74 SUPPLEMENT ON 



the fact is proved in the case of bees in summer, which when 

 crowded together, perspire most profusely. 



The tracheae, or air-vessels, by which insects respire, have 

 been already mentioned. The larvae have them as well as 

 the perfect insect, but a very remarkable change in these, as 

 well as in the other parts of the body, takes place at the 

 period of transmutation. Some aquatic insects in particular, 

 respire in a manner totally different, in their three states of 

 larva, nymph, and imago. 



We see in a great number of diptera, while they are yet 

 in the larvae state, the orifices of the tracheae diversely grouped 

 towards the final rings of the body. In the larvae of the 

 stratiomys, for instance, is remarked a kind of aigrette, 

 formed of barbed hairs. In the centre of this aigrette, the 

 respiratory organ is observable. In the larvae and nymphs 

 of the dragon -flies or libellulae, the mode of respiration is 

 peculiarly singular. The water penetrates into their rectum 

 by a sort of inspiration : it seems probable that it leaves there 

 the oxygen gas, which is combined with it. In the thickness 

 of the parietes of this intestine, are seen a great number of 

 tracheae, which represent five great leaves or nervures of leaves, 

 composed of small tracheae, which repair into four principal 

 trunks, two of which, still thicker, are subdivided in all the 

 parts of the body. This mode of respiration in the larvae of 

 which we are speaking, is rendered sensible to the eye, by 

 letting them stop a few minutes in a coloured water, and then 

 putting them into other water very limpid. At each move- 

 ment of respiration the coloured water issues from the anus 

 after having washed the tunics of the intestines ; moreover, 

 the animal employs this mode of respiration to facilitate its 

 conveyance or movement in the water, availing itself of the 

 resistance which the jet proceeding from the anus receives 

 upon the liquid mass. The body of the insect thus resting 



