The ultrastructure of the germinal epithelium of the mouse ovary

It was demonstrated that the germinal (surface) epithelium around the mouse ovary consists of simple squamous, cuboidal and columnar arrangements of cells. With the electron microscope it was shown that these cells have the usual cytoplasmic constituents such as the Golgi complex, mitochondria, ergastoplasm, and free ribosomes. Their nuclei are surrounded by a bilamellar envelope with coarse granular masses of nuclear material being distributed along its inner surface. From the surface of these cells extend numerous microprojections which usually are irregular in squamous cells, but are villus‐like on the cuboidal and columnar forms. These microvilli appear to be simply extensions of the cell surface and apparently reflect the capacity of mesothelium for such specialization at its free surface. The intercellular boundaries are seen to consist of wavy, downward extensions of the plasma membrane or a complex irregular interdigitation of coarse lateral processes. The latter form is especially prominent between squamous cells. A membrane is present at the basal cell surface. The observations concerning the presence of microprojections and the nature of the intercellular boundaries were discussed in the light of the controversies on these subjects which appear in the early literature. The possible permeability of the germinal epithelium and its functional significance during maturation of the ovary were also discussed.