part of part of located in located in in taxon composed primarily of leukocyte Elasmobranchii Holocephali Leydig's organ A hemopoietic organ found in elasmobranchs. Along with the spleen and special tissue around the gonads, this structure produces red blood cells and it is nestled along the top and bottom of the esophagus. UBERON:0000040 Found in elasmobranchs (sharks and rays) but with some exceptions. Phenotype notes: Leydig's organ can be quite large - a 1.6-kilogram (3.5-pound) one was reported from a 1.8-metre (6-foot) long Bluntnose Sixgill Shark (Hexanchus griseus). Structure notes: divided into dorsal and ventral patches, gradation varies between species. Lacks erythroblasts and fat cells[Honma 1983] Wikipedia:Leydig's_organ wall of esophagus hematopoietic system immune system hemopoietic organ immune organ