318 Distribution of Moths of the Sub-family Bistonince. 



to separate them ; what little there is lies in the loss in 

 Apocheima, of the huge vesical cornutus peculiar to Microbiston 

 and the primitive Phigalia, together with that unerring mark 

 of progress in the Bistonines, the disappearance of the posterior 

 middle spurs. So close are the two genera that the only 

 opinion one can form is that Apocheima was evolved from 

 Microbiston. This latter genus occupies a somewhat limited 

 tract in West Central Asia, and seems never to have departed 

 far from it. In consequence, in that very area Apocheima 

 took its rise. But Microbiston originated from Phigalia. 

 Therefore, in view of the apparent lack of enterprise displayed 

 by Microbiston in colonising new ground, Phigalia too, must 

 have, in its early days, gone forth from localities much the 

 same. In both cases this allocation fits in exactly with the 

 facts, for the tract in question is precisely half way between 

 the disconnected habitats of Apocheima hispidaria, and 

 likewise lies midway between the extreme outliers of Phigalia 

 and its more modern derivatives. 



Phigalia, however, we have regarded as of Middle Pliocene 

 origin ; Apocheima must necessarily be assigned to later days. 

 Developing in the same lands, with the same preferences for 

 an oak diet, and under conditions not dissimilar, both journeyed 

 forth along the same paths. Making the most of its start, 

 Phigalia wandered further afield, its outposts reaching Japan 

 in the east and America in the west. Apocheima, on the other 

 hand, seems to have stopped short in Europe. 



Obviously, this lack of coincidence in the areas occupied, 

 primarily caused by the later development of Apocheima, was 

 actually brought about by interruptions in the land-bridges, 

 or rather by unfavourable climatic conditions on them when 

 Apocheima was speeding on. 



Be that as it may, Apocheima hispidaria, the less highly 

 specialised of the Apocheima forms, striking to the north-west, 

 soon after its rise (direct western movement being as we 

 know impossible), proceeded America- wards in some land of 

 high northern latitudes where now rolls an Iceberg-strewn 

 sea. Ere its goal was attained, that event, so often pictured 

 before, swept the oak-belt southward and with it the insect. 

 Not being of a very adaptable nature as regards food, no 

 lasting substitute was adopted and the earliest stages of the 

 Glacial Epoch saw it in full possession of the non-coniferous 

 forests of Central Europe. Here its stay was but temporary. 

 The piling up of the ice fields in the north was followed by the 

 sweeping of the Alpine ice to the lowlands and the oak forests 

 were obliterated, the trees surviving to perpetuate their race 

 being hurried south in two divisions, one retreating through 

 France and on to Spain and the other to the Balkan Peninsula. 



Clearly the retreat due south would afford more facilities 



Naturalist, 



