part_of part of circulatory system lymphoid system lymphatic part of lymphoid system An organ system subdivision that is a network of vessels capable of removing accumulating protein and fluid from the interstitial space and returning it to the vascular space. In some species, this network is connected to the immune system via lymph nodes and lymphocyte-producing organs, with the whole being the lymphoid system. lymphatic system lymphatic tree system lymporeticular system organ system subdivision