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INTRODUCTION. 
The history of insects, fruitful as it is in all its 
branches, in instances of nice adaptations and in- 
genious mechanism, presents few topics more de- 
serving of consideration than are afforded by the 
proceedings of these caterpillars when they change 
their skin, and when they prepare to enter upon that 
dormant state which precedes the development of the 
perfect fly. The proximate cause of the moulting 
or change of skin, is the internal growth of the body, 
which thus becomes too bulky for the envelope in 
which it is enclosed. The latter can scarcely bo 
said to grow, hut is merely capable of being dilated 
to a certain point, after which it offers so much re- 
sistance to the expansion of the enclosed animal, 
that it becomes necessary to throw it off entirely. 
It must be evident, however, that it is no easy task 
to withdraw the body from a shell in which every 
separate limb and articulation is closely encased, 
without any assistance being derived from without. 
This, however, the animal accomplishes so adroitly, 
that the cast-off skin appeal's almost entire, and even 
retains all the spines and other appendages with 
which it may have been furnished. The operation, 
which seems to be a painful one, and even at times 
attended with fatal consequences, is thus described 
by Reaumur : — 
A day or two before the critical moment arrives, 
the caterpillars cease to eat, and become very inac- 
tive, usually remaining stationary on a single spot. 
They select some place where they may he in greater 
