws for mastica- tion ; the term mandible is re- stricted in entomology to the upper and outer pair of jaws. Manduca'ta, insects furnished with jaws, xxii. Man'tle, the external soft con- E E 434 INDEX. tractile skin of the mollusca, which covers the viscera and a great part of the body like a cloak. Marl, earth principally composed of decayed shells and corals, a mix- ture of clay and lime. Marsu'pial animals found in the oolite, 674. Marsupia'ha (Latin, marsupium, a purse), an order of the Mammalia having a tegumentary pouch, in which the embryo is received after birth, and protected during the completion of its development. iVlassive rocks, 646. Mastica'tion, 334 ; confined to the mammalia, 341. Mas'todon (Gr. paaroQ^ a teat ; odov, a tooth), a genus of extinct quadrupeds allied to the elephant, but having the grinders covered with conical protuberances like teats, 687. Ma'trix, the organ in which the embryo is developed, 475. Matter and mind, to be contemplated together, 29. Maxil'la (Lat. maxilla^ a jaw-bone), in entomology restricted to the inferior pair of jaws. Me'dian, having reference to the middle line of the body. Medul'la oblonga'ta, the oblong me- dullary column at the base of the brain, from which the spinal chord or marrow is continued, 89. Medu'sa, development of the, 527 — 529. Medu'sa, a class of soft radiated ani- mals, or acalephs, so called because their organs of motion and pre- hension are spread out like the snaky hair of the fabulous Medusa. Megalosau'rus, an extinct reptile, 673. Mergan'ser, an aquatic bird allied to the goose, 593. Memory, 188. Mes'entery (Gr. /iiecroc, intermediate ; and evTspoQf entrail), the mem- brane which forms the medium of connection between the small intestines and the abdomen. Mesotho'rax (Gr. peaog, middle; Oopa^j the chest), the intermediate of the three segments which form the thorax in insects. Metacar'pus, the wrist, 276. Metamor'phic rocks, 647. Metamo/phoses (Gr. ptTap,op(po)GiQy change of form), of animals, 548 ; of vegetables, 549. Metatar'sus, one division of the bones of fhe foot, 267. Metatho'rax (Gr. /ifrcr, after ; Oopa^, the chest), the hindmost of the three segments which compose the thorax of an insect. Migra'tion little prevalent among the mammalia, 594. Miriepeds (Lat. mille, a thousand ; peSf a foot), animals with many feet, as the wood-louse. Millepores' (Lat. millef a thousand ; Gr. TTopog, a minute hole\ a genus of lithophytes, having their sur- face penetrated by numerous little holes. Miocene' (Gr. peiov^ less ; Katvog, recent), the stage of the tertiary epoch in which a minority of the fossil shells are of recent species, 650. Modern age, the reign of man, 658, 684—686. Molar (Lat. molaris^ grinding) teeth, 341. Molecules' (of moles, a mass), mi- croscopic particles. Mollusca (Lat. mollis, soft), or Mol'- lusks, a primary division of the animal kingdom, xxii. Mollusca, 70, 662; of the trias period, 670; in the oolite, 673 ; nervous system, 116; digestive organs, 318 — 321; jaws, 336; circulation, 368 ; respiration, 380, 405. Mon'ad (Gr. povag, unity), the IlS-DEX. 435 genus of the most minute and simple microscopic animalcules, shaped like spherical cells. Monocotyledons, plants with a single seed lobe, 72. Monoc'ulus (Gr. fiovog, single ; Lat. oculuSf an eye), the animals which have but one eye. Monomy'ary (Gr. iiovog, single ; fivov, a muscle), a bivalve whose shell is closed by one adductor muscle. Monothal'amous TGr. jxovog, single ; OaXa/jLog, a chamber), a shell forming a single chamber, like that of the whelk. Motion, 205 — 307 ; apparatus of, 205 — 227 ; locomotion, 228 — 288; standing, and modes of progression, 289—307. Mo'tory, the nerves which control motion. Moult'ing, the shedding of feathers, hair, &c., 412. Mul'tivalve (Lat. multus, many ; valvce, folding doors). Mus'cular tissue, one of the primary forms of animal tissues having the power of contraction, 44, 54. Myri'apods (Gr. fivpiog, ten thou- sand ; TTovg, foot), the order of^ insects characterized by their nu- merous feet. Na'creous (Fr. nacre), pearly, like mother-of-pearl. Natato'res (Lat. nato, I swim), birds with webbed feet for swimming,xxi . Na'tatory, an animal or part formed for swimming. Natural history, extent of the study of, 30. Nature, ages of, 656 — 690. Nautilus, cephalopods with cham- bered shells, xxii. Nep'tunic,orwater-formedrocks,646. Nerves, structureof the primary fibres of, 80, 81; their termination, 82 — 119. Nerves, pairs of, their several offices, 97—114. Ner'vous system of man, 84 — 95 ; of other classes of animated beings^ 92 — 119; special senses,120 — 184. Nervous system, the, and general sensation, 76 — 79. Ner'vous tissue, 45, 55 ; its structure, 80, 81 ; termination, 82. Ner'vures (Lat. nervus, a sinew), the delicate frame of the mem- branous wings of insects. Neurapoph'yses (Gr. vtvpov, nerve ; dirocpvaLg, a process of bone), those vertebral elements which enclose and protect the spinal cord and brain. Neu ral-spine, the spinous processes of the vertebra. Neurilemma (Gr. vtvgov, a nerve ; XiifjLfjLa, a covering), the mem- brane which surrounds the ner- vous fibre. Neurop'tera (Gr. vevpov, a nerve; Trrepov, a wing), the order of in- sects with four wings, character- ized by their numerous nervures, like those of the dragon-fly. Nodule (dim. of nodus, a knot), a little knot-like eminence. Normal (Lat. norma, rule), accord- ing to rule, ordinary or natural. Notosau'rus, an extinct saurian, 672. Nuclea'ted, having a nucleus or cen- tral particle ; applied to the ele- mentary cells of animal tissues, the most important properties of which reside in the nucleus, 38,56. Nu'cleus and nu'cleolus, 56 Nu'dibrachiate (Lat. nudus, naked ; Gr. jSpayxia, arms), the polyps, whose arms are not clothed with vibratile cilia. Nu dibran chiata' (Lat. nudus, naked ; Gr. (3pavxia, gills), an order of gasteropods, in which the gills are exposed. Nutrition, 308 — 349 ; digestion, 3.12 —349 436 INDEX. 3cel'li (Latin), minute eyes, 138. Oc'topods (Gr. ofcro, eight ; tzovq, di foot), animals with eight feet ; the name of the tribe of Cephalo- pods with eight prehensile organs attached to the head. (Esoph'agus, the gullet, or tube lead- ing from the mouth to the sto- mach, 345. Olfac'tory (Lat. olfactus, the sense of smelling) nerves, 97. Ornniv'ora (Lat. omne, all; voro, I devour), feeding upon all kinds of food, 343, Oolite' (Gr. wov, egg ; XiQoq, stone), an extensive group of secondary limestones, composed of rounded particles, like the roe or eggs of a fish. Oolit'ic formation, 650. Oper'culum (Latin, a lid), applied to the horny or shelly plate which closes certain univalve shells ; also to the covering of the gills in fish, and to the lids of certain eggs. Optic lobes, in man, 88. Optic nerves, 98, 99, 101. Ophid'ians (Gr. 6(pig, a serpent), ani- mals of the serpent kind, xxi. O'ral (Lat. os, the mouth), belong- ing to the mouth or the speech. Orders, a group of the animal