96 
INTRODUCTION. 
be enclosed in two separate cocoons. An example 
of this may be seen in the Yellow Tussock-moth 
f Dafi/chira pudihunda, ). 
The perfect insect extricates itself from the pupa- 
case neai'ly in the same way as butterflies ; but the 
majoritj’ have the additional task awaiting them of 
making their way through the walls of the cocoon. 
The firm consistence of the latter, in many instances, 
may reasonably be supposed to render this a matter 
of no easy accomplishment to creatures destitute of 
jaws or other instmments for eroding hard sub- 
tances; and unless the difficulty were provided 
against by prospective wisdom, the structures which 
they fabricate with so much skill and labour to 
protect them during their state of repose, Avould 
often prove their tombs. It is sometimes the moth 
tliat is furnished with the means of effecting her 
oivn liberation, and in other cases it is provided for 
by the caterj)illar, through some peculiarity in the 
construction of the cocoon. Of the former descrip- 
tion are ,jlhe puss-moth, and several other lands, 
which ate proidded with an acid secretion, ivhich 
they disjiihargc on the end of the cocoon from which 
they desire egress, and by its solvent power the com- 
pact wall soon loses its cohesion and gives way to 
the slightest pressure. Others possess the means of 
breaking the threads at one end, employing for that 
purpose, according to Reaumur’s opinion, the minute 
facets of the eyes, which are the only hard organs 
in the head, after the manner of a file. Generally, 
hoAvever, the texture is loosened by some solvent 
