A zoomed scan area of the midpiece of a human spermatozoon. (A) SNOM topography, (B) 3D representation of the topography, (C) SNOM optical reflection and (D) SNOM transmission. The white arrow in (D) indicates the point where a marked variation in optical contrast along the spermatozoon can be detected. The red arrows in (D) indicate the area with ovoid elements where mitochondria are located as illustrated in the sketch of Figure . (E) longitudinal profile from arrow 1 to arrow 2. Arrowheads indicate additional discontinuities.