250 THE ENTOMOLOGIST. 



Bat now Merrifield,* with another Geometer with a leaf-Hke 

 cut to its wings, Ennomos autumnaria, could in Hke manner pro- 

 dace a darkening of the upper side of the ochreous moth by cold, 

 although it has only one brood in England, and also in Germany. 

 It looks as if this must still be the direct effect of cold ; still we 

 cannot maintain this without going further into the matter. It 

 might be reversion to a more darkly coloured parent form. The 

 remarkable alterations have already been above referred to in 

 passing, which Dorfmeister, Merrifield, and Standfuss obtained 

 in butterflies by the application of ice or of great heat to their 

 pupae, and it was then noted, that Dr. Dixey considered the 

 majority of these aberrations as reversions to earlier forms, and 

 that for particular cases, at any rate, he has made this very 

 probable. But this can scarcely apply to all, and some of these 

 alterations of colour may well be regarded as the direct influence 

 of temperature on the colour-chemistry of the wings. 



Now my experiments with the Neapolitan Chrysophanus 

 phloeas prove that such temperatures as create alterations slowly 

 influence the germ-plasm also, and thereby enable the alteration 

 to become hereditary ; so these direct alterations of colour by 

 the climate cannot well be entirely without significance, although 

 they certainly have less significance for the metamorphism of 

 the species of Lepidoptera, than I formerly ascribed to them 

 before the recognition that a large part of seasonal dimorphism 

 must depend upon selection. 



Perhaps the future will place us in the position of being able 

 from the critical period of the effect of temperature to draw in- 

 ferences as to the nature of the alteration. Should the view 

 given by me above be confirmed, and the observations which at 

 present stand opposed to it be explained in another way, we 

 should be in such a position ; but at present the facts are not 

 yet sufficient for it. The very carefully carried out experiments 

 of Merrifield above referred to do not yet afford any safe con- 

 clusion on the question, whether the critical time for the coming 

 into activity of one of the two double-determinants always lies 

 in the beginning of the pupal period, and whether alterations of 

 colour, which in the end proceed from the influences of tempera- 

 ture, are always to be regarded as direct alterations of the colour- 

 chemistry. 



With Selenia illiistraria the pupae of the summer brood, which 

 were iced immediately, produced winter form with dark colouring 

 and marking ; pupae of the same brood, which were iced for 

 twelve weeks and then forced at 27° C, produced a much brighter 

 moth with rather dark marking. 



Merrifield concludes from this, that the critical time for the 



- Merrifield, " Conspicuous Effects on the Markings and Colouring of 

 Lepidoptera caused by Exposure of the Pupae to different Temperature-Con- 

 ditions," Trans. Ent. Boc. Lend. 1891, p. 155. 



