ii!!i!llitll!!|lll}uui!!ililllllitl!U|j|l}ijiJ!liliiii! ^^BBlflfflJMffifflllllJH^ . - r- j- tr i-n CD ^n o CD CD m CD 1930 Gift of Robert R. Shrock 1983 IV. Modern Age. III. Tertiary Age. II. Secondary Age. I. Palaeozoic Age. Metamorphic Rocks.. ;T 0>F TOI IA&TO Ai Upper Tertiary Formation. Lower Tertiary " Cretaceous " Oolitic " Trias " Carboniferous " Devonian " Upper Silurian " Lower Silurian " TO PRINCIPLES OF ZOOLOGY: TOUCHING THE STRUCTURE, DEVELOPMENT, DISTRIBUTION, AND NATURAL ARRANGEMENT OF THE RACES OF ANIMALS, LIVING AND EXTINCT WITH NUMEROUS ILLUSTRATIONS. PART I. COMPARATIVE PHYSIOLOGY. FOR THE USE OF SCHOOLS AND COLLEGES. BY LOUIS AGASSIZ AND A. A. GOULD. REVISED EDITION. BOSTON: GOULD AND LINCOLN, 59 WASHINGTON STREET. 1851. Entered, according to Act of Congress, in the year 1851, BY GOULD AND LINCOLN, In the Clerk's Office of the District Court for the District of Massachusetts. STEREOTYPED AT THE BOSTON STEREOTYPE FOUNDRY. G. C. Rand & Co., Printers, Cornhill. PREFACE. THE design of this work is to furnish, an epitome of the leading principles of the science of Zoology, as deduced from the present state of knowledge, so illustrated as to be intelligible to the begin- ner. No similar treatise now exists in this country, and, indeed, some of the topics have not been touched upon in the English lan- guage, unless in a strictly technical form, and in scattered articles. On this account, some of the chapters, like those on Embryology and Metamorphosis, may, at first, seem too abstruse for scholars in \ our common schools. This may be the case, until teachers shall have made themselves somewhat familiar with subjects comparatively new to them. But so essential have these subjects now become to a correct interpretation of philosophical zoology, that the study of them will hereafter be indispensable. They furnish a key to many phenomena ; ' / which have been heretofore locked in mystery. Being intended for American students, the illustrations have been drawn, as far as possible, from American objects : some of them are presented merely as ideal outlines, which convey a more definite idea than accurate sketches from nature ; others have been left ira- ', perfect, except as to the parts especially in. question ; a large propor- ^ tion of them, however, are accurate portraits from original drawings. ~ Popular names have been employed as far as possible, and to the ^scientific names an English termination has generally been given; : but the technical terms have been added, in brackets, whenever mis- understanding was apprehended. Definitions of those least likely to be understood, may be found in the Index. 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. The authors gratefully acknowledge the aid they have received, in preparing the illustrations and working out the details, from Mr. 1* 6 PREFACE. E. Desor, for many years an associate of Professor 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 first part is devoted to Comparative Anatomy, Physiology, and Embryology, as the basis of Classification, and also to the illus- tration of the geographical distribution and the geological succession of Animals ; the second to Systematic Zoology, in which the prin- ciples of Classification will be applied, and the principal groups of animals will be briefly characterized. Should our aim be attained, this work will produce more enlarged ideas of man's relations to Nature, and more exalted conceptions of the Plan of Creation and its Great Author. BOSTON, June 1, 1848. PREFACE TO THE REVISED EDITION. IN revising the present work, the authors have endeavored to render more precise those passages which admitted of too broad a signification or of a double interpretation ; and to correct such errors as had arisen from inadvertence, or such as the rapid progress of Sci- ence has disclosed. They are indebted for many suggestions on these points to several distinguished teachers who have used the work as a text book, and more especially to Professor Wyman, of Harvard University. Several entirely new paragraphs have also been added. A list of some of the principal authors who have made original researches, or of treatises which enter more into detail than was ad- missible in an elementary work, has been given at the close of the volume, for the use of those who would pursue the subject of Zoology in a more extended manner. The work having thus been revised and enlarged, the authors sub- mit it to the public with increased confidence in its accuracy and usefulness. BOSTON, February 1, 1851. TABLE OF CONTENTS. Page INTRODUCTION . . 17 CHAPTER FIRST. THE SPHERE AND FUNDAMENTAL PRINCIPLES OF ZOOLOGY . 25 CHAPTER SECOND. GENERAL PROPERTIES OF ORGANIZED BODIES .... 35 SECTION I. Organized and Unorganized Bodies 35 SECTION II. Elementary Structure of Organized Bodies • 36 SECTION III. Differences between Animals and Plants 41 CHAPTER THIRD. FUNCTIONS AND ORGANS OF ANIMAL LIFE . . . 44 SECTION I. Of the Nervous System and General Sensation 44 8 TABLE OF CONTENTS. SECTION II. Page Of the Special Senses 48 1. Of Sight 48 2. Of Hearing 55 3. Of Smell 60 4. Of Taste 62 5. OfTouch 63 6. Of the Voice 64 CHAPTER FOURTH. OF INTELLIGENCE AND INSTINCT . ... 67 CHAPTER FIFTH. OF MOTION 73 SECTION I. Apparatus of Motion 73 SECTION II. Of Locomotion 79 1. Plan of the Organs of Locomotion 82 2. Of Standing, and the Modes of Progression ... 88 Walking 90 Running 91 Leaping 91 Climbing 92 Flying 92 Swimming 93 CHAPTER SIXTH. OF NUTRITION 96 SECTION I. Of Digestion 97 Digestive Tube 97 Chymification 100 Chylification 100 Mastication 101 Insalivation 108 Deglutition 108 TABLE OF CONTENTS. CHAPTER SEVENTH. Page OF THE BLOOD AND CIRCULATION Ill CHAPTER EIGHTH. I Or RESPIRATION . . . 118 CHAPTER NINTH. OF THE SECRETIONS . . 126 CHAPTER TENTH. EMBRYOLOGY 131 SECTION I. Of the Egg . 131 Form of the Egg .... Formation of the Egg ... . . 133 Ovulation ... . . 134 Laying ........... 135 Composition of the Egg 137 SECTION II. Development of the Young icithin the Egg . . 139 SECTION III. Zoological Importance of Embryology . 153 CHAPTER ELEVENTH. PECULIAR MODES OF REPRODUCTION 156 • SECTION I. Gemmiparous and Fissiparous Reproduction .... 156 SECTION II. Alternate and Equivocal Reproduction ... . 158 i 10 TABLE OF CONTENTS. SECTION III. Page Consequences of Alternate Generation 167 CHAPTER TWELFTH. METAMORPHOSES OP ANIMALS 174 » " CHAPTER THIRTEENTH. GEOGRAPHICAL DISTRIBUTION OF ANIMALS .... 186 SECTION I. General Laws of Distribution 186 SECTION II. Distribution of the Faunas 194 I. Arctic Fauna 197 II. Temperate Faunas 198 III. Tropical Faunas 204 SECTION III. Conclusions 207 CHAPTER FOURTEENTH. GEOLOGICAL SUCCESSION OF ANIMALS ; OR, THEIR DISTRIBUTION IN TIME 214 SECTION I. Structure of the Earth's Crust 214 SECTION II. Ages of Nature 221 Palaeozoic Age 223 Secondary Age . . . 227 Tertiary Age 233 Modern Age 235 Conclusions 237 EXPLANATION OF THE FIGURES. FRONTISPIECE. — The diagram opposite the title page is intended to present, 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 221, are represented by four zones, of different shades, each of which is subdivided by circles, indicating the number of formations of which they are composed. The whole disk is divided by radiating lines into four segments, to include the four great departments of the Animal Kingdom ; the Vertebrates, with Man at their head, are placed in the upper compartment, the Articulates at the left, the Mollusks at the right, and the Radiates 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 to represent the primitive egg, with its germinative vesicle and germinative dot, (278,) indicative of the universal origin of all animals, and the epoch of life when all are appar- ently alike, (275, 276.) Surrounding this, at the point from which each department radiates, are placed the symbols of the several departments, as explained on page 155. The zones are traversed by rays which repre- sent the principal types of animals, and their origin and termination in- dicates the age at which they first appeared or disappeared, all those which reach the circumference being still in existence. The width of the ray in- dicates the greater or less prevalence of the type at different geological ages. Thus, in the class of Crustaceans, the Trilobites appear to com- mence in the earliest strata, and to disappear with the carboniferous for- mation. The Ammonites also appeared in the Silurian formation, and did not become extinct before the deposition of the Cretaceous rocks. The Belemnites appear in the lower Oolitic beds ; many 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 later than in the earlier Ages. Below the circle is a section, intended to show more distinctly the rel- ative position of the ten principal formations of stratified rocks (461) composing the four great geological ages ; the numerals corresponding to those on the ray leading to Man, in the circular figure. See also figure 154. 12 EXPLANATION OF THE FIGURES. THE CHART OF ZOOLOGICAL REGIONS, page 195, is intended to show the limits of the several Faunas of the American Continent, correspond- ing to the climatal regions. And as the higher regions of the mountains correspond 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. Simple cell, magnified, as seen in the house-leek. 2. Cells when altered by pressure upon each other ; from the pith of elder. 3. Nucleated cells, (a,) magnified; b, nucleolated cells. 4. Cartilaginous tissue from a horse, magnified 120 diameters. 5. Osseous tissue from a horse, magnified 450 diameters. 6. Nervous fibres, showing the loops as they terminate in the skin of a frog. 7. Gray substance of the brain, magnified. 8. Head of an embryo fish, to show its cellular structure throughout. 9. Diagram, to show the nervous system of the Vertebrates, as found in a monkey. 10. Diagram of the nervous system of the Articulates, as seen in a lobster. 11. Diagram of the nervous system of the Mollusks, as found in Natica heros. 12. Diagram of the nervous system of the Radiates, as found in Scutella, ( Echinarachnius parma. ) 13. Section of the eye. a, optic nerve ; b, sclerotic coat ; c, choroid coat; d, retina ; e, crystalline lens ; ft cornea ; g, iris ; h, vitreous body ; i, chamber, divided by the iris. 14. Diagram, showing the effect of the eye on rays of light. 15. Position of the eye of the snail. 16. Eyes (ocelli) of the spider. 17. Eye-spots of a star-fish, (Echinaster sanguinolentus.) 18. Compound eyes, showing the arrangement of the faoettes, and their connection with the optic nerve, as seen in a crab's eye. 19. Diagram of the human ear, to show the different chambers, canals, and bones. 20. Tympanum and small bones of the ear, twice the natural size ; ct tympanum ; m, malleus ; n, incus ; o, orbiculare : s, stapes. 21. Section of the brain of a crow, showing the origin of the nerves of the special senses. 22. Diagram of the larynx, in man. 23. Larynx of the merganser, (Mergus merganser.) 24. Nests of Ploceus Philippinus, male and female. 25. Distribution of nerves to the muscular fibres* 26. Test, or crust-like covering of an Echinoderm, (Cidaris.) EXPLANATION OF THE FIGURES. 13 FIG. 27. Muscular ribbons of the willow-moth, (Cossits ligniperda.) 28. Vertebra of a cod-fish. 29. Disposition of the muscles of the trout, (Salmo trutta.) 30. Disposition of the muscles of an owl, (Strix brachyotis.) 31. Jelly-fishes, (Stomobrachium cruciatum, Hippocrene Bougainvillii.) 32. Leech, showing the terminal cups. 33. Portion of a Nereis, showing the gills as organs of motion. 34-43. Modifications of the fore-arm. 34. Monkey. 35. Deer. 36. Tiger. 37. Whale. 38. Bat. 39. Pigeon. 40. Turtle. 41. Sloth. 42. Mole. 43. Whale. 44. Leg of a beetle. 45. Leg of a lizard. 46. Skeleton of a tiger. 47. Cuttle-fish, (Loligo illecebrosa.) 48. Sea-anemone, (Actinia marginata ;) a, mouth ; b, stomach ; c, general cavity of the body. 49. Planaria, showing the mouth, stomach, and its branches. 50. Jaws, stomach, and intestine of a sea-urchin, (Echinus lividus.) 51. Plan of the digestive organs of an insect. 52. Plan of the digestive organs of a land-slug, ( Tebennophorus Carolini- ensis. ) 53. Globules of chyle. 54. Portion of intestine, showing the lacteals of man, and their entrance into a vein. 55. Jaws of an Echinoderm, (Echinarachnhts parma.} 56. Jaws of a sea-ur.chin, (Echinus granulatus.} 57. Beak of a cuttle-.fish. 58. Portion of the tongue of a mollusk, (Natica heros,) magnified. 59. Jaws of an Annelide, (Nereis.) 60. Trophi (organs for taking food) of a beetle. 61. " of a bee. 62. 63. " of a squash-bug. 64. " of a butterfly. 65. " of a Rotifer, (Brackiomts.) 66. Jaws of ditto, magnified. 67. Skull of a tiger, showing the muscles for mastication. 68. Head of a snapping-turtle, (Emysaurus serpentina.} 69. Head of a Whale, showing the whalebone. 70. Head of an ant-eater. 71. Head of an alligator. 72. Head of a skate-fish, (Myliobatis,) showing the palate bone. 73. Head of a monkey, showing the three different kinds of teeth. 74. Teeth of an insectivorous animal, the mole. 75. Teeth of a carnivorous animal, the tiger. 76. Teeth of a rodent. 14 EXPLANATION OF THE FIGURES. FlG. 77. A polyp, (Tiibularia indivisa •) m, mouth ; o, ovaries ; p, tentacles. 78. Blood disks in man, magnified. 79. " " in birds, " 80. " " in reptiles, " 81. " " in fishes, " 82. Portion of a vein opened, to show the valves. 83. Network of capillary vessels. 84. Dorsal vessel of an insect, with its valves. 85. Cavities of the heart of mammals and birds. 86. " " " of a reptile. 87. " " " of a fish. 88. Heart and bloodvessels of a gasteropod mollusk, (Natica.) 89. Tracheae, or air tubes of an insect ; s, stigmata ; t, trachea. 90. Relative position of the heart and lungs in man. 91. Respiratory organs of a naked mollusk, (Polycera illuminata.) 92. Respiratory organs (gills) of a fish. 93. Vesicles and canals of the salivary glands. 94. Section of the skin, magnified, to show the sweat glands ; a, the cutis ; b, blood-layer ; c, epidermis ; g, gland imbedded in the fat-layer^/.) 95. Egg of a skate-fish, (Myliobatis.) 96. Egg of hydra. 97. Ege of snow-flea, (Podurella.) 98. Section of an ovarian egg ; d, germinative dot ; g, germinative vesi- cle ; s, shell membrane ; v, vitelline membrane. 99. Egg cases of Pyrula. 100. Monoculus bearing its eggs, a a. 101. Section of a bird's egg ; a, albumen ; c, chalaza ; e, embryo ; s, shell ; y, yolk. 102. Cell-layer of the germ. 103. Separation of the cell-layer into three layers ; s, serous or nervous layer; m, mucous or vegetative layer; v, vascular or blood layer. 104. Embryo of a crab, showing its incipient rings. 105. Embryo of a vertebrate, showing the dorsal furrow. 106-8. Sections of the embryo, showing the formation of the dorsal canal. 109. Section, showing the position of the embryo of a vertebrate, in re- lation to the yolk. 110. Section, showing the same in an articulate, (Podurella.) 111-22. Sections, showing the successive stages of development of the embryo of the white-fish, magnified. 123. Young white-fish just escaped from the egg, with the yolk not yet fully taken in. 124, 125. Sections of the embryo of a bird, showing the formation of the allantois ; e, embryo ; x x, membrane rising to form the amnios ; a, allantois ; y, yolk. 126. The same more fully developed. The allantois (a) is further de- EXPLANATION OF THE FIGURES. 15 FlG. veloped, and bent upwards. The upper part of the yolk (d d ) is nearly separated from the yolk sphere, and is to become the in- testine. The heart (A) is already distinct, and connected by threads with the blood-layer of the body. 127. Section of the egg of a mammal ; v, the thick vitelline membrane, or chorion ; y, yolk ; s, germinative dot ; g, germinative vesicle. 128. The same, showing the empty space (k) between the vitelline sphere and chorion. 129. Shows the first indications of the germ already divided in two layers, the serous layer, (s,) and the mucous layer, (m.) 130. The mucous layer (m) expands over nearly half of the yolk, and be- comes covered with many little fringes. 131. The embryo (e) is seen surrounded by the amnios, (6,) and covered by a large allantois, (a;) p e, fringes of the chorion ; p m, fringes of the matrix. 132. Hydra, showing its reproduction by buds. 133. Vorticella, showing its reproduction by division. 134. Polyps, showing the same. 135. A chain of Salpse. 136. An individual salpa ; m, the mouth ; a, embryos. 137. Cercaria, or early form of the Distoma. 138. Distoma, with its two suckers. 139. Nurse of the Cercaria. 140. The same, magnified, showing the included young. 141. Grand nurses of the Cercaria, enclosing the young nurses. 142. Stages of development of a jelly-fish, (Medusa ;) a, the embryo in its first stage, much magnified ; b, summit, showing the mouth ; ctfi ff> tentacles shooting forth ; e, embryo adhering, and form- ing a pedicle ; h, i, separation into segments ; d, a segment be- come free ; k, form of the adult. 143. Portion of a plant-like polyp, (Campanularia ;) a, the cup which bears tentacles ; b, the female cup, containing eggs ; c, the cups in which the young are nursed, and from which they issue. 144. Young of the same, with its ciliated margin, magnified. 145. Eye of the perch, containing parasitic worms, (Distoma.) 146. One of the worms magnified. 147. Transformations of the canker-worm, (Geometra vemalis •) a, the canker worm ; 6, its chrysalis ; c, female moth ; d, male moth. 148. Metamorphoses of the duck -barnacle, (Anatifa;) a, eggs, magnified ; b, the animal as it escapes from the egg ; c, the stem and eye ap- pearing, and the shell enclosing them ; d, animal removed from the shell, and further magnified ; e,f, the mature barnacle, affixed. 149. Metamorphoses of a star-fish, (Echinaster sanguinolentits,) showing the changes of the yolk, (e ;) the formation of the pedicle, (p;) and the gradual change into the pentagonal and rayed form. 16 EXPLANATION OF THE FIGURES. FIG. 150. Comatula, a West India species, in its early stage, with its stem. 151. The same detached, and swimming free. 152. Longitudinal section of the sturgeon, to show its cartilaginous ver- tebral column. 153. Amphioxus, natural size, showing its imperfect organization. 154. Section of the earth's crust, to show the relative positions of the rocks composing it ; E, plutonic or massive rocks ; M, metamor- phic rocks ; T, trap rocks ; L, lava. 1. Lower Silurian forma- tion ; 2. Upper Silurian ; 3. Devonian ; 4. Carboniferous ; 5. Trias, or Saliferous ; 6. Oolitic ; 7. Cretaceous ; 8. Lower Terti- ary or Eocene ; 9. Upper Tertiary, or Miocene, and Pleiocene ; 10. Drift. 155. Fossils of the Paleozoic age ; a, Lingula prima ; b, Lepteena alter- nata ; c, Euomphalus hemisphericus ; d, Trocholites ammonius ; e, Avicula decussata ; f, Bucania expansa ; g, Orthoceras fusi- forme ; i, Cyathocrinus ornatissimus, Hall ; j, Cariocrinus orna- tus, Say ; k, Melocrinus amphora, Goldf. ; I, Columnaria alveo- lata ; m, Cyathophyllum quadrigeminum, Goldf. ; n, o, Caninia fiexuosa ; p, Chseietes lycoperdon. 156. Articulata of the Palaeozoic age ; a, Harpes ; b, Arges ; c, Brontes ; d, Platynotus ; e, Eurypterus remipes. 157- Fishes of the Palaeozoic age ; a, Pterichthys ; b, Coccosteus ; c, Dipterus ; d, palatal bone of a shark ; e, spine of a shark. 158. Representations of the tracks of supposed birds and reptiles in the sandstone rocks. 159. Supposed outlines of Ichthyosaurus, (a,) and Plesiosaurus, (6.) 160. Supposed outline of Pterodactyle. 161. Shells of the Secondary age ; a, Terebratula ; b, Goniomya ; c, Trigonia ; d, Ammonite. 162. Supposed outline of the cuttle-fish, (a,) furnishing the Belemnite. 163. Radiata from the Secondary age ; a, Lobophyllia flabellum ; b, Litho- dendron pseudostylina ; c, Pentacrinus briareus ; d, Pterocoma pinnata ; e, Cidaris ; f, Dysaster ; ff, Nucleolites. 164. Shells of the Cretaceous formation ; a, Ammonites ; b, Crioceras ; c, Scaphites ; d, Ancyloceras ; e, Karaites ; f, Baculites ; g, Turrilites. 165. Shells of the Cretaceous formation ; a, Magas ; b, Inoceramus ; c, Hippurites ; d, Spondylus ; e, Pleurotomaria. 166. Radiata from the Cretaceous formation; a, Diploctenium cordatum; b, Marsupites ; d, Galerites ; c, Salenia ; e, Micraster cor- anguinum. 167- Nummulite. 168. Supposed outline of Paleotherium. 169. Supposed outline of Anoplotherium. 170. Skeleton of the Mastodon, in the cabinet of Dr. J. C. Warren. INTRODUCTION, EVERY art and science has a language of technical terms peculiar to itself. With those terms every 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 lion, 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 in every object 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 2* 18 INTHODUCTION. founded upon some of the minor peculiarities of anatomical structure, such as the number, disposition, or proportions of the teeth, claws, fins, dec., 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, jackal, 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 color, size, proportions, sculpture, &c. Thus we have different kinds, or species, of duck, different species of squirrel, different species of monkey, &c., varying from each 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 peculiarities, generally induced by some modification of native habits, such as are seen in domestic animals. These are called varieties, 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 ale wives, herrings, shad, &c., form a family called Clupeidas ; the crows, black- birds, jays, &c., form the family Corvidse. Families are combined to form orders, and orders form classes, and finally, classes are combined to form the four primary divisions, or departments, of the Animal Kingdom. For each of these groups, whether larger or smaller, we involuntarily 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 employ 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. INTRODUCTION. 19 Thus, we have a general idea of a bird ; but this idea does not correspond 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 because 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, however, 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, and so on. As we must necessarily make frequent allusions to ani- mals, with reference to their systematic arrangement, it seems requisite 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. The Animal Kingdom consists of four great divisions, which we call DEPARTMENTS, namely : I. The department of Vertebrates. II. The department of Articulates. III. The department of Mollusks. IV. The department of Radiates. I. The department of VERTEBRATES 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. 20 INTRODUCTION. 3. Reptiles. 4. Fishes. The class of MAMMALS is subdivided into three orders : a. Beasts of prey, (Carnivora.) b. Those which feed on vegetables, (Herbivora.) c. Animals of the whale kind, (Cetaceans.) The class of BIRDS is div.ided into four orders, namely, a. Perching Birds, (Insessores.) b. Climbers, (Scansores.) c. Waders, (Grallatores.) d. Swimmers, (Natatores.) The class of REPTILES is divided into five orders : a. Large reptiles with hollow teeth, most of which are now extinct, (Rhizodonts.) b. Lizards, (Lacertians.) c. Snakes, (Ophidians.) d. Turtles, (Chelonians.) e. Frogs and Salamanders, (Batrachians.) The class of FISHES is divided into four orders : a. Those with enamelled scales, like the gar-pike, (Ganoids,') fig. 157. c. 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.) INTRODUCTION. 21 d. Those whose scales are entire, and whose fin rays are soft, like the salmon, (Cycloids.) II. Department of ARTICULATES. Animals whose body is composed of rings or joints. It embraces three classes : 1. Insects. 2. Crustaceans, like the crab, lobster, &c. 3. Worms. The class of INSECTS includes three orders : a. Those with a trunk for sucking fluids, like the butter- fly, (Suctoria,) fig. 62-64. b. Those which have jaws for dividing their food, (Man- ducata,) fig. 60. c. Those destitute of wings, like spiders, fleas, millipedes, &c., (Aptera.) The class CRUSTACEANS may be divided as follows : a. Those furnished with a shield, like the crab and lob- ster, (Malacostraca.) ~b. Such as are not thus protected, (Entomostraca.) c. An extinct race, intermediate between these two, (Trilobites,) fig. 156. The class of WORMS comprises three orders : a. Those which have thread-like gills about the head, ( Tubulibranchiates.) b. Those whose gills are placed along the sides, (Dor- sibranchiates.) c. Those who have no exterior gills, like the earth-worm, (Abranchiates,) and also the Intestinal Worms. 22 INTRODUCTION. III. The department of MOLLUSKS is divided into three classes, namely : 1. Those which have arms about the mouth, like the cuttle-fish, (Cephalopods,) fig. 47. 2. Those which creep on a flattened disk or foot, like snails, (Gasteropods,} fig. 88. 3. Those which have no distinct head, and are inclosed in a bivalve shell, like the clams, (Acephals.) The CEPHALOPODS may be divided into a. The cuttle-fishes, properly so called, ( Teuthideans,) fig. 47. 1). Those having a shell, divided by sinuous partitions into numerous chambers, (Am?nonites^) fig. 164. c. Those having a chambered shell with simple par- titions, (Nautilus.} The GASTEROPODS contain four orders : a. The land snails which breathe air, (Pulmonates.) I. The aquatic snails which breathe water, (Branch- ifers,} fig. 88. c. Those which have wing-like appendages about the head, for swimming, (Pteropods.) d. A still lower form allied to the Polyps by their gen- eral appearance, (Rhizopods or Fora?ninifera.) The class of ACEPHALS contains three orders : a. Those having shells of two valves, (bivalves,) like the clam and oyster, (Lamellibrancliiates.} b. Those having two unequal valves, and furnished with peculiar arms, (Brachiopods.) INTRODUCTION. 23 c. Mollusks living in chains or clusters, like the Salpa, fig. 135 ; or upon plant-like stems, like Flustra, (Bryo- zoa.) IV. The department of RADIATES is divided into three classes : 1. Sea-urchins, bearing spines upon the surface, (Echin- oderms,) figs. 12, 26. 2. Jelly-fishes, (Acalephs,) fig. 31. 3. Polyps, fixed like plants, and with a series of flexible arms around the mouth, figs. 48, 77, 143. The ECHINODERMS are divided into four orders : a. Sea-slugs, like biche-le-mar, (Holothurians.) T). Sea-urchins, (Echini,) fig. 26. c. Free star-fishes, (Asterida,') fig. 17. d. Star-fishes mostly attached by a stem, (Crinoids,) figs. 150, 151. The ACALEPHS include the following orders : a. Those furnished with vibrating hairs, by which they move, (Ctenophorce.) 1. The Medusas, or common jelly-fishes, (Discophora,) figs. 31, 142. c. Those provided with aerial vesicles, (Siphonophora.) The class of POLYPS includes two orders. a. The so-called fresh-water polyps, and similar marine forms, with lobed tentacles, (Hydroids,) fig. 143. b. Common polyps, like the sea-anemone and coral- polyp, (Actinoids,) fig. 48. In addition to these, there are numberless kinds of micro- 24 INTRODUCTION. scopic animalcules, commonly united under the name of infusory animals, (Infusoria,) from their being found specially abundant in water infused with vegetable matter. These minute beings do not, however, constitute a natural group in the Animal Kingdom. Indeed, a great many that were for- merly supposed to be animals are now found to be vegetables. Others are ascertained to be crustaceans, mollusks, worms of microscopic size, or the earliest stages of development of larger species. In general, however, they are exceedingly minute, and exhibit the simplest forms of animal life, and are now grouped together, under the title of Protozoa. But, as they are still very imperfectly understood, notwithstand- ing the beautiful researches already published on this sub- ject, and as many of them are likely to be finally distributed among vegetables, and the legitimate classes in the Animal Kingdom to which they belong, we have not assigned any special place for them. PHYSIOLOGICAL ZOOLOGY. CHAPTER FIRST. THE SPHERE AND FUNDAMENTAL PRINCIPLES OF ZOOLOGY. 1. ZOOLOGY is that department of Natural History which relates to animals. 2. To enumerate and name the animals which are found on the globe, to describe their forms, and investigate then- habits and modes of life, are the principal, but by no means the only objects of this science. Animals are worthy of our regard, not merely when considered as to the variety and ele- gance of their forms, or their adaptation to the supply of our wants ; but the Animal Kingdom, as a whole, has a still higher signification. It is the exhibition of the divine thought, as carried out in one department of that grand whole which we call Nature ; and considered as such, it teaches us most important lessons. 3. Man, in virtue of his twofold constitution, the spiritual and the material, is qualified to comprehend Nature. 3 26 SPHERE AND FUNDAMENTAL Being 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 other animals, he is also in a condition to understand the mechanism of organs, and to appreciate the necessities of matter, as well as the influence which it exerts over the in- tellectual element throughout the domain of Nature. 4. The spirit and preparation we bring to the study of Nature, is a matter of no little consequence. When we would study with profit a work of literature, we first endeavor to make ourselves acquainted with the genius of the author ; and in order to know what end he had in view, we must have regard to his previous labors, and to the circumstances under which the work was executed. Without this, although we may perhaps enjoy its perfection as a whole, and ad- mire the beauty of its details, yet the spirit which pervades it will escape us, and many passages may even remain un- intelligible. 5. So, in the study of Nature, we may be astonished at the infinite variety of her products ; we may even study some portion of her works with enthusiasm, and neverthe- less remain strangers to the spirit of the whole, ignorant of the plan on which it is based, and fail to acquire a proper conception 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 pres- ent time, this picture also embraces the extinct races which are now known to us by their fossil remains only. And these are of the greatest importance, since they furnish us with the means of ascertaining the changes and modifica- tions which the Animal Kingdom has undergone in the sue- PRINCIPLES OF ZOOLOGY. 27 cessive creations, 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 knowledge in Zoology. A century ago, the number of known animals did not exceed 8000 ; that is to say, from the whole Animal Kingdom, fewer species were then known than are now contained in many private collections of certain families of insects merely. At the present day, the number of living species which have been satisfac- torily made out and described, is more than 50,000.* The fossils already described exceed 6000 species ; and if we * The number of vertebrate animals may be estimated at 20,000. About 1500 species of mammals are pretty precisely known, and the num- ber may probably be carried to about 2000. The number of Birds well known is 4 or 5000 species, and the probable number is 6000. The Reptiles number about the same as the Mammals, 1500 described species, and they 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 Mollusks already in collections probably reaches 8 or 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, therefore, 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 col- lections 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 so 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, including echini, star-fishes, me- dusae, and polypi, and we have about 250,000 species of living animals ; and supposing the number of fossil species only to equal them, we have, at a very moderate computation, half a million of species. 28 SPHERE AND FUNDAMENTAL consider that wherever any one stratum of the earth has been well explored, the number of species 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 enlarged, it at the same time becomes more intelligible to those who are competent to seize its promi- nent traits. 9. To give a detailed account of each and all of these animals, and to show their relations to each other, is the task of the Naturalist. The number and extent of the vol- umes already published upon the various departments of Natural History show, that only a mere outline of a domain so vast could be fully sketched in an elementary work, and that none but those who make it their special study can be expected to survey its individual parts. 10. Every well-educated person, however, is expected to have a general acquaintance with the great natural phe- nomena constantly displayed before his eyes. There is a general knowledge of man and the subordinate animals? embracing their structure, races, habits, distribution, mutual relations, &c., which is not only calculated to conduce es- * 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. PRINCIPLES OF ZOOLOGY. 29 sentially to our happiness, but which it would be quite inex- cusable to neglect. This general view of Zoology, it is the purpose of this work to afford. 