MALARIA AND MOSQUITOES 51 



tlie microscope for examination, they nnderg-o a develop- 

 ment entirely ditt'erent from the sporulating- form. Some 

 of them grow large, others put out slender filamentary 

 arms, or tlagella, as they are called, which separate from 

 the body of the organism and fuse with those which do 

 not Hagellate. This is the true sexual generation of the 

 parasite, the flagellating forms representing- the male sex 

 and the receptive forms the female sex. The develop- 

 ment up to this point will take place anywhere outside of 

 the human body — in the stomach of mosquitoes of the 

 genus Culex, or, presumably, of other biting insects, but 

 it is onl}^ in the stomachs of the genus Anopheles, so far 

 as observed, that a further development takes place. 

 After the fusing of the flagella Avith the female germs in 

 the stomach of the Anopheles moscpiitoes, the fertilized 

 organisms attach themselves to the walls of the stomach, 

 penetrate the inner walls, and locate themselves just 

 under the outer muscular wall. They then rapidly 

 increase in size until they eventually become five times 

 as large as at first. They are now known as zygotes. 

 Clear spaces begin to appear on the surface. These 

 clear spaces are known as centromeres, and they are 

 rapidly surrounded by minute short dark lines, which, 

 when seen under a very high power of the microscope, 

 are shown to be spindle-shaped cells, known as blasts. 

 These blasts rapidly increase in number until eventually 

 they till the entire zygote, obscuring the centromeres, and 

 when this condition of affairs is reached the zygote bursts 

 and the blasts are liberated through the muscular wall of 

 the stomach into the body cavity of the mosquito. They 



