SEASONAL DIMORPHISM OF LEPIDOPTERA. 203 



the hind wings ; but the spots 1, 2, and 3 of the costa have not 

 become smaller. Now, if the black of the costa behaves diffe- 

 rently from that on the basal part of the wing, another factor 

 must co-operate here, as I have already maintained elsewhere, 

 and sought to explain theoretically. This can only be, as it 

 appears to me, the influence which the previous history can exert 

 on any particular part of the wing according to circumstances. 

 If for a particular spot every kind of the otherwise similar ances- 

 tral determinants of the stem form were conveyed into the 

 germ-plasm, then the normal colouring can be considerably 

 interfered with by the action of an unusual temperature and 

 the way cleared for a reversion to an ancestral form or to a 

 mixed form. 



The polar variety of V. urticce also shows that with natural 

 varieties other factors co-operate besides mere climatic in- 

 fluences. The specimens of this species from Lapland are 

 clearly distinguished from the German specimens, but still the 

 difference does not lie in an important alteration of the marking. 

 Several specimens, however, of Vanessa urticce from the northern 

 island of Japan (Yezo) are known to me through the kindness 

 of Dr. Fritze, which possess a black transverse band in lieu of 

 the spots II. and 8 ; the space between these spots, with the 

 Lapland yolaris, is only somewhat flushed with black ; here a 

 broad deep black bridge is formed between both spots, similarly 

 as with the Californian Vanessa milbertii. And this variety lives 

 on the 43rd to the 45th parallel of north latitude. Can this 

 then be a direct result of the climate, which is not very different 

 from that of Southern Germany ? Or must not something else, 

 perhaps sexual selection, have co-operated with it ? Is it a 

 primitive form from which the var. polaris from Siberia and 

 Lapland has been formed by the loss of the bridge between 

 spot 11. and 8 ? or is it the other way about, and is polaris 

 striving after this var. yezoensis by gradual increase of the 

 blackish shading between II. and 8 ? These are questions, 

 which it is easier to ask than to answer, but which enable us to 

 recognise how cautious we should be in the assumption of a 

 reaction purely of temperature in a particular case. 



Among the species experimented upon by me, Pararge egeria 

 and meione present a third case of direct alteration by climate. 

 With this species, as with Vanessa urticce, it is nowhere a 

 question of seasonal dimorphism, although the species produces 

 two broods, wherever it occurs. This is simply explained by the 

 fact that it is not the pupae but the larvae of the winter brood 

 which hybernate ; the pupae, therefore, are not formed until the 

 temperature has already become almost summer-like. Now, as 

 the temperature which acts on the larvae does not influence the 

 perfect insect in colour or marking, and the conditions of tem- 

 perature, which affect the pupae of both broods, are not very 



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