242 THE DOCTRINE OF DESCENT. 



though the feline beasts of prey make themselves con- 

 spicuous; and among the great Tertiary beasts of prey 

 are some which have a range as great as the tiger of the 

 present age. The territory of the extinct sabre-toothed 

 tiger (Machairodus) at that time extended over a great 

 part of America and Europe. Let us also mention that 

 the canine animals appear somewhat later, and that the 

 bears are of still more recent origin. At this period the 

 most abundant material still favours the ungulates. 

 Cloven feet still preponderate. Pigs and musk-animals 

 are the most constant. But the tapir, in shape like the 

 older forms, is now joined by the rhinoceros, the true 

 horses, and the elephants. If the origin of the rhinoceros 

 is somewhat obscure, the extraction of the mastodon, the 

 older form of the elephant, is hitherto quite unknown.'^ 

 And yet though we search in vain through the known 

 mammalian fauna of the Eocene period for the most 

 nearly allied parent forms, there are numerous tokens 

 that even in Europe and Asia, " the most of the Eocene 

 must be regarded as the true root forms of the Miocene 

 genera." (R.) This is shown by the discoveries at 

 Nebraska in North America, where important genera, 

 which, like the Paljeotherium, disappeared from the Old 

 World in the Eocene period, took refuge in company 

 with newer genera. We likewise find there, intermediate 

 forms between the lama and the camel, which in this 

 case alone gives its true significance to the once unmean- 

 ing word, vicarious genera. At Nebraska we moreover 

 find the triple-hoofed horse (Anchitherium), and we hence 

 know the origin of the single-hoofed horse of the Old 

 and New Worlds. 



What has happened in the Old World since that age 



