terrestrial snails

Pulmonata

Vertigo pusilla

gonad

gametogenesis

Gonads of V. pusilla at various growth stages were examined with standard histological methods. The first gonial cells appeared at the stage of 3.3 whorls: few and poorly developed gonad vesicles contained fine mitotically dividing cells and cells in meiotic prophase, with the first growing oocytes in the peripheral parts of the vesicles. At 4-whorl stage the oocytes entered vitellogenesis and increased in volume. In subadult individuals the oocyte volume and the gonad volume increased considerably; besides the advanced vitellogenic oocytes new oocytes appeared, the number of spermatids increased and the first spermatozoa were observed. The gonad of pre-reproductive adults contained numerous late-vitellogenic oocytes, young growing oocytes and many spermatozoa. In post-reproductive individuals there were no mature oocytes, spermatozoa were few, but the presence of young oocytes and mitotically dividing cells indicated resumption of gamete production.