It has been accepted for inclusion in Investigations of the Ichthyofauna of Nicaraguan Lakes by an authorized administrator of

Abstract. The rectal glands of elasmobranchs perform the function of salt-excreting organs. These glands are smaller and show regressive changes in speci-mens of the bull shark, Carcharhinus leucas found in fresh-water environment, compared}<,Jith specimens of this and other species from a marine habitat. The physiological significance of the rectal gland was obscure for a long time, though some morphological in-vestigations were made (I). Recently the excretion of sodium chloride was reported as the main function of the gland (2). Elasmobranchs are marine fish, but a few adapt to the fresh-water environment (3). The bull shark, Car-charhinus leu cas (Muller and Henle), is common in the Gulf of Mexico an