In the purest white, the epidermis easily loses its transparency as soon as the colour deepens. The sub-cutaneous veins can then only be recognised by their swelling. It is only with individuals whose skin is very fine and transparent, that the course of the veins is marked by the well-known bluish colour. Whenever this trait is exhibited by any population whatever, it may with certainty be connected with the white type. For this reason I have not hesitated to place among the Allophylians some of the most savage tribes of the north western shores of North America, and the Tchukchees, of whom I have just spoken. The populations with a black skin are far from being as homogeneous as the preceding. All _black men_ are not _Negroes_; there are some, who, from the sum of their more important characters, are closely connected with the white stock. Such, for example, are the Bicharis and other negröid populations, on the borders of the Red Sea, whose skin is much blacker than that of some negroes, but whose hair and characters are perfectly Semitic. Among Negroes properly so called, the tints vary, perhaps, much more than with the White. Without going further than Cairo, individuals may be seen, who, without any traces of the mixture of races, are of a brown colour with a considerable mixture of black. The Yolofs are of a bluish black, resembling the wing of a raven, and Livingstone speaks of some tribes on the Zambesi who are the colour of _café au lait_. But, perhaps, mixture of races has some action in this extreme modification of the colour. Populations with a yellow skin present facts analogous with the preceding, but not so numerous nor so striking. Perhaps this difference is only due to the difficulty of recognising the shades of the fundamental colour. Nevertheless, a more or less pronounced yellow colour equally characterises the great Mongolian stock, and the Houzouana or Bosjesman race, which it is impossible to separate from the Negroes. On the other hand, this same tint is so well marked among the mulattoes that they are often designated by the name of _yellows_, in distinction to the Blacks and the Whites. Of the four groups into which the colour of human races may be divided, the least characteristic is the red. It has been attempted to make it the attribute of the Americans. This is a mistake. On the one hand, in America the Peruvian, Autisian, Araucanian, and other races are more or less deep brown, the Brazilio-Guaranians of a yellowish colour slightly tinted with red, etc. On the other hand, in Formosa a tribe has been found as red as the Algonquins, and more or less copper tints are met with among Corean, African populations, etc.