Such is the description given by Humboldt, a witness of the extraordinary scene. The employment of their electric powers is evidently spontaneous, and exhausts the nervous energy. Like voluntary muscular effort, it needs repose, and the creatures require an abundance of nourishment and rest before a fresh accumulation of electricity is produced. In the dry season they form deep circular holes for themselves in the mud of water-courses, and marshes which remain filled with moisture, and they are thus able to support existence in their usual localities, while alligators and turtles have to retire to the larger pools or rivers. In the shallow ponds of the forest they are easily driven out with long poles. Bates amused his native companions, who had thus caught some of the creatures, by showing them how the electric shock could pass from one person to another. They joined hands in a line, while he touched the biggest and freshest of the animals on the head with the point of his hunting-knife. He found, however, that the experiment did not succeed more than three times with the same eel when out of the water, for the fourth time the shock was scarcely perceptible. The limbs even of the strongest man are benumbed, and he is struck down helpless, by a discharge from the battery of the gymnotus. The organs which produce this curious electrical effect are placed along the under side of the tail. They may be compared to a series of columns inclosed in a thin membrane packed closely together, which, consisting of a series of fiat discs, may be imitated by placing a number of coins with their discs parallel to each other, and with a bladder between each, separated by a gelatinous substance. These columns are technically called septa; and La Cepede calculates that two hundred and forty transverse membranes are packed in each inch, thereby giving to an electric eel eight feet in length an organ cavity of two hundred and forty-six square feet--an enormous extent, as may be supposed, of electricity producing surface. The whole apparatus is supplied with nerves which run through the entire length of the body. STING-RAYS.