170 PHILOSOPHY OF ZOOLOGY. 



The nerves of the organs arise from the medulla oblonga- 

 ta. Each organ is liberally supplied by three large trunks, 

 which, after communicating a few filaments to the gills, ra- 

 mify in every direction between the columns, and send in 

 small branches upon each partition. 



The electrical organs of the Gymnotus electricus, as ex-^ 

 amined by HUNTER*, differ considerably from those of the 

 Torpedo. The largest, or superior organs, consist each of 

 a series of thin tender membranes, parallel to one another, 

 extending longitudinally the whole length of the organ ; 

 and, in breadth^ reaching from their central to the dermal 

 surface. The uppermost membranes are concave dorsad, 

 the middle ones are nearly horizontal ; and the inferior ones 

 are concave sternad. Their dermal edges are united with 

 the skin and its muscles, their central edges with the mid- 

 dle partition, the air-bag, and the dorsal muscles. They 

 are farthest distant from each other at their dermal edges, 

 and gradually approach as they proceed to their central aU 

 tachment Where the organ becomes narrower towards 

 the tail, two of the membranes sometimes unite, and form 

 into one. In a fish, 2 feet 4 inches in length, they are 

 2*7 tli of an inch distant from one another ; and the whole 

 organ, where broadest, is an inch and a quarter in br t eadth, 

 and contains thirty-four membranes. In the inferior or 

 smaller organ, the membranes are nearer each other, being 

 only about ^th of an inch asunder. The superior ones 

 are the broadest, and they decrease in breadth the nearer 

 they are situated to the ventral line of the animal. In both 

 organs there are numerous partitions, dividing the spaces 

 included between the different layers, into narrow vertical 

 transverse cells. Each cell is in the form of a compressed qua- 



Phil. Trans. 1775, p, 339. 



