Size Relations of Lymphomyeloid Organs in Some Cartilaginous Fish

In elasmobranchs (sharks, rays) the total weight of lymphomyeloid structures isolated by dissection varied between about 0.6 and 1.0% of the body weight. In a holocephalan (Chimaera) the corresponding value was 1.7%. Reciprocal size relations may exist between different types of lymphomyeloid organs. A thymus was found in adult specimens of rays (Raja) and the rabbit-fish (Chimaera). The lymphomyeloid organs supposedly are active in haemopoiesis and the immune responses.