fpiracula in the a ir ; during this time he obferved, that when the
infeft moved itfelf, little dreams o f bubbles iffued from the anterior
fpiracula on the left fide; from this and many other experiments
it appeared to him, that amongft all the eighteen fpiracula,
the two anterior and the two poderior are o f the greatefl ufe in
refpiration.* Sometimes, when the mouths o f thefe have been
Hopped with oil, the caterpillar has fell into convulfions. I f the
poflerior part has been oiled, that part will become paralytic.
Notwithftanding thefe experiments, and many'more -which have
been made, the fubject is far from being decided, and many dill
doubt whether there is any refpiration in infefls fimilar to ours,
at lead at certain periods o f their life.
This opinion feems to be further confirmed by the experiments
o f M. Lyonet. He placed feveral o f the large mufk beetle,
probably the cerambyx mofchatus, under a glafs, where he had
been burning fulphur, and which he kept burning while they
were there; and though the vapour was fo thick that he could
not fee them, and that he kept them therein more than half an
hour, they did not feem in the lead incommoded, h
When we condder the great folidity o f the cafes, or cones, o f
the pupas o f different infers, it is not eafy to conceive how they
can live feveral months under the earth, in fpaces fo confined,
and almod impervious to the air. I f refpiration was abfolutely
neceffary to their exidence, and indeed i f they did refpire, the
fame fituation feems to preclude a continuance o f the operation,
as the air would foon be corrupted, and unfit for the offices o f
life.
* Philof. Tranf. vol. xlv. p. 300.
+ Letter Theologie des InfeSes, tom. 1, p. 124. Ibid, p, 126,
M i c r o s c o p i c a l E s s a y s .
life. As the trachea are divided and fubdivided to a prodigious
degree of minutenefs, it has been conjectured by fothe writers,
that they may aft as fo many fieves, which, by reparations properly
contrived, filtrate the air, and fo furnifh it to the body of
different degrees o f purity and fubtilty, agreeable to the purpofes
and nature of the various parts. The experiments that have been
made with the air-pump are by no means conclufive; the injury
the infeft fudains when the atmofpheric prefi’ure is taken from the
body, does hot prove that it infpired and exfpired the air that we
have removed; it only fiiews that an incumbent preffure is
neceffary to their comfortable exidence, as it prevents the fluids
from difengagmg themfelves in an aerial form, and as it counterbalances
and re-afts on the principle o f life, and by keeping the
aftion thereof in proper tone and order, confines and regulates
its energies.
Though it is difficult to afeertain whether fome infefis refpire
at lead at certain periods o f their exidence, yet there are others
to whom the infpiration and exfpiration o f air feems abfolutely
neceffary : there are many aquatic infefts who are obliged to keep
their tails fufpended on the furface o f the water for this purpofe,
^ o prove this, keep the tail under water, and you will perceive
the infea to be agitated and uneafy, and to feek for fome opening
to expofe this part to the air; if it finds none, it foon goes
to the bottom and dies. Some aquatic beetles refid the trial for
a confiderable time, while their larva can only fupport it for a few
minutes. There is a circumdance which renders all experiments
on this fubjeft with infects doubtful and difficult, namely, the vad
tenacioufnefs o f the life principle in the lower orders o f animated
nature, and it’s diffemination through their whole frame. 1 1 I M. Muf