The importance which amphimixis thus has in connexion with the adaptation of organisms lies, if I mistake not, in the necessity for co-adaptation, that is, in the fact that in almost all adaptations it is not merely a question of the variation of a single determinant, but of the correlated variations of many--often very numerous--determinants, of 'harmonious adaptation,' as we have already said. Many-sided adaptation of this kind seems to me impossible without a continually recurrent sifting and recombining of the germ-plasms, and this can only be effected by amphimixis. It may be objected that, apart from amphimixis, variation can be brought about in many parts of an organism, as in purely asexual reproduction. A plant, for instance, may vary when it is transferred to a strange soil or climate; and even in that case the variations seem to be harmonious, at least the harmony of the parts is so far maintained that the plant continues to flourish, at any rate under cultivation. A plant species may be incited by abundant nourishment to gigantic growth, and caused to vary in many of its parts, and the abundant food may even directly affect the germ-plasm so that all or some of these variations may become hereditary; and yet this is far from being a case of adaptation, it is merely a case of simultaneous variations, and it is questionable whether they will make the continued existence of the plant under the new conditions possible or not. It might easily happen, for instance, that the plant, though it became larger and bore more abundant blossoms, would be sterile, and therefore unfitted for continued existence in a natural state. Variations are not necessarily adaptations; the latter can never come about solely through direct influence upon the germ-plasm. What direct influence upon the germ-plasm could, for instance, make the hind-legs of a mammal long and strong and the fore-legs short and weak? Obviously neither an increase nor decrease in the food-supply, nor a higher or lower temperature--in short, no direct influence, because all these affect the germ-plasm as a whole, and therefore cannot possibly influence two homologous groups of determinants in opposite directions. This, it seems to me, is only possible when amphimixis brings about in one individual a favourable coincidence of the chance germinal variations of the determinants of the fore- and hind-limbs; and just as it is with the two variations in this simple hypothetical case, so it will be in the actual processes of adaptation where there are involved numerous--we know not how numerous--variations essential to a 'harmonious adaptation.'