106 TROPICAL MEDICINE AND HYGIENE 



essential for prophylaxis. They differ in their habits 

 greatly. 



(i) Culex fatigans is found in numbers only in the vicinity 

 of human habitations, and is abundant in even the largest 

 towns provided there is still water, fresh or stagnant, in 

 the vicinity. The eggs are laid in rafts floating on the 

 surface of the water and hatch after about two days. 

 The larvae are provided with a tapering respiratory siphon 

 of medium length and the larvae feed mainly on sub- 

 stances floating in the water. The " brushes," or tufts of 

 hairs placed on either side of the mouth, are long and 

 composed of numerous fine hairs. 



When food is abundant these larvae, after casting their 

 skins ecdysis four or five times, pupate in from six to 

 nine days, according to the temperature, and the pupa 

 now enclosed in a pupal case requires no further feeding. 

 There is no mouth and no anus, and air is supplied 

 through the thorax by the two respiratory tubes. Two 

 days after pupation the pupal case is split down the back 

 and the imago slowly emerges. 



Favourite breeding places are roadside trenches, cess- 

 pits, and any small pools where fish are not abundant. 

 They also breed freely in the water of barrels, tanks, and 

 other artificial receptacles. The larvae are hardy, but will 

 not stand desiccation, and the eggs also, if thoroughly 

 dried or immersed in water, die. The eggs cannot remain 

 unhatched for long; they either hatch out in a few days, 

 dependent on temperature, or they die. 



The measures to be adopted consist of limitation of 

 mosquito breeding places, and the destruction of such 

 larvae as are found. This would seem to be more easy 

 than the destruction of Stegomyia fasciata, as the eggs are 

 so much more easily destroyed. In practice this is not so, 

 as the adults imagines are stronger and travel further. 

 With the Stegomyia the breeding places are close to the 

 house, and a house can often be freed from such mos- 

 quitoes by the destruction of the breeding places in the 

 one compound. 



