45 2 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. Gtinther 

 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 premaxillse, 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 bon_y ; 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, 



