Many naturalists believe that climate has a direct and determining effect on colour, and contend or imply that it is hereditary. Mr. J. A. Allen correlates a decrease in the intensity of colour with a decrease in the humidity of the climate. Mr. Charles Dixon, in his "Evolution without Natural Selection," says, "The marsh-tit (_Parus palustris_) and its various forms supply us with similar facts [illustrative of the effects of climate on the colours of birds]. In warm, pluvial regions we find the brown intensified; in dry, sandy districts it is lighter; whilst in Arctic regions it is of variable degrees of paleness, until, in the rigorous climate of Kamschatka, it is almost white." Mr. Dixon does not think that these changes are the result of natural selection. "Depend upon it," he says, with some assurance,[BZ] in considering a different case, "it is the white of the ptarmigan (modified by climatic influence) that has sent the bird to the snowy wastes and bare mountain-tops, and rigorously keeps it there; not the bird that has assumed, by a long process of natural selection, a white dress to conceal itself in such localities." Professor Eimer[CA] contends that in the Nile valley the perfectly gradual transition in the colour of the inhabitants from brownish-yellow to black in passing from the Delta to the Soudan is particularly conclusive for the direct influence of climate, for the reason that various races of originally various colours dwell there. Mr. A. R. Wallace says[CB] of the island of Celebes "that it gives to a large number of species and varieties (of Papilionidæ) which inhabit it, (1) an increase of size, and (2) a peculiar modification in the form of the wings, which stamp upon the most dissimilar insects a mark distinctive of their common birthplace." But this similarity may largely, or at least in part, be due to mimicry. Most interesting and valuable are the results of Mr. E. B. Poulton's experiments on caterpillars and chrysalids.[CC] They show that there is a definite colour-relation between the caterpillar (e.g. the eyed hawk-moth, _Smerinthus ocellatus_) and its food-plant, adjustable within the limits of a single life; that the predominant colour of the food-plant is itself the stimulus which calls up a corresponding larval colour; that there is also a direct colour-relation between the chrysalids of the small tortoiseshell butterfly (_Vanessa urticæ_) and the surrounding objects, the pupæ being dark grey, light grey, or golden, according to the nature and colour of the surroundings; and that the larvæ of the emperor moth (_Saturnia carpini_) spin dark cocoons in dark surroundings, but white ones in lighter surroundings. These are but samples of the interesting results Mr. Poulton has obtained.