in a reference to the different animals which man has thus made subservient to his social condition. We shall here allude only to the laws of distribution of wild animals in their natural condition.

It has already been stated, that the present distribution of animals agrees with the distribution of extinct types belonging to earlier geological periods, so that the laws which regulate the geographical distribution of animals seem to have been the same at all times, though modified in accordance with the successive changes which the animal kingdom has undergone from the earliest period of its creation to the present day. The universal law is, that all animals are circumscribed within definite limits. There is not one species which is uniformly spread all over the globe, either among the aquatic races or among the terrestrial ones. Of the special distribution of man, who alone is found everywhere, we shall speak hereafter. The special adaptation of animals to certain districts is not merely limited to the individual species. We observe a similar adaptation among genera, entire families, and even whole classes. For instance, all Polypi, Medusa, and Echinoderms, that is to say all Radiata, without exception, are aquatic.* That large group of animals has not a single terrestrial representative upon any point of the surface of the globe; and during all periods of the history of our earth, we find that they have always been limited to the liquid element. And they are not only aquatic, they are chiefly marine, as but exceedingly few of them are found in fresh waters. Among Mollusca we find almost the same adaptation. Their element also is the sea. The number of fresh-water species is small, compared with that of marine types; and we find terrestrial species in only one of their classes. In former periods, also, Mollusca were chiefly marine; fluviatile and terrestrial types occurring only in more recent periods.

*The following statements have been strictly considered, and are made in reference to a revised classification of the animal kingdom, the details of which must, however, be omitted here, as they would extend this article beyond our allotted bounds.

With the Articulata, we find another state of things. Two of their classes, the worms and Crustacea, are chiefly marine, or at least aquatic, as we have a number of fresh-water worms, and some fresh-water Crustacea. But insects are, for the most part, chiefly terrestrial, feeding upon terrestrial plants, at least in their full-grown condition; though a large number of these animals are fluviatile, and even some marine, during their earlier periods of life. In the Vertebrata, the adaptations are more diversified. Only one class of these animals is entirely aquatic-the fishes; and the number of the marine species is far greater than that of the fresh-water kinds. Among reptiles there are many which are aquatic, either throughout life, or through the earlier period of their existence. But, as if animal life rose to higher organization, as it leaves the ocean to inhabit dry land or fresh waters, we find that the greater number of the aquatic reptiles are fluviatile, and but a few marine. This fact agrees wonderfully with the natural gradation of the classes already mentioned. The lower type of animals, the Radiata, is almost exclusively marine. Among Mollusca, we have a greater number of marine types, a large number of fluviatile species, and fewer terrestrial, and these are the highest in their class. Again, among Articulata, the lower classes, worms and Crustacea, are marine, or at least fluviatile, whilst the highest class, that of insects, is chiefly terrestrial or fluviatile, during the earlier periods of their growth. Among the Vertebrata we see the lowest form, that of fishes, entirely aquatic, and the same rule applies partially to the reptiles; but as the class rises, the number of the fluviatile species is greater than that of the marine types. Next, among birds, which by their structure are exclusively adapted to live in the atmospheric air, we find the larger number to be terrestrial, and only the lower ones to live upon water, or dive occasionally into it, always seeking the surface, however, to breathe and to perform their most important vital functions. It is, nevertheless, not a little strange, that this class should by nature be adapted to rise into the air, just as if the first tendency towards liberating them from the aquatic element had been

carried to an excess, and gave them a relation to the earth which no other class, as a whole, holds to that degree, except, perhaps, the insects, which are placed among the Articulata in the same relation to the lower classes and the natural element, which the class of birds maintains among Vertebrata. The highest class of Vertebrata affords us examples of these three modes of adaptation, the lowest of these being entirely aquatic, and even absolutely marine; next, we have fluviatile types of the large terrestrial mammalia, in the family of Manatees, again, a swimming family among Carnivora, another flying, most of them however walking upon their four extremities on solid ground, but at the head of all, man, standing upright, to look freely upwards, and to contemplate the whole universe.

