OCEANIC ISLANDS. 199 



nection of the land with the continent, or the lack 

 of such connection ; (2) upon their distance from 

 the mainland ; (3) upon the prevalence of winds 

 and currents to assist in immigration of individuals; 

 and (4) upon the antiquity of the island. The 

 significance of these facts is plain. 



It must not be supposed, however, that the life of 

 oceanic islands offers no puzzling problems, for 

 some cases occur where explanation is not yet 

 found. We occasionally find upon oceanic islands 

 species not related to the nearest mainland, but to 

 more distant countries. The Bermuda lizard has 

 its nearest ally in Africa, and three of the Bermuda 

 birds are European species. The land shells of St. 

 Helena are European in their affinities. Again, it is 

 surprising to find that the different islands of the 

 same group may have different species. The Gala- 

 pagos islands, for instance, do not have a uniform 

 fauna and flora, many species being confined to 

 separate islands only a few miles from each other. 

 It would seem that a few miles of the calm Pacific 

 served as a more effectual barrier to prevent the 

 crossing of individuals than the five hundred miles 

 of stormy sea which separate the Bermudas from 

 the continent. It has indeed been shown that 

 in the Malayan Archipelago such narrow straits 

 have the effect of practical barriers. A body of 

 water of fifteen miles in width between Bali and 

 Loudock separates effectually two radically distinct 

 faunas, one belonging to Asia and the other to 

 Australia. 



