436 • FISHES 



held in the hand. It has been supposed that the plates in this 

 case are developed from club-shaped cells like those seen in the 

 epidermis but there is no proof of this, and one investigator 

 thinks it is still possible that the organ in this case as in others 

 is derived from muscular tissue. 



There are two questions concerning the electric organs of 

 fishes on which we have still to confess almost complete ignor- 

 ance, firstly how the electricity is produced, secondly how the 

 evolution of these organs is to be explained. With regard to 

 the first we know that the passage of a stimulus along a nerve 

 and a contraction in a muscle are accompanied by electric 

 phenomena, in other words the normal functions of nerve and 

 muscle produce electricity. When either nerve or muscle is at 

 rest no electric current is produced, but when a stimulus passes 

 along the nerve or a contraction along the muscle, the part of 

 the nerve affected by the stimulus, or the part of the muscle 

 which is contracting, becomes electrically negative to the parts 

 at rest and if the negative part is joined by a wire to any other 

 part a current passes along the wire. In the electric organ we 

 have the electric plate derived from a muscle-fibre and the ter- 

 mination of a nerve-fibre on one side of it. The electric plate 

 however does not contract and we do not know in what way it 

 takes part in the production of electricity. If we suppose that 

 the side where the nerve terminates becomes negative because 

 it is strongly stimulated, while the opposite side remains un- 

 stimulated and is therefore positive, we have some idea how 

 the electric organ is able to give electric shocks. From the 

 fact that the nerves to the organs are so enormously developed 

 and the fact that the tissue of the organ, originally muscular, 

 has lost its power of contraction, we may conclude that the 

 nervous part of the organ plays the chief part in the production 

 of electricity. When two points some distance apart on the 

 organ are joined by a conducting body one point will be nega- 

 tive to the other and a sudden discharge, that is a momentary 

 current of very high voltage passes through the conducting 

 body and has the same effect on other animals as an electric 

 shock produced in any other way. The ['power of the 

 Gymnotus is so great that when travellers cross a ford over a 

 river where these fish are abundant their beasts of burden are 

 frequently thrown to the ground as though struck by lightning. 



