part of develops from Nebenkern axial complex Nebenkern derivative Structure that develops from the Nebenkern during spermatid elongation. During late onion stage, the Nebenkern begins to unfurl and elongate. At comet stage it splits into two mitochondrial derivatives, which elongate and become unequal in size during mid elongation stage. The mitochondrial derivatives assume a characteristic position to a plane that splits the central pair of axoneme microtubules which changes slightly through elongation. fly_anatomy.ontology FBbt:00004951 cell component male-specific anatomical entity