238 THE GROUSE IN HEALTH AND IN DISEASE 



differentiated sporocysts within them (Figs. 67-70). Each sporocyst, if ingested by 

 another Grouse, can develop two active, motile germs or sporozoites (Figs. 71-76). 

 which can penetrate the intestinal epithelium especially of the duodenum and 

 so begin a new infection. Though the oocysts and spores are the most obvious 

 external manifestation of Coccidiosis, it is usual, and certainly more convenient, to 

 begin the life-cycle of the Coccidium with the minute sporozoite (PI. xxxiv., 

 Fig. 2), the agent whereby primary infection is brought about. 



The sporozoites are minute, falciform, or vermicular bodies (PI. xxxiv., Fig. 2) 



capable of fairly rapid movement, and possessing great penetrative powers. They 



measure from 7u to 10 in length. The ends of the sporozoite are rather 



Young 



growing pointed, the extremity that moves foremost being slightly more acuminate 

 than the posterior end. The general body cytoplasm is more or less homo- 

 geneous, exhibiting but very fine granulations. The nucleus has a definite rounded 

 or oval contour. The chromatin is evenly distributed throughout the nucleus. 



When the sporozoites are liberated from the investing sporocyst (PI. XXXVIL, 

 Figs. 74-76), by the action of the pancreatic juice of the Grouse, they are capable of 

 active movement. The usual method of progression resembles that of the sporozoite 

 or motile trophozoite of a gregarine. The organism moves forward with a slow 

 gliding movement, the forward progression being facilitated by the secretion of a 

 viscid proteid substance that rapidly hardens. On the smooth surface thus pro- 

 vided the coccidian sporozoite glides forward. The track of the sporozoite, as 

 shown by its trail, can be stained, and the organism then shows the gelatinous or 

 proteid material issuing from near the posterior region of its body (PI. xxxiv., 

 Fig. 2). During the gliding movement waves travel down the body of the sporo- 

 zoite, recalling what is seen on a larger scale in the billowy undulations of the foot of 

 a snail. On other occasions a more rapid movement of the sporozoite occurs. The 

 two ends of the organism become approximated and then rapidly straightened, the 

 effect being to propel the organism forwards much more quickly than when the 

 gliding movement alone is used. 



The sporozoite thus makes its way to an epithelial cell of the duodenum and 

 proceeds to penetrate the cell. As it forces its way inwards (PI. xxxiv., Figs. 3, 4), 

 so the sporozoite curves on itself (Fig. 7) and becomes round and immobile (Figs. 5, 

 6, 8). The young, rounded parasite (Figs. 8-10) is now on the trophic phase of 

 existence, and continues to grow for some time, feeding passively on the food-materials 

 of the host-cell. During this period the parasite is called a trophozoite (Figs. 8-12). 



