The main antithesis at present is the following. On the one side, the “all-sufficiency of natural selection” is maintained, that is, progressive evolution is regarded as coming about without direct self-exertion on the part of the organisms themselves, simply through the fact that fortuitous variations are continually presenting themselves, and are being selected and established according to their utility in the struggle for existence. On the other side—with Lamarck—the progress is regarded as due to effort and function on the part of the organism itself. (Increased use of an organ strengthens it; a changed use transforms it; disuse causes it to degenerate. Thus new characters appear, old ones pass away, and in the course of thousands of years the manifold diversity of the forms of life has been brought about.) Further, by those of the one side variation is regarded as occurring by the smallest steps that could have selective value in the struggle for existence. To the others variation seems to have taken place by leaps and bounds, with relatively sudden transformations of the functional and structural equilibrium on a large scale. In regard to these the _rôle_ of the struggle for existence must be merely subsidiary. This saltatory kind of evolution-process is called “halmatogenesis,” or, more neatly, “kaleidoscopic variation,” because, as the pictures in a kaleidoscope change not gradually but by a sudden leap to an essentially new pattern, so also do the forms of life. Associated with this is the following contrast. One side believes in free and independent variation of any organ, any part, any function, physical or mental, any instinct, and so on, apart from change or persistence in the rest of the organism; the other side believes in the close connectedness of every part with the whole, in the strict “correlation” of all parts, in variation in one part being always simultaneously associated with variation in many other parts, all being comprised in the “whole,” which is above and before all the parts and determines them. And further, to one school variation seems without plan in all directions, simply plus or minus on either side of a mean; to the other, variation seems predetermined and in a definite direction—an “orthogenesis,” in fact, which is inherent in the organism, and which is indifferent to utility or disadvantage, or natural selection, or anything else, but simply follows its prescribed path in obedience to innate law. The representatives of this last position differ again among themselves. Some regard it as true in detail, in regard, for instance, to the markings of a butterfly’s wing, the striping of a caterpillar, the development of spots on a lizard; while others regard it as governing the general process of evolution as a whole. Finally, there is the most important contrast of all. On the one side, subordination, passivity, complete dependence on the selective or directive factors in evolution,