11. A sketch of this nature should render prominent the more general features of animal life, and delineate the ar- rangement of the species according to their most natural relations and their .rank in the scale of being ; thus giving a panorama, as it were, of the entire Animal Kingdom. To accomplish 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 peculiar office in the economy of nature ; and a complete adaptation to fulfil all the purposes of its creation, 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 limited in its operation ; in others, extremely complicated, and capable of exercising a great variety of functions. 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, an animal, like a quad- ruped, or a .bird, which has the five senses fully developed, and which has, moreover, the faculty of readily trans- porting 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, when separately considered, is found to have every degree of complication, and, consequently, every degree of nicety in the perform- ance of its function. Thus, the eye-spots of the star-fis-h and jelly-fish are probably endowed with merely the fac- 30 SPHERE AND FUNDAMENTAL ulty of perceiving light, without the power of distinguishing objects. The keen eye of the bird, on the contrary, dis- cerns minute objects at a great distance, and when compared with the eye of a fly, is found to be not only more perfect, 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 exam- ination of their structure ; they must never be disjoined, and must precede the systematic distribution of animals into classes, families, 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 even serve for very dif- ferent uses. Analogy, on the contrary, indicates the simi- larity of purposes or functions performed by organs of dif- ferent structure. 17. Thus, there is an analogy between the wing of a bird and that of a butterfly, since botli of them serve for flight. But there is no affinity between them, since, as we shall hereafter see, they differ totally in their anatomical relations. On the other hand, there is an affinity between the bird's wing and the hand of a monkey ; since, although they serve for different purposes, the one for flight, and the other for climbing, they are both constructed on the same plan. Accordingly, the bird is more nearly allied to the monkey than to the butterfly, though they both have in common the faculty of flight. Affinities, and not analogies, therefore, must guide us in the arrangement of animals. PRINCIPLES OF ZOOLOGY. 31 18. Our investigations should not be limited to adult animals, but should also include 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 predomi- nant character in the full-°;rown animal, but which are shaded O ' off, and vanish, as we revert to the earlier periods of life. 19. Thus, for example, by regarding only adult individu- als, we might be induced to divide all animals into two groups, according to their mode of respiration ; uniting, on the one hand, all those which breathe by gills, and, on the other, those which breathe by lungs. But this distinction loses its importance, when we consider that various animals, for example, frogs, which respire by lungs in the adult state, have only gills when young. It is thence evident that the respiratory organs cannot be taken as a satisfactory basis of our fundamental classification. They are, as we shall see, subordinate to a more important system, namely, the nervous system. 20. Again, we have a means of appreciating the relative grade of animals by the comparative study of their devel- opment. It is evident that the caterpillar, in becoming a butterfly, passes from a lower to a higher state. Clearly, therefore, animals resembling the caterpillar, the worms, for instance, must occupy a lower rank than those approaching the butterfly, like most insects. There is no animal which does not undergo a series of changes similar to those of the o o 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 egg some days previous to the time of hatching, we find in it a living ani- mal, which, although imperfect, is nevertheless a chicken : 32 SPHERE AND FUNDAMENTAL it has been developed from a hen's egg, and we know that, should it continue to live, it would infallibly display all the characteristics of the parent bird. Now, if there existed in Nature an adult bird as imperfectly organized as the chicken on the day, or 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 at length be- come entirely dissimilar. For example, the myriads of minute aquatic animals embraced under the name of Infu- soria, generally very simple in their organization, 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 are found members of all the lower classes of animals, mollusks, crustaceans, worms, &c. ; and many of them are even found to belong to the Vegetable Kingdom. 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 from those of tropical regions. Certainly, no one will maintain it to be the effect of accident that the monkeys, the most perfect of all brute animals, are found only in hot countries ; or that by chance merely the white bear and reindeer inhabit only cold regions. 24. Nor is it by chance that most of the largest animals, of every class, the whales, the aquatic birds, the sea-turtles, the crocodiles, dwell in the water rather than on the land. And while the water affords freedom of motion to the largest, it is also the home of the smallest of living beings, allow- ing a degree of liberty to their motion, which they could not enjoy elsewhere. PRINCIPLES OF ZOOLOGY. 33 25. Nor are our researches to be limited to the animals now living. 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 present day. Many of these remains present forms so extraordinary that it is almost im- possible to trace their alliance with any animal now living. In general, they bear a striking analogy to the em- bryonic forms of existing species. For example, the curi- ous fossils known under the name of Trilobites (Fig. 156) 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 do not hesitate to refer them to the crustaceans. We shall also see that some of the Fishes of ancient epochs present shapes altogether peculiar to them- selves, (Fig. 157,) but resembling, in a striking manner, the embryonic forms of our common fishes. A determination of the successive appearance of animals in the order of time is, therefore, of much importance in assisting to decide the relative rank of animals. 26. Besides the distinctions to be derived from the varied structure of organs, there are others less subject to rigid analysis, but no less decisive, to be drawn from the imma- terial principle with which every animal is endowed. It is this which determines the constancy of species from genera- tion to generation, and which is the source of all the varied exhibitions of instinct and intelligence which we see dis- played, from the simple impulse to receive the food which is brought within their reach, as observed in the polyps, through the higher manifestations, in the cunning fox, the sagacious elephant, the faithful dog, to the exalted intellect of man, which is capable of indefinite expansion. 27. Such are some of the general aspects in which we are to contemplate the animal creation. Two points of 34 FUNDAMENTAL PRINCIPLES OF ZOOLOGY. view should never be lost sight of, nor disconnected, namely, the animal in respect to its own organism, and the animal in its relations to creation as a whole. By adopting too exclusively either of these points of view, we are in danger of falling either into gross materialism, or into vague and profitless pantheism. He who beholds in Nature nothing besides organs and their functions, may persuade himself that the animal is merely a combination of chemical and mechanical actions and reactions, and thus becomes a mate- rialist. 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 physical laws by virtue of which all beings preserve their characteristics, will be very likely to confound the Creator with the creature. 29. It is only as it contemplates, at the same time, matter and mind, that Natural History rises to its true character and dignity, and leads to its worthiest end, by indicating to us, in Creation, the execution of a plan fully matured in the beginning, and undeviatingly pursued ; the work of a God infinitely wise, regulating Nature according to immutable laws, which He has himself imposed on her. CHAPTER SECOND. GENERAL PROPERTIES OF ORGANIZED BODIES. SECTION I. ORGANIZED AND UNORGANIZED BODIES. 30. NATURAL 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 organ- ized bodies, (vegetables and animals.) These two groups have nothing in common, save the universal properties of matter, such as weight, extension, &c. They differ at the same time as to their form, their structure, their chemical composition, and their mode of existence. 32. The distinctive characteristic of inorganic bodies is rest ; the distinctive trait of organized bodies is independent motion, LIFE. The rock or the crystal, once formed, never changes from internal causes ; its constituent parts or mole- cules 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 36 ELEMENTARY STRUCTURE OF ORGANIZED BODIES. the tree, the blood flows through the animal, and in both there is, besides, the incessant movement of growth, decom- position, and renovation. 33. Their mode of formation is also entirely different. Unorganized bodies are either simple or made up of ele- ments unlike themselves ; and when a mineral is en- larged, 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 interstitially, by the successive assimilation of new particles, derived from various sources. 34. Finally, organized bodies are limited in their duration. Animals and plants are constantly losing some of their parts by decomposition during life, which at length cease to be supplied, and they die, after having lived for a longer or shorter period. Inorganic bodies, on the contrary, contain within themselves no principle of destruction ; and unless subjected to some foreign influence, a crystal or a rock would never change. The limestone and granite of our mountains remain just as they were formed in ancient geological epochs ; while numberless generations of plants and ani- mals have lived and perished upon their surface. SECTION II. ELEMENTARY STRUCTURE OF ORGANIZED BODIES. 35. The exercise of the functions of life, which is the essential characteristic of organized bodies, (32,) requires a degree of flexibility of the organs. This is secured by means of a certain quantity of watery fluid, which pene- ELEMENTARY STRUCTURE OF ORGANIZED BODIES. 37 trates all parts of the body, and forms one of its principal constituents. 36. All living bodies, without exception, are made up of tissues so constructed as to be permeable to liquids. There is no part of the body, no organ, however hard and compact it may appear, which has not this peculiar structure. It ex- ists in the bones of animals, as well as in their flesh and fat ; in the wood, however solid, as well as in the bark and flowers of plants. It is to this general structure that the term or- ganism 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 of the organic struc- tures, 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 Fig. 1. from each other are called intercellular passages or spaces, (m.} When the cellules are very numerous, and crowd each other, their outlines become angular, and the intercel- lular spaces disappear, as seen in figure 2, which represents * Formerly, animals and plants were said to Reorganized, because they are furnished with definite parts, called organs, which execute particular functions. Thus, animals have a stomach, a heart, lungs, &c. ; plants have leaves, petals, stamens, pistils, roots, &c., which are indispensable to the maintenance of life and the perpetuation of the species. Since the discovery of the fundamental identity of structure of animal and vegetable tissues, a common denomination for this uniformity of texture has been justly preferred ; and the existence of tissues is now regarded as the basis of organization. 4 38 ELEMENTARY STRUCTURE OF ORGANIZED BODIES. the pith of the elder. They then have the form of a honey-comb ; whence they have derived their name of cellules. 38. All the organic tissues, whether animal or vegetable, originate from cells. The cell is to the organ- Fig. 2. ized 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 a o cells ; but they alike contain a central dot or vesicle, called nucleus. Hence such cells are called nucleated cells, (Fig. 3, a.) Sometimes the nucleus itself contains a still smaller dot, called nucleolus, (b.) 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 exam- ination, to detect their original cellular structure. 40. Several kinds of tissues have been designated in the animal structure ; but their differences 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. The areolar tissue consists of a network of delicate fibres, intricately interwoven so as to leave numberless communicating interstices, filled with fluid. It is inter- posed 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. 42. The cartilaginous tissue is composed of nucleated ELEMENTARY STRUCTURE OF ORGANIZED BODIES. 39 Fig. 4. Fig. 5. cells, the intercellular spaces being filled with a more com- pact substance, called the hyaline matter. Figure 4 repre- sents a slip of cartilage from the horse, under a magnifying power of one hundred and twen- ty diameters. 43. The osseous or bony tissue differs from the cartilaginous tissue, in having its meshes filled with salts of lime, instead of hyaline sub- stance, whence its compact and solid appear- ance. 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, as is seen in figure 5, representing a section of a bone of a horse, magnified four hundred times. 44. The muscular tissue, which forms the flesh of ani- mals, is composed of bundles of parallel fibres, which pos- sess the peculiar property of contracting or shortening them- selves, under the influence of the nerves. In the muscles under the control of the will, the fibres 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. 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 figure 6, representing nervous threads as they terminate in the skin of a frog. The same fibrous structure is found in the white portion of the brain. But the gray substance of the brain is composed of very minute granulations, interspersed with clusters of larger cells, as seen in figure 7. Fig. 7. Fig. 6. 40 ELEMENTARY STRUCTURE OF ORGANIZED BODIES. 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 made up of nothing but cells in contact with each other. Such is the case with the polyps; yet they contract, secrete, absorb, and repro- duce; and most of the Infusoria move freely, by means of little fringes on their surface, arising from a peculiar kind of 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, con- tains not only all the tissues we have mentioned, namely, bone, cartilage, muscle, nerve, brain, and membranes, but also bloodves- sels, glands, pigments, &c. Let us, however, examine it during the embryonic state, while it is yet in Fig. 8. the egg, and we 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 sur- rounding the eye a little larger, and those beneath being still larger, (Fig. 8.) It is only at a later period, after still further development, 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. DIFFERENCES BETWEEN ANIMALS AND PLANTS. 41 SECTION III. DIFFERENCES BETWEEN ANIMALS AND PLANTS. 49. At first glance, nothing would seem more widely different than animals and plants. What is there in com- mon, for instance, between an oak or an elm, and the bird which seeks shelter amid their foliage ? 50. The differences are usually so obvious, that this question would be superfluous if applied only to the higher forms of the two kingdoms. But this contrast diminishes, in proportion as their structure is simplified ; and as we descend to the lower forms, the distinctions are so few and so feebly characterized, that it becomes at length dif- ficult 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 of the polypi, that they have generally been classed among animals, although in reality they be- long to the vegetable kingdom. 51. Animals and plants differ in the relative predomi- nance of the elements, oxygen, carbon, hydrogen and nitro- gen, of which they are composed. In vegetables, only a small proportion of nitrogen is found ; while it enters largely into the composition of the animal tissues. 52. Another peculiarity of the Animal Kingdom is, the presence of large, distinctly limited cavities, usually intended for the lodgment of certain organs ; such is the skull and the chest in the higher animals, the cavity of the gills in fishes, and of the abdomen, or general cavity of the body, which exists in all animals, without exception, for the pur- pose of digestion, or the reception of the digestive organs. 53. The well-defined and compact forms of the organs 4* 42 DIFFERENCES BETWEEN ANIMALS AND PLANTS. 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 lungs, instead of being condensed into one organ, are scattered independently in countless numbers over the branches. Nor is there any organ corresponding to the brain, the heart, the liver, or the stomach. 54. Moreover, the presence of a proper digestive cavity involves marked differences between the two kingdoms, in respect to alimentation or the use of food. In plants, the fluids absorbed by the roots are carried, through the trunk and all the branches, to the whole plant, before they arrive at the leaves, where they are to be digested. In animals, on the contrary, the food is at once received into the diges- tive cavity, where it is elaborated ; and it is only after it has been thus dissolved 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 substances ; and they produce albumen, sugar, starch, &c., while animals consume them. 55. Plants commence their development from a single point, the seed, and, in like manner, all animals are devel- oped 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 limit 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, generally 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 develop- DIFFERENCES BETWEEN ANIMALS AND PLANTS. 43 ment of new branches. Some of the lowest animals, how- ever, the polyps for instance, increase in a somewhat analo- gous manner, (§ 329, 330.) 56. 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 de- structive to animal life ; while plants, by respiration, which they in most instances perform by means of the leaves, reverse the process, and thus furnish oxygen, which is so essential to animals. If an animal be confined in a small portion of air, or water containing 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 no difficulty is experienced. The practical effect of this compensation, in the economy of Nature, is obviously most important ; vegetation restoring to the atmosphere what is consumed by animal respiration, combustion, &c., and vice versa. 57. But there are two things 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 perceiv- ing other objects or their influences ; in other words, volun- tary motion and sensation. 58. All animals are susceptible of undergoing 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 de- gree of cold, or to the action of poisons. But they have no consciousness of these influences, and suffer no pain ; while animals under similar circumstances suffer. Hence they have been called animate beings, in opposition to plants, which are inanimate beings. CHAPTER THIRD. FUNCTIONS AND ORGANS OF ANIMAL LIFE. SECTION I. OF THE NERVOUS SYSTEM AND GENERAL SENSATION. 59. LIFE, in animals, is manifested by two sorts of func- tions, viz. : First, the peculiar functions of animal life, or those of relation, which include the functions of sensation and voluntary motion ; those which enable us to approach, and perceive our fellow beings and the objects about us, and to bring us into relation with them : Second, the functions of vegetative life, which are nutrition in its widest sense, and reproduction ; * those indeed which are essential to the maintenance and perpetuation of life. 60. The two distinguishing characteristics of animals, namely, sensation and motion, (57,) depend upon special systems of organs, which are wanting in plants, the nervous system and the muscular system under its influence. 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. * 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, p. 112. NERVOUS SYSTEM AND GENERAL SENSATION. 45 61. Greatly as the form, the arrangement, and the vol- ume of the nervous system va.ry in different animals, they may all be reduced to four principal types, which correspond, moreover, to the four great departments of the Animal Kingdom. In the vertebrate animals, namely, the fishes, reptiles, birds, and mammals, the nervous svs- j tern is composed of two prin- cipal masses, the spinal mar- row, (Fig. 9, c,) which runs along the back, and the brain, contained within the skull.* The volume of the brain is proportionally larger as the animal occupies a more elevated rank in the scale of being. Man, who stands at the head of Crea- tion, is in this respect also the most highly endowed being. Fig. 9. 62. With the brain and spinal marrow are connected the nerves, which are distributed, in the form of branching threads, through every part of the body. The branches which unite with the brain are twelve pairs, called the cere- * The brain is composed of several distinct parts which vary greatly, in their relative proportions, in different animals, as will appear hereafter. They arc — 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 9 and 21.) The spinal marrow is made up by the union of four nervous columns. 46 NERVOUS SYSTEM AND GENERAL SENSATION. bral nerves, and are designed chiefly for the organs of sense located in the head. Those which join the spinal marrow are also in pairs, one pair for each vertebra or joint of the back. The number of pairs varies, therefore, in different classes and families, according to the number of vertebrae. Each nerve is double, in fact, being composed of two threads, which at their junction with the spinal mar- row are separate, and afterwards accompany each other throughout their whole course. The anterior thread trans- mits the commands of the will which induce motion ; the other receives and conveys impressions to the brain, to pro- duce sensations. 63. In the Articulated animals, comprising the crabs, barnacles, worms, spi- ders, insects, and oth- er animals formed of rings, the nervous sys- 10. tern consists of a se- ries of small centres or swellings, called ganglions, (Fig. 10,) placed beneath the alimentary canal, on the floor of the gen- eral cavity of the body, and connected by threads ; and of a more considerable mass placed above the oesophagus or throat, connected with the lower ganglions by threads which form a collar around the alimentary canal. The number of ganglions generally corresponds to the number of rings. 64. In the Mollusks, (Fig. 11,) the nervous system con- sists of a single ganglionic circle, the principal swell- ings of which are placed symmetrically above and below the oesophagus, and from whence the filaments, Fig- 11- which supply the organs in different directions, take their origin. NERVOUS SYSTEM AND GENERAL SENSATION. 47 Fijr. 12. 65. In the Radiata, (Fig. 12,) the nervous system is re- duced to a single ring, encircling the mouth, and giving off threads towards the circumference. It dif- fers essentially from that of the Mollusks, by being disposed in a horizontal position, and by its star- like form. 66. The nerves branch off and diffuse sensibility to every portion of the body, and thereby men and the higher animals are enabled to gain a knowledge of the general properties of the objects which surround them ; every point of the body being made capable of determining whether an object is hot or cold, dry or moist, hard or soft, &c. There are some parts, however, the ends of the fingers, for exam- ple, in which this sensibility is especially acute, and these also receive a larger supply of nerves. 67. On the contrary, those parts which are destitute of sensibility, such as the feathers of birds, the wool of ani- mals, or the hair of man, are likewise destitute of nerves. But the conclusive proof that sensibility resides in the nerves is, that when the nerve which supplies any member of the body is severed, that member at once becomes insensible. 68. There are animals in which the faculty of percep- tion is limited to this general sense ; but their number is small, and, in general, they occupy the lowest place in the series. Most animals, in addition to the general sensibility, are endowed with peculiar organs for certain kinds of per- ceptions, which are acted upon by certain kinds of stimuli, as light, sound and odor, and which are called the SENSES. These are five in number, namely : sight, hearing, smell, taste, and touch. 48 SPECIAL SENSES. SECTION II. OF THE SPECIAL SENSES. 1. Of Sight. 69. Sight is the sense by which light is perceived, and by means of which the outlines, dimensions, relative posi- tion, color and brilliancy of objects are discerned. Some of these properties may be also ascertained, though in a less perfect manner, by the sense of touch. We may obtain an idea of the size and shape of an object, by handling it ; but the properties that have a relation to light, such as color and brilliancy, and also the form and size of bodies that are be- yond our reach, can be recognized by sight only. 70. The EYE is the organ of vision. The number, struc- ture, and position of the eyes in the body is considerably varied in the different classes. But whatever may be their position, these organs in all the higher animals are in connec- tion with particular nerves, called the optic nerves, (Fig. 13, a.) In the vertebrates, these are the second pair of the cer- ebral nerves, and arise directly from the middle mass of the brain, (Fig. 21, &,) which, in the embryo, is the most con- siderable of all. 71. Throughout the whole series of vertebrate animals, the eyes are only two in num- ber, and occup)' bony cavities of the skull, called the orbits. The organ is a globe or hollow sphere formed by three princi- pal membranes, enclosed one within the other, and filled with transparent matter. Figure 13 «^i..UiUU.iu>u.!y..uu...n,.u, represents a vertical section OF SIGHT. 49 through the eye, from before backwards, and will give an idea of the relative position of these different parts. 72. The outer coat is called the sclerotic, (o ;) it is a thick, firm, white membrane, having its anterior portion transparent. This transparent segment, which seems set in the opaque portion, like a watch-glass in its rim, is called the cornea, (f.) 73. The inside of the sclerotic is lined by a thin, dark- colored membrane, the cJioroid, (c.) It becomes detached from the sclerotic when it reaches the edge of the cornea, and forms a curtain behind it. This curtain gives to the eye its peculiar color, and is called the iris, (g.) The iris read- ily contracts and dilates, so as to enlarge or diminish an open- ing at its centre, the pupil, according as more or less light is desired. Sometimes the pupil is circular, as in man, the dog, the monkey ; sometimes in the form of a vertical ellipse, as in the cat ; or it is elongated sidewise, as in the sheep. 74. The third membrane is the retina, (fZ.) It is formed by the optic nerve, which enters the back part of the eye, by an opening through both the sclerotic and choroid coats, and expands upon the interior into a whitish and most delicate membrane. It is upon the retina that the images of objects are received, and produce impressions, which are conveyed by the nerve to the brain. 75. The fluids which occupy the cavity of the eye are of different densities. Behind, arid directly opposite to the pupil, is placed a spheroidal body, called the crystalline lens, (e.) It is tolerably firm, perfectly transparent, and composed of layers of unequal density, the interior being always more compact than the exterior. Its form varies in different classes of animals. In general, it is more convex in aquatic than in land animals ; whilst with the cornea it is directly the con- trary, being flat in the former, and convex in the latter. 76. By means of the iris, the cavity, (i,) in front of the crys- 5 50 SPECIAL SENSES. talline lens is divided into two compartments, called the an- terior and posterior chambers. The fluid which fills these chambers is a clear watery liquid, called the aqueous humor. The portion of the globe behind the lens, which is much the largest, is filled by a gelatinous liquid, perfectly transparent, like that of the chambers, but somewhat more dense. This is called the vitreous humor, (h.} 77. The object of this apparatus is to receive the rays of light, which diverge from all points of bodies placed before it, and to bring them again to a point upon the retina. It is a well-known fact, that when a ray of light passes obliquely from one medium to another of different density, it will be refracted or turned out of its course more or less, according to the difference of this density, and the obliquity at which the ray strikes the surface. This may be illustrated by the following figure, (Fig. 14.) A/ E Fig. 14. The ray a c, which strikes the cornea A B perpendicularly, continues without deviation, until it reaches the bottom of the eye at c. But the rays a m and a n, which strike the eye obliquely, change their direction, and instead of proceeding onward to m g and n d, take the direction m i and n f. A. still further refraction, though less considerable, is occasioned by passing through the crystalline lens C D, and the vitreous humor, so that the two rays, m i and nf, will at last meet in a point. This point is called the focus, (c,) and in distinct vision is always precisely at the retina, E F. 78. From this arrangement, the image found upon the OF SIGHT. 51 retina will be inverted. We may satisfy ourselves of this by direct observation. The eye of the white rabbit being destitute of the black pigment of the choroid, is quite trans- parent. Take the eye, soon after the death of the animal, and arrange it in one end of a tube, so that the cornea will face outwards ; then if we look in at the other end of the tube, we may see objects to which it is directed exactly pictured upon the retina, but in a reversed position. 79. The mechanical structure of the eye may be per- fectly imitated by art. Indeed, the camera obscura is an instrument constructed on the very same plan. By it, exter- nal objects are pictured upon a screen, placed at the bottom of the instrument, behind a magnifying lens. The screen represents the retina ; the dark walls of the instrument represent the choroid ; and the cornea, the crystalline lens and the vitreous humor combined, are represented by the magnifying lens. But there is this important difference, that the eye has the power of changing its form, and of adapt- ing itself so as to discern with equal precision very remote, as well as very near, objects. 80. By means of muscles which are attached to the ball, the eyes may be rolled in every direction, so as to view ob- jects on all sides, without moving the head. The eyes are usually protected by lids, which are two in the mammals, and generally furnished with a range of hairs at their edges, called eye-lashes. Birds have a third lid, which is vertical ; this is also found in most of the reptiles and a few mam- mals. In fishes, the lids are wanting, or immovable. 81. The eye constructed as above described is called a simple eye, and belongs more especially to the vertebrate animals. In man, it arrives at its highest perfection. In him, the eye also performs a more exalted office than mere vision. It is a mirror, in which the inner man is reflected. His passions, his joys, and his sorrows, his inmost self, are 52 SPECIAL SENSES. revealed, with the utmost fidelity, in the expression of his eye, and it has been rightly called " the window of the soul." 82. Many of the invertebrate animals have the eye constructed upon the same plan as that of the vertebrate animals, but with this essential difference, that the optic nerve which forms the retina is not derived from a ner- vous centre, analogous to the brain, but arises from one of the ganglions. Thus, the eye of the cuttle-fish contains all the essential parts of the eye of the superior animals, and, what is no less important, they are only two in number, placed upon the sides of the head. 83. The snail and kindred animals have, in like manner, only two eyes, mounted on the tip of a long stalk, (the tentacle,} or situated at its base, or on a short pedestal by its side. Their struc- ture is less perfect than in the cuttle- Fig. 15. fish? but still there is a crystalline lens, and more or less distinct traces of the vitreous body. Some bivalve mollusks, the scollops for example, have likewise a crystalline lens, but instead of two eyes, they are furnished with numerous eye-spots, which are arranged like a border around the lower margin of the animal. 84. In spiders, the eyes are likewise simple, and usually eight in number. These little organs, usually called ocelli, instead of being placed on the sides of the body or of the head, occupy the anterior part of the back. All the essen- . 