The fine structure of Leucocytozoon simondi. I. Gametocytogenesis

Abstract

Merozoites from hepatic and megaloschizonts are bounded by a single membrane and are slightly irregular in shape. They possess a single nucleus and mitochondrion, and electron-dense paired organelles associated with a polar ring. Hepatic merozoites develop in polychromatic and mature erythrocytes to form round gametocytes. Those from megaloschizonts develop in white cells, primarily lymphocytes, to form elongate gametocytes. Unlike hepatic merozoites the sex of the megalomerozoites can be recognized while they are still within the schizont. The cytoplasm of female merozoites, like that of mature gametocytes, is considerably darker than that of the male because of the density of ribosomes in the former. Mature macrogametocytes contain a compact nucleus, accumulations of dense material, mitochondria, lipid inclusions, and small electron-dense bodies. Microgametocytes have a lighter cytoplasm containing a large nucleus bounded by a double membrane with invaginations in which mitochondria are found. Mature gametocytes are bounded by an 11-layered pellicle. Endogenous bands of microtubules were observed in elongate gametocytes but not in the round forms. Feeding appears to be restricted to diffusion in immature gametocytes and to pinocytotic uptake of host cytoplasm in maturing forms. The peculiar dimorphism of gametocytes and their possible significance in the life cycle are discussed.