SPOROZOA 469 



in the horse is Sarcocystis bertrami; in sheep and goats, S. tenella; 

 in swine, S. miescheriana ; and in man, S. lendemanni. 



THE GENUS COCCIDIUM 



This genus belongs to the sporozoan order Coccidiida. This 

 order is characterized by having in the adult an oval or spherical 

 form, not motile. Sporulation takes place within an endocellular 

 cyst. The genus Coccidium is differentiated by the formation 

 of four sporocysts or sporoblasts, each of which contains two 

 sporozo'ites. The life-history is relatively complex, and varies 

 in some details in different species. 



The organism is taken into the body with food in the form 

 of a cyst, which ruptures and allows the escape of the spindle- 

 shaped sporozoites. These penetrate the epithelial cells of the 

 intestinal walls or other membranes. The sporozoTte on entering 

 the cell rounds up into a sphere, and then grows rapidly in size 

 at the expense of the host cell. These growing organisms are 

 called at this stage schizonts. The nucleus of the mature schizont 

 fragments, and the protoplasm then breaks up into a considerable 

 number of spindle-shaped cells, called merozoites, somewhat re- 

 sembling the sporozoites. These break out of the mother schizont 

 and infect new cells. They may then develop as schizonts and 

 repeat the same cycle, or may develop into sexual reproductive 

 cells. Some of these are of considerable size and correspond to 

 an egg; these are termed the macrogametes. Others, called micro- 

 gametocytes, develop similarly at first, then form a considerable 

 number of very slender, thread-like cells called microgametes. A 

 microgamete fuses with a macrogamete to form the oocyte. This 

 then continues to enlarge, and secretes a chitinous wall; i. e., 

 becomes encysted. When mature, the contents of the cyst divide 

 to form four spherical bodies called sporoblasts. These become 

 somewhat elongated and spindle-shaped. In each of the sporo- 

 blasts two still more slender fusiform sporozoites develop. The 

 cyst is freed, and upon ingestion by a suitable host the cycle be- 

 gins again. 



Coccidiosis occurs in many of the invertebrates, which do not 

 seem to be seriously affected, but in the vertebrates serious and 

 even fatal disease may be caused by the organisms. 



