The professor one day dropped a live fish, five inches long, into the tub; upon which the Gymnotus turned round in such a manner as to form a coil inclosing the fish, the latter representing a diameter across it, and the fish was struck motionless, as if lightning had passed through the water. The Gymnotus then made a turn to look for his prey, which having found, he bolted it, and then went about seeking for more. A second smaller fish was then given him, which being hurt, showed little signs of life; and this he swallowed apparently without “shocking it.” We are informed by Dr. Williamson, in a paper he communicated some years ago to the Royal Society, that a fish already struck motionless gave signs of returning animation, which the Gymnotus observing, he instantly discharged another shock, which killed it. Another curious circumstance was observed by Professor Faraday—the Gymnotus appeared conscious of the difference of giving a shock to an animate and an inanimate body, and would not be provoked to discharge its powers upon the latter. When tormented by a glass rod, the creature in the first instance threw out a shock, but as if he perceived his mistake, he could not be stimulated afterward to repeat it, although the moment the professor touched him with his hands, he discharged shock after shock. He refused, in like manner, to gratify the curiosity of the philosophers, when they touched him with metallic conductors, which he permitted them to do with indifference. It is worthy of observation, that this is the only specimen of the Gymnotus Electricus ever brought over alive into this country. The great secret of preserving his life would appear to consist in keeping the water at an even temperature—summer and winter—of seventy-five degrees of Fahrenheit. After having been subjected to a great variety of experiments, the creature is now permitted to enjoy the remainder of its days in honorable peace, and the only occasion upon which he is now disturbed, is when it is found necessary to take him out of his shallow reservoir to have it cleaned, when he discharges angrily enough shock after shock, which the attendants describe to be very smart, even though he be held in several thick and well wetted cloths, for they do not at all relish the job. The Gymnotus Electricus is not the only animal endowed with this very singular power; there are other fish, especially the Torpedo and Silurus, which are equally remarkable, and equally well known. The peculiar structure which enters into the formation of their electrical organs, was first examined by the eminent anatomist John Hunter, in the Torpedo; and, very recently, Rudolphi has described their structure with great exactness in the Gymnotus Electricus.