INSECTS AND DISEASE 369 



ment, a rather long breathing tube, the tip of which is thrust 

 just above the surface of the water when they come up to 

 breathe. Other larvae do not have such a breathing tube, the 

 spiracles which open into the trachea being situated on the 

 surface of the eighth segment. The pupas of all species are 

 active but take no food. The two trumpet-shaped breathing 

 tubes of the pupae are situated on the thorax, and when the 

 pupas come to rest these extend just above the surface of the 

 water. When the adult is ready to issue the pupal skin splits 

 along the back and the mosquito slowly comes forth, usually 



FIG. 157. Mosquito pupae, T. incident, resting at the surface of the water. 



(Enlarged.) 



resting for a short time on the cast-off pupal skin until the wings 

 become dry and firm enough to use. 



Malaria-carrying Mosquitoes. In the United States only 

 mosquitoes belonging to the genus Anopheles carry malaria, so 

 it is important to be able to distinguish the members of this 

 genus in their various stages. The eggs of Anopheles are laid 

 singly, but are often found together in groups of three or four 

 floating on the surface of the water. Each egg is provided with 

 characteristic membranous expansions on each side near the 

 middle. These keep the eggs afloat. The larvae feed largely 

 on minute plants or other organisms at the surface of the water, 

 and when feeding lie nearly horizontally, with the body touch- 

 ing the surface at several points. The absence of a breathing 

 tube, and this habit of always lying with the body parallel to the 

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