Chap. XII. OCEANIC ISLANDS. 403 



Porto Santo possess many distinct but representative 

 land-shells, some of which live in crevices of stone ; and 

 although large quantities of stone are annually trans- 

 ported from Porto Santo to Madeira, yet this latter 

 island has not become colonised by the Porto Santo 

 species : nevertheless both islands have been colonised 

 by some European land-shells, which no doubt had some 

 advantage over the indigenous species. From these 

 considerations I think we need not greatly marvel at 

 the endemic and representative species, which inhabil 

 the several islands of the Galapagos Archipelago, not 

 having universally spread from island to island. In 

 many other instances, as in the several districts of the 

 same continent, pre-occupation has probably played an 

 important part in checking the commingling of species 

 under the same conditions of life. Thus, the south-east 

 and south-west corners of Australia have nearly the 

 same physical conditions, and are united by continuous 

 land, yet they are inhabited by a vast number of distinct 

 mammals, birds, and plants. 



The principle which determines the general character 

 of the fauna and flora of oceanic islands, namely, that 

 the inhabitants, when not identically the same, yet are 

 plainly related to the inhabitants of that region whence 

 colonists could most readily have been derived, — the 

 colonists having been subsequently modified and better 

 fitted to their new homes, — is of the widest applica- 

 tion throughout nature. We see this on every moun- 

 tain, in every lake and marsh. For Alpine species, 

 excepting in so far as the same forms, chiefly of plants, 

 have spread widely throughout the world during the 

 recent Glacial epoch, are related to those of the sur- 

 rounding lowlands ; — thus we have in South America, 

 Alpine humming-birds, Alpine rodents, Alpine plants, 

 &c, all of strictly American forms, and it is obvious 



