68 INTERNAL ANATOMY OF INSECTS. 
But when we consider that it is by the action of a pneu- 
matic apparatus that the absorption and expulsion of the 
water takes place, and that the animal when it has been 
taken out of that element, upon being restored to it, 
immediately has eager recourse to this action a , we shall 
feel inclined rather to adopt the opinion of those great 
physiologists Reaumur, Lyonet, and Cuvier, and admit 
that it absorbs water for the purpose of respiration. I 
shall now explain how this takes place. 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 ?*£- 
spiratory organs. When this orifice is opened, the parts 
that are above it are drawn back in an opposite direction, 
so that the five last segments of the abdomen become 
entirely empty, and form a chamber to receive the water 
that enters by it. When the water is to be expelled, 
the whole mass of air-vessels which had receded towards 
the trunk, is pushed forwards, and forms a piston 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 dis- 
covered 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 trachea:, which decompose the water, and 
absorb the air contained in it. He also discovered that 
each of these tubes gave birth to another outside the 
rectum, which connected itself with one of the six great 
longitudinal trachea: ; two of which are of enormous size, 
* Reaum. vi. 391—. 
