78 The Colours of Animals. 



colour, being brown in summer and white in winter. 

 So are the arctic fox and the ermine, to whom it 

 is then an advantage to be white, not to avoid 

 danger, but in order that they may be the more 

 easily able to steal unpercejved upon their prey. 



7. Many of the cases in which certain insects 

 escape danger by their similarity to plants are well 

 known ; the leaf insect and the walking-stick 

 insect* are familiar and most remarkable cases. 

 The larvae of insects afford, also, many interesting 

 examples, and in other respects teach us, indeed, 

 many instructive lessons. It would be a great 

 mistake to regard them as merely preparatory 

 stages in the development of the perfect insect. 

 They are much more than this, for external circum- 

 stances act on the larvae, as well as on the perfect 

 insect : both, therefore, are liable to adaptation. 

 In fact, the modifications which insect larvae under- 

 go may be divided into two kinds developmental, 

 or those which tend to approximation to the mature 

 form ; and adaptational or adaptive, those which 

 tend to suit them to their own mode of life. 



8. It is a remarkable fact, that the forms of larvae 

 do not depend on those of the mature insect. In 

 many cases, for instance, very similar larvae produce 

 extremely dissimilar insects. In other cases, similar, 

 or comparatively similar, perfect insects have very 



* These are insects which inhabit warm regions, and they are so 

 called because they so strikingly resemble leaves, and bits of stick, 

 respectively. 



