Light- and electron-microscopic study of the endolymphatic sac of the tree frog, Hyla arborea japonica.

The endolymphatic sac of the tree frog and its crystals were observed by light- and electron microscopy. Scanning electron microscopy revealed that the crystals have a faceted body and two pointed ends. Light- and transmission electron microscopy revealed that the endolymphatic sac is composed of many small chambers. In their lumina, numerous "ghosts" of crystals that resulted from decalcifications were observed. The ghosts were demarcated by a linear dense material or embedded in a flocculent substance. The epithelium of the endolymphatic sac is simple squamous or cuboidal and peculiar cytoplasmic granules are found in most cells. The granules are surrounded by a limiting membrane and have varying electron density. Some granules contain a core and/or tubular structures. Vacuoles containing large ghosts are also found in the epithelial cells. These ghosts were quite similar to those in the lumen and sometimes coexist with cell debris. The fine structure of the endolymphatic sac and its crystals is discussed.