The eyes are small, flat, and of a blueish colour, placed a little behind the nostrils. The whole body from a few inches below the head, was distinguished into four longitudinal parts, clearly divided from each other by lines. The carina begins a few inches below the head, and widening as it proceeds, reaches as far as the tail, where it is thinnest. The situation of the _anus_ is very remarkable, being an inch more forward than the pectoral fins. Across the body, there are a number of small bands, annular divisions, or rather rugæ of the skin; by means of which the fish seems to partake of the vermicular nature, having the power of lengthening and shortening its body like a worm, and by means of which it can swim backwards as well as forwards.—For an anatomical description of this fish, see the appendix to the 2d. vol. of Mr. Cavallo’s “Complete treatise” page 303. The Gymnotus has the astonishing property of giving the electric shock to any person or number of persons, either by the immediate touch of the hand or by the mediation of any metallic conductor. The shock is interrupted by the intervention of a non-conducting substance. If the animal be touched only with one hand, a kind of tremor is felt in that hand only. The power of giving shocks depends entirely on the will of the animal. As nature is ever provident for her creatures, both with regard to their preservation and support, she has endowed the Gymnotus with a peculiar instinctive faculty, so that if it be pursued by an enemy, it never fails to communicate a shock, in consequence of which it eventually makes its escape. In obtaining food it likewise makes use of its electrical property by which it kills small fish, and afterwards devours them. But the most remarkable instinct of this fish is, that when any substance approaches it, it is sensible whether it be a conductor or non-conductor. In order to exhibit this wonderful phenomenon, a variety of methods were contrived, the easiest and most satisfactory one was the following. The extremities of two wires were dipped into the water of the vessel, in which the animal was kept, after which they were extended to a considerable distance, where they terminated in two separate glasses full of water. These wires being supported by silk at some distance from each other, the circuit was, of course, incomplete. In these circumstances if a person completed the circuit, by placing one hand in one of the glasses and the other in the other, the fish which never went purposely towards the wires, while the circuit was interrupted, would now go immediately towards them and give the shock, and this though the completion of the circuit was made out of his sight.