Leydig's organ
Leydig's organ is a unique structure found only in some, but not all, elasmobranchs. Nestled along the top and bottom of the esophagus, it produces red blood cells, as do the spleen and special tissue around the gonads. Heterophilic and eosinophilic granulocytes are produced, closely resembling structures of mammalian plasma cells. Leydig's organ is part of the immune system.
