VII THE COLOURS OF THE LEPIDOPTERA 141 
relations existing between larvae and their environ¬ 
ment. Mr. Poulton divides the colours of larvae into 
two classes: (1) colours due to pigments derived 
from the food, and (2) colours due to pigments 
formed by the larvae. Of the chemical nature of the 
pigments belonging to the second group we un¬ 
fortunately know nothing ; they appear to be usually 
though not invariably dark in colour, and are de¬ 
posited in the cuticle or in the epidermis. Their 
stability and their insolubility in alcohol suggest the 
possibility that they may belong to the same group 
as the dark pigments found in the adult. 
The pigments belonging to the first group are 
green, yellow, or brown and are described by Mr. 
Poulton as “ modified chlorophyll ” and xanthophyll. 
Xanthophyll, as we have already explained, is the 
lipochrome pigment which can be obtained from the 
solutions of chlorophyll formed by steeping green 
leaves in alcohol. The chlorophyll was recognised 
in the larvae solely by certain resemblances between 
the spectroscopic characters of the larval pigment 
and those of green leaves. These pigments occur 
primarily in the digestive tract, whence they seem to 
reach the blood ; while from the blood they may be 
deposited in the subcutaneous connective tissues. In 
most cases it is only when they occur in the last 
position that they are important in producing 
coloration. In his first paper (1885) Mr. Poulton 
supported his position that these pigments were 
derived from the food by a number of arguments, 
as well as by the results of spectroscopic examina¬ 
tion. More recently (1893) h e has been able to 
demonstrate experimentally that the pigments are 
