The objectives of this experiment are to perform natural fertilization and to achieve embryonic development in microgravity. Pleurodeles waltl, an urodele amphibian, is considered by CNES and NASA to be suitable experimental material for achieving in vivo fertilization in space. Previously inseminated females can be embarked in the Frog Environmental Unit (FEU) developed by NASA. Laying of eggs will be provoked by hormonal stimulation in flight and development will be followed. Various technical problems have been resolved in laboratory experiments and during parabolic flights : the time of hormone stimulation after insemination, choice of hormone guaranteeing [correction of guarenteing] 95% success, other factors conditioning [correction of conditionning] the laying, experimental procedures to study developmental kinetics at phenotypic levels, and selection of cellular and molecular markers of development.