There are few, if any, structures in the animal kingdom the origin of which is more difficult to account for than the electric organs of Fishes. Darwin recognised in the electric organs one of the “special difficulties of the Theory of Natural Selection;“ and, although we now understand their structure and development, it is still “impossible to conceive by what steps these wondrous organs have been produced.” Although the structure and development of the electric organ of the Torpedo has been determined, we are as ignorant as before of its phylogeny. Almost the only chance of our obtaining a hint as to how the organ passed through its initial stages, as to the causes which were at work while the muscular fibres were in process of conversion into electric cells or discs, seems to be by turning to the so-called“ pseudo-electric” organ of the Skate.