COLORATION IN PIERIS 201 



Brecher advances evidence which suggests that the photochemical 

 action of black, and other dark surfaces, depends upon the ultra- 

 violet rays which they reflect stimulating melanin formation, while 

 infra-red rays tend to inhibit the development of that pigment. 

 She also found that tyrosinase was less active in the blood of green 

 pupae than that contained in the blood of darkly coloured pupae. 

 Her researches present a line of approach towards the fundamental 

 nature of the phenomena observed, but further investigation is 

 obviously needed, including the influence of temperature as well 

 as light rays. 



Przibram (1922), by electrical cauterisation of the eyes of the 

 larvae, and also by decapitation, came to the conclusion that the 

 action of the light rays takes place through the eyes, since he 

 obtained the same results as in darkness, whatever the surround- 

 ings of the larvae were. Brecher (1924) confirmed these results 

 by painting the larval eyes with a transparent yellow varnish, 

 when the pupae became green in Pieris and golden in Vanessa ; 

 when blue varnish was used the pupae were darkly coloured, as 

 under blue surroundings. It would, therefore, appear that light 

 of different wavelengths exerts a differential stimulus through 

 the larval eyes on the nervous system, but the nature of the 

 phenomenon is unexplained. 



Durken (1923) and Fraulein Brecher (1923) have further 

 experimented on the influence of orange light in inhibiting the 

 development of grey and black pupae in Pieris brassicce, thus 

 allowing the green pigment to become evident. Their results are 

 in conformity with those already quoted, and they further suggest 

 that the tendency to produce green pupae is an inheritable 

 property. Larvae descended from the orange glass cultures, 

 when allowed to pupate under ordinary light conditions, gave 

 rise to more green pupae than ocqurred among the controls. 

 Durken repeated the exposure to orange-coloured rays for two 

 generations, and when the larvae finally transformed under normal 

 non-coloured surroundings, almost all the pupae were green. 

 Experiments by Harrison (1928a) afford support to the conclusion 

 that the induced green coloration is inherited. In the species 

 Pieris napi a mixed lot of eggs was obtained from six captured 



