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 truc 
horses, and the elephants. Ifthe 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, “ 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 Palaotherium, 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 un- 
meaning 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 
