66 THE TRANSFORMATIONS OF THE ANIMAL WORLD 



have been peopled by means of migration. If 

 we except actual species daily brought over by cur- 

 rents, winds, or in the claws of birds, there remains 

 in each of these islands a special fauna, composed 

 of distinct species, which yet preserves incontestable 

 analogies with that of the neighbouring continents 

 whence these forms have been brought at a more 

 or less early epoch. It is thus that we can explain 

 to ourselves the analogies of the fauna of the Azores 

 with that of Southern Europe, the fauna of the 

 Galapagos Islands with that of America, the fauna 

 of the Sandwich Islands with that of Australia, 

 the fauna of St. Helena with that of tropical Africa, 

 etc. These faunas, degenerated by a long stay in 

 restricted and not very favourable surroundings, are, 

 in general, bound to succumb before the more 

 vigorous animals and plants of the existing fauna 

 imported by man or by natural phenomena. 



It is also by modifying at his will the external 

 or internal conditions of animals that man has 

 succeeded in creating among the domestic races 

 those strange varieties which have been studied in 

 so masterly a manner by Darwin. 



These facts of modification and separation of 

 specific types by isolation or, on the contrary, by 

 migration, will necessarily exercise the greater in- 

 fluence as the observation of them extends 

 over a longer period. It is therefore natural to 

 expect to see these causes of variation play a pre- 

 dominant part, if instead of contenting ourselves 

 with observing the effects at this present time, we 

 go far back into geological times. 



Notwithstanding the importance of the gaps 



