On the ultrastructure of modified Sertoli cells in the terminal segment of seminiferous tubules in the boar.

The seminiferous tubules are linked to the tubuli recti by a short terminal segment which is lined by a single layer of modified Sertoli cells whose long cytoplasmic processes occlude the lumen and form a plug-like structure in the 'receptacle. The main features of the modified Sertoli cells are: enormous numbers of microtubules and microfilaments, many crystalloids, abundance of rough endoplasmic reticulum, and paucity of smooth endoplasmic reticulum. The intercellular spaces are considerably dilated, and the cells posses intracellular spaces having well developed microvilli. Degenerated spermatozoa were seen engulfed by the modified Sertoli cells. Desmosome-like devices and tight junctions were observed joining adjacent cells. The configuration of the epithelium and the fine structure of the cells of the terminal segment are discussed in relationship to their possible roles as modifiers of the seminiferous tubule fluid and as regulators of fluid reflux from the rete testis into the seminiferous tubules.