16. tial parts of a simple eye, the cornea, the crystalline lens, the vitreous body, are found in OF SIGHT. 53 them, and even the choroid, which presents itself in the form of a black ring around the crystalline lens. Many in sects, in their caterpillar state, also have simple eyes. 1 85. Rudiments of eyes have been observed in very many of the worms. They generally appear as small black spots on the head ; such as are seen on the head of the Leech, the Planaria and the Nereis. In these latter animals there are four spots. According to Muller, they are small bodies, rounded behind, and flattened in front, composed of a black, cup-shaped membrane, containing a small white, opaque body, which seems to be a continuation of the optic nerve. It cannot be doubted, therefore, that these are eyes ; but as they lack the optical apparatus which produces images, we must suppose that they can only receive a general impression of light, without the power of discerning objects. 86. Eye-spots, very similar to those of the Nereis, are found at the extremity of the rays of some of the star-fishes, ^ in the sea-urchins, at the mar- gin of many Medusae, and in some Polypi. Ehrenberg has shown that similar spots also exist in a large number of the Infusoria. Fig. 17. 87. In all the above-mentioned animals, the eyes, what- ever their number, are apart from each other. But there is still another type of simple eyes, known as aggregate eyes. In some of the millipedes, the pill-bugs, for instance, the eyes are collected into groups, like those of spiders ; each eye inclosing a crystalline lens and a vitreous body, surrounded by a retina and choroid. Such eyes consequently form a 5* 54 SPECIAL SENSES. natural transition to the compound eyes of insects, to which we now give our attention. 88. Compound eyes have the same general form as simple eyes ; they are placed either on the sides of the head, as in insects, or supported on pedestals, as in the crabs. But if we examine an eye of this kind by a magnifying lens, we find its surface to be composed of an infinite number of angular, usually six-sided faces. If these fafettes are re- moved, we find beneath a corresponding number of cones, (c,) side by side, five or six times as long as they are broad, and arranged like rays around the optic nerve, from which each one receives a little filament, so as to present, according to Miiller, the following disposition. (Fig. 18.) The cones are per- fectly transparent, but sepa- rated from each other by walls of pigment, in such a manner that only those rays which are parallel to the axes can reach the retina A ; all those which enter ob- liquely are lost ; so that of all the rays which proceed from the points a and Z>, only the central ones in each pencil will act upon the optic nerve, (d ;) the others will strike against the walls of the cones. To compensate for the disadvantage of such an arrangement, and for the want of motion, the number of facettes is greatly multi- plied, so that no less than 25,000 have been counted in a single eye. The image on the retina, in this case, may be compared to a mosaic, composed of a great number of small images, each of them representing a portion of the figure. The entire picture is, of course, more perfect, - 18- OF HEARING. 55 in proportion as the pieces are smaller and more nu- merous. 89. Compound eyes are destitute of the optical apparatus necessary to concentrate the rays of light, and cannot adapt themselves to the distance of objects ; they see at a certain distance, but cannot look at pleasure. The perfection of their sight depends on the number of facettes or cones, and the manner in which they are placed. Their field of vision is wide, when the eye is prominent ; it is very limited, on the contrary, when the eye is flat. Thus the dragon-flies, on account of the great prominency of their eyes, see equally well in all directions, before, behind, or laterally ; whilst the water-bugs, which have the eyes nearly on a level with the head, can see to only a very short distance before them. 90. If there be animals destitute of eyes, they are either of a very inferior rank, such as most of the polypi, or else they are animals which live under unusual circumstan- ces, such as the intestinal worms. Even among the ver- tebrates, there are some that lack the faculty of sight, as the Myxine glutinosa^ which has merely a rudimentary eye concealed under the skin, and destitute of a crystalline lens. Others, which live in darkness, have not even rudimentary eyes, as, for example, that curious fish (Aniblyopsis spelceiis,} which lives in the Mammoth Cave, and which appears to want even the orbital cavity. The craw-fishes, (Astacus pettucidus,) of this same cave, are also blind ; having merely the pedicle for the eyes, without any traces of fa9ettes. 2. Hearing. 91. To hear, is to perceive sounds. The faculty of per- ceiving sounds is seated in a peculiar apparatus, the EAR, which is constructed with a view to collect and augment the sonorous vibrations of the atmosphere, and convey them to 56 SPECIAL SENSES. the acoustic or auditory nerve, which arises from the poste- rior part of the brain. (Fig. 21, c.) 92. The ears never exceed two in number, and are placed, in all the vertebrates, at the hinder part of the head. In a large proportion of animals, as the dog, horse, rabbit, and most of the mammals, the external parts of the ear are generally quite conspicuous ; and as they are, at the same time, quite movable, they become one of the promi- nent features of physiognomy. 93. These external appendages, however, do not consti- tute the organ of hearing, properly speaking. The true seat of hearing is deeper, quite in the interior of the head. It is usually a very complicated apparatus, especially in the supe- rior animals. In mammals it is composed of three parts, the external ear, the middle ear, and the internal ear ; and its structure is as follows : (Fig. 19.) ./f Fig. 19. 94. The external ear, which is popularly regarded as the ear, consists of the conch, (a,) and the canal which leads from it the external auditory passage, (&.) The first is a OF HEARING 57 gristly expansion, in the form of a horn or a funnel, the object of which is to collect the waves of sound ; for this reason, animals prick up their ears when they listen. The ear of man is remarkable for being nearly immovable. Therefore, persons, whose hearing is deficient, employ an artificial trumpet, by which the vibrations from a much more extended surface may be collected. The external ear is peculiar to mammals, and is wanting even in some aquatic species of these, such as the seals and the Orni- thorhyncus. 95. The middle ear has received the name of the tym- panic cavity, (&.) It is separated from the auditory passage by a membranous partition, the tymj)anum or drum, (c ;) though it still communicates with the open air by means of a narrow canal, called the Eustachian tube, (i,) which opens at the back part of the mouth. In the interior of the chamber are four little bones, of singular forms, which anatomists have distinguished by the names of malleus, (Fig. 20, c,) incus, (n,] stapes, (s,) and os orbicu- lare, (o ;) which are articulated to- gether, so as to form a continuous chain, as here represented, magnified. 96. The internal ear, which is also denominated the labyrinth, is an irregular cavity formed in the most solid part of the temporal bone, beyond the chamber of the middle ear, from which it is separated by a bony partition, which is perforated by two small holes, called, from their form, the round and the oval apertures, the fora- men rotundum, (Fig. 19, g,) and the foramen ovale, (h.) The first is closed by a membrane, similar to that of the tympa- num, while the latter is closed by the stapes, one of the little bones in the chamber. 58 SPECIAL SENSES. 97. Three parts are to be distinguished in the labyrinth, namely, the vestibule, which is the part at the entrance of the cavity ; the semicircular canals, (c/,) which occupy its upper part, in the form of three arched tubes ; and the cochlea, which is a narrow canal placed beneath, at the lower part of the vestibule, having exactly the form of a snail-shell, (e.) The entire labyrinth is filled with a watery fluid, in which membranous sacs or pouches float. Within these sacs, the auditory nerve (f) terminates. These pouches, therefore, are the actual seat of hearing, and the most essential parts of the ear. The auditory nerve is admitted to them by a long passage, the internal auditory canal. 98. By this mechanism, the vibrations of the air are first collected by the external ear, whence they are conveyed along the auditory passage, at the bottom of which is the tympanum. The tympanum, by its delicate elasticity, aug- ments the vibrations, and transmits them to the internal ear, partly by means of the little bones in the chamber, which are disposed in such a manner that the stapes exactly fits the oval aperture, (foramen ovale;] and partly by means of the air which strikes the membrane covering the round aperture, (g,} and produces vibrations there, corresponding to those of the tympanum. After all these modifications, the sonorous vibrations at last arrive at the labyrinth and the auditory nerve, which transmits the impression to the brain. 99. But the mechanism of hearing is not so complicated in all classes of animals, and is found to be more and more simplified as we descend the series. In birds, the middle and interior ears are constructed on the same plans as in the mammals ; but the outer ear no longer exists, and the audi- tory passage, opening on a level with the surface of the head behind the eyes, is merely surrounded by a circle of peculi- arly formed feathers. The bones of the middle ear are also lessjiumerous, there being generally but one. OF HEARING. 59 100. In reptiles, the whole exterior ear disappears ; the auditory passage is always wanting, and the tympanum be- comes external. In some toads, even the middle ear also is completely wanting. The fluid of the vestibule is charged with salts of lime, which frequently give it a milky appear- ance, and which, when examined by the microscope, are found to be composed of an infinite number of crystals. 101. In fishes, the middle and external ear are both wanting; and the organ of hearing is reduced to a mem- branous vestibule, situated in the cavity of the skull, and surmounted by semicircular canals, from one to three in number. The liquid of the vestibule contains chalky con- cretions of irregular forms, which are called Otolites, the use of which is doubtless to render the vibration of sounds more sensible. 102. In crabs, the organ of hearing is found on the lower face of the head, at the base of the large antennae. It is a bony chamber closed by a membrane, in the interior of which is suspended a membranous sac filled with water. On this sac, the auditory nerve is expanded. In the cuttlefish, the vestibule is a simple excavation of the cartilage of the head, containing a little membranous sac, in which the audi- tory nerve terminates. 103. Finally, some insects, the grasshopper for instance, have an auditory apparatus, no longer situated in the head, as with other animals, but in the legs ; and from this fact, we may be allowed to suppose, that if no organ of hearing has yet been found in most insects, it is because it has been sought for in the head only. 104. It appears from these examples, that the part of the organ of hearing which is uniformly present in all animals furnished with ears, is precisely that in which the auditory nerve ends. This, therefore, is the essential part of the or- gan. The other parts of the apparatus, the tympanum, auditory passage, and even the semicircular canals, have for 60 SPECIAL SENSES. their object merely to aid the perception of sound with more precision and accuracy. Hence we may conclude that the sense of hearing is dull in animals where the organ is re- o o duced to its most simple form ; and that animals which have merely a simple membranous sac, without tympanum and auditory passage, as the fishes, or without semicircular canals, as the crabs, perceive sounds in but a very imper- fect manner. 3. Of Smell. 105. SMELL is the faculty of perceiving odors, and is a highly important sense to many ani- mals. Like sight and hearing, smell depends upon special nerves, the olfacto- n/i (a?) which are the first pair of cer- ebral nerves, and which, in the em- bryo, are direct pro- longations of the brain. 106. The organ of smell is the NOSE. Throughout the series of vertebrates, it makes a part of the face, and in man, by reason of its prominent form, it becomes one of the dominant traits of his countenance ; in other mammals, the nose loses this prominency by degrees, and the nostrils no longer open downwards, but forwards. In birds, the position of the nostrils is a little different ; they open farther back and higher, at the origin of the beak, (/.) 107. The nostrils are usually two in number. Some fishes have four. They are similar openings, separated by a par- tition upon the middle line of the body. In man and the Fig. 21. a, olfactory nerve ; b, optic nerve ; c, audi- tory nerve ; d, cerebrum ; e, cerebellum ; f, nostril. OF SMELL. 61 mammals, the outer walls of the nose are composed of carti- lage ; but internally, the nostrils communicate with bony cav- ities situated in the bones of the face and forehead. These cavities are lined by a thick membrane, the pituitary mem- brane, on which are expanded the nerves of smell, namely, the olfactory nerves, and some filaments of the nerve which goes to the face. 108. The process of smelling is as follows. Odors are particles of extreme delicacy which escape from very many bodies, and are diffused through the air. These particles excite the nerves of smell, which transmit the impressions made on them to the brain. To facilitate the perception of odors, the nostrils are placed in the course of the respiratory passages, so that all the odors which are diffused in the air inspired, pass over the pituitary membrane. 109. The acuteness of the sense of smell depends on the extent to which the membrane is developed. Man is not so well endowed in this respect as many animals, which have the internal surface of the nostrils extremely complicated, as it is especially among the beasts of prey. 110. The sense of smell in Reptiles is less delicate than in the mammals ; the pituitary membrane, also, is less de- veloped. Fishes are probably still less favored in this respect. As they perceive odors through the medium of water, we should anticipate that the structure of their apparatus would be different from that of animals which breathe in the air. Their nostrils are mere superficial pouch- es, lined with a membrane gathered into folds which gen- erally radiate from a centre, but are sometimes arranged in parallel ridges on each side of a central band. As the perfection of smell depends on the amount of surface exposed, it follows that those fishes which have these folds most multiplied are also those in which this sense is most acute. 6 62 SPECIAL SENSES. 111. No special apparatus for smell has yet been found in Invertebrates. And yet there can be no doubt that insects, crabs, and some mollusks perceive odors, since they are attracted from a long distance by the odor of objects. Some of these animals may be deceived by odors similar to those of their prey ; which clearly shows that they are led to it by this sense. The carrion fly will deposit its eggs on plants which have the smell of tainted flesh. 4. Of Taste. 112. TASTE is the sense by which the flavor of bodies is perceived. That the flavor of a body may be perceived, it must come into immediate contact with the nerves of taste ; these nerves are distributed at the entrance to the digestive tube, on the surface of the tongue and the palate. By this sense, animals are guided in the choice of their food, and warned to abstain from what is noxious. There is an inti- mate connection between the taste and the smell, so that both these senses are called into requisition in the selection of food. 113. The nerves of taste are not so strictly special as those of sight and hearing. They do not proceed from one single trunk, and, in the embryo, do not correspond to an isolated part of the brain. The tongue, in particular, receives nerves from several trunks ; and taste is perfect in proportion as the nerves which go to the tongue are more minutely dis- tributed. The extremities of the nerves generally terminate in little asperities of the surface, called papilla. Sometimes these papillae are very harsh, as in the cat and the ox ; and again they are very delicate, as in the human tongue, in that of the dog, horse, &c. 114. Birds have the tongue cartilaginous, sometimes be- set with little stiff points; sometimes fibrous or fringed at the edges. In the parrots, it is thick and fleshy ; OF TOUCH. 63 or it is even barbed at its point, as in the woodpeckers. In some reptiles, the crocodile for example, the tongue is adherent ; in others, on the contrary, it is capable of extensive motion, and serves as an organ of touch, as in the serpents, or it may be thrust out to a great length to take prey, like that of the chameleon, toad, and frog. In fishes, it is usually cartilaginous, as in birds, generally adherent, and its surface is frequently covered with teeth. 115. It is to be presumed, that in animals which have a cartilaginous tongue, the taste must be very obtuse, especial- ly in those which, like most fishes, and many granivorous birds, swallow their prey without mastication. In fishes, especially, the taste is very imperfect, as is proved by then readily swallowing artificial bait. It is probable that they are guided in the choice of their prey by sight, rather than by taste or smell. 116. Some of the inferior animals select their food with no little discernment. Thus, flies will select the sugary portions of bodies. Some of the mollusks, as the snails for example, are particularly dainty in the choice of their food. In general, the taste is but imperfectly developed, except in the mammals, and they are the only animals which enjoy the flavor of their food. With man, this sense, like others, may be greatly improved by exercise ; and it is even capable of being brought to a high degree of delicacy. 5. Of Touch. 117. The sense of TOUCH is merely a peculiar manifesta- tion of the general sensibility, seated in the skin, and dependent upon the nerves of sensation, which expand over the surface of the body. By the aid of this general sensi- bility, we learn whether a body is hot or cold, wet or dry. We may also, by simple contact, gain an idea, to a certain 64 SPECIAL SENSES. extent, of the form and consistence of a body, as, for exam- ple, whether it be sharp or blunt, soft or hard. 118. This faculty resides more especially in the hand, which is not only endowed with a more delicate tact, but, owing to the disposition of the ringers, and the opposition of the thumb to the other fingers, is capable of so moulding itself around objects, as to multiply the points of contact. Hence, touch is an attribute of man, rather than of other animals ; for among these latter, scarcely any, except the monkeys, have the faculty of touch in their hands, or, as it is technically termed, of palpation. 119. In some animals, this faculty is exercised by other organs. Thus the trunk of the elephant is a most perfect organ of touch ; and probably the mastodon, whose numer- ous relics are found scattered in the superficial layers of the earth's crust, was furnished with a similar organ. Serpents make use of their tongue for touch ; insects employ their palpi, and snails their tentacles, for the same purpose. 6. The Voice. 120. Animals have not only the power of perceiving, but many of them have also the faculty of producing sounds of every variety, from the roaring of the lion to the song of the bird as it salutes the rising sun. It is moreover to be remarked that those which are endowed with a voice, likewise have the organ of hearing well developed. 121. Animals employ their voice either for communica- tion with each other, or to express their sensations, their en- joyments, their sufferings. Nevertheless, this faculty is en- joyed by but a small minority of animals; with but very few exceptions, only the mammals, the birds, and a few reptiles are endowed with it. All others are dumb. Worms and insects have no true voice ; for we must not OF THE VOICE. 65 mistake for it the buzzing of the bee, which is merely a noise created by the vibration of the wings ; nor the grating shriek of the Locust, (grasshopper,) caused by the friction of his legs against his wings ; nor the shrill noises of the cricket, or the tell-tale call of the katydid, produced by the friction of the wing covers upon each other, and in numerous similar cases which might he cited. 122. Consequently, were the mammals, the birds, and the frogs to be struck out of existence, the whole Animal King- dom would be dumb. It is difficult for us, living in the midst of the thousand various sounds which strike our ear from all sides, to conceive of such a state. Yet such a state did doubtless prevail for thousands of ages, on the surface of our globe, when the watery wrorld alone was inhabited, and be- fore man, the birds, and the mammals were called into being. 123. In man and the mammals, the voice is formed in an organ called the larynx, situated at the upper part of the windpipe, below the bone of the tongue, (a.) a \\ The human larynx, the part called Adam's apple, is composed of several cartilaginous b~\ pieces, called the thyroid cartilage, (&,) the I cricoid cartilage, (c,) and the small arytenoid ^_ cartilages. Within these are found two large folds of elastic substance, known by the name Fig. 22. of the vocal cords, (m.) Two other analogous folds, the superior ligaments of the glottis , (n,} are situated a little above the preceding. The glottis (o) is the space between these four folds. The arrangement of the vocal cords, and of the interior of the glottis in man, is indicated by dotted lines, in Fig. 22. 124. The mechanism of the voice is as follows : the air, on its way to the lungs, passes the vocal cords. So long as these are in repose, no sound is produced ; but the moment they are made tense they narrow the aperture, and oppose 6* 66 OF THE VOICE. an obstacle to the current of air, and it cannot pass without causing them to vibrate. These vibrations produce the voice ; and as the vocal cords are susceptible of different degrees of tension, these tensions determine different sounds ; giving an acute tone when the tension is great, but a grave and dull one when the tension is feeble. 125. Some mammals have, in addition, large cavities which communicate with the glottis, and into which the air reverberates, as it passes the larynx. This arrangement is especially remarkable in the howling monkeys, which are dis- tinguished above all other animals for their deafening howls. 126. In birds, the proper larynx is very simple, destitute of vocal cords, and incapable of producing sounds ; but at the lower end of the windpipe there is a second or inferior larynx, which is very complicated in structure. It is a kind of bony drum, (a,) having with- in it two glottides, formed at the top of the two branches (bb) of the windpipe, (c,) each provided with two vocal cords. The dif- ferent pieces of this apparatus are moved by peculiar muscles, the number of which varies in different families. In birds which have a very monotonous cry, such as the gulls, the herons, the cuckoos, and the mergansers, (Fig. 23,) there is but one or two pairs ; parrots have three ; and the birds of song have five. 127. Man alone, of all the animal creation, has the power of giving to the tones he utters a variety of definite or ar- ticulate sounds ; in other words, he alone has the gift of speech. Fig. 23. CHAPTER FOURTH. OF INTELLIGENCE AND INSTINCT. 128. BESIDES the material substance of which the body is constructed, there is also an immaterial principle, which, though it eludes detection, is none the less real, and to which we are constantly obliged to recur in considering the phenomena of life. It originates with the body, and is de- veloped with it, while yet it is totally apart from it. The study of this inscrutable principle belongs to one of the highesj branches of Philosophy ; and we shall here merely allude to some of its phenomena which elucidate the devel- opment and rank of animals. 129. The constancy of species is a phenomenon depend- ing on the immaterial nature. Animals, and plants also, produce their kind, generation after generation. We shall hereafter show that all animals may be traced back, in the embryo, to a mere point in the yolk of the egg, bearing no resemblance whatever to the future animal ; and no in- spection would enable us to declare with certainty what that animal is to be. But even here an immaterial principle is present, which no external influence can essentially modify, and determines the growth of the future being. The egg of the hen, for instance, cannot be made to produce any other animal than a chicken, and the egg of the codfish produces only the cod. It may therefore be said with truth, that the chicken and the cod existed in the egg before their formation as such. 130. PERCEPTION is a faculty springing from this princi- ple. The organs of sense are the instruments for receiving 68 INTELLIGENCE AND INSTINCT. sensations, but they are not the faculty itself, without which they would be useless. We all know that the eye and ear may be open to the sights and sounds about us ; but if the mind happens to be preoccupied, we perceive them not. We may even be searching for something which actually lies within the compass of our vision; the light enters the eye as usual, and the image is formed on the retina ; but, to use a common expression, we look without seeing, unless the mind that perceives is directed to the object. 131. In addition to the faculty of perceiving sensations, the higher animals have also the faculty of recalling past impressions, or the power of memory. Many animals retain a recollection of the pleasure or pain they have experi- enced, and seek or avoid the objects which may have pro- duced these sensations ; and, in doing so, they give proof of judgment. 132. This fact proves that animals have the faculty of comparing their sensations and of deriving conclusions from them ; in other words, that they carry on a process of reasoning. 133. These different faculties, taken together, constitute intelligence. In man, this superior principle, which is an emanation of the divine nature, manifests itself in all its splendor. God " breathed into him the breath of life, and man became a living soul." It is man's prerogative, and his alone, to regulate his conduct by the deductions of reason ; he has the faculty of exercising his judgment not only upon the objects which surround him, and of apprehending the many relations which exist between himself and the ex- ternal world ; he may also apply his reason to immaterial things, observe the operations of his own intellect, and, by the analysis of his faculties, may arrive at the conscious- ness of his own nature, and even conceive of that Infinite Spirit, " whom none by searching can find out." INTELLIGENCE AND INSTINCT. 69 134. Other animals cannot aspire to conceptions of this kind ; they perceive only such objects as immediately strike their senses, and are incapable of continuous efforts of the reasoning faculty in regard to them. But their conduct is frequently regulated by another principle of inferior order, still derived from the immaterial principle, called INSTINCT. 135. Under the guidance of Instinct, animals are enabled to perform certain operations, without instruction, in one imdeviating manner. When man chooses wood and stone, as the materials for his dwelling, in preference to straw and leaves, it is because he has learned by experience, or be- cause his associates have informed him, that these materials are more suitable for the purpose. But the bee requires no instructions in building her comb. She selects at once the fittest materials, and employs them with the greatest econo- my ; and the young bee exhibits, in this respect, as much discernment as those who have had the benefit of long experience. She performs her task without previous study, and, to all appearances, without the consciousness of its utility, being in some sense impelled to it by a blind impulse. 136. If, however, we judge of the instinctive acts of ani- mals when compared with acts of intelligence, by the relative perfection of their products, we may be led into gross errors, as a single example will show. No one will deny that the honey-comb is constructed with more art and care than the huts of many tribes of men. And vet, who would presume to conclude from this that the bee is superior in intelligence to the inhabitant of the desert or of the primitive forest? It is evident, on the contrary, that in this particular case we are not to judge of the artisan by his work. As a work of man, a structure as perfect in all respects as the honey-comb would indicate very complicated mental operations, and probably would require numerous preliminary experiments. 137. The instinctive actions of animals relate either to 70 INTELLIGENCE AND INSTINCT. the procuring of food, or to the rearing of their young ; in other words, they have for their end the preservation of the individual and of the species. It is by instinct that the leopard conceals himself and awaits the approach of his prey. It is equally by instinct that the spider spreads his web to entangle the flies which approach it. 138. Some animals go beyond these immediate precau- tions ; their instinct leads them to make provision for the future. Thus the squirrel lays in his store of nuts and acorns during autumn, and deposits them in cavities of trees, which he readily finds again in winter. The hamster digs, by the side of his burrow, compartments for magazines, which he arranges with much art. Finally, the bee, more than any other animal, labors in view of the future ; and she has become the emblem of order and domestic economy. 139. Instinct exhibits itself, in a no less striking manner, in the anxiety which animals manifest for the welfare of their anticipated progeny. All birds build nests for the shelter and nurture of their young, and in some cases these nests are made exceedingly comfortable. Others show very great ingenuity in concealing their nests from the eyes of their enemies, or in placing them beyond their reach. There is a small bird in the East Indies, the tailor bird, (Sylvia sutoria,) which works wool or cotton into threads, with its feet and beak, and uses it to sew together the leaves of trees for its nest. 140. The nest of the fiery hang-bird, (Icterus Baltimore,) dangling from the extremity of some slender, inaccessible twig, is familiar to all. The beautiful nest of the humming- bird, seated on a mossy bough, and itself coated with lichen and lined with the softest down from the cotton-grass or the mullein leaf, is calculated equally for comfort and for es- caping observation. An East Indian bird, (PloceusPhilippi- nus,) not only exhibits wonderful devices in the construction, INTELLIGENCE AND INSTINCT. 71 security, and comfort of its nest, but displays a still further advance towards intelligence. The nest is built at the tips of long pendulous twigs, usually hanging over the water. It is composed of grass, in such a manner as to form a com- plete thatch. The entrance is through a long tube, run- ning downwards from the edge of the nest ; and its lower end is so loosely woven, that any serpent or squirrel, attempting to enter the aper- ture, would detach the fibres, and fall to the ground. The male, however, who has no occasion for such protection, builds his thatched dome, sim- ilar to that of the female, and by its side ; but makes simply a perch across the base of the dome, without the nest-pouch or tube. 141. But it is among insects that this instinctive solici- tude for the welfare of the progeny is every where exhibited in the most striking manner. Bees and wasps not only prepare cells for each of their eggs, but take care, before closing the cells, to deposit in each of them something ap- propriate for the nourishment of the future young. 142. It is by the dictate of instinct, also, that vast numbers of animals of the same species associate, at certain periods of the year, for migration from one region to another ; as the swallows and passenger pigeons, which are sometimes met with in countless flocks. 143. Other animals live naturally in large societies, and labor in common. This is the case with the ants and bees. Among the latter, even the kind of labor for each member of the community is determined beforehand, by instinct. 72 INTELLIGENCE AND INSTINCT Some of them collect only honey and wax ; while others are charged with the care and education of the young ; and still others are the natural chiefs of the colony. 