Once this supposition is made, however, all the objections we have mentioned in connection with factorial mutation (_e.g._ the subnormality of its products, its intra-specific nature, etc.) return to plague the speculator, and, in addition to these, he is confronted with the new difficulty of explaining how the redundance of duplicate genes can be removed and replaced by coördinate differentiation in their respective specificities. Now we have no factual evidence whatever of such a solidaric redifferentiation of the germinal factors, that would modify harmoniously the composition and rôle of each and every gene in the factorial complex. Nor is there any possibility whatever of accounting for this telic superregulation of the germinal regulators upon a purely mechanistic basis. How can the ultimate chemical determinants of heredity be thus redetermined? Consequently, although there is gametic incompatibility between diploid races and the tetraploid races, which are said to have arisen from the former, we are not, nevertheless, warranted, by what has been experimentally verified, in regarding tetraploid races as new species, or as progressive steps in the process of organic evolution. To conclude, therefore, we have experimental verification of the efficacy of the similifying process said to have been at work in evolution, namely, inheritance. The same, however, cannot be said of the correlative diversifying process of trans-specific variation, which is said to have superficially modified old structures into new species. The latter process, accordingly, is but a pure postulate of science known to us only through the effect hypothetically assigned to it, namely, the adaptive modification.