The Fine Structure of the Electric Organ of the Electric Eel and Torpedo Ray

Electric organs or tissues have been described in seven families of fish (Dahlgren, 1), but all of them have several features in common. The tissues occur as a series of more or less flattened plates or electroplaques, each of which consists of a nucleated cytoplasmic syncytial plate having a relatively large surface area. The plates are supplied with nerve endings on one surface only. On one or both surfaces of the electroplaques, tiny rodlets or Stabchen have been frequently described. Examination of the electric organs of Electrophorus dectricus and Torpedo occidentalis with the electron microscope has confirmed these features, but has also revealed further interesting details. Fig. 1 is a photomicrograph at low magnification showing half a dozen electroplaques of Electrophorus electricus cut in cross-section, each suspended in an individual rectangular connective tissue compartment. Numerous papillae appear on both the anterior and posterior surfaces (the top and bottom respectively in the photograph) of each electroplaque. The surfaces of both anterior and posterior papillae bear minute rodlets which are not visible at this magnification. Fig. 2 is an electron micrograph of the anterior surface, similar to the area outlined by the upper rectangle in Fig. 1. The rodlets are now seen to consist of invaginations of the delicate plasma membrane of the electroplaque. These apparently tubular structures (t) measure 500 to 1000 A in diameter, and several micra in length. Groups of isolated vesicles (v) are seen frequently near the tubular invaginations. The posterior surface of the electroplaque of the eel also displays tubula.r structures of similar character. This surface differs from the anterior one in the possession of a wealth of nerve endings. These terminate, as a rule, upon the papillae at close enough intervals to show a sectioned nerve on the average of every ten micra. One such ending is illustrated in Fig. 3 which represents an