Ultrastructural observations of the intra-erythrocytic merozoite in Theileria sergenti.

The intra-erythrocytic merozoite of Theileria sergenti was 2.2 to 2.4 micron long; several mitochondria and a large nucleus lay at the anterior and posterior part of the cell, respectively, and free ribosomes were evenly scattered in the cytoplasm. A micropore located at the antero-ventral side of the protozoon was framed by the local thickening of the plasma membrane with high electron-density, nearby a large food vacuole containing erythrocytic matrix-like substances. The highly developed rough endoplasmic reticulum was abundant around the vacuole. On the other hand, the erythrocytes including many strongly basophilic stipplings seem to be the erythrocytes with a large quantity of highly electron dense granules. Uneven-surfaced reticulocytes with a certain amount of fine granules through-out the cytoplasm possessed some pinosomes, a considerable number of degenerating mitochondria and smooth endoplasmic reticulum.