terrestrial in their habits, generally feeding upon plants, and, although some exotic locusts are beautifully ornamented, their bright tints, according to Mr. Darwin, do not seem to fall under the head of sexual coloration. On the other hand, the dragon-flies, which live in the open air, possess splendid green, blue, yellow, and vermilion metallic tints, and the sexes often differ in their coloration. Every one has admired the extreme beauty of many butterflies, especially of the males. Amongst the Fishes, living in a medium through which bright colours may be observed at a distance, we often find, besides protective colours, conspicuous hues which are especially intense and visible during the pairing time. Among the Reptiles, the little lizards of the genus Draco especially deserve attention; they glide through the air on their rib-supported parachutes, and the beauty of their colours baffles description. Mammals, on the other hand, do not generally present the splendid tints so common among male birds; and the brighter colours of certain arboreal mammals serve chiefly as means of concealment. These phenomena seem to show that sexual colours have been evolved for the purpose of _being seen_. They can scarcely be due merely to the fact that coloration is connected with the degree of vitality, since the Mammals, for instance, are certainly not less vigorous than any of the other Vertebrate orders. It may perhaps be suggested that, as flying animals more easily escape their enemies than terrestrial, they may with less danger be decorated with conspicuous hues. But here we have to observe the most important fact, that animals which do not possess sexual colours generally have some other means of making themselves discoverable. Flowers which need the help of insects for fertilization attract them, in some cases, not by bright colours, but by peculiar odours. And as we do not find conspicuous colours in plants fertilized by the wind, so flowers have no perfume except where it is of real use. The most brilliant flowers, as a rule, are those which possess least odour, whilst many of them have no scent at all. White or very pale flowers are generally the most odoriferous. M. Mongredien gives a list of about 160 species of hardy trees and shrubs with showy flowers, and another list of sixty species with fragrant flowers; but only twenty of the latter are included among the showy species, and these are almost all white-flowered.[1501] Most of the white flowers are scented only at night, or their perfumes are most powerfully emitted at that time; the reason being that white flowers are fertilized chiefly by night-flying insects. We arrive thus at two conclusions: first, that powerful odours and conspicuous colours as guides to insect fertilizers are, as a rule, complementary to each other; secondly, that they occur alternately in the way most useful to the species.