390 
GEOGEAPHICAL DISTEIBUTION. 
Chap. XII. 
yet many have become naturalised on it, as they have 
on New Zealand and on every other oceanic island 
which can be named. In St. Helena there is reason to 
believe that the naturalised plants and animals have 
nearly or quite exterminated many native productions. 
He who admits the doctrine of the creation of each 
separate species, will have to admit, that a sufficient 
number of the best adapted plants and animals have 
not been created on oceanic islands; for man has unin¬ 
tentionally stocked them from various sources far more 
fully and perfectly than has nature. 
Although in oceanic islands the number of kinds 
of inhabitants is scanty, the proportion of endemic 
species (^. e. those found nowdiere else in the world) 
is often extremely large. If we compare, for instance, 
the number of the endemic land-shells in Madeira, or 
of the endemic birds in the Galapagos Archipelago, with 
the number found on any continent, and then compare 
the area of the islands with that of the continent, we 
shall see that this is true. This fact might have been 
expected on my theory, for, as already explained, spe¬ 
cies occasionally arriving after long intervals in a new 
and isolated district, and having to compete with new 
associates, will be eminently liable to modification, and 
will often produce groups of modified descendants. But 
it by no means follows, that, because in an island nearly 
all the species of one class are peculiar, those of another 
class, or of another section of the same class, are pecu¬ 
liar ; and this difference seems to depend partly on the 
species which do not become modified having immi¬ 
grated with facility and in a body, so that their mutual 
relations have not been much disturbed ; and partly on 
the frequent arrival of unmodified immigrants from the 
mother-country, and the consequent intercrossing with 
them. With respect to the effects of this intercrossing, 
