Summary. A method has been developed for establishing from electron micrographs the radius of curvature of rabbit and guinea-pig sperm nuclei in head-to-tail section (the major axis), and of guinea-pig spermatozoa with intact acrosomes in transverse section (the minor axis). Radii of curvature of head-to-tail sections lie, for the most part, between 7 and 100 μm in both species. Guinea-pig sperm nuclei in transverse section show a range of radii between 3 and 10 μm, and approximate, therefore, caps of prolate spheroids. The method is not applicable to rat and mouse spermatozoa but Nomarski light microscopy suggests that these nuclei are straight in the longitudinal direction. The distribution of the radii of curvature in rabbit sperm nuclei is similar to that of the radii of curvature of penetration slits through the zona pellucida of the rabbit egg. It is suggested that longitudinal curvature of sperm heads is correlated with any curvature of the penetration slit.
Keywords: mammalian spermatozoa; head shape; penetration slit; zona pellucida
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