GEOGRAPHICAL DISTRIBUTION 193 



creation of mammals; many volcanic islands are suffi- 

 ciently ancient, as shown by the stupendous degradation 

 which they have suffered, and by their tertiary strata; 

 there has also been tim.e for the production of endemic 

 species belonging to other classes; and on continents it 

 is known that new species of mammals appear and dis- 

 appear at a quicker rate than other and lower animals. 

 Although terrestrial mammals do not occur on oceanic 

 islands, aerial mammals do occur on almost every island. 

 New Zealand possesses two bats found nowhere else in 

 the world: Norfolk Island, the Yiti Archipelago, the 

 Bonin Islands, the Caroline and Marianne Archipelagoes, 

 and Mauritius, all possess their peculiar bats. Why, it 

 may be asked, has the supposed creative force produced 

 bats and no other mammals on remote islands ? On my 

 view this question can easily be answered; for no ter- 

 restrial mammal can be transported across a wide space 

 of sea, but bats can fly across. Bats have been seen 

 wandering by day far over the Atlantic Ocean; and two 

 North American species either regularly or occasionally 

 visit Bermuda, at the distance of 600 miles from the 

 mainland. I hear from Mr. Tomes, who has specially 

 studied this family, that many species have enormous 

 ranges, and are found on continents and on far-distant 

 islands. Hence we have only to suppose that such wan- 

 dering species have been modified in their new homes 

 in relation to their new position, and we can understand 

 the presence of endemic bats on oceanic islands, with the 

 absence of all other terrestrial mammals. 



Another interesting relation exists, namely, between 

 the depth of the sea separating islands from each other 

 or from the nearest continent, and the degree of affinity 



