In the sixth chapter we have examined at some length Darwin’s interpretation of the secondary sexual characters. His explanation has been found insufficient in many cases to account for the conditions. That these organs do play in some cases a role in the relation of the sexes to each other may be freely admitted. In other words, in some animals the organs in one sex appear in the light of adaptations to certain instincts in the other sex. It would, perhaps, appear to simplify the problem to deny outright that any such relation exists; but I think, in the light of the evidence that we have, this procedure would be like that of the proverbial ostrich, which is supposed to stick its head in the sand in order to escape an anticipated danger. If we assumed this agnostic position, we might attempt to account for the appearance of secondary sexual organs as mutations that had appeared in one sex, and had no immediate connection with the other sex; and, so long as these organs were not directly and seriously injurious, we might assume that the animals in which such structures had appeared might be able to exist. But, on the other hand, I think that an examination of the evidence will show that this way out of the difficulty is not very satisfactory, for the organs in question appear, in some cases at least, to be closely connected with certain definite responses in the other sex. Moreover, as Darwin has so insistently pointed out, the action of the males is of such a sort that it is evidently associated with the presence of the secondary sexual organs which they often display before the other sex. Furthermore, the greater and often exclusive development of these organs during the sexual period distinctly points to them as in some way connected with the relation of the sexes to each other. And finally, there is a small, although not entirely convincing, body of evidence, indicating that the female is influenced by the action of the male; but I do not think that this evidence shows that she selects one individual at the expense of all other rivals. We meet here with a problem that is as profoundly interesting as it is obscure. In fact, if we admit that this relation exists we have a double set of conditions to deal with: first, the development in the males of certain secondary sexual organs; and secondly, the instinct to display these organs. The supposed influence of the display on the female may also have to be taken into account, although, for all we know to the contrary, the same results might follow were there no secondary sexual character at all, as is, in fact, the case in most animals.