"GROUSE DISEASE"— COCCIDIOSIS 241 



The merozoites originally produced in the duodenum pass lower down the gut 

 and reach the caeca. At the ileo-caecal junction the epithelium is attacked again, 

 and the merozoites rapidly grow to schizonts, which produce new generations of 

 merozoites, so that the caeca soon contain very large numbers of the parasites. 



Probably Coccidiosis set up in the duodenal wall is sufficient to kill very young 

 chicks, e.g., chicks eight to ten days old, while older chicks dying at the age of 

 about four to six weeks may have partially recovered from duodenal Coccidiosis, 

 but succumb to Coccidiosis in the caecum (typhlitic Coccidiosis). In cases of 

 intense duodenal Coccidiosis, merozoites are found free 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 gametocytes or mother 

 cells of the gametes (PI. xxxv.. Figs. 26-28 ; PI. xxxvi., Fig. 37) are modified 

 schizonts which are of slow growth, and therefore can accumulate more reserve 

 food material in the form of granules within their cytoplasm. The processes 

 leading to the formation of the gametes may be termed gametogony, which we 

 may now consider. 



Sexual differentiation is characteristic of the gametes of Coccidia, and in the 

 case of Eimeria avium the differentiation is apparent in the gametocyte phase. 

 Two forms of gametocytes can be distinguished. The first group are intra- 

 cellular parasites containing large granules of food reserve within their gonj'- 

 cytoplasm. These are the macro-gametocytes (PI. xxxv., Fig. 26) which give 

 rise each to one female gamete. On the other hand, the micro - gametocytes 

 (PI. XXXVI., Fig. 37) or male progenitors contain a little reserve food material 

 in the form of very minute granules, distributed evenly throughout the body 

 substance. Each micro-gametocyte gives rise to many microgametes. 



The structure of the macro-gametocyte and of the single macrogamete that arises 

 from it is very difficult to interpret in Eimeria avium, on account of 

 the large amount of reserve food material contained within the cytoplasm. game°ocyte 

 Further, it is very difficult to draw the exact dividing line between the gamete?'^" 

 macro-gametocj'te and the female gamete, as the one gradually merges 

 into the other. These forms vary from 11 "8^ to 17 '5^ in length by 6/x to 11^ in 



VOL. I. Q 



