232 STATES OF INSECTS. (Larva.) 
monly form their cocoons of the substances I have indi- 
cated ; but when by any cause they are prevented from 
access to them, they often substitute such other materials 
as are at hand. Reaumur fed a larva that formed its 
cocoon of minute fragments of paper, which with its 
mandibles it had cut from the piece that covered the 
glass vessel that contained it*: and the same circum- 
stance happened to Bonnet. 
Upon a former occasion I described to you the cases 
of various kinds formed and inhabited by the insects of 
the Zrichoptera Order, commonly called case-worms?. 
As these serve for the pupa as well as the larva, they 
may be regarded as a kind of cocoon. I shall not re- 
peat here what I then said; but having purchased from 
the collection of the late Mr. Francillon some that seem 
to belong to this or some cognate tribe, that are of a 
curious construction, [ shall give you some account of 
two or three of them in this place. The first is not 
quite three inches long, of a sublanceolate shape, but 
rather widest towards one end. It consists of an in- 
ternal tough and thick bag or cocoon, of a silk resem- 
bling fine wool of a dirty white colour, which is closely 
covered transversely by pieces of the stalk of a plant, 
about three-fourths of an inch in length, and crossing 
each other at an obtuse angle. The next is thicker and 
shorter: the internal bag is just covered with small frag- 
ments of wood like sawdust; over these are fastened ir- 
regularly, short stout pieces of a pithy stick or stalk, and 
the whole is clothed with a very close-woven ash-co- 
loured web. It seems difficult to conceive how the in- 
closed animal could contrive to cover her habitation with 
* Reaum. i. 540. > See above, Vor: I, 464—. II. 261. 
