Now, if there be any correlation between the power of resisting damp and the colour an animal bears, it is quite probable that animals of this colour, whether or no it be conspicuous, are likely to survive in preference to those who are more protectively coloured. There is some evidence that in certain cases, at any rate, resistance to climate is correlated with colour peculiarities. For example, some fanciers assert that yellow-legged poultry resist cold and damp better than those whose legs are not yellow. Fowls which have yellow legs have also yellow skins. In this connection the almost universal assumption of orange feet by domestic guinea-fowls is significant. Normally the feet of these birds are black, and their natural African habitat is a dry one. A grey or white colour appears to be correlated with resistance to cold. In birds this may perhaps be explained by the fact that the feathers in some light-coloured varieties are longer than in those of normally-coloured ones. Thus mealy-coloured canaries have longer feathers than brightly-coloured ones. The Arctic Skua, having no enemies to fear, stands in no need of protective colouration. It would therefore seem that the white-breasted form of this bird becomes more numerous as it nears the north pole, not because of the closer assimilation of its plumage to the colour of the snowy surroundings, but because the bird has to resist the greater degree of cold the farther north it finds itself. Similarly, in the region of the south pole the albino form of the Giant Petrel (_Ossifraga gigantea_) becomes common. Both these birds are themselves predatory and not liable to be preyed upon. The curious china-white legs of some desert birds—as, for example, coursers and larks—would seem to indicate a power of resisting the hot rays radiating from the sand on which these creatures dwell. White quills do not wear well either in domestic birds or in wild albinos. This may explain why it is that when a white wild species of bird has any black in its plumage the black is almost invariably on the tips of the wings. White quill-feathers are one of the commonest variations observed in domesticated birds, nevertheless they are as rare as complete whiteness among birds in their natural state. A chestnut or bay colour in mammals appears to be correlated with a high rate of speed, as in the thoroughbred horse. This perhaps explains why so many of the swiftest species of antelope, such as the hartebeests and sassaby (_Damaliscus lunatus_), are chestnut bay in colour. It is further a remarkable fact that in the Black-buck (_Antilope cervicapra_) and the Nilgai (_Boselaphus tragocamelus_) the females, which are faster than the males, are not black or grey like their respective males, but reddish.