We should, in the first place, note the fact that the ancestors of our more important domesticated animals, those which have been longest in subjugation, have commonly disappeared from the wild state--the species, except for the cultivated forms, having gone into the irrecoverable past. This is the case with the wild kindred of our bulls, horses, sheep, and camels, there probably being none of the original wild species of these groups now living, except those which have been more or less completely subjugated by man, and then have returned to the wilderness. The fact is, that with any large mammal the domestication of the species tends to bring about the destruction of the remaining wild forms. If we go back in fancy to the time when the dog was taken in from the wilderness, we readily perceive how certainly the subjugated individuals would have mingled with their wild kindred, so that either the wild would have become tame or _vice versa_. The same incompatibility which exists between slavery and freedom in our own species in any given territory may be said to hold in the case of captive animals. It is particularly on this account that I am disposed to think that our races of dogs have been derived from one or more original species of truly canine ancestors, the wild forms of which have long since disappeared from the earth. [Illustration: St. Bernard] Although there are no species of wild dogs now in existence to which we can refer the origin of our household friends, there are several known to us only in their fossil state, from which they may possibly--indeed, we may say probably--have been derived. These creatures are, of course, represented only by their skeletons, and even these remains have only been found in an imperfect state of preservation. It is evident, however, that these extinct species, or at least certain of them, lived down to the time when man had come upon the earth, and was beginning to speculate on his surroundings for such company and help as he might win therefrom. It may interest the reader to know that a species of American dog existed in the Southern Appalachians down to a very recent time--recent, at least, in a geological sense. The remains of one of these animals were found by the writer in a cave in East Tennessee, near Cumberland Gap. From the fragments of the skeleton, Mr. J. A. Allen has described the species. The animal appears to have been of moderate size, and, from the position of the bones, it seems tolerably certain that it lived but a few centuries ago.