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 ca^des 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 

 whales, lemurs, and many strange ancestral forms of pro- 

 boscidea.^ 



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 Avorld, we must fall back 

 upon some such supposition as Ave 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. 



Geological Distribution of Mammalia. 



Fishes . 

 Ampliibia 

 Reptiles 

 Birds . 

 Mammalia 



^ For fuller details, see the author's Geographical Distribution of Animals, 

 and Heilpriu's Geographical and Geological Distribution of A nimals. 



