Geographical Distribution. avi 
types, where fresh-water faunas are concerned, than 
almost any other. But why should this be the case 
on any intelligible theory of special creation? Why, 
in the depositing of species of newly created fresh- 
water fish, should the presence of an impassable: 
mountain-chain have determined so uniformly a dif- 
ference of specific affinity on either side of it? The 
question, so far as I can see, does not admit of an 
answer from any reasonable opponent. 
Turning now from aquatic organisms to terrestrial, 
the body of facts from which to draw is so large, 
that I think the space at my disposal may be best 
utilized by confining attention to a single division 
of them—that, namely, which is furnished by the 
zoological study of oceanic islands. 
In the comparatively limited—but in itself extensive 
—class of facts thus presented, we have a particularly 
fair and cogent test as between the alternative theories 
of evolution and creation. For where we meet with a 
volcanic island, hundreds of miles from any other land, 
and rising abruptly from an ocean of enormous depth, 
we may be quite sure that such an island can never 
have formed part of a now submerged continent. In 
other words, we may be quite sure that it always has 
been what it now is—an oceanic peak, separated 
from all other land by hundreds of miles of sea, 
and therefore an area supplied by nature for the 
purpose, as it were, of testing the rival theories of 
creation and evolution. For, let us ask, upon these 
tiny insular specks of land what kind of life should 
we expect to find? To this question the theories 
of special creation and of gradual evolution would 
