THE DONKEY'S ANCESTORS. 193 



another even more specialised type, plio- 

 hippus, in which the lateral toes have become 

 reduced to mere splint-bones, as in our exist- 

 ing species. Here, we have all often been 

 told, we have probably preserved for us 

 several distinct steps in the evolution of our 

 horses and donkeys. One solid hoof on each 

 foot gives unarmed herbivorous animals of 

 their peculiar habits the best possible chance 

 in the struggle for life ; and so towards the 

 development of this one hoof they have been 

 slowly verging ever since eocene times, by 

 the gradual enlargement of the central toe, 

 and the gradual suppression of all the rest. 

 They have no horns like the bison and the 

 buffalo ; but by their swiftness and sureness 

 of foot wild horses are able easily to hold 

 their own against all carnivorous enemies on 

 the grassy pampas of South America, as 

 zebras do on the great South African plateau, 

 and onagers on the broad steppes of Central 

 Asia. 



Most people, however, do not know that 



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