ABSTRACT
The structure of the ovary and cellular events of oogenesis of Ophionereis schayeri were documented by light and electron microscopy. Oogenesis in O. schayeri is follicular with oocytes surrounded by follicle cells throughout their development. The oocytes are attached to the germinal epithelium at the animal pole by attachment cells. Cell processes of the attachment cells and the oocyte interdigitate with each other, thereby anchoring the oocyte to the germinal epithelium. The follicles consist of somatic cells and the underlying connective tissue layer, with incorporated haemal fluid which forms an eosinophilic and PAS+ halo around each oocyte. Ovulation involves rupture of the follicle and empty U-shaped follicles are prominent in the ovaries after spawning. Vitellogenic oocytes and the surrounding haemal fluid are PAS+, suggesting the transfer of material from the haemal sinus to the oocytes. Endocytosis is prevalent throughout oogenesis, providing evidence for the incorporation of extraovarian vitellogenic material, potentially derived from the haemal sinus. Yolk formation in 0. schayeri oocytes involves ER/Golgi activity. Some yolk bodies however are not associated with ER and Golgi and may arise in association with ribosomes in the cytoplasm. It appears that yolk formation in this species involves both autosynthetic and heterosynthetic mechanisms.
