530 Dynamic Theory. 



before and the other behind the cells. The cells themselves are pyram- 

 idal, the apices of one half pointing into the precellular fluid, and 

 those of the other half into the post cellular fluid. The cell layer is 

 electrically positive, the fluid space in its rear and the vertical plates 

 are negative. The fluid in front is neutral, and a conductor from one 

 to couple to another. ' ' The whole represents the ternary type of the 

 voltaic pile. The Torpedo's structure is according to the binary type. " 

 ( Owen. ) The nerves running to the electric organs in the Gymnotus 

 are supplied by branches from the spinal nerves, of which there are 

 about 200 pairs. Filaments from these run down the middle aponeu- 

 rotic partition and ramify thence upon the horizontal layers. Other fil- 

 aments from the same nerves pass down the skin and reach the layers 

 at their outer edges. This is a very different arrangement from that of 

 the Torpedo, whose electric nerves are all from the encephalic pairs. 

 But the organs of the Torpedo lie on each side of the head, while those 

 of the Grymnotus are entirely back of the head and extend to the tail. 

 In each case, the nerves engaged are those directly opposite the organs 

 to be supplied. The electric eel is about seven feet long. 



The electric organ of the Malapterurus is a hollow cylinder surround- 

 ing the whole body except the head and fins. Directly inside of the 

 electric cylinder is another of cellular tissue, in which the nerves and 

 blood vessels which supply the electric organs, are buried ; inside of 

 this cylinder is a third composed of non-conducting, fatty tissue. 

 .Within the fatty layer is the muscle cylinder, bearing the vertebral col- 

 umn and containing within its cavity the organs of the animal. (Fig. 

 251.) The battery cells of the electric organ are lozenge-shaped, about 

 a third of a line in size, and separated from each other by fine membranes. 

 The nerves supplying this organ originate from the upper end of the 

 spinal cord, and run back as an independent system, giving off branches 

 to the organ. 



In the Mormyrus longipinnis the electric organs are on the tail. There 

 are four of them, two on each side. In each organ there are about 150 

 membranous partitions running lengthwise of the fish, and placed ^ of 

 an inch apart, the spaces being filled by an albuminous fluid. ( Owen's 

 Comp. Anat.} 



Electric organs are quite analogous to a voltaic pile in which elec- 

 trical energy is accumulated in a state of tension. The nerves which 

 liberate the discharge, are of the same class as the motor nerves which 

 run to the muscles and liberate the energy which causes their contrac- 

 tion. Like those motor nerves, they are connected with the anterior 

 tracts of the medulla oblongata or spinal cord, as the case may be. A 

 voltaic pile, of the ternary type alluded to, may be made by alternate 

 leaves of silver, zinc and woolen cloth arranged as in fig. 254. Zinc 



