68 INTERNAL ANATOMY OF INSECTS. 
The pieces both internal and external that close the anal 
orifice have been before described; the others employed 
in the admission and expulsion of the water are evidently 
respiratory organs. When this orifice is opened, the 
parts that are above it are drawn back in an opposite di- 
rection, so that the five last segments of the abdomen be- 
come entirely empty, and form a chamber to receive the 
water that enters by it. When the water is to be ex- 
pelled, the whole mass of air-vessels which had receded 
towards the trunk, is pushed forwards, and forms a pis- 
ton that again expels the water in a jet. It consists of 
an infinite number of bronchia, entangled with each other, 
which proceed from the middle and posterior end of the 
trachea. M. Cuvier in the interior of the rectum of 
the larva discovered twelve longitudinal rows of little 
black spots, in pairs, which exhibited the resemblance of 
six pinnated leaves. ‘These are minute conical tubes, of 
the spiral structure of trachee, which decompose the wa- 
ter, and absorb the air contained in it. He also disco- 
vered that each of these tubes gave birth to another out- 
side the rectum, which connected itself with one of the six 
great longitudinal ¢rachee ; two of which are of enor- 
mous size, and appear to serve as reservoirs, since they 
furnish air by transverse branches to two other tubes ; 
they have each a recurrent branch, which follows the 
course of the intestinal canal, and furnishes it with an 
infinity of bronchie*. These trachee are found in the 
perfect insect. The principal ones in some send forth 
many branches, terminating in vesicles, which in shape 
* Reaum. vi. 394—. Cuv. Anat. Copp irnaaes M 
d’ Hist. Nat. xvii. 540—, eas - MN. Dict. 
