The electric organs (main, Sachs' and Hunter's) of a 23 cm and a 38 cm long Electrophorus electricus were studied by histological methods. The results were compared with 12 cm (Keynes, '61) and 140 cm (Couceiro and Ackermann, '48) specimens. All three electric organs originate from striated muscle fiber as indicated by the presence of a striated structure in the undeveloped electroplates. The three organs do not develop simultaneously but in succession: first Sachs' organ, then the main organ and finally Hunter's organ, with considerable overlap in time. In all three cases, the anterior extremity of the organ develops last. The classical notion that the main organ originates from the lateralis imus muscle is not supported by the present findings.