king- dom, XX. ; subdivided into families and genera, xx. Organism, 36. Organized bodies, general properties of, 30 — 75 ; organized and unor- ganized bodies, 30 — 34 ; elemen- tary structure of organized bodies, 35 — 56 ; differences between ani- mals and plants, 57 — 75. Ornithichni'tes (Gr. opvig, a bird), the fossil footsteps of birds, 670. Orthop'tera (Gr. opOog, straight Trrepov, a wing), the order of in- sects with elytra and longitudi- nally folded wings. Os'seous (Lat. os, a bone) tissue, 43. Oto liths (Gr. an ear ; XiOog, a stone), the stony or chalky bo- dies belonging to the internal ear, 156. Ova'rium (Lat, ovum, an egg), the organ in which the eggs or their elementary and essential parts are formed. Ovary, detachment of the ovum from the, 481. Ovig'erous (Lat, ovum, an egg ; gero, I bear), parts containing or sup- porting eggs. Ovip'arous (Lat. ovum, an egg ; pario, I bring forth), animals which bring forth eggs, 434. Ovo-vivip'arous (Lat. ovum, an egg ; vivus, alive ; pario, I produce), animals which produce living young, hatched in the egg within the body of the parent without any connection with the womb, 439. Ovula'tion, the production of eggs, 437, 438. O'vum (Lat. ^negg), detachment from the ovary, 481. Ox'ygen, quantity consnmedby vari- ous animals, 396*. Pachyder'mata (Gr. iraxvQj thick, skin), thick-skinnedanimals, like the elephant, hog, &c., 343. Palaeontology (Gr. TvaXawc, an- cient ; ovra, beings ; \6yog, dis- course), the history of ancient ex- tinct organised beings. Palaeontology, an essential branch of zoology, 645. Palaeozo'ic age, 658, 659 — 667. Palaeothe'rium (Gr. naXg, an- cient; 0r)pLov, beast), an extinct genus of Pachydermata, 680. Pal'lial (Lat. pallium, a cloak), re- lating to the mantle or cloak of the mollusca. Palpa'tion, the act of feeling, 175. li^DEX. 437 Papillae (Lat. a nipple), minute soft prominences, generally adapted for delicate sensation, 413. Pal'pi palpo, I touch), the or- gans of touch developed from the lahium and maxillae of insects. Parasit'ic (Ldit. par asitus), living on other objects. Paren'chyma, the soft tissue of organs ; generally applied to that of glands, 372. Pari'etes (Lat. paries, a wall), the walls of the different cavities of an animal body. Pas'serine (Lat. passer, a sparrow), birds of the sparrow kind Patel'la, the, 265. Pectina'ted (Lat. pecten, a comb), toothed like a comb. Pectinibranchia'ta (Lat. pecten, a comb ; /3j0ayxt«, gills;, the order of gasteropods, in which the gills are shaped like a comb. Ped (Lat. pes), Poda (Gr. Trovq, a foot), a termination classifying cer- tain kinds of animals by their feet ; as quadruped, gasteropod ; which see. Ped'iform (Lat.jt?c^, afoot), shaped like a foot. Pedun'cle (Lat. pedunculus), a stalk. Pelag'ic (Gr. TreXayog, sea), belong, ing to the deep sea. Pel'vic arch, the, 263. Pe'lvis (Latin), the cavity formed by the hip bones. Pentacrinite' (Gr. TTfvra, five; Kpivog, hair), a pedunculated star-fish with five rays ; they are for the most part fossil. Periph'eral circulation, 372 — 375. Periph'ery (Gr. Trepi, about ; (ptpoj, ] bear), exterior surface. Peristal'tic (Gr. Trepi, about ; Lat. stello, I range), motion, the vermi- cular contractions and motions of muscular canals, as the alimentary, the circulating, and generative tubes. Peritone'al (Gr. TrepiTovcaog, the covering of the abdomen), re- stricted to the lining membrane of that cavity. Perpetual snow, limits of, 638. Phal'anges (Latin), the