an
migrants in their western course, and thus have reached the British
Islands. Nevertheless, the majority of the mammals belonging to the
eastern element of the British fauna (_vide_ p. 95) have undoubtedly
originated in Siberia. The Polecat (_Mustela putorius_) and the Harvest
Mouse (_Mus minutus_), for instance, are members of that eastern
migration. Both occur throughout Central Europe and a large portion of
Siberia, but are absent from the extreme north and south of Europe and
also from all the Mediterranean Islands. A Siberian species, which has
never penetrated so far west as the British Islands, nor even so far
north as Scandinavia or south to Italy, is what is known in Germany as
the "Hamster" (_Cricetus frumentarius_), a little Rodent which spends
the winter asleep in its burrows, and surrounds itself with a great
accumulation of food-material carried there during autumn. The common
English Hare, which I formerly regarded as an instance of a Siberian
mammal, must now find a place among the Oriental migrants. Its history
is very instructive, and I shall have an opportunity later on to refer
to it again. Meanwhile, it may be mentioned that though this Hare
inhabits Europe in two varieties or races, one of which, _Lepus
mediterraneus_, is confined to Southern Europe, the latter owes its
origin to an earlier migration from Asia.

When we come to consider the eastern birds, we have to distinguish
between resident species and migratory ones. The Black-throated Thrush
(_Turdus atrigularis_), which has been twice obtained in the British
Islands, is a mere straggler to Europe, and is not known to breed there
at all. Better known birds, perhaps, are the Golden Thrush (_Turdus
varius_), which has even occurred as far west as Ireland, the
Rock-Thrush (_Monticola saxatilis_) and the Scarlet Grosbeak
(_Carpodacus erythrinus_), which breed in Eastern Europe, but are known
only as occasional visitors in the west.

To judge by their distribution, the Bullfinches (_Pyrrhula_) are of
Asiatic origin, for seven species out of ten are confined to that
continent. Our common Bullfinch (_P. europaea_) probably came with the
Oriental migrants, or perhaps its ancestors did. But the larger Northern
or Russian Bullfinch (_P. major_) has no doubt entered our Continent
directly from the east. We have in many groups similar instances of
closely allied species or varieties, one of which, originating at a
somewhat later stage than the other,