Possible secretory function of the rhoptries of Eimeria magna during penetration of cultured cells.

Ultrastructure of the penetration of Eimeria magna sporozoites into embryonic bovine trachea cells demonstrated that the host cell membrane was not broken during entry of the parasite. This membrane did, however, undergo alterations characterized by blebbing of vesicles, thickening, and eventual disorganization once penetration was completed. Concurrent with the entrance of the parasite into the cell, and the subsequent membrane alterations, was the appearance of empty membrane saccules, probably rhoptries, in the apical region of the sporozoite. It was proposed that rhoptry secretions aided penetration by changing cell surface characteristics which produced an eventual breakdown of the invaginated protion of the host cell membrane.