[Differentiation of gonadal sex in the prosobranch molluscViviparus viviparus L.].

InViviparus viviparus, the differences between the gonads of young males and young females appear first at the morphological level. The ovary is organised as a poorly branched tubule, whereas the testis is very compact and highly ramified. In the ovary, the non-germ cells (future follicular cells) surround the germ cells and the premeiotic processes begin early. During the morphogenesis of the testis contrary, several successive stages are observed. After a period of intensive cell proliferation concomitant with the ramification of the gonad, the lumen is formed by the death of the central cells. The non-germ cells become nurse cells close to the basal lamina, while the spermatogonia differentiate. The male gametes appear late.