144. Finally, there are certain animals so guided by their instinct as to live like pirates, on the avails of others' labor. The Lestris or Jager will not take the trouble to catch fish for itself, but pursues the gulls, until, worn out by the pursuit, they eject their prey from their crop. Some ants make war upon others less powerful, take their young away to their nests, and oblige them to labor in slavery. 145. There is a striking relation between the volume of the brain compared with the body, and the degree of intelli- gence which an animal may attain. The brain of man is the most voluminous of all, and among other animals there is every gradation in this respect. In general, an animal is the more intelligent, in proportion as its brain bears a greater resemblance to that of man. 146. The relation between instinct and the nervous system does not present so intimate a correspondence as exists between the intellect and the brain. Animals which have a most striking development of instinct, as the ants and bees, belong to a division of the Animal Kingdom where the nervous system is much less developed than that of the ver- tebrates, since they have only ganglions, without a proper brain. There is even a certain antagonism between instinct and intelligence, so that instinct loses its force and peculiar character, whenever intelligence becomes developed. 147. Instinct plays but a secondary part in man. He is not, however, entirely devoid of it. Some of his actions are entirely prompted by instinct, as, for instance, the attempts of the infant to nurse. The fact, again, that these instinctive actions mostly belong to infancy, when intelligence is but slightly developed, goes to confirm the two last propositions. CHAPTER FIFTH. OF MOTION. SECTION I. APPARATUS OF MOTION. 148. THE power of voluntary motion is the second grand characteristic of animals, (57.) Though they may not all have the means of transporting themselves from place to place, there is no one which has not the power of executing some motions. The oyster, although fixed to the ground, opens and closes its shell at pleasure ; and the little coral animal protrudes itself from its cell, and retires again at its will. 149. The movements of animals are effected by means of muscles, which are organs designed expressly for this pur- pose, and which make up that portion of the body which is commonly called flesh. They are composed of threads, which are readily seen in boiled meat. These threads are again composed of still more delicate fibres, called mus- cular fibres, (45,) which have the property of elongating and contracting. 150. The motions of animals and plants depend, therefore, upon causes essentially different. The expansion and closing of the leaves and blossoms of plants, which are their most 7 74 APPARATUS OF MOTION. obvious motions, are due to the influence of light, heat, moisture, cold, and similar external agents ; but all the mo- tions peculiar to animals are produced by a cause residing within themselves, namely, the contractility of muscular fibres. 151. The cause which excites contractility resides in the nerves, although its nature is not precisely understood. We only know that each muscular bundle receives one or more nerves, whose filaments pass at intervals across the muscular fibres, as seen in Fig. 25. It has also been shown, by experi- ment, that when a nerve entering a muscle is sev- Fig. 25. erecl, the muscle instantly loses its power of contracting under the stimulus of the will, or, in other words, is par- alyzed. 152. The muscles may be classified, according as they are more or less under the control of the will. The con- tractions of some of them are entirely dependent on the will, as in the muscles of the limbs used for locomotion. Others are quite independent of it, like the contractions of the heart and stomach. The muscles of respiration ordinarily act inde- pendently of the will, but are partially subject to it : thus, when we attempt to hold the breath, we arrest, for the mo- ment, the action of the diaphragm. 153. In the great majority of animals, motion is greatly aided by the presence of solid parts, of a bony or horny structure, which either serve as firm attachments to the muscles, or, being arranged so as to act as levers, to in- crease the precision and sometimes the force of movements. The solid parts are usually so arranged as to form a sub- APPARATUS OF MOTION. 75 stantial framework for the body, which has been variously designated in the several classes of animals, as the test, shell, O carapace, skeleton, fyc. The study of these parts is one of the most important tranches of comparative anatomy. Their characters are the most constant and enduring of all others. Indeed, these solid parts are nearly all that remains of the numerous extinct races of animals of past geological eras ; and from these alone are we to determine the struc- ture and character of the ancient fauna. 154. Most of the Radiata have a calcareous test or crusty shell. In the Polypi, this structure, when it exists, is usually very solid, sometimes assuming the form of a simple inter- nal skeleton, or forming extensively branched stems, as in the sea-fans ; or giving rise to solid masses, furnished with numerous cavities opening at the surface, from which the movable parts of the animals are protruded, with the power, however, of retracting themselves at pleasure, as in the corals. In the Echinoderms, the test is intimately con- nected with the structure of the soft parts. It is composed of numer- ous little plates, sometimes con- solidated and immovable, as in the sea-urchins, (Fig. 26,) and sometimes so combined, as to -pio. 2 allow of various motions, as in the star-fishes, (Fig. 17,) which use their projecting rays, both for crawling and swimming. 155. In the Mollusks, 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 parts which they cover. These shells are generally so constructed as to afford complete protection to the animal within their cavities. In a few, the shell is too small for this purpose ; and in some it exists only at a very early period, 76 APPARATUS OF MOTION. and is lost as the animal is developed, so that at last there is no other covering than a slimy skin. In others, the skin 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. As a general thing, the solid parts do not aid in locomotion, so that the mol- lusks are mostly sluggish animals. It is only in a few rare cases that the shell becomes a true lever, as in the Scollops, (Pecten,) which use their shells to propel themselves in swimming. 156. The muscles of mollusks either form a flat disk un- der the body, or large bundles across its mass, or are dis- tributed 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 the disposition may be, they 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 other animals. This peculiar aspect no doubt arises from the numerous small cavities extending between the muscles, and the secre- tion of mucus which takes place in them. 157. In the Articulated animals, the solid parts are ex- ternal, 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 structure. The rings differ in the several classes of this department, merely as to volume, form, solid- ity, 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 we see in the crabs. In others, they are membranous, and the body is capable of assuming various forms, as in the leeches and worms generally. APPARATUS OF MOTION. 77 158. A variety of appendages are attached to these rings, such as jointed legs, or in place of them stiff bristles, oars fringed with silken threads, wings either firm or mem- branous, antennae, movable pieces which perform the office of jaws, &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, com- bine to form but a single internal cavity, in which all the or- gans are enclosed, the nervous system, as well as the organs of vegetative life, (63.) 159. The muscles which move all these parts have this peculiar- ity, that they are all enclosed with- in the more solid framework, and not external to it, as in the verte- brates ; and also that the muscular bundles, which are very consider- able in number, have the form of ribbons, or fleshy strips, with par- allel fibres of remarkable white- Figure 27 represents the Fig. 27. ness. disposition of the muscles of the caterpillar which destroys the willow, (Cossus ligniperda.] The right side represents the superficial layer of muscles, and the left side the deep- seated layer. 160. The Vertebrata, like the articulated animals, have solid parts at the surface, as the hairs and horns of mam- mals, the coat of mail of the armadillo, the feathers and claws of birds, the bucklers and scales of reptiles and fishes, &c. But they have besides this, along the interior of the whole body, a solid framework not found in the invertebrates, well known as the SKELETON. 161. The skeleton is composed of a series of separate bones, called vertebrae, united to each other by ligaments. 7* 78 APPARATUS OF MOTION. a Each vertebra has a solid centre with four 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 (a) along the region of the trunk, which encloses the spinal marrow, and in the head re- ceives the brain, (61.) The lower arches (Z>) form another cavity, similar to the superior one, which contains the organs of nutrition and reproduction ; their branch- es generally meet below, and when dis- joined, 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, or the tail, we have only differences in the degree of development of the body of the ver- tebra, or of its branches, and not in reality different plans of organization. 162. The muscles which move this solid framework of the vertebrata are disposed around the vertebrae, as is Fig. 28. Fig. 29. well exemplified among the fishes, where there is a band of muscles for each vertebra. In proportion as limbs LOCOMOTION. 79 are developed, this intimate relation between the muscles and the vertebrae diminish- The muscles are un- es. equally distributed and are concentrated about the limbs, where the greatest amount of muscular force is required. For this rea- son, the largest masses of flesh in the higher verte- brates are found about the shoulders and hips ; while in fishes they are concen- trated about the base of the Fig. 30. tail, which is the part principally employed in locomotion. SECTION II. OF LOCOMOTION. 163. One of the most curious and important applications of this apparatus of bones and muscles is for LOCOMO- TION. By this is understood the movement which an animal makes in passing from place to place, in the pursuit of pleas- ure, sustenance, or safety, in distinction from those motions which are performed equally well while stationary, such as the acts of respiration, mastication, &c. 164. 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 80 LOCOMOTION. equally concerned in effecting locomotion, or only some of its parts are employed for the purpose. 165. The jelly-fishes (Medusae) swim by contracting their umbrella-shaped bodies upon the water below, and its resistance urges them forwards. Other animals are provided with a sac or siphon, which they may fill with water, and suddenly force out, producing a jet, which is resisted by the surrounding water, and the animal is thus propelled. The Biche-le-mar, (Holothuria,) the cuttle-fishes, the Salpse, &c., move in this way. 166. Others contract small portions of the 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. 167. Some have, at the extremities of the body, a cup or some other organ for maintaining a firm hold, each extremity acting in turn as a fixed point. Thus the Leech has a cup or sucker at its tail, by which it fixes itself ; the body is then elongated by the contraction of the muscular fibres which encircle the animal ; the mouth is next fixed by a similar suck- Fig. 32. er and by the contraction of muscles running lengthwise the body is shortened, and the tail, losing its hold, is brought forwards to repeat the same process. Most of the bivalve mollusks, such as the clams, LOCOMOTION. 81 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 enclosing it. Snails, and many similar animals, have the fleshy under surface of their body composed of an infinitude of very short muscles, which, by successive contractions, so minute, indeed, as scarcely to be detected, enable them to glide along smoothly and silently, without any apparent muscular effort. 168. In the majority of animals, however, locomotion is effected by means of organs specially designed for the pur- pose. The most simple are the minute, hair-like cilia,) which fringe the body of most of the microscopic infu- sory animalcules, and which, by their incessant vibrations, cause rapid movements. The sea-urchins and star-fishes have little thread-like tubes issuing from every side of the body, furnished 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, and usually wings also. 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 fringe-like gills for paddles. (Fig. 33.) 169. Among the Vertebrata, we find the greatest diversity in the organs of locomotion and the modes of their applica- tion, as well as the greatest perfection, in whatever element 82 ORGANS OF LOCOMOTION. they may be employed. The sailing of the eagle, the bound- ing 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 admits a great display of force, gives to the motions, at the same time, a great degree of precision. 1. Plan of the Organs of Locomotion. 170. 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 ob- serve the modifications, oftentimes very slight, by which a very simple organ is adapted to every variety of move- ment. No part of the animal structure more fully illustrates the unity of design, or the skill of the Intellect which has so adapted a single organ to such multiplied ends. On this account, we shall illustrate this subject somewhat in detail. 171. It is easy to see that the wing which is to sustain the bird in the air must be different from the leg of the stag, which is to serve for running, or the fins of the fish that swims. But, notwithstanding their dissimilarity, 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. In order to show this, it is necessary to give a short de- scription of the composition of the arm or anterior extremity. 172. The anterior member, in the vertebrates, is invaria- bly composed of the following bones: 1. The shoulder- llade, or scapula, (a,) a broad and flat bone, applied upon the bones of the trunk ; 2. The arwi, (£,) formed of a single OKGANS OF LOCOMOTION. 83 A a long cylindrical bone, the humerus ; 3. The fore-arm, com- posed of two long bones, the radius, (c,) and ulna, (d,) which are often fused into one ; 4. The hand, which is composed of a series of bones, more .0 or less numerous in different classes, and which is divided into three parts, namely, the carpus, or wrist, (e,] the metacarpus, or palm, (/",) and the pha- langes, or fingers, (g.} The clavicle or collar-bone, (o,) when it exists, belongs also to the anterior member. It is a bone of a cylindrical form, fixed as a brace between the breast-bone and shoulder-blade. Its use is to keep the c shoulders separated ; to this end, we find it fully developed in all animals which raise the limbs from the sides, as the birds and the bats. On the other hand, it is rudimentary, or entirely want- ing in animals which move them back- wards and forwards only, as with most quadrupeds. 173. The following outlines, in which corresponding bones are indicated by the same letters, will give an idea of the modifications which these bones present in different classes. In the arm of man, (Fig. 34,) the shoulder-blade is flat and triangular ; the bone of the arm is cylindrical, and en- larged at its extremities ; the bones of the fore-arm are somewhat shorter than the humerus, but more slender ; the hand is composed of the following pieces, namely, eight small bones of the carpus, arranged in two rows, five meta- carpal bones, which are elongated, and succeed those of the wrist ; five fingers of unequal length, one of which, the thumb, is opposed to the four others. fj Fig. 34. Fig. 35. 84 ORGANS OF LOCOMOTION. 174. In the stag, (Fig. 35,) the bones of the fore-arm are rather longer than that of the arm, and the radius no longer turns upon the ulna, but is blended with it; the meta- carpal, or cannon bone, is greatly developed ; and, being quite as long as the fore-arm, it is apt to be mistaken for it. The fingers are reduced to two, each of which is surrounded by a hoof, at its extremity. 175. In the arm of the lion, (Fig. 36,) the arm bone is Fig. 36. stouter, the carpal bones are less numerous, and the fingers are short, and armed with strong, retractile claws. In the whale, (Fig. 37,) the bones of the arm and fore-arm are much shortened, and very massive ; the hand is broad, the fingers strong, and distant from each other. Fig. 38. Fig. 39. In the bat, the thumb, which is represented by a small hook, is entirely free, (Fig. 38 ;) but the fingers are elon- gated in a disproportionate manner, and the skin is stretched ORGANS OF LOCOMOTION. 85 across them, so as to serve the purpose of a wing. In birds, the pigeon for example, (Fig. 39,) there are but two fingers, which are soldered together, and destitute of nails ; and the thumb is rudimentary. 176. The arm of the turtle (Fig. 40) is peculiar in having, Fig. 41. Fig. 42. besides the shoulder-blade, two clavicles ; the arm-bone is twisted outwards, as well as the bones of the fore-arm, so that the elbow, instead of being behind, is turned forwards ; the fingers are long, and widely separated. In the Sloth, (Fig. 41,) the bones of the arm and fore-arm are very greatly elongated, and at the same time very slender ; the hand is likewise very long, and the fingers are terminated by enor- mous non-retractile nails. The arm of the Mole (Fig. 42) is still more extraordinary. The shoulder-blade, which is usually a broad and flat bone, becomes very narrow ; the arm-bone, on the contrary, is contracted so much as to seem nearly square ; the elbow projects backwards, and the hand is excessively large and stout. 177. In fishes, the form and arrangement of the bones is so peculiar, that it is often difficult to trace their correspond- ence to all the parts found in other animals ; nevertheless, the bones of the fore-arm are readily recognized. In the Cod 8 86 ORGANS OF LOCOMOTION. (Fig. 43) there are two flat and broad bones, one of which, the ulna, (d,) presents a long point, anteriorly. The bones of c 9 c - C_x~ Fig. 43. the carpus are represented by four nearly square little bones. But in these again there are considerable variations in dif- ferent fishes, and in some genera they are much more irreg- ular in form. The fingers are but imperfectly represented by the rays of the fin, (g,) which are composed of an infini- tude of minute bones, articulated with each other. As to the humerus and shoulder, their analogies are variously in- terpreted by different anatomists. 178. The form of the members is so admirably adapted to the special offices which they are designed to perform, that by a single inspection of the bones of the arm, as repre- sented 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 its ulna, the delicate and pliable fingers, and the thumb opposed 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 incon- venient for walking on the ground, but appropriate for seizing upon the branches of the trees, on which these animals live. The short fingers, armed with retractile nails, indicate the lion, at first glance, to be a carnivorous animal. The arm of the stag, with his very long cannon-bone, and that of the horse, also, with its solitary finger enveloped in a hoof, are organs especially adapted for running. The very slender and greatly elongated fingers of the bat are admirably con- ORGANS OF LOCOMOTION. 87 trived for the spread of a wing, without increasing the weight of the body. The more 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 the mass of the flesh, presents, externally, a mere delicate balancer, the pectoral fin. 179. The posterior members are identical in their structure with the anterior ones. The bones of which they are composed, are, 1. The pelvis, (Fig. 46,) which corresponds to the shoulder blade ; 2. The thigh bone, or femur-) which is a single 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, which are divided, like those of the hand, into three parts, the tarsus or ankle, the metatarsus or instep, and the toes. The modifications are generally less marked than in the arm, inasmuch as there is less diversity of function ; for in all animals, without exception, the posterior extremities are used exclusively for support or locomotion. 180. The anterior extremity of the vertebrates, however varied in form, whether it be an arm, a wing, or a fin, is thus shown to be composed of essen- tially the same parts, and con- structed upon the same general plan. This affinity does not ex- tend to the invertebrates ; for al- though in many instances their Fig. 44. Fig: 45. limbs bear a certain resemblance to those of the vertebrates, and are even used for similar purposes, yet they have no real 88 OF STANDING AND PROGRESSION. affinity. Thus the leg of an insect, (Fig. 44,) and that of a lizard, (Fig. 45 ;) the wing of a butterfly and the wing of a bat. are quite similar in form, position, and use; but in the bat and the lizard, 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, (157.) It is by ascertaining and regarding these real affinities, or the fundamental differences, existing between similar organs, that the true natural grouping of animals is to be attained. 2. Of Standing, and the Modes of Progression. 181. Standing, 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 poste- rior 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 horizontal. Man alone is designed to stand upright, with his head supported on the summit of the vertebral col- umn. Some monkeys can rise upon the hind legs into the erect posture ; but it is evidently a constrained one, and not their habitual attitude. 182. That an animal may stand, it is requisite that the limbs should be so disposed that the centre of gravity, in other words, the point about which the body balances itself, should fall within the space included by the feet. If the centre of gravity is outside of these limits, the animal falls to the side to which the centre of gravity inclines. On this account, the albatross, and some other aquatic birds OF STANDING. 89 which have the feet placed very far back, cannot use them for walking;. O 183. The more numerous and the more widely separated are the points of support, 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 thev should have a broad base. Thus we see that •/ most quadrupeds have slender legs, touching the earth by only a small surface. 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. Moreover, the muscles of the toes are so disposed that the weight of the bird causes them to grasp firmly ; hence it is enabled to sleep standing in perfect security upon the roost, without effort. Fig. 46. 184. In quadrupeds, the joints at the junction of the limbs with the body bend freely in only one direction, 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 antag- onism 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 8* 90 MODES OF PROGRESSION. backwards, and the fore-arm forwards. Different terms have been employed to express the various modes of progression, according to the rapidity or the succession in which the limbs are advanced. 185. PROGRESSION is a forward movement of the body, effected by successively bending and extending the limbs. WALKING 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 while one leg sustains the body, the other is thrown forwards to prevent it from falling, and to sustain it in turn. For this reason, walking has been defined to be a continual falling forwards, continually interrupted by the projection of the legs. 186. The throwing forwards of the leg, which would require 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 suffi- cient of itself to maintain the limbs in place, without the as- sistance of the muscles. This may be proved by experi- ment. If we cut away all the muscles around the hip joint, the thigh bone still adheres firmly to the pelvis, but separates the moment a hole is pierced, so as to admit air into the socket. 187. In ordinary walking, the advancing leg touches the ground just 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, but with this difference, that the body always rests on at least two legs. The limbs are raised in a deter- minate order, usually in such a manner that the hind-leg of one side succeeds the fore-leg of the opposite side. Some MODES OF PROGRESSION. 91 animals, as the giraffe, the lama, and the bear, raise both legs of one side at the same moment. This is called am- bling, or pacing. 188. RUNNING consists in the same succession of motions as walking, so accelerated that there is a moment be- tween 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 to say, 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-limbs are raised to- gether as well as the hind-legs ; it is then termed a gallop. 189. LEAPING 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 again at a certain distance in advance. 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 the frog, the kangaroo, jerboa, and even the hare. Leaping is also com- mon among certain birds, especially among the sparrows, the thrushes, &c. Finally, there is also a large number of leaping insects, such as the flea, the large tribe of grass- hoppers and crickets, in which we find that pair of legs with which leaping is accomplished much more developed than the others. 92 MODES OF PROGRESSION. 190. CLIMBING is merely walking upon an inclined or even upright surface. It is usually accomplished by means of sharp nails ; and hence many carnivorous animals climb with great facility, such as the cat tribe, the lizards ; and many birds, the woodpecker, for instance. Others employ their arms for this purpose, like the bears when they climb a tree ; or their hands, and even their tails, like the mon- keys ; or their beaks, like the parrots. Lastly, there are some whose natural mode of progression is climbing. Such are the sloths, with their arms so long, that, when placed upon the ground, they move very awkwardly ; and yet their struc- ture is by no means defective, for in their accustomed move- ments upon trees they can use their limbs with very great adroitness. 191. 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 Podurella3. Still 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.) 192. 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 support, for the moment, upon which the bird is sustained. But as this support very soon yields, owing to the slight density of the air, it follows that the bird must make the greater and more MODES OF PROGRESSION. 93 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. 30.) To facili- tate its progress, the bird, after each flap of the wings, brings them against the body, so as to present as little surface as possible to the air ; for a still further diminution of resistance, all birds have the anterior part of the body very slender. Their flight would be much more difficult if they had large heads and short necks. 193. Some quadrupeds, such as the flying-squirrel and Galeopithecus, have a fold of the skin at the sides, which may be extended by the legs, and which enables them to leap from branch to branch with more security. But this is not flight, properly speaking, since none of the peculiar operations of flight are performed. There are also some fishes, whose pectoral fins are so extended as to enable them to dart from the water, and sustain themselves for a consider- able time in the air ; and hence they are called flying-fish. But this is not truly flight. 194. SWIMMING is the mode of locomotion employed by the greater part of the aquatic animals. Most animals which live in the water swim with more or less facility. Swimming has this in common with flight, that the medium in which it is performed, the water, becomes also the support, and read- ily yields also to the impulse of the fins. Only, as water is much more dense than air, and as the body of most aquatic animals is of very nearly the same specific gravity as water, it follows that, in swimming, very little effort is requisite to keep the body from sinking. The whole power of the mus- cles is consequently employed in progression, and hence swimming requires vastly less muscular force than flying. 195. Swimming is accomplished by means of various or- gans designated under the general term, fins, although in an 94 MODES OF PROGRESSION. anatomical point of view these may represent very different parts. In the Whales, the anterior extremities and the tail are transformed into fins. In Fishes, the pectoral fins, which represent the arms, and the ventral fins, which represent the legs, are employed for swimming, but they are not the prin- cipal organs ; for it is by the tail, or caudal fin, that pro- gression is principally effected. Hence the progression of the fish is precisely that of a boat under the sole guidance of the scull ing-oar. In the same manner as a succes- sion of strokes alternately right and left propels the boat straight forwards, so the fish advances by striking alternately right and left. To advance obliquely, it has only to strike a little more strongly in the direction opposite to that which he wishes to take. The Whales, on the contrary, swim by striking the water up and down ; and it is the same with a few fishes also, such as the rays and the soles. The air- bladder facilitates the rising and sinking of the fish, by ena- bling it to vary the specific weight of the body. 196. 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 and duck, have webbed feet ; that, is to say, the fingers are united by a membrane, which, when expanded, acts as a paddle. 197. There is also a large number of invertebrate animals in which swimming is the principal or the only mode of progression. Lobsters swim by means of their tail, and, like the Whales, strike the water up and down. 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 little water boatmen, (Gyrinus, Dytiscus,) whose mazy dances on the summer streams every one must have observed. The cuttle-fish uses its long ten- MODES OF PROGRESSION. 95 tacles as oars, (Fig. 47 ;) and some star-fishes (Comatula, Euryale) use their arms with great adroitness, (Fig. 151.) Finally, there are some insects which have their limbs con- structed for running on the surface of water, as the water- spiders, (Ranatra, Hydrometra.) Fig. 47. 198. A large number of animals have the faculty of mov- ing both in the air and on land, as is the case with most birds, and a great proportion of insects. Others move with equal facility, and by the same members, on land and in water, as some of the aquatic birds and most of the reptiles, which latter have even received the name Amphibia, on this account. There are some which both walk, fly, and swim, as the ducks and water-hens ; but they do not excel in either mode of progression. 199. However different the movements and offices per- formed by the limbs may appear to us, according to the ele- ment in which they act, we see that they are none the less the effect of the same mechanism. The contraction of the same set of muscles causes the leg of the stag to bend for leaping, the wing of the bird to flap in the air, the arm of the mole to excavate the earth, and the fin of the whale to strike the water. CHAPTER SIXTH. NUTRITION. 200. THE second class of the functions of animals are those which relate to the maintenance of life and the per- petuation of the species ; the functions of vegetative life, (59.) 201. The increase of the volume of the body must re- quire additional materials. There is also an incessant waste of particles which, having become unfit for further use, are carried out of the system. Every contraction of a muscle expands the energy of some particles, whose place must be supplied. These supplies are derived from every natural source, the animal, vegetable, and even the mineral king- doms ; 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 appropriation of it to the growth and sustenance of the body, is called NUTRITION in the widest sense of that term. 202. In early life, during the period of growth, the amount of substances appropriated is greater than that which is lost. At a later period, when growth is completed, an equilibrium between 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. 203. The solids and fluids taken into the body as food are OF DIGESTION. 97 subjected to a process called Digestion, by which the solid portions are reduced to a fluid state also, the nutritive sepa- rated 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 require 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 breathe, 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 back the particles which are to be either reno- vated or expelled. This circuit is what is termed the Circu- lation. The function of Nutrition, therefore, combines sev- eral distinct processes. SECTION I. OF DIGESTION. 