246 THE GROUSE IN HEALTH AND IN DISEASE 



The sporocysts when quite ripe tend to become more pointed at one end 

 (PI. xxxvi., Fig. 60; PL XXXVIL, Figs. 71, 75, 76), where a slight thickening or small 

 Stieda's plate (Fig. 71) may appear, which is a point of weakness, for here a rupture 

 may occur under the action of the digestive juices of the fresh host, forming a sort 

 of micropyle through which the sporozoites escape. Partially ruptured sporocysts 

 are sometimes found (PL xxxvi., Figs. 59, 60). In the case of Grouse chicks dying 

 from acute Coccidiosis, ripe sporocysts have been found in the ceecal walls 

 themselves, as well as in the caecal contents, though usually mature sporocvsts 

 are found in caecal droppings that have been exposed. 



The oocysts of Eimeria avium show a fair amount of variation among them- 

 selves. Usually the oocysts are oval (PL xxxvu., Figs. 65-68, 71, 72, 77, 78), 

 actually measured specimens varying from 25/* to 35/x in length and from 14^ to 

 20/x in breadth. Sometimes the oocysts are not oval but subspherical (Fig. 70), 

 and these are from 18/ to 20/x in diameter. Somewhat pyriform or egg-shaped 

 oocysts (Fig. 69) are intermediate in size between the oval and subspherical forms. 

 Morse (1908) noted the occurrence of both round and oval oocysts when investi- 

 gating white diarrhoea of fowls, in which Coccidiosis played an important part. 



Among the oocysts of E. avium certain were found with somewhat squarish 

 ends (Fig. 78), while others had a slight depression at the apex (Fig. 79), but their 

 development was identical with that of the more common forms. Occasionally, 

 oocysts with two sporocysts only (Figs. 81, 82) were found, but these were abnormal 

 forms, as was also a parasite (Fig. 83) in which the cytoplasm extended in a cone 

 or funnel-like fashion to the edge of the oocyst. 



The size and shape of the oocysts are largely determined by the space in which 

 the macrogamete develops and the amount of food available for the parasite. When 

 there are many Eimeria present in any particular region of the gut, the oocysts 

 produced are relatively small, while where abundance of space arid 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. Uni-nucleate oocysts mature their 

 sporocysts in two to three days. The period for the total life-history of the 

 parasite would be from eight to ten days. 



The larvae and imagines of Svatoplmga stercoraria, the dung-fly, ingest the 

 oocysts of E. avium along with the Grouse faeces. The oocysts pass through the 

 bodies of the larvse uninjured, and are scattered with the excrement, thus serving 

 to disperse the spores to some extent. 



