250 



ANIMAL LIFE 



which may converge to a point and close, or may 

 diverge and open. Connected with the siphon are 

 breathing tubes or tracheae 

 that supply all parts of the 

 body with air, and in particular 

 a little group of tracheal gills 

 placed near the siphon. Ac- 

 cordingly, when the larva rises 

 to the surface it closes the valves 

 and so pierces the surface- 

 film. It now opens them, and 

 they rest upon the elastic film- 

 membrane without breaking it, 

 just as muslin or gauze remains 

 unwetted. The pull of the film 

 on the five-lobed plate suspends 

 the larva. To descend, it closes 

 the valves, thus reducing the 

 tension, and is drawn down- 

 wards by its own weight. The 

 food of the larva consists of 

 minute organisms which it 

 sweeps into its mouth by the 

 tireless action of its jaws. 



After three or four moults, 

 being a week old, the larva 

 passes into the pupal state for 

 two days, but, unlike the pupae 

 we have so far considered, that 

 of the gnat is an active organism. It consists of a large 



FIG. 52. The larva of the 

 common gnat ( Culex 

 pipiens] in its characteristic 

 attitude. It is attached 

 to the surface-film of the 

 water by its breathing 

 siphon, and hangs head 

 downwards. (FromMialFs 

 ' Natural History of 

 Aquatic Insects? By 

 permission of Messrs. 

 Macmillan 6* Co.) 



