(A) Microvasculature of the intertubular space. Co-cells encase the capillaries, Leydig cells and the seminiferous tubule. Modified from Ref. . (B) The human spermatozoon. (1) Light microscopical aspect, (2) Virtual preparation of the spermatozoon showing the acrosome, the nucleus and nuclear envelopes, the mitochondrial sheath of the main piece of the flagellum, (3–11) Cross sections of the human spermatozoon of different levels indicated in (12) longitudinal section of the human spermatozoon. Semi-schematic drawing on the basis of electron micrographs. From Ref. .