In mammals, the vas deferens is the duct that transports sperm from the testicle to the urethra. As a part of the complex system of the male ejaculatory system, the vas deferens transport sperm, along with the other components of semen, into the urethra prior to ejaculation. A vasectomy is a surgical procedure in which the vas deferens are cut so that sperm are unable to enter the semen – this is a form of contraception.