100 



ONE-CELLED ANIMALS— PHYLUM PROTOZOA 



Certain of the merozoites grow in the plasma of the blood and become 

 male and female gametocytes which may function in sexual reproduction 

 which takes place in the mosquito's body. If the proper kind of 

 mosquito bites and sucks up at least one of each kind of gametocyte, 

 the cycle continues in the mosquito's stomach. The female gametocyte 

 becomes an egg without much change, but the male gametocyte gives 

 off from four to eight slender sperms which break off and swim to the 

 egg. One unites with the egg and produces the zygote. This zygote be- 



CULEX 



ANOPHOLES 



Eggs 



Larvae 



Adults 



Fig. 7.10. Diagram showing how the Culex can be distinguished from the Anopheles 

 mosquito by body position and egg distribution in three stages of the life history. 



comes amoeboid in nature and squeezes itself between the cells of the 

 stomach wall and forms a cyst on the outside of this wall. The zygote 

 divides within this cyst until large numbers of spores, the sporozoites, 

 are produced. The cyst then breaks and the sporozoites migrate 

 through the body cavity, some of them reaching the salivary glands of 

 the mosquito. This cycle requires about 10 to 12 days, so a mosquito 

 is not infective until at least this long after it has bitten a person with 

 malaria. Once it becomes infective, however, it is likely to remain so 

 for its entire life, which may be several months. Each zygote produces 

 about 10,000 sporozoites. 



