withdraws him from the lurking view of hidden enemies, while the strong beast of prey may conceal himself behind a rock, by the aid of the color of which he can the more easily steal unobserved upon his prey. Only such animals as fear no enemies display so conspicuous a color as black. "What strikes the traveler," says Carl Vogt, "when he comes to the desert from the coast, where the greenness of vegetation predominates, is the absence of all lively colors—of red, green, and blue, in the animals." The fullgrown ostrich is white and black; it is so large and swift that it has nothing to be afraid of but mounted men, and its food is not of such a kind that it needs a protective coloring in order to approach it without observation. The great desert crow (Corvus umbrinus), in which the negro of the Soudan perceives and worships his "uncle," is strong enough to keep off all its enemies, and agile enough to seize its prey when it has once had its eye upon it. The beetles, too, of the desert are black; not the "black beetles" of the Mediterranean region, but other kinds such as often have bright colors or a metallic luster. Carl Vogt asserts that these beetles are defended by an offensive odor or taste, that they have highly arched wing-covers and a depressed corselet or a withdrawn head, and can feign death when they believe they are threatened. When driven into close quarters, they become motionless, assume the likeness of the excrement of gazelles or goats, and thus avoid pursuit.
The coloring of the other animals is often remarkably like that of the pebbly sand. Those creatures—beasts of prey, ruminants, and birds—which are not confined to the soil, but roam or fly around, are tawny, but sometimes striped with different tints. Fowls, larks, stone-chats, running and wading birds, do not form local races with clear or dark feathers, and have not the faculty of changing their color according to the background against which they may for the time find themselves. Another rule prevails with those animals which occur in districts of limited extent. The snakes and lizards of the desert, even when they are of the same species, wear different vestures according to their dwelling-places, while the colors of the same individual, of the lizards at least, are themselves changeable. The proverbial chameleon is not the only animal which is capable of unconsciously adapting its colors to those of its surroundings. Eminently accomplished in this respect are the plaice, while our brook-trout, frogs, and many lizards possess the useful faculty in a less degree. The spring-tailed lizard (Uromastix acanthinurus), which Carl Vogt observed in captivity, presented in darkness and the shade a dullgray slate color with indefinite blackish marblings, but when exposed to direct sunlight became brighter and brighter, and at last appeared of a dirty cream-color, with small, deep-black spots,
