Which structure is responsible for protecting the testes and maintaining their temperature?

The scrotum is the structure that plays a crucial role in protecting the testes as well as regulating their temperature. The testes need to be slightly cooler than the body temperature for optimal sperm production and health. The scrotum is located outside the body, allowing it to adjust the position of the testes; it can contract to bring the testes closer to the body for warmth or relax to allow them to move further away to cool down. This thermoregulation is essential for male fertility.

The other choices do not fulfill this protective or temperature-regulating role. The penis, primarily involved in sexual reproduction, does not have a role in temperature regulation. The epididymis is responsible for sperm maturation and storage, and the vas deferens functions in transporting sperm but does not serve to protect or regulate the temperature of the testes.