282 STATES OF INSECTS. (Pupa.) 
to tremble for the fate of the moth incarcerated in such 
an impervious dungeon—but without cause: what an 
aqueous solvent cannot effect, an acid is competent to ; 
and with a bag of such acid our moth is furnished. The 
contents of this she pours out as soon as she has forced 
her head through the skin of the chrysalis, and upon the 
opposite end of the cocoon. The acid instantly acts upon 
the gum, loosens the cohesion of the grains of wood, and 
a very gentle effort suffices to push down what was a mi- 
nute ago so strong a barrier. How admirable and effec- 
tual a provision! But there is yet another marvel con- 
nected with it. Ask a chemist, of what materials a vessel 
ought to be to contain so potent an acid: he will reply, 
—of glass. Yet our moth has no glass recipient: her 
bottle is a membranous bag; but of so wonderful a fabric 
as not to be acted upon by a menstruum which a gum, 
apparently of a resinous nature, is unable to resist! ‘This 
fact can only be explained by the analogous insensibi- 
lity of the stomach to the gastric juice, which in some 
animals can dissolve bone,—and it is equally worthy of 
admiration. In both cases, the vitality of the membra- 
nous or fleshy receptacle secures it from the action of 
the included fluid ; but Aow—who shall explain ? 
Ordinarily it is the moth that breaks the cocoon; but 
in the goat-moth and many Tortrices it is the pupa it- 
self that performs the work, either wholly or partially. 
The pupa of the former is for this purpose furnished 
with sharp points upon the head, capable of effecting 
this object*. The locust-moth, another species of Cossus 
(C. Robinia), whose history has been admirably detailed 
* Lyonet 16. 
