1910.] MORPHOLOGY OF EIMERIA AVIUM. 677 



central (PI. LV. figs. 20, 21) or somewhat towards one end 

 (PI. LV. fig. 22, PI. LVI. fig. 23). The nucleus of the merozoite 

 is small, and the presence of a karyosome is often not veiy 

 evident, though there is a small granule of chromatin — repre- 

 senting the kaiyosome — usually to one side of the nucleus 

 (fig. 24). The ends of the merozoites are rather less pointed 

 than those of the sporozoites, a feature that E. avium has in 

 common with E. schtobergi as described by Schaudiiin. 



When the merozoites reach a new host-cell, they enter, become 

 i-ound, and proceed to grow as trophozoites in the same way as did 

 their parent organism, and undergo later nuclear fi'agmentation 

 in a similar manner. As the result of this, many more merozoites 

 are produced, and as schizogony may be continued thi-ough 

 several generations, the destruction of the gut epithelium is very 

 extensive (PL LY. fig. 1). 



Towai-ds the end of schizogony — especially in the c?ecum — 

 relatively smaller schizonts with lai-ger and fewer merozoites 

 (fig. 25), about five in number on the average, are produced. 

 These larger merozoites appear to be formed near the end of 

 infection, in company with large numbers of gametocytes, so far 

 as evidence is available. 



These differences in the schizonts might be taken by some 

 investigators to be indicative of difference of species — in other 

 words, that more than one species of Coccidium may occur in the 

 gut of grouse. I do not state that this is not so, but personally 

 prefer the view that the differences in the schizonts and 

 merozoites noted are reflexes of the condition of nutriment of 

 the parasite. Wenyon (1907) has some interesting observations 

 on the variations in the schizogony of E. fcdciformis in the 

 mouse, and states that the variations are due to the nourishment 

 available for the parasite. Again, the species found in the liver 

 and gut of the rabbit {Coccidium ovifoi-me and C.perforans) are 

 now usually united into one species, Eimeria stiedce. 



The merozoites originally produced in the duodenum pass lower 

 down the gut and i^each the cfeca. At the ileo-C!©cal junction, 

 the epithelium is attacked again, and the merozoites rapidly grow 

 to schizonts which produce new generations of merozoites, so 

 that the cfeca soon contain very large numbers of the parasites. 



Probably coccidiosis set up in the duodenal wall is sufiicient to 

 kill very young chicks, e.g. chicks 8 to 10 days old, while older 

 chicks dying at the age of about 4 to 6 weeks may have pai-tially 

 recovered from duodenal coccidiosis, but succumb to coccidiosis 

 in the caecum (typhlitic coccidiosis). In cases of intense duodenal 

 coccidiosis, merozoites are found fi'ee in the intestinal contents 

 and even in freshly shed faeces. 



Sooner or later a limit is reached, both to the power of the 

 grouse chick to provide nourishment for the parasite, and to 

 the multiplicative capacity of the parasite itself. In other words, 

 the host begins to react on the parasite. Consequent on the 

 now unfavourable environment, the parasite proceeds to form 

 gametes, in order that its species may be perpetuated. The 



