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 



