Introduction 



entirely to the animals of this country, but 

 deals to some extent with those of other parts 

 of the world as well. We know how the his- 

 tory of the United States has more or less to do 

 with that of England, Holland, and France; 

 and just so the story of the past can not be told 

 without referring to that of other regions than 

 ours. No animal nor any group of animals 

 stands by itself; each and all have somewhat 

 in common with others. 



Nowadays the animals of different parts of 

 the earth are so unlike, that its surface may be 

 mapped into regions each distinguished by par- 

 ticular kinds of animals : Africa has its ante- 

 lopes, North America its deer and bison, South 

 America its monkeys with prehensile tails. 

 But it was not always so : far back in the past, 

 when conditions appear to have been much the 

 same throughout the world, many animals were 

 similar. More than this : the so-called solid 

 earth is not so stable as it seems, and there 

 have been times in the past when lands now 

 separated by the sea have been so joined that 

 there was an interchange of animals. So it fre- 



