164 THE ENTOMOLOGIST. 



Testing Building Material, whose Director, Prof. L. Tetmayer, 

 has assisted me in these experiments in the kindest manner. 



Firstly, warmth and cold experiments. The principal results 

 of these are dealt with in the ' Handbuch der palaearktischen 

 Gross-schmetterlinge,' and are summarised as follows : — 



Species from northern sources — that is to say, species which 

 themselves, as well as the majority of their relatives, live in 

 northern regions, and would therefore probably emanate from 

 there — give retrogressive forms by the application of cold, but 

 progressive forms by the application of warmth. 



On the other hand, species of southern origin, mostly species 

 which have penetrated from the south in a northerly direction, 

 and whose relatives are entirely, or nearly so, denizens of tropical 

 and subtropical regions, produce retrogressive forms by the 

 application of warmth, and progressive forms by the application 

 of cold. 



In all cases as yet dealt with the retrogressive and progressive 

 forms indicate : — 



1. That seasonal forms are obtained, that is, forms whose 

 appearance is constant at certain seasons of the year. Apart 

 from the well-known case of V. levana, L., and its var. prorsa, 

 L., of Dorfmeister and Weismann ; Vanessa c-album, L., can be 

 changed by cold from the first or summer generation to the 

 second or autumn generation, and the second generation partly 

 to the first by the application of warmth. We have good 

 grounds for the belief that V. c-album is a northern insect, and 

 that its autumn form is the more ancient, the summer form 

 being a recent introdaction — that is to say, the younger. This 

 would explain the fact why the first generation retrogressed, and 

 the second generation progressed by this experiment. Large 

 numbers of the summer generations of Papilio podalirius, L. 

 (Wallis), Pieris daplidice, L. (Berlin), and Polyommatiis amphi- 

 damns, Esp.* (Leipzig) produced by the application of cold the 

 forms from hybernated pupse only. 



2. Local forms can be obtained— that is, forms which in 

 certain localities are found as local races. I succeeded in 

 obtaining Vanessa urticce, L., var. polaris, Stgr., of Lapland, 

 direct from Zurich pupse by submitting them to low tempera- 

 tures, and forms approaching var. ichnusa, Bon., of Corsica and 

 Sardinia, with high temperatures. As V. urtica is also probably 

 a northern species, var. polaris would be the older, and var. 

 ichnusa the newer form. 



The change effected in the swallow-tail, P. machaon, through 

 the influence of warmth, were especially noteworthy. By special 



* The contrary was also successful with P. amphidamas, Esp., a direct 

 change of the winter generation to the summer generation being obtained in 

 the majority of cases by placing the pupae at the end of March and beginning 

 of April for eleven to fourteen days in a temperature of + 37° C. 



