350 DESERT SANDS 



meadow ! But as soon as they begin to run towards their 

 burrows the white patch by their tails inevitably betrays 

 them ; and this betrayal seems at first sight like a failure 

 of adaptation. Certainly many a rabbit must be spotted and 

 shot, or killed by birds of prey, solely on account of that 

 tell-tale white patch as he makes for his shelter. Never- 

 theless, when we come to look closer, we can see, as Mr. 

 Wallace acutely suggests, that the tell-tale patch has its 

 function also. On the first alarm the parent rabbits take 

 to their heels at once, and run at any untoward sight or 

 sound toward the safety of the burrow. The white patch 

 and the hoisted tail act as a danger-signal to the little 

 bunnies, and direct them which way to escape the threatened 

 misfortune. The young ones take the hint at once and 

 follow their leader. Thus what may be sometimes a dis- 

 advantage to the individual animal becomes in the long 

 run of incalculable benefit to the entire community. 



It is interesting to note, too, how much alike in build 

 and gait are these three thoroughbred desert roamers, the 

 giraffe, the ostrich, and the camel or dromedary. In their 

 long legs, their stalking march, their tall necks, and their 

 ungainly appearance they all betoken their common adapta- 

 tion to the needs and demands of a special environment. 

 Since food is scarce and shelter rare, they have to run about 

 much over large spaces in search of a livelihood or to escape 

 their enemies. Then the burning nature of the sand as 

 well as the need for speed compels them to have long legs 

 which in turn necessitate equally long necks, if they are to 

 reach the ground or the trees overhead for food and drink. 

 Their feet have to be soft and padded to enable them to 

 run over the sand with ease ; and hard horny patches must 

 protect their knees and all other portions of the body 

 liable to touch the sweltering surface when they lie down 

 to rest themselves. Finally, they can all endure thirst for 



