The mitochondria of a spermatozoon are concentrated in the

Explanation

A spiral sheath of mitochondria wraps the middle piece and supplies the ATP that the flagellum needs for the long journey to the oviduct. Placing them immediately behind the head puts the energy source next to the machinery that uses it. Almost none of these mitochondria enter the egg at fertilisation, which is why human mitochondrial DNA is inherited from the mother alone.