joints of the fingers and toes, 277. Phar^ynx, the dilated beginning of the gullet. Phytoph'agous (Gr. fpvrov, a plant ; 0ayo, I eat), plant-eating animals. Pia' ma'ter, 85. Pig'ment (Lat. pipmentum),&colom:- ing substance. Pin'nate (Lat. pinna, a feather or fin), shaped like a feather, or pro- vided with fins. Pisces (Latin), fishes ; the fourth class of vertebrate animals, xxi. Pitu'itary (Lat. pituita, phlegm), membrane, 164. Placen'ta (Latin), the organ by which the embryo of mammals is attached to the mother, 476. Plac'oids, fishes with a rough skin, like the shark or skate. Plant lice ; see Aphides. Plants and animals, differences be- tween, 57 — 74 ; resume, 75. Plan'aria, a genus of worms. Plas'ma, the fluid part of the blood, in which the red corpuscles float, also called liquor sanguinus, Plas'tron, the under part of the sheU of the crab and tortoise. Pleiocene' (Gr. 'kXuov, more ; fcat- vog, recent), the stage of the tertiary strata, which is more recent than the miocene, and in which the major part of the fossil testacea belong to recent species, 650. Pleistocene' (Gr. TrXsiarog, most ; Kaivog, recent), the newest of the tertiary strata, which contains the largest proportion of living species of shells, 685. Plesiosau'rus (Gr. TrXrjaiog, almost; aavpog, a lizard),an extinct marine 438 INDEX. saurian, remarkable for its long neck, 671. Pleurotoma'ria, an extinct genus of univalve shells. Plex'us (Gr. TrXfcfco, I twine), a bun- dle of nerves or vessels interwoven or twined together. Pli'cae (Lat. plica^ a fold), folds of membrane. Plumose' {L'dX.pluma^ a feather), fea- thery, or like a plume of feathers. Plutonic or igneous rocks, 646. Pneumat'ic (Gr. TTvevpa, breath), belonging to the air, and air- breathing organs. Pneumogas'tric nerve, 105. Podurel'la, a genus of insects, their mode of progression, 299. Polygas'tria (Gr. ttoXvq, many ; ya(TT8p, a stomach), infusorial animalcules which have many assimilative sacs or stomach. Pol'ypi (Gr. ttoXvq, many ; Trovg, a foot), radiated animals with many prehensile organs radiating from around the mouth. Polypifera, digestion in the, 313, 317. Prehen'sion, act of grasping. Primary, or palaeozoic age, the reig-n of fishes, 658, 659 — 669. Primitive fibres of the nerve, 80. Progression, modes of, 289 — 307. Prolig'erous, the part of the egg bearing the embryo. Protho'rax (Gr. Trpo, before, and Oopa^), the first of the three seg- ments which constitute the thorax in insects. Protraet'ile, capable of being ex- tended. Pro'teus, a genus of batrachian rep- tiles, 626. Protosau'rus (Gr. Trpwroc;, first ; (Tavpog, a lizard), an extinct genus of saurian reptiles, 672. Protozoa (Trpwroc, first ; ^ibov, ani- mal), the, assumed, simplest forms of animal life, xxiv. Pterich'thys (Gr. Trrepov, av^ing; iX^vg, a fish), an extinct fish, of very peculiar form, 667. Pterodac'tylus (Gr. Trrtpov, a wing; SdtcTvXog, a finger), an extinct fly- ing reptile, 671. Pter'opods (Gr. irrspovy a wing; TTovg, a foot), mollusks, in which the organs of motion are shaped like wings, xxiii. Pul'mogrades (Lat. pulmo, a lung ; gradior^ I walk), medusae which swim by contractions of the res- piratory disc. Pul'monata (Lat. lung), gaste- ropods that breathe by lungs, xxxiii. Pu'pa (Latin, doll^ or little image) y the passive state of an insect im- mediately preceding the last. Pylo'rus (Gr. TrvXojpog), the aper- ture which leads from the stomach to the intestine. Pyr'iform (Lat. pyrwriy a pear), pear- shaped. Py'rula, a