(Redrawn after Markell and Voge 1971)
Trophozoites are almost always found one per erythrocyte, except in heavy infections. When young they are round with a peripheral chromatin mass and a central vacuole, hence are often termed "ring" stages. As the trophozoite ages it enlarges and the margins may become more irregular. The central vaculole becomes less prominent in the oldest trophozoites and they become more ameboid. Once nuclear division has occurred the parasite is now in the schizont stage. Eventually cytokinesis occurs to produce individual merozoites which soon rupture the erythrocyte. Some trophozoites will transform into gametocytes, which have a large nucleus and do not develop further until ingested by the mosquito vector.