In all the birds which I have enumerated as having a bright or pleasingly coloured mouth cavity, acquired, as I believe, through the agency of sexual selection, the sexes are alike, both in regard to this special feature, and also in their plumage and general appearance. They are alike also in their habit of opening and shutting the bill, as it were, at one another, and in their other nuptial actions or antics. The first of these two identities involves no difficulty. In many birds of bright plumage the female is as gaudy, or almost as gaudy, as the male, and it is then assumed (by those, at least, who follow Darwin) that each successive variation in the hue and markings of the latter has, by the laws of inheritance, been transmitted in an equal or only slightly less degree to the former. As far, therefore, as the particular kind of beauty which I am here considering is, in itself, concerned, the arguments for or against its acquirement by the male, through the choice of the female, are the same as in regard to that of any other kind, nor do they extend any farther; but in the display of it by the female as well as by the male a fresh element enters into the problem, as it does also in the case of any other nuptial display common to the two sexes. The brilliant mouth cavity can, of course, only be exhibited by the opening of the bill, and in doing this--in the particular way, and with the accompaniments described in each case--both sexes act alike. In other words, if there is really a conscious display in the matter then each sex displays to the other. What conclusion are we to draw from this? Either, as it appears to me, we must assume that both the male and female equally strive to please one another, or that, while the actions of the male mean something, those of the female mean nothing, or nothing in particular, having been transmitted to her, through him, by those same laws of inheritance which have given her, in these and other cases, his own ornamental plumage, and not in accordance with any principle by virtue of which she has been rendered more and more attractive to him. For, except in some special cases where the female is larger and handsomer than the male, the Darwinian theory does not suppose that the hen bird has been modified to please the taste of the cock, whose eagerness, it is assumed, has made this quite unnecessary.