THE DISTRIBUTION OF ANIMALS 457 



rents arc largely responsible for all but the aerial fauna. Many 

 small animals may be carried for considerable distances on 

 floating objects and eventually be cast up on some such island. 

 The paucity of mammals on these islands is significant, I 

 entire mammalian fauna being frequently restricted to a sin 

 species of bat and a mouse. Within recent years man has vol- 

 untarily and involuntarily, through commerce and colonization, 

 greatly altered the natural distribution of animals. The rein- 

 deer and the bear were within historic time inhabitants of Great 

 Britain. Horses and swine have been brought to North Amer- 

 ica from the Old World, and through the zeal of the hunter many 

 valuable wild animals are rapidly approaching extinction. 



