ABSTRACT
The thymus is an acknowledged lymphoid organ. However, under certain circumstances the thymus has also been found to display erythropoiesis in various avians. Examination of tissue sections of lobes from large thymi revealed the cortical regions were comprised of typical lymphocytes with some areas also demonstrating early erythrocytic precursors, polychromatophilic erythroblasts and mature erythrocytes. In the case of the enlarged thymi of breeding adults, the entire cortex of most lobes was packed with the foregoing erythroid cells with few thymic lymphocytes present. In addition, some of the medullae of lobes from large thymi also presented erythroblasts and erythrocytes. Early and more mature erythroid progenitors were identified on the basis of morphologic criteria that characterize the erythroid lineage. A relationship seems to exist in the bird between the appearance/disappearance of erythropoiesis and degeneration/ regeneration of the lymphoid and epithelial reticular components perhaps establishing a certain microenvironment.
