part of axial complex spermatid axoneme Flagellar organelle that grows out from the basal body embedded at the base of the nucleus, on an onion stage spermatid. It elongates throughout the elongation stage to extend the length of the sperm tail. It is surrounded by a double membrane (axonemal sheath) and has the characteristic 9+2 disposition, with 9 outer doublet microtubules surrounding a central pair of singlet microtubules. During development, a projection from each doublet microtubule extends to form an accessory microtubule which becomes densely stained. Radial spokes develop that connect the outer doublets with the central region of the axoneme. fly_anatomy.ontology FBbt:00004950 axial filament cell component male-specific anatomical entity