VII 
THE COLOURS OF THE LEPIDOPTERA 
M3 
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, 