204. Digestion, or the process by which the nutritive parts of food are elaborated and pre- pared to become part of the body, is effected in certain cavities, the stomach and intestines, or alimen- tary canal. This canal is more or less complicated in the various classes of animals ; but there is no animal, however low its organiza- tion, without it, in some form, (54.) 205. In the polypi, the digestive apparatus is limited to a single cavity. In the Sea Anemone, (Ac- tinia,) for example, it is a pouch, (Fig. 48, 5,) suspended in 9 Fig. 48. 98 NUTRITION. the interior of the body. When the food has been sufficiently digested there, it passes, by imbibition, into the general cav- ity of the body, (c,) which is filled with water, and mingling with it, flows thence into all parts of the an- imal. The jelly-fishes, (Medusas,) and some Worms, have a distinct stomach, with appendages branching off in every direction, (Fig. 31,) in which a more complete elabo- ration takes place. The little worms known by the name of Planaria, present a striking example of these ramifications of the intes- tine, (Fig. 49, e.) But here, likewise, the product of digestion mingles with the fluids of the cavity of the body which surround the intestine (d) and its branches, and cir- culation is not yet distinct from diges- Fig. 49. tion. 206. As we rise in the scale of animals, the functions concerned in nutrition become more and more distinct from each other. Digestion and circulation, no longer confounded, are accomplished separately, in distinct cavities. The most important organs concerned in di- gestion are the stomach, and the small and large intestine. The first indications of such a distinc- tion are perceived in the higher Radiata, such as the sea-urchins, (Fig. 50,) in which the stomach (s) is broader than either extremity of the intestine. The dimensions and form of the cavities of the intestine vary considerably, according to the mode of life of the ani- mal ; but the special functions assigned to them are invaria- ble ; and the three principal cavities succeed each other, in Fig. 50. OF DIGESTION. 99 every animal where they are found, in an invariable order ; first, the stomach, (s,) then the intestine, which is small at first, but often enlarged towards its termination. This arrangement may be seen by the follow- ing diagrams from a bee- tle and a land mollusk, where the same letters indicate corresponding parts, (Figs. 51, 52.) 207. From the mouth, (m,) the food passes into the stomach through a narrow tube in the neck, called the (Esophagus or gullet, (o.) This is not Fig. 51. Fig. 52. always a direct passage of uniform size ; but there is some- times a pouch, the crop, (c,) into which the food is first intro- duced, and which sometimes acquires considerable dimen- sions, especially in birds, and in some insects and mollusks, (Fig. 51.) In the stomach, the true digestive process is be- gun. The food no sooner arrives there than changes com- mence, under the influence of a peculiar fluid called the gas- tric juice, which is secreted by glands lining the interior of the stomach. The digestive action is sometimes aided by the movements of the stomach itself, which, by its strong contrac- tions, triturates the food. This is especially the case in the gizzard of some birds, which, in the hens and ducks, for in- stance, is a powerful muscular organ. In some of the Crus- tacea and Mollusks, as the Lobster and Aplysia, there are even solid organs for breaking down the food within the stomach itself. 208. The result of this process is the reduction of the food 100 NUTRITION. 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 lower animals, and chyme is circu- lated throughout the body ; this is the case in Polypi and Jelly- fishes, and some Worms and Mollusks. In other animals, however, the chyme thus formed is transferred to the intes- tine, by a peculiar movement, like that of a worm in creep- ing, which has accordingly received the name of vermicular or peristaltic motion. 209. The form of the small intestine (i) is less variable than that of the stomach. It is a narrow tube, with thin walls, coiled in various directions in the vertebrate animals, but more simple in the invertebrates, especially the insects. 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 sepa- ration of the truly nutritious parts, in the form of a milky liquid called chyle. The process is called chylification ; and there are great numbers of animals, such as the Insects, Crabs, and Loosters, some Worms, and most of the Mollusks, in which the product of digestion is not further modified by respiration, but circulates throughout the body as chyle. 210. The chyle is composed of minute, colorless globules, of a somewhat flattened form, (Fig. 53.) In the higher animals, the Vertebrates, it is taken up and carried into the blood by means of very minute vessels, called lymphatic vessels or lacteah, which are distributed every where in the walls of the intestine, and communicate OF DIGESTION. 101 with the veins, forming also in their course several glandular masses, as seen in a portion of intestine connected with a vein, in Fig. 54 ; 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. FlS- 54> 211. 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 the moutii of those animals that feed on solid substances, which serve for cutting or bruising the food into small fragments before it is swallowed ; and, in many of the lower animals, these organs are the only hard portions of the body. This process of subdividing or chewing the food is termed jnasti- cation. 212. Beginning with the Radiata, we find the apparatus for mastication partaking of the star-like arrangment which characterizes those animals. Thus in Scutella, (Fig. 55,) we have a pentagon composed of five triangular jaws, con- verging at their summits towards a central aperture which corresponds to the mouth, each one bearing a cutting 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 ob- jects which come between them. In some of the sea-urchins, 9* 102 NUTRITION. (Echinus,) this apparatus, which has been called Aristotle's Fig. 55. Fig. 56. lantern, (Fig. 56,) consists of 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 Scutella; only instead of being placed horizontally, they form an inverted pyramid. 213. Among the Mollusks, a few, like the cuttle-fishes, have solid jaws or beaks closely resembling the beak of a parrot, (Fig. 57,) which move up and down as in birds. But a much larger number rasp their food bv means of a flat tf Fig. 57. blade coiled up like a watch- Fig. 58. spring, the surface of which is covered with innumerable minute tooth-like points of a horny consistence, as seen in a highly magnified portion of the so-called tongue of Natica, (Fig. 58, a,) which, however, is only a modification of the beaks of cuttle-fishes. 214. The Articulata are remarkable, as a class, for the diversity and complication of their apparatus for taking and dividing their food. In some marine worms, Nereis, for example, the jaws consist of a pair of Fig. 59. curved, horny instruments, lodged in a sheath, (Fig. 59.) In spiders, these jaws are external, and OF DIGESTION. 103 sometimes mounted on long, jointed stems. Insects which masticate their food have, for the most part, at least two pairs of horny jaws, (Figs. 60, 61, m,j,) besides several additional pieces which serve for seizing and holding their food. Those which live on the fluids which they extract either from plants or from other animals, have the masticatory organs transformed into a trunk or tube for that purpose. This trunk is sometimes rolled up in a spiral manner, as in the butterfly, (Fig. 64;) or it is stiff, and folded beneath the V Fig. 61. Fig. 62. Fig. 63. Fig. 64. chest, as in the squash-bugs, (Fig. 62,) containing several piercers of extreme delicacy, (Fig. 63,) adapted to penetrate the skin of animals or other objects whose juices they extract ; or they are prolonged so as to shield the tongue when thrust out in search of food, as in the bees, (Fig. 61, t.) The crabs have their anterior feet transformed into a kind of jaws, and several other pairs of articulated appendages performing ex- o' 65. Fig. 66. clusively masticatory functions. Even in the microscopic Rotifers, we find very complicated jaws, as seen in a Brachi- onus, (Fig. 65,) and still more magnified in Fig. 66. But 104 NUTKITION. amidst this diversity of apparatus, there is one thing which characterizes all the Articulata, namely, the jaws always move sideways ; while those of the Vertebrates and Mollusks move up and down, and those of the Radiata concentrically. 215. In the Vertebrates, the jaws form a part of the bony skeleton. In most of them the lower jaw only is movable, and is brought up against the upper jaw by means of very strong mus- cles, the temporal and masseter Fig. 67. muscles, (Fig. 67, t, »i,) which perform the principal motions requisite for seizing and mas- ticating food. 216. The jaws are usually armed with solid cutting instruments, the TEETH, or else are enveloped in a horny covering, the beak, as in the birds and tortoises, (Fig. 68.) In some of the whales, the true teeth remain concealed in the Fig. 68. jaw-bone, and we have instead a range of long, flexible, horny plates or fans, fringed at the margin, which serve as strainers to separate the minute marine ani- mals on which they feed from the water drawn in with them, (Fig. 69.) A few are entirely des- titute of teeth, as the ant-eater, (Fig. 70.) 217. Though all the vertebrates possess jaws, Fig. 69. 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 , OF DIGESTION. 105 food ; some using them merely for seizing 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 the alligator, (Fig. 71,) the porpoises, and many fishes. A few of the latter, some of Fig. 70. Fig. 71. Fig. 72. the Rays, for example, have a sort of bony pavement, (Fig. 72,) composed of a peculiar kind of teeth, with which they crush the shells of the mollusks and crabs on which they feed. 218. The Mammals, however, are almost the only verte- brates which can properly be said to masticate their food. Their teeth are well developed, and pre- sent great diversity in form, arrangement and mode of inser- tion. Three kinds of teeth are usually distinguished in most of these animals, whatever may be Fig. 73. their mode of life ; namely, the cutting teeth, incisors ; the 106 NUTRITION. tusks or carnivorous teeth, canines ; and the grinders, molars, (Fig. 73.) The incisors (a) occupy the front of the mouth, the upper ones being set in the intermaxillary bones ; they are the most simple and the least varied, have generally a thin cutting summit, and are employed almost exclusively for seizing food, except in the elephant, in which they assume the form of large tusks. The canines (b) are conical, more elongated 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 carnivora 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 mastica- tion ; as in the babyroussa, &c. The molars (c) are the most important 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, to those with broad and level summits, as in the ruminants and rodents. 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. 219. The harmony of organs already spoken of (22-24) is illustrated, in a most striking manner, by the study of the teeth of the mammals, and especially of their molar teeth. So constantly do they correspond with the structure of the 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 show whether it feeds on flesh or vegetables, or both, but also to determine the particular group to which it is related. Thus, those beasts of prey which feed on insects, and which on that account have been called Insectivora, such OF DIGESTION. 107 as the moles and bats, have the molars terminated by several Fig. 74. Fig. 76- Fig. 75. sharp, conical points, (Fig. 74,) so arranged that the eleva- tions of one tooth fit exactly into the depressions of the tooth opposite to it. In the true Carnivora, (Fig. 75,) on the con- trary, the molars are compressed laterally, so as to have sharp, cutting edges, as in the bats ; and they shut by the side of each other, like the blades of scissors, thereby di- viding the food with great facility. 220. 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,) like the elephant, and some of the gnawers, (rodentia,) like the hare, (Fig. 76,) 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 subsist. Finally, the omnivora, those which feed on both flesh and fruit, like man and the monkeys, have the molars terminating in several rounded tubercles, being thus adapted to the mixed nature of their food. 221. Again, the mode in which the molars are combined with the canines and incisors furnishes excellent means of characterizing families and genera. Even the internal struc- ture of the teeth is so peculiar in each group of animals, and yet subject to such invariable rules, that it is possible to determine with precision the general structure of an animal, 108 NUTRITION. merely by investigating the fragment of a tooth under a mi- croscope. 222. Another process, subsidiary to digestion, is called insalivation. Animals which masticate their food have glands, in the neighborhood of the mouth, which secrete a fluid called saliva. This fluid mingles with the food as it is chewed, and prepares it also to be more readily swallowed. The salivary glands are generally wanting, or rudimentary, »r otherwise modified, in animals which swallow their food without mastication. After it has been masticated and min- gled with saliva, it is moved backwards by the tongue, and passes down through the oesophagus, into the stomach. This act is called deglutition or swallowing. 223. The wisdom and skill of the Creator is strikingly illustrated in the means he has afforded to every creature for securing the means for subsistence. Some animals have no ability to move from place to place, but are fixed to the soil ; as the oyster, the polyp, &c. These are dependent for subsistence upon such food as may stray or float near, and they have the means of securing it when it comes within their reach. The oyster closes its shell, and thus entraps its prey ; the polyp has flexible arms, (Fig. 77,) capable of great extension, which it throws instantly around any minute animal that comes in con- tact with it. The cuttle-fish, also, has elongated arms about the mouth, furnished with ranges of suckers, by which it secures its prey, (Fig. 47.) 224. Some are provided with instruments Fig. 77. for extracting food from places which would be otherwise inaccessible. Some of the mollusks, with their rasp-like tongue, (Fig. 58,) perforate the shells of other ani- mals, and thus reach and extract the inhabitant. Insects have various piercers, suckers, or a protractile tongue for the OF DIGESTION. 109 same purpose, (Figs. 61-64.) Many Annelides, the leeches for example, have a sucker, which enables them to produce a vacuum, and thereby draw out blood from the perforations they make in other animals. Many microscopic animals are provided with hairs or cilia around the mouth, (Fig. 65,) which by their incessant motion produce currents that bring within reach the still more minute creatures or particles on which they feed. 225. 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, even movable, and admirably adapted for the purpose. The woodpeckers have long, bony tongues, barbed at the tip, with which they draw out insects from deep holes and crevi- ces in the befrk 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 his tongue, the enlarged end of which is covered with a glutinous sub- stance to which they adhere. The elephant, whose tusks and short neck prevent him from bringing 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 abundant in this country, was furnished with a similar organ. Man and the monkeys employ the hand exclusively, for prehension. 226. 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 difficult to say how far aquatic animals re- quire 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 10 110 OF DIGESTION. known that they frequently 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. 226 a. Besides the more conspicuous organs above de- scribed, there are among the lower animals various micro- scopic apparatus for securing their prey. The lassos of polypi have been already mentioned incidentally, (223.) They are minute cells, each containing a thin thread coiled up in its cavity, which may be thrown out by inversion, and extend to a considerable length beyond the sac to which it is at- tached. Such lassos are grouped in clusters upon the ten- tacles, or scattered upon the sides of the Actinia and of most polypi. They occur also in similar clusters upon the tentacles and the disk of jelly-fishes. The nettling sensa- tion produced by the contact of many of these animals 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 movable stalk. The clasps, which may open and shut al- ternately, 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 diameter may seize and retain shrimps of half that length, notwithstanding their efforts to disentangle them- selves. CHAPTER SEVENTH. OF THE BLOOD AND CIRCULATION. 227. THE nutritive portions of the food are poured into the general mass of fluid which pervades every part of the body, out of which every tissue is originally constructed, and from time to time renewed. This fluid, in the general acceptation of the term, is called blood ; but it differs greatly in its essential constitution in the different groups of the Animal Kingdom. In polypi and medusse, it is merely chyme, (208 ;) in most mollusks and articulates it is chyle, (209 ;) but in vertebrates it is more highly organized, and constitutes what is properly called BLOOD. 228. 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 disks. Fig. 78. These vary in number with the natural heat of the animal from which the blood is taken. Thus, they are more nu- 112 OF THE BLOOD merous 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, (Fig. 78 ;) they are some- what larger, and of an oval form, in birds and fishes, (Figs. 79, 81 ;) and still larger in reptiles, (Fig. 80.) 229. The color of the blood in the vertebrates is bright red ; but in some invertebrates, as the crabs and mollusks, the nutritive fluid is nearly or quite colorless ; while in the worms and some echinoderms, it is variously colored yellow, orange, red, violet, lilac, and even green. 230. The presence of this fluid in every part of the body is one of the essential conditions of animal life. A per- petual current flows from the digestive organs towards the remotest parts of the surface ; and such portions as are not required for nutriment and secretions return to the centre of circulation, 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 in the liver. The blood is kept in an incessant CIRCULATION for this purpose. 231. 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, which occupy a somewhat higher rank, a similar liquid is distributed by pro- longations of the principal cavity to different parts of the body, (Fig. 31.) Currents are produced in these, partly by the general movements of the animal, and partly by means of the incessant vibrations of microscopic fringes, called vibratile cilia, which overspread the interior. In most of the mollusks and articulates, the blood (chyle) is also in immediate contact with the viscera, water being mixed with it in mollusks ; the vessels, if there are any, not forming a AND CIRCULATION. 113 complete circuit, but emptying into various cavities which interrupt their course. 232. In animals of still higher organization, as the verte- brates, we find the vital fluid enclosed in an appropriate set of vessels, by which it is successively conveyed throughout the system to supply nutriment and secretions, and to the respiratory organs, where it absorbs oxygen, or, in other words, becomes oxygenated. 233. The vessels in which the blood circulates are of two kinds : 1. The arteries, of a firm, elastic structure, which may be distended or contracted, according to the volume of their contents, and which convey the blood from the centre towards the surface, distributing it to every point of the body. 2. The veins, of a thin, membranous structure, furnished within with valves, (Fig. 82, v,) which aid in sustaining the column of blood, only allowing it to flow from the peri- phery towards the centre. The arteries con- stantly subdivide into smaller and smaller branches ; while the veins commence in minute twigs, and are gathered into branches and larger trunks, to unite finally into a few stems, near the J £ Ig. centre of circulation. 234. The extremities of the arteries and veins are con- nected by a net-work of extremely delicate vessels, called capillary ves- sels, (Fig. 83.) They pervade eveiy portion of the body, so that almost no point can be pricked without drawing blood. Their office is to o distribute the nutritive fluid to the organic cells, where all the important processes of nutrition are performed, such as the alimentation and growth of all organs and tissues, the elaboration of bile, milk, saliva, and 10* Fig. 83. 114 OF THE BLOOD other important products derived from blood, the removal of effete particles and the substitution of new ones, and all those changes by which the bright blood of the arteries be- comes 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. 235. 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, -p.CT 8, so arranged that, when the ves- sel contracts, the blood can flow only towards the head, and, being thence distributed to the body, is returned again into the dorsal vessel, (Fig. 84,) by fissures at its sides. 236. In all the higher animals there is a central organ, the hearty which forces the blood through the arteries to- wards the periphery, and receives it again on its return. The HEART is a hollow, muscular organ, of a conical form, which dilates and contracts at regular intervals, independ- ently 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 respiratory organs, and indicate the higher or lower rank of an animal, as determined by the quality of the blood distributed in those organs. 237. In the mammals and birds the heart is divided by a vertical partition into two cavities, each of which is again divided into two compartments, one above the other, as seen in the diagram, (Fig. 85.) The two upper cavities are called AND CIRCULATION. 115 auricles, and the two lower ventricles. Reptiles have two Fig. 85. Fig. 86. Fig. 87. auricles and one ventricle, (Fig. 86.) Fishes have one auri- cle and one ventricle only, (Fig. 87.) 238. 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 a valve, to prevent its reflux ; while the ventricles, by their contractions, force the blood through arteries into the lungs, and through the body gen- erally. 239. The two auricles dilate at the same instant, and also contract simultaneously ; so also do the ventricles. These successive contractions and dilatations constitute the pulsa- tions of the heart. The contraction is called systole, and the dilatation is called diastole. Each pulsation consists of two movements, the diastole or dilatation of the ventricles, during which the auricles contract, and the systole or con- traction 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. 240. The course of the blood in those animals which have four cavities to the heart is as follows, beginning with the left ventricle, (Fig. 85, I. v.) By the contraction of this 116 OF THE BLOOD ventricle, the blood is driven through the main arterial trunk, called the aorta, (Fig. 90, a,) and is distributed by its branches throughout the body ; it is then collected by the veins, carried back to the heart, and poured into the right auricle, (Fig. 85, r a,) which sends it into the right ventricle rv.) The right ventricle propels it through another set of arteries, the pulmonary arteries, (Fig. 90, £>,) to the lungs, (/ ; ) it is there collected by the pulmonary veins, and con- veyed to the left auricle, (Fig. 85, I a,) by which it is returned to the left ventricle, thus completing the circuit. 241. Hence the blood in performing its whole circuit passes twice through the heart. The first part of this cir- cuit, 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 cir- culation : this double circuit is said to be a complete circu- lation. In this case the heart may be justly regarded as two hearts conjoined, and in fact the whole of the lesser cir- culation intervenes in the passage of the blood from one side of the heart to the other ; except that during the embryonic period there is an opening between the two auricles, which closes as soon as respiration commences. 242. In reptiles, (Fig. 86,) the venous blood from the body is received into one auricle, and the oxygenated blood from the lungs into the other. These throw their contents 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 luno-s in a single circuit, the circulation is said to be incomplete. In the Crocodiles, the ventricle has a partition which keeps sep- arate the two kinds of blood received from the auricles ; but the mixture soon takes place by means of a special artery, which passes from the pulmonary artery to the aorta. 243. In fishes, (Fig. 87,) the blood is carried directly AND CIRCULATION. 117 from the ventricle to the gills, which are their chief respir- atory organs ; thence it passes into arteries for distribution to the system in general, and returns by the veins to the auricle. Here the blood, in its circuit, passes but once through the heart ; but the heart of a fish corresponds nev- ertheless to the heart of a mammal, and not to one half of it, as has often been maintained, for the gills are not lungs. 244. Crabs and other Crustacea have but a single ventri- cle, without an auricle. In the mollusks, there is likewise but a sinsjle ven- O tricle, as in Natica, (Fig. 88, 7i.) Some have in addition one or two auri- cles. These auricles are sometimes so disioined •I as to form so many isolated hearts, as in the cuttle-fish. Among Radiata, the sea-urchins are provided with a tubular heart. CHAPTER EIGHTH. OF RESPIRATION. 245. FOR 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 RESPIRATION to bring the blood into communication with the air. 246. Among animals which breathe in the open air, some have a series of tubes branching through the interior of the body, called trachea, (Fig. 89, ^,) opening externally upon the sides of the body, by small aper- tures, called stigmata, (s ; ) as in insects and in some spiders. But the most com- mon mode of respiration is by means of LUNGS, a pair of peculiar spongy or cel- lular organs, in the form of large pouches, which are the more complicated in pro- portion to the quantity of air to be con- sumed. 247. In the lower vertebrata, provided with lungs, they form a single organ ; but in the higher classes they are in pairs, placed in the cavity formed by the ribs, one on each side of Fig. 89. OF RESPIRATION. 119 Fig. 90. the vertebral column, and enclosing the heart (h) between them, (Fig. 90, Z Z.) The lungs communicate with the atmos- phere by means of a tube composed of cartilaginous rings which arises from the back part of the mouth, and divides below, first into a branch for each organ, and then into in- numerable branches penetrating their whole mass, and finally terminating in minute sacs. This tube is the trachea or windpipe, (w?,) and its branches are the bronchi. In the higher air-breath- ing animals the lungs and heart occupy an apartment by themselves, the chest, which is separated from the other con- tents of the lower arch of the vertebral column, (161,) by a fleshy partition, called the diaphragm, passing across the cavity of the body, and arching up into the chest. The only access to this apartment from without is by the glottis, (Fig. 22, 0,) through the trachea. 248. The mechanism of respiration by lungs may be com- pared 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 enlargment causes the air to rush in through the trachea, distending the lung so as to fill the additional space. When the diaphragm is again relaxed, and the ribs are allowed to subside, the cavity is again dimin- ished, and the air expelled. These movements are termed inspiration or inhalation, and expiration. The spongy pul- monary substance being thus distended by air, the blood sent from the heart is brought into such contact with it as to allow the requisite interchange to take place, (235.) 249. The respiration of animals breathing in water is ac- 120 OF RESPIRATION. complished by a different apparatus. The air is to be 9 derived from the water, in which more or less is always diffused. The organs for this purpose are Fig. 91. called branchice or gills, and are either delicate tufts or plumes floating outside of the body, as in some of the marine worms, (Fig. 33,) and many mollusks, (Fig. 91, g ;) or they consist of deli- cate combs and brushes, as in fishes, (Fig. 92,) crabs, and most mollusks, (Fig. 88, g.) These gills are al- Fig. 92. ways so situated that the water has free access to them. In the lower aquatic animals, such as the polypi, and some jelly-fishes and mollusks, respiration takes place by the incessant motions of vibratory cilia, which fringe both the outside and the cavities of the body ; the cur- rents they produce bringing constantly fresh supplies of water, containing air, into contact with the respiratory surface. 250. Many animals living in water, however, rise to the surface and breathe the atmosphere there, or are furnished with the means of carrying away a temporary supply of air, whilst others are furnished with reservoirs in which the blood requiring oxygenation may be accumulated, and their stay under water prolonged. This is the case with the seals, whales, tortoises, frogs, many insects and mollusks, &c. 251. 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, car- bonic 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. OF RESPIRATION. 121 252. An immediately obvious effect of respiration in the red-blooded animals is a change of color ; the blood, in passing through the respiratory organs, being changed from a very dark purple to a bright scarlet. In the great circula- tion (241) the scarlet blood occupies the arteries, and is usu- ally called red blood, in contradistinction from the venous blood, which is called Hack blood. In the lesser circulation, on the contrary, the arteries carry the dark, and the veins the red blood. 253. The quantity of oxygen consumed by various ani- mals in a given time has been accurately ascertained by ex- periment. It has been found, for instance, that a common- sized man consumes, on an average, about 150 cubic feet in twenty-four hours ; and as the oxygen constitutes but 21 per cent, of the atmosphere, it follows that he inhales, during a day, about 700 cubic feet of atmospheric air. In birds, the respiration is still more active, while in reptiles and fishes it is much more sluggish. 254. The energy and activity of an animal is, therefore, somewhat dependent on the activity of its respiration. Thus the toad, whose movements are very sluggish, respires much more slowly than the mammals, birds, and even insects ; and it has been ascertained that a butterfly, notwithstanding its comparatively diminutive size, consumes more oxygen than a toad. 255. The circulation and respiration have a reciprocal in- fluence upon each other. If the heart be powerful, or if on violent exercise a more rapid supply of blood to repair the consequent waste is demanded, (201,) respiration must be proportionally 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 is rendered more stimulating by greater oxygenation, and causes an ac- 11 122 OF RESPIRATION. celeration of the circulation. The quantity of air consumed varies, therefore, with the proportion of the blood which is sent to the lungs. 256. The proper temperature of an animal, or what is termed ANIMAL HEAT, depends on the combined activity of 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 mam- mals it is generally from 95° to 105°. These bear the general designation of warm-blooded animals. 257. Reptiles, fishes, and most of the still lower 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 often, however, a little above it when the external tempera- ture is very low, though some may be frozen without the loss of life. For this reason, they are denominated cold-blooded animals ; and all animals which have such a structure of the heart that only a part of the blood which enters it is sent to the respiratory organs, are among them, (243.) 258. The production of animal heat is obviously connected 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. Flow 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 OF RESPIRATION. 123 uniform distribution of heat through the body, has not yet been satisfactorily ascertained. 259. 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 HIBERNATION, 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 attending it fully illustrate the laws already stated, (254-8.) 