Eimeria tenella is the pathogen of cecal coccidiosis in chicks. The entire life cycle is shown in a culture of primary chick kidney epithelial cells. Simultaneous and time-lapse shots show all the developmental stages: sporulated oocysts, free sporocysts, excystation of sporozoites from the sporocyst, invasion of the sporozoites into the tissues of the host organism with the orientation and migratory phases. The phase of asexual multiple fission (schizogony): transformation of sporozoites into polymorph trophozoites and then into schizonts (merozoites 1 and 2). The maturation phase of male microgamonts and female macrogamonts to micro- and macrogametes = zygote (gamogony). Sporogony of oocysts.