double process of sexual selection seems the only available explanation. Only when the female is plain and unadorned, and the male gaudy, does it seem primâ facie evident that the latter, alone, has been selected for his beauty. But it is just this last class of cases that has attracted the largest amount of notice, for, as might have been expected, it is precisely here that we find the males—often the most ornate of birds—indulging in the most extraordinary antics, which, of course, arrest attention. In observing these birds, however, the sexes are at once, and without difficulty, distinguished, and as the females do not share in such antics, we assume, when we see similar ones on the part of birds, the sexes of which are indistinguishable, that here, also, the same law holds good, though there is by no means the same presumption that this should be the case. Confronted with a certain effect, which implies a corresponding causal process, in one case, we assume this same process in another, though we cannot there see the effect. We see, for instance, one stock-dove manifestly court another, and at once assume that the courting bird is the male. The courtship, as is often the case, ends in a pretty severe battle, where blows with the wing are given and received on either side. We may be surprised to see the female so belligerent, but we do not yet doubt the fact of her being the female. The courting bird is, at last, repelled, and a fight of much the same description takes place between him and another stock-dove. This one might just as well be a female as the first, but in
