"103 *^^ mouse that never drinks 



That must have saved many a hfc in Africa and Australia 

 as v^ell as in America. And if you accept the most mechani- 

 cal theory of evolution, then the more erratically a rodent 

 leaped and the longer tail he had, the better were his 

 chances to survive and to hand on his longer tail to a 

 goodly number of progeny. 



Other kinds of rodents didn't develop in the same di- 

 rection because most of them live where cover is available. 

 But in the desert cover is scarce and the ability to elude 

 capture by unpredictable movement much more impor- 

 tant. On this assumption the tuft at the end of the tail, 

 which is as characteristic of the jerboa as it is of the kanga- 

 roo rat, simply makes the tail more effective as a rudder. 

 One observer reports that a captive Dipo who had lost a 

 considerable part of his tail in some accident, still leaped 

 high but landed any old way instead of on his feet. 



Among themselves Dipos seem rather quarrelsome. 

 Mine, the merriami, are said to be the most peaceable of 

 the tribe, and it is also said that for that reason several 

 individuals of this species can be kept together in captivity. 

 I have not found it so. My pair, even though they are male 

 and female, have to be kept separated most of the time or 

 they will soon take to boxing and from boxing to biting 

 in a manner alarming to anyone anxious to keep them in 

 good health. They seem, on the other hand, to have little 

 fear of man and no tendency, even under provocation, to 

 be aggressive toward him. They will run away if you ap- 

 proach them at liberty, but once caught, they will rest 

 quietly on a human hand and, in fact, often come to it if 

 one reaches down into a cage. It is said that even when 

 roughly handled, merriami, at least, will make no attempt 

 to bite, and mine have showed no resentment even when. 



