196 



PS 2 LHE. 



[ December 1891. 



Cocoon. The larvae turn bluish and enter 

 the ground to pupate, forming a cell lined 

 with silk. 



Pupa. Cylindrical, rounded at both ends, 

 long in comparison with its width ; uniform 

 shiny black. The wing cases are wrinkled. 

 The cremaster consists of two very short 

 spines, some distance apart, and projecting 

 almost laterally from the last segment, which 

 nevertheless hold to the silken web with 

 considerable firmness. 



Length 26 mm. ; width S mm. 



Food plants. Poplar (Populus) and willow 

 (Salix). 



Larvae from Yosemite Valley, Cal. Two 

 broods a year, the winter being passed in the 

 pupa state. 



Temperature experiments. 

 24 Vernon Terrace. Brighton. 



10 Sept., iSgi. 



Editor of Psyche. Dear Sir: — I have to 

 thank you for the number of Psyche contain- 

 ing an abstract of one of my papers on the 

 temperature experiments I have been making 

 on some Lepidoptera. Will you permit me 

 to point out a typographical error which 

 maybe misleading. In "general conclusion" 

 no. 5, the figures "7" and "5" have been trans- 

 ferred, making my figures "57°" read as "75 ." 

 I may perhaps add that in order to bring out 

 the full deep colouring in the spring emer- 

 gence of illustraria, a somewhat lower tem- 

 perature than 57 seems necessary, though 

 that 57 is very effective. I find both emer- 

 gences of all three of the English Selenias 

 affected by temperature in the pupal stage, in 

 colour, — as to markings I am not yet quite 

 sure as regards lunaria and illunaria. 



I am very glad you have seen fit to publish 

 the experiments in America. I have always 

 thought a country with such an abundance of 

 Lepidoptera and such extremes of heat and 

 cold would be especially productive of ma- 

 terials for such experimentation. Your dis- 

 tinguished naturalist, Mr. W. II. Edwards, 

 has done much, and indeed I have onlv en- 



deavoured to follow in his footsteps and work 

 out results that he has not been able to follow 

 out. We want such experiments also on 

 single brooded species, some of which (e. g. 

 Ennomos autumnaria) are certainly affected ; 

 and as to these it remains to be ascertained 

 whether Prof. Weismann's theory applies (I 

 by no means say it does not). Then the 

 pupal period when the application is effective 

 wants ascertaining. I have reason to think 

 that (as in the Ajax experimented on by Mr. 

 Edwards) the earliest stage is the sensitive 

 one, and this makes it difficult to get in Eng- 

 land American pupae in the proper stage. 

 Hoping that some of your readers will take 

 up this very interesting question- — which will 

 offer them the compensation for their labours 

 certainly of presenting them with some beau- 

 tifully coloured and probably not before seen 

 varieties, and thanking you, I beg to remain, 

 Yours very truly, 



F. Merrifield. 



Choice of food. — In Psyche for October, 

 page 166, is a note with the above title con- 

 cerning Platysamia ceanothi. The habit 

 mentioned does not appear abnormal when 

 the species is observed in its native country, 

 as many, if not most species in California 

 seem to prefer the tender leaves at the ends 

 of the twigs. This is true, not only of Bom- 

 bycids, but of many butterflies. It is, prob- 

 ably, due to the fact that the leaves of many 

 of the native trees become quite hard when 

 mature, as for example, the live oak upon 

 which the larvae of Thecla grunus feed. 

 These larvae are unable to eat the nearly 

 mature leaves, anil starve if not furnished 

 with growing tender ones. The principal 

 food plants of P. ceanothi as observed by me 

 in Yosemite were Ceanothus integerrimus 

 and Rhatnnus calij r or 'nica. The leaves of the 

 former are very thin and tender, even when 

 old, and the larvae readily ate them ; of the 

 latter, they preferred the young leaves at the 

 ends of new shoots. 



Harrison G. Dyar. 



