In connection with the muscles reference has to be made to the _Electric organs_ with which certain fishes are provided, as it is more than probable, not only from the examination of peculiar muscular organs occurring in the Rays, _Mormyrus_, and _Gymnarchus_ (the function of which is still conjectural), but especially from the researches into the development of the electric organ of _Torpedo_, that the electric organs have been developed out of muscular substance. The fishes possessing fully developed electric organs, with the power of accumulating electric force and communicating it in the form of shocks to other animals, are the electric Rays (_Torpedinidæ_), the electric Sheath-fish of tropical Africa (_Malapterurus_), and the electric Eel of tropical America (_Gymnotus_). The structure and arrangement of the electric organ is very different in these fishes, and will be subsequently described in the special account of the several species. The phenomena attending the exercise of this extraordinary faculty also closely resemble muscular action. The time and strength of the discharge are entirely under the control of the fish. The power is exhausted after some time, and it needs repose and nourishment to restore it. If the electric nerves are cut and divided from the brain the cerebral action is interrupted, and no irritant to the body has any effect to excite electric discharge; but if their ends be irritated the discharge takes place, just as a muscle is excited to contraction under similar circumstances. And, singularly enough, the application of strychnine causes simultaneously a tetanic state of the muscles and a rapid succession of involuntary electric discharges. The strength of the discharges depends entirely on the size, health, and energy of the fish: an observation entirely agreeing with that made on the efficacy of snake-poison. Like this latter, the property of the electric force serves two ends in the economy of the animals which are endowed with it; it is essential and necessary to them for overpowering, stunning, or killing the creatures on which they feed, whilst incidentally they use it as the means of defending themselves from their enemies. CHAPTER VI. NEUROLOGY.