By this strong chain of reasoning (to which my brief _>résumé_ of course cannot do justice) Mr. Wallace shows that Darwin needlessly introduced the principle of Sexual Selection into animal courtship; and at the same time furnishes a new confirmation of Darwin’s compliment that he has “an innate genius for solving difficulties.” What makes Mr. Wallace’s argument the more cogent is the fact that Darwin himself, in speaking of the lowest classes of animals, explains their beauty on the same principles as those which Mr. Wallace applies to the higher animals. Thus he says: “We can, in our ignorance of most of the lowest animals, only say that their bright tints result either from the chemical nature or the minute structure of their tissues, independently of any benefit thus derived.” “It is almost certain that these animals have too imperfect senses, and much too low mental powers, to appreciate each other’s beauty or other attractions, or to feel rivalry.” “Nor is it at all obvious how the offspring from the more beautiful pairs of hermaphrodites would have any advantage over the offspring of the less beautiful, so as to increase in number, _unless indeed vigour and beauty generally coincided_.” And once more, “The sedentary annelids become duller-coloured, according to M. Quatrefages, after the period of reproduction; and this I presume may be attributed to their less vigorous condition at that time.” So far we have only considered the origin of animal colours in general. Mr. Wallace, however, has not only made clear the general connection between beautiful and vivid colours and health, but, by utilising his own researches and those of Mr. Bates and other naturalists, he has been able to show to what a great extent we can explain even the _particular_ colours of the various classes of animals. He distinguishes four classes of animal colours—Protective, Warning, Sexual, and Typical. (1) _Protective Colours._—These “are exceedingly prevalent in nature, comprising those of all the white arctic animals, the sandy-coloured desert forms, and the green birds and insects of tropical forests. It also comprises thousands of cases of special resemblance—of birds to the surroundings of their nests, and especially of insects to the bark, leaves, flowers, or soil on or amid which they dwell. Mammalia, fishes, and reptiles, as well as mollusca, present similar phenomena; and the more the habits of animals are investigated, the more numerous are found to be the cases in which their colours tend to conceal them, either from their enemies or from the creatures they prey upon.”