260. There is another point of view in which respiration should be considered, namely, with reference to the buoy- ancy of animals, or their power of rising in the atmosphere, and their ability to live at different depths in the water, under a diminished or increased pressure. The organs of res- piration of birds and insects are remarkably adapted for the purpose of admitting at will a greater quantity of air into their body, the birds being provided with large pouches ex- tending from the lungs into the abdominal cavity and into the bones of the wing. In insects the whole body is pene- trated 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 micro- scopic tubes, penetrating from the surface into the substance, or the cavities of the body, 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 mollusks they are more numerous in the fleshy parts, as, for example, in the 124 OF RESPIRATION. foot, which they help to distend, and communicate with the main cavity of the body, supplying it also with liquid ; in echinoderms they pass through the skin, and even through 260 a. In order fully to appreciate the homologies between the various respiratory apparatus observed in different animals, it is ne- cessary to resort to a strict comparison of the fundamental connec- tions of these organs with the whole system of organization, rather than to the consideration of their special adaptation to the elements in which they live. In Vertebrates, for instance, there are two sets of distinct respiratory organs, more or less developed at different pe- riods of life, or in different groups. All Vertebrates, 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 res- piration 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 growth. Again, all Vertebrates have lungs, opening in or near the head ; but the lungs are fully devel- oped only in Mammalia, birds, and the higher reptiles, in propor- tion as the branchial respiration is reduced ; whilst in fishes the air- bladder constitutes a rudimentary lung. 260 b. In Articulates, there are also two sorts of respiratory or- gans ; aerial, called tracheae in insects, and lungs in spiders ; and aquatic, in Crustacea and worms, called gills. But these trachea and lungs open separately upon the two sides of the body, (air never being admitted through the mouth or nostrils in Articulates ;) the gills are placed in pairs ; those which are like the trachea? occupying a similar position, so that there are nearly as many pairs of tracheae and gills as there are segments in these animals, (Figs. 89 and 33.) The different respiratory organs in Articulates are in reality mere modifications of the same apparatus, as their mode of formation and successive metamorphoses distinctly show, and cannot be compared with either the lungs or gills of Vertebrates ; they are special organs not found in other classes, though they perform the same functions. The same may be said of the gills and lungs of mollusks, which are essentially alike in structure, the lungs of snails and slugs being only a modification of the gills of aquatic mollusks ; but these two kinds of organs differ again in their structure and relations from the tracheae and gills of Articulates, as much as from the lungs and gills OF RESPIRATION. 125 the hard shell, whilst in polyps they perforate the walls of the general cavity of the body, which they constantly fill with water. of Vertebrates. In those Radiates which are provided with distinct respiratory organs, such as the Echinoderms, we find still another typical structure, their gills forming bunches of fringes around the mouth, or rows of minute vesicles along the radiating segments of the body. 11* CHAPTER NINTH. OF THE SECRETIONS. 261. WHILE, by the process of digestion, a homogeneous fluid is prepared from the food, and supplies 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 purposes, while other portions of it which have become useless or injurious to the system are taken up by different organs, and expelled in different forms. This process is termed SECRETION. 262. The organs by which these operations are per- formed are much varied, consisting either of flat surfaces or membranes, of minute simple sacs, or of delicate elongated tubes, all lined with minute cells, called epithelium cells, which latter are the real agents in the process. Every sur- face of the body is covered by them, and they either dis- charge their products directly upon the surface, as on the mucous membrane, or they unite in clusters and empty into a common duct, and discharge by a single orifice, as is the case with some of the intestinal glands, and of those from which the perspiration issues upon the skin, (Fig. 94.) OF THE SECRETIONS. 127 263. 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, such as the salivary glands, the kidneys, and the liver. In these, clusters of sacs "pv" "s" open into a common canal, and this canal unites with similar ones forming larger trunks, such as we find in the salivary glands, (Fig. 93,) and finally they all discharge by a single duct. 264. 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 saliva, tears, milk, &c., some of which differ but little in their composition from that of the blood itself, and might be 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. tt 265. 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. 266. We have already seen (37) that all animal tissues admit of being traversed by liquids and gases. This mutual transmission of fluids from one side of a membrane to the other is termed endosmosis and exosmosis, or imbibition and transudation, and is a mechanical, rather than a vital, phe- nomenon, inasmuch as it takes place in dead as well as in 128 OF THE SECRETIONS. living tissues. The bloodvessels, 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 superficial loss is termed exhalation. It is most active where the bloodvessels most abound, and accord- ingly 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 exhalation, five eighths of the whole weight of the substances received into it. 267. The skin, or outer envelop of the body, is otherwise 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 some- times gradual and continual, as in man. In fishes and many mollusks, it comes off in the form of slime, which is, in fact, composed of cells detached from the surface of the skin. Sometimes the loss is periodical, when it is termed moulting. Thus, the mammals cast their hair, and the deer their horns, the birds their feathers, the serpents their skins, the crabs their test, the caterpillars their outer envelop, with all the hairs growing from it. 268. The skin presents such a variety of structure in the different groups of animals as to furnish excellent distinctive characters of species, genera, and even families, as will hereafter be shown. In the vertebrates we may recognize several distinct layers, of unequal thickness, as may be seen in figure 94, which represents a magnified section of the human skin, traversed by the sudoriferous canals. The lower and thickest layer, (a,) is the cut-is, 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 network of bloodvessels, OF THE SECRETIONS. 129 usually termed the vascular layer. The superficial layer (c) is the epidermis, or cuticle. The cells of which it is com- posed are distinct at its inner portion, but become dried and flattened as they are pushed outwards. It is supplied with neither vessels nor nerves, and, conse- quently, is insensible. Between these two layers, and more especially con- nected with the cuticle, is the rete muco- sum, (&,) 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 Fig. 94. mammals, and the solid coverings of the Crustacea, are merely modifications of the epidermis. On the other hand, the feathers of birds and the scales of fishes arise from the vascular layer. 269. Of all the Excretions, if we except that from the Lungs, the bile seems to be the most extensive and im- portant ; and hence a liver, or some analogous organ, by which bile is secreted, is found in animals of every depart- ment ; while some, or all, of the other glands are want- ing in the lower classes of animals. In Vertebrates, the liver is the largest of all the organs of the body. In mol- lusks, it is no less preponderant. In the gasteropods, like the snail, it envelopes the intestine in its convolutions, (Fig. 52 ;) and in the acephala, like the clam and oyster, it generally surrounds the stomach. In insects it is found in the shape of long tubes, variously contorted and interlaced, (Fig. 51.) In the Radiata, this organ is largely developed, especially among the echinoderms. In the star-fishes it extends into 130 OF THE SECRETIONS. all the recesses of the rays ; and, in color and structure, re- sembles the liver of mollusks. Even in polyps, we find pe- culiar brown cells lining the digestive cavity, which, proba- bly, perform functions similar to those of the liver in the higher animals. 270. The great importance of the respiratory organs in discharging carbon from the blood has already been spoken of, (245, 251.) The substances removed by the liver and the lungs are of the same class, being those which are desti- tute of nitrogen. These organs seem, in some sense, sub- sidiary to each other ; and hence, in those animals where the respiratory organs are largely developed, the biliary organs are comparatively small, and vice versa. Another and opposite class of impurities, and no less pernicious if retained in the blood, is removed by the KIDNEYS ; and, consequently, organs answering to the kidneys are found very far down in the series of animals. Most of the peculiar ingredients of the urine are capable of assuming solid, crys- talline forms ; and, in some animals, as in reptiles and birds, the whole secretion of the kidneys is solid. In most cases, however, the urinary salts are largely diluted with water ; arid, as the lungs and liver are supplementary to each other in the removal of carbon, so the lungs, the kid- neys, and the skin mutually relieve each other in the removal of the watery portions of the blood. CHAPTER TENTH. EMBRYOLOGY. SECTION I. OF THE EGG. 271. THE functions of vegetative life, of which we have treated in the preceding chapters, namely, digestion, circu- lation, respiration, and secretion, have for their end the pres- ervation of the individual. We have now to treat of the functions that serve for the perpetuation of the species, namely, those of reproduction, (200.) 272. It has been generally admitted that animals as well as plants are the offspring of individuals of the same kind ; and vice versa^ that none of them can give birth to individ- uals differing from themselves : but recent investigations o * o have modified to a considerable extent this view, as we shall see hereafter. 273. Reproduction in animals is almost universally accom- plished by the association of individuals of two kinds, males and females, living commonly in pairs or in flocks, each of them characterized by peculiarities of structure and external appearance. As this distinction prevails throughout the ani- mal kingdom, it is always necessary, if we would obtain a correct and complete idea of a species, to take into account the peculiarities of both sexes. Every one is familiar with the differences between the cock and the hen, the lion and the lioness, &c. Less prominent peculiarities are observed in 132 EMBRYOLOGY. most Vertebrates. Among Articulata, the differences are no less striking, the males being often of a different shape and color, as in crabs, or having even more complete organs, as in many tribes of insects, where the males have wings, while the females are destitute of them, (Fig. 147.) Among mol- lusks, the females have often a wider shell. 274. Even higher distinctions than specific ones are based upon peculiarities of the sexes ; for example, the whole class of Mammalia is characterized by the fact that the female is furnished with organs for nourishing her young with a peculiar liquid, the milk, secreted by herself. Again, the Marsupial, such as the opossum and kangaroo, are dis- tinguished by the circumstance that the female has a pouch into which the young are received in their immature con- dition at birth. 275. That all animals are produced from eggs, (Omne vivum ex 000,) is an old adage in Zoology, which modern researches have fully confirmed. In tracing back the phases of animal life, we invariably arrive at an epoch when the incipient animal is enclosed within an egg. It is then called an embryo, and the period passed in this condition is called the embryonic period. 276. Before the various classes of the animal kingdom had been attentively studied during the embryonic period, all animals were divided into two great divisions : the ovip- arous, comprising those which lay eggs, such as birds, reptiles, fishes, insects, mollusks, &c., and the viviparous^ which bring forth their young alive, like the mammalia, and a few from other orders, as the sharks, vipers, &c. This distinction lost much of its importance when it was shown that viviparous animals are produced from eggs, as well as the oviparous ; only that their eggs, instead of being laid before the development of the embryo begins, undergo their early changes in the body of the mother. Production from OF THE EGG. 133 Fig. 95. eggs should, therefore, be considered as a universal charac- teristic of the Animal Kingdom. 277. Form of the Egg. — The general form of the egg is more or less spherical. The eggs of birds have the form of an elongated spheroid, narrow at one end ; and this form is so constant, that the term oval has been universally adopted to designate it. But this is by no means the usual form of the eggs of other animals. In most instances, on the contra- ry, they are spherical, especially among the lower animals. Some have singular appendages, as those of the skates and sharks, (Fig. 95,) which are shaped like a hand-barrow, with four hooked horns at the corners. The eggs of the hydra, or fresh water polyp, are thickly covered with prickles, (Fig. 96.) Those of certain insects, the Podurella, for example, are furnished with fila- ments which give them a hairy aspect, (Fig. 97 ;) others are cylindrical or prismatic ; and frequently the surface is sculptured. 278. Formation of the Egg. — The egg originates within peculiar organs, called ovaries, which are glandular bodies, usually situated in the abdominal cavity. So long as the eggs remain in the ovary, they are very minute in size. In this condition they are called ovarian, or primitive eggs. They are identical in all animals, being, in fact, merely little cells (u) containing yolk, (?/,) and including other smaller cells, the germinative vesicle, (g,) and the germinative dot, (tZ.) The yolk itself, with its membrane, (•y,) is formed while the egg remains in the ovary. It is afterwards enclosed in another envelope, the shell membrane, which may remain soft, (s,) 12 Fig. 96. Fig. 97. Fig. 98. 134 EMBRYOLOGY. or be further surrounded by calcareous deposits, the shell proper, (Fig. 101, s.) The number of these eggs is large, in proportion as the animal stands lower in the class to which it belongs. The ovary of a herring contains more than 25,000 eggs ; while that of birds contains a much smaller oJD f number, perhaps one or two hundred only. 279. Ovulation. — Having attained a certain degree of maturity, which varies in different classes, the eggs leave the ovary. This is called ovulation, and must not be con- founded with the laying of the eggs, which is the subsequent expulsion of them from the abdominal cavity, either imme- diately, or through a special canal, the oviduct. Ovulation takes place at certain seasons of the year, and never be- fore the animal has reached a particular age, which is commonly that of its full growth. In a majority of species, ovulation is repeated for a number of years consecutively, generally in the spring in terrestrial animals, and frequently several times a year ; most of the lower aquatic animals, how- ever, lay their eggs in the fall, or during winter. In others, on the contrary, it occurs but once during life, at the period of maturity, and the animal soon afterwards dies. Thus the but- terfly and most insects die, shortly after having laid their eggs. 280. The period of ovulation is one of no less interest to the zoologist than to the physiologist, since the peculiar characteristics of each species are then most clearly marked. Ovulation is to animals what flowering is to plants ; and, indeed, few phenomena are more interesting to the student of nature than those exhibited by animals at the pairing season. Then their physiognomy is the most animated, their song the most melodious, and their attire the most brilliant. Some birds appear so different at this time, that zoologists are always careful to indicate whether or not a bird is represented at the breeding season. Fishes, and many other animals, are ornamented with much brighter colors at this period. OF THE EGG. 135 281. Laying. — After leaving the ovary, the eggs are either discharged from the animal, that is, laid ; or they continue their development within the parent animal, as is the case in some fishes and reptiles, as sharks and vipers, which, for that reason, have been named ovo -viviparous animals. The eggs of the mammalia are not only developed within the mother, but become intimately united to her ; this peculiar mode of development has received the name of gestation. • 282. Eggs are sometimes laid one by one, as in birds ; sometimes collectively and in great numbers, as in the frogs, the fishes, and most of the invertebrates. The queen ant of the African termites lays 80,000 eggs in twenty-four hours ; and the common hair- worm, (Gordius,) as many as 8,000,000 in less than one day. In some instances they are united in clusters by a gelatinous envelop ; in others they are -pig. 99. enclosed in cases or between membranous disks, forming long strings, as in the eggs of the Pyrula shell, (Fig. 99.) The conditions under which the eggs of different animals are placed, on being laid, are very different. The eggs of birds, and of some insects, are deposited in nests constructed for that purpose by the parent. Other animals carry their eggs attached to their bodies ; sometimes under the tail, as in the lobsters and crabs, sometimes hanging in large bun- dles on both sides of the tail, as in the Mo- noculus, (Fig. 100, «.) Fig. 100. 283. Some toads carry them on the back, and, what is most extraordinary, it is the male which undertakes this office. Many mollusks, the Unio for example, have them enclosed between the folds of the gills during incubation. In the jelly fishes and polyps, they hang in clusters, either 136 EMBRYOLOGY. outside, (Fig. 77, o,) or inside, at the bottom of the cavity of the body. Some insects, such as the gad-flies, deposit their eggs on other animals. Finally, many abandon their eggs to the elements, taking no further care of them after they have been laid ; such is the case with most fishes, some insects, and many mollusks. As a general rule, it may be said that animals take the more care of their eggs and brood as they occupy a higher rank in their respective classes. 284. The development of the embryo does not always take place immediately after the egg is laid. A considera- ble time, even, may elapse before it commences. Thus, the first eggs laid by the hen do not begin to develop until the whole number which is to constitute the brood is deposited. The eggs of most butterflies, and of insects in general, are laid in autumn, in temperate climates, and remain unchanged until the following spring. During this time, the principle of life in the egg is not extinct, but is simply inactive, or in a latent state. This tenacity of life is displayed in a still more striking manner in plants. The seeds, which are equivalent to eggs, preserve for years, and even for ages, their power to germinate. Thus, there are some well- authenticated cases in which wheat taken from the ancient catacombs of Egypt has been made to sprout and grow. 285. A certain degree of warmth is requisite for the hatching of eggs. Those of birds, especially, require to be submitted, for a certain length of time, to a uniform tem- perature, corresponding to the natural heat of the future chicken, which is naturally supplied by the body of the parent. In other words, incubation is necessary for their growth. Incubation, however, is not a purely vital phenom- enon, but may be easily imitated artificially. Some birds of warm climates dispense with this task ; for example, the ostrich often contents herself with depositing her eggs in the sand of the desert, leaving them to be hatched by the sun. In OF THE EGG. 137 like manner, the eggs of most birds may be hatched by main- taining them at the proper temperature by artificial means. Some fishes are also known to build nests and to sit upon their eggs, as the sticklebacks, sun-fishes, and cat-fishes ; but whether they impart heat to them or not, is doubtful. Before entering into the details of embryonic transfor- mations, a few words are necessary respecting the composi- tion of the egg. 286. Composition of the Egg. — The egg is composed of several substances, varying in structure, as well as in appearance. Thus, in a hen's egg, (Fig. 101,) we have first a calcareous shell, (s,) lined by a double membrane, the shell membrane, (m ;) then an albuminous substance, the white, (a,} in which several layers may be distinguished ; within this we find the yolk, (y,) enclosed in its membrane ; and before it was laid, there was in the midst of the latter a mi- nute vesicle, the germinative vesicle, (Fig. 98, g,) containing a still smaller one, the germinative dot* (d.) These different parts are not equally important in a physiological point of view. The most conspicuous of them, namely, mi the shell and the white, are not es- sential parts, and therefore are often wanting ; while the yolk, the ger- minative vesicle, and the germina- tive dot are found in the eggs of all animals ; and out of these, and of these only, the germ is formed, in the position shown by Fig. 101, e. 287. The vitellus or yolk (Fig. 101, y) is the most essen- tial part of the egg. It is a liquid of variable consistence, sometimes opaque, as in the eggs of birds, sometimes trans- parent and colorless, as in the eggs of some fishes and mollusks. On examination under the microscope, it appears to be composed of an accumulation of granules and oil-drops. 12* Fig. 101. 138 EMBRYOLOGY. The yolk is surrounded by a very thin skin, the vitelline membrane, (Fig. 98, v.) In some insects, when the albumen is wanting, this membrane, surrounded by a layer of pecu- liar cells, forms the exterior covering of the egg, which, in such cases, is generally of a firm consistence, and sometimes even horny. 288. The germinative vesicle (Fig. 98, g) is a cell of ex- treme delicacy, situated, in the young egg, near the middle of the yolk, and easily recognized by the greater transpar- ency of its contents when the yolk is in some degree opaque, as in the hen's egg, or by its outline, when the yolk itself is transparent, as in eggs of fishes and mollusks. It contains one or more little spots, somewhat opaque, appearing as small dots, the germinal dots, (d.) On closer examination, these dots are themselves found to contain smaller nucleoli. 289. The albumen, or white of the egg, (Fig. 101, a,) is a viscous substance, generally colorless, but becoming opaque white on coagulation. Voluminous as it is in birds' eggs, it nevertheless plays but a secondary part in the histo- ry of their development. It is not formed in the ovary, like the yolk, but is secreted by the oviduct, and deposited around the yolk, during the passage of the egg through that canal. On this account, the eggs of those animals in which the ovi- duct is wanting, are generally without the albumen. In birds, the albumen consists of several layers, one of which, the clialazcB, (c,) is twisted. Like the yolk, the albumen is surrounded by a membrane, the shell membrane, (w,) which is either single or double, and in birds, as also in some reptiles and mollusks, is again protected by a calcareous covering, forming a true shell, (s.) In most cases, how- ever, this envelop continues membranous, particularly in the eggs of the mollusks, most crustaceans and fishes, salaman- ders, frogs, &c. Sometimes it is horny, as in the sharks and skates. DEVELOPMENT OF THE YOUNG WITHIN THE EGG. 139 SECTION II. DEVELOPMENT OF THE YOUNG WITHIN THE EGG. 290. The formation and development of the young ani- mal within the egg is a most mysterious phenomenon. From a hen's egg, for example, surrounded by a shell, and com- posed, as we have seen, (Fig. 101,) of albumen and yolk, with a minute vesicle in its interior, there is produced, at the end of a certain time, a living animal, composed apparently of elements entirely different from those of the egg, en- dowed with organs perfectly adapted to the exercise of all the functions of animal and vegetative life, having a pul- sating heart, a digestive apparatus, organs of sense for the reception of outward impressions, and having, moreover, the faculty of performing voluntary motions, and of experi- encing pain and pleasure. These phenomena are certainly sufficient to excite the curiosity of every intelligent person. 291. By opening eggs which have been subjected to incu- bation during different periods of time, we may easily satisfy ourselves that these changes are effected gradually. We thus find that those which have undergone but a short incu- bation exhibit only faint indications of the future animal ; while those upon which the hen has been sitting for a longer period include an embryo chicken proportionally more developed. Modern researches have taught us that these gradual changes, although complicated, and at first sight so mysterious, follow a constant law in each great division of the Animal Kingdom. 292. The study of these changes constitutes that peculiar branch of Physiology called EMBRYOLOGY. As there are differences in the four great departments of the Animal 140 EMBRYOLOGY. Kingdom perceptible at an early stage of embryonic life, quite as obvious as those found at maturity, and as the phases of embryonic development furnish important indi- cations for the natural classification of animals, we propose to give the outlines of Embryology, so far as it may have reference to Zoology. 293. In order to understand the successive steps of em- bryonic development, we must bear in mind that the whole animal body is formed of tissues, the elements of which are cells, (39.) These cells, however, are more or less diversi- fied and modified, or even completely metamorphosed in the full grown animal ; but, at the commencement of embry- onic life, the whole embryo is composed of minute cells of nearly the same form and consistence, originating within the yolk, and constantly undergoing changes under the influence of life. New cells are successively formed, while others disappear, or are modified and so transformed as to become bones, muscles, nerves, &c. 294. We may form some idea of this singular process, by noticing how, in the healing of a wound, new substance is supplied by the transformation of blood. Similar changes take place in the embryo, during its early life ; only, instead of being limited to some part of the body, they pervade the whole animal. 295. The changes commence, in most animals, soon after the eggs are laid, and are continued without interruption until the development of the young is completed ; in others, birds for example, they proceed only to a certain extent, and are then suspended until incubation takes place. The yolk, which at first consists of a mass of uniform appearance, grad- ually assumes a diversified aspect. Some portions become more opaque, and others more transparent ; the germinal vesicle, which was in the midst of the yolk, rises to its upper part where the germ is to be formed. These early changes DEVELOPMENT OF THE YOUNG WITHIN THE EGG. 141 are accompanied, in some animals, by a rotation of the yolk within the egg, as may be distinctly seen in some of the mollusks, especially in the snails. 296. At the same time, the yolk undergoes a peculiar process of segmentation. It is first divided into halves, forming distinct spheres, which are again regularly sub- divided into two more, and so on, till the whole yolk as- sumes the appearance of a mulberry, each of the spheres of which it is composed having in its interior a transparent vesicle. This is the case in mammalia, most mollusks, worms, &c. In many animals, however, as in the naked reptiles and fishes,* this segmentation is only partial, the divisions of the yolk not extending across its whole mass. 297. But whether complete or partial, this process leads to the formation of a germ comprising the whole yolk, or rising above it as a disk-shaped protuberance, composed of little cells, which has been variously designated under the names of germinative disk, proligerous disk, blastoderma, germinal membrane. In this case, however, that portion of the yolk which has undergone less obvious changes forms, nevertheless, part of the growing germ. The disk again gradually enlarges, until it embraces the whole, or nearly the whole, of the yolk. 298. At this early epoch, namely, a few days, and some- times a few hours, after development has begun, the germ proper con- sists of a single layer composed Fig. 102. Fig. 103. * In the Birds and higher reptiles we find, in the mature egg, a peculiar organ, called cicatricula, which may, nevertheless, have been formed by a similar process before it was laid. 142 EMBRYOLOGY. of very minute cells, all of which are alike in appearance and form, (Fig. 102, g.) But soon after, as the germ increases in thickness, several layers may be discerned, in vertebrated animals, (Fig. 103,) which become more and more distinct. 299. The upper layer, (s,) in which are subsequently formed the organs of animal life, namely, the nervous sys- tem, the muscles, the skeleton, &c., (59,) has received the name of serous or nervous layer. The lower layer, (m,) which gives origin to the organs of vegetative life, and espe- cially to the intestines, is called the mucous or vegetative layer, and is generally composed of larger cells than those of the upper or serous layer. Finally, there is a third layer, (v,) interposed between the two others, giving rise to the formation of blood and the organs of circulation ; whence it has been called blood layer, or vascular layer. 300. From the manner in which the germ is modified, we can generally distinguish, at a very early epoch, to what de- partment of the animal kingdom an individual is to belong. Thus, in the Articulata, the germ is divided into segments, indicating the transverse divisions of the body, as, for example, in the embryo of the crabs, (Fig. 104.) The germ of the vertebrated ani- mals, on the other hand, displays a longitudinal furrow, which marks the position the future back-bone is to occupy, (Fig. 105.) 301. The development of this furrow is highly important, as indicating the plan of structure of vertebrated animals in general, as will be shown by the following figures, which represent vertical sections of the embryo at different epochs.* Fig. 104. Fig. 105. * In these figures, the egg is supposed to be cut down through the mid- dle, so that only the cut edge of the embryo is seen ; -whereas, if viewed DEVELOPMENT OF THE YOUNG WITHIN THE EGG. 143 At first the furrow (Fig. 106, 1} is very shallow, and a lit- Fig. 106. Fig. 107. Fig. 108. tie transparent, narrow band appears under it, called the primitive stripe, (a.) The walls of the furrow consist of two raised edges formed by a swelling of the germ along both sides of the primitive stripe. Gradually, these walls grow higher, and we perceive that their summits have a tendency to ap- proach each other, as seen in Fig. 107 ; at last they meet and unite completely, so that the furrow is now changed into a closed canal, (Fig. 108, Z>.) This canal is soon filled with a peculiar liquid, from which the spinal marrow and brain are formed at a later period. 302. The primitive stripe is gradually obliterated by a peculiar organ of a cartilaginous nature, the dorsal cord, formed in the lower wall of the dorsal canal. This is found in the embryos of all vertebrates, and is the representative of the back-bone. In the mean time, the margin of the germ gradually extends farther and farther over the yolk, so as finally to enclose it entirely, and form another cavity in which the organs of vegetative life are to be developed. Thus the embryo of vertebrates has two cavities, namely, the upper one, which is very small, containing the nervous system, and the lower, which is much larger, for the intes- tines, (161.) 303. In all classes of the Animal Kingdom, the embryo proper rests upon the yolk, and covers it like a cap. But the direction by which its edges approach each other, and from above, it would extend over the yolk in every direction, and the furrow at b, of Fig. 106, would appear as in Fig. 105. 144 EMBRYOLOGY. Fig. 109. unite to form the cavity of the body, is very unlike in dif- ferent animals ; and these several modes are of high importance in classification. Among the Vertebrates, the embryo lies with its face or ventral surface towards the yolk, (Fig. 109,) and thus the suture, or line at which the edges of the germ unite to enclose the yolk, and which in the mammals forms the navel, is found in front. Another suture is found along the back, arising from the actual folding upwards of the upper surface of the germ, to form the dorsal cavity. 