142 
COLOUR IN NATURE 
CHAP. 
absent in the larvae when they do not occur in the 
food. 
Mr. Poulton’s Experiment 
For the purpose of this experiment Mr. Poulton 
obtained a large number of the eggs of Tryphcena 
pronuba , the Yellow Underwing. Immediately after 
hatching, the larvae were divided into three sets. The 
first set was furnished with the yellow etiolated 
leaves from the heart of a cabbage, the second with 
the white midribs from the same leaves after the 
removal of the whole of the blade, and the third with 
the ordinary green outer leaves of the cabbage. All 
the specimens were kept in the dark, in order to 
avoid the risk of the conversion of the etiolin into 
chlorophyll, and were only brought to the light to be 
examined and fed. The larvae in the first and third 
sets developed well and showed almost identical 
colouring. In the early stages they were mostly pale 
green, but as development proceeded the colour 
deepened to dark green, and before maturity was 
reached most had turned dark brown. In addition 
to the conspicuous green or brown pigment in the 
connective tissue, or in the epidermis, the cuticle 
showed spots and patches of dark pigment, which 
were most conspicuous in the regions where the cuticle 
was especially thick, such as the head, the true legs, 
etc. This pigment is called by Mr. Poulton “ true ” 
pigment, and as is shown by the condition of the 
second set of larvae is not dependent for its formation 
upon the presence of pigment in the food. 
The larvae in this second set developed badly and 
out of a large number only one reached complete 
