Surface epithelium of the fetal guinea-pig ovary: a light and electron microscopic study

The surface epithelium in fetal guinea-pig ovaries was examined from the time of early sexual differentiation, about 34-days, until approximately ten days before birth. At day 34 the epithelium varied greatly in appearance as seen in the light microscope and possessed a superficial layer of flattened or culoidal cells. By day 58 the epithelium had changed into one layer of regularly arranged columnar cells. During the same period the number of germinal cells decreased. Connections between the germinal cords and the surface epithelium were observed from day 34, being especially numerous and broad at days 34 and 42 and decreasing in number and size from day 46 onwards. The basement membrane beneath the epithelium gradually increased in thickness. In the electron microscope two types of somatic cells could be distinguished. One type formed a superifical single layer connected by junctional complexes and exhibited intracellular bundles 60 A microfilaments running straight through the apical part of the cell, attached to junctional complexes on either side. These bundles were found frequently between days 34 and 42, but were rarely seen after the forth-sixth day. Microvillous projections into the coelomic cavity were especially numerous from day 34 to day 46. The other type of somatic cells lay in close proximity to the germinal cells: microfilaments or junctional complexes were not observed. The subepithelial basement lamina was continuous with that surrounding the connections and the germinal cords.