RAYS 65 



The most interesting feature of these rays is, of course, the 

 electrical organs. Each of these consists of a large, flat 

 body, made up of a number of upright hexagonal tubes or 

 columns, separated from one another by walls composed of 

 fibrous tissue. These tubes are very numerous, and as many 

 as 470 have been counted in each organ. Each column is 

 filled with a clear, jelly-like substance, and is divided up 

 into a number of compartments, each of which contains a 

 flat electric plate. Every plate is connected by fine nerve 

 tendrils with the main nerve supplying the electric organ, 

 which is in turn connected with a special lobe of the brain. 

 The side of the electric plate to which the nerve tendrils are 

 attached has been shown to be negative, the other side to be 

 positive, and the current passes from the upper or positive 

 side of the whole organ to the lower or negative side. 



It is of interest to consider the manner in which these 

 complicated organs were acquired. In all animals the 

 contraction of a muscle is accompanied by the generation of a 

 minute amount of electricity, and the electrical organs of 

 the Torpedoes, as may be ascertained by a study of their 

 development in the embryos, are known to have been evolved 

 through the modification of muscular tissue — tissue which 

 would normally go to form muscles connected with move- 

 ments of one of the gill-arches. What has actually happened 

 is that the electrical properties inherent in all muscles have 

 here been accentuated at the expense of the mechanical 

 properties. 



The electrical discharge may be produced as the result of a 

 simple reflex action, or it may be under the control of the 

 fish. It produces all the usual effects of electricity. In order 

 to obtain the full shock it is necessary to complete the circuit 

 by touching the fish at two points, either directly or through 

 the medium of some conducting body. It has been found 

 that a quite powerful sensation of numbness can be produced 

 through the medium of a stream of water, that is to say, by 

 pouring water on to a living fish. The frequency of the 

 shocks is very high, amounting to about 150 per second. 

 Repeated use of the electric organs weakens their power, 

 and a period of rest and feeding is necessary before the fish is 

 fully restored. 



