What is the tightly coiled tube in the scrotal sac that connects the testes with the vas deferens?

The epididymis is the structure that fits the description provided in the question. It is a tightly coiled tube located at the back of each testis and plays a crucial role in the maturation and storage of sperm. The epididymis connects the testes, where sperm is produced, to the vas deferens, which carries sperm to the ejaculatory duct.

Understanding this structure's function and location is essential in grasping how the male reproductive system operates. The vas deferens, while also part of the reproductive tract, is responsible for transporting sperm but does not have the same coiled form or connection to sperm maturation. The scrotum is the external pouch that holds the testes and regulates their temperature but is not a tubular structure. The testicles, or testes, are the organs responsible for sperm production and hormone secretion but again do not fit the description of a coiled tube. Thus, the epididymis is the correct answer as it fulfills both structural and functional aspects pertinent to the question.