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4a NATURAL HISTORY. 
to caft forth the internal coat of their inteftines with their food, in the 
changes which they fo frequently undergo. But the inteftines take up 
but a fmall part of the animal’s body, if compared to the fatty fub- 
ftance in which they are involved. This fubftance changes its colour 
when the infeét’s metamorphofis begins to approach; and from white 
it is ufually feen to become yellow. If to thefe parts, we add the ca- 
terpillar’s implements for fpinning, (for all caterpillars fpin at one 
time or another) we fhall have a rude tketch of this animal’s confor- 
mation : however we fhall referve the defcription of thofe parts, till we 
come to the hiftory of the filk-worm, where the manner in which thefe 
infeéts {pin their webs, will moft properly find place. 
The life of a caterpillar feems one continued fucceflion of changes $ 
and it is feen to throw off one fkin only to aflame another; which alfo 
is divefted in its turn; and thus for eight or ten times fucceffively. 
We muft not, however, confound this changing of the {kin with the 
great metamorphofis which it is afterwards to undergo. The throw- 
ing off one fkin, and affluming another, feems, in comparifon, but a 
flight operation among thefe animals: this is but the work of a day; 
the other is the great adventure of their lives. Indeed, this faculty of 
changing the fkin, is not peculiar to caterpillars only, but is common - 
to allthe infe&t kind; and even to fome animals that claim ahigher rank 
in Nature. We have already feen the lobfter and the crab out-grow- 
ing their firft fhells, and then burfting from their confinement, in order 
to aflume a covering more roomy and convenient.» It is probable that 
the loufe, the flea, and the fpider, change their covering from the 
fame neceffity ; and growing too large for the cruft in which they have 
been for fome time inclofed, burft it for another. This period is pro- 
bably that of their growth; for as foon as their new fkin is hardened 
round them, the animal’s growth is neceflarily circumfcribed, while it 
remains within it. With refpe& to caterpillars, many of them change 
their tkins five or fix times in a feafon; and this covering, when caft 
off, often feems' fo complete, that many might miftake the empty 
fkin for the real infeé@t. Among the hairy caterpillars, for inftance, 
the caft fkin is covered with hair; the feet, as well griftly as mem- 
braneous, remain fixed to it; even the parts which nothing but a mi- 
crofcope can difcover, are vifible in it; in fhort, all the parts of the — 
head; not only the fkull but the teeth. 
In proportion as the time approaches in which the caterpillar is to 
caft its old ikin, its colours become more feeble, the {kin feems to wither 
and grow dry, and in fome meafure refembles a leaf, when it is no 
longer fupplied with moifture from the ftock. At that time, the infedt 
begins to find itfelf under a neceflity of changing; and it is not effedt- 
ed without violent labour, and perhaps pain. A day or two before 
' the critical hour approaches, the infect ceafes to eat, lofes its ufual ac- 
tivity, and feems to reft immoveable. It feeks fome place to remain 
in fecurity; and no longer timorous, feems regardlefs even of the 
touch. It is now and then feen to bend itfelf and elevate its backs 
again it ftretches to its utmoft extent: it fometimes lifts up the head, 
and then lets it fall again; it fometimes waves at three or four times 
from fide to fide, and then remains in quiet. At length, fome of the 
rings of its body, particularly the firft and fecond, are feen to fwell 
gonfiderably, the old tkin diftends and burfts, till, by repeated {wel 
ibgs 
