MORPHOLOGY AND CLASSIFICATION 



157 



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 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 



FIG. 79. Forms 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, Segmentation. The pigment is shown in E, F and G. 



(After Doflein,} 



coccidia in the asexual cycle. The garnet ocytes 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 

 host, the mosquito. In the stomach of this insect the gametes 

 unite and the fertilized cell (ookinet) actively penetrate? the 

 epithelium and beneath it develops into a large oocyst, 30 to 90^ 

 in diameter, enclosed in the elastic tunic of the stomach wall of the 

 mosquito. As the oocyst enlarges the nucleus divides and eventu- 



