INSECTA 



125 



Two groups of flies have been found to be the means of com- 

 municating tropical diseases, as malaria and sleeping sickness. 



Malaria. The family Culicidae of Diptera, the gnats 

 or mosquitoes, consists of some 1000 species, and a section of 

 the family containing about 100 species is the Anopheline 

 group, important from their role in the transmission of malaria. 



The eggs of the mosquito are laid by the female on the 

 surface of water of ponds, canals, streams and the like. The 

 egg is flattened and boat-shaped, provided at the sides with 



Larva 



Pupa 



Larva Pupa 





Culex 



FIG. 59. Diagram to illustrate the life-histories of anopheline and culicine 

 mosquitoes. The larvae and the adults are shown in the resting position. 



ribbed floats, and is laid singly in the case of the Anophelines, in 

 rafts in that of the Culicines. In about two to four days the egg 

 of the former liberates an active larva. The larva is resolved into 

 head, thorax, and abdomen. The head possesses small lateral 

 eyes, short antennae, and strong mandibles and maxillae. The 

 segments of the thorax are broad and fused. The abdomen 

 is of nine segments ; the eighth segment bears the stigmata 

 or spiracles, the two openings surrounded by a shield. There 

 is no siphon as in the larva of their near allies the culicine 

 mosquitoes. The presence or absence of the siphon makes 



