The historical evidence of modification in successive generations, which is inadequate to prove the specific identity of the several races of Dogs, is much more fully supplied in the case of some other domesticated animals; and suffices to show that although the tendency to spontaneous variation may seem to have nearly exhausted itself heretofore in the production of the most divergent forms, still there remains enough to originate new races, distinguished by well-marked pecu liarities of conformation, even under our own eyes. Some of our most valuable information on this subject, is derived from the changes which have taken place in the races of do mesticated animals introduced into the West Indies and South America, by the Spaniards, three centuries and a half since. Many of these races have multiplied extremely in a soil and in a climate congenial to their na ture; and several of them have run wild in the vast forests of America, and have lost all the most obvious appearances of domestica tion, whilst they have acquired various pecu liarities which distinguish them from their domesticated progenitors, some of these, per haps, being indications of a partial restoration to the primitive characteristics of their re spective races. The greatest part of our knowledge on this subject is derived from the researches of M. Roulin (already referred to) which relate to New Grenada and Venezuela, and from the well-known and justly esteemed work of D'Azara on the natural history of Paraguay.
No zoologist has any doubt whatever, that the wild boar is the original of our domesti cated swine; the change from the one form and condition to the other being capable of accomplishment in the course of a few gene rations. Yet, as Blumenbach has remarked, the difference between the two forms of crania is as great as that between the Negro and the European skulls. And the same eminent physiologist has pointed out, that the varie ties of swine in various countries, all clearly referable to one stock, exceed in their extent of divergence from it, the very widest de partures of the human conformation from any one type. Thus, swine with solid hoofs were known to the ancients ; and large breeds of them arc found in Hungary and Sweden, as also in some parts of England. In some other breeds there are five distinct toes, each having its own hoof. The European swine, first carried by the Spaniards to the island of Cubagua, in 1509, have been the progenitors of a race now found there, possessing toes of half a span in length. The hogs which were first introduced into South America by the Spaniards at about the same period, rapidly extended themselves over the northern and central parts of that continent ; and whilst wandering at large in the vast forests of the New World, and feeding on their original diet of fruits and seeds, they have reverted very nearly to the type of the European boar. Their colour, too, has lost the variety ob servable in the domestic breeds, the wild hogs of the American forests being for the most part uniformly black, The hogs which cover the mountains of the Paramos, where they are subject to severe cold and deficient nourishment, are small and of a stunted figure ; but their skins are covered with thick fur, often somewhat crisp, beneath which is found in some individuals a species of wool. In
some of the warmest regions, the swine are not uniformly black, but red like the young peccari ; and elsewhere there are some, whose blackness gives place under the belly to a white band, which reaches up to the back.
The question of the original source of the various breeds of ox, will not be now dis cussed; it is sufficient for our present pur pose to notice some of the most remarkable departures from the European type, which have shown themselves in the South Ameri can descendants of the individuals first intro. duced there by the Spaniards. In the year 1770, as we learn from D'Azara, a hornless bull was produced in Paraguay, which has been the progenitor of a race of hornless cattle that has since multiplied extensively in that country. So, again, as we are informed by M. Roulin, in some of the hot provinces of South America, a variety of ox has been produced, which is noted for its extremely rare and fine fur. This variety tends to per petuate itself ; but it is not encouraged, be cause the "pelones" (as they are termed) are too delicate in constitution to bear the cold of the Cordilleras, to which the cattle are driven for the provision of the towns situated upon them. These pelones obviously con stitute a variety adapted for a particular climate ; oxen of other breeds frequently perishing when driven into the provinces in habited by them, or being with difficulty acclimatised.* But the same hot provinces occasionally produce another curious variety, characterised by the entire absence of hair ; these naked-skinned oxen, which are called " calongos," are, like the pelones, unable to bear a cold climate, and are very delicate and weak. Another remarkable fact, relative to the oxen of South America, is recorded by M. Roulin. In Columbia, the practice of milking cows was laid aside, owing to the great extent of the farms and other circum stances. In a few generations, the natural structure of the parts and the natural state of the function have been restored ; the se cretion of milk taking place only so long as the calf remains with the mother, and ceasing if it dies or is removed. Hence we have a valuable confirmation of the belief previously entertained, that the continued production of milk by the European breeds of cows is a modified function in the animal economy, originating in an artificial habit kept up through manygenerations, and depend ent upon a modification of structure which that habit has been the means of inducing.