England, most of the northern ones are confined to Scotland, whilst
Ireland is occupied chiefly by southern animals. This, however, is only
a very rough-and-ready method of sub-dividing the British Islands into
their component parts according to the origin of their faunas. On closer
study such a division is found to be unsatisfactory. The eastern species
do not really stop at the Scottish frontier, they range far into
Scotland. Nor are the northern forms confined to the latter country.
Many of them range into Ireland, and also into England. I have
constructed a map of the British Islands showing approximately the
boundaries of the northern, eastern, and southern species (p. 7), but
even this may not altogether meet with the views of an ornithologist or
conchologist. For every group of animals the boundaries would probably
require to be marked differently. There is also a good deal of
overlapping, so that the attempt to define the limits of the various
elements meets with great difficulties. But the map represents, I think,
fairly well the general impression one receives as to the disposition of
its component elements, after a careful study of the British fauna as a
whole.

The distribution of the British plants has been worked out much more
thoroughly than that of the animals. It need not surprise us, therefore,
that the first attempt to separate the British Islands into natural
divisions was made by a botanist--the late Mr. Watson. As he himself
pointed out, in making these divisions he did not take into
consideration the origin of the British species. They represent merely
groups of assemblages of plants of different types of vegetation. Edward
Forbes, on the other hand, founded his districts on the origin of
plants. His work is not only the first of the kind, but it is a
classical essay, and remains one of the most remarkable contributions to
the literature on the geographical distribution of living organisms
known to science. The vegetation of the British Islands, he informs us
(p. 4), presents a union of five well-marked floras, four of which are
restricted to definite provinces, whilst the fifth, besides exclusively
claiming a great part of the area, overspreads and commingles with all
the others. These are--

I. Mountainous districts of South-west }
and West of Ireland. } Lusitanian type.

II. South-west of England, and }
South-east of Ireland. } Gallican ty