All these cases are quite in harmony with our conception of amphimixis, which, now that we have investigated the facts throughout the animate kingdom, we may sum up in the following propositions. In the whole organic world, from unicellular organisms up to the highest plants and animals, amphimixis now means an augmentation of the organism's power of adaptation to the conditions of its life, since it is only through amphimixis that simultaneous harmonious adaptation of many parts becomes possible. It effects this by the mingling and constant recombination of the germ-plasm ids of different individuals, and thus gives the selection-processes the chance of favouring advantageous variational tendencies and eliminating those which are unfavourable, as well as of collecting and combining all the variations which are necessary for the further evolution of the species. This indirect influence of amphimixis on the capacity of organisms for surviving and being transformed is the fundamental reason for its general introduction and for its persistence through the whole known realm of organisms from unicellulars upwards. The reason for its _first_ introduction among the lower forms of life must have been a direct effect which had a favourable influence on the metabolism, and this is so far coincident with the subsequent import of amphimixis, inasmuch as it may be regarded not only as a heightening of the power of adaptation, but as an immediate and direct increase and extension of the power of assimilation. In any case, amphimixis is not necessary to the actual preservation of life itself, but it does bring about a wealth and diversity of organic architecture which without it would have been unattainable. If amphimixis has been abandoned in the course of phylogeny by isolated groups of organisms, this has happened because other advantages accrued to them in consequence, which gave them greater security in the struggle for existence; but it must be admitted that they thereby lost their perfect power of adaptation, and that they have thus bartered their future for the temporary securing of their existence. In addition to this variational influence, amphimixis has also played a part in the evolution of sharply defined organic types, especially of specific types; but of this we shall have more to say later on. LECTURE XXXI THE INFLUENCES OF ENVIRONMENT