In vertebrates, the lymphatic system, also known as the lymphoid system, is an organ system that is a part of the immune system and works in conjunction with the circulatory system. Lymphatic tissues, lymph nodes, lymphatic or lymphoid organs, and a vast network of lymphatic veins make up this system. The vessels transport a clear fluid known as lymph, which is carried back towards the heart for re-circulation (the Latin name lympha refers to the goddess of fresh water.