Ultrastructure of Sarcocystis tenella (Sarcocystis ovicanis).

The ultrastructure of the parasitophorous cyst, the metrocytes and merozoites of Sarcocystis tenella (S. ovicanis) was studied. The general ultrastructural features of the cyst wall and the cells of the protozoan, previously described by other authors, were confirmed. The vesicle-like invaginations of the unit membrane (primary wall) of the cyst are identical with the micropinocytic pits of other animal cells, and we believe that they contribute to the nutritional process of the cyst. The Golgi apparatus must be related to the granular endoplasmic reticulum, since the first cisterna of the curved side of the stack appeared to originate from it. The structure of the micropore was similar to that previously described by other workers, the only difference being that in this study, material was frequently observed inside the lumen. This observation led us to support the previously suggested nutritive role. In addition, crystalloid material limited by cytoplasmic membrane was often observed, but the manner of its formation and role remain unknown.