Si8 



Malaria 



and steins of plants, and remain alive until the waters rise again, be- 

 fore hatching. Dry eggs are sometimes able to remain alive for long 

 periods, and may even be frozen without being killed. Cazeneuve 

 hatched eight larvae from eggs obtained by thawing a block of 

 ice taken from a swamp in North China, where the temperature 



Fig. 195. — Method of withdrawing the digestive tube of the mosquito for 



study (Blanchard.) 



had gone as low as — 32°C. When conditions are favorable the 

 eggs hatch in two or three weeks. The anopheles larvae feed at 

 the surface of the water along the banks where they are protected by 

 the vegetation. They are voracious feeders and satisfy their appetites 



Fig. 196. — Method of withdrawing the salivary glands of the mosquito for 



study (Blanchard). 



with all kinds of minute vegetable and animal organisms or rem- 

 nants. In a day or two the larvae molt for the first time. In 

 five or six days, having grown larger, they molt a second time and 

 pupate. The appearances of the larvae and pupae are shown in the 

 accompanying diagrams. The pupa floats at the surface of the water, 

 is comparatively inactive and does not feed. If disturbed, it 

 is capable of swimming vigorously to escape. In about three days 

 the imago issues and is ready to fly. Anopheles do not fly great 

 distances; a few hundred yards is the common range of their activi- 

 ties. They do not always return to the same pools from which they 

 issued, any similar pool or stream is good enough for oviposition. 



