An infect that muft caft off it’s exuvia, of moult five times be-
fore it attains the pupa ftate, may be confidered as compofed of
five organized bodies, inclofed within each other, and nourifhed
by common vifcera, placed in the center: what the bud of the
tree is to the invifible buds it contains, fuch is the exterior part
of' tlie Caterpillar to the interior bodies it conceals in it’s bofom:
Four ofthefe bodies have the fame effential ftrufture, namely,
that which is peculiar to the infeft in it’s larva or caterpillar ftate :
the fifth body is that o f the pupa. The refpeftive ftate of thefe
bodies is in proportion to their diftance from the center o f the
animal; thofe that are fartheft off have moll confiftrence, or unfold
themfelves fooneft.
"When the exterior body has attained it’s full growth, that interior
one which is next in order is confiderably unfolded; it is
then lodged in too narrow a compafs, therefore it ftretches on all
fidesthe Iheath which covers i t ; the veffels which nourilh the external
covering, being broken by this violent diftenfion, ceafe to
adt, the lkin wrinkles and dries up ; at length it opens, and the
infeft is cloathed with a new fkin, and new organs.
The infeft generally fafts for a day or two preceding each
change; this is probably occafioned by the violent ftate in which
it then is, or it may be neceffary to prevent obftruftrons, &c. let
this be as it may, the infeft is always very weak after it has
changed it’s fkin, the parts being as yet affefted by the- exertions
they have gone through. The fcaly parts, as the head and legs,
are almoft entirely membranaceous, and imbrued with a fluid
that infinuates itfelf between the two fkins, and thus facilitates
their
their reparation-, this moifture evaporates by degrees, all the
parts acquire a confiftence, and the infect .is then in a condition
to aft.
The firft life that fome caterpillars, who live on leaves, make
of their new form, is to devour greedily their exuvia ; fometimes
they do not wait till their jaws have acquired their full ftrength ;
fome have been- feen to gnaw the fhell from which they proceeded
and even the eggs of fuch caterpillars as have not been,
hatched.
When we have once formed the idea that all the exterior parts
are inlaid, or included one within the other, the production of
new organs does not appear fo embarraffmg, being nothing more
than a Ample developement; but it is more difficult to
form any conception of the changes that happen in the vifcera
before and after the transformation, the various modifications
they undergo eluding our refearches. We have already obferved,
that a little before the change the caterpillar rejefts the membrane
that lines the inteftinal b a g : this bowel has hitherto digefted
only grofs food, whereas it muft hereafter digeft that which is
very delicate : a fluid that circulates in the caterpillar, from the
hind part towards the head, circulates a contrary way after lransr
formation. Now if this inverfion is as real as obfervation feems
to indicate, how amazing the change the interior parts of the animal
muft have undergone ! When the caterpillar moults, final!!
clufters of the tracheal veffels are caft off with the exuvia, and
new ones are fubftituted in their room ; but how is this effefted,
how are the lungs r. placed by other lungs ? The more we
endeavour