296 Distribution of Moths of the Sub-family Bistonincc. 



retreat followed. As with thousands of other arrivals in 

 Europe, the oncome of the ice forced it back, further back indeed 

 than many, for oaks, to which it is attached, are very impatient 

 of icy soils. Once again, too, the reunited invaders were dis- 

 joined, for local glaciers in Central Europe occupied the plain, 

 one contingent withdrawing to Spain and the other to South- 

 eastern Europe, here outstaying the inclemencies of glacial 

 days. 



Nevertheless, the latter were not to last ; warmer suns 

 returned to smile on Europe, and in its turn the ice fell back. 

 Again Biston strataria passed slowly forth, following hard on 

 the oaks to which it was bound. Like other insects of similar 

 diet, an example of which we met in Poecilopsis pomonaria, 

 the Eastern division was able to repopulate Central Europe 

 and Southern Scandinavia, that from Spain just reaching 

 Britain, and penetrating to the Midlands, ere its impulse was 

 lost by Britain becoming an island. 



But this latter restricted occupation of the British Islands 

 has not to be dismissed as a minor point ; a like peculiarity 

 is stamped on nearly all oak feeders, and suggests that all such 

 beings repopulated Western Europe from the Spanish Peninsula. 

 We shall not linger on the matter here, for we shall reserve it for 

 subsequent full consideration when we take up the study of 

 the genus Apocheima. 



Still one more feature remains for treatment, and that is 

 the break-down of the range of the group in Western and Central 

 Asia. When Biston was advancing, Central Asia was a land 

 totally dissimilar from that of our days. It was well-watered, 

 less elevated and conditions were ideal for deciduous trees. 

 Gradually, however, the Great Central Sea dried up and rains 

 became infrequent. Hard on this diminishing rainfall the 

 wooded areas contracted ; where once oaks and similar trees 

 flourished, nothing could succeed save drought resisting shrubs 

 like Eleagnus and Lycium. Upon these Biston could not 

 maintain itself, and thus the geographical continuity of the 

 genus was broken. Nor was this all ; great uprisings took place 

 and from the ' Roof of the World ' eastward for many miles life 

 for trees became hopeless. As a result existence for creatures 

 of arboreal tendencies became impossible, and the gap was 

 widened. 



Such, too, has been the history of many cases of like dis- 

 continuity in distribution, prominent amongst which is the 

 well-known case of the two Blue Jays (Cyanopica cooki and 

 C. cyanea) — prominent, not because their case is unique, but 

 because it is so well-known. 



Mr. J. Groves contributes a memoir on the late Clement Reid, with 

 portrait, in The Journal of Botany for June. 



Naturalist, 



