SEASONAL DIMORPHISM OF LEPIDOPTERA. 251 



marking is the beginning of the pupal period, but for the ground 

 colour the end of it. Now the "marking" is only something 

 separated from the ''ground colour" in our ideas; as a matter of 

 fact it is not here, as in a picture, where there is first the drawing 

 and then the colour is laid on it ; but w^iat we call "marking" 

 is only another stripe of colour of the one layer of coloured 

 scales, which determines the colouring of the wing. "Marking" 

 therefore is genetically the same as " colouring," and biologically 

 also, in so far as they work together for a sympathetic or striking 

 colouring. I will not, however, deny that under certain circum- 

 stances colourings may appear, which are actually of different 

 origin from the pattern of colour originated in the germ-plasm ; 

 I see, for example, such a case in the black powdering of the 

 southern form of Chrysophanus phlceas, the var. eleus ; but if the 

 surface of the wings is sympathetically coloured, as is certainly 

 the case with this Selenia, then the whole pattern of colour is 

 already contained in the germ by natural selection, and makes 

 up the biological value of the colouring. To which it may 

 be added that with Selenia illiistraria the markiug of the sum- 

 mer form is exactly the same as that of the winter form, only 

 much fainter, and to some extent almost or entirely washed 

 out; it is nothing quite new as with Vanessa prorsa^ as opposed 

 to levana. On this account the changes of colour observed by 

 Merrifield would perhaps be more appropriately explained by the 

 fact that the determinant of the winter form is set free by cold, 

 but that the summer temperature following later on enables the 

 summer determinant also to become active, and that the two 

 determinants now work together and produce an intermediate 

 form. But this would be a contradiction of my view that the 

 beginning of the pupal period is actually the critical moment for 

 the double determinants contained in the germ. The questions 

 here stated can only be answered by further experiments de- 

 finitely directed to this point on as many species as possible. 



We may now at any rate go so far as to say, that the tem- 

 perature before pupation has no influence on the colour and 

 marking of the perfect insect. My experiments with pldoeas 

 already pointed to this, in so far as in this case the larvae which 

 hatched from Neapolitan eggs produced very different butterflies, 

 although the pupae only had been subjected to different tempera- 

 tures, but the larvae were all treated exactly alike. Merrifield 

 has shown for Ennomos autumnaria, that the very different tem- 

 peratures in which the larvae may be reared are without influence 

 on the colouring of the perfect insect. Therefore although, as 

 we have recently learnt, the form of the wings of the imago is 

 outlined very early in the larva,* yet the decision as to w^hich of 



'!' E. Verson, ' La formazione delle all neJla larva del Bomhyx mori,' 

 Padova, 1890; and J. Gonin, ' Kecherclies sur la metamorphose des Lepi- 

 dopteres,' Lausanne, 1894. 



