Fine structure of the interstitial cells of leydig in the boar

The interstitial cells of the testis of the boar have been characterized by electron microscopy. The bulk of the cytoplasm, to one side of an eccentrically placed nucleus, consisted predominately of a tightly packed agranular endoplasmic reticulum in a system of anastomosing tubules. Free ribosomes and a few short strands of granular endoplasmic reticulum were present only in a perinuclear or subplasmalemmal location. Mitochondria were abundant as a cluster in the center of the cytosome. Surrounding them were dense bodies, most of which were bounded by a single limiting membrane. The internum of the dense bodies exhibited a variety of appearances. Filaments of 70 Å were common but they were absent near the plasmalemma. Between contiguous cells, irregularly disposed microvilli protruded into an intercellular space of variable dimensions. Some sites of membrane fusion, resulting in maculae occludentes, were observed between adjacent cells, while small desmosomes were observed but rarely. Coated vesicles were frequent near to and continuous with the plasmalemma as well as deeper within the cell, especially in association with elements of the Golgi apparatus.