The vas deferens, also known as the ductus deferens or sperm duct, is a long muscular tube that is part of the male reproductive system. Its primary function is to transport mature sperm from the epididymis to the urethra before ejaculation. The vas deferens begins in the scrotum, which is the sac containing the testicles, and then travels from the testicle into the body. It continues until it joins with the duct of the seminal vesicle to create the ejaculatory duct. The vas deferens is surrounded by the spermatic cord and is approximately 30-45 cm (almost 12-18 inches) long. The tube is described as being fibromuscular, meaning that it is made of fibrous tissue and muscle tissue.

In summary, the vas deferens is responsible for transporting mature sperm from the epididymis to the urethra before ejaculation.