MAMMALS ON OCEANIO ISLANDS. 415 



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 

 terrestrial mammal can be transported across a wide space 

 of sea, but bats can fly across. Bats liave been seen wan- 

 dering by day far over the Atlantic Ocean; and two North 

 American species, either regularly or occasionally, visit Ber- 

 muda, at the distance of 600 miles from the mainland. I 

 hear from Mr. Tomos, 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 ter- 

 restrial 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 aflinity 

 of their mammalian inhabitants. Mr. Windsor Earl has 

 made some striking observations on this head, since greatly 

 extended by Mr. Wallace's admirable researches, in regard 

 to the great Malay Archipelago, which is traversed near 

 Celebes by a space of deep ocean, and this separates two 

 widely distinct mammalian faunas. On either side, the 

 islands stand on a moderately shallow submarine bank, 

 and these islands arc inhabited by the same or by closely 

 allied quadrupeds. I have not as yet had time to follow 

 up this subject in all quarters of the world; but as far as I 

 have gone, the relation holds good. For instance, Britain 

 is separated by a shallow channel from Europe, and the 

 nnimmals are the same on both sides; and so it is .vith all 

 the islands near the shores of Australia. The West Indian 

 Islands, on the other hand, stand on a deeply submerged 

 bank, nearly one thousand fathoms in depth, and liere we 

 find American forms, but the species and even the genera 

 are quite distinct. As the amount of moditicatiou which 

 animals of all kinds undergo partly depends on the lapse 

 of time, and as the islands which are separated from each 

 other, or from the mainland, by shallow channels, are more 

 likely to have been continuously united within a recent 

 period than the islands separated by deeper channels, we 



