those of the most ancient deposits have, in general, preserved only the apophyses of their vertebræ, whilst the vertebræ then selves are wanting. Were the Sturgeons of the Amer ican rivers to become petrified, they would be found in a similar state of preservation. As the apophyses are the only bony portions of the vertebral column, they alone would be preserved. Indeed, fossil Sturgeons are known, which are in precisely this condition. 395. From the fact above stated, we may conclude that the oldest fossil fishes did not pass through all the metamorphoses which our osseous fishes undergo; and, consequently, that they were inferior to analogous species of the present epoch which have bony vertebræ. Similar considerations apply to the fossil crustacea and to the fossil Echinoderms, when compared with living ones, and will, probably, be true of all classes of the Animal Kingdom, when fully studied as to their geological succession. 16* CHAPTER THIRTEENTH. GEOGRAPHICAL DISTRIBUTION OF ANIMALS SECTION I. GENERAL LAWS OF DISTRIBUTION. 396 No animal, excepting man, inhabits every part of the surface of the earth. Each great geographical or climatal region is occupied by some species not found elsewhere; and each animal dwells within certain limits, beyond which it does not range while left to its natural freedom, and within which it always inclines to return, when removed by accident or design. Man alone is a cosmopolite. His domain is the whole earth. For him, and with a view to him, it was created. His right to it is based upon his organization and his relation to Nature, and is maintained by his intelligence and the perfectibility of his social condition. 397. A group of animals which inhabits any particular region, embracing all the species, both aquatic and terrestrial, is called its FAUNA; in the same manner as the plants of a country are called its Flora. To be entitled to this name, it is not necessary that none of the animals composing the group should be found in any other region; it is sufficient that there should be peculiarities in the distribution of the families, genera, and species, and in the preponderance of certain types over others, sufficiently prominent to impress upon a region well-marked features. Thus, for example, in the islands of the Pacific are found terrestrial animals, alto gether peculiar, and not found on the nearest cont.nents. There are numerous animals n New Holland differing from any found on the continent of Asia, or, indeed, on any other part of the earth. If, however, some species inhabiting both shores of a sea which separates two terrestrial regions are found to be alike, we are not to conclude that those regions have the same Fauna, any more than that the Flora of Lapland and England are alike, because some of the sea-weeds found on both their shores are the same. 398. There is an evident relation between the fauna of any locality and its temperature, although, as we shall here after see, similar climates are not always inhabited by similar animals, (401, 402.) Hence the faunas of the two hemis pheres have been distributed into three principal divisions, namely, the arctic, the temperate, and the tropical faunas: in the same manner as we have arctic, temperate, and tropi cal floras. Hence, also, animals dwelling at high elevations upon mountains, where the temperature is much reduced resemble the animals of colder latitudes, rather than those of the surrounding plains. 399. In some respects, the peculiarities of the fauna of a region depend upon its flora, at least so far as land animals are concerned; for herbivorous animals will exist only where there is an adequate supply of vegetable food. But taking the terrestrial and aquatic animals together, the limitation of a fauna is less intimately dependent on climate than that of a flora. Plants, in truth, are for the most part terrestrial, (marine plants being relatively very few,) while animals are chiefly aquatic. The ocean is the true home of the Animal Kingdom; and while plants, with the excep tion of the lichens and mosses, become dwarfed, or perish under the influence of severe cold, the sea teems with animals of all classes, far beyond the extreme limit of flowering plants, 400. The influence of climate, in the colder regions, acıs merely to induce a greater uniformity in the species of animals. Thus the same animals inhabit the northern polar regions of the three continents. The polar bear is the same in Europe, Asia, and America, and so are also a great many birds. In the temperate regions, on the contrary, the species differ on each of the continents, but they still pre serve the same general features. The types are the same but they are represented by quite different species. In consequence of these general resemblances, the first colonists of New England erroneously applied the names of European species to American animals. Similar differences are observed in distant regions of the same continent, within the same parallels of latitude. The animals of Oregon and of California are not the same as those of New England. The difference, in certain respects, is even greater than between the animals of New England and Europe. In like manner, the animals of temperate Asia differ more from those of Europe than they do from those of America. 401. Under the torrid zone, the Animal Kingdom, as well as the Vegetable, attains its highest development. The animals of the tropics are not only different from those of the temperate zone, but, moreover, they present the greatest variety among themselves. The most gracefully proportioned forms are found by the side of the most grotesque, decked with every combination of brilliant coloring. At the same time, the contrast between the animals of different continents is more marked; and, in many respects, the animals of the different tropical faunas differ not less from each other than from those of the temperate or frozen zones. Thus, the fauna of Brazil varies as much from that of Central Africa as from that of the United States. 402. This diversity upon different continents cannot depend simply on any influence of the climate of the tropics if it were so uniformity ought to be restored in proportion as we reced from the tropics towards the antarctic tem perate regions. But, instead of this, the differences continue to increase; so much so, that no faunas are more in contrast than those of Cape Horn, the Cape of Good Hope, and New Holland. Hence, other influences must be in operation besides those of climate; influences of a higher order, which are involved in a general plan, and intimately associated with the development of life on the surface of the earth. 403. Faunas are more or less distinctly limited, according to the natural features of the earth's surface. Sometimes two faunas are separated by an extensive chain of moun tains, like the Rocky Mountains. Again, a desert may intervene, like the desert of Sahara, which separates the fauna of Central Africa from that of the Atlas and the Moorish coast, the latter being merely an appendage to the fauna of Europe. But the sea effects the most complete limitation. The depths of the ocean are quite as impassable for marine species as high mountains are for terrestrial animals. It would be quite as difficult for a fish or a mollusk to cross from the coast of Europe to the coast of America, as it would be for a reindeer to pass from the arctic to the antarctic regions, across the torrid zone. Experiments of dredging in very deep water have also taught us that the abyss of the ocean is nearly a desert. Not only are no materials found there for sustenance, but it is doubtful if animals could sustain the pressure of so great a column of water, although many of them are provided with a system of pores, (260,) which enables them to sustain a much greater pressure than terrestrial animals. 404. When there is no great natural limit, the transition from one fa ina to another is made insensibly. Thus, in passing from he arctic to the temperate regions of North |