120 ACQUIRED CHARACTERS sec. 



female of I'rorsa (Fig. 6). But as there are many more 

 intermediate forms than those figured by AVeismann, this 

 explanation requires furtlier confirmation. Afterwards Prorsa 

 chrysalids were placed by AVeismann in a temperature of 

 0°-l°.25 C. in the ice-chamber : out of twenty butterflies, fifteen 

 now changed into Porima, and amomj^ these were three which 

 w^ere almost indistin<^uishable from Levana. Five remained 

 unaffected by the cold and emerged as the summer form l*rorsa. 



Dorfmeister had never applied such low^ temperatures, and 

 had only succeeded in obtaining Porima. 



The converse experiment of Weismann to rear Prorsa from 

 Prorsa by raising the temperature succeeded, among forty 

 chrysalids which were kept in a forcing-house at 15°- 31° 

 C, only with four, of which three were Prorsa and one Porima ; 

 all the rest produced Levana in the next spring. 



The majority of the species of our white butterflies 

 (Pierid?e) show very strikingly a winter and a summer form. 

 In the winter form of Pieris Napi the roots of the wings are 

 much powdered on the upper side. In this case Weismann, 

 by keeping the chrysalids of the progeny of the winter form 

 three months in the ice- cellar and allowing them to emerge 

 in the hothouse, obtained perfect winter forms. But there is 

 a variety of P. napi wiiich lives in the Swiss Alps, in the Jura, 

 and in the polar regions, and wiiich can be described as a 

 very dark form of the winter variety of Napi : P. Bryonire. 

 The male of Bryonire is almost exactly similar to the ordinary 

 winter form of ISTapi, from wiiich the female differs by the 

 gray -bro war powdering of the entire upper surface. In the 

 polar regions BryonioB is the only form of Napi ; in the Alps 

 (excepting some isolated regions) it is mixed with the or- 

 dinary Xapi. I agree witli AVeismann that Bryonife 

 must be the ancestral form of Napi, basing my opinion on 

 the fact that, as "VVeismann's figures show, a series exists 

 from the female of the former as starting-point through 



