84 



CLASS PISCES. 



above the other. Each compartment is filled with gelatin- 

 ous tissue, through the middle of which runs a horizontal plate 

 composed of a finely granular nucleated substance and of numer- 

 ous nerve-endings. This is the electrical plate. The electrical 

 plates correspond to a certain degree to the copper and zinc ele- 

 ments of the voltaic pile, the gelatinous matter representing the 

 moist intermediate layers ; while the connective tissue frame- 

 work serves to hold the parts together and to carry the blood- 

 vessels and nerves. The face of the plate on which the nerves 

 ramify is the same in all the columns of the same organ, and is 

 always electro -negative, the other surface being positive. In 

 Torpedo the nerve enters on the lower surface of the plates, the 



upper surface is therefore electro- 

 positive. The organ is supplied 

 by five strong nerves, of which 

 the anterior is a branch of the 

 facial, the four posterior being 

 branches of the vagus group. 



In the electric Teleostei the 

 electric organs are placed in the 

 trunk and tail, and are supplied 

 by spinal nerves. They are simi- 

 larly constituted, but the col- 

 umns are horizontally placed. In 

 Malapterurus they lie along the 

 body beneath the skin, and the 

 posterior surface of the plates, the surface on which the nerve 

 enters, is electro-positive. This apparent exception is explained 

 by the fact that the nerves pass through the plate and 

 are distributed on the anterior surface, which is electro-nega- 

 tive. In the electric eel (Gymnotus electricus) the electric 

 organ lies at the side of the tail, and consists of long horizontal 

 columns (Fig. 46). 



The so-called pseudo-electric organs found in the tail of Raja 

 and of Mormyrus have a similar structure, but manifest only 

 feeble electric phenomena. They constitute a very good example 

 of an organ which is practically of no use to its possessor, and 

 which we should entirely fail to understand the meaning of were 

 it not for the cases in which the electric organ is fully developed. 

 VASCULAR SYSTEM. The blood is generally red ; it is white 



FIG. 46. Longitudinal section through 

 two columns of the electric organ of 

 Gymnotus. a horizontal partition ; 

 I transverse partition walls, convex 

 headwards ; e electric plates (from 

 Gegenbaur, after Max Schultze). 



