RESUMEN
Most terrestrial snails are oviparous and only some are ovoviviparous. The physiology of the reproductive system and its activity in these two groups have received little attention. We compared the month-to-month dynamics of reproductive cell formation between two species of Clausiliidae snails: Ruthenica filograna (an ovoviviparous species) and Clausilia bidentata (an oviparous species). Our aim was to test the hypothesis that the seasonal activity of gametogenesis is determined by reproductive strategy (oviparity /ovoviviparity). The results showed that the frequency and number of reproductive cells in different stages varied month-to-month, within each species, and between the two species. Ruthenica filograna maintained its reproductive activity throughout the entire observation period, whereas the gonadal activity of C. bidentata changed with the seasons (it was temperature dependent). Our results are in tune with the hypothesis of Baur, that ovovivipary has some advantage over oviparity under harsher environmental conditions.