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Structural sperm features. Spermatozoa are composed of two main parts: head and tail (or flagellum). The sperm head is constituted basically by the acrosome and nucleus. The sperm tail includes: the neck that contains mainly the proximal centriole; the midpiece which is composed by mitochondria, outer dense fibers (ODF) and axoneme; principal piece containing the fibrous sheath and axoneme; and terminal piece.
