covered, enabling the palaeontologist to unfold the relations of fossil plant-life, its distribution in space, and its progress in time, even as the botanist now determines its existing relationships, and maps out its centres and areas of geographical arrangement.

2. ITS FAUNA OR ANIMAL LIFE.

As with plants, so with animals. While we find them everywhere on the earth, in the air, and in the waterson the substances of plants, and even in the living tissues of other animals-they are as imperatively governed by the influences of climate, food, and other external conditions as the Vegetable world, though possessed for the most part of a locomotion which at first sight might seem to confer on them an ubiquity of habitat. Thus, the FAUNA of the tropics is essentially different from that of the temperate zone, and the animals which people the temperate zone have but little in common with those of the arctic regions. It is true that some, like Man and his companions, the dog, horse, and other domesticated animals, have a range all but universal; but generally speaking, the zones of Animal Life-horizontally and vertically-are about as sharply defined as those of vegetation. The elephant and rhinoceros that luxuriate in the low tropical jungle would fare but indifferently on the lofty slopes of the Himalayas; while the buffalo and bison which herd at these heights would cease to exist were they raised but a few thousand feet higher. As with altitude on land, so with depth in the ocean; and thus the sea-weeds and shells that grow and live within the influence of the tides constitute a Littoral zone very different from the Laminarian or broad sea-tangle zone which extends, in British seas, from 40 to 90 feet in depth; this again is

essentially distinct from the Coralline zone, which ranges from 90 to 300 feet, and is the great theatre of marine life; while beyond this lies the Coral zone, the region of the strong calcareous corals extending from 300 to 600 feet in depth from the shore line. But it is not alone to climate and external conditions that we must look for the variety and distribution of animal life. There is an aboriginal diffusion of different tribes and families from certain centres and over certain areas, for which science can as yet offer no satisfactory reason. Thus, why should the giraffe, or ostrich, or hippopotamus, be restricted to the continent of Africa, while the forests, and plains, and river-swamps of South America enjoy the same tropical sun, and seem every way equally adapted to identity of vitality? The pampas of America, as has been proved by experience, are as well fitted for the increase of the horse as the plains of Europe or the steppes of Tartary; and yet, till man carried him thither a few hundred years ago, no horse of the current epoch existed there. The ornithorhynchus burrows only in the river banks of Australia; the apteryx is unknown beyond the limits of New Zealand; the sloth is confined to the tropical forests of America; the armadillo to the same region; and not one of the Old World monkeys is identical with any of those of the New. Nor is it alone the terrestrial tribes that are thus limited and restricted; the aërial and aquatic, though possessing superior facilities for dispersion, are equally circumscribed, each within its own geographical habitat. The humming-birds flutter only over the flowers of the New World; the pheasants are unknown beyond the coverts of the Old; the shark-like cestraciont frequents alone the waters of the Southern Pacific; and the trigonia never carries its shell beyond the shores of Australasia. Such restrictions we cannot explain unless by ascribing them to independent centres of creation,

or to means of distribution that prevailed during former geological epochs, but which ceased to exist when sea and land received their present relations. And this brings us to remark on what are termed by zoologists the law of identity and the law of representation; that is, that different regions, though not peopled by identical species, may be peopled by animals which perform analogous functions, and represent them, as it were, in the great plan of vital economy. Thus, the ostrich of Africa is represented in South America by its congener the rhea; the jaguar and puma of the New World represent the tiger and lion of the Old; the camel of Arabia finds its analogue in the llama of Peru; and similar functions are at once discharged by the gavial of the Ganges, the crocodile of the Nile, and the alligator of the Amazon. Over and above these physical relationships there is also that which has reference to the size of the animal, and the element in which it is destined to live. As a general rule, and each within its own order or family, the aquatic members are larger than the terrestrial; the amphibious bulkier than those that are strictly terrestrial; the marine superior in size to those of fresh-water habitat; and the terrestrial more massive than the arboreal. mitting these relations, and reasoning from the present to the past, the comparative bulk of organic remains may often become an index to external conditions of life, and throw light over the investigations of the palæontologist, when other indications are uncertain and obscure.

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Besides these distinctions and restrictions imposed on vitality by external conditions, there are those connected with the functions they have to perform in the economy of nature. Some, for instance, are fitted to live on a purely vegetable diet, others to prey on the flesh of other creatures; some are constructed so as to feed only on seeds and grains, others to prey solely on insects; many earn their subsist

ence by a life of ceaseless activity and toil, others are formed for parasitic attachment to the living tissues of larger animals, and there find life and enjoyment without a single effort or care of their own. And as these varied functions necessarily require for their performance a special adaptation of organs—a tooth to cut or a tooth to grind, a foot to seize or a foot to dig, a limb to run or a limb to fly-so will similar modifications afford to the paleontologist an evidence of functions performed in bygone ages, and enable him, not only to reconstruct forms of harmonious organs, but to assign to these organs the part they had to play in the great drama of vitality. In the performance of these varied functions many animals have to make long periodic migrations, either for the immediate purpose of procuring food and shelter for themselves, or prospectively for their future young. From colder to warmer regions, and from warmer to colder-from land to water, and from water to land-from sea to river, and from river to sea-there is ever, among certain animals, an incessant interchange; and though paleontology has yet been unable to detect such migrations in the past, we may rely on their occurrence, and be prepared to admit the fact into our inferences and reasonings.

Coexistent with and beyond all this, there are those innumerable differences of species and kind and family and class, which we can only resolve into the eternal will of the Creator. Why, for instance, should the polype differ from the star-fish, the star-fish from the crab, the crab from the turtle, the turtle from the fish, the fish from the bird, or the bird from the quadruped? It is in vain to tell us that the one is but a progressive or developmental form of the other that the reptile is but a transmutation, in time and under new external conditions, from the fish, and that the fish is but the lineal descendant of the shell-fish. Admit

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ting that such was the true genetic origin of the various grades of vitality, there still lies behind and unaccounted for the orderly plan in which such development shall occur, and the reason for the definite specific forms which the descendants invariably assume. Grant, we again repeat, that all vitality were indissolubly interwoven into one great genetic mesh, still that mesh presents, at determinate times and over determinate areas, definite variety and speciality of pattern. Whence this orderly variety? Wherefore these special and distinctive patterns? At the most, Science can only note the distinctions, it can never hope to assign the reason. To do so would be to place the intelligence of the finite creature on the same level with the prescience of the infinite Creator. It is our high privilege, however, to observe and reason; and, reasoning, to arrange and classify the animal kingdom according to their different grades and affinities, and so arrive at some intelligible comprehension of the great scheme of vitality.

As in Botany, so in Zoology this arrangement is greatly facilitated by the fact that, numerous as animal forms are, they are all constructed after a few primal types and patterns. Some are furnished with a bony skeleton, the leading feature of which is the vertebral column or backbone— these are the VERTEBRATES; others have no such osseous framework-these constitute the INVERTEBRATES. As the leaf was the primary organ in the plant's development, so the vertebra seems to be the primal organ in the vertebrate skeleton; and by its modifications and adaptations for special ends, the Creator has produced every form of terrestrial, aërial, and aquatic existence. According to the modern doctrines of anatomy, the skull, or brain-case, is composed of vertebral bones, modified and adapted for a special purpose so are the limbs, whether for running, flying, or swimming; so also the ribs, whatever their form or num

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