The structure and ultrastructure of the lymphomyeloid epigonal and Leydig organs of the dogfishScyliorhinus caniculaL. were investigated. The tissues produce leucocytes, mainly granulocytic cells, but also some lymphocytes and plasma cells. Lymphocytes sometimes form nodule-like aggregations, especially in the epigonal organ. Granulocytes are probably stored within the lymphomyeloid tissues and enter the circulation on maturation. They may also release biologically active substances into the blood.
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