ey occur in
many parts of the world on very small islands, if close to a continent; and
hardly an island can be named on which our smaller quadrupeds have not
become naturalised and greatly multiplied. It cannot be said, on the
ordinary view of creation, that there has not been time for the creation of
mammals; many volcanic islands are sufficiently ancient, as shown by the
stupendous degradation which they have suffered and by their tertiary
strata: there has also been time for the production of endemic species
belonging to other classes; and on continents it is thought that mammals
appear and disappear at a quicker rate than other and lower animals. Though
terrestrial mammals do not occur on oceanic islands, aerial mammals do
occur on almost every island. New Zealand possesses two bats found nowhere
else in the world: Norfolk Island, the Viti Archipelago, the Bonin Islands,
the Caroline and Marianne Archipelagoes, and Mauritius, all possess their
peculiar bats. Why, it may be asked, has the supposed creative force
produced bats and no other mammals on remote islands? On my view this
question can easily be answered; for no {395} terrestrial mammal can be
transported across a wide space of sea, but bats can fly across. Bats have
been seen wandering by day far over the Atlantic Ocean; and two North
American species either regularly or occasionally visit Bermuda, at the
distance of 600 miles from the mainland. I hear from Mr. Tomes, who has
specially studied this family, that many of the same species have enormous
ranges, and are found on continents and on far distant islands. Hence we
have only to suppose that such wandering species have been modified through
natural selection in their new homes in relation to their new position, and
we can understand the presence of endemic bats on islands, with the absence
of all terrestrial mammals.

Besides the absence of terrestrial mammals in relation to the remoteness of
islands from continents, there is also a relation, to a certain extent
independent of distance, between the depth of the sea separating an island
from the neighbouring mainland, and the presence in both of the same
mammiferous species or of allied species in a more or less modified
condition. Mr. Windsor Earl has made some striking observations on this
head in regard to the great Malay Archipelago, which is traversed near
Celebes by a space of deep ocean; and this space separates two widely
distinct mammalian fauna