Cases of this nature are common, and are, as we shall hereafter see, inexplicable on the theory of independent creation.

This view of the relation of the species of one region to those of another, does not differ much from that advanced by Mr.

Wallace, who concludes that "every species has come into existence coincident both in space and time with a pre-existing closely allied species.

" And it is now well known that he attributes this coincidence to descent with modification.

The question of single or multiple centres of creation differs from another though allied question, namely, whether all the individuals of the same species are descended from a single pair, or single hermaphrodite, or whether, as some authors suppose, from many individuals simultaneously created.