278 THE CAUSES WHICH 



being less bright in colour.^ On the Continent Dr. Vitis Graber 

 speaks of three forms of this butterfly which are seasonal in their 

 appearance. He says there is found in Germany a summer and 

 winter variety; that the former in warmer Italy becomes the 

 winter form^ and that this in tm-n there produces a new and more 

 southern summer form. 



In the glacial epoch, when the summers were, there can be 

 little doubt, shorter, we on reflection perceive many insects would 

 appear alone in their spring forms in the Northern Hemisphere, 

 and these, supposing distribution constant, on the advent of 

 more genial conditions would generate their present summer 

 varieties. Nor is this subject theoretically sterile. Let us 

 suppose the case of Araschnia Prorsa. If we regard the form, 

 colour, venation, and antennae, the usual criterion of butterfly 

 classification, we seem to witness in its spring variety, not alone 

 a form of the glacial epoch, but a further passage back from the 

 Red Admiral family to the stronger angular- winged Fritillaries, 

 that yet approximate them in habit and form of the larva. 

 Another minor link between the Red Admiral and Painted Lady 

 was long ago figured by the Rev. Mr. Bree, as found on the 

 flanks of the Himalayas ; and could we so proceed to trace in all 

 the minor transitions and affinities, we might at length positively 

 affirm the Vanessidi are in a state of differentiation, and a recent 

 group ; and then, as evidence of this, we might allude to the exist- 

 ing distributive migrations of Painted Ladies and Camberwell 

 Beauties as proving an active dissemination of the species. 

 Actually we find evidence of general laws appertaining to the 

 moulding and selection of varieties lingering in operation along 

 the limits of migrative distribution. Here species of all orders 

 betray the impress of melanochroism and leucochroism.f Dark, 

 suffused, or colourless varieties of moths, with confluent markings, 

 meet our view in the cloudy mountainous tracts of Scotland, 

 Ireland, the Isle of Man, and north-western counties, where 



* See "British Butterflies," "Naturalist's Library," Stainton's "British 

 Butterflies," Coleman's "Brit. But.," Entomologist'' s Monthly Magazine, 

 Vol. IV., pp. 73—77; Vol. XV., pp. 241—244. 



t E. Birchall, F. Buchanan White, M.D., W. A. Forbes, E. K. Eobinson, Dr. 

 Jordan, and others ; Ent. Mon. Mag. and Entomologist for 1876 and 1877 

 respectively. 



