The nebenkern is a mitochondrial formation in the sperm of some insects such as Drosophila. After the completion of meiosis, spermatid mitochondria wrap around each other to form a spherical aggregate, adjacent to the nucleus.^[1] The nebenkern proceeds to elongate into a double-stranded helical structure.^[1][2] During flagellum elongation the nebenkern unfolds and the two derivatives (major and minor mitochondrial derivatives) elongate down the bundle of microtubules that constitute the axoneme core of the flagellum.^[3]