QUANTITATIVE DATA ABOUT GAMETOGENESIS AND EMBRYONIC-DEVELOPMENT IN HYDRA-VULGARIS PALL (CNIDARIA, HYDROZOA)

This paper reports on the reproductive behavior of gametogenically active polyps of Hydra vulgaris (Pallas, 1766) strain ''Scotland 1989'' covering an observation period of 4 years (1989-93). The monitored sexually active hermaphrodites and all their asexually generated offspring produced gametes in uninterrupted series of individual sexual periods, which did not exclude reproduction by budding. Quantitative data are given about the investments made by polyps into gametogenesis in the course of a sexual period. A growing oocyte incorporates more than 10,000 nurse cells (interstitial cells) into the ooplasm by phagocytosis. Various observations suggest that male and female gametes derive independently from separate predetermined stocks of stem cells which are autonomous in their turn from the cell populations committed to somatic renewal processes. Only a small number of the fast and slow developing embryos survived a critical post-hatching period.