ge in
that direction. South-eastward, of course, a highway had long ago been
open, and Alpine forms which were able to migrate towards the incoming
Oriental stream, had no difficulty in doing so. When they arrived in
Greece, some turned westward again and populated Sicily, Southern Italy,
Sardinia, Corsica, and Northern Africa, while others crossed over to
Asia Minor, which was then connected with Greece, and wandered towards
the Central Asiatic or the Himalayan Mountains.

But, as I remarked, few of the typical Alpine species reached
Scandinavia and Lapland. I have already referred to the similarity
between the Northern Scandinavian and the Alpine faunas in a previous
chapter, and I have shown that this resemblance cannot altogether be
explained by the supposition of an interchange in the faunas of the two
regions. That this has taken place to some extent is probable, but the
resemblance appears more especially due to the fact that the Alps and
Scandinavia have been peopled from the same centres of distribution.

In order to make this matter quite clear, I will give a familiar example
as an instance of the manner in which the present distribution can be
explained without taking recourse to direct migration from the Alps to
Scandinavia or _vice versa_. The example I will take is that of a family
of birds, not only of extreme interest from the fact of its northern
range, but also from the pleasure it gives to those addicted to sport.
This is the grouse family, the _Tetraonidae_.

Let us commence with our British Grouse (_Lagopus scoticus_), which is
peculiar to the British Islands. In Norway we find a Grouse (_L. albus_)
which differs in habit, and in the fact of its turning white in winter;
otherwise it is so closely allied to our Grouse that many ornithologists
do not separate them specifically. No doubt the British Grouse is a
descendant of this Scandinavian Willow-grouse. The latter is known also
to inhabit Greenland and Arctic North America, and it is even found
beyond Behring Straits in Northern Siberia. _En route_ between
Scandinavia and Asia, travelling in a westward direction, we meet with
two other very local species of Grouse, which may be looked upon as
offshoots of _L. rupestris_--viz., _L. hyperboreus_ of Spitsbergen, and
_leucurus_ of Western North America. In Asia we then again find two
kinds of Grouse, very closely related, and by some indeed regarded as
belonging to the same species. These are _L. rup