CH. III.] INSECTS WHICH FORM COCOONS. 69 



apart, they could not possibly be brought together, 

 nor could the edges be made to fit closely to each 

 other, and yet the insect has neither compasses, 

 rules, nor planes, Avithout which a carpenter would 

 make but a bungling job of his cupboard doors. 

 When, therefore, these two walls or wings are of a 

 proper size, the insect, which always keeps be- 

 tween them, attaches threads to the outer edge of 

 one of them, at the lower part, which it then applies 

 to the opposite outer edge of the other ; these 

 threads are then pulled until the edges are brought 

 into contact, when it fastens them with shorter silk- 

 en threads, and in this way proceeds upwards until 

 the whole of the two edges are brought together, as 

 represented in figure B, the insect being enclosed 

 within them. 



But another difficulty here arises ; a concave, but 

 not deep space, has been formed within these walls 

 upon the bark of the twig; but the walls thus 

 brought together are flat, and, like the closed doors 

 of some oldfashioned cupboards, form an acute an- 

 gle, not only in front, but at each side, which would 

 necessarily be very inconvenient to a cylindrical 

 chrysalis within ; the insect, therefore, by repeat- 

 edly pushing against the walls when brought to- 

 gether, from within, with its head, causes them to 

 assume a convex figure. The opening which is ob- 

 served at the broadest part of the cone at the upper 

 end of the figure is also subsequently closed in the 

 same manner, and when the whole is thus comple- 

 ted, the seams are so nicely joined as to be imper- 

 ceptible ; the inside is then lined Avith a fine coating 

 of silk, and the insect undergoes its transformation 

 in security, being well protected by the great resem- 

 blance of the cocoon to the bark upon which it is 

 affixed, and of which in fact it is composed. 



Other caterpillars introduce the leaves of the 



plants upon which they feed into the structure of 



' their cocoons, and these are arranged with more or 



