TEM micrographs of sperm head region of P. kaempferi. A Longitudinal section of sperm head, showing apex of acrosome (a), tapered nucleus (n) B Cross-section of the sperm head, showing acrosome (a) and subacrosomal space (ss) C–F Cross-sections of the sperm head, showing acrosome (a) and two acrosomal processes with numerous microtubules G Cross-section of the sperm head, showing nucleus (n) and an acrosomal process. Scale bars: 500 nm (A), 200 nm (B–G).