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TUBE-BLADDERED GROUP. 
As a genus, the electric eel is characterised by the absence of the caudal and 
dorsal fins, by the anal extending to the extremity of the tail, the absence of scales, 
the single series of conical teeth, and the minute eyes. Abundant in the rivers 
and lagoons of certain parts of Brazil and the Guianas, the electric eel grows to a 
length of fully 6 feet, and is capable of giving a more powerful shock than any of 
the other fishes endued with electric power. It will be unnecessary to give any 
description of the electric organs here; and it will accordingly suffice to mention 
that they form two pairs of longitudinal structures lying between the skin and the 
muscles; one pair being situated on the back of the tail, and the other along the 
sides of the base of the anal fin. That these organs are capable of giving shocks 
sufficient to kill other fish and small mammals is undoubted; but Dr. Gunther 
considers that the description by Humboldt of the capture of electric eels by horses 
driven into water, in order to receive the shocks and thus exhaust the fishes, seems 
to be the result of the imagination of some person who related the supposed 
incident, or to rest on some isolated incident, since no recent travellers to the 
district have found evidence of the existence of the practice. 
SECTION NEMATOGNATHI. 
The Cat-Fishes or Sheath-Fishes, —Family Silurid 
Although represented only by a single European species, and that confined to 
the rivers to the eastward of the Rhine, the great family of cat-fishes is one of 
extreme importance in tropical and subtropical countries, its members being extremely 
abundant in the fresh waters and estuaries of the Oriental region, as they are in 
those of South America. An essential characteristic of the family is the invari¬ 
able absence of scales, the skin being either smooth or covered with bony tubercles 
or plates; and this character, together with the presence of the barbels from which 
they derive their popular title, will always serve to distinguish the cat-fishes from 
the other great fresh-water family of the carps. In the skull an essential feature is 
the absence of a subopercular element to the gill-cover; while the margin of the 
upper jaw is formed mainly by the premaxillae, the maxillae being more or less 
rudimental. A rayed dorsal fin may be absent, but the fatty dorsal is generally 
present; and when an air-bladder is developed, it may be either free in the 
abdominal cavity or enclosed in bone, but always communicates with the ear by 
the intervention of the auditory ossicles, which are somewhat lenticular in form. 
The skull is characterised by the full ossification of its lateral region, the septum 
between the eyes being also bony ; and in many instances the skull is prolonged 
backwards by the development of a kind of bony helmet over the nape of the 
neck, formed by dermal ossifications overlying some of the bones of the pectoral 
girdle. Frequently this shield, as well as the hinder bones of the skull, are 
ornamented with a tuberculated sculpture. Many of these fishes have also a 
powerful spine at the front of the dorsal fin, which can be locked into a fixed, erect 
position by a rudimental spine acting as a kind of bolt at its base, and is itself 
articulated to the vertebrae, and also joined by a ring to a second spine, in a manner 
similar to that obtaining in the angler-fish. To support this spine certain special 
modifications exist in the structure of the pectoral girdle. Some of the genera. 
