STRICTLY INCOG. 59 



representations of the soft shadow cast by a rib or vein, and 

 the local colour is precisely what a painter would have had 

 to use in order to produce the corresponding effect. The 

 shadow of yellowish green is, of course, always purplish 

 or lilac. It may at first sight seem surprising that a 

 caterpillar should possess so much artistic sense and dex- 

 terity ; but then the penalty for bungling or inharmonious 

 work is so very severe as necessarily to stimulate his imitative 

 genius. Birds are for ever hunting him down among the 

 green leaves, and only those caterpillars which effectually 

 deceive them by their admirable imitations can ever hope 

 to survive and become the butterflies who hand on their 

 larval peculiarities to after ages. Need I add that the 

 variations are, of course, unconscious, and that accident in 

 the first place is ultimately answerable for each fresh step 

 in the direction of still closer simulation ? 



The geometric moths have brown caterpillars, which 

 generally stand erect when at rest on the branches of trees 

 and so resemble small twigs ; and, in order that the resem- 

 blance may be the more striking, they are often covered with 

 tiny warts which look like buds or knots upon the surface. 

 The larva of that familiar and much-dreaded insect, the 

 death's-head hawk-moth, feeds as a rule on the foliage of 

 the potato, and its very varied colouring, as Sir John Lub- 

 bock has pointed out, so beautifully harmonises with the 

 brown of the earth, the yellow and green of the leaves, 

 and the faint purplish blue of the lurid flowers, that it can 

 only be distinguished when the eye happens accidentally to 

 focus itself exactly upon the spot occupied by the 

 unobtrusive caterpillar. Other larvae which frequent 

 pine trees have their bodies covered with tufts of green hairs 

 that serve to imitate the peculiar pine foliage. One queer 

 little caterpillar, which lives upon the hoary foliage of 

 the sea-buckthorn, has a grey-green body, just like the 



