The truth seems to be that colour subserves the same purpose in both of the great kingdoms of the organic world. Just as flowers are coloured that insects may recognize where honey is to be found, and thus may be led to promote fertilization, so the sexual colours of animals have been developed to make it easier for the sexes to find each other during the pairing time. Protective colours are useful so far as they conceal the animal from its enemies, but, at the same time, they conceal it from individuals of its own species. Sexual colours are therefore useful as well, because they make the animal more visible. It is quite in accordance with the theory of natural selection that, where such colours occur, the advantage from them should be greater than the disadvantage. We can see the reason for the brilliant colours of humming-birds, as these birds, on account of their great activity “are practically unmolested,”[1494] and for the bright hues of the rose chafers, who are saved from attack by a combination of protecting characters.[1495] But generally there is danger in sexual colours, so that nature has given them with the utmost cautiousness. Usually they occur in males only, because of the females’ greater need of protection.[1496] They are not developed till the age of reproduction, and they appear, in a great many species, only during the pairing season. The greatest advantage is won with the least possible peril. It is a fact of great importance that sexual colours occur exactly in those species whose habits make these colours most visible. Thus the nocturnal moths, taken as a body, are much less gaily decorated than butterflies, all of which are diurnal in their habits, although, according to Mr. Wallace, the general influence of solar light and heat is no adequate cause for the variety, intensity, and complexity of the colours. The females of the ghost moth are yellow with darker markings, whereas the males are white, that they may be more easily seen by the females whilst flying about in the dusk; and it is remarkable that, in the Shetland Islands, the male of this moth, instead of differing widely from the female, frequently resembles her closely in colour,—as Mr. Fraser suggests,[1497] because, at the season of the year when the ghost moth appears in these northern latitudes, the whiteness of the males is not needed to render them visible to the females in the twilight night. Both Mr. Darwin[1498] and Mr. Wallace[1499] think that, in this case, colour may be a means of recognition. Sexual colours occur chiefly in species which, because of their manner of living, are to be seen at a distance; they seldom occur in sedentary or slowly moving terrestrial animals.[1500] The members of the lowly organized order Thysanura are wingless and dull-coloured. The Hemiptera, which usually lurk about plants, and prey upon hapless insects, are not, as a rule, remarkable for conspicuous hues. The Orthoptera are all