108 THE AMERICAN NATURALIST. | [Vor. XXXV. 
same way to its Arctic home. For this bird to have found a way 
to America there must at the time have existed a route fairly 
well.outlined by islands more extensive and more numerous 
than now, and the very fact that this route of the extension of its 
distribution (for it belongs to an exclusively Old-World genus) 
became an annual migration-route points plainly to the exist- 
ence of such an interrupted land bridge some time in the 
glacial period. However, the total absence of the reindeer, 
the hare, the lemming, the ermine, and the musk ox in Iceland 
is incontrovertible proof that the Arctic mammalian invasion 
into western Europe did not come by way of Iceland. 
There remains then only Norway as the last possible home 
of these animals if they arrived from the north at all. The 
question, however, at once presents itself: If they arrived in 
Scotland from Norway by way of the North Sea bridge, by what 
route did they then come into Norway? It is of course out of 
the question to suppose that they originated in that country 
situated at the extreme northwest periphery of the Old World, 
as they are all closely allied to species of arctogcean derivation. 
On the other hand, there seems to have been no other land con- 
nection at that period between Scandinavia and the rest of the 
Eurasian continent than that with Scotland. It is pretty gen- 
erally agreed that the sea then covered the lowlands of northern 
Russia to the east, thus effectually cutting off any communi- 
cation between Siberia and Lapland. Apart from the consid- 
erations which have influenced that conclusion it would be 
very difficult to explain the absence from the Scandinavian 
peninsula of a number of both Arctic and Siberian animals 
had there been a land connection in that region during the 
earlier and middle stages of the glacial period. The total 
absence of Cuniculus torguatus and the musk ox is particularly 
significant. 
It would then appear that we are compelled to conclude that 
the mammals and birds in question did not come to Great 
Britain and Ireland from the north at all. They certainly did 
not come from the west, and it is equally certain that they 
formed no part of the Lusitanian fauna. There seems then to 
be no other way by which they could have reached England 
