INSECTS 



the body segments project laterally groups of long hairs, 

 some of which are branched in certain species. The rear 

 end of the body appears to be forked, being divided into an 



upper and a lower branch. The 

 upper branch (c), however, is 

 really a long tube projecting dor- 

 sally and backward from the next 

 to the last segment. The lower 

 branch is the true terminal seg- 

 ment of the body and bears the 

 anal opening of the alimentary 

 canal at its extremity. On the end 

 of this segment four long, trans- 

 parent flaps project laterally (d), 

 two groups of long hairs are situ- 

 ated dorsally, and a fan of hairs 

 ventrally (Fig. 174 E). 



The principal characteristic of 

 the mosquito larva is the speciali- 

 zation of its respiratory system. 

 The larva breathes through a 

 single large aperture situated on 

 the end of the dorsal tube that 

 projects from the next to the last 

 segment of the body (Fig. 175, 

 PSp). This orifice opens by two 

 inner spiracles into two wide 

 tracheal trunks (Tra) that extend 

 forward in the body and give off" 

 branches to all the internal organs. 

 The mosquito larva, therefore, can breathe only when the 

 tip of its respiratory tube projects above the surface of the 

 water, and, though an aquatic creature, it can be drowned 

 by long submergence. Yet the provision for breathing at 

 the surface has a distinct advantage: it renders the 

 mosquito larva independent of the aeration of the water 

 it inhabits, and allows a large number of larvae to thrive 



Fig. 175. Structure of a 



Culex mosquito larva 

 a, mouth brushes; Ab, 

 abdomen; Ant, antenna; b> 

 eye; c, respiratory tube; d, 

 terminal lobes; //, head; 

 PSp, posterior spiracle; 

 Th, thorax; Tra, dorsa 

 tracheal trunks 



