56 



[Proc. B.N.F.O., 



colonies, they may be blown across the sea to an island and thus 

 colonise it. It is possible that some of our species may have thus 

 originally reached Ireland. But how are we to account for the 

 presence in Irish Ants' nests of the blind white Woodlice just 

 referred to ? They are delicate frail creatures, exposure to the 

 sun's rays soon kills them, they could not survive immersion in 

 sea water for many minutes ; winds could not blow them away for 

 they live underground. Hence we must conclude that for their 

 dispersal a continuous land surface is requisite, a marine channel 

 being an impassable barrier. The presence of the blind VVoodlouse 

 in Ireland thus demonstrates, if nothing else does, that our Island 

 must have been connected by land with the Continent — no doubt 

 by way of Great Britain. Moreover since this and other allied 

 species occur in the Mediterranean region, we assume that the 

 genus to which it belongs originated in the south, and our species 

 spread from there northward, step by step along the Atlantic coast, 

 at a time when Continental Europe extended as far west as Ireland. 

 If you examine the map of the geographical range of this species, 

 Platyarthrus hoffmannseggii, you will notice its absence from 

 Eastern Europe, and its curiously discontinuous distribution in 

 the British Isles. It is confined to the south and Midlands of 

 England and southern Ireland, and to a few isolated localities in 

 Scotland. A discontinuous range of that nature suggests that the 

 creature has survived in certain spots, having become extinct in 

 others, at a time when the conditions of life became unfavourable. 

 Whatever opinions we may have as to the nature and cause 

 of the Ice Age, there can be little doubt that it had a destructive 

 effect on the fauna in certain areas. It is quite possible that our 

 little blind Woodlouse, having entered Great Britain in pre-Glacial 

 times, was decimated over much of its range, and is only now 

 endeavouring to regain the lost territories in Ireland and England 

 where isolated colonies survived, while in Scotland it seems only 

 just to maintain itself as a relict of past times. 



