Surface of the Equatorial Segment of the Mammalian Acrosome

Surface replicas were made of spermatozoa of 8 mammalian species, which had been fixed after either brief washing in isotonic Hank’s BSS or exposure to hypotonic Hank’s for several minutes. In bull, rabbit, hamster, guinea pig, degu and Rhesus monkey the surface of the outer acrosomal membrane in the equatorial region was found to be composed of regular rows of hexagonally packed particles with center-to-center spacing of 170A. These particles are limited to the equatorial segment. The majority of the surface of the outer acrosomal membrane in mouse and rat was composed of similar 170A spaced particles suggesting that the major portion of the acrosomal surface in mouse and rat is analogous to the equatorial segment of other species. The postacrosomal region in several species was found to be composed of material arranged in parallel ridges with center-to-center spacing of 1 50A.