MALARIA 131 



thus seen that stagnant water is necessary for mosquitoes 

 to breed. Both wrigglers and pupae come to the surface 

 of the water at brief intervals in order to breathe. If a 

 film of oil is floated on the surface of the water the wrig- 

 glers and pupae soon die of asphyxiation. 



Fig. 42. — Life cycle of mosquito. Chart showing how the com- 

 mon house mosquito breeds: 1, The eggs, as deposited on the sur- 

 face of the water; 2, separating from the mass. The larva, 3, 4, 

 forming; 5, emerging, about the thickness of a thread; 6, breath- 

 ing through the tail; 7, changing to pupa. The pupa (8, descend- 

 ing from the surface, when disturbed; 9, 10, breathing; 11, 12, 

 changing to insect). The complete insect (13, emerging; 14, 

 allowing its wings and body to harden and expand ready for flight, 

 using the pupal skin, 15, as a float). The eggs and young of the 

 malaria-carrying mosquitoes go through a similar process of devel- 

 opment. 



The mosquitoes which transmit malaria belong to the 

 family called Anopheles. The commonest variety of this 

 is broT\Ti in color and has four dark brown markings on 

 each wing. Anopheles mosquitoes breed in fresh-water 

 swamps and in stagnant water in fields and woods. Their 

 extermination therefore requires the drainage of marsh 

 lands, the filling-in, draining or oiling of ponds, and 

 similar measures. 



In contrast to the anopheles, the mosquitoes which 



