THE CATFISHES OR SHEATHFISHES 2825 



other fishes endued with electric power. It will be unnecessary to give any descrip- 

 tion 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. Giinther 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 travelers to the district have found evidence 

 of the existence of the practice. 



SECTION NEMATOGNATHI 

 THE CATFISHES OR SHEATHFISHES Family SILURID^E. 



Although represented only by a single European species, and that confined to 

 the rivers to the eastward of the Rhine, the great family of catfishes is one of ex- 

 treme 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 invariable 

 absence of scales, the skin being either smooth or covered with bony tubercles 

 or plates; and this characteristic, together with the presence of the barbels from 

 which they derive their popular title, will always serve to distinguish the catfishes 

 from the other great fresh-water family of the carps. In the skull an essential fea- 

 ture is the absence of a subopercular element to the gill cover; the margin of the 

 upper jaw is formed mainly by the premaxillse, the maxillae being more or less rudi- 

 mental. 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 inclosed in bone, but always communicates with the ear by the intervention of 

 the auditory ossicles, which are somewhat lenticular in form. The skull is charac- 

 terized by the full ossification of its lateral region, the septum between the eyes be- 

 ing also bony; and in many instances the skull is prolonged backward by the devel- 

 opment 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 struc- 

 ture of the pectoral girdle. Some of the genera, such as the one represented by the 

 eel-like catfish, have additional breathing organs; in this particular instance taking 

 the form of a branched structure attached to the gills. On the other hand, in the 