304. The embryo in the Articulata, on the contrary, lies with its back upon the yolk, as seen in the following figure, which represents an embryo of Podurella ; consequently the yolk enters the body on that side ; and the suture, which in the vertebrates is found on the belly, is here found on the back. In the Cephalopoda the yolk communicates with the lower side of the body, as in Vertebrates, but there is no dorsal cavity formed in them. In the other Mollusks, as also in the Worms, there is this peculiarity, that the whole yolk is changed at the beginning into the substance of the embryo ; whilst in Vertebrates, and the higher Articulates and Mollusks, a part of it is reserved, till a later period, to be used for the nourishment of the em- bryo. Among Radiata, the germ is formed around the yolk, and seems to surround the whole of it, from the first.* 305. The development of the embryo of the vertebrated animals may be best observed in the eggs of fishes. Being Fig. 110. * These facts show plainly that the circumstance of embryos arising from the whole or a part of the yolk is of no systematic importance. DEVELOPMENT OF THE YOUNG WITHIN THE EGG. 145 transparent, they do not require to be cut open, and, by sufficient caution, the whole series of embryonic changes may be observed upon the same individual, and thus the suc- cession in which the organs appear be ascertained with pre- cision ; whereas, if we employ the eggs of birds, which are opaque, we are obliged to sacrifice an egg for each obser- vation. 306. To illustrate these general views as to the develop- ment of the embryo, we will briefly describe the principal phases, as they have been observed in the White-fish of Eu- rope, which belongs to the salmon family. The following magnified sections will illustrate this development, and show the period at which the different organs successively appear. Fig. 111. Fig. 112. Fig. 113. 307. The egg, when laid, (Fig. ill,) is spherical, about the size of a small pea, and nearly transparent. It has no albu- men, and the shell membrane is so closely attached to the membrane of the yolk, that they cannot be distinguished. Oil-like globules are scattered through the mass of the yolk, or grouped into a sort of disk, under which lies the germina- tive vesicle. The first change in such an egg occurs a few hours after it has been laid, when the shell membrane sepa- rates from the yolk membrane, in consequence of the ab- sorption of a quantity of water, (Fig. 112,) by which the egg increases in size. Between the shell membrane (s m) and the yolk, (?/,) there is now a considerable transparent space, which corresponds, in some respects, to the albumen found in the eggs of birds. 308. Soon afterwards we see, in the midst of the oil-like 13 146 EMBRYOLOGY. globules, a swelling in the shape of a transparent vesicle, (Fig. 113, g,) composed of very delicate cells. This is the first indication of the germ. This swelling rapidly enlarges until it envelops a great part of the yolk, when a depression Fig. 114. Fig. 115. Fig. 116. is formed upon it, (Fig. 114.) This depression becomes by degrees a deep furrow, and soon after a second furrow ap- pears at right angles with the former, so that the germ now presents four elevations, (Fig. 115.) The subdivision goes on in this way, during the second and third days, until the germ is divided into numerous little spheres, giving the sur- face the appearance of a mulberry, (Fig. 116.) This ap- pearance, however, does not long continue ; at the end of the third day, the fissures again disappear, and leave no visible traces. After this, the germ continues to extend as an envelop around the yolk, which it at last entirely encloses. 309. On the tenth day, the first outlines of the embryo begin to appear, and we soon distinguish in it a depression between two little ridges, whose edges constantly approach Fig. 117. Fig. 118. Fig. 119. each other until they unite and form a canal, (Fig. 117, Z>, DEVELOPMENT OF THE YOUNG WITHIN THE EGG. 147 as has been before shown, (Fig. 107.) At the same time, an enlargement at one end of the furrow is observed. This is the rudiment of the head, (Fig. 118,) in which may soon be distinguished traces of the three divisions of the brain, (Fig. 119,) corresponding to the senses of sight, (m,) hear- ing, (e,) and smell, (p.] 310. Towards the thirteenth day, we see a transparent, cartilaginous cord, in the place afterwards occupied by the back-bone, composed of large cells, on which transverse Fig. 120. Fig. 121. Fig. 122. divisions are successively forming, (Figs. 120, 121, c.) This is the dorsal cord, a part of which, as we have before seen, is common to all embryos of vertebrated animals. It always precedes the formation of the back-bone ; and in some fishes, as the sturgeon, this cartilaginous or embryonic state is permanent through life, and no true back-bone is ever formed. Soon after, the first rudiments of the eye appear, in the form of a fold in the external membrane of the germ, in which the crystalline lens (Fig. 121, a;) is afterwards formed. At the same time we see, at the posterior part of the head, an elliptical vesicle, which is the rudiment of the ear. At this period, the distinction between the upper and the lower layer of the germ is best traced ; all the changes mentioned above appertaining to the upper layer. 311. After the seventeenth day, the lower layer divides into two sheets, the inferior of which becomes the intestine. 148 EMBRYOLOGY. The heart shows itself about the same time, under the form of a simple cavity, (Fig. 121, /«,) in the midst of a mass of cells belonging to the middle or vascular layer. As soon as the cavity of the heart is closed in, regular motions of contraction and expansion are perceived, and the globules of blood are seen to rise and fall in conformity with these motions. 312. There is as yet, however, no circulation. It is not until the thirtieth day that its first traces are manifest in the existence of two currents, one running towards the head, the other towards the trunk, (Fig. 122,) with similar returning currents. At this time the liver begins to be formed. Mean- while, the embryo gradually disengages itself, at both ends, from its adherence to the yolk ; the tail becomes free, and the young animal moves it in violent jerks. 313. The embryo, although still enclosed in the egg, now unites all the essential conditions for the exercise of the functions of animal life. It has a brain, an intestine, a pul- sating heart and circulating blood, and it moves its tail spon- taneously. But the forms of the organs are not yet complete ; nor have they yet acquired the precise shape that character- izes the class, the family, the genus, and the species. The young White-fish is as yet only a vertebrate animal in gen- eral, and might as well be taken for the embryo of a frog. 314. Towards the close of the embryonic period, after the fortieth day, the embryo acquires a more definite shape. The head is more completely separated from the yolk, the jaws protrude, and the nostrils approach nearer and nearer to the end of the snout ; divisions are formed in the fin which surrounds the body ; the anterior limbs, which were indicated only by a small protuberance, assume the shape of fins ; and finally, the openings of the gills appear, one after the other, so that we cannot now fail to recognize the type of fishes. 315. In this state, the young white-fish escapes from the Fig. 123. DEVELOPMENT OF THE YOUNG WITHIN THE EGG. 149 egg, about the sixtieth day after it is laid, (Fig. 123,) but its development is still incomplete. The out- lines are yet too indis- tinct to indicate the genus and the species to which the fish be- longs ; at most we distinguish its order only. The opercula or gill-covers are not formed ; the teeth are wanting ; the fins have as yet no rays ; the mouth is underneath, and it is some time before it assumes its final position at the most projecting point of the head. The remainder of the yolk is suspended from the belly, in the form of a large bladder, but it daily diminishes in size, until it is at length completely taken into the animal, (304.) The duration of these metamorphoses varies extremely in different fishes ; some accomplish it in the course of a few days, while in others, months are required. 315 a. In frogs and all the naked reptiles, the development is very similar to that of fishes. It is somewhat different in the scaly rep- tiles, (snakes, lizards, and turtles,) which have peculiar membranes surrounding and protecting the embryo during its growth. From one of these envelopes, the allantois, (Fig. 125, «,) is derived their common name of Allantotdian Vertebrates, in opposition to the naked reptiles and fishes, which are called Anattantotdian. 315 b. The AllantoTdian Vertebrates differ from each other in several essential peculiarities. Among Birds, as well as in the scaly Fig. 124. Fig. 125. reptiles, we find at a certain epoch, when the embryo is already dis- 13* 150 EMBRYOLOGY. 316. As a general fact, it should be further stated, that the envelopes which protect the egg, and also the embryo, are the more numerous and complicated as animals belong to a higher class, and produce a smaller number of eggs. This is particularly evident when contrasting the innumer- able eggs of fishes, discharged almost without protection engaging itself from the yolk, a fold rising around the body from the upper layer of the germ, so as to present, in a longitudinal section, two prominent walls, (Fig. 124, xx.') These walls, converging from all sides upwards, rise gradually till they unite abo.ve the middle of the back, (Fig. 125.) When the junction is effected, which in the hen's egg takes place in the course of the fourth day, a cavity is formed between the back of the embryo (Fig. 126, e) and the new membrane, whose walls are called the amnios. This cavity becomes filled with a peculiar liquid, the amniotic water. 315 c. Soon after the embryo has been enclosed in the amnios, a shallow pouch forms from the mucous layer, below the posterior ex- tremity of the embryo, between the tail and the vitelline mass. This pouch, at first a simple little sinus, (Fig. 125, a,) grows larger and larger, till it forms an extensive sac, the allaniois, turning backwards and upwards, so as completely to separate the two plates of the am- nios, (Fig. 126, a,) and finally enclosing the whole embryo, with its Fig. 123. amnios, in another largo sac. The tubular part of this sac, which is nearest the embryo, is at last transformed into the urinary bladder. The heart (A) is already very large, with mniute arterial threads DEVELOPMENT OF THE YOUNG WITHIN THE EGG. 151 into the water, with the well-protected eggs of birds, and still more with the growth of young mammals within the body of the mother. 317. But neither in fishes, nor in reptiles, nor in birds, does the vitelline membrane, or any other envelope of the egg, take any part in the growth of the embryo ; while on the Fig. 127. Fig. 128. passing off from it. At this period there exist true gills upon the sides of the neck, and a branchial respiration goes on. 315 d. The development of mammals exhibits the following peculiarities. The egg is ex- ceedingly minute, almost micro- scopic, although composed of the same essential elements as those of the lower animals. The vitel- line membrane, called chorion, in this class of animals, is comparatively thicker, (Fig. 127, v,) always soft, surrounded by peculiar cells, being a kind of albumen. The chorion soon grows proportionally larger than the vitelline sphere itself, (Fig. 128, y,) so as no longer to invest it directly, being sepa- rated from it by an empty space, (&.) The germ is formed in the same position as in the other classes of Vertebrates, namely, at the top of the vitellus, (Fig. 129 ;) and here also two layers may be distinguished, the up- per or serous layer, (s,) and the lower or mu- cous layer, (m.) As it gradually enlarges, the surface of the chorion becomes cov- ered with little fringes, which, at a later epoch, will be attached to the mother by means of similar fringes arising from the walls of the matrix, or organ which contains the embryo. 315 e. The embryo itself undergoes, within the chorion, changes Fig. 129. Fig. 130. 152 EMBRYOLOGY. • contrary, in the mammals, the chorion, which corresponds to the vitelline membrane, is vivified, and finally becomes attached to the maternal body, thus establishing a direct con- nection between the young and the mother ; a connection which is again renewed in another mode, after birth, by the process of nursing. similar to those described in birds : its body and its organs are formed in the same way ; an amnios encloses it, and an allantols grows out of the lower extremity of the little animal. As soon as the allantoTs has surrounded the embryo, its blood vessels become more and more numerous, so as to extend into the fringes of the chorion, (Fig. 1 3 1, p e ;) while, on the other hand, similar vessels from the mother extend into tlfc corresponding fringes of the matrix, (p m,} but without directly communicating with those of the chorion. These two sorts of fringes soon become interwoven, so as to form an intri- cate organ filled with blood, called the pla- Fig. 131. centa, to which the embryo remains sus- pended until birth. 315 f. From the fact above stated, it is clear that there are three modifications of embryonic development among vertebrated animals, namely, that of fishes and naked reptiles, that of scaly reptiles and birds, and that of the mammals, which display a gradation of more and more complicated adaptation. In fishes and the naked reptiles, the germ simply encloses the yolk, and the embryo rises and grows from its upper part. In the scaly reptiles and birds there is, besides, an amnios arising from the peripheric part of the embryo and an allantols growing out of the lower cavity, both enclosing and protecting the germ. ITS ZOOLOGICAL IMPORTANCE. 153 SECTION III. ZOOLOGICAL IMPORTANCE OF EMBRYOLOGY. 318. 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 verte- brates, it may be said, that the organs of the body are suc- cessively formed in the order of their organic importance, the most essential 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. 319. Thus we have seen that, in the fish, the first changes relate to the segmentation of the yolk and the formation of the germ, which is a process common to all classes of ani- mals. 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 vertebrates ; an indication afterwards fully confirmed by the successive appearance of the brain and the organs of sense. Later still, the intestine is formed, the limbs be- come 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. 320. 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 154 EMBRYOLOGY. almost the whole period of embryonic life, the young fish and the young frog scarcely differ at all, (313 :) 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 further back in the history of development, we come to a period when no appreciable difference whatever is to be discovered between the embryos of the various departments. The embryo of the snail, when the 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 ; the class and the group are not yet indicated. 321. After this account of the history of the development of the egg, the importance of Embryology to the study of systematic Zoology cannot be questioned. For evidently, if the formation 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 classifi- cation. 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 Vertebrates, the Articulates, the Mollusks, and the Radiates, corresponds perfectly with the gradations displayed by Embryology. 322. This classification, as has been already shown, (61,) is founded essentially on the organs of animal life, the ner- vous system and the parts belonging thereto, as found in the perfect 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 vegetative 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 after- ITS ZOOLOGICAL IMPORTANCE. 155 wards. Therefore 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 us with new proof that there is a general plan displayed in every kind of development. 323. Combining these two points of view, that of Embry- ology with 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. 324. The type of Vertebrates, 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 cen- tre, and closing above, as well as below. 325. The type of Articulata, having but one cavity, grow- ing from below upwards, and the nervous system forming a series of ganglions, placed below the intestine, is repre- sented by a single crescent, with the horns directed up- wards. 326. The type of Mollusks having also but one cavity, the nervous system being a simple ring around the oesophagus, with ganglions above and below, from which threads go off to all parts, is represented by a single crescent with the horns turned downwards. 327. Finally, the type of Radiata, 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. GEMMIPAROITS AND FISSIPAROUS REPRODUCTION. 328. 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, gemmiparous reproduction, or multiplication by means of buds, and fissip- arous reproduction, or propagation by division ; and also some still more extraordinary modifications yet involved in much obscurity. 329. Reproduction by buds occurs among the polyps, me- dusse, and some of the infusoria. On the stalk, or even on the body of the Hydra, (Fig. 132,) and of many infusoria, there are formed buds, like those of plants. On close exam- ination they are found to be young animals, at first very imperfectly formed, and commu- nicating at the base with the parent body, from which they derive their nourishment. By Fig. 132. . degrees, the animal is developed ; in most cases, the tube by which it is connected with the parent GEMMIPAROUS AND FISSIPAROtTS REPRODUCTION. 157 withers away, and the animal is thus detached 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 the polyps, as in trees, budding is only an accessory mode of reproduction, which pre- supposes a trunk already existing, originally the product of ovulation. 330. Reproduction by division, or fissiparous reproduction, is still more extraordinary ; it takes place only in polyps and some infusoria. A cleft or fissure at some part of the body takes place, very slight at first, but constantly increasing in depth, so as to become a deep furrow, like that observed in the yolk, at the beginning of embry- onic development ; at the same time the contained organs are di- vided 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 Vpjticella, (Fig. 133,) and in some Polyps, (Fig. 134,) and sometimes trans- Fig. 133. Fig. 134. versely. In some Infusoria, the Paramecia, for instance, this division occurs as often as three or four times in a day. 331. 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 arms of the star-fishes. The tail of a lizard is also 14 158 REPRODUCTION. readily reproduced. Salamanders even possess the faculty of reproducing parts of the head, including the eye with all its complicated 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. 332. 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 polyp, be divided into several pieces, the injury is soon repaired, each fragment speedily becoming a perfect animal. Something like this reparative faculty is seen in the vegetable kingdom, as well as the animal. A willow branch, planted in a moist soil, throws out roots below and branches above ; and thus, after a time, assumes the shape of a perfect tree. 333. These various modes of reproduction do not exclude each other. All animals which propagate by gemmiparous or fissiparous reproduction also lay eggs. Thus the fresh- water polyps (Hydra) propagate both by eggs and by buds. In Vorticella, according to Ehrenberg, all three modes are found ; it is propagated by eggs, by buds, and by division. Ovulation, however, is the most common mode of reproduc- tion ; the other modes, and also alternate reproduction, are only additional means employed by Nature to secure the per- petuation of the species. SECTION II. ALTERNATE AND EQUIVOCAL REPRODUCTION. 334. 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 trans- ALTERNATE AND EQUIVOCAL REPRODUCTION. 159 mission 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 ^j '.- .-. " A most valuable, complete, and comprehensive summary of the existing facts of sci- ence ; it is replete with interest, and ought to have a place in every well appointed li- brary."— Worcester Spy. li We commend it to all who wish what has just been found out ; to all who would like to discover something themselves, and would be glad to know how : and to all who think they have invented something, and are desirous to know whether any one else has been before hand with them." — Puritan Recorder. "This is one of the most valuable works which the press has brought forth during the present year. A greater amount of useful and valuable information cannot be obtained from any book of the same size within our knowledge." — Washington Union. "This important volume will prove one of the most acceptable to our community that has appeared for a long time."— Providence Journal. "This is a neat volume and a useful one. Such a book has long been wanted in Amer- ica. It should receive a wide-spread patronage." — Scientific American, New York. "It meets a want long felt, both among men of science and the people. No one who feels any interest in the intellectual progress of the age, no mechanic or artisan, who as pires to excel in his vocation, can afford to be without it. A very copious and accurate index gives one all needed aid in his inquiries."— Phil. Christian Chronicle. " One of the most useful books of the day. Every page of it contains some useful in formation, and there will be no waste of time in its "study."— Norfolk Democrat. "It is precisely such a work as will be hailed with pleasure by the multitude of intelli gent readers who desire to have, at the close of each year, a properly digested record of its progress in useful knowledge. The project of the "editors is an excellent one, and de serves and will command success."— North American, Philadelphia. "Truly a most valuable volume."— Charleston (S. C.) Courier. " There are few works of the season whose appearance we have noticed with more sin- cere satisfaction than this admirable manual. The exceeding interest of the subjects to which it is devoted, as well as the remarkably thorough, patient and judicious manner in which they are handled by its skilful editors, entitle it to a warm reception by all the friends of solid and useful learning." — New York Tribute. FOOT-PRINTS OF THE CREATOR; — OR THE ASTEROLEPIS OF STROMNESS. BY HUGH MILLEK. WITH MANY ILLUSTRATIONS. IROM THE THIUD LONDON E D I T I O >*.— WI T II A MEMOIR OF THE AUTHOB BY LOUIS AGASSIZ. In its purely geological character, the 'Foot-prints' is not surpassed by any modern of the same Glass. In this volume, Mr. Miller discuses 'lie development hypothesis, or the hvpotbe.sH ot' natural law, as maintained by Lamarck, and by the author of the 'Vestiges of Creation,' and has subjected it, in its geological aspect, to the mo-a vigorous examination. llv.- ha-; stripped even of its semblance of truth, and restored to the Creator, as govemor cf the universe, that power and those functions which lie was supposed to hava resigned at its birth. * * * The earth has still to surrender mighty secrets, — and great rev- elations are yet to bsue from sepulchres of stone. It is from the vault.? to which ancient life has been consigned that the history of the dawn of life -is to be composed."— ^VoriA Britisli Review. " Scientific knowledge equally remarkable for comprehensiveness and accuracy ; a style at all times singularly clear, vivid, and powerful, ranging at will, and without effort, from the most natural and gTaceful simplicity, through the playful, the graphic, and the vigor- ous, to the impressive eloquence of great thoughts greatly expressed; rca-onmg at once comprehensive in scope, strong in grasp, and pointedly direct in application, — these qual- ities combine to render the. 'Foot-prints ' one of the most perfect refutations of error, and defences of truth, that ever exact science has produced."— Free Church Magazine. DK. BUCKLAND, at a meeting of the; British Association, said he had never been so much astonished in his life, by the powers of any man. as he had been by the geological descriptions of Mr. Miller. That wonderful man der.c'ribed these objects with a facility which made him ashamed of the comparative meagreness and poverty of his own descriptions in the •' Bridge- water Treatise," which had cost him hoars and days of labor. He would_ give his left hand to possess such powers of description as (Ms ma/t ; and if it pleased Providence to spare his useful life, he, if any one, would certainly render science attractive and popular, and do equal service to theology and geology. " The style of this work is most singularly clear and vivid, rising at times to eloquence, and always impressing the reader with the idea that he is brought in contact with great thoughts. Where, it is necessary, there are engravings to illustrate the geological remains. The whole work forms one of the best defences of Truth that science can produce." — Albany State Register. "The ' Foot-Prints of the Creator1 is not onlv a good but a great book. All who have read the ' Vestiges of Creation ' should study the ' Foot-Prints of the Creator.' This vol- ume is especially worthy the attention of those who are so fearful of the skeptical tenden- cies of natural science. We expect this volume will meet with a very extensive sale. It should be placed in every Sabbath School Library , and at every Christian fireside. "—.Boston Traveller. "Mr. Miller's style is remarkably pleasing; his mode of popularising geological knowl- edge unsurpassed, perhaps unequalled; and the deep vein of reverence for Divine llevela- tion pervading all, adds interest and value to the volume." — New York Com. Advertiser. "The publishers have again covered themselves with honor, by giving to the American public, with the Author's permission, an elegant reprint of a foreign work of science. We earnestly bespeak for this work a wide and free circulation, among all who love science much and religion more." — Puritan Recorder. " The book indicates a mind of rare gifts and attainments, and exhibits the workings of poetic genius in admirable harmony with the generalizations of philosophv. It is, withal pervaded by a spirit of devout reverence and child-like humilitv, such as all men delight to behold in the interpreter of nature. We are persuaded that no intelligent reader will go through the chapters of the author without being instructed and delighted with the views they contain,"— Providence Journal. " Hugh Miller is a Scotch geologist, who, within a few years, has not onlv added largely to the facts of science, but has stepped at once among the leading scientific writers of the age, by his wonderfully clear, accurate, and elegant geological works. Mr. Miller, taking *i „,!„,*=, _, _,L___>I_ s_ .... a. ness, ease, and elegance that are both astonishing and delightful. Throughout, the. entire geologic portion, thereasoningismarkeii.lv close, shrewd, 'and intelligible — the facts art, evidently at the finger's end of the author — and the most unwilling, I'autimis. and antago- nistic reader is compelled to yield his thorough assent to the argument."— Boston Post. " GOFLD ASP LTNCOI,X; PUBIJSHKBS, BOSTON. FOOT-PRINTS OF THE CREATOR. NOTICES OF THE PEESS. l* This is a very rich and valuable book. It is rich in the treasures of scientific knowledge, which are interwoven in an argument, remarkably clear, in a style graceful, vigorous, graphic, and of great power— rendering it a most perfect refutation of the atheistical error propagated in the work entitled, the ' Vestiges of Creation.' "—Philad. Christian Observer. '•Around the name of Hugh Miller already gathers the halo of a most pure and grateful famo. Receiving hi- geological education among the rocks of the quarry, where he labored for fifteen .tears; writing in a style of peculiar simplicity and elegance, and devoting the exact knowledge derived from walking in the Creator's*' foot-prints ' to the, cause of true in doing him honor, have o mnlgation."— Springfield reliu. m, the proudest devotees of science have taken pleasure in delighted to listen to his teachings, and rejoiced to aid in their pro lit i itohcan, " This is one of the most remarkable and deeply profound works of the present ago. author's name will not be soon forgotten, in the scientific world,— and his productio not tail to bo read and admired, wherever true science is promulgated. aMv clear, concise, and powerful, in his arguments; profound in his rese sive in his reasoning."— JV«e fork Farmer and Mechanic. The oductions will He is most remark- researches, and conclu- "There is poetry and philosophy combined in this work. The author had a mind which revelled, so to speak, in the beauties and wonders of science. From a child, almost, he delighted in the works of nature. . . . He has gone from one step to another, till now he is justly esteemed as among the great Geologists of the world. It is a book in which the mau of science will delight, but it is also one which the general reader will peruse with instruct- ion and satisfaction."— Baltimore Patriot. "The publishers are entitled to the thanks, not only of scientific men but of Christians, in this country, for presenting this work to the American public.1'— Christian Secretary. "A remarkable work by a remarkable man. Mr. Miller is self-made, and has elevated himself, by the force of his genius, from the position of an ordinary laborer in a stone quarry, to that of one of the first Geologists of the age. For careful investigation, accuracy, fullness, and beauty of description, combined with "a proper estimate of the true claims of science, and a high reverence for sacred things, he is not surpassed by anv writer on natural science at the present day. All who have taken any interest in the discussion of geological topics, and particularly their connection with the Sacred Writings, will read this volume with admiration and advantage. Its subject, spirit, style, and manner of publication, all commend it ; and it is destined to an extensive circulation. It is one of the noblest and most admirable contributions lately made to Science and Christianity."— Christian Herald. "Within a few days, this enterprising house, has republished one of the most charming scientific works of "modern times — a work which, from the simple love of truth which per- vades it, its clearness, authenticity, and wonderful revelations, may be called a work of genius, as appropriately as a fine poem. It is entitled ' Foot-Prints of the Creator.'— Willis' Ilome Journal. "A work so beautifully written, filled with such curious, new, and interesting facts, and breathing in every page the purest philosophy and Christianity, could scarcely meet with adequate praise, in a limited space. It should be added to the library of every one." — Washington Union. " We have never read a work of the kind with so much interest. Its statements of fact and its descriptions are remarkably clear. From minute particulars it leads us on to broad views of the creation ; and the earth becomes the witness of a succession of miracles, as wonderful as any recorded in the Scriptures." — Christian Register. " This splendid work should be read by every man in our land. We recommend the study of this science to our young men; let' them approach it with open, and not unfaithful breasts, — for amid our mountains, grand and tall, our boundless plains, and flowing rivers, vast and virgin fields for exploration yet present themselves." — Scientific American. "This is one of the most able and learned works which has ever been issued from the American press. The North British Review says 'That in its geological character it is not surpassed by anymodem work of the same class.' The style of the'work is clear, rich, and strong; its statements of truth are plain and accurate, and its arguments are, presented with mastcrlv force. Its author, Hugh Miller, is a man of very superior talents and attain- ments." — New York Christian Messenger. " The author resembles Burns, in the freshness, and vigor, and enthusiasm of genius; and had he ventured into the realm of poetry, the greatest of Scottish bards might have wel- comed his company. We hope the volume, mav be widelv circulated, especially among intelligent Christians. . . . This work is written in a bold and eloquent style, and though penetrating to the inner shrine of the Geological temple, and necessarily dealing w.Hh hard words and harder tilings, it will secure many readers."