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 climate, and there may be almost all 
types of surface—mountain, wood, steppe, tundra, and 
so forth. Thus, while 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 naturalists, 
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 earlier months of the year (February— 
May). Here the vegetation is scanty, and xerophytic 
in character, the most important plant from the 
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