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It has been known that the hemolymph node is one of the lymphoid organs found normally in ruminants and some rodents, and this organ shares morphological and functional characteristics of lymph node and spleen. To clarify the rigorous definition of morphological structures and functions of the hemolymph node in Sprague-Dawley(SD) rats, we examined these organs of SD rats gross anatomically and light microscopically. The hemolymph nodes were normally found in the abdominal cavity and in the neck of SD rats. This organ was surrounded by a thin connective tissue capsule and there was a hilus. The parenchyma comprised a cortex of lymphatic nodules and diffuse lymphatic tissues, and a medulla of diffuse lymphatic tissues arranged in cords. Afferent and efferent lymph vessels were observed but there was no extensive subcapsular and medullary sinuses. These sinuses were filled with erythrocytes. The stroma of hemolymph nodes was composed of reticular cells and fibers, and many lymphocytes, granulocytes, erythrocytes, plasma cells, macrophages and megakaryocytes were supported by the reticular network. The above findings suggest that the hemolymph nodes of SD rats may take part in blood formation, blood filtration and immune reaction.
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