[Ultrastructural study of the epithelium of the indifferent gonad in human embryogenesis]

Gonads from 10 human embryos (28 days -- 6 weeks of development) have been studied (stage of the indifferent gonad). The material is fixed in 3% glutaraldehyde, treated in 2% osmium tetraoxide solution and after dehydratation in alcohols embedded in araldit. Ultrathin sections are contrasted in uranyl-acetate saturated alcohol solution and then in lead citrate. The sections are studied by means of the electron microscope Tesla-613. At early stages of embryogenesis (28-32 days) the cells of the germ epithelium are polar; their main organells are localized in apical parts. The granular endoplasmic reticulum is especially well developed, its membranes have the form of either a spiral or concentric circuses, mitochondria accumulate as large clusters. The cells discharge, into the celoma, their secret containing certain structures which are morphologically identical to the elements of the agranular endoplasmic reticulum. By the 33d day of embryogenesis primary sex cords appear, their cells lose polarity. In these cells Golgi complex is especially well developed. Complex plexuses of cellular processes and powerful contacts of a lock type are formed. Divergent differentiation of the gonadal epithelium into superficial and sex cord epithelium is started. With an increasing size of the gonad, the latter predominates. It begins to perform the secretory function, while the superficial epithelium becomes less active.