Light microscopy of fetal testis showing intertubular region with clusters of fetal Leydig cells stained deep purple. Fetal Leydig cells secrete androgens essential for masculinization of the fetus. Capillaries are noted and many mesenchymal cells that are capable of developing into new Leydig cells. Around the time of birth fetal Leydig cells are sparse. The adult population of Leydig cells begin to appear at puberty. Magnification x 500 when printed at 10cm.