100 THE HORSE. 



expected from the similarity of their cerebral organ- 

 ization. The patience of the ass, the high spirit of 

 the horse, the obstinacy of the mule, have long been 

 proverbial. It is very remarkable that, out of so 

 many species, two only should have shown any apti- 

 tude for domestication, and that these, too, should 

 have been from time immemorial the universal and 

 most useful companions and servants of man, while 

 all the others remain in their native freedom to this 

 day. It is, however, still a question whether this 

 really arises from a different mental constitution, 

 causing a natural capacity for entering into relations 

 with man, or whether it may not be owing to their 

 having been brought gradually into this condition 

 by long-continued and persevering efforts, when the 

 need of their services was keenly felt. It is quite 

 possible that one reason why nearly all of the at- 

 tempts to add new species to the list of our domestic 

 animals in modern times have ended in failure, is 

 that it does not answer to do so in cases in which 

 existing species supply all the principal purposes to 

 which the new ones might be put. It can hardly be 

 expected that zebras and quaggas fresh from their 

 native mountains and plains can be brought into 

 competition as beasts of burden and draught with 

 horses and asses, whose naturally useful qualities 

 have been augmented by the training of thousands 



