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Description: Sperm diagram showing ultrastructural details. The apical ridge shows at the top of the head. The acrosomal cap terminates at the nuclear ring. The cell membrane has been removed to show the mitochondrial helix surrounding the principal piece of the tail and terminating at the junction with the midpiece. The cross sections show an outer ring of nine coarse fibers, an inner ring of nine fine fibers, and two central fibers. Bull sperm average about 0.8 mm in length, the head accounting for about 10% of the overall length.