washed but unincubated sperm heads had all of the fine structural characteristics of normal spermatozoa : intact plasma membrane , acrosome , equatorial segment , postacrosomal sheath , subacrosomal space filled with fine granular material , dense nucleus containing conspicuous nuclear vacuoles of differing sizes and numbers , and faintly discernible nuclear membrane .
C0007610
nucleus
C0028584
nuclear membrane