GEOGRAPHICAL DISTRIBUTION 359 



searched the oldest voyages, and have not found a single instance, 

 free from doubt, of a terrestrial mammal (excluding domesticated 

 animals kept by the natives) inhabiting an island situated about 

 300 miles from a continent or great continental island; and many 

 islands situated at a much less distance are equally barren. The 

 Falkland Islands, which are inhabited by a wolf -like fox, come 

 nearest to an exception; but this group cannot be considered as 

 oceanic, as it lies on a bank in connection with the mainland at 

 a distance of about 280 miles; moreover, icebergs formerly brought 

 bowlders to its western shores, and they may have formerly 

 transported foxes, as now frequently happens in the arctic re- 

 gions. Yet it cannot be said that small islands will not support 

 at least small mammals, for they occur in many parts of the world 

 on very small islands, when lying close to a continent; and hardly 

 an island can be named on which our smaller quadrupeds have 

 not become naturalized and greatly multiplied. It cannot be said, 

 on the ordinary view of creation, that there has not been time for 

 the creation of mammals; many volcanic islands are sufficiently 

 ancient, as shown by the stupendous degradation which they have 

 suffered, and by their tertiary strata: there has also been time 

 for the production of endemic species belonging to other classes; 

 and on continents it is known that new species of mammals ap- 

 pear and disappear at a quicker rate than other and lower ani- 

 mals. 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: Nor- 

 folk Island, the Viti 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 wandering 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 



