eographical Distribution in its
wider sense.

Hitherto the following thought ran through the minds of most writers:
Wherever we examine two or more widely separated countries their
respective faunas are very different, but where two faunas can come into
contact with each other, they intermingle. Consequently these faunas
represent centres of creation, whence the component creatures have
spread peripherally so far as existing boundaries allowed them to do so.
This is of course the fundamental idea of "regions." There is not one
of the numerous writers who considered the possibility that these
intermediate belts might represent not a mixture of species but
transitional forms, the result of changes undergone by the most
peripheral migrants in adaptation to their new surroundings. The usual
standpoint was also that of Pucheran ("Note sur l'equateur zoologique",
"Rev. et Mag. de Zoologie", 1855; also several other papers, ibid. 1865,
1866, and 1867.) in 1855. But what a change within the next ten years!
Pucheran explains the agreement in coloration between the desert and
its fauna as "une harmonie post-etablie"; the Sahara, formerly a marine
basin, was peopled by immigrants from the neighbouring countries, and
these new animals adapted themselves to the new environment. He also
discusses, among other similar questions, the Isthmus of Panama with
regard to its having once been a strait. From the same author may be
quoted the following passage as a strong proof of the new influence:
"By the radiation of the contemporaneous faunas, each from one centre,
whence as the various parts of the world successively were formed and
became habitable, they spread and became modified according to the local
physical conditions."

The "multiple" origin of each species as advocated by Sclater and
Murray, although giving the species a broader basis, suffered from the
same difficulties. There was only one alternative to the old
orthodox view of independent creation, namely the bold acceptance of
land-connections to an extent for which geological and palaeontological
science was not yet ripe. Those who shrank from either view, gave up
the problem as mysterious and beyond the human intellect. This was the
expressed opinion of men like Swainson, Lyell and Humboldt. Only Darwin
had the courage to say that the problem was not insoluble. If we admit
"that in the long course of time the individuals of the same species,
and likewise of allied species,