430 On the Colours of certain Lepidopterous Larve. 
the larves are fed upon leaves without chlorophyll or etiolin. But 
over the general surface of the body the cuticle is very thin, and 
only contains the black spots and patches of true pigment, while the 
brown or green ground colour, derived from plant pigments, is sub- 
cuticular in position. Hence in a larva fed on pigmentless parts of 
leaves, represented in fig. 3, this latter ground colour is replaced by 
a creamy tint which is due to the uncoloured tissues of the body, 
especially the fat, and to the contents of the digestive tract. This 
creamy ground colour, combined with the spots of true pigment in 
the cuticle, produces the general greyish appearance of these larve. 
The posterior segments of the larva, painted at the same date, 
x 4 diameters, are also represented in the figure, indicating that the 
thickened cuticle of the supra-anal plate (which possessed a sharper 
outline than that represented in the figure) contains both brown 
eround colour and black spots of true pigment, while the general 
surface presents the combination of a white ground colour and dark 
spots, conferring a grey appearance. 
