It is an established fact that the colours of flowers serve a definite end. Through them the flowers are recognized by insects in search of honey; and the insects, during their visits, involuntarily carry the pollen of one flower to the stigma of another, and thus effect cross-fertilization, which is proved to be of great importance for the vigour and fertility of the next generation of plants. Now it is extremely interesting to note that brilliant colours are found only in species of flowers to which they are useful as means of attracting insects; they never occur in plants which are fertilized by the wind.[1489] Mr. Wallace observes that plants rarely need to be concealed, because they obtain protection by their spines, or their hardness, or their hairy covering, or their poisonous secretions. Hence there are very few cases of what seems to be true protective colouring among them.[1490] In animals, on the contrary, colour is greatly influenced by their need of protection from, or warning to, their numerous enemies; colours of other kinds must always, to a certain extent, be dangerous for the species. Is it probable, then, that, whilst gay colours occur only in the flowers of those plants to which they are of real use, conspicuous colours should occur in animals to which they are of real danger—merely because the females find them beautiful? Mr. Wallace, whose well-known criticism of Mr. Darwin’s theory of sexual selection[1491] seems, in many points, to be conclusive, suggests that the very frequent superiority of the male bird or insect in brightness or intensity of colour is due to the greater vigour and activity and the higher vitality of the male. This intensity of coloration is therefore most manifest in the male during the breeding season, when the vitality is at a maximum. It would be further developed by the combats of the males for the possession of the females; and the most vigorous and energetic usually leaving the most numerous and most healthy offspring, natural selection would indirectly become a preserver and intensifier of colour.[1492] Mr. Wallace has made it very probable that there is some connection between vigour and colour, but another question is whether this connection, depending on some unknown physiological law, is so necessary that it takes place even when colour is positively disadvantageous to the species. Nothing of the kind is found in the vegetable kingdom. We know, as Mr. Wallace himself remarks, that colours which rarely or never appear in the species in a state of nature, continually occur among cultivated plants and domesticated animals—a fact which shows that the capacity to develop colour is ever present.[1493] Among wild plants such colour variations are never preserved except when they are useful. Is it not most reasonable to suppose that the like is the case with animals?