Zehnder has recently defined the effect of amphimixis as a 'strengthening of the power of adaptation,' and he infers that the 'digestive fistellæ' (Biophors) of two individuals, which have somewhat different powers of digestion, are, when they combine, able to assimilate more kinds of food than either was able to assimilate by itself. But I confess that I do not see how an advantage for the whole would be gained through this alone, since half of the digestive biophors would have to work for the nutrition of the mass of the individual _A_, the other half of the differently constituted biophors for that of the individual _B_, and the nutritive capacity would thus remain exactly what it was before conjugation. Nevertheless I believe that Zehnder was right in his supposition that conjugation is concerned with strengthening the power of adaptation, and I have long maintained and defended this interpretation with regard to true amphimixis in nucleated organisms. In these cases it is quite obvious that the communication of fresh ids to the germ-plasm implies an augmentation of the variational tendencies, and thus an increase of the power of adaptation. Under certain circumstances this may be of _direct_ advantage to the individual which results from the amphimixis, but in most cases the advantage will be only an indirect one, which may not necessarily be apparent in the lifetime of this one individual, but may become so only in the course of generations and with the aid of selection. For amphimixis must bring together favourable as well as unfavourable variations, and the advantage it has for the species lies simply in the fact that the latter are weeded out in the struggle for existence, and that by repetition of the process the unfavourable variational tendencies are gradually eliminated more and more completely from the germ-plasm of the species.