The male reproductive system is a set of organs which produce male gametes (sperm cells) and deliver them to the uterus of the female. The primary male reproductive organs are the testicles and scrotum. The testes or testicles generate sperms. The formation of sperms is activated by the hormone testosterone (male hormone). The sperms pass from the testes into the vas deferens through the epididymis. Sperm cells are mixed with liquid in the seminal vesicles to form semen. The semen is ejaculated out of the penis.