It will be found that the progress of domestication, the natural result of civilized improvement, tends more materially to operate a wonderful change in the animal conformation, than any other supposed agency. The head of the domestic pig differs as much from that of the wild one as the Negro's from the Caucasian's. At Padua, it has been observed that fowls have a cranium perforated by numerous holes, and hollowed out like a shell. In some countries, nay districts, cattle and sheep have or have not horns; and in other instances sheep have so many of them as to have acquired the epithet of _polycerateous_. Wild animals continuing to inhabit the place that bore them, undergo little or no change, and their fossil remains and skeletons are similar to the present species; but nothing can form a stronger contrast to this specific uniformity than the numerous varieties to be found in those races that have been crossed in breed and domesticated by man. We could scarcely imagine that our sheep owe their origin to the mouflon or argali, (_ovis ammon_,) an animal large in size, fleet, and fierce. The sheep of Senegal and India are those that have undergone the least degradation; while those of Barbary, Egypt, Arabia, and Persia, have experienced greater degeneration. We daily see dogs degenerate before our eyes, and it has not yet been satisfactorily ascertained whether they arise from one or several species. Cuvier, in his diligent researches, has concluded that our oxen do not originate in the urus or bison of the ancients formerly found in various parts of Europe, and still met with in the forests of Lithuania, and on the Carpathian and Caucasian chains; but he is of opinion, from the examination of fossil remains, that, like the camel and the dromedary, the species has been destroyed by civilization: the causes of these changes do not appear to operate by altering the parents but disposing them to produce offsprings more or less dissimilar in colour, form, and disposition. Dr. Prichard observes, that the negro slaves of the third and fourth generation differ materially from the natives of Africa. In opposition to this doctrine, which admits this wonderful degeneration under the plastic influence of domestication, it has been shown that, as far as we know, the lapse of ages has not produced any change in the generality of animals. The zoological descriptions given by Aristotle twenty-two centuries ago apply distinctly to the same species of the present day, and every work of art in which these animals are represented corroborates the fact. Geoffroy de St. Hilaire brought numerous mummies of animals from the sepulchres of Egypt, and found no more difference between their skeletons and the osseous conformation of the present races, than in the relics of the human mummy and the bones of our contemporaries.