Again, melanism is more highly developed in fowls than in man. It has long been held as a recognised fact that the skull of the Negro is more darkly coloured than that of the White. The fact is true. But M. Gubler has proved that the skull of a very dark-complexioned White was coloured exactly in the same manner as that of the Negro, and that this peculiarity was sometimes individual, and sometimes hereditary in certain families. In fowls also, melanism penetrates to the interior; but it is not only the meninges which present peculiarities similar to those presented by the _black man_. With them all the mucous, fibrous, and aponeurotic membranes, even to the muscular sheaths, possess the same colouring. The flesh also assumes a repugnant appearance, and it is for this reason that the propagation of black fowls is prevented as much as possible. The difference in colouring is easily explained. We now know beyond a doubt that the skin of the Negro is exactly the same in composition as that of the White. We find the same layers in both; the _dermis_, the _mucous layer_ and the _epidermis_ present exactly the same structure. The layers are merely thicker in the Negro. In these two great races, the mucous layer, situated between the other two, is the seat of colour. It is formed of cells which are of a pale yellow colour in the _fair White_, of a more or less brownish yellow in the _dark White_, and of a blackish brown in the Negro. External causes have, moreover, an influence upon the organ and modify the coloured secretion. Simon has shown that freckles are nothing more than spots upon the skin of the _White_ presenting the characteristics of the skin of the Negro, and we know that an unusual exposure to the sun in the men and women of our race, and pregnancy in the latter, is sufficient to determine the formation of these spots. Why, then, should it be thought strange that a number of circumstances, a constant heat, a bright light, &c., should influence the whole body and perpetuate those modifications which in us are only circumscribed and transitory. In treating of the formation of the human races we shall have to bring forward facts which will clearly prove that this is not merely hypothesis. Finally, the colour of the skin depends upon a simple secretion which is subject to modification under a number of circumstances, as is the case with many others. There is, therefore nothing strange in the fact that some human groups, differing widely in other respects, should resemble each other in the matter of colour. This is the reason why the Hindoo (_Aryan_), the Bisharee and the Moor (_Semitic_), although belonging to the _White race_, assume the same, and even a darker hue than the _true Negro_. It also explains the fact that the colour of the Negro approximates in certain cases, to that of peoples belonging to the white stock who are more or less of a brown colour, or assumes a hue which exactly recalls that of the yellow races.