Chap. XII. OCEANIC ISLANDS. 395 



fied through natural selection in their new homes in 

 relation to their new position, and we can understand 

 the presence of endemic bats on islands, with the ab- 

 sence of all terrestrial mammals. 



Besides the absence of terrestrial mammals in rela- 

 tion to the remoteness of islands from continents, there 

 is also a relation, to a certain extent independent of 

 distance, between the depth of the sea separating an 

 island from the neighbouring mainland, and the pre- 

 sence in both of the same mammiferous species or of 

 allied species in a more or less modified condition. Mr. 

 Windsor Earl has made some striking observations on 

 this head in regard to the great Malay Archipelago, 

 which is traversed near Celebes by a space of deep 

 ocean ; and this space separates two widely distinct 

 mammalian faunas. On either side the islands are 

 situated on moderately deep submarine banks, and they 

 are inhabited by closely allied or identical quadrupeds. 

 No doubt some few anomalies occur in this great archi- 

 pelago, and there is much difficulty in forming a judg- 

 ment in some cases owing to the probable naturalisation 

 of certain mammals through man's agency ; but we 

 shall soon have much light thrown on the natural 

 history of this archipelago by the admirable zeal and 

 researches of Mr. Wallace. I have not as yet had time to 

 follow up this subject in all other quarters of the world ; 

 but as far as I have gone, the relation generally holds 

 good. We see Britain separated by a shallow channel 

 from Europe, and the mammals are the same on both 

 sides ; we meet with analogous facts on many islands 

 separated by similar channels from Australia. The 

 West Indian Islands stand on a deeply submerged bank, 

 nearly 1000 fathoms in depth, and here we find American 

 forms, but the species and even the genera are distinct. 

 As the amount of modification in all cases depends to 



