Vas deferens

The vas deferens, also called ductus deferens, (Latin: "carrying-away vessel") is part of the human male anatomy. There are two of them; they are muscular tubes (surrounded by smooth muscle) connecting the left and right epididymis to the ejaculatory ducts in order to move sperm. Each tube is about 30 centimeters long.
During ejaculation the wall of the vas deferens thickens and thins itself, thus propelling the sperm forward.

Vasectomy is a method of contraception where the vasa deferensa are permanently cut.