II. The colouring of the skin is one of the most striking characteristics, and one which is most apparent to the eye. This has given rise to the expressions White, Yellow, and Black, which are most improperly used to designate the three fundamental groups of mankind. We will first prove that these names possess the grave inconvenience of giving rise to ideas which are entirely erroneous. Amongst the _Whites_ there are entire populations, whose skin is as black as that of the darkest Negro. I shall only quote the Bishareen and other tribes inhabiting the African coasts of the Red Sea, the black Moors of Senegal, etc. On the other hand, there are yellow _Negroes_, as the Bosjesmans, who are the colour of light mahogany, or of café au lait, as Livingstone tells us. It is no less true that colour is by far the most variable characteristic in man, and when we place the _coal black Negro_ side by side with the _fair White_ with his pinkish complexion, the contrast is striking. But this contrast is repeated in several races of animals, in the dog, for example, whose skin is generally blackish, but white in the white poodle. It is the same among horses, a fact which was known even to Herodotus, who pronounces white horses with a black skin as superior to all others. The races of our domestic fowls alone present the three extreme colours observed in man. The French fowl has a white skin; in the cochin-china it approaches to yellow; it is black in _black fowls_. Sometimes they present a peculiarity similar to that which I mentioned in reference to the horse: a dark skin accompanying a white plumage as in the _silk hen_ of Japan. These same _black fowls_ possess several interesting peculiarities from our present point of view. In Europe, melanism appears from time to time in our poultry-yards, and would infallibly spread if the fowls attacked by it were not destroyed. It is perhaps from want of this precaution that black fowls have been developed in various parts of the globe, among others in the Philippines, in Java, in the Cape Verd Islands, and upon the plateau of Bogota, all of which have been derived from European stocks. Melanism appears moreover, in groups of fowls which differ most strikingly in other respects, in the silk hen as well as in our ordinary races. We see that _black fowls_ are in no sense a distinct species, and that the appearance of the black colour is merely an accidental character, which may be produced in races very dissimilar in other respects, and afterwards propagated by heredity. Why then admit that it has been otherwise in man?