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374, necessarily common to two families whose modes of life are so exactly analogous. No better practical specimen of the new biological methods than that afforded by this essay could possibly come into the hands of readers with good common-sense and little special scientific knowledge.

The fifth and sixth essays, on "The Colors of Animals and Sexual Selection," and on "The Colors of Plants and the Origin of the Color-Sense," lead us at once into the region of controversy. They appeared originally in Macmillan's Magazine, but they have since been enriched by numerous additions and alterations, in accordance with suggestions from Mr. Darwin or other correspondents. In the first of these two papers, Mr. Wallace brings a powerful battery to bear against the accepted doctrine of sexual selection, and it must be confessed not without effect in shaking, if not in demolishing, that stronghold of Darwinism. He contends that color is a natural product of organic forms, which may be checked or intensified by natural selection, but whose occurrence is quite normal, and so stands in need of no separate explanation. All colors in animals may be classified under four heads—protective colors, warning colors, sexual colors, and typical colors. The two former do not now require further definition; but sexual differences of hue he attributes not to conscious selection of mates, the occurrence of which is emphatically doubted, but to. a special necessity for concealment in one or other sex; as, for example, in the incubating females of birds, or in the males among those species in which that sex undertakes the duty of hatching. This explanation would refer the variety in coloring to natural selection alone, acting unequally upon the several sexes, and so causing a partial suppression of bright tints. The vast majority of animal markings Mr. Wallace attributes to typical coloring; that is to say, a conventional or meaningless distribution of pigment, serving mainly for purposes of recognition between the members of the same species. Though it would be rash too readily to accept or reject these careful and well-reasoned conclusions, it seems probable that an intermediate belief will ultimately prevail. Certainly, Mr. Wallace has shown beyond a doubt that natural selection will adequately and simply account for many curious phenomena which Mr. Darwin believed to be due to conscious preference. The partial elimination of this markedly Lamarckian element in the theory of descent cannot but be regarded as a distinct gain, though few readers will be inclined entirely to agree with the author in his total rejection of sexual selection.

The sixth essay applies the same general principles to the colors of plants, and contains some interesting speculations on the beauty of Alpine flowers, and on the difference between succulent fruits and nuts. It also touches briefly on the question of the development in insects and vertebrates of a faculty for the perception of colors, with remarks upon the theories lately advanced by Geiger, Magnus, and Gladstone. This and the succeeding paper are chiefly noticeable for their exposition of the author's opinions upon certain ultimate teleological questions. In his book upon the Malay Archipelago, Mr. Wallace advocated the belief that all the beauty of the external world was due to natural causes, without any divine afterthought as to its effects upon the human mind. But, since that time, the implications contained in the doctrine of evolution seem to have clashed with earlier prejudices, and driven this otherwise acute and vigorous thinker into a coquetry with so-called spiritualism, which has vitiated much of his later work. In the present volume he suggests that the colors of the organic world, though developed by ordinary laws, may have been specially directed by some superior agency with reference to the final enjoyment of their beauty by man. In short, he inclines to the purely gratuitous supposition that butterflies, birds, and flowers, acquired brilliant tints in the Secondary and Tertiary periods, partly in order that men might look upon them in the Quaternary. And the essay which we are now considering concludes with the ominous sentence, "The emotions excited by color and by music, alike, seem to rise above the level or a world developed on purely utilitarian principles." It is greatly to be regretted that the joint discoverer of the theory of natural selection should allow himself to make use of such painfully dyslogistic and unscientific language.

The seventh essay, the presidential address, bears the title of "By-paths in the