II FLIES WITH AQUATIC LARV^ i6l 



towards the water, while the bend is turned away from 

 it. The larva frequents pools which are overgrown 

 with vegetation. It creeps upon leaves which rise a 

 little way out of the water, and lies upon them with 

 its head and tail close to the edge of the water. The 

 bend is commonly above the water-line, but is com- 

 pletely wetted ; it does not break the surface-film. 

 Even when the larva has crept above the water-line it 

 is, strictly speaking, submerged, for it takes with it a 

 watery film ; the body is bent into a V, the apex of 



Fig. 48. — Head of larva of Dixa, side-view. 



which travels foremost, and each half of the V alter- 

 nately shoves the body onwards. Larvae placed in a 

 cup of water often wander to a distance and perish 

 nby drying up. The respiratory cup is the only part 

 I of the body which is dry, and this is in free com- 

 imunication with the air. The head is commonly 

 sunk into the water, but close beneath the surface. 

 The ciliary organs which surround the mouth are 

 constantly employed, like those of a Gnat larva, in 

 sweeping microscopic particles into the gullet, and 

 |this action is greatly promoted by the extraordinary 



M 



