OAK-BARK CATERPILLARS. 173 



mathematical precision, that they fit exactly when they 

 are afterwards brought into contact. As soon as the little 

 architect has completed these walls, which resemble very 

 much the feathers of an arrow, it proceeds to draw them 

 together in a manner similar to that which the leaf- rolling 

 caterpillars employ in constructing their abodes, by pulling 

 them with silken cords till they bend and converge. Even 

 when the two longest sides are thus joined, there is an 

 opening left at the upper end, which is united in a similar 

 manner. When the whole is finished, it requires close 

 inspection to distinguish it from the branch, being formed 

 of the same materials, and having consequently the same 

 colour and gloss. Concealment, indeed, may be supposed, 

 with some justice, to 'be the final object of the insect in 

 producing this appearance, the same principle being ex- 

 tensively exemplified in numerous other instances. 



