Sporozoa 305 



found in a variety of blood-forming cells, while other avian parasites 

 apparently prefer lymphoid-macrophage cells (55). 



The erythrocytic cycle in Plasmodiidae is initiated by merozoites from 

 an exoerythrocytic merogony. Growth into a schizont is followed by 

 merogony (Fig. 6. 21, C-E), and the surviving merozoites enter other 

 erythrocytes to repeat the process. The periodicity of erythrocytic merog- 

 ony varies with the species, or even strains within a species, and the 

 cycle covers a period of one to several days in different malarial parasites. 



Fig. 6. 22. AH. Hacmoproteus cnlumhae: oocysts on portion of s^ut in 

 Lyncliia luaura (A), xl05; and sporozoite (B), xl740 (after Adie); tropho- 

 zoite in leucocyte (C); merohlasts, produced by division of a trophozoite, 

 have undergone nuclear division in preparation for merogony (D); young 

 and approximately niatme macrogametocytes (E, F); young and mature 

 microgametocytes (G, H); C-H, xl320 (after Aragao). I, J. Macro- and 

 microgametocytes of Leucocytozoon coccyzus, x2136 (after Coatney and 

 West)'. 



Sooner or later, gametocytes (Fig. 6. 21, F, G) are developed, and the 

 blood of the host is then infective for the vector. 



The Order Plasmodiida may be divided into two families, the Haemo- 

 proteidae and the Plasmodiidae, differentiated by the absence of erythro- 

 cytic merogony in the former. Only the gametocytes of Haemoproteidae 

 are to be expected in erythrocytes. 



Family 1. Haemoproteidae. These are blood parasites of birds and 

 reptiles. Merogony is exoerythrocytic, primarily in endothelial cells of 

 visceral caj^illaries {Haemoprotens), or in lymphoid-macrophage cells of 

 the viscera (e.g., spleen, liver) as in Leucocytozoon simondi (53). Schizonts 



