32 THE COLOURS OF ANIMALS 



deeper layers beneath are brown or green, or mixed 

 brown and green ; these tints become visible over a 

 large part of the surface, owing to the breaking 

 away of the thin layer. Hence the colour of the 

 branches is brown or green, mottled with grey, and 

 not only are these the exact tints of the larva, 

 but the way in which the colours are blended is 

 precisely similar in the animal and the plant. The 

 marvellous fidelity with which the details are thus 

 reproduced, probably implies that the relation between 

 the larva and this species of food-plant is extremely 

 ancient. It will be shown below that this caterpillar 

 can also adjust its colour to that of its individual 

 surroundings, so that it would become greenish if it 

 passed its life among young green shoots, and brown 

 if it lived upon the older twigs. It is altogether one 

 of the most perfectly concealed forms in existence. 



When, however, such * stick caterpillars ' are 

 young, they do not sit upon the branches, but upon 

 the leaves of their food-plant, and the twig-like 

 attitude would then be inappropriate, for we do not 

 see twigs projecting from leaves. In some cases the 

 caterpillars are green (e.g. Ephyra omicronaria) , and 

 so possess a general harmony with the colour of the 

 surface behind them ; but in other cases they are 

 brown, and then the attitude is often modified into 

 a different form of Special Eesemblance. The 

 caterpillar twists itself into a very irregular spiral 

 (e.g. Ephyra pendularia, &c.), or into an exceedingly 



