Ultrastructural studies on the endogenous development of Eimeria brunetti.

The schizonts of Eimeria brunetti were studied in the epithelial cells of the small intestine of infected chickens. The morphology of the host/parasite relationship was typical of that reported for other Eimeria spp. The initial dedifferentiation of the infecting organism generally occurred within the parasite cytoplasm but it was also observed that cytoplasm containing organelles could be budded off into the parasitophorous vacuole. Development into the schizont was accompanied by cytoplasmic growth and nuclear division. During nuclear division an eccentrically located nuclear spindle was present. Merozoite formation was initiated just below the limiting membrane of the schizont and was associated with the final nuclear division. The merozoites developed as protrusions from the schizont surface and merozoite organelles developed within these cytoplasmic projections. From this early stage, the developing merozoite grew and matured and the fully formed merozoites were found attached to a small residual mass of schizont cytoplasm. The 1st generation schizont is the only one which can be separately characterized. It differs from those of subsequent generations in a) possessing a refractile body, b) being larger and producing a larger number of merozoites, c) possessing invaginations of the limiting membrane, and d) the intra vacuolar folds of its parasitophorous vacuole are more extensive.