FIG. veloped, and bent upwards. The upper part of the yolk (dd) is nearly separated from the yolk sphere, and is to become the in testine. The heart (h) 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 becomes covered with many little fringes. 131. The embryo (e) is seen surrounded by the amnios, (b,) 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 Salpæ. 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. [41. 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; c, f, g, tentacles shooting forth; e, embryo adhering, and forming 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 vernalis ;) a, the canker worm; b, 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 appearing, 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 sanguinolentus,) showing the changes of the yolk, (e;) the formation of the pedicle, (r;) and the gradual change into the pentagonal and rayed form. 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, metamorphic rocks; T, trap rocks; L, lava. 1. Lower Silurian formation; 2. Upper Silurian; 3. Devonian; 4. Carboniferous; 5. Trias, or Saliferous; 6. Oölitic; 7. Cretaceous; 8. Lower Tertiary or Eocene; 9. Upper Tertiary, or Miocene, and Pleiocene; 10. Drift. 155. Fossils of the Paleozoic age; a, Lingula prima; b, Leptæna alternata; c, Euomphalus hemisphericus; d, Trocholites ammonius; e, Avicula decussata; f, Bucania expansa; g, Orthoceras fusi forme; i, Cyathocrinus ornatissimus, Hall; j, Cariocrinus ornatus, Say; k, Melocrinus amphora, Goldf.; 1, Columnaria alveo lata; m, Cyathophyllum quadrigeminum, Goldf.; n, o, Caninia flexuosa; p, Chætetes lycoperdon. 156. Articulata of the Paleozoic age; a, Harpes; b, Arges; c, Brontes, d, Platynotus; e, Eurypterus remipes. 157. Fishes of the Paleozoic 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, (b.) 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, Lithodendron pseudostylina; c, Pentacrinus briareus; d, Pterocoma pinnata; e, Cidaris; f, Dysaster; g, Nucleolites. 164. Shells of the Cretaceous formation; a, Ammonites; b, Crioceras ; c, Scaphites; d, Ancyloceras; e, Hamites; f, Baculites; 9, Turrilites. 165. Shells of the Cretaceous formation; a, Magas; b, Inoceramus; 0, 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. upposed outline of Paleotherium. 169 Supposed outline of Anoplotherium. 170 Skeleton of the Mastodon, in the cabinet of Dr. J. C. Warreu. 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 sparrowhawk; 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 rounded upon some of the minor peculiari ies of anat、 mica. structure, such as the number, disposition, or proportions of the teeth, claws, fins, &c., and usually includes several kinds. Thus, the lion, tiger, leopard, cat, &c., agree in the structure cf 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 alewives, herrings, shad, &c., form a family called Clupeidae; the crows, blackbirds, jays, &c., form the family Corvida. 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 truits 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 deas of the class, family, or genus to which it belongs. 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 titlepage. The Animal Kingdom consists of four great divisions, which we call DEPARTMENTS, namely: I. The department of Vertebrates. 1. 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.) |