THE LYMPHOMYELOID (HEMOPOIETIC) SYSTEM OF THE ATLANTIC NURSE SHARK, GINGLYMOSTOMA CIRRATUM

¹ Department of Zoophysiology, University of Göteborg, Sweden

The lymphomyeloid system of nearly adult nurse sharks, Ginglymostoma cirratum, was investigated. Lymphomyeloid structures detectable by the naked eye at dissection are the epigonal organ and the spleen. Microscopic examination shows that the epigonal organ produces granulocytes and lymphocytes. The white pulp of the spleen is lymphoid, whereas the red pulp is mainly erythropoietic. Cells with the morphological characteristics of plasma cells occur in the epigonal organ and the spleen. Peroxidase-positive granulated cells are found in the epigonal organ. In contrast to many other elasmobranchs, the nurse shark lacks the Leydig organ, i.e. the lymphomyeloid structure of the esophagus; but the epigonal organ is well developed and averages 0.60% of the body weight. The spleen weighs about 0.26% of the body weight. The mode of life of the nurse shark in shallow tropical waters probably puts a considerable demand on its immune system. Cells produced by the epigonal organ may be important in immune responses and in inflammatory processes.

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