THE DRAMA OF LIFE 31 



fall far short of the tartan standard. We have inserted 

 two illustrations which show how extraordinarily close the 

 approximation may be. 



The protective value of a colour-resemblance between an 

 animal and its surroundings is probably increased when the 

 form and pose of the creature is like something else. We 

 do not, however, know very much in regard to the degree 

 of attention which the enemies of these protected animals 

 pay to form. As many animals appear to be alert in de- 

 tecting movements of their prey, there will be an advantage 

 if the latter are shaped like other things. A walking-stick 

 insect that is creeping or swaying about on a twig, will be 

 less likely to be seen as a moving object because of its 

 strong form-resemblance to a group of twigs. 



Here we have the well-known cases of butterflies like 

 leaves, of caterpillars like little twigs, of spiders like lichens, 

 and so on. It is interesting to notice that the perfection 

 of the resemblance is often due to combination of items. 

 Thus in the famous case of Kallima, which is like a pendent 

 withered leaf when it settles down, usually head down- 

 wards, on a branch, there is similarity in colouring, there is 

 resemblance in shape, the mid-rib and veins of the leaf are 

 counterfeited by the nervures of the wings, the likeness 

 is heightened by marks on the wings which look like 

 fungus marks on the leaves, and so on. Moreover, in 

 Kallima there is much individual variation in the markings 

 on the under surfaces of the wings, ' simulating all degrees 

 of decay and discoloration and fungus attack '. It seems 

 reasonable to suppose that this variability of pattern is 

 even more effective than if the Kallima were tied down to 

 resembling only one kind of withered leaf. 



Subtlest of all these misleading resemblances to other 



