"GROUSE DISEASE"— COCCIDIOSIS 247 



IV. Summary of the Life-History of Eimeria 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 iu Text-Fig. 1, A-T (p. 248). Beginning as a sporozoite (PI. 

 XXXIV., Fig. 2 ; Text-Fig. 1, A) liberated by the action of the pancreatic juice of the 

 Grouse, the parasite rapidly penetrates an epithelial cell of the duodenum (Text-Fig. 

 1, B) and entering the cell rounds up (Text-Fig. 1, C) and becomes a passive growing 

 trophozoite (PI. XXXIV., Figs. 3-7; Text-Fig. 1, D). After a period of rapid growth, 

 during which time the trophozoite (Figs. 8-11) practically destroys the cell harbour- 

 ing it, the parasite enters upon an asexual, multiplicative phase termed schizogony. 



The schizont is at first uni-nucleate (Fig. 12 ; Text-Fig. 1, D) but the nucleus soon 

 fragments (Figs. 12, 13), the daughter nuclei migrate to the periphery (Figs. 14-16 ; 

 Text-Fig. 1, E), cytoplasm segregates around each (Text-Fig. 1, F), and the daughter 

 forms thus produced become meridionally arranged, like the segments of an orange, 

 the arrangement of the merozoites being "en barillet" (PI. xxxiv., Figs. 17-22; 

 PI. XXXV,, Figs. 23-25 ; Text-Fig. 1, 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. 1, H), and the free germs seek out and enter an hitherto uninfected cell 

 where the parasite again assumes the trophic phase and then undergoes division as 

 before. Several successive generations of schizonts and merozoites are thus pro- 

 duced, resulting in a great destruction of the gut-epithelium of the host. Finally 

 a limit is reached to the ability of the host to provide nourishment and to the 

 multiplicative powers of the parasite, and this results in the onset of sexual 

 differentiation. Gametogony may occur both in the duodenum and caecum. 



Certain schizonts become considerably modified in one of two directions. In 

 the first case, food material accumulates, and a large, uni-nucleate food-laden form 

 is produced (Figs. 26-30). This is the macro-gametocyte (Text-Fig. 1, I 9), destined 

 to give rise to a single macrogamete (Text-Fig. 1, J ?). In the second instance (Text- 

 Fig. 1, I <? ), nuclear multiplication of a finely granular parasite (PI. xxxvi.. Fig. 37) 

 occurs, and the many minute nuclei produced reach the periphery of the host-cell 

 (Figs. 38-42), and ultimately the now multi-nucleate micro-gametocyte (Text-Fig. 1, 

 Jc?) gives rise to a large number of small, motile microgametes (Figs. 43-46 ; Text- 

 Fig. 1, Kt?). The macrogamete early invests itself with a cyst-wall (Figs. 35, 

 36) in which a thin part or micropyle is left for the entry of the microgamete 



