An Electron Microscopic Study on the Toad

In spite of numerous investigations, the nature and function of the subcommissural organ (SCO) located beneath the posterior commissure was not clear owing to poor staining methods, and for a long time this organ was regarded as one of the most mysterious organs. However, since recently a variety of special staining methods including GOMORI's chrome alum hematoxylin and other histochemical techniques was introduced in studies of this organ, remarkable advances have been made in this field by many investigators, and the fact that the SCO throughout the series vertebrates displays either rudimentary or intensive secretory activity and that the stainable sec retory substances which are presumed to contain mucopolysaccharide-protein comlex are discharged from the apical portion of the cell into the ventricle lumen has been established. On the other hand, it has been also confirmed that in most of the lower vertebrates, occasionally even in a few mammals, besides the apical secretion the other mode of transport of secretory substances occur by which they are released via cell processes into capillaries or the subarachnoidal lumen (OKSCHE 1956, OKADA 1956, MURAKAMI, BAN and AIURA 1957, HOFER 1958 and VIGH et al. 1961). Though a large amount of light microscopical studies about it were performed, investigations of the SCO using electron microscope have been hitherto published only by a few authors (AFZELIUS and OLSSON 1957, MURAKAMI 1959 and MURAKAMI et al. 1962). MURAKAMI and his collaborators (1962) studied the SCO of histamin treated Gecko with the electron microscope and stated that the secretory substances are pro duced in the rough surfaced endoplasmic reticulum located in the supranuclear region. But the problem to what extent the GOLGI complex is involved in the formation of secretory substances remained unsolved. In the present paper the fine structure of the toad subcommissural cell as well as of the hypendymal cell was observed and at the same time the origin of secretory sub stances was discussed.