Mammalian Spermatozoa

Mammalian spermatozoa are free motile cells composed of heads and tails. The tail of mammalian spermatozoa vary considerably in length depending on the species. The middle piece is the part of the tail characterized by the presence of closely packed mitochondria forming a sheath. The general organization of the Fibrous Sheath is similar in sperm tails of mammals and reptiles, but is modified in birds. The demonstration has been made that the tail of spermatozoa cannot be equated to the flagellae of unicellular organisms. Irons suggested that it may serve to channel proteins from the surrounding cytoplasm toward the connecting piece and the developing tail. Since the narrow periaxonemal cytoplasmic compartment is then eliminated from the proximal segment of the forming tail, one can speculate that the precursor proteins have a facilitated access to the outer dense fibers anlagen.