STATES OF INSECTS. (Pupa.) 277 
extrication, when become moths, from their silken co- 
coons, is not less ingenious. Those of Eviogaster lanestris 
(of which I have lately said so much,) and others, form 
oblong cocoons, which, viewed externally, you would at 
the first glance assert were of one solid piece: but on 
examining them more narrowly, you perceive one end of 
them to be a distinct lid, of a size large enough to per- 
mit the moth to issue out; and that it is kept in its place 
by a few slight threads, easily broken by pressure from 
within*. A few pages back? I mentioned a cocoon formed 
by the larva of Tortrix prasinana, of the shape of a 
boat reversed, composed of two inclined walls fastened 
together at the top and ends. In constructing this cocoon, 
it firmly glues to each other the top and one end, so as to 
form an impermeable suture; but the other end, at which 
the moth is to issue, though externally it seems as strong 
as the rest, is merely drawn close by a slender thread or 
two fastened on the inside, and easily broken from within. 
And, what is particularly singular in the construction of 
this ingenious habitation, the sides forming the end last 
mentioned, though originally requiring force to draw 
them into their required position, become so elastic as to 
close again when the moth has passed between them and 
made her escape; the cocoon preserving its usual shape, 
even when deprived of its inhabitant®. A similar cocoon 
is constructed by another leaf-rolling caterpillar, that of 
Tortrix chlorana*, Many similar proofs of contrivance 
in the construction of silken cocoons might be adduced, 
but I shall confine myself to one more only—I mean that 
* Ros. I. iv. 209. ¢. Ixiii. cexii. > See above, p. 216. 
° Bonnet, Quvr, ii, 229. 2 De Geer i1.-477. 
