Weightlessness and the developing frog egg.

This paper describes the results of the flight of fertilized frog eggs in the manned orbital flights Gemini 8 and Gemini 12. The experiment was designed to determine the effect of weightlessness or near weightlessness on the ability of the cell to divide normally and on subsequent differentiation and embryogenesis. Eggs were fixed periodically in flight so that recovered material could be carefully compared to simultaneous ground controls with respect to gross morphology and histology. Some embryos were recovered alive after 4 days in orbit. In general, no abnormalities were detected which were inconsistent with the controls. Death, shortly after recovery, of the embryos recovered alive in Gemini 12, remains unexplained. The protocol of the experiment and the experimental hardware is described. Rationale for future experiments is discussed.