The vas deferens is a muscular tube in the male reproductive system that transports sperm from the epididymis to the ejaculatory duct. It is about 30 centimeters long and plays a crucial role in the process of ejaculation, helping to propel sperm during sexual activity. During ejaculation, the vas deferens contracts to push sperm into the urethra, where it mixes with fluids from the seminal vesicles and prostate gland to form semen. This process is essential for reproduction, as it allows sperm to be delivered to the female reproductive system.