THE EDENTATA, OR ANIMALS POOR IN TEETH. 121 



between them are necessary for the development 

 of these transitions. 



In order to arrive at a right estimation of this 

 and of all the other similar cases which we 

 shall have to allude to later, it will he well to 

 explain our views by a graphic example. Let us 

 suppose that there existed by the side of our 

 present one-toed horse, a three-toed form like 

 that of Hipparion which possessed, in addition 

 to the middle toe (corresponding with the horse's 

 toe), other two toes, smaller, withdrawn from the 

 ground and which had reached a stage of entire 

 disuse. This is by no means a capricious idea. 

 For, in the same way as ' circumstances ' led to 

 the disappearance of the one-toed horse in America, 

 circumstances might have preserved the three-toed 

 form in Asia or Europe, somewhere by the side of 

 the races that were being transformed into a one- 

 toed family. But even granting the existence of a 

 three-toed animal, a non-scientific person would 

 scarcely realise the length of time necessary for the 

 deviation and for the formation of the existing form 

 of horse. Hipparion disappeared from the scenes as 

 early as the Upper Miocene, and yet our horse was 

 not what he now is, immediately before our present 

 geological formation, as is proved by the order for- 



