302 Sporozoa 



The Haemosporidia may be divided into the Plasmodiida and the 

 Babesiida. The life-cycle of the Plasmodiida resembles that of Coccidia, 

 with well-marked merogony and sporogony. The life-cycles of many 

 Babesiida are incompletely known. Some species apparently undergo 

 fission in red corpuscles of the vertebrate host. Merogony in lymphocytes 

 has been reported for certain others. The fusion of similar gametes has 

 been described in Babesia (27). 







'Zi' 



it.. 



J ■- ; -*^i^v ■■■2 »'■ />■'.' 



Fig. 6. 20. Plasmodiuiyi circunifJexum, stages in mosquitoes (after Reiche- 

 now): macroganiete (A) and ookinete (B), x3640; ookinete in cell of gut wall 

 (C), xl950; young oocyst with four nuclei (D), x3640; portion of a section 

 through an older oocyst, remnant of gut cell shown (E), xl950; portion of a 

 section through a mature oocyst, just before sporogony (F), xl850; a sporozoite 

 (G), x3960. 



Order 1. Plasmodiida. Throughout the order, merogony occurs in endo- 

 thelial or related tissue cells of the vertebrate host. In one family, me- 

 rogony is apparently restricted to parasites in such tissue cells. In the 

 malarial parasites, however, merozoites from the basic merogonic cycle 

 invade red blood cells and undergo a series of erythrocytic cycles of 

 merogony. Gametocytes develop from some of these erythrocytic mero- 

 zoites. In other Plasmodiida, only the gametocytes appear in blood cells. 

 In either case, gametocytes are ingested by an invertebrate host in which 

 syngamy and sporogony occur. 