genus of univalve shells. Quad'rifid (Lat. quatuor, four ; findo, I cleave), cleft in four parts. Quadruma'nous (Lat. quatuor, four ; manus, a hand), four-handed ani- mals, as monkeys. Quad'ruped (Lat. quatuor, four; pes, a foot), animals with four legs. Radia'ta (Lat. radius, a ray), or Radiates, the lowest primary divi sion of the animal kingdom, xxi. Radia'ta, nervous system of the, 117; jaws, 335 ; of the trias period, 670; of the oolite, 674. Ra'dius, one of the bones of the arm, 273. Ramose' (Lat. ramus, a branch), branched. Reasoning, 189. Relation, functions of, 76. Remak, band of, 55. Ren'iform (Lat. ren, a kidney), kid- ney-shaped. INDEX. 439 Reproduction, peculiar modes of, 510 — 547 ; gemmiparous and fissipa- rous, 5] 0 — 515 ; alternate and equi- vocal, 516 — 532 ; consequences of alternate generation, 533 — 547. Rep'tiles or Reptil'ia, jaws of, 340 ; circulation of the blood, 366 ; re- spiration, 384. Rep'tiles, reign of, 658, 670 — 677. Reptil'ia (Lat.rejo^o, I creep), orRep'- tiles ; the third class of vertebrate animals with imperfect respiration and cold blood, xxi. Respira'tion, 376 — 405 ; in the echi- nodermata, 378, 405 ; in mollusca, 380, 405 ; in Crustacea, 381, 405 ; in annelida, 382 ; in fishes, 383 ; in reptiles, 384 ; in insects and arachnida, 385 ; in man, 386 ; in birds, 388 ; lungs of man and the mammalia,389,390 ; two sorts of respiratory organs in articulata,405 Rest, the distinctive character of in- organic bodies, 32. Re'te muco'sum, the cellular layer between the scarf-skin and true skin, which is the seat of the pe- cuhar colour of the skin, 413. Ret'ina (Latin), the seat of vision, 125. Retract'ile, that may be drawn iDack. Rhi'zodonts, an order of extinct rep- tiles, xxi. 672. Rhizo'poda ; see Foraminifera. Rocks, what, in a geological sense, 646 ; their different kinds, 646, 647. Ro'dents (Lat rodo, I gnaw), quad- rupeds with teeth for gnawing, 343. Rotif'era (Lat. rota^ a wheel ; fero, I bear), infusorial animalcules characterised by the vibratile and apparently rotating ciliary organs upon the head. Rotifera, eggs of the, 546. Ru'minants (Lat. ruminus)^ quadru- peds which chew the cud ; as the bull and stag, 343. Running, 296. Sac'ciform, shaped like a sac or bag. Salif'erous, or salt-hearing forma- tion, 650. Sal'pians (Gr. caXirr]^ a kind of fish), tunicated mollusks which float in the open sea, xxiii. 519. Sau'rians (Gr. aavpoQy a lizard), a class of reptiles, including the ex- isting crocodiles, and many spe- cies of large size, 673. Scan'sores (Lat. scando^ I climb), birds adapted for climbing, xxi. Scap'ula, the, or shoulder blade, 270. Scap'ular arch, the, 269. Sclerot'ic, the principal coat of the eye, 123. Seba'ceous (Lat. sebuniy tallow) like lard or tallow. Secondary age, the reign of rentiles, 658, 670—677. Secretions, the, 406 — 428 ; structure of glands, 419 — 425 ; elementary parts, 426 ; origin of glands, 427 ; distribution of their vessels, 428. Sediment'ary or stratified rocks, 646 ; alone contain fossils, 649. Seg'ment, portion of a circle or sphere. Segmenta'tion, the act of dividing into segments. Semilu'nar, crescent-shaped, like a half moon. Sensation, 76 — 119. Senses, the special, 120 — 184 Sep'ta (Latin), partitions. Se'rous, (Lat. serum) ^ watery. Serrat'ed (Lat.serrfl, a saw), toothed like a saw. Ses'sile (Lat. sessilis)^ attached by a base. Se'tae (Lat. setUy a bristle), bristles or similar oarts. Shell, 218. Shoulder blade, the, 270. Sight, sense of 120 — 144. Si'lex (Latin), flinty rock. Sili'ceous (Lat. silese, flint), flinty, I Silk-worm, metamorphoses of the, 1 551. 