The extraordinary modification of the peripheral extremities of nerves by which electricity is generated and discharged is found in four genera of fishes, and in no other class of the vertebrata. The best known of these fishes are the torpedo and the electrical eel; the former will be separately treated under its own name, and the latter, with two others for which there is no common name, in this article. - The electrical eel (gym-notus electricus, Linn.), though apodal and eellike in general appearance, differs from the eels in the completeness of the jaws, the presence of ribs, and the jointed fin rays; it has neither ventral nor dorsal fin; the anal reaches to the point of the tail, and like the pectorals is enveloped in a thick skin which conceals the rays; the skin is soft and scaleless; the head is oval and flat, the mouth furnished with broad lips, and opening not quite as far as under the eyes; the anterior nostrils are small tubes in a slight depression on the side of the lips; the posterior are behind and above them; lateral line distinct; about 50 pointed teeth on the upper jaw, and 60 on the lower, a second row of about six behind the middle of the upper ones, and four small teeth in two rows along the symphysis; the vent opens before the branchial orifices, and behind it is a small opening and a slender papilla.

The only species known inhabits the rivers of the northern parts of South America; it attains a length of 5 or 6 ft., and is brown and yellowish. The electric apparatus which has rendered this fish so celebrated occupies the space between the pectorals and the tail, for a large part of the lower bulk of the body; the organs are four in number, two on each side, the upper and larger organ being separated from the lower by a thin stratum of muscle and membrane, and the organs of one side are distinct from those of the other; the apparatus consists of an assemblage of membranous horizontal plates, nearly parallel and intersected by delicate vertical plates; the cells thus formed are filled with a glutinous matter; the septa, according to Hunter, are about 1/30 of an inch from each other, and one inch in length contains 240 cells, giving a very great surface to the electric organs. The system is abundantly supplied with nerves from the 200 pairs of ventral spinal nerves, but not from the lateral continuation of the trigeminus and vagus nerves from which the electric system of the torpedo is supplied.

The electric eel seems to be a mere appendage to the anterior part of its battery for moving it about, as all the other organs are confined to a very small space, even the vent opening under the head; and the nerves supplying the electric organs are much larger than those sent to any sensory or motor organs. According to Humboldt, the South American Indians capture these eels by driving horses and mules into the water inhabited by them; the electric powers of the fish being exhausted on the quadrupeds, the former are harpooned and thrown on shore; the horses suffer greatly, many of them being killed by the electric discharges of the fish which glide beneath their bodies. By grasping the head of the eel with one hand and the tail with the other, painful and almost insupportable shocks were received in the experiments of Faraday. This fish is neither voracious nor fierce, but uses its battery to secure its prey, and to defend itself from its numerous enemies. - The third electrical fish belongs to the family of siluridoe, and the genus malapterurus (Lacep.). The M. electricus (Lacep.) differs from the common siluroids in having no anterior dorsal fin nor pectoral spine; the skin is naked and scaleless; there is an adipose dorsal fin near the caudal; the ventrals are just behind the middle, and the anal occupies about half the distance between them and the rounded caudal; the body is stout, the tail thick, and the head short and conical; the lips are fleshy, with six barbels; five villiform teeth in each jaw, none on the vomer.

The fish attains a length of 18 or 20 in., and is found in the Nile, Senegal, and other rivers of northern and central Africa; the color is cinereous or olive above, spotted and irregularly marked with black, whitish below; anterior nostrils tubular. The existence of a fish with benumbing powers in the Nile has been known for more than 300 years, but Geoffroy and Ru-dolphi were the first to give detailed descriptions of the electric organs. Valenciennes describes these as forming on each side of the body, between the skin and the muscles, two thin layers of spongy cellular tissue uniting together small lozenge-shaped cells filled with gelatinous fluid, and six or more fine longitudinal membranes; combining the structure of these organs in the torpedo and gymnotus, and receiving the nervous influence both from the lateral branch of the vagus and from the ventral branches of the spinal nerves. The shock given by this fish is comparatively feeble, the , discharge taking place when the head is touched; no shock is felt when the tail is grasped, as the electric organs do not extend to this part; in giving a shock the tail is moved, as if the muscles were active. This fish is much esteemed as food.

The Arabs call it raash (thunder). - The fourth electrical fish belongs to the order plectognathi, family dio-dontidoe, and genus tetraodon (Cuy.). The upper and under jaws are divided by a median suture, so that they seem to have two teeth above and two below, incorporated with the jaws; in most of the species of the genus, the body, except the head and tail, is rendered rough by spines made erectile by the inflation of the skin, or naturally erect; but in the electric species (T. electricus, Paterson) the skin is destitute of spines, in conformity with the ascertained law that no electric fishes have either scales or spines; the body is brown above, yellow on the sides, sea-green below, and varied with red, green, and white spots. It attains a length of 7 or 8 in., and is found in the lagoons of the Pacific. Its electric powers are comparatively feeble. - The most characteristic feature of all these batteries is their enormous supply of nervous matter; the electric organs generate the electricity, which is rendered active by nervous influence.

In the torpedo the shock is best received when one hand is placed on the back and the other on the abdomen of the fish; in the gymnotus the intensity of the shock is in proportion to the length of the fish included between the hands; actual contact with the torpedo is not essential, as it is well known by the Neapolitan fishermen that the shock is felt when the water is dashed upon it, the electric current passing up along the stream, the circuit being completed through the earth to the ventral surface of the fish; the dorsal surface is always positive, and the ventral negative. That this is the same as common electricity has been shown by Matteucci and Faraday; it renders the needle magnetic, and decomposes chemical compounds; by it heat is evolved, and the electric spark is obtained. The exciting nerves terminate in loops, as in the muscular tissue, and they arise like motor nerves from the anterior tract of the cord; the reception and conveyance of impressions, and the voluntary act which results in the shock, are of the same nature and follow the same course as the muscular contractions; a division of the electric nerves at their origin arrests all voluntary shocks, but an irritation of the ends of the nerves in connection with the organ is followed by an involuntary electric discharge, just as an irritation of the end of a divided motor nerve in connection with muscle is followed by its contraction.

The electric like the muscular power is exhausted by exercise, and recovered by rest; both are increased by energetic respiration and circulation, and both are exalted by the action of strychnine, which produces tetanic contraction of the muscles, and a rapid succession of involuntary electric discharges. The phenomena displayed by these fishes afford no ground for the opinion that nervous influence is identical with electricity; the former is no more identical with the latter than it is with muscular contractility; the contractility of the muscle resides in its fibre, and the electricity is generated in the battery of the fish; both are brought into play through nervous influence, but neither resides in or is a property of the nerves. The phenomena of heat, electricity, and phosphorescence within the animal body depend on chemical actions, which take place in the system just as they would in the chemist's laboratory, modified always by the mysterious vital principle. According to Faraday, the shock of the electrical eel is equal to that of 15 Leyden jars of 3,500 square inches of surface.

Electrical Eel (Gymnotus electricus).

Electrical Eel (Gymnotus electricus).

Malapterurus Electricus.

Malapterurus Electricus.