408 
DARWINISM 
CHAP. 
and even sometimes to existing families. Thus, in the Eocene 
we have remains of the opossum family; bats apparently 
belonging to living genera; rodents allied to the South 
American cavies and to dormice and squirrels; hoofed animals 
belonging to the odd-toed and even-toed groups; and an¬ 
cestral forms of cats, civets, dogs, with a number of more 
generalised forms of carnivora. Besides these there are 
O 
whales, lemurs, and many strange ancestral forms of pro- 
boscidea. 1 
The great diversity of forms and structures at so remote 
an epoch would require for their development an amount of 
time, which, judging by the changes that have occurred in 
other groups, would carry us back far into the Mesozoic 
period. In order to understand why we have no record of 
these changes in any part of the world, we must fall back 
upon some such supposition as we made in the case of the 
dicotyledonous plants. Perhaps, indeed, the two cases are 
really connected, and the upland regions of the primeval world, 
which saw the development of our higher vegetation, may 
have also afforded the theatre for the gradual development 
of the varied mammalian types which surprise us by their 
sudden appearance in Tertiary times. 
Notwithstanding these irregularities and gaps in the record, 
the accompanying table, summarising our actual knowledge of 
the geological distribution of the five classes of vertebrata, 
1 For fuller details, see the author’s Geographical Distribution of Animals, 
and Heilpriu’s Geographical and Geological Distribution of Animals. 
