Moreover, the red tint appears as the sole effect of the crossing between races, neither of which possess it. Fitzroy informs us that in New Zealand it frequently characterises the half-breeds of English and Maories. This fact also explains why it should be met with among many of the populations mentioned above. With man it is one of those facts which show how intercrossing can give rise to the appearance of new characters. Finally we see that the colour of the skin, although furnishing excellent secondary characters, cannot be taken as a starting point in the classification of human races For man, as well as for plants, we ought to recall the aphorism of Linnæus: “_nimium ne crede colori_.” The same may be said still more emphatically of the colour of the eyes. Doubtless, the black colour is generally found among coloured races, and sky-blue scarcely exists except among fair populations. The former tint appears even to be constant among the yellows and certain allophylian Whites. But, even among the Negroes, we often meet with brown eyes, and sometimes with grey eyes. Just as with the colour of the skin, the colour of the eyes is a resultant due to the combination of the tints reflected by the different layers of the iris, intensified by the colour of the blood and seen through the transparent cornea. Hence arises the difficulty experienced by painters in rendering the general effect. VII. _The skin and its principal annexes._ The skin, which covers the entire body, is a real covering composed of organs which are anatomically and physiologically distinct. The principal one is the _cutaneous organ_ or _skin properly so called_, to which are annexed the _organs productive of villosities_, the _sudoriparous glands_, the _cutaneous glands_, and some others which do not concern us. In extreme cases, the surface of the skin is sometimes dry and rough, sometimes supple and like satin. The first variety is generally met with among Arctic races, the second among inhabitants of hot countries, as the Negroes and Polynesians. The two facts are easily explained by the sole action of the temperature. Cold contracts the tissues, drives the blood towards the interior, or checks its circulation towards the surface of the body. It must consequently diminish the functional activity of the skin properly so called, and partially diminish _perspiration_. Heat, on the contrary, causes a flow of blood to the surface of the body, and renders the functions of the skin, and especially the perspiration, more active. The latter, by the production of a constant evaporation on the surface of the body, maintains the suppleness of the epidermic layer, and the general freshness which causes Negresses to be sought after in harems. From this action of heat, and the increased activity of the cutaneous organs which is its consequence, other results follow which explain some of the facts noticed by travellers and anthropologists.