M 2.44 i c r o s c o p i c a l E s s a y s .
M. Mufchenbrock inclofed the pupa o f a moth in a glafs tube,
nearly o f the fame fize with the moth itfelf.
A B
The end A o f the tube was drawn out into a capillary form,
the other end was covered with a piece o f wet bladder, to exclude
the a ir; the capillary end was then plunged in Water, which rofe
to D. He placed the capillary part o f the tuhe before a micro-
fcope, on a fmall micrometer, in order to obferve any motion or
change in the fituation o f the water; as it is evident the exlpira-
tk>n or infpiration o f air by the infeft would make it rife or fall
alternately.
In the firft experiment he obferved a fmall degree o f motion at
diftant intervals, not above two or three times in an hour; in a
fecond experiment on another fubjeft, he could obferve no
motion at all. He then placed fome pupas under the receiver o f
an air-pump, in water which he had previoufly purged o f it’s air;
on exhaufting the air from the receiver, he obferved one bubble
to arife in a part near the tail, and a few near the wings. The
pupa did not fwell under the operation; on the contrary, on
letting in the air, it was found to be diminifhed' in a fmall degree,
but in lefs than a quarter o f an hour it recovered it’s former
figure. Mr. Martinet publifhed at Leyden, in 1753, a dilferta-
tion, in which, it is faid, he has clearly proved, by a number of
experiments, that the pupa o f the caterpillar and fome other
infefts do not refpire : I have not feen the work.
Among
Among the infecls in which the refpiration Teems to be moll
clearly proved, is the larva a queue de rat (mufca pendula,Lm.);
thefe live under water in the mud, to which they affix themfelves ;
though they live under water, the refpiration of frefli air is neceffary
to their exifience j for this purpofe they are furnilhed with a tail,
which oftenappears o f an exceflive length relative to their b o d y ; the •
body is feldom more than three quarters of an inch m length, while
the tail is frequendy more than four inches ; it is compofed o f two
tubes which run one into the other, fomething. fimilar to the
tubes’ of a refraHing telefcope. Befides this, the materials o f
which the tubes are compofed are capable of a great degree of
extenfion. When the tail is at it’s full length, it is exceeding
fmall, not being larger near the extremity than a horfe-hair;.
there is a little knob at the end, which is furnithed with final!
hairs, to extend on the water, fomething fimilar to. thofe at the
tail of the mufca chameleon.
In the body of the larva are two large tracheal velfels ; thefe
air-veffels extend from the head to the tail, and terminate in the
refpiring tubes, and receive the air from them. The larva quits .
the water when the time o f it’s transformation approaches, and
enters in the earth, where the fkin hardens and forms a cafe, m
which the pupa is formed; foon after the change, four tubes, or
horns, are feen projeaing from the cafe’, thefe M. de Reaumur
fuppofes to be organs for communicating air to the interior parts
o f the infect; they are conneSed with little bladders which are
found filled with air, and by which it is conveyed to the fpimcula
of the pupa. The larva of gnats, and other fmall aquatic mlefcls
o f the fame kind, are furnilhed with fmall tubes, that p ay on.
(nr fa re o f the water, and convey the air from thence to t e