O n the R espiration of Insects.
As refpiration is one of the moll important actions in the life of
every animal, great pains have been taken by many naturalifts to
inveftigate thé nature o f this aftion in infeös; to prove it’s exiftence,
and explain in what manner it is carried on. Malphigi,
Swammerdam, Reaumur, and Lyonet, have difcovered in the
caterpillar two air-velfels placed the whole length o f the infect,
thefe they have called the tracheae; they have alfo fliewn that an
infinite number o f ramifications proceed from thefe, and are dif-
perfed through thewhöle body; that the tracheal veflels communicate
with particular openings on the {kin of the caterpillar,
termed fpiracula; there are nine o f thefe on each fide o f the
body. Thefe velfels feem calculated for the reception of a ir ;
they contain no fluids, are o f a cartilaginous nature, and when
cut preferve their figure, and exhibit a well-terminated opening.
Notwithflanding this difcovery, the exiftence o f refpiration has
not been proved in many fpecies o f infects, and the mechanifm
thereof is very obfcure in all; and it is no more furprizing, that
refpiration does not exift in the embryo ftate o f infects, than in
that o f other animals, where we find that refpiration, which after
their birth is abfolutely neceflary for their exiftence, to be by no
means fb before it.
M. de Reaumur thought that the air entered by the fpiracula
into the trachea, but did not come out by the fame orifice, and
confequently that the refpiration o f infects1 was carried on in a
manner totally different from that o f other animals, that the air
was exfpired through a number of fmall holes, or pores, which
are to be found in the fkin o f the caterpillar, after having been
conducted
conduced to them through the extremities of the finer ramifications
o f the tracheal veffels: whereas M. Bonnet, in confequence
o f a great variety o f experiments, fuppofed that the infpiration
and exfpiration of the air was through the fpiracula, and that
there was no exfpiration o f air through the pores of the fkm#
Thefe experiments were made either by plunging the caterpillars
into water, or anointing them with fat and greafy fubffances>
fome all over, others only partially. The number o f fmall bubbles
which are obferved to cover the furface of their bodies, when
they are immerged in water, does not arife from the air which
is included within,, and then proceeding from them, but they are
formed by the air which is lodged near the furface of their bodies,
in the fame manner that it is about all other fubftances. To render
the experiments more accurate, and prevent the air from
adhering to the fkm, before he plunged the caterpillars in water
he always brufhed them over with an hair p encil; after this, veiy
few air bubbles will be found on their bodies when they are im-
merged in water.
A caterpillar will remain a confiderable time under water,
without deftroying the principle o f life; and they alfo recover, in
general, foon after they are taken out. T o know whether a few
only of the fpiracula might not be fufficient for. the purpofes of
refpiration, he plunged fome partially in water, fo that only two
or more fpiracula remained in the open air: in thefe cafes the
caterpillar did not become torpid as it did when they were all
immerged in water.
One caterpillar, upon which M. Bonnet made his experiments,
lived eight days fufpended in water, with only two o f it s anterior
G g fpiracula