Abstract
The endolymphatic sac of the guinea pig was observed by light and electron microscopy. The endolymphatic sac was divided into three portions by the morphological feature of the epithelium as previously described by Guild (1927); the proximal, intermediate and distal portion. The epithelial cells of the sac were classified into two types. One was characterized by numerous mitochondria, a large number of pinocytotic vesicles in the cytoplasm and well-developed microvilli at the apical surface (type 1), suggesting higher cellular activity of reabsorption of endolymph.
The other was characteristic for poorly developed cytoorganelles, fewer in number of microvilli and numerous intracellular filaments occupying the cytoplasmic matrix (type 2), suggesting supporting functions of the epithelium of the sac. Further, a few intermediate type cells between them are also present. The previous classification (i. e. light cell and dark cell, Lundqueist; 1965) is supposed to be owing to shrinkage of the cytoplasm by poor techniques of the specimen preparation. Neither type 1 cells or type 2 cells are so dark in their cytoplasms as dark cells reported in the previous papers. When the tissue materials are fixed by the perfusion method with glutaraldehyde solution, “dark cells” which have been reported in various organs are difficult to recognize. Similar opinions have been reported for various organs such as liver, exocrine pancreas, central nervous system, and so on.
In addition, some special regards were also given to the endocytotic activity of the endolymphatic sac. The luminal space of the sac was filled with India ink particles, 24 hours after the injection of the ink particles into the cochlear duct. Not only free floating cells in the luminal space of the endolymphatic sac, which were probably macrophages, but also both types of the epithelial cells took them up. Ink particles taken up are stored in large or small cytoplasmic vacuoles. The type 1 epithelial cells took them up better than the type 2 cells.
