Wiedersheim enumerates nearly a hundred parts thus in process of degeneration: this means that nearly a hundred structures in Man are at the present time in process of variation, and this could not be so unless amphimixis were continually mingling the hereditary contributions anew from generation to generation, so that the minus-variations of the parts in question, starting from the germ-plasm in which they arose at one time as chance variations, and confirmed in their direction by means of germinal selection, are gradually being transmitted to all the germ-plasms of the species. We thus see that even in a period of species-life, which we may fairly call a period of constancy, variations of a phyletic kind are continually in process, which could not become general without the co-operation of amphimixis. Now, we have already seen that personal selection plays no part, or, at least, no important part in such degenerations, because the variations which are here concerned do not usually attain to selection value, but it is just such variations proceeding with infinite slowness that occur in functionally important organs likewise, and in the progressive advance of which personal selection and mutual adaptation probably play a part, so that in this way we can understand why the preservation of amphigony by natural selection must be effected. It is impossible--for obvious reasons--to name particular instances with certainty, as we can do in the case of the rudimentary organs, but even on general considerations we might expect that among the incipient variations of the determinants of the germ-plasm there would be some which were in an ascending direction, and that among these there would be some which, advanced by germinal selection, would go on ascending until they attained selection value. Wiedersheim reckons, for instance, the gradually increasing differentiation of the cortical zone of the human brain among the parts which are still in process of ascending variation, and he is probably right in doing so. But if variations, so slow as to be unnoticeable, are still of abundant occurrence in Man, we have no reason to doubt that similar processes are going on in other animals; among the higher Vertebrates at least there is hardly a species which does not exhibit regressive variations even now, and in many cases progressive variations also are occurring, although we cannot give definite proofs of this.