Ductus Deferens. The ductus deferens, also known as the vas deferens, is a tiny muscular tube in the male reproductive system that carries sperm from the epididymis to the ejaculatory duct.he ductus deferens serves dual functions in the male reproductive system: 1  Transporting sperm from the testes to the ejaculatory duct and urethra. 2  Storing sperm until it is ready to be ejaculated.