tion--that "colonisation or
occasional dispersal is insufficient to account for the character of
the faunas and floras of oceanic islands; and I believe that the normal
mode in which islands have been peopled, has been by direct continuity
with the land at some former period, or by contiguity so close as to be
equivalent to junction" (p. 15). "That a slight intermixture," he
continues, "due to Mr. Darwin's colonisation, occurs in many (probably
in all) I am ready to admit; and from instances to be afterwards
noticed, I am disposed to reckon the proportions of such intermixtures
in the flora, in the most favourable circumstances, at not more than two
per cent. In the fauna I think it must be much less."

Mr. Murray's views, though they relate only to oceanic islands, are
likewise applicable to continental islands such as our own. I think we
might take the admixture in the British fauna due to occasional,
including human introduction, as amounting to five per cent. It is
better to take a high estimate, so as to include all the species about
whose native land there might be some reasonable doubt. Now of what
importance, after all, is this five per cent.? The remaining ninety-five
per cent. of the species of animals belonging to the British fauna
undoubtedly migrated to these islands in the normal way by land.

It is of great importance, in dealing with the question of the origin of
the British fauna, to thoroughly grasp this conclusion--_that
ninety-five per cent. of the animals have reached us by land_. We can
afford in fact to ignore the five per cent. altogether. It is an
insignificant factor. As regards the botanical aspect of the question,
botanists are quite in accord with the zoologists, and entirely share
their views in the belief of a former land-continuity between the
British Islands and the Continent. "It cannot be denied," says Professor
Blytt (p. 32), "that a plant of one or another species may, in an
exceptional case, migrate, without human assistance, all at once, across
large tracts of land and sea, and that such migration, if operating
during geological periods, might introduce a number of species even into
distant oceanic islands; but when the question is of whole communities
of plants, such as the above enumerated elements in our flora, then such
an accidental and sudden transport across large tracts can only be
conceived to be at all probable in the case of Arctic plants carried by
drifting ice to a ba