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 re 

 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 trachete. 

 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 tracheae ; two of which are of enormous size, 



* Reaum. vi, 394. 



