ISLAND FAUNAS 145 



mountain animals, like those of steppes or forests, are 

 exposed to virtually uniform conditions of climate, &c., 

 no such uniformity exists in the case of islands. We 

 speak, it is true, of insular climates, meaning that the 

 proximity of the sea has a certain moderating effect, 

 more especially if there is a large expanse of ocean all 

 round, or if the prevailing winds blow from such an 

 expanse. But even within the same island there may be 

 great variations of chmate, and there may be almost all 

 types of surface — mountain, wood, steppe, tundra, and 

 so forth. Thus, wMle the inhabitants of islands may 

 be readily counted and classified, and form a statistical 

 unity, they do not form a biological unity in the sense 

 that the animals of the other natural regions do, and 

 there are few general statements which can be made 

 of them as a whole. 



The special features of island faunas may best be 

 illustrated by a few examples, and we may begin by 

 a consideration of the Galapagos Islands, an interesting 

 group which has been studied by various naturahsts, 

 including Darwin. 



This archipelago consists of a group of islands lying 

 some seven hundred miles off the coast of Ecuador, 

 and on the equator. They are of volcanic origin, the 

 surface being covered with extinct craters, and are 

 placed upon a submarine bank, which rises steeply 

 from the depths of the Pacific. The climate is singu- 

 larly cool for the position, this being due to the fact 

 that the islands are washed by the cold Humboldt 

 current. In the lower regions of the islands the rain- 

 fall is markedly deficient, rain only falling in small 

 amounts in the earMer months of the year (February- 

 May). Here the vegetation is scanty, and xerophytic 

 in character, the most important plant from the 



1404 E 



