194 
THE GEOGRAPHICAL DISTRIBUTION OF THE 
MOTHS OF THE SUBFAMILY BISTONINAE. 
J. W. HESLOP HARRISON. B.Sc. 

(Continued from page 166). 
We begin now to trace what may be regarded as the history 
of the modern wanderings of the two species L. ursaria and L. 
hirtaria and we shall discuss our own insect first. 
As it reached the Balkans and wended its way through that 
ancient land Dalmatia, it found the passage thence via Central 
and Southern Italy, Sicily to Tunis still open and if, as we 
surmised, the genus Lycia is of northern origin, then we have 
excellent grounds for surmising that this Dalmatia-Italy-Tunis 
land passage existed just at the closing stages of Pliocene times, 
and possibly into early Pleistocene times. At any rate, soon after 
the insect made the passage, the Adriatic Sea was formed and 
the land mass which cut the Mediterranean Sea into an eastern 
and a western section, ceased to exist and left the isolated colon- 
ies of L. hirtaria stranded in the hill gorges of Tunis and Algiers 
and in the elevated portion of Abruzzi in Italy, where they 
remain interned and decadent to-day, just as do similar colonies 
of other European and African plants and animals at varying 
points on the broken land bridge. 
However, as the climate oscillated, so must we suppose the 
range of L. hirtaria varied, until, at length, the lengthy period of 
amelioration known as the interglacial period to some geologists, 
and as an interglacial period to others, saw the species migrating 
in all its vigour northward, westward and eastward, in the two 
former cases following the line of advancing birches (for birch is 
the food in nature of the species) along the valleys of the Danube, 
Rhine, Elbe and Vistula. By flanking the Carpathians to the 
east, and utilising the Vistula valley, it very early reached the 
limits of its Scandinavian area, after passing over the dry beds of 
the Sound, Skagerrack and Cattegat. Even at the present day 
dredgings from interglacial beds at the bottom of these channels, 
bring before our eyes the remains of the birches which supplied 
the conquering hosts with food. By contrasting the ease of the 
route to Scandinavia with the long and tedious route to Britain, 
it is clear that the forms which issued from their retreats, joined 
those which had survived the ‘ winter of their discontent ’ in 
Scandinavia, long anterior to a similar reunion in the British 
Islands. This, supplemented by the Boreal and Alpine forms 
which reached Scandinavia at the same period from the East 
via North Russia and Lapland, caused that area to be amongst 
the first in Europe to have its full complement of Alpine and 
Boreal forms and explains why certain of such forms failed to 
Naturalist, 
