44 THE COLOURS OF ANIMALS 



caterpillar. Hence all we can see is an oval convex 

 mass of a substance resembling white cotton wool, an 

 appearance very suggestive of a cocoon (see fig. 12). 

 The caterpillar's body is almost invisible ; but on 

 looking carefully we can just make out a dim curved 

 shape beneath the white covering, just as a caterpillar 

 or chrysalis appears through the walls of its cocoon : 



PIG. 12. -The larva of Miller Moth (Aero- FIG. 13. -Thelarva of Miller Moth (Aero- 

 nyctaleporina), at rest on a birch leaf ; nycta leporina), wandering about on 



adult ; natural size. bark before forming cocoon ; natural 



size. 



furthermore, the larva is very short and thick, and thus 

 resembles the contracted state of a caterpillar before 

 turning to a chrysalis. This perfect Special Eesem- 

 blance is kept up until the caterpillar is full-fed, 

 when it wanders over the bark and finally burrows 

 in it. But a cocoon is a motionless object, and 

 the resemblance, if continued, would be fatal, for it 

 would attract attention. But as soon as the larva 



