In the dog, indeed, the changes of form are consider able, even in the general shape of the skeleton, and in that of the skull, as well as in the size, the hair, and the colour. An additional claw, and a superfluous tooth, have even been produced by breeding, as has a perma nently divided nose; yet, even in all these cases, the rela tions of the bones always continue essentially the same.
From all these considerations, it is concluded, that animals have definite and fixed characters for each spe cies, which are capable of resisting every influence, of whatever nature; and that there is no reason to expect that length of time, even were it extended to thousands of years, could do what has not been done within our ex perience. To confirm this opinion, Curler has examined all the most ancient representations of animals which he could find in sculptures, as well as various mummied specimens from Egypt, such as the cat, the ibis, the dog, the monkey, the crocodile, and the bull, as well as the human species, yet without finding the slightest difference between these and the corresponding animals of the pre sent day.
In addition to this, he also concludes, that if he has thus established that the Paixotherium, Alegalonix, Mas todon, and other lost animals, could not have been the sources or progenitors of any existing species, so those fossil species which most resemble the present, may also be different ones. If, as has been asserted, for example, the ancient fossil elephant, elk, rhinoceros, or bear, are no further different from the living one, than the several varieties of dogs now are from each other, it would not for that reason follow, that they are of the same species, as the one set had always been in that wild state in which no such variations are known to occur ; whereas, the varie ties of the other are the consequences of long continued domestication and artificial habits.
It is a question, under what circumstances those which are no longer supposed to exist have been lost. It does not appear that any general explanation of this fact is admissible, and we must probably seek for more causes than one. When animals of this character are found in such situations as the has, where there is a probability of their having been exposed to some of the most extensive revolutions of the globe, these catastrophes offer one ready solution of the question. In other cases, it is easy to con ceive that numerous indis iduals have been destroyed by such partial revolutions as produced the singular succession of strata in the basin of Paris, or gave rise to the present condition of Italy. But that a genus or a species should
have been entirely extinguished by such revolutions, the habitations of such animals must themselves have been limited. From what we know of the partial distribution of certain animals at present, such an explanation is plau sible. Were New Holland, for example, now to undergo a revolution of such a nature, the kangaroo, the wombat, the ornithorinchus, and other animals that appear limited to this tract of country, would become extinct.
'We also know, that in many other cases, animals which once had a wider range, are becoming more concentrated, or are diminishing in numbers; while they are also en tirely disappearing in places which they once inhabited, from various causes into which we need not here inquire. Combining such facts as these with local revolutions of the nature alluded to above, we have another clue to the explanation of lost species, without the necessity of seek ing for revolutions and catastrophes of a general nature, or recurring to a far more hypothetical explanation, viz. that of a successive extinction and a creation of new beings. Indeed, without any revolutions at all of the earth itself, it appears established, that certain animals are even now becoming extinct, from change of climate in some cases, consequent on alterations in the mass of vegetation in particular districts, whether these affect themselves imme diately or their food; from the reactions of animals on each other, and of man on the whole ; in some cases, pos sibly, from epidemic diseases, or from other causes affect ing their fecundity or propagation, respecting which we can scarcely conjecture. That which happens now may well have happened in former days ; and thus we are enabled, in some measure, to explain, on very ordinary principles, the extinction of some of the buried species. We had occasion to mention, in a former part of this article, that the elephant was once an inhabitant of Germany, as well as of Italy ; and many observations recently made in Siberia, prove that animals of analogous characters in habited northern Asia, in times which, like the former, are probably within the limits of historical record: The disappearance of these animals seems to connect modern with more ancient days; and with respect to a few that are still found living in secluded regions, such as the long haired white bull of the stony mountains of North Ameri ca, little seems wanting to give it a place with the former among extinct species.