440 IITDEX. S’lu'rian formations, 650. Sia'uous (Lat. sinuatuSy winding), bending in and out. Si'nus (Latin), a dilated vein or receptacle of blood. Siplion'ophori, soft radiates, xxiii. Skeleton, the, 225 ; of man, 235 — 278 ; corresponding organs of loco- motionin other animals, 282 — 288. Skin, the, 412, 413. Smell, sense of, 162 — -168. Species, ordinarily the lowest term in the divisions of the animal kingdom, xix. ; occurrence of va- rieties, XX. Species, living, their number, 7, and note. Speech, gift of, confined to man, 184. Spermatozo'a (Gr. airkpixa, seed ; an animal), the peculiar mi- croscopic moving filament and es- sential parts of the fertihsing fluid. Sphinc'ter (Gr. (70tyr£p), the circu- lar muscles which contractor close natural apertures. Spic'ula (Lat. spiculurrij a point or dart), fine pointed bodies like needles. Spi'nal cord, in man, 89 ; see Nerv- ous system. Spi'nal nerves, 108. Spir'acles (Lat. spiro, 1 breathe), the breathing pores in insects. Sponges, doubtful nature of, 58, and note. Spontaneous generation, old theory of, unfounded, 543. Spores, the germs of sea-weeds, ferns, &c. Squa'mous (Lat. squama, a scale), arranged like scales. Standing, and modes of progression, 289—307. Stapes, the, or stirrup, 149. Ster 5 ii, the aspect of the body where the sternum or breast-bone is situated. Stig'mata (Gr. anyua, a mark), the breathing pores of insects. Stomach ; see Digestive organs. Stra'ta (Latin, beds or layers), ar* rangement of, 648. Strat'ified rocks, 646. Sucto'ria (Lat. sugo, I suck), ani- mals provided with mouths tor sucking, and the appendages of other parts organised for suck- ing or adhesion, xxiii. Supra-oesopha'geal (Latin, supra, above), above the gullet. Supreme Intelligence, direct inter- vention of the, in the geographical distribution of organized beings, 641. Su'ture (Lat. suo, I sew), the im- moveable junction of two parts by their margins. Swimming, 302. Sympathetic nerves, great, 109 ; op- posite views regarding, 110 — 115. Sys'tole (Gr. avaroXi)), the contrac- tion of the heart to force out the blood, 363. Tarsus (Gr. rapaoQ, a part of the foot), applied to the last segments of the legs of insects- Tar'sus, the, in man, 266 Taste, sense of, 169 — 173. Tectibranchia'ta (Lat. tego, 1 cover; jSpay^ta, gills), mollusks in which he gills are covered by the mantle. Teeth, the, 339—341. Temperate fauna, the, 605 — 615. Temperature, equalizing effects of large sheets of water on, 636. Tem'poral (Lat. tempora), relating to the temples. Te'ntacle (Lat. tentaculum), the horn-like organs on the head of mollusks usually bearing the eyes. Terebrat'ula (Lat. terebro, 1 bore), a genus of brachiopodous mollusks. Ter'gal (Lat. tergum, the back), be- longing to the back. Ter'tiary (Lat. tertius, the third) age, the reign of mammals, 658, 676 —683. INDEX. 