EIMERIA AVIUM 



143 



the influence of the powerful digestive juices (especially the pancreatic) now en- 

 countered, the oocysts soften, as do the sporocysts, and ultimately two sporozoites 

 emerge from each sporocyst. The sporozoites are from 7 ^ to IO/A long, and each is 

 vermicular with a uniform nucleus (fig. 69, A). After a short period of active move- 

 ment in the gut, each sporozoite penetrates an epithelial cell (figs. 68 spz, 69, B), and 

 once within, gradually becomes rounded (fig. 69, B, c). It grows rapidly, feeding on 

 the contents of the host cell and living as a trophozoite (fig. 69, D). When the parasite 

 is from 10 /* to 12/1 in diameter, usually multiplication by schizogony (fig. 69, E-H) 

 begins. The nucleus of the parent cell, now called a schizont, divides into a number 

 of portions that become arranged at the periphery (fig. 69, E). Cytoplasm collects 

 around each nucleus (fig. 69, E, F) and gradually a group of daughter individuals 

 (merozoites) is produced (fig. 69, G), the nucleus of each merozoite showing a 

 karyosome. 



The merozoites of Eimeria avium are arranged "en barillet," like the segments of 





mz 



FIG. 68. Small piece of epithelial lining of gut of heavily infected Grouse chick, show- 

 ing various stages in life -history of the parasite Eimeria avium ', par, parasite (trophozoite) ; 

 mz, merozoite ; sch, schizont ; spz, sporozoite ; ooc, oocyst ; c? , male gametocyte ; ? , female 

 gametocyte. X 750. (After Fantham.) 



an orange (figs. 68 mz, 69, G), therein differing from those of E. schubergi^ which are 

 arranged " en rosace." They separate from one another (fig. 69, H), penetrate other 

 epithelial cells, where they may, in turn, become schizonts. Eight to fourteen mero- 

 zoites are usually formed by each schizont, twenty have been found, while in cases 

 of intense infection when space has become limited, the number may be only four. 



After a number of generations of merozoites have been formed, a limit is reached 

 both to the multiplicative capacity of the parasite and to the power of the bird 

 to provide the invader with food. Consequently, resistant forms of the parasite 

 are necessary, and the trophozoites begin to show sexual differentiation instead 

 of forming schizonts, that is, gametogony commences. 



Certain trophozoites store food and become large and granular. These are 

 macrogametocytes (fig. 69, I, ?). The microgametocytes (fig. 69, I, <^) are 

 smaller and far less granular. The macrogametocyte continues to grow, and 



