ELECTRICAL ORGANS. 



141 



the branchial pouches and the anterior cartilages of the pectoral 

 fins, and consist of a number of perpendicular columns enclosed by 

 walls of connective tissue. The columns are divided by a great 

 number of membranous transverse partitions into a series of com- 

 partments placed one above another. Each of the latter contains a 

 layer of gelatinous tissue, and a finely granular plate containing 

 nerve endings and large nuclei (electrical plate). The latter corre- 

 sponds in a certain degree to the copper and zinc elements of the 

 Voltaic pile, the former to the moist intermediate layers ; while the 

 connective tissue framework seerns to serve only to carry the nerves 

 and blood-vessels. Each transverse partition contains a rich network 

 of nerves, which is distributed on the electrical plates. The face on 

 which the nerves ramify is the same in all the columns of the same 



T 



FIG. 591. Alimentary canal and generative organs of Clupea Harengus (after Brandt). Sr, 

 gills; Oe, ossophagus; V, stomach; Ap, pyloric appendages; D, intestine; A, anus; 

 Vn, swimming bladder ; Dp, pneumatic duct ; S, spleen ; T, testis ; Vd, vas deferens ; 

 Gp, genital pore. 



organ, and is always electro-negative, the opposite free surface 

 being positive. In Malapterurus, the other surface of the plate (the 

 posterior surface) on which the nerves enter is electro-positive, but 

 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 -negative. In the electric Eel (Gymnotus electricus) the 

 electric organ lies at the side of the tail and consists of long horizon- 

 tal columns; in Malapterurus it lies along the body beneath the skin. 

 Similar organs in Mormyrus are distinguished as pseudelectric organs, 

 since although they have a similar structure, they give rise to no 

 electric phenomena. 



The digestive organs vary much in structure. The mouth, which 

 is placed at the anterior end of the head, usually has the form of a 

 transverse slit, and can sometimes be extended forward by means of 



