Distribution of Moths of the Sub-family Bistonine. 381 
but still following the same course, the species regained much 
of its lost ground. It did not penetrate far to the north, 
barely reaching Southern Scandinavia, where its advance was 
limited by climate; otherwise, it followed its relative and 
kept to much the same boundaries. 
The contingent left separated in Asia Minor could now only 
pass out in one direction, and that it did to the north east, 
gradually flanking the Caucasus mountains round the coastal 
plain to emerge finally on the steppes of Southern Russia, 
and giving rise in its course through Armenia to the allied 
species N. imcisaria. Once on the plains, the arid steppes 
worked their will, and out of the species was evolved the dwarfed 
local race I have called var. rossica. Under this guise, it 
spread in South Russia, eventually passing, with the con- 
traction of the Caspian Sea, into the Uralsk and the lower 
slopes of the South Ural Mountains. 
We must now consider the other species of the genus. 
Very early in its being, Nyssia zonaria had reached the 
Alps of Central Europe and here had yielded the species Nyssia 
alpina which penetrated every valley and accessible mountain 
in Switzerland and the Tyrol, swinging right round to the 
Mountains of the Piedmont. But what was its fate during the 
Glacial Period ? Was it, or was it not forced to retreat down 
the Apennines of sunny Italy? Possibly it was, but in my 
view the chances are that part yielded ground, but part re- 
mained. 
The Flora and Fauna of the Alps was not wholly banished. 
If we grant that it was, then the difficulty of explaining the 
present Alpine animals and plants is enormous. Either we have 
to assume a wholesale Post-Glacial evolution of the endemic 
forms of all groups from worms upward and downward or, in the 
case of many plants and animals not confined to the Alps, a 
simultaneous evolution there and in the Altai and other Moun- 
tains of Central Asia—an absurdity, more especially when it is 
coupled with the fact that over ten per cent. of such plants 
fail in the Caucasus and a much heavier percentage in Asia 
Minor. Grant that part of N. alpina stayed in the Alps and it 
is plain that the species would have to have special adaptations 
to permit of its survival, and the special device adopted was 
the familiar one of passing several winters in the pupal con- 
dition. Of all species, N. alpina is the very worst in this 
respect, whole broods going over up to seven winters unchanged. 
Presumably, it did not persist in all its stations, but certainly 
it did in some, returning to its older posts as once more they 
became available. 
The group which took refuge in the Apennines slowly, by 
reason of geographical isolation, diverged and yielded the 
species N. italica which, although close to N. alpina is quite 
1916 Dec. 1. 
