Illustration of newly developed sperm cells (spermatozoa) moving through the seminiferous tubules in a testis (testicle). Seminiferous tubules are the site of sperm cell development (spermatogenesis). Spermatozoa mature as they travel through these tubules to the epididymis, a structure behind the testes, where they are stored until ejaculation. Spermatozoa are reproductive cells (gametes) which can fertilise the egg during sexual reproduction, and carry one set of chromosomes from one parent.