441 Test, the brittle crust covering the crustaceans, &c. Test, what, 218 ; in the echinidae, asteriadaj, and crinoidae, 219 ; in the mollusca, 220 ; in the articu- lata, 222. Tetrabranchia'ta (Gr. rsTpaj four; /^joayxia, gills), cephalopods with four gills. Teuthid'eans, the family of cuttle fishes, xxii. Thoracic, belonging to the thorax. Tho'rax, the, or chest, 261, 262. Thigh, the, 264. Tibia, one of the bones of the leg, 265. Tissues, the various, 41 — 56. Toes, the, 268. Torrid zone, development of animal and vegetable life in the, 583. Tortoises, first traces of, 674. Touch, sense of, 174 — 176. Tra'cheae (Gr. rpa^eia, the rough artery or windpipe), the breath- ing tubes of insects. Trias formation, 650. Trias period, fauna of the, 670. TriTobite (Gr. Tpig, three ; Xo/3oc, a lobe), an extinct genus of Crusta- cea, the upper surface of whose body is divided into three lobes, xxii. 665, 671. Tro'phi, organs for feeding, of insects, crabs, &c. Tropical fauna, the, 616 — 622. Trunk, the, 252 — 263. Tubulibranchiates, articulates, with gills about the head, xxii. Tunica'ta (Lat. tunica^ a cloak), ace- phalous mollusks enveloped in an elastic tunic not defended by a shell. Tym'panum (Lat. a drum)y the mem- brane separating the internal and external ear, 150. Type (Gr. TV7roQ),3.n ideal image, xx. Type of the vertebrata, 506 ; of the articulata, 507 ; of the mollusca, 508 ; of the radiata, 509. Ul'na (Latin), one of the bones of the arm, 273. Un'cinated (Lat. unguis ^ a nail or claw), beset with bent spines like hooks. U'nivalve (Lat. unus, one ; valvos, doors), a shell composed of one calcareous piece. Upper Silurian formation, 650. • Upper tertiary formation, 650. Varieties, in the animal kingdom, on what based, xx. Vas'cular (Lat. vasculum), composed of vessels. Vegetation, geographical distribution of, 639—641. Veins, 357. Ven'tral (Lat. venter^ the belly), re- lating to the inferior surface of the body. Ventric'ular (Lat. ventriculus, a ventricle or small cavity, hke those of the heart or brain), belonging to a ventricle, 361. Ver'mes (Lat. vermis, a worm), w’orm-like animals : applied in a very extensive sense by Linnaeus, xxii Vermic'ular, or worm-hke, motion, 331. Ver'tebrae, the, 259 ; number of, in different animals, 260. Vertebra'ta (Lat. vertebra, a bone of the back : from vert ere, to turn), or Vertebrates, the highest divi- sion of the animal kingdom, cha- racterised by having a back bone, xxi, 73; digestive organs, 328, 329 ; jaws of, 338—344. Vesic'ulae (Lat. vesica, a bladder), receptacles like little bladders. Ves'tibule (Lat. vestibulum,d^poxQ}e^, the entrance to one of the cavities of the ear, 158. Vi'bratile (Lat. vibratilis), moving to apd fro. Vil'li (Latin), small processes like the pile of velvet. G a 442 iraEX. Vis'cus, Vis'cera, plural (Latin), intes- tinesi^ bowels. Vitelline (Lat. vitellus, yolk), of, or belonging to the yolk. Vitel'lus, or yolk of eggs, 444. Vit'reous humour (Lat. vitreus^ glassy), the humour of the eye on which the retina or expansion of the optic nerve is extended, 127. Vivip'arous (Lat. vivus, alive I bring forth), animals which bring forth their young alive, 434. Vocal cords, 180. Voice, the, 177 — 184 ; speech con- fined to man, 184. Voluntary (Lat. voio^ I will), under control of the will. Voluntary and involuntary motions, 211. Walking, 293 — 295. Warm-blooded animals, as birds, mammals, &c. 399. Water, equalizing effects of large sheets of, 636. Water-tubes of aquatic animals, 403. Whales, mode of swimming, 304, 307. Worms, or Ver'mes, class of, xxii. Yolk of egg, 444. Young, development of the, 447 — 449. Zoolog'ical regions, chart of, ex- plained, xii. Zool'ogy, its sphere and fundamental principles, 1 — 29. Zo'ophytes (Gr. animal, (pvrovy a plant), the lowest primary divi- sion of the animal kingdom, which includes many animals that are fixed to the ground and have the form of plants, 68. FKINTED BY W. 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