THE CELLULAR STRUCTURE OF THE LEYDIG ORGAN IN THE SHARK,ETMOPTERUS SPINAX(L.)

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Abstract
In Etmopterus spinax, a small deep water shark, the predominating lymphomyeloid tissue is the so-called Leydig organ. This consists of bone marrow-like tissue situated between the muscularis and the mucosa of the esophagus. Examination by light microscopy and EM shows that the Leydig organ produces large numbers of granulocytes and lymphocytes. Two main types of granulocytes occur, tentatively called heterophilic and eosinophilic. The heterophilic cells may be subdivided into 3 types which differ in the ultrastructure of the granules. Cells structurally resembling mammalian plasma cells are common. The presence of these cells indicates that the tissue is part of the shark immune system.