128 THE UNIVERSE. 



fined to one region of the body. In the insects it has a 

 much larger field of action. The air diffuses itself every- 

 where, and after having overfloAved the internal organs by 

 means of particular vessels, the trachece, which are easily 

 distinguished by their pearly tint, it reaches the extreme 

 terminations of the feet and the antennae. For this pur- 



74. Larva of tlie Common Gnat — Cuhx pipiens (Linnaeus), seen with the Microscope. 



pose these are provided with a most remarkable structure. 

 They are composed of a fine cartilaginous lamina, rolled in 

 Hke the metallic thread in an elastic brace. This arrange- 

 ment serves to keep their walls constantly separated, and 

 to facilitate the free circulation of air through their im- 

 perceptible canals. 



Every person has seen, and with some disgust too, a 

 white larva with a long tail, which lives in the filthy stag- 

 nant Avaters of our courts and roads, and which is vulgarly 

 called the rat-tailed mafigot. When I Avas yoring this crea- 

 ture inspired me Avith the same repugnance as other people; 

 but since I have examined it by the aid of a lens, and 

 studied its halnts, repugnance has given Avay to admiration. 

 The extraordinary tail to Avhich the animal OAves its name 

 is an organ of respiration. It contains tAvo A^essels Avhich 

 disseminate the air through all the body of this fly-larva, 



