the
same genus, though inhabiting the most distant quarters of the world,
must originally have proceeded from the same source, as they are
descended from the same progenitor. In the case of those species which
have undergone, during whole geological periods, little modification,
there is not much difficulty in believing that they have migrated from
the same region; for during the vast geographical and climatical
changes which have supervened since ancient times, almost any amount of
migration is possible. But in many other cases, in which we have
reason to believe that the species of a genus have been produced within
comparatively recent times, there is great difficulty on this head. It
is also obvious that the individuals of the same species, though now
inhabiting distant and isolated regions, must have proceeded from
one spot, where their parents were first produced: for, as has been
explained, it is incredible that individuals identically the same should
have been produced from parents specifically distinct.

SINGLE CENTRES OF SUPPOSED CREATION.

We are thus brought to the question which has been largely discussed by
naturalists, namely, whether species have been created at one or more
points of the earth's surface. Undoubtedly there are many cases of
extreme difficulty in understanding how the same species could possibly
have migrated from some one point to the several distant and isolated
points, where now found. Nevertheless the simplicity of the view that
each species was first produced within a single region captivates the
mind. He who rejects it, rejects the vera causa of ordinary generation
with subsequent migration, and calls in the agency of a miracle. It is
universally admitted, that in most cases the area inhabited by a species
is continuous; and that when a plant or animal inhabits two points so
distant from each other, or with an interval of such a nature, that the
space could not have been easily passed over by migration, the fact
is given as something remarkable and exceptional. The incapacity of
migrating across a wide sea is more clear in the case of terrestrial
mammals than perhaps with any other organic beings; and, accordingly,
we find no inexplicable instances of the same mammals inhabiting distant
points of the world. No geologist feels any difficulty in Great Britain
possessing the same quadrupeds with the rest of Europe, for they were
no doubt once united. But if the same species can be prod