SEXUAL SELECTION.--Professor Romanes, after referring to those facts, which are considered in detail by his great predecessor, states the theory of sexual selection as follows: "There can be no question that the courtship of birds is a highly elaborate business, in which the males do their best to surpass one another in charming the females. Obviously the inference is that the males do not take all this trouble for nothing; but that the females give their consent to pair with the males whose personal appearance, or whose voice, proves to be the most attractive. But, if so, the young of the male bird who is thus _selected_ will inherit his superior beauty; and thus, in successive generations, a continuous advance will be made in the beauty of plumage or of song, as the case may be,--both the origin and development of beauty in the animal world being thus supposed due to the esthetic taste of the animals themselves." It is not necessary to refer particularly to the evidence in support of the theory of sexual selection. There can be no doubt that it is a most important factor in the perpetuation and increase of certain characters, those which come within the category of "beautiful," the very existence of which proves them to be beneficial to the stock to which the animals exhibiting them belong. The fundamental fact is that they have "the effect of charming the females into a performance of the sexual act;" an opinion which is supported by the more general fact that "both among quadrupeds and birds, individuals of the one sex are capable of feeling a strong antipathy against, or a strong preference for, certain individuals of the opposite sex." These statements are applicable also to man, with whom the principle of sexual selection must have been influential to at least the same degree as among the lower animals. It may be expected, indeed, to be more influential, as the esthetic taste with which it is associated becomes more highly developed with man than with any member of the animal kingdom. Even here it is not a question of mere coloration. The theory of sexual selection as framed by Darwin is concerned, as Romanes points out, not so much with color itself as with the particular disposition of color in the form of ornamental patterns. These have a kind of _structural_ value, and certain birds, moreover, possess actual structural peculiarities, such as ornamental appendages to the beak, the only use of which would appear to be to charm the female during courtship. We may suppose, therefore, that sexual selection has affected not merely what may be termed the superficial characters of man, but to some extent, at least, those which have a structural value.