Supposing now that it has been demonstrated--which it has not--that the races of any group can _never_ engender a durable and permanent line by an intermixture with any of the others, can we infer from this that the races of the same group are equally incapable of producing by their intermixture mongrels indefinitely prolific? Just as little as the sterility of the union between the dog and the fox would enable us to infer the sterility between the wolf and the dog; these conclusions would be as little physiological as the former. Such as deny the fecundity of the reciprocal cross-breeds of the five chief primary races might err in some points, and be right as to others. But those who extend this by far too general negation in applying it to the intermixture of secondary races of the same group commit a more serious error. They have reasoned like the monogenists, who knowing from experience that _certain_ human races may become mixed without limitation, have affirmed that _all_ the races, without exception, are in a similar condition. There obtains thus a strange contradiction in these two schools; the one maintains resolutely that all races may intermix, and that their offspring and their descendants will be as prolific as if they were of a pure race, whilst the second as firmly sustains that no mixed race can have any other but an ephemeral existence. Between these opposite assertions we may well ask where lies the truth? Facts must answer the question. We shall endeavour to examine a few. Some of the facts are in favour of the monogenists, others support the opinion of their adversaries, from which we shall be enabled to infer that in the _genus homo_, as in the genera of their mammalia, there are different degrees of homœogenesis, according to the races or species; that the cross-breeds of certain races are perfectly eugenesic; that others occupy a less elevated position in the series of hybridity; and finally, that there are human races the homœogenesis of which is still so obscure, that the results even of the first intermixture are still doubtful. SECTION II. OF EUGENESIC HYBRIDITY IN MANKIND.