certainly would be of greater danger. In his work on ‘Darwinism,’ Mr. Wallace expresses the opinion that the various sounds and odours which are peculiar to the male serve as a call to the female, or as an indication of his presence; and, as he says, “the production, intensification, and differentiation of these sounds and odours are clearly within the power of natural selection.”[1509] Mr. Wallace has also shown the immense importance of colour as a means of recognition. The theory here set forth thus, in fact, very nearly approaches his views. The only difference is that the sexual colours have been classified under the head of “colour for recognition,” though the positive cause by which they have been produced may be a surplus of vital energy. We have still to consider certain secondary sexual characters which, according to Mr. Darwin, must be regarded as ornaments. With these he classes the great horns which rise from the head, thorax, and clypeus of many male beetles; the appendages with which some male fishes and reptiles are provided; the combs, plumes, crests, and protuberances of many male birds; and various crests, tufts, and mantles of hair which are found in certain mammals. But some of these characters may be of use to the males in their fights for females, or serve as means of recognition. Mr. Wallace suggests that crests and other erectile feathers may have been useful in making the bird more formidable in appearance, and in thus frightening away enemies; while long tail or wing feathers might serve to distract the aim of a bird of prey.[1510] Moreover, characters of which we cannot yet perceive the use may in the future be brought under the law of utility, as has been the case in so many other instances. According to Mr. Wallace, the ornamental appendages of birds and other animals are due to a surplus of vital energy, leading to abnormal growths in those parts of the integument where muscular and nervous action are greatest.[1511] And where these “ornaments” are of no positive disadvantage to the species, certainly no other explanation is needed.