The production of several successive generations of megalospheric schizonts, alternating with phases of sexual reproduction, was observed in laboratory cultures of Ammonia tepida. The isolation of megalospheric schizonts facilitated observations on the formation of reproductive cysts and the nearly total decalcification of the parental test during schizogony. These studies also follow the ontogenic development of the test in individuals produced by schizogony. Irregularities during development of the early stages lead to adults with characteristic malformations. This study brings new materials for a better understanding of the trimorphic cycle of Ammonia tepida.