474 Studies in the Theory of Descent. 



relatively small, and to a certain extent superficial, 

 changes, we should expect less typical transforma- 

 tions in the great majority of caterpillars which 

 live on the exterior of plants or in their softer 

 parts (most of the Micro-lepidoptera). The great 

 diversity in the forms of caterpillars depends 

 essentially upon a different formation of the skin 

 and its underlying portions. The skin is sometimes 

 naked, and can then acquire the most diverse 

 colours, either protective or conspicuous, or it may 

 develop offensive or defensive markings ; in other 

 cases it may be covered with hairs which sting, 

 or with spines which prick ; certain of its glands 

 may develop to an enormous size, and acquire 

 brilliant colours and the power of emitting stinking 

 secretions (the tentacles of the Papilionidaz and 

 Cuspidate larvae) ; by the development of warts, 

 angles, humps, &c., any species of caterpillar may 

 be invested with the most grotesque shape, the 

 significance of which with respect to the life of the 

 insect is as yet in most cases by no means clear : 

 typical portions are not, however, essentially 

 influenced by these manifold variations. At most 

 only the form of the individual segments of the 

 body, and with these the shape of the whole insect, 

 become changed (onisciform larvae of Lyccenidte), 

 but a segment is never suppressed, and even any 

 considerable lengthening of the legs occurs but 

 very seldom (Stauropus Fagi}. 

 "" [This lengthening of the true legs is mimetic accord!"'- 



