NATURAL HISTORY. 
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body. That these vessels serve to convey the air, appears 
evidently, from the famous experiment of Malpighi ; who, by 
stopping up the mouths of the stigmata with oil, quickly suf- 
focated the animal, which was seen to die convulsed the in- 
stant after. In order to ascertain his theory, he rubbed oil 
upon other parts of the insect’s body, leaving the stigmata 
free ; and this seemed to have no eflect upon the animal’s 
health, but it continued to move and eat as usual : he rub- 
bed oil on the stigmata of one side, and the animal under- 
went a partial convulsion, but recovered soon after. How- 
ever, it ought to be observed that air is not so necessary to 
these as to the nobler ranks of animals, since caterpillars 
will live in an exhausted receiver for several days together; 
and though they seem dead at the bottom, yet, when taken 
out, recover, and resume their former vivacity. 
If the caterpillar be cut open longitudinally along the back, 
its intestines will be perceived running directly in a straight 
line from the mouth to the anus. They resemble a number of 
small bags opening into each other; and strengthened on 
both sides by a fleshy cord, by which they are united. These 
insects are, upon many occasions, seen to cast forth the in- 
ternal coat of their intestines with their food, in the changes 
which they so frequently undergo. But the intestines take up 
but a small pan of the animal’s body, if compared to the 
fatty substance in which they are involved. This substance 
changes its colour when the insect’s metamorphosis begins 
to approach ; and from white it is usually seen to become 
yellow. If to these parts, we add the caterpillar’s implements 
for spinning, (for all caterpillars spin at one time or another) 
we shall have a rude sketch of this animal’s conformation. 
The life of a caterpillar seems one continued succession 
of changes; and it is seen to throw off one skin only to as- 
sume another; which also is divested in its turn : and thus 
for eight or ten times successively. 
How laborious soever this operation may be, it is per- 
formed in the space of a minute; and the animal, having 
thrown off its old skin, seems to enjoy new vigour, as well 
as to have acquired colouring and beauty. Sometimes it 
happens that it takes a new appearance and colours very 
different from the old. Those that are hairy, still preserve 
their covering, although their ancient skin seems not to have 
lost a single hair ; every hair appears to have been drawn 
like a sword from the scabbard. The fact, however is, 
that a new crop of hair grows between the old skin and the 
new, and probably helps to throw off the external covering. 
The caterpillar having in this manner continued for severa,. 
