to a pure theory of natural selection, and call to our aid an, even now, rather obscure phenomenon, occurring in connection with sexual impregnation, which has been called “the expulsion of the polar bodies,” an extrusion of minute qualities of germ-plasm from the germ-cells while in union. By the processes of crossing, which continually recur, a vast number of the most manifold hereditary tendencies are united in the germ-material. Then certain of these are ejected, so that others acquire supremacy; and in this manner the way is opened for the origination of a vast number of possible combinations. In this way the path is clear to a theory of perfect mechanical variability, in which the germ-material has only to transmit the characters which spontaneously arise in it, and yet affords an investigator endowed with any imagination the possibility of understanding the origin of the great variety and final purpose of the world. It is Frohschammer’s “principle of the imagination as the creator of the world” translated into comprehensible formulæ. The simplicity thus reached by the elimination of all direct influences from the external world, has won the adherency of many investigators following in Darwin’s steps, particularly in England; but whilst Wallace, Galton, Ray Lankester, and others have expressed their full assent to it, other and not less eminent authorities, as Herbert Spencer, Haeckel, Fritz Müller, and Virchow, have emphatically rejected it. The reasons in favor of this assumption are, as is indeed the whole view itself, mainly of a theoretical nature; the arguments of the opposition are divided into philosophical and experiential propositions. The philosophical opposition is mainly based on the fact that, from the very beginning, there is assigned to the germ-material, as it unceasingly continues its existence, an infinite variety of capacities which the external world cannot affect, and that all progress and advancement takes place as the result of the _loss_ of the originally endowed powers and tendencies. On this theory a family of acrobats or race-horses would not acquire their powers through the gradual augmentation by practice of their feats of skill and endurance, but because these powers were originally resident in them, and every factor incompatible with them was gradually eliminated. On the other hand, these views approach in a dangerous degree to the theories of predestination and preformation, the overthrow of which has been justly regarded as one of the greatest advances of science.