THE existence of striated myofibril structures persisting in the electroplaques of adult fish had led several authors1–3 to consider muscle as the tissue of origin of the electric organs of Mormyridae, but no data have been published to justify this assumption. Recently I have presented circumstantial evidence showing indirectly that the electric organ of the Mormyridae does in fact arise from the deep lateral muscle4 ; however, direct experimental evidence was still lacking.