The reticulum plays an important part in the regeneration of lymph nodes autoplastically transplanted into the abdominal wall of the albino rat. The necrosis which follows transplantation involves mainly the lymphocytes. A margin of lymphocytes is preserved only at the periphery. This may be due to early lymphatic connection with the marginal sinus of the node. The reticulum cells are apparently more resistant since for the most part they do not degenerate. There are three possible origins of the lymphocytes of the regenerated node. They may arise by proliferation of lymphocytes retained at the periphery of the plant. The presence of a few mitotic figures among lymphocytes in the marginal region confirms the possibility of this mode of origin. They may also be derived from lymphocytes brought into the transplant by the blood or lymph circulation. Though some lymphocytes are present in the marginal sinus, and an occasional lymphocyte is seen in the capillaries which enter at the hilus, we believe that this source of origin of the lymphocytes is negligible. On the other hand, the hyperplastic reticulum appears to be the important source of lymphocyte production. These may be derived from the reticulum directly as small lymphocytes, or may be formed through the intermediary stage of large lymphoid cells. This capacity is not limited to lymphatic reticulum, as small foci of lymphocyte formation are found in the connective tissue in the vicinity. of the transplants. The reticular origin of lymphoctes is most easily observed in the earlier stages of regeneration before the picture is obscured by the numerous small lymphocytes.
Two structures in the regenerating node are directly traceable to the same structures of the transplanrt. These are the marginal sinus and the hilus. The marginal sinus of thef transplant is preserved, and is probably an important means by which lymphatic communication is established with the surrounding tissue. The hilus is the site of entry of the blood vessels, and the hilus of the regenerated node is the same as that of the transplant.