Sperm production. Coloured scanning electron micrograph (SEM) of healthy spermatozoa (sperm, green) passing along a tube in the rete testis of a testis. The testes are the male organs that produce sperm, the male gametes (sex cells). The rete testis is a network of tiny tubes that links the seminiferous tubules, where the sperm are formed, to the efferent ducts (vasa efferentia). These ducts carry the sperm to the epididymis, a structure behind the testis where the sperm mature and are stored ready for ejaculation. Magnification unknown.