162 THE ENTOMOLOGIST. 



Firstly, the Temperature Experiments. — The temperature ex- 

 periments which concern us here (searching temperature experi- 

 ments in other directions are mentioned in my ' Handbuch der 

 palaearktischen Gross-schmetterlinge,' pages 137-153) have been 

 chiefly devoted to the pupal stage, and may therefore be con- 

 sidered as a continuation and supplement of the methodical 

 experiments first made by G. Dorfmeister, Aug. Weismann, and 

 W. H. Edwards in the sixties and seventies. 



To the experiments begun b}' others must be added experi- 

 ments made by me in quite another direction, relating to in- 

 heritance of the new characters acquired by these experiments. 



The studies of the three gentlemen in question related chiefly 

 to the appearance in nature of Wallace's so-called " Seasonal 

 Dimorphism." What is seasonal dimorphism? The fact that 

 species which attain the imago stage twice or more during 

 the course of a year generally exhibit marked differences in 

 the size, shape, or colour of the imagines of these two genera- 

 tions. 



The most noteworthy example is to be found in our smallest 

 Vanessa, the so-called map-butterfly, V. levana, L., in which the 

 difference between the imagines from hybernated pupae and those 

 of the summer brood are so great that the two forms were for a 

 long time considered to be two different species. This insect 

 was therefore one of the first to be experimented with by Dorf- 

 meister and Weismann. Weismann, to whom we owe the best 

 work on this subject, which appeared in 1875, placed the summer 

 pupae of V. levana for twenty-four weeks in an ice safe or ice 

 cellar, and winter pupae in a conservator}^ with a temperature of 

 + 15° to + 30° C. By this means the summer form was changed 

 directly to the winter form ; but, on the other hand, it was found 

 to be very much more difficult to change the winter form by 

 warmth to the summer, and in most cases it was an entire 

 failure. Weismann concluded therefore that the species was a 

 northern one, and that the winter form T". levana was the oldest 

 and most constant, and the summer form — var. prorsa — a later 

 innovation, that is to say, only recently introduced into the life- 

 history of the species. 



This supposition is probably correct, as the species no doubt 

 emanates from Northern Asia, where there are to be found four 

 nearly related species, the only living relatives of this insect on 

 the earth ; and, moreover, V. levana itself is found there, in some 

 places actually with only one generation in the year from hyber- 

 nated pupae — for example, at Nicolajefsk and Chabarofka. Var. 

 prorsa is therefore a recent introduction, which, by lowering the 

 temperature of the pupal stage, can be immediatel}' made to 

 resume its ancient characters. The "phylogenetic" — or, we may 

 well say, the younger — form can be directly changed to the 

 older. Further experiments with Papiliu ajax, L., Pieris napi. 



