528 Dynamic Theory. 



Besides the fishes named above, the following possess electric organs, 

 the functions of which are, however, not so strongly developed ; Mor- 

 myrus longipinnus, Mormyrus oxyrhynchus, Mormyrus dorsalis, Tri- 

 chiurus electricus, Gymnarchus niloticus, and Tetraodon electricus. There 

 are many others, the total number of species being about fifty. The 

 electric plates of the Torpedo are mostly hexagonal in shape, and be- 

 ing piled upon each other vertically they form hexagonal prisms, which 

 extend from the skin of the back to that of the ventral side of the fish. 

 The plates themselves consist of delicate membranes, and are separated 

 from each other by flattened cells, each cell consisting of two layers of 

 epithelium separated by a thin layer of limpid, fluid, albuminous mat- 

 ter. The hexagonal columns are separated from each other and from 

 the skin above and below, by a thin envelope of glistening aponeurosis 

 ( a membrane ). Between the epithelium of the flat cells and the apo- 

 neurotic partitions, is an unorganized layer, in which the nerve fibres 

 and blood vessels terminate. The nerves form loops as they do in the 

 muscles. In each of the two electric organs of the Torpedo, there are 

 about 470 of the prismatic columns. The supply of nervous energy to 

 these organs is very great, and is conveyed by one branch from the 5th 

 pair of nerves ( trigeminum ), and four branches from the par vagum 

 ( 10th pair ). Four of these nerves are very large ; each one exceeding 

 the spinal cord in thickness. They enter the organs upon their inner 

 edges, and as they pass through they cut in two some of the prismatic 

 columns. They subdivide and send fibres to all the partitions between 

 the prisms. There are enlargements of the olivary and restiforme 

 bodies at the point where the electric nerves connect with them which 

 have been, not very properly, denominated electric lobes. They are 

 made up of the vagal and trigeminal enlargements of those nerves at 

 their junction with the medulla oblongata. The Torpedo is from one to 

 two and a half feet long. 



In the Gymnotus, as mentioned above, the aponeurotic partitions lie 

 horizontally, while the plates stand perpendicularly, reaching from one 

 partition to another. Some of these layers are nearly as long as the 

 whole animal except the head and tail. The ventral half of the animal 

 consists of these electric organs, while the dorsal half contains the 

 spinal column, muscles and air bladder. The -digestive and respiratory 

 apparatus, and reproductive and excretory organs, heart, &c. , as well as 

 the brain and organs of sense, all lie in front of the electric organs. 

 The electric organs are four in number, two on each side. The upper 

 one on each side is separated from the lower by a thin muscle la} T er and 

 membrane. The upper ones are much larger than the lower ones. A 

 median partition extending lengthwise through the animal divides the 

 organs of one side from those o the other. This partition branches 



