Fine Structure of the Sperm Head in Ejaculate and Uterine Spermatozoa of the Rabbit

Summary. The microstructure of the rabbit sperm head in ejaculate and in uterine spermatozoa has been examined with the electron microscope. The normal structure of the sperm head is described, and it is suggested that the properties of the plasma membrane may vary over different regions. No morphological change in the acrosome cap, which might account for the functional difference in capacitated spermatozoa, has been observed. There are indications, however, that the plasma membrane is more easily separable from the anterior and lateral edges of the underlying acrosome cap in spermatozoa recovered from the uterus. Abnormal forms of acrosome cap development are described, and are discussed particularly in relation to similar abnormalities described previously in bull and boar spermatozoa.