778 PATHOGENIC PROTOZOA 



Transmission is solely by various species of anopheles mosquitoes. 

 Although there are fifty or more recognized species, only sixteen have 

 been proved malarial carriers. The more important are Anopheles 

 quadrimaculatus in the United States, Anopheles albimanus in the 

 American tropics, Anopheles maculipennis in Europe, Anopheles sen- 

 ensis in India, and Anopheles costalis in Africa. 



Description of the Mosquito. It is impractical to give more than 

 a hasty description of mosquitoes, and the reader is referred to larger 

 works on the subject (Howard, Dyer and Knab; Theobald or "Medi- 

 cal Entomology," Patton and Cragg, London, Madras and Calcutta, 

 1913). It may be noted, however, that the Culicidce, or mosquitoes, 

 belong to the Diptera, or two-winged insects. They pass through four 

 distinct stages in their development, the egg, larval, pupal and adult 

 or imago stage. The eggs are invariably laid in water where, if the 

 temperature is warm, they hatch in one to four days. Anopheles 

 eggs are single and oval, supported on the surface of the water by 

 ornamental air cells; those of culex are cemented together when laid 

 in raft-like masses. 



The larva? are aquatic and die quickly out of water. They are 

 both bottom and top feeders, eat voraciously, consuming algae and 

 other vegetable matter, and some varieties are cannibalistic. The 

 larvaa are provided with a breathing tube or respiratory siphon pro- 

 jecting upward from the dorsal surface at the caudal end, and in 

 breathing this is thrust upward to the surface of the water and the 

 larva hangs suspended from the surface film. In the anophelines the 

 breathing tube is short and its angle with the body is such that the 

 larva lies parallel with the surface; with culex and other genera the 

 body lies at an angle with the surface. The larval stage lasts about 

 six to fourteen days, depending upon the temperature and food sup- 

 ply, and is followed by the pupal stage, during which no feeding 

 occurs; the pupa, however, needs air and is provided with a short 

 respiratory tube at each side of the head. The habit of coming to the 

 surface of the water to obtain air, Which obtains in all mosquitoes 

 except the Mansonia, gives a point of attack in combating them, since a 

 layer of mineral oil on the surface of the water occludes the respira- 

 tory siphon and so kills them. 



The adult, or imago, emerges from the pupa when the latter is one 

 to three days old; the pupal case ruptures along its dorsum and the 

 emerging imago rests on the floating pupal case until its wings are 

 dry. Since this is a critical stage in its life history and demands 



