Ultrastructural study of crystalloids in Sertoli cells of the three-toed sloth (Bradypus tridactylus).

Crystalloids were found in Sertoli cells of the testis of the three-toed sloth by examination at the light- and electron-microscopic levels. Needle-, or spindle-shaped crystalloids, varying in length, were located in the basal part of the Sertoli cells. They consisted of bundles of filaments each measuring approximately 11 nm in diameter. Several filaments were packed hexagonally to form a bundle. The center-to-center distance between individual filaments of a bundle was approximately 17 nm. Periodical lateral projections emanated from the filaments. Cross sections of crystalloids showed that the projections radiated from each filament in three directions, forming an equilateral triangle with a side length of approximately 15 nm. Scattered polyribosomes were found between and around the bundles.