APPARITION OF SPECIES 115 



The application of these questions to the animals 

 referred to will serve farther to show their significance 

 as to limitations of derivation. Pictet catalogues 

 eleven species of Eocene PalceotJieria. Without 

 inquiry as to the origin of these, let us confine our 

 selves to their progress. Under the hypothesis of 

 derivation, each of these had capacities for improve 

 ment, probably all leading to that line of change 

 ending in the production of the horse. If so, then 

 each of our Palezotheria, passing through intermediate 

 changes, may be the predecessor of some of the equine 

 animals of the Post-Pliocene and Modern periods. 

 But if, as seems probable, the time intervening be 

 tween the Eocene and the Modern was unfavourable 

 to the multiplication of such species, then several may 

 have perished utterly in the process, and all might 

 have perished. Supposing, on the contrary, the time 

 to have been favourable to the increase of such 

 creatures, we might have had hundreds of species of 

 equine animals instead of the small number extant at 

 present. Again, what possibilities of change remain 

 in the horse ? Can he be supposed capable of going 

 on still farther in the direction of his progress from 

 Palceotheriwn or EoJiippus, or has he attained a point 

 at which further change is impossible ? Will he then, 

 in process of time, wheel round in his orbit, and re 

 turn to the point from which he set out ? Or will he 

 continue unchanged until he becomes extinct ? Or 

 can he at a certain point diverge into a new series of 



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