VII THE COLOURS OF THE LEPIDOPTERA 143 



maturity. This was probably due to the fact that 

 the cut mid-ribs dried up rapidly and rendered it 

 difficult for the larvae to obtain sufficient food, 

 especially in the early stages when the mandibles 

 were weak. The larvae in this set were throughout 

 of a pale cream colour with no trace of green tint, 

 but with the cuticular markings quite distinct ; the 

 cuticular pigment being as usual most conspicuous 

 in the parts of the body where the cuticle was 

 thickest. The single larva which attained maturity 

 had, therefore, cuticular pigment developed as fully 

 as usual, but was otherwise quite colourless. 



From this experiment Mr. Poulton draws the 

 natural conclusion that the green or brown ground- 

 colour of these larvae is produced by modified pig- 

 ments derived from the food, and is dependent for 

 its production upon the presence of these pigments 

 in the food, while the dark cuticular pigment is not 

 so dependent. Further, as the colour of the larvae 

 fed on yellow leaves is the same as that of larvae fed 

 on green leaves, it would seem that the larvae can 

 transform the yellow pigment into a green one. 

 The exact nature of this green pigment is still 

 uncertain ; it is unlikely that it is chlorophyll. The 

 brown colour is probably the result of an oxidation 

 of the green pigment By developing control speci- 

 mens in the light, Mr. Poulton found that the only 

 difference produced by the absence of light was the 

 assumption by the larvae of a brown ground-colour 

 before reaching maturity, while larvae developed in 

 light usually remained green till maturity. 



Although there has been relatively little experi- 

 mentation, there is, according to Mr. Poulton, 



