Abstract
The thyroid gland of normal adult specimens of teleosts, the Semicossyphus reticulatus and the Sebastiscus marmoratus obtained in the Inland Sea of Seto in June, were observed with the electron microscope.
The fine structure of the thyroid follicle cell is generally more similar to that of the higher vertebrates than to that of the cyclostome such as a lamprey in the cytoplasmic structures especially in the well developed rough-surfaced endoplasmic reticulum and numerous intracellular granules and droplets, though the classification of the granules and droplets is not so easy as those of higher vertebrates. The characteristic of the follicular cell is the occurrence of aggregates of filamentous structures, myelin bodies, small dense bodies, vesicular structures, and irregularly shaped dense substances in large colloid droplets. They might be formed by fusion of the altered colloid droplet and cytolysome.
The capillary endothelial cells show a pored structure as those of the higher vertebrate, though those of the Seriola quinqueradiata and Anguilla japonica have been reported to be non-pored. In the endothelial cell of the capillary and the arteriole of the thyroid of the Sebastiscus marmoratus, small groups of fine filaments were seen.
