It is in the family of dragonflies (order Neuroptera) that we first meet with numerous cases of distinctive sexual coloration. In some of the Agrionidae the males have the bodies rich blue and the wings black, while the females have the bodies green and the wings transparent. In the North American genus Hetaerina the males alone have a carmine spot at the base of each wing; but in some other genera the sexes hardly differ at all. The great order of Lepidoptera, including the butterflies and moths, affords us the most numerous and striking examples of diversity of sexual colouring. Among the moths the difference is usually but slight, being manifested in a greater intensity of the colour of the smaller winged male; but in a few cases there is a decided difference, as in the ghost-moth (Hepialus humuli), in which the male is pure white, while the female is yellow with darker markings. This may be a recognition colour, enabling the female more readily to discover her mate; and this view receives some support from the fact that in the Shetland Islands the male is almost as yellow as the female, since it has been suggested that at midsummer, when this moth appears, there is in that high latitude sufficient twilight all night to render any special coloration unnecessary.[120] Butterflies present us with a wonderful amount of sexual difference of colour, in many cases so remarkable that the two sexes of the same species remained for many years under different names and were thought to be quite distinct species. We find, however, every gradation from perfect identity to complete diversity, and in some cases we are able to see a reason for this difference. Beginning with the most extraordinary cases of diversity--as in Diadema misippus, where the male is black, ornamented with a large white spot on each wing margined with rich changeable blue, while the female is orange-brown with black spots and stripes--we find the explanation in the fact that the female mimics an uneatable Danais, and thus gains protection while laying its eggs on low plants in company with that insect. In the allied species, Diadema bolina, the females are also very different from the males, but are of dusky brown tints, evidently protective and very variable, some specimens having a general resemblance to the uneatable Euplaeas; so that we see here some of the earlier stages of both forms of protection. The remarkable differences in some South American Pieridae are similarly explained. The males of Pieris pyrrha, P. lorena, and several others, are white with a few black bands and marginal spots like so many of their allies, while the females are gaily coloured with yellow and brown, and exactly resemble some species of the uneatable Heliconidae of the same district. Similarly, in the Malay Archipelago, the female of Diadema anomala is glossy metallic blue, while the male is brown; the reason for this reversal of the usual rule being, that the female