SINGULAR ORGANS OF RESPIRATION. 175 



the large trachea, or breathing vessel of the insect, 

 running along its body. The air entering these 

 gills, and thus being exposed to a large surface of 

 water containing dissolved gas, loses its impurities, 

 and absorbs the pure gas from the water, whence 

 it is then conveyed to the various parts of the 

 body. In many species of these larvae the whole 

 series of gills are moved to and fro incessantly, and 

 so quickly as to be scarcely perceptible to the eye. 

 Some of them use them as oars, moving with in- 

 conceivable rapidity, and being capable of darting 

 both backwards and forwards with great quick- 

 ness. They have also the power of leaping or 

 springing in the water to a considerable distance ; 

 and feed on minute aquatic larvse, and on vegeta- 

 ble matters. 



The only other instance of this kind that we 

 shall quote will be that of the terrible larva of 

 the dragon-fly, whose deeds of insect murder came 

 before us on a former occasion. The apparatus 

 provided for them is very singular, and has been 

 described with his usual accuracy by the talented 

 Reaumur. It exists in the tail of the insect, and 

 may be readily watched in action by adopting the 

 following expedient: Pour into a small glass, in 



