The testes (or testicles) are the male gonads and sit below the penis within a sac called the scrotum. They are 4-5 cm long, 2.5 cm in diameter, and covered with two membranous layers, the tunica albuginea and the tunica vaginalis. The testes generate sperm, the male sex cells, as well as testosterone and other sex hormones. The production of sperm is constant and occurs within numerous lobules in each testis. First, structures called seminiferous tubules generate stem cells. These cells, the spermatogonia, divide into spermatocytes, and then divide further to become spermatids. The process is called spermatogenesis. Spermatids move from the testis to the epididymis and mature into sperm.
A cadaver view of the penile urethra from Stony Brook University School of Medicine. The Body Online.
Male reproductive system terms from the Des Moines University Online Medical Terminology Course.