Page:The American Cyclopædia (1879) Volume VI.djvu/507

ELECTRIC FISHES 499 branchial orifices, and behind it is a small opening and a slender papilla. The only spe- cies 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 $ of an inch from each other, and one inch in length contains 240 cells, giving a very great sur- face to the electric organs. The system is abundantly supplied with nerves from the Malapterurus Electricus. 200 pairs of ventral spinal nerves, but not from the lateral continuation of the trigemi- nus and vagus nerves from which the electric system of the torpedo is supplied. The elec- tric 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 Hum- boldt, 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 dis- charges 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 bat- tery to secure its prey, and to defend itself from its numerous enemies. The third elec- trical fish belongs to the family of silurida, and the genus malapterurus (Lacep.). The M. electricus (Lac6p.) differs from the com- mon 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 cau- dal; 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 vorner. 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 benumb- ing powers in the Nile has been known for more than 300 years, but Geoffroy and Ru- dolphi were the first to give detailed descrip- tions of the electric organs. Valenciennes de- scribes these as forming on each side of the body, between the skin and the muscles, two thin layers of spongy cellular tissue uniting to- gether small lozenge-shaped cells filled with gelatinous fluid, and six or more fine longitu- dinal 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 ven- tral 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- dontidai, and genus tetraodon (Cuv.). The up- per 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 elec- tric species (T. electricus, Paterson) the skin is destitute of spines, in conformity with the as- certained law that no electric fishes have either scales or spines; the body is brown above, yellow on the sides, sea-green below, and va- ried with red, green, and white spots. It at- tains 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 ac- tive 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