The ultrastructure of the ejaculated human sperm follows the general pattern known from other mammalian sperms. However, certain features are peculiar to the human sperm. The chromatin is often granular giving it an unmature appearance, the mitochondrial helix is often unorderly arranged, the longitudinal columns of the fibrous sheath and the annular ring are not very conspicuous. The nucleus is covered by the acrosome with its anterior, reactive and posterior, unchangeable equatorial segment and most posteriorly by the postnuclear cap. Generally the gross and fine morphology of the human sperm is more varying and less regular than it is known from other mammalian sperms.