Among the 24 native clausiliids, 15 were subject to laboratory observations. Eleven of them were found to be oviparous, three — egg retainers and one — ovoviviparous. Batches, containing most often one to about a dozen of partly calcified, ellipsoidal or spherical eggs, appeared usually in the spring and autumn (in non-hibernating individuals throughout the year). Probably the main factors determining the onset of reproduction are humidity and temperature while the photoperiod has no significant effect. The incubation period is ca. two weeks (room temperature), the hatching is synchronous or asynchronous. Cases of intra-batch and inter-batch cannibalism were observed. The minimum time from hatching/birth till adult size is ca. 3–9 months and after further 5–8 months the snails start producing eggs/babies. Clausiliids are iteroparous. Anatomical studies on the development of the reproductive system show that just before lip completion the reproductive system is still incompletely developed. Penis, epiphallus and spermatheca develop within the first month after growth completion (which would indicate attainment of ability to copulate), and the reproductive system becomes wholly mature only after a few months. The clausiliid development strategy is probably the following: the quickest possible growth and attainment of adult size, then development of the reproductive system and attainment of sexual maturity.