1910.] MORPHOLOGY OF EIMERIA AVIUM. 683 



wliifh tlie cytoplasm extended in a, cone or fiiuiiel like fashion to 

 the edge of the oocyst. 



The size and shape of the oocysts are largely a factor of the 

 space in which the inacrogamete develops and tlie amount of food 

 available for the pai'asite. When tliere ai-e many Eimeria present 

 in any particular region of the gat, the oocysts produced are 

 relatively small, while Avhere abundance of space and nourishment 

 are available, the oocysts tend to be large. 



From experiments made by feeding birds with Coccidian 

 oocysts, I conclude that schizogony takes from four to five days. 

 Uninucleate oocysts mature their sporocysts in two to tfiree days. 

 The period for the total life-history of the parasite would be from 

 eight to ten days. 



The larvpe and imagines of Scaiopliaga slercoraria, the dung- fly, 

 ingest the oocysts of E. avium along with the grouse ffeces. The 

 oocysts pass through the bodies of the larvje uninjui'ed, and are 

 scattered with the excrement, thus serving to disperse the spores 

 to some extent. 



V. Summary of the Life-History of Eimeiua avium. 



The life cycle of Eimeria avium is complicated, even though 

 the organism completes its development within one host. The 

 life-history may be represented diagrammatically as in text- 

 fig. 65, A-T (p. 684). Beginning as a sporozoite (PI. LV. fig. 2 ; 

 text-fig. 65, A) liberated by the action of the pancreatic juice of 

 the grouse, the parasite rapidly penetrates an epithelial cell of the 

 duodenum (text-fig. 65, B), and, entering the cell, rounds up 

 (text-fig. 65, C) and becomes a passive growing trophozoite 

 (PL LV. figs. 3-7; text-tig. 65, D). After a period of rapid 

 growth, during which time the trophozoite (figs. 8-11) practically 

 destroys the cell harbouring it, the parasite enters upon an 

 asexual, multiplicative phase termed schizogony. 



The schizont is at first uninucleate (fig. 12; text-fig. 65, D) 

 but the nucleus soon fragments (figs. 12, 13), the daughter nuclei 

 migrate to the periphery (figs. 14-16 ; text-fig. 65, E), cytoplasm 

 segregates around each (text-fig. 65, F), and the daughter forms 

 thus produced become ineridionally arranged, like the segments of 

 an orange, the arrangement of the merozoites being " en barillet " 

 (PI. LV. figs. 17-22, PL LVI. figs. 23-25; text-fig. 65, G). 



Each merozoite is a small, vermicular organism, having a 

 nucleus with a somewhat ill-defined karyosome usually to one 

 side (fig. 24). The groups of merozoites break up (text-fig. 65, H), 

 and the free germs seek out and enter an hitherto uninfected 

 cell where the parasite again assumes the trophic pliase and then 

 undergoes division as before. Several successive generations of 

 schizonts and merozoites are thus jDroduced, I'esulting in a great 

 destruction of the gut epithelium of the host. Finally a limit is 



