240 ROMANCE OF THE INSECT WORLD CHAP. 



is protective, because the lighter larvae were far better 

 concealed on the green leaves and stems than the 

 darker ones would have been. There are species in 

 which the larvae become green when they are reared 

 among green shoots and leaves, so that the con- 

 cealment is wonderfully perfect (see Figs. 46 and 47). 



It is a still more interesting fact that the cater- 

 pillars of certain species can adjust the colour of 

 their cocoon to the environment. Of this class of 

 Variable Protective Resemblance little is known. 

 The stimulus of surrounding colour surely makes itself 

 felt on the larva, and probably the effects are pro- 

 duced through the medium of the nervous system. 

 The power of colour variation in perfect insects as the 

 result of a stimulus, in correspondence with the pre- 

 vailing tint of the district, also awaits investigation. 



The cases of ordinary protective resemblance, as 

 we have seen, can be well explained by the operation 

 of natural selection. Given the rudest resemblance 

 to their surroundings in the first place, those insects 

 which best possessed this qualification even in the 

 most minute degree, would tend to escape de- 

 struction, and their less fortunate fellows would fall 

 victims to their foes. Generation after generation 

 this selecting action would continue, until those most 

 wonderful appreciable disguises imitative of a leaf or 

 some such object had been built up and perpetuated. 

 Indefinite variation is controlled by natural selection, 

 and heredity is an important element. It is to be 

 observed that no explanation is given of the cause of 

 the original variations in the colour of the insects,; in 

 a word, no explanation is offered of the origin of 



