LUNGS of Insects. In the fly-class, the stigmata
are extremely numerous; and the trachea which they
terminate are branched and divaricated all over the
body in an amazing manner, as if every part and par-
ticle of the bodies of these little creatures had occasion
for its particular air-vessels: besides these, however,
flies are provided with proper lungs. They have two;
and those so very large, that they frequently take up
half, and sometimes two thirds, of the body of the ani-
mal.—These are two bladders placed side-ways, one by
the other, alike in shape and size; and having their
origin at the junction of the corcelet and body, and, in
many flies whose bodies are composed of five rings,
extending to the third, and sometimes to the fourth.
The size and figure of each of these bladders is such
as is necessary to fill almost entirely that cavity of the
body in which it is lodged. They each of them touch
the sides of this cavity; the part where they join one
another is flat, and this commissure forms a line run-
ning straight down the body; they are, however, in
this part, though so closely in contact, yet not at all
joined to one another. This commissure, however, does
not reach quite up to the back, or quite down to the
belly: there is a small cavity left between each, which
was very necessary in both places; the one to give pas-
sage to the great artery, the other to the excrements.