The fine structure of the limiting membrane of the seminiferous tubule in the rat
The limiting membrane of the seminiferous tubule in the rat testis is composed of two concentric PA-Schiff staining layers referred to as internal (epithelial side) and external (vascular side) lamellae. Enclosed between the lamellae there is a single continuous layer of flattened cells. Outside the external lamella a second continuous sheath is formed by other flattened cells. Under the electron microscope, the cytoplasm of the cells seen between the lamellae shows (a) a few organelles (mitochondria, aggregates of RNA-containing granules, and rough-surfaced vesicles) seen generally close to the nucleus; (b) smooth surfaced vesicles, which may arise from the numerous invaginations seen along the cell membrane; (c) a dense meshwork of delicate filaments. These characteristics make these elements similar to smooth muscle cells. The cytoplasm of the cells applied outside the external lamella does not contain the filamentous component and the invaginations at the cell surface are less numerous. These cells are probably connective tissue elements. The internal connective tissue lamella contain three layers; an inner and an outer layer made up of homogeneous dense substance and an intermediate layer made up of fibrils probably collagenous in nature. The external lamella is composed almost exclusively of the homogeneous substance.