88 



Sierra Club Bulletin. 



The great mountain chains of Europe run east and west 

 (instead of north and south as in North America) and so when 

 the ice-sheets of the Glacial Epoch swept southward hosts of 

 species of plants and animals were crushed out of existence 

 between the ice and the mountain barriers. A few species, 

 more plastic and adaptable than the others, became modified 

 sufficiently rapidly to the Arctic conditions to avoid extinc- 

 tion. From them the present-day fauna and flora of Europe 

 have largely descended. 



In the light of this probable evolutionary relationship of the 

 warm weather butterflies of Europe to their cold weather 

 forms, and in the further light of the famihar so-called "bio- 

 genetic law" of Hseckel and Fritz Miiller which declares that 

 each individual of a species passes in its personal development 

 from egg cell to adult, through a swift and incomplete but 

 suggestively revealing recapitulation of the ancestral develop- 

 ment, or evolution, of the species to which it belongs, Fischer 

 made the hypothesis that the southern varieties of the mourn- 

 ing-cloak were the descendants of the northern varieties, or, 

 more precisely, that all the varieties were the successive de- 

 scendants from the most northern or truly Arctic form, which 

 could be looked on as the persisting Glacial Epoch form itself. 

 If this were true, and the biogenetic law is true, he argued 

 that the reproduction of a glacial time climate during the de- 

 velopment of a southern mourning-cloak ought to arrest its 

 development at a glacial time stage, and a northern variety 

 should issue from the chrysaHd of a southern individual. As 

 a matter of fact Fischer was able, after some experimenting, 

 to produce at will, by proper refrigeration of the chrysalids 

 of southern (Italian) mourning-cloaks, almost any one of the 

 northern forms even to the most northern or Arctic one itself. 

 Since then other investigators have tried similar and modified 

 experiments with other species, and their results have on the 

 whole clearly substantiated Fischer's hypothesis. It is true 

 that low temperatures tend to produce, whatever the ancestry 

 of the individual, a darkening of color and certain changes in 

 pattern. But this directly environmental effect need not be 

 confused with the effect of an arrest of development at an 

 earlier ancestral stage. For the exact reproduction of the color 



