IV VANESSA PRORSA AND VANESSA LEV AN A 119 



Such causes were assumed by Weismann for the origin of 

 season-dimorphism, i.e. the formation of winter and summer 

 forms pf animals. 1 He tried accordingly, by raising the 

 temperature in winter, to rear Prorsa directly from the 

 offspring of Prorsa, and conversely, by lowering the tempera- 

 ture in summer, to rear Levana directly from the brood of Levana. 

 Similar experiments had already previously been made by 

 the Styrian entomologist Georg Dorfmeister. It seems, how- 

 ever, that such experiments have been even more widely 

 made, for an acquaintance told me that as a boy he had 

 practised the same thing with his companions successfully at 

 his home in Darmstadt, and indeed on Vanessa Levana and 

 Prorsa. Weismann put chrysalids of Vanessa Prorsa, which 

 he had reared from the caterpillars of butterflies which 

 emerged in April, into an ice-box with a temperature of 10- 

 12. 5 C. This temperature, however, was not low enough 

 to produce Levana again ; but the experiment succeeded so 

 far " that instead of the Prorsa form to be expected under 

 ordinary conditions most of the butterflies emerged as the so- 

 called Porima, i.e. as an intermediate form between Prorsa and 

 Levana, occasionally observed in nature, which possesses more 

 or less of the markings of Prorsa, but still mingled with much 

 of the yellow of Levana." 



As already remarked, the Levana, not the Prorsa, is the 

 original form. Weismann's figures of this single case again 

 seem to give support to my view that the males, as a rule, are 

 a stage in advance in evolution, and that therefore their 

 characters indicate those of the variety or species which 

 follows next in evolution. The male in the Levana figured 

 by Weismann in Fig. 1 has the greatest likeness to the 

 female Porima which passes through its male (Fig. 3) into the 



1 I would suggest instead of the word season - dimorphism, first used by 

 Wallace, which is in every respect monstrous, the word hora-dimorphism, or the 

 shorter expression season-variation. 



