ANIMAL LIFE IN THE GREAT DESERT 249 



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 full- 

 grown 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 ap- 

 proach it without observation. The great desert crow (Corvus 

 umbrinus), in which the negro of the Soudan perceives and wor- 

 ships his " uncle," is strong enough to keep off all its ene- 

 mies, 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 corselet or a withdrawn head, and can feign death when they be- 

 lieve they are threatened. "When driven into close quarters, they 

 become motionless, assume the likeness of the excrement of ga- 

 zelles 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, rumi- 

 nants, 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 pre- 

 vails with those animals which occur in districts of limited ex- 

 tent. 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 cha- 

 meleon is not the only animal which is capable of unconsciously 

 adapting its colors to those of its surroundings. Eminently accom- 

 plished 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 dull- 

 gray 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, 



