122 EVOLUTION OF LIE. 
Paleotherium (Fig. 151) and Anoplotherium (Fig. 152), 
living during the early part of this age, are extremely 
interesting, being regarded as the progenitors of the odd- 
and equal-toed Mammalia. The conclusions of Cuvier as 
to the nature of the Paleotherium, based only on fragment- 
ary remains, were perfectly confirmed by the discovery of 
an almost entire skeleton. Since that time many allied 
forms have been described, principally by Prof. Owen; some 
of which, uniting the Rhinoceros, Tapir, and Horse, make 
the group of odd-toed, while others, associated with the 
Hog, Hippopotamus, etc., form that of the equal-toed. 
Prof. Leidy has described many kinds of horses found fossil 
in the western part of the United States, etc. (these dis- 
coveries are confirmed by those of Owen and Rutimeyer), 
which represent the transient stages through which the 
modern horse passes, so that the descent of the Horse 
from some paleotheroid form is completely made out. As 
regards the Flora of the Tertiary Age, as compared with 
that of the Cretaceous and Modern periods, according to 
Brown, the Apetale (Fig. 133) were greatly in excess 
during the Cretaceous period, the Diapetalz were repre- 
sented by a few species, while the Gamopetale (Fig. 131) 
had not appeared. In the Tertiary Age the Diapetale 
exceed the Apetalze, the Gamopetalae being comparatively 
well represented; while at the present day the great 
number of Gamopetalous genera seems to indicate that 
this order of plants is increasing most rapidly. These 
facts are very significant when compared with what is said 
of the structure of these plants. The age following the 
Tertiary, that in which we live, is known as the Age of 
Man, whose early condition, etc. will be treated of in the 
chapter on Anthropology. Repeating that great caution 
must be exercised in accepting the generalization of Geolo- 
gists as to the relative and absolute age of rocks, a 
resume of their fossil remains seems to exhibit the following 
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