432 



INSULAE FLOEAS AND FAUNAS CONSIDERED. 



[Ch. XLL 



species^ or tlie degree in whicli those of different archipe- 

 lagos or of different islands of the same group agree with 

 each other, has an unmistakable relation to the known faci- 

 lities enjoyed by each class of crossing the ocean. Such a 

 relationship accords well with the theory of Variation and 

 Nataral Selection, but with no other hypothesis yet suggested 

 for explaining the origin of species. 



-«u 



