140 
COLOUR IN NATURE 
CHAP. 
development of optical colours, it is almost unnecessary 
to add that optical colours are almost always absent 
from the larva, however brilliant they may be in 
the adult. These statements refer especially to the 
Lepidoptera where the contrast between the two 
parts of the life-history is very marked. It may also 
be noted that caterpillars are free living forms, more 
or less completely exposed to air and sunlight, and 
we know that, whatever be the explanation of the 
fact, this mode of life tends to favour the develop¬ 
ment of pigment. We are thus justified in selecting 
the Lepidoptera as a suitable group with which to 
begin the study of the colour phenomena of insects. 
Both stages of the life-history frequently display 
beautiful coloration, so that the contrasts between 
the pigments of larvae and adults present themselves 
here in the most vivid form. 
Pigments of Caterpillars 
Butterflies and caterpillars are such familiar forms 
that we need not discuss their characters, either of 
structure or of coloration, but may pass at once to 
consider their pigments. 
It is remarkable that in spite of the attention 
which has been directed to the colours of the Lepi¬ 
doptera very little is certainly known of the chemical 
nature of the pigments of caterpillars, and this in 
spite of the fact that, as has been already mentioned, 
there are several painstaking researches on the 
colouring - matters of butterflies’ wings. What 
information we have is mostly due to Prof. E. B. 
Poulton, who has experimented especially on the 
