COMMUNITIES IN DRY, OPEN LANDS 467 



cephalus, and the lacertid Scapteira. The feathering of the tarsi and 

 toes and the web in the sand grouse (Syrrhaptes) , and the well-devel- 

 oped lateral hairs of the soles of the feet in the jumping mouse {Dipus) , 

 exhibit similarly increased surfaces for running over sand. Even in 

 tenebrionid beetles of the north African and Asiatic deserts, the flat 

 tarsus is widened by long chitinous hairs. 78 Snakes may be driven to 

 the novel "sidewinding" type of locomotion. 79 



Desert animals in all parts of the world tend toward a resemblance 

 in color and pattern to the pale colors of their environment, though 

 with exceptions, equally world-wide, in which a striking black colora- 

 tion is developed. Because of the lack of cover, color adaptation to 

 the substratum may have some biotic importance for desert animals. 

 The pale yellowish or reddish color of the desert floor recurs in many. 

 Numerous Orthoptera, 80 most of the snakes and lizards, very many 

 birds, and mammals of numerous genera have this yellowish or reddish 

 coloration. The crested larks {Galerida) , which have dark brown colors 

 on the dark cultivated fields of northern Algeria, are sand colored in 

 sandy wastes to the south, and grayish in the rocky deserts. 81 A resting 

 grasshopper, a lark, or a desert courser, sitting quietly, is unusually 

 hard to distinguish. A large number of animals with nocturnal habits 

 have the desert type of coloration, especially among mammals and 

 reptiles, as well as those tenebrionid beetles that are not black. It is 

 evident that faded colors arise as the direct result of climatic influences 

 and thus occur in both diurnal and nocturnal animals, though only in 

 the former case do they have full selective value from coincident biotic 

 adaptation. Besides these, numerous black animals occur in the palae- 

 arctic desert belt, which contrasts strikingly with the substratum. 

 These seem to be protected in some peculiar manner 82, 83 from possible 

 injury due to the penetration of the shorter wave lengths rather than 

 by direct biotic advantage. Numerous black tenebrionid beetles possess 

 a very hard exoskeleton and often have the elytra fused with the body 

 wall and reduced antennae or legs. 



The concentration of life at certain localities under the extreme 

 conditions in the desert is striking. Wherever a depression carries down 

 to a greater proximity to the ground-water level, a more abundant 

 plant life springs forth, and there animal life also congregates. Every 

 bush, every briar, is an oasis in itself, full of specialized forms of ani- 

 mal life. In many places in the Algerian desert, every large stone affords 

 protection for a host of insects, myriapods, arachnids, isopods, often 

 also for lizards and snakes and even for small mammals and birds. 

 With conditions here close to the limits of existence, a few advantages 

 are decisive in the choice of a dwelling place. 