— Christian Chronicle. GOULD AND LINCOLN, PUBLISHERS, BOSTON. THE OLD 11KD SANDSTONE; OK NEW WALKS IN AN OLD FIELD. BY HUGH MILLEK, PROM THE FOURTH LONDON EDITION — ILLTJSTKAT O A writer, in noticing Mr. Miller's "First Impressions of England and the People," in the New En glan der, of May, 1850, commences by saying, "We presume it is not necos- sar.r formally to introduce Hugh Miller to our readers; the author of 'The Old Eed Sand- stone ' placed himself, by that production, which was first, among the most successful geologists, and the best writers of the age. "We well remember with what mingled emotion and delight AVC first read that work. Rarely has a more remarkable book come from the press. . . . For, besides the important contributions which it makes to the science of Geol- ogy, it is written in a style which places the author at once among the most accomplished waiters of the age. . . . He proves himself to be in prose what Burns has been in poetry. "We are not extravagant in saying that there is no geologist living who, in the descriptions of the phenomena of the science, has united such accuracy of statement with so much poetic beauty of expression. What Dr. Buckland said was not a mere compliment, that 'he had never been so much astonished in his life, by the powers of any man, as he had been by the geological descriptions of Mr. Miller. That wonderful man described these objects with a felicity which made him ashamed of the comparative meagreness and pov- erty of his own descriptions, in the Briclgewatcr Treatise, which had cost him hours and days of labor.1 For our own part we do not hesitate to place Mr. Milicr in the front rai.k of English prose writers. Without mannerism, without those extravagances which give a factitious reputation to so many writers of the day, Li; c;tyle has a classic purity and ele- gance, which remind one of Goldsmith and Irving, while there is an ease and a naturalness in the illustrations of the imagination, which belong only to men of true genius." "The excellent and lively work of our meritorious, self-taught count) pman, Mr. Miller, is as admirable for the clearness of its descriptions, and the sweetness of its composition, as for the purity and gracefulness Wnich pervade it."— Edinburgh Review. "A geological work, small in size, unpretending in spirit and manner; itj contents, the conscientious narration of fact; its style, the beautiful simplicity of truth; and altogether possessing, for a rational reader, an interest superior to that of a novel." — Dr. J. Pye Smith. "This admirable work evinces talent of the highest order, a deep and healthful mora. feeling, a perfect command of the finest language, and a beautiful union of philosophy and poetry. Xo geologist can peruse this volume without instruction and delight. "—Silli- man's American Journal of Science. "Mr. Miller's exceedingly interesting book on this formation is just the sort of work to render any subject popular. It is written in a remarkably pleasing style, and contains n wonderful amount of information." — Westminster Review. " In Mr. Miller's charming little work will be found a very graphic description of the Old Kedfishes. I know not of a more fascinating volume on any branch of British geology." — MantelVs Medals of Creation. SIR RODERICK MrRCHisoN, giving an account of the investigations of Mr. Miller, spoke in the highest terms of his perseverance and ingenuity as a geologist. With no other advan tages than a common education, by a careful use of his means, he had been able to give himself an excellent education, and to elevate himself to a position which any man, in any sphere of life, might well envy. He had seen some of his papers on geology, written in a style so beautiful and poetical as to throw plain geologists, like himself, in the shade. GOULD AND LINCOLN, PUBLISHERS, BOSTOX. THE POETRY OF SCIENCE; OB, STUDIES OF THE PHYSICAL PHENOMENA OF NATURE BY ROBERT HUNT, AUTHOR OF "PANTHEA," " RESEARCHES ON LIGHT," ETC. NOTICES OF THE PRESS. " We know of no work upon science which is so well calculated to lift the mind from the admiration of the wondrous works of creation to the belief in, and worship of, a First Great (/ause, One of the most readable epitomes of the present state and progress of science we have perused."— Mornin a Herald, London. "The design of Mr. Hunt's volume is striking and good. The subject is very well dealt with, and the object very well attained; it displays a fund of knowledge, and is the work of an eloquent and earnest man." — The Examiner, London. , _ the orbit of a star, or in the color of a flower — the more awakened will be his wonder and his veneration, and the more call will there be upon his highest powers of the intellect and the imagination." — Boston Post. " It was once supposed that poetry and science were natural antipodes ; and lo ! they now are united in loving bonds. Mr. lUint has certainly demonstrated that the divinest poetry lies hidden in the depths of science, and needs but a master spirit to evoke it in shapes of beauty. ' '— Christian Chronicle. " It may be read with interest, by the lovers of nature and of science." — N. T. Tribune. "Itis written in a style not unworthy of the grandeur of the subject." — N. Y. Eve. Post. " The author, while adhering to true science, has set forth its truths in an exceedingly captivating style."— Neic York Commercial Advertiser. ork re-nublished in America. It is a book " We arc hoar til v glad to see this interesting w that is a book." — Scientific American. " From the arcana of science especially, has the author gleaned what may be properly termed her pnotn-. which will make the book one of the most interesting character to the intelligent reader."— Christian Herald. " It is re all v a scientific treatise, fitted to instruct and enlarge the mind of the reader, but at the same time it invests the subjects it describes with the radiance of the imagination, and with the channinu association of poetry. The book well deserves the title it bears, and ii! their ultimate facts, he leads his reader by inductive processes, to the contemplation of vast eternal truths. Though full of information, the facts cited in hi- pa.es are not collected solelv because they are such, but with true philo- sophical acumen, t<> build ur> the edifice : and if curious or rare, they are selected merely to strengthen the position in which they are placed." — Wasldngion Union. " We anticipate a wide circulation for it in this country." — Albany State Register. " The scientific com;>ass of the volume is large, and its execution is exceedingly fine and Interesting." — Zion's Herald. " We noticed this eloquent work, while, it wa« in the course of publication. It is now out in beautiful stvle, and makes with the notes, which are full and as valuable as the text, a volume of nearly four hundred r>a,iU:ic:rl details, and presented only in its ^rande^t features. It thus- not. only places iieiiire us most instructive f.'.cts relating to the condition of the eiith, but al=o awakens within us n stronger sympathy with the beings that inbuilt it, und a pioibuniii-i revcr-nce for the beneficent Creator who formed it, and of whose character it is a manli'i 'station and expression. They abound with tho richest intr-rost and instruction to every intclli- ge.r.-. jecder, and especially fitted to awaken enthusiasm iuui *l.\;j!a in all who :.co devoted .^ the study either of natural *ei; are, or the history of mankind." — Providence Journal. :c Geography is here presented under a now a:id attractive pr.^so ; it is no !o;;':er e dry description of the. features of the earth's surface. The influence of soil scenery and climate upini character, has not yet received ths consideration duo to it fio:n I;is- tor'mns and philosophers. In the volume before us tho profound invcsligations of Ilurn- bolilt, tlittur and others, in Physical Geography, are presented in a popular form, a::d with the clearness and vivacity so characteristic of Frcn-jli tieati.-":-" on sfience. Tha work should be introduced into our higher schools." — Ths Independent, _\Vzr Yuri:. " Geography is hero m^fle to assume a dignity, not heretofore attached to it. Tha knowledge communicated in these Lectures is curious, unexpected, ab»orhiii-r."— Christian Mirror, Portland, CONTRIBUTIONS TO THEOLOGICAL SCIENCE. BY JOHN HARRIS, D. D. I. THE PRE-ADAMITE EARTH. NOTICES OF THE PRESS. :< As we have examined every page of this work, and put forth, our best efforts to un- derstand the full import of its varied and rich details, the resistless impression has come over our spirits, that the respected author has been assisted from on high in his labo- rious, but successful undertaking. May it please God yet to aid and uphold him, to complete his whole design ; for we can now see, if we mistake not, that there is great unity as well as originality and beauty in the object which he is aiming to accomplish. If we do not greatly mistake, this long looked for volume, will create and sustain a deep impression in the more intellectual circles of the religious world." — London Evan- gelical Magazine. '* The man who finds his element among great thoughts, and is not afraid to push into the remoter regions of abstract truth, be he philosopher or theologian, or both, will read it over and over, and will find his intellect quickened, as if from being in con- tact with a new and glorious creation." — Albany Argus. "Dr. Harris states in a lucid, succinct, and often highly eloquent manner, all the leading facts of geology, and their beautiful harmony with the teachings of Scrip- ture. As a work of paleontology in its relation to Scripture, it will be one of the mosfc complete and popular extant. It evinces great research, clear and rigid reasoning, and a style more condensed and beautiful than is usually found in a work so profound. It will be an invaluable contribution to Biblical Science." — New York Evangelist. " He is a sound logician and lucid reasoner, getting nearer to the groundwork of a subject generally supposed to have very uncertain data, than any other writer within our knowledge." — New York Com. Advertiser. " The elements of things, the laws of organic nature, and those especially that lie afc the foundation of the divine relations to man, are here dwelt upon in a masterly man- ner."— Christian Reflector, Boston. II. MAN PRIMEVAL; OR THE CONSTITUTION AND PRIMITIVE CONDITION OF THE HUMAN BEING. WITH A FINE POETRAIT OF THE AUTHOR. NOTICES OF THE PRESS. "It surpasses in interest its predecessor. It is an able attempt to carry out the author's grand conception. His purpose Ls to unfold, as far as possible, the successive steps by which God is accomplishing his purpose to manifest His All-sufficiency. * * * The reader is led along- a pathway, abounding with rich and valuable thought, going on from the author's opening propositions to their complete demonstration. To stu- dents of mental and moral science, it will be a valuable contribution, and will assuredly secure their attention." — Christian Chronide, Philadelphia. " It is eminently philosophical, and at the same time glowing and eloquent. It can- not fail to have a wide circle of readers, or to repay richly the hours which are given to its pages." — New York Recorder. '" The reputation of the author of this volume is co-extensive with the English lan- guage. Tiie work before us manifests much learning and metaphysical acumen. Its great recommendation is, its power to cause the reader to think and reflect." — Boston Recorder. "Reverently recognizing the Bible as the fountain and exponent of truth, he is as in- dependent and fearless as he is original and forcible ; and he adds to these qualities consummate skill in argument and elegance of dinion." — X. Y. Com. Advertiser. "' His copious and beautiful illustrations of the successive laws of the Divine Mani- festation, have yielded us inexpressible delight." — London Eclectic Revieiv. "The distribution and arrangement of thought in this volume, are such as to afford ample scope for the author's remarkable powers of analysis and illustration. In look- ing with a keen and searching eye at the principles which regulate the condxict of God towards man, as the intelligent inhabitant of this lower world, Dr. Karris has laid down for himself three distinct, but connected views of the Divine procedure : First, The End aimed at \)j God ; Second, the Reasons for the employment of it. In a very masterly way does our author grapple with almost every difficulty, and perplexing subject which comes within the range of his proposed inquiry into the constitution and condition >f Man Primeval." — London Evangelical History. III. THE FAMILY; ITS CONSTITUTION, PROBATION AND HISTORY. - - -. • - CLASSICAL STUDIES. ESSAYS ON ANCIENT LITERATURE AND ART. With the Biography and Correspondence of Eminent Philologists. By BARNAS SEARS, President of Newton Theol. Institution, B. B. EDWARDS, Prof. Anclover Theol. Seminary, and C. C. FELTON, Prof. Harvard University. 12mo. Price $1.25. SECOND THOUSAND. " The collection is a most, attractive one, and would be acceptable in any circum- •tances. The discourses, particularly those of Jacobs, are written in words that burn. A general could not exhort his troops with more energy and spirit, than are used by the German Professor in stimulating the youth before him to labor in the acqui- sition of classical learning. The biographical portions of the book, naturally lesi exciting, no less tend to the same end." — London Lit. Examiner, by John Forster, Esq. " This elegant book is worthy of a more extended notice than our limits at present will permit us to give it. Groat labor and care have been bestowed upon its typo- graphical execution, which does honor to the American press. It is one of the rare beauties of the page, that not a woid is divided at the end of a line. The mechanical part of the work, however, i.s its least praise. It is unique in its character — standing alone among the innumerable books of this book-making age. The authors well deserve the thanks of the cultivated and disciplined portion of the community, for the service which, by this publication, they have done to the cause of letters. The book is of a high order, and worthy of the attentive perusal of every scholar. It is a noblo monument to the taste, and judgment, and sound learning of the projectors, and will yield, we doubt not, a rich harvest of fame to themselves, and of benefit to our literature.'' — Christian Review. " It is refreshing, truly, to sit down with such a book as this. When the press is teeming with the hasty works of authors and publishers, it is a treat to take up a book that is an honor, at once, to the arts and the literature of our country." — New York Observer. " This is truly an elegant volume, both in respect to its literary and its mechanical execution. Its typographical appearance is an honor to the American press ; and with equal truth it may be said, that the intrinsic character of the work is highly credit- able to the age. It is a novel work, and may be called a plea for classical learning. To scholars it must be a treat 5 and to students we heartily commend it." — Boston Recorder. " This volume is no common-place production. It is truly refreshing, wnen we are obliged, from week to week, to look through the mass of bonks which increases upon our table, many of which are extremely attenuated in thought and jejune in style, to find something which carries us back to the pure and invigorating influence of the master minds of antiquity. The gentlemen who have produced this volume deserve the cordial thanks of the literary world." — New England Puritan. " We heartily welcome this book as admirably adapted to effect a most noble and much desired result. We commend the work to general attention, for we feel sure it must do much to awaken a zeal for classical studies, as the surest means of attaining the refinement and graceful dignity which should mark the strength of every nation." — Ncto York Tribinie. "We make no classical pretensions, or we might say more about the principal articles in this volume ; but it needs no such pretensions to commend, as we heartily do, a book so full of interest and instruction as the present, for every reader who is ut all imbued with a love of literature." — Salem Gazette. "This book will do good in our colleges. Every student will want a copy, anj many will be stimulated by its perusal to a more vigorous and enthusiastic pursuit of that higher and more solid learning which alone deserves to be called 'classical.' The recent tendencies have been to the neglect of this, and we rejoice in this timely effort of minds so well qualified for such a work." — Christian Reflector. " The volume is, in every way, a beautiful affair of its kind, and we hazard nothing in recommending it to the literary world.' — Christian Secretary, Hartford. " The design is a noble and generous one, and has been executed with a taste and good sense, that do honor both to the writers and the publishers." — Prov. Journal- C H A M B E B. S ' rf . CYCLOPEDIA OF ENGLISH LITERATURE. A. SELECTION1 OF THE CHOICEST PRODUCTIONS OF ENGLISH AUTHORS, FROM THH EARLIEST TO THE PRESENT TIME: CONNECTED BV A CRITICAL AND BIOGRAPHICAL HISTORY. EDITED BY ROBERT CHAMBERS. ASSISTED BV ROBERT C ARKUTHER3 A \ J uTH.'R E.'.j'lN/lNT C " .NTLEMEX . Complete in two imperial octavo volu/ncs, of r. .">/•/; than fourteen hundred pages of double column Ictta'prc^x, and ^(c.u'ds of three hundred elegant illustrations. This valuable work has now become so general! ;t !;noa:i ami appreciated, that there nt-id scarcely be any thing said in commendation, except to those who have iu-i yet seen it. The icork embraces about One Thousand Jiuih,irs, dtrtmotogicaily arranged and classed Ie(e/'i!i.--ici::t:s, Dinnes, etc., with choice selectionsfrom their writings, coiincfLcd b>_: a Biugrayhital, lii.^toric-il, ,i;i.l Critical JVarra- live ; thus presenting a complete vie,- of English Literature, fn-m Hie iarlie.--t.to the present time. Let the reader open where he will, he cunn.ittf.til infant muli.cr fur projit and delight, which, for the most part, too, repeated perusals will only .--errs t,i nwlie. hi, a enjoy the more. We have indeed infinite riches in a little room. .Yj an-, who u t.a.--!c far literature, should allow himself, for a trifling consideration, to be without a work which throws so much light upon the progress of the English lanjtif;?e. The select i./ns arc ^c ;;?.} — a mass of valuable information in a condensed and elegant f EXTRACTS FROM COMMENDATORY NOTICES. From W. II. Prescott, Jln'Jwr of"Fc,-:i::-nnl «.;.•/ A ;r,^ '-/;." u The p]:-.u of the \vcrk is" very judicious. * * It will put the reader in the proper point of view, for survey- ing tlu- whole ground over which h.- i; tivivi.'iiiiig. s ~ :r'uc.h readers c".;:not tail to profit largely by the labors of the critic; who h is tl\e i .\\s\\\ ::irl ta"<:in:iinu, and trace his mother-tongue from its rude infancy to its present maturity, i. -1: ^a;ice, and richness .' " Christian Mirror, Portland. •.* Ths Publishers of the AMERICAN Edition of this valuable v.-urk desire to st.ite t'nr t, ^-ii.lt s the numerous pictorial illustrations in the English Edition, tliey have greatly enriched the work Ly the addition of fine steel and mezzotint engravings of the heads of Shakspeare, AddUon, Byron ; a full length portrait of Dr. Johnson, and a beautiful scenic representation of Oliver Goldsmiih and Dr. Johnson. These impor- tant and elegant additions, together with superior pap^r and bin/iing, must eive this a decided preference all oilier editions. FOR SCHOOL AND FAMILY LIBRARIES, CHAMBER'S MISCELLANY OF USEFUL AND ENTERTAINING KNOWLEDGE, TEN VOLUMES, ELEGANTLY ILLUSTRATED. The design of the MISCELLANY is to supply the increasing demand for useful, instructive, and entertaining reading, and to bring all the aids of literature to bear on the cultivation of the feeling's and understanding' of the people — to impress correct views on important moral and social questions — to furnish an unobtrusive friend and guide, a lively fireside companion, as far as that object can be attained through the instrumentality of books. This work is confidently commended to Teachers, School Committees, and all others interested in the formation of "School Libraries," as the very best work for this purpose. Its wide range of subjects, presented in the most popular style, makes it exceedingly interesting and instructive to all classes. The most flat- tering testimonials from distinguished school teachers and others, expressing an earnest desire to have it introduced into all school libraries, have been received by the publishers. From George 8. Emerson, Esq., Chairman of the Book Committee of the Boston Schools. — "I have examined with a good deal of care ' Chambers's Miscellany of Useful and Entertaining Knowledge,' particularly with reference to its suitableness to form parts of a library for young persons. It is, indeed, a library in itself, and one of great value, containing very choice selections in history, biography, natural history, poetry, art, physiology, elegant fiction, and various departments of science, made with great taste and judgment, and with the highest moral and philanthropic purpose. It would be difficult to find any miscellany superior or even equal to it ; it richly deserves the epithets ' useful and entertaining,' and I would recommend it very strongly, as extremely well adapted to form parts of a library for the young, or of a social or circulaiing library, in town or country." From the Rev. John 0. Choulcs, D. D. — "I cannot resist the desire which I feel to thank you for the valuable service which you have rendered to the public by placing this admirable work within the reach of all who have a desire to obtain knowledge. I arn not acquainted with any similar collection in the English lan- guage that can compare with it for purposes of instruction or amusement. I should rejoice to see that set of books in every house in our country. I cannot think of any method by which a father can more materially benefit his children than by surrounding them with good books ; and if these charming and attractive volumes can be placed in the hands of the young, they will have their tastes formed for good reading. I shall labor to see the Miscellany circulated among my friends, and shall lose no opportunity to commend it every where." " They contain an excellent selection of historical, scientific, and miscellaneous articles in popular style, from the best writers of the language. The work is ele- gantly printed and neatly illustrated, and is sold very cheap." — Independent Dem- ocrat, Concord, N. H. " It is just the book to take up at the close of a busy day ; and especially will it ehed a new charm over autumn and winter in-door scenes." — Christ. World, Boston. "The information contained in this work is surprisingly great; and for the fire- side, and the young particularly, it cannot fail to prove a most valuable and enter- taining companion." — New York Evangelist. 1 We are glad to see an American issue of this publication, and especially in so neat and convenient a form. It is an admirable compilation, distinguished by the good taste which has been shown in all the publications of the Messrs. Chambers. It unites the useful and the entertaining." — New York Commercial Advertiser. "It is an admirable compilation, containing interesting memoirs and historical sketches, which are useful, instructive, and entertaining. Every head of a family should supply himself with a copy for the benefit of his children." — Corning Journal. "The enterprising publishers deserve the thanks of every lover of the beautiful and true, for the cheap and tasteful style in which they have spread this truly val- uable work before the American people." — People's Advocate, Pa. " It is filled with subjects of interest, intended for the instruction of the youthful mind, such as biography, history, anecdotes, natural philosophy, &c." — New Orleans Bee. Iklucxbk Sdjool JBooks. THE ELEMENTS OF MORAL SCIENCE. By FUASCIS WATLAND, D.D. President of Brown University, and Professor of Moral Philosophy. Fortieth Thousand. 12mo. cloth. Price $1.25 *** This work has been extensively and favorably reviewed and adopted as a class-book In most of the collegiate, theological, and academical institutions of the country. From Rev. Wilbur Fisk, Presi lent q ' t!'t W.s1<:ian Unh-e-\-ity. "I have examined it with great satisfaction and interest. The work was greatly needed, and is well executed. Dr. Waylaiid deserves the trrateful acknowledgments :uid liberal patronage of the public. I need say nothing farther to express my high estimate of tha work, than that we shall immediately adopt it as a text-book in our university." From lion. James Kent, hito Chancellor of Xew York. " The work has been read by me attentively and thoroughly, and I think very highly tf It The author himself is one of the most estimable of men, and I do not kno-.v :f IEY ethical treatise, in which our duties to God and to our fellow-men ore laid down with rr»>*'e precision, simplicity, clearness, energy, and truth." " The work of Dr. Wayland has arisen gradually from the necessity of correcting the false principles and fallacious reasonings of Puley. It is a radical inj.-take, in the ed'.'/1?- tion of youth, to permit any bonk to be used by students as a text-book, which contains erroneous doctrines, especially when these are fundamental, and tend to vitiate the whole system of morals. We have been greatly pleased with tiie method which President Way- land has adopted ; he goes back to the simplest and most fundamental principles ; and, in the statement of his views, he unites perspicuity with conciseness and precision. In 011 the author's leading fundamental principles we entirely concur." — Biblical Repository. " This is a new work on morals, for academic use, and we welcome it with much satis- faction. It is the result of several years' reflection and experience in teaching, on the part of its justly distinguished author ; and if it is not perfectly what we could wish, yet, in the most important respects, it supplies a want which has been extensively felt. It is, we think, substantially sound in its fundamental principles ; and being comprehensive and elementary in its plan, and adapted to the purposes of instruction, it will be gladly adopted by those who have for a long time been dissatisfied with the existing works of Paley." The Literary and Theological Review. MORAL SCIENCE, ABRIDGED, by the Author, and adapted to the use of Schools and Academies. Twenty-fifth Thousand. ISmo. half cloth. Price 25 cents. The more effectually to meet the desire expressed for a cheap edition, the present edition is issued at the reduced price of 25 cents per copy, and it is honed thereby to extend the benefit of moral in- struction to all the youth of our lan.l. Teachers and all others engaged in the training of youth, are invited to examine this work. " Dr. Wayland has published an abridgment of his work, for the use of schools. Of this step we can hardly speak too highly. It is more than time that the study of moral philosophy should be introduced into all our institutions of education. We are happy to see the way so auspiciously opened for such an introduction. It has been not merely- abridged, but also re-wriiten. We cannot but regard the labor as well bestowed." — 2?orth American Review. "We speak that we do know, when we express our high estimate of Dr. Wayland's ibility in teaching Moral Philosophy, whether orally or by the book. Having listened to his instructions, in this interesting department, we can attest how lofty are the principles, how exact and severe the argumentation, how appropriate and strong the illustrations •which characterize his system and enforce it ou the mind." — The Christian Witness. "The work of which this volume is an abridgment, is well known as one of the best and most complete works on Moral Philosophy extant. The author is well known as one of the most profound scholars of the age. That the study of Moral Science, a science which teaches goodness, should be a branch of education, not onlv iu our colleges, but in iv.,r schools and academies, we believe will not be denied. The abridgment of this work seems to us admirably calculated for the purpose, and we hope it will be extensively applied to the purposes for which it is intended." — The Mercantile Journal. "We hail the abridgment as admirably adapted to supply the deficiency which has lonjs, been felt in common school education, — the study of moral obligation. Let the child ^p.»-7 be taught the relations it sustains to man and' to its Maker, the first acciuuinting it •"TV the duties owed to society, the second with the duties owed to God. and wbo can toreteil how many a sad and disastrous overthrow of character will be prevented, and ho» elevated and pure will be the sense of integrity and virtue?" — Evening Gazette. Daluabie Scijool CLEMENTS OF POLITICAL SCONOSIY. By F \V.\YLANO, D.D., Pre«iii<-::t of Brown TJniver.sit v. Fifteenth Thousand. 12mo. cloth. Price $1.25 " His object has been to write a bock, which any one who chooses mr.y understand. Ha has, therefore, labored to express the general principles ic the plainest manner possible, ind to illustrate tb.em by ca^cs wiili which every j.'tTsoii is familiar. It has been to th* author a source of regret, that the rour-e of discussion in t'ne fol lowing pages, has, uno vouk'.bly, led him over ground which has frequently been the arena of poli'.ieui coiilr1). ver:-y. In all such cases, he has endeavored to state what seemed to liirn to be truth, without fear, favor, or idiection. lie is conscious to himself of 1:0 bias tow;a:l.= nnv party whatever, and he thinks that lie who will read the whole work, will be convinced that ho h;w been inlluenced by none." — Extrwt from the Preface. POLITICAL ECONOMY, ABSIDGED, by the Author, an. adapted to the use of Schools and Academies. Seventh Thousand. 18rno. half morocco. Price 50 cents. %* The success which has attended the abridgment of " The Elements of Moral S-'ience"has induced the author to prepare an abridgment of this work. In this case, as in the other, the work has been wholly re-writto'j, and an attempt has been made to adapt it to the attainments of youth. '' The original work of the author, on Political Economy, has already been noticed on our pages ; and the present abridgment stands in no need of a recommendation from us. We may be permitted, however, to say, that both the rising and risen generations are deeply indebted to Dr. "Wa}-!'nvJ, for the skill and power lie has nut forth to bring a highly important subject distinctly before them, within such narrow limits. Though ' abridged for the use of academies,' it deserves to be introduced into every private family, and to be studied by every man who has an interest in the wealth and prosperity of his country. It is a subject little understood, even practically, by thousands, and still less understood theoretically. It is to be hoped, this will form a class-book, and be faithfully studied in our academies ; and that it will find its way into every family library ; not there to be shut up unread, but to afibrd rich material for thought and discussion in the family circle. It is fitted to enlarge the mind, to purify the judgment, to correct erroneous popular impressions, and assist every man in forming o inking cf public measures, which will abide the test of time and experience." — Boston Jtucordi ,'. " An abridgment of this clear, common sense work, desip-.ed for the us>e of academies is just published. We rejoice to see such treatises spreading amoTig the people; and we urge all who would be intelligent free men, to read iheiri." — ^~<:iv York I'ruiirrript. " \Ve can say, with safety, that the topics are well selected and arranged ; that the author's name 'is a guarantee' for more than usual excellence. "\Vewishitanextensive circulation." — ^eio York Wjscrver. " It is well adapted fo hi v\ schools, and embraces the soundest system of republican polities! economy cf any treatise extant." —Daily Advocate. I HO TIGHT Sou the present Collegiate System in the United States. By FEAXCIS WAYT,AXD, D.D. Price 50 cents. " These Thoughts come from a source entitled to a very respectful a'ti-ntion : and as the author goes over the whole ground of collegiate education, criticising freely all the arrange- ments in every department and in all their bearings, the bock is very full of matter, we hope it will prove the beginning of a thorough discussion." P A L E Y ' S 5T A T U B A L THEOLOGY. Illustrated by forty plates, and Selections from the notes of Dr. I'axton, with additional Notes, original and selected, for this edition ; with a vocabulary of Scientific Terms. Edited by JOHN WAKE, M.D. 12mo. sheep. Price $1.25. " The work before us is one which deserves rather to be studied than merely read. Indeed, without diligent attention and study, neither the excellence*; r.f it can be fully dis- covered, nor its advantages realized. It is, therefore, gratifying. to find it introduced, as a text-book, into the colleges .and literary int-tKutioiis of our country. The edition before us is superior to uuv we have seen, and, we believe, superior to any that has yet been pub- lished." — Spirit of the I'UfrriwK. "Perhaps no one of our author's works gives greater satisfaction to all classes of readers, the young and the old, the ignorant and the enlightened. Indeed, we recollect no book in which the arguments for the existence and attributes of the Supreme Being, to be drnwq from Ms works are exhibited in a manner more attractive and more convincing. " Christian Examiner,