Examination was made of the ultrastructure of the epithelial lining of the ovarian wall and the ovigerous lamellae in the ovary of female masked greenling, Hexagrammos octogrammus, to determine the origin of the jelly-like ovarian fluid present in the ovarian lumen during the spawning period. The surface of the ovarian wall and ovigerous lamellae were each covered with monolayered epithelium resting on the basement membrane. During the spawning period, microvilli were present on the apical surface, and remarkable increases in mitochondria, rough-surfaced endoplasmic reticula and Golgi apparati were noted. Many secretory vesicles were separate from the Golgi apparatus. Microapocrine secretion and exocytosis occurred at the tips and basal parts of the microvilli, respectively, throughout the spawning period. In one case macroapocrine secretion from the ovarian wall epithelium was observed and is suggested as representing the time of most active secretion. The endocytotic uptake of secretory substances at the basal and lateral parts of the epithelium was evident from an experiment using horseradish peroxidase as a tracer. The results indicated that the components of the jelly-like ovarian fluid are synthesized and secreted not only from ovarian wall epithelium, but also from ovigerous lamella epithelium, the modes of secretion from these epithelia comprising microapocrine, macroapocrine and exocytotic mechanisms.