In the matter of “Secondary Sexual Characters,” indeed, the Lepidoptera exhibit very little difference between the sexes. As a rule the females are larger, often strikingly so, but in the matter of coloration they show far less disparity. But there are exceptions to every rule. A striking illustration of this is afforded by the genus Ornithoptera. The butterflies of this superb group are of huge size, and the females are larger than their consorts, and commonly are extremely different therefrom both in coloration and habits. In _Ornithoptera paradisea_ this disparity attains its maximum. The female, remarks Mr. David Sharp, “is a large, sombre creature of black, white and grey colours, but the male is brilliant with gold and green, and is made additionally remarkable by a long tail of unusual form on each wing.” But a glance at the two sexes will show that the female, though less gorgeously arrayed, still disports a livery which is of a highly specialized or elaborated character. How are we to account for her differences in shape, size and coloration on the older interpretation of Sexual Selection? The perceptual powers, the mentality, of a Butterfly are surely of a far lower grade than those of a bird, or even a fish. Here, therefore, we cannot attribute the same possibilities of response to form and colour which we can ascribe with tolerable safety to the vertebrates. Yet the Sexual Selection theory as generally understood demands this. So far so good. And now as to the part played by Sexual Selection among the Lepidoptera. Darwin, in formulating this, found its application to the Lepidoptera a very disconcerting problem, being naturally disposed to regard the extraordinary wealth of colour which these insects exhibit as the outcome of a process of female selection, in every way comparable to that which he held to obtain among the birds. He did not postulate a conscious, deliberate, selection; but a final abandonment on the part of the female to the male which, by his beauty and demonstrativeness, pleased her most. He assumed that at this critical time she would always be surrounded by rival suitors, offering varying if slight degrees of difference: and, indeed, in many cases she is thus surrounded. He remarks, in discussing the case of Butterflies: “The males sometimes fight together in rivalry, and many may be seen pursuing or crowding round the same female.” But in the case of the Silk-moths—and here is another illustration of the merciless criticism to which he submitted his own theories—he remarks: “The females appear not to evince the least choice in regard to their partners.” This fact, which is certainly true in the case of both Butterflies and Moths, and these gorgeous hues, disconcerted him, as is shown in the passage: “Unless the female prefer one male to another, the pairing must be left to mere chance, and this does not appear probable.”