224 STATES OF INSECTS. (Larva.) 
their head all round the inside of the cavity; and which, 
drying in a short time, becomes a powder that effectually 
renders it opake. ‘This is not, as might be conjectured, 
an excrement, but a true secretion, evidently intended 
for this very purpose: and, according to Reaumur, a 
similar powder, but white, derived from the varicose in- 
testines, is used by the caterpillars of Gastropacha quer- 
cifolia, &c.2 The other material, which is still more 
frequently employed, and which is occasionally mixed 
with the former, is the hair which every one has observed 
to cover so thickly the bodies of some caterpillars. This, 
after spinning a sufficient envelope, they tear, or in some 
instances cut off with their mandibles, and distribute all 
round them, pushing it with their head amongst the in- 
terstices of the silk, so as to make the whole of a regular 
thick texture. After this process, which leaves the body 
_ completely denuded, and often seems to give them great 
pain, they conclude by spinning another tissue of slight 
silk, in order to protect the forthcoming pupa from the 
surrounding prickly points. It should be observed, how- 
ever, that though many hairy larva, as those of Acro- 
nycta Aceris, Euprepia Caja, and others, employ their 
hairs in the composition of their cocoons, the rule is not 
general, several never making any such use of them. 
Nor do all that do so employ them distribute them in 
the same manner as those above described, which rarely 
attempt to arrange them in any regular position. Reau- 
mur has noticed a small hairy caterpillar that feeds on 
lichens, which is more methodical: this actually places 
its hairs upright, side by side, as regularly as the pales 
a Reaum, ii. 284. 
