Ultrastructure of Babesia bigemina gametes obtained in "in vitro" erythrocyte cultures.

Propagation of Babesia bigemina in "in vitro" erythrocyte cultures resulted in the appearance of the sexual stage of the parasite, characterized by cytoplasmic projections and microtubules. These morphologically distinct parasites were found to adhere to each other, with later fusion of their membranes. No nuclear fusion was observed. The ultrastructure of the sexual stages was described.