The point I wish especially to urge is this. Before Darwin's work appeared, the great majority of naturalists, and almost without exception the whole literary and scientific world, held firmly to the belief that _species_ were realities, and had not been derived from other species by any process accessible to us; the different species of crow and of violet they are now, and to have originated by some totally unknown process so far removed from ordinary reproduction that it was usually spoken of as "special creation." There was, then, no question of the origin of families, orders, and classes, because the very first step of all, the "origin of species," was believed to be an insoluble problem. But now this is all changed. The whole scientific and literary world, even the whole educated public, accepts, as a matter of common knowledge, the origin of species from other allied species by the ordinary process of natural birth. The idea of special creation or any altogether exceptional mode of production is absolutely extinct! Yet more: this is held also to apply to many higher groups as well as to the species of a genus, and not even Mr. Darwin's severest critics venture to suggest that the primeval bird, reptile, or fish must have been "specially created." And this vast, this totally unprecedented change in public opinion has been the result of the work of one man, and was brought about in the short space of twenty years! This is the answer to those who continue to maintain that the "origin of species" is not yet discovered; that there are still doubts and difficulties; that there are divergencies of structure so great that we cannot understand how they had their beginning. We may admit all this, just as we may admit that there are enormous difficulties in the way of a complete comprehension of the origin and nature of all the parts of the solar system and of the stellar universe. But we claim for Darwin that he is the Newton of natural history, and that, just so surely as that the discovery and demonstration by Newton of the law of gravitation established order in place of chaos and laid a sure foundation for all future study of the starry heavens, so surely has Darwin, by his discovery of the law of natural selection and his demonstration of the great principle of the preservation of useful variations in the struggle for life, not only thrown a flood of light on the process of development of the whole organic world, but also established a firm foundation for all future study of nature.