UNDER THE BARK. 51 



themselves so well that they need a practised eye to 

 see them, and even though the greatest care be taken 

 are often accidentally destroyed. It is extremely pro- 

 voking, after selecting an apparently safe spot for the 

 chisel, to see a white creamy fluid run along the blade, 

 and then to know that the tool has passed through 

 the body of a chrysalis which has hidden itself so 

 cleverly as to escape observation. 



The most successful of these hiders is the Puss 

 Moth (Cerura vinula), the chrysalis of which lies 

 hidden in a singularly ingenious cocoon. When the 

 caterpillar is full fed it crawls to the trunk of the 

 tree and looks about for a crevice in the rough bark. 

 Into this crevice it insinuates itself, and begins at 

 once to nibble the bark into tiny chips, which it 

 fastens together with the silk-fluid discharged from its 

 spinnerets, and so makes a cocoon which completely 

 shelters it. Owing to the materials of which the 

 cocoon is made, it exactly resembles the bark and can 

 scarcely be distinguished from it, and as the caterpillar 

 took care to retire into the crevice before spinning, the 

 surface of the cocoon does not project beyond that of 

 the bark in general. Very often when the eye fails in 

 detecting a cocoon the touch succeeds, the material of 

 the cocoon being soft ; but this is not the case with 

 the Puss Moth, whose cocoon is much harder than the 

 bark of which it was made, the silk-fluid forming a 

 wonderfully firm and tough cement. 



As for woodlice, millipedes, armadillos, and Genti- 

 le 2 



