Final answer:
The primary lymph sacs develop into the thoracic duct and right lymphatic duct, which are essential for lymph circulation in the body.
Step-by-step explanation:
The primary lymph sacs eventually develop into the thoracic duct and right lymphatic duct. These structures are key components of the lymphatic system that transport lymph fluid throughout the body. The thoracic duct especially is responsible for draining a significant portion of the body's lymph fluid into the left subclavian vein, while the right lymphatic duct drains lymph from the right upper side of the body into the right subclavian vein. Both of these ducts play crucial roles in the circulation of lymph and the functioning of the immune system.