40 THE COLOURS OF ANIMALS 



and the green contents of the alimentary canal. The 

 dark shading is the only part of the appearance caused 

 in the usual way by superficially placed pigment. 

 Nearly all the colours of this animal are non- 

 significant in many other insects. 



Eeply to objection that methods of concealment 

 would certainly be detected 



It has been sometimes objected that these methods 

 of concealment cannot be intended as a means of 

 defence, because insect-eating animals would be 

 sharp-sighted enough to penetrate the disguise. Of 

 course, the progressive improvement in the means 

 of concealment has been attended by a corresponding 

 increase in the keenness of foes, so that no species 

 can wholly escape. But so long as a well-concealed 

 form remains motionless, it is easy to prove by 

 experiment that enemies are often unable to recog- 

 nise it. Thus I have found that the insect-eating, 

 wood-haunting Green Lizard (Lacerta viridis) will 

 generally fail to detect a ' stick caterpillar ' in its 

 position of rest, although it is seized and greedily 

 devoured directly it moves. The marvellous resem- 

 blance of Cleora lichenaria (see p. 35) even deceived 

 one of these lizards after the larva had moved more 

 than once. The instant the caterpillar became rigid 

 the lizard appeared puzzled, and seemed unable to 

 realise that the apparent piece of lichen was good to 



