MORPHOLOGY AND CLASSIFICATION 



163 



the growing parasites do not divide into merozoits but become 

 differentiated into male and female cells (gametocy tes) . The 

 male gametocyte gives rise to a large number of elongated motile 

 microgametes, one of which approaches and penetrates the 

 ripened macrogamete. The nuclei of the two gametes fuse and 

 the fertilized cell quickly forms a protective wall around itself and 

 then divides into eight cells which are enclosed in pairs within 

 secondary cysts known as spores. This form of the organism 

 passes out of the host, and after a passive existence in the external 



Pig. 81. — Porms in the asexual cycle of Plasmodium falciparum, the parasite 

 of tropical malaria. A, Multiple infection of a red blood cell; B to E, various forms 

 of the growing parasite; B and C show also the Maurer granulations; F, full-grown 

 parasite with many nuclei; G, Segme^ntation. The pigment is shown in E, F and G. 

 {After Doflein.) 



world may gain entrance to a new host, whereupon the spore wall 

 ruptures and the enclosed cells, sporozoits, emerge to penetrate 

 new host cells. 



The Plasmodia.- — Plasmodium includes the malarial parasites, 

 forms parasitic in red blood cells and closely analogous to the 

 coccidia in the asexual cycle. The gametocytes are also similar to 

 those of Eimeria except that the gametes are not formed within 

 the mammalian host, but only after the blood has been drawn. 

 The sexual cycle of development takes place in a definite secondary 