This wonderful adaptation of the whole range of animals, as it exists at present, shews the most intimate connection with the order of succession of animals in former geological periods. The four great types, Radiata, Mollusca, Articulata, and Vertebrata, were introduced at the beginning simultaneously. However, the earliest representatives of these great types were all aquatic. We find in the lowest beds which contain fossils, Polypi, together with star-fishes, bivalve shells, univalves, chambered shells, cases of worms, and Crustacea, being representatives of at least seven out of nine classes of invertebrate animals, if we are not allowed to suppose that Medusa existed also, and if insects were still wanting for a time. But, in addition to these, fishes among Vertebrata are introduced, but fishes only, all of which are exclusively marine. At a somewhat later period insects come in. We find next reptiles in addition to fishes-the lower classes, or invertebrates, continuing to be represented through all subsequent epochs, but by species changing gradually at each period, as all classes do after they have been once introduced. The first representatives among reptiles are marine, next huge terrestrial ones, some, perhaps, flying types, and with them, and perhaps even before them, birds, allied to the wading tribes: still later, Mammalia, beginning again with marine and huge terrestrial types, followed by the

higher quadrupeds; and, last only, Man,-at the head of the creation, in time as well as in eminence, by structure, intelligence, and moral endowments.

Besides the general adaptation of animals to the surrounding media, there is a more special adaptation, which seems not less important, though it is perhaps less striking. Animals, as well as plants, do not live equally at all depths of the ocean, or at all heights above its surface. There must be a deep influence upon the geographical distribution of animals in a vertical direction derived from atmospheric pressure above the surface of the waters, and from the pressure of the water itself at greater and greater depths,-the level of the ocean, or a small elevation above its surface, or a shallow depth under its surface, being the field of the most extensive. and intensive development of animal life. And it is not a little remarkable that in the same classes we should find lower types at greater depths in the ocean, and also lower types at greater heights above. We will quote a few examples, to shew how much we may expect from investigations pursued in this direction, for at present we have but little information which can aid us in ascertaining the relationship between atmospheric and hydrostatic pressure and the energies of animal life.

Among Polypi, the higher forms, such as Actiniæ, are more abundant in shallow water than the lower coral-forming types. Among Medusa, the young are either attached to the bottom, or grow from the depth, while the perfect free forms of these animals come to the surface. Among Echinoderms, the Crinoids are deep-water forms; free star-fishes and Echini, and, above all Holothuria, living nearer the surface. Among Mollusca, the Acephala, which are lowest, have their lower types,-the Brachiopods, entirely confined to deep waters; the Monomyarians appear next, and, above them, the Dimyarians; among these latter, the highest family, the Nayades, rises above the level of the ocean into the fresh waters, and extends even to considerable heights above the sea, in lakes and rivers. A number of examples of all classes should be mentioned, to shew that this is the universal case; as, for instance, among Crustacea the Macrura are, in general VOL. XLIX. NO. XCVII.-JULY 1850.

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species of deeper water than the true crabs, of which some come even upon dry land. Again, on the slopes of our mountains, the highest forms among Mammalia which remain. numerous are the Ruminants and Rodents. There are no Carnivora living in high regions. Among birds of prey, we have the vultures, rising above the highest summits of mountains, while eagles and falcons hover over the woods and plains, by the water sides, and along the sea-shores. Among reptiles, salamanders, frogs, and toads occur higher than any turtles, lizards, &c. But the same adaptation may be traced with reference to the latitudes under which animals are found. Those of the higher latitudes, the arctic and antarctic species, resemble both the animals of high, prominent mountain chains, and those of the deep sea-waters, which there meet in the most unexpected combinations (and it is surprising to see how extensively this is the case); while, in lower latitudes, towards the tropics, we find everywhere the higher representatives of the same families. For instance, among Mammalia we observe monkeys only in warm latitudes, and they die out in the warmer parts of the temperate zone. The great development of Digitigrades-lions, tigers, &c., takes place within the tropics, smaller species, like wolves and foxes, weasels, &c., occurring in the north, whilst the Plantigrades, which come nearer and nearer to the seal, follow an inverse progression, the largest and most powerful of them being the arctic ice bear, which meets there his family relations, the Pinnipedia, that are so numerous in the polar regions. Again, the families of Ruminants and Pachyderms seem to form an exception, for though belonging to the lower types of Mammalia, they prevail in the tropical zone; but let us remember that they were among the earlier inhabitants of our globe, and the fact of their occurring more extensively in warm climates is rather a reminiscence of the plan of creation in older times, than an adaptation to the law regulating at present the distribution of organized beings. The gradation of animals among birds being less satisfactorily ascertained, we do not venture to say anything respecting their geographical distribution, in relation to climates. But among reptiles, we cannot overlook the fact, that the crocodiles, which are