"Naked" spinal cord on a non-segmented baton-like bony structure in the tail of the electric fish Eigenmannia virescens (gymnotoidei).

The caudal spinal cord of Eigenmannia virescens is not enclosed in a neural canal of the vertebral column. In fact, a segmented vertebral column with neural and ventral arches is lacking and replaced by a non-segmented baton-like bony structure on which the free spinal cord is located. The baton cosists of calcified bone tissue with bone cells. Individual differences exist as far as the length of the rod is concerned. The "electromotor neurons" of this caudal part of the spinal cord are histochemically acetylcholinesterase-positive. The electrocytes which surround this part of the spinal cord show strong enzymatic activity on the posterior innervated face. However, there is also activity on the non-innervated lateral and anterior faces.