Observations on the fine structure of vole spermatozoa with particular reference to cytoskeletal elements in the mature sperm head

Epididymal spermatozoa from two species of vole demonstrate cytoskeletal structures closely associated with the plasma membrane. Microtubule-like elements (2O–24 nm in diameter) form a parallel sheath radiating from the posterior ring to the inferior acrosomal margin just beneath the plasma membrane. Fine filaments (5–8 nm in diameter) are associated with the cell surface, especially in the region of the concave curvature of the acrosomal hook. Both of these elements may aid in stabilizing these respective areas and it is suggested that microtubule-like and filamentous structures may serve important cytoskeletal roles in the mature sperm head.