A number of the old-school naturalists believed that when an animal's colouring assumed the snowy-white coat of its arctic surroundings, this was due to the natural tendency on the part of its hair and fur to assume the colourings and tints of their habitat. This, however, is absolutely false; and no better proof of it can be offered than the case of the arctic musk-ox, who is far more polar in his haunts than even the polar bear, and is therefore exposed to the whitening influence of the wintry regions more than the bear. Yet he never turns white, but is always brown. The only enemy of this northern-dweller is the arctic wolf, and against this enemy he is protected by powerful hoofs, thick hair, and immense horns. He does not need to conceal himself, and therefore does not simulate the colour of his surroundings. [Illustration: _American Museum of Natural History, New York_ THE INDIANS CLAIM THAT THE MOTHER BISON FORCED HER CALF TO ROLL OFTEN IN A PUDDLE OF RED CLAY, SO THAT IT MIGHT BE INDISTINGUISHABLE AGAINST ITS RED CLAY BACKGROUND.] [Illustration: _American Museum of Natural History, New York_ THE ZEBRA IS ONE OF THE CLEVEREST OF CAMOUFLAGERS. THE BLACK-AND-WHITE STRIPES OF HIS BODY GIVE THE EFFECT OF SUNLIGHT PASSING THROUGH BUSHES.] Mimetic resemblances are worked out with great difficulty, except in such cases as the nocturnal animals, which simply become one with their surroundings. Mice, rats, moles, and bats wear overcoats that are very inconspicuous, and when suddenly approached they appear almost invisible. Some of the North American Indians claimed that buffaloes made their calves wallow in the red clay to prevent them from being seen when they were lying down in the red soil. The kinds of protection from these mimetic resemblances are many and varied: the lion, because of his sandy-colouring, is able to conceal himself by merely crouching down upon the desert sands; the striped tiger hides among the tufts of grass and bamboos of the tropics, the stripes of his body so blending with the vertical stems as to prevent even the natives from seeing him in this position. The kudu, one of the handsomest of the antelopes, is a remarkable animal in several ways. His camouflage is so perfect that it gives him magnificent courage. With his spiral horns, white face, and striped coat tinted in pale blue, he is almost invisible when hiding in a thicket. The perfect harmony of his horns with the twisted vines and branches, and the white colourings with blue tints in the reflected sunlight conceal him entirely. The snow-leopard, which inhabits Central Asia, is stony-grey, with large annular spots to match the rocks among which he lives. This colouration conceals him from the sheep, upon which he preys; while the spotted and blotchy pattern of the so-called clouded tiger, and the peculiarly-barred skin of the ocelot, imitate the rugged bark of trees, upon which these animals live.