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Rh and a dull dark crimson." As further remarked:—"In the dark bosom of the earth a green leaf would be quite useless, and as a matter of fact there is not a single plant whose green tissue is situated in the depths of the soil."

Even the obscure problem of the colouration of mankind may have originally—and before migration became such an important factor in modification—been due to a more or less assimilative colouration. Thus, in Central Africa, Schweinfurth has remarked:—"The complexion of the Bongo in colour is not dissimilar to the red-brown soil on which they reside; the Dinka, on the other hand, are black as their own native alluvium." And again:—"Any traveller who has followed the course of the main sources of the White Nile into the heathen Negro countries, and who has hitherto made acquaintance only with Shillooks, Nueir, and Dinka, will, on coming amongst the Bongo, at once recognise the commencement of a new series of races extending far onwards to the south. As trees and plants are the children of the soil from which they spring, so here does the human species appear to adapt itself in external aspect to the red ferruginous rock which prevails around. The jet-black Shillooks, Nueir, and Dinka natives of the dark alluvial flats stand out in marked distinction to the dwellers upon the iron-red rocks, who, notwithstanding their diversity in dialect, in habit, or in mode of life, present the characteristics of a connected whole." Dr. Schweinfurth also observes that "the circumstance is suggestive of Darwin's theory of 'protective resemblance' among animals." But as such a view of protective resemblance has not hitherto been applied to the colour of mankind, and as it would be extremely difficult to defend such a proposition, it might at least be suggested as probable that we have here another survival of an original and somewhat universal assimilative colouration. Similar observations have been made by many travellers. Livingstone describes the colour of the soil composing the plain of the Kalahari Desert as in general "light-coloured soft sand, nearly pure silica," and that the Bushmen inhabiting these plains are