DEFENCES OF INSECTS 



237 



the other part, confirming Mr. Poulton's experiments 



to the effect that the eyes have nothing to do with 



the influence. The influence of two colours did not 



produce parti-coloured pupae, as some observers had 



suggested might be the case. Had parti-coloured 



pupae been obtained, it would seem probable that the 



light acts directly 



upon the skin. 



Since they were 



not obtained, it 



would appear that 



the light affects 



the termination of 



nerves in the skin, 



" and that the 



pupal colours are 



produced through 



the medium of the 



nervous system." 



It should be es- 

 pecially noted that 

 certain dimorphic 

 pupae show not 

 the slightest trace 

 of susceptibility to 

 the surroundings. The chrysalis of the Swallow- 

 tailed Butterfly (Papilio macJiaon), for instance, appears 

 in two forms, being sometimes dark and sometimes 

 green, but these chrysalides have no power of 

 adjustment to dark and green surfaces respectively. 

 Fritz Muller, experimenting upon a South American 

 Swallow-tail {Papilio poly damns) which, like our own 



FIG. 47. The larva of Peppered Moth reared amid 

 dark-brown twigs as well as leaves. 



