196 §=©Distribution of Moths of the Sub-family Bistoninac. 
colonies are totally distinct in origin. This conclusion necess- 
arily carries with it the corollary that the repopulation of the 
British Islands, when the ice waned, was not wholly from the 
South and East as we are generally asked to believe, and this 
conclusion is backed up by the present distribution of all ot the 
elements of our Flora and Fauna, which are not of general 
occurrence. Northern species show unmistakable signs of hav- 
ing advanced from the North and are therefore northern and 
western in distribution, as can readily be perceived from a 
consideration of such species as the moths, Larentia caesiata, 
and Cloantha solidaginis, the spider, Caledonia evansi1, the 
plant, Empetrum mgrum, chosen at random from a host of 
similar examples in all groups. In the same way, forms of 
Southern afid Eastern origin are southern and eastern in distri- 
bution and it would be but repeating the obvious to select 
illustrative examples. Without doubt, these phenomena are 
not matters of chance and, when we meet with this curious 
circumstance of double distribution, we cannot but conclude 
that we are concerned with two branches, one of which has 
advanced with the southern species and another which has 
accompanied one of the hosts of northern invaders. 
That the northern division came last, is proved by the fact 
that, whilst the southern colony has settlements in Ireland 
which are bound to have reached Ireland via Wales, 1.e. bya land 
connection which broke early, on the other hand, the northern 
section has no Irish advanced posts, in spite of the long continu- 
ed existence of the Mull-Islay-Donegal isthmus. 
The conclusion is unavoidable that the wave of immigration 
which gave Britain her northern L. hirvtavia was set in motion by 
events to the north of our island, which so lessened the habitable 
areas in Scandinavia, that a great proportion of the Flora and 
Fauna of that country had to seek other shores ; this factor was 
the development of that last phase of the Glacial Period, the 
huge Baltic Glacier, which affected our own islands (if it did 
affect them at all), but little. The ice, ploughing its way from 
the Scandinavian Mountains eastward and southward, advanced 
over the bed of the Baltic Sea, driving in front of it the water to 
form an arm of the sea which stretched out far across Holstein 
into the North Sea plain, and incidentally overwhelming Den- 
mark and North Germany. Thus, plants and animals, which 
had to retreat, were deflected westward, reaching, in the process 
of time, with many other Boreal forms, the Scotch localities they 
now possess, occupying them solidly just as the retreat was 
stopped and climatic and geographical conditions, approximat- 
ing more or less closely to those of the present day, intervened.* 

* From the above line of reasoning it will be seen that I place the origin 
of the British Flora and Fauna as far as the Boreal forms are concerned, 
as Interglacial. Again it is well to state that I refuse to believe that the 
Natvrelist 
