ON THE POSTEMBRYONIC DIFFERENTIATION OF A CUTANEOUS ELECTRORECEPTOR ORGAN

In order to decrease the rare of postembryonic development of electror eceptor organs, excisions of epidermis and deafferentations were carri ed our in the gymnotid fish Eigenmannia virecens. Twenty-five days lat er, the epidermis showed electroreceptor organs without innervation. S ome of these at the beginning of their development consisted of masses of identical cells, whereas others showed presumed sensory cells whos e cytoplasm contained rudimentary synaptic structures. The epidermis a lso showed differentiated tuberous organs with a low number of sensory cells. In all these organs, radioactive thymidine was fixed in the nu clei of the platform accessory cells. Thirty-five-40 days after surger y, tuberous organs were identical to the functional organs, and thymid ine was detected in the nuclei of the cavity accessory cells. These re sults show that the gymnotid electroreceptor organs can develop before any nervous contact occurs, and suggest that they might originate fro m epidermal cells.