ELECTRIC FISHES. 893 



more or less perfectly insulated, that other than static currents can be 

 detected in it. 



Similar electric currents exist in all Warm-blooded Yertebrata, and are 

 probably universal in the Cold-blooded Vertebrata. In the frog they are re- 

 markably strong, and the animal itself, so far as its muscular system is con- 

 cerned, and probably also as regards its nervous system, is peculiarly suscep- 

 tible to electric influences. 



It is amongst the Cold-blooded Vertebrata only, and in the lowest Class of 

 these, viz., in Fishes, that the singular power exists of generating and accu- 

 mulating within certain organs, a large amount of electricity, which can be 

 discharged from the body in the form of a shock, either involuntary, or appa- 

 rently, also, at the will of the animal. Electric fishes are found in almost all 

 climates ; but they belong to different genera. There are eight species known 

 at present to possess this power. Of these five are marine :"three of these are 

 Torpedoes belonging to the Ray family ; they inhabit the Mediterranean and 

 the Atlantic, and are sometimes even used as food. The fourth is the Tri- 

 chiurus or Sword-fish of the Indian Seas. The fifth marine species is the 

 Tetraodon, found amongst the Comoro Islands. The fresh-water or river 

 species of electric fishes are the Silurus or Malapterurus, a salmon-like fish of 

 the Nile, Niger, and Senegal rivers of Africa ; the Momyrus, or Nile Pike, and 

 lastly, the celebrated Gymnotus or Electric Eel, found only in the Amazon and 

 other large rivers of South America. 



In the Torpedoes, which are true flat fishes, the electric organs consist of 

 two compressed oval masses, lying one on each side of the head, and reaching 

 from between the gills into the body ; they are supported in front and exter- 

 nally, by a cartilaginous border. They consist of a strong membranous in- 

 vestment, inclosing a soft pulpy structure, divided by septa into hexagonal 

 columns, which have their ends directed towards the upper and under surface 

 of the fish. Each column is subdivided, by delicate and extremely vascular 

 partitions, into numerous separate cells, and each cell is filled with a clear 

 fluid, of which y th part is albumen, with traces of common salt. Owing to 

 the large proportion of water in them, the specific gravity of the electric 

 organs is only 1026, whilst that of the body of the fish is 1060. These remark- 

 able organs are supplied with very large nerves, larger than any other nerves 

 in the body, and larger than any nerve in animals of the same size. The 

 nerves arise from a special nervous ganglion, called the electric lobe, connected 

 with the medulla oblongata, immediately behind the cerebellum ; at their 

 roots, these nerves have apparent connections with the fifth and .eighth pairs ; 

 their finest branches end in close plexuses, upon the delicate partitions between 

 the cells of the columnar portions of the electric organ. The electric organs 

 of the Gymnotus are four in number, arranged in two pairs, one larger than 

 the other ; they form one-third of the entire bulk of the animal, and extend 

 nearly its whole length. Their structure is similar to that just described in 

 the Torpedo ; but the prismatic columns of cells are larger, fewer in number, 

 and of greater length, for they are placed lengthwise in the electric organ and 

 body of the Fish. The nerves are derived, it is said, from the spinal cord 

 only, and are upwards of 200 on each side of the body. Some of its nerves 

 proceed from the fifth cranial nerve, but most of them, it is asserted, from the 

 spinal cord. 



In the Silurus, there is no such distinct electric organ ; but a dense fibrous 

 tissue, having albuminous substance contained in its interstices, surrounds 

 the whole body, and is regarded as the homologue of the more perfect organs 

 of the Gymnotus and Torpedo. 



The power of the Torpedo to give shocks is comparatively small, but these 

 excite much pain. The shock of the Silurus, and of the largest Gymnoti, 

 which measure twenty feet in length, is sufficient to kill small animals, and to 

 paralyze men and horses, both as regards sensation and motion. The electric 

 power depends upon the integrity of the nerves connected with the electric 

 organs, as is proved by the results of partial or complete division of those 

 nerves. Small portions of the organ, connected with the body by no other 



