98 NATURAL HISTORY OF AQUATIC INSECTS CH. 



larva ordinarily rests in 

 such a position that the tip 

 of the respiratory siphon 

 is flush with the surface of 

 the water, and, thus sus- 

 pended, it feeds inces- 

 santly, breathing uninter- 

 ruptedly at the same time. 

 It is of obvious advan- 

 tage to the larva that it 

 should in this way divide 

 the operations of breathing 

 and feeding between the 

 two ends of the body, for 

 the breathing must be done 

 at the surface, and the 

 feeding beneath the sur- 

 face. Observe that the 

 arrangement requires one 

 thing unusual in floating 

 objects viz., that the body 

 shall be, in some parts at 

 least, if not altogether, 

 heavier than water. If it 

 were lighter than water 



o 



it could not maintain a 

 vertical position, but would 

 lie along the surface like 



O 



a stick, and would be quite 



FIG. 22.- Larva of Gnat (Culex), in Unable tO SWCCp about in 



side view. 



search of the minute or- 

 ganisms which inhabit the water beneath. When 



