The instance already referred to, where hybridity was thus presented, was as follows:—The mule, as is well-known, is the offspring of the horse and ass. It does not, in its turn, reproduce itself, therefore the horse and ass were different species. Prichard and others applied this test, or marked this test, in the case of human beings, of whites and negroes, and proved by it that they were of the same species. It was seen that white men cohabited with negro women, and the offspring in turn, reproduced itself, and consequently that the parents were of the same species. Or, as this has passed as current coin hitherto, and seemed perfectly satisfactory, indeed wholly unanswerable to naturalists and men of science as well as others, it is best, perhaps, to place it in distinct and categorical terms before the reader. 1st. It is universally admitted by naturalists that incapacity in the offspring to reproduce itself demonstrates the different species of the progenitors, while, on the contrary, a capacity in the offspring to beget offspring in its turn demonstrates similarity of species in the progenitors. 2d. The mule, or the offspring of the horse and ass, does not reproduce itself, therefore the horse and ass are different species. 3d. The mulatto offspring of the white man and negro woman does beget offspring, therefore the white man and negro woman are of the same species. This was the assumption and the reasoning of Prichard and other European ethnologists, and if hybridity were a unit, or principle of rigid and uniform character in all cases, in human beings as in animals and vegetables, in the case of the white man and negress, exactly as in that of the horse and ass—then, indeed, would the inference seem unavoidable that whites and negroes constituted in fact a single species. But they were guilty of two fundamental errors in this matter—an error of fact, and an error of reasoning, or perhaps it would be more correct to say that both were errors of fact. At all events, _facts_ that demonstrate difference of species in whites and negroes beyond possibility of doubt were distorted into proofs which seemed to demonstrate sameness or similarity of species with equal certainty.