an important part in the evolution of
the European fauna, that it forms the key to the solution of the wider
problem. In it five elements are recognisable, of which the Lusitanian
element is the oldest, and the Siberian the most recent. It has been
deemed advisable to conclude this chapter with a short review of the
history of the Glacial period in its climatic effects on the animals and
plants of Europe. A number of writers are quoted who have conducted
special researches in determining the temperature of our continent at
the time. The fauna of Europe is frequently described as having been of
an Arctic nature, but as a matter of fact there existed during the Ice
Age a striking and most remarkable mingling of a northern and a southern
fauna. The presence of Siberian mammals in Europe is said to have been
due to the prevalence of a dry steppe climate, but this view is not
supported by other evidence. The Alpine flora in a wide sense is
probably pre-glacial in origin, and appears to have survived the Ice Age
where it is now known to exist. A few words on the phenomena of
glaciation are added before bringing the chapter to a close.

CHAPTER III.

THE FAUNA OF BRITAIN.

The British Islands are, as I have remarked, very suitable as a
starting-point for our investigations. Their fauna and flora are fairly
well known, and the distribution of the large animals at any rate, which
are of course of much importance in these researches, has been as much
studied as that of any other area in Europe. We possess in England an
abundance of the remains of past animal life, and a combination of the
data furnished by both of these important factors will enable us to draw
up a history of the origin of the present British fauna.

In the first chapter I indicated that in the fauna of the British
Islands three divisions or elements are recognisable--a northern, a
southern, and an eastern. These elements correspond to migrations which
can be proved to have arrived in this country at different periods in
past times. When we investigate these migrations more closely, the
eastern is found to be composed partly of European and partly of
Siberian species. The southern is made up of European and of Central and
Southern Asiatic species. To make matters still more complex, the
southern and eastern migrations insensibly merge into one another, so
that it is often very difficult to determine to which of them an animal
may belong. The European