STATES OF INSECTS. (Larva.) 233 
this web without going wholly out of it. The third is 
the most curious and remarkable of all. It is nearly six 
inches long, and about four-fifths of an inch in diameter. 
It consists of a bag of thick cinereous silk web, to which 
are fastened, in a sextuple series, pieces of stick about an 
inch long, the end of one mostly resting upon the base 
of another: between each series a space of about three- 
tenths of an inch intervenes, but at the apex they all 
converge. This probably imitates the branch or stem 
of some tree or plant, in which the leaves are linear, and 
diverge but little from the stem. A label-upon it states 
its country to be New Holland. I suspect the inhabi- 
tants of the two last cocoons to be terrestrial animals : 
the first is probably a true aquatic case-worm. 
The same purpose for which the cocoons above de- 
scribed serve, is answered in the case of numerous Di- 
pterous insects, by a humble and less artificial contri- 
vance—the skin, namely, of the larva; which, as was be- 
fore observed, is never cast, but, when the insect is about 
to enter into the pupa state, assumes a different form and 
colour ; becomes of a thicker and more rigid texture ; 
and defends the included pupa, which is separate from it, 
till its exclusion. In this case the mouth of the larva is 
constantly different from that of the perfect insect, or at 
least has not with it those relations as to number and 
kind of organs, which have been observed in the mouth 
of other larvae compared with the insects that they pro- 
duce. The animal, immediately after it is clothed with 
this skin, if it is opened, exhibits only a soft gelatinous 
pulp, in the surface of which the exterior organs of the 
* See above, Vot. I. p. 67. 
