84 COMPARATIVE ANATOMY. 



The general hue of the animal is blackish, relieved by a number of lighter 

 spots, some of them having a reddish tinge. Lateral line double, one pass- 

 ing near the median line of back, in other in line with the anal fin. Pec- 

 toral fins small, anal fin long, caudal fin obtuse. (Blooch.) 



Anatomy. The abdominal cavity is short ; anus placed a short distance 

 behind branchial cleft. The electrical organs occupy nearly one-third of its 

 whole bulk. They are formed by two series of tendinous membranes, one 

 of which consists of horizontal plates running from the abdominal cavity 

 towards the tail, placed one above another, with short distances between 

 them ; the other of perpendicular plates, forming, along with the other series, 

 small quadrangular cells, which are filled with a semi-gelatinous transparent 

 substance. This structure is divided longitudinally into two pairs of distinct 

 organs, one considerably larger than the other. The greater pair lies above 

 the other, and immediately beneath the long muscle of the tail. They are 

 separated from one another by part of these muscles, by the air bladder, 

 and by a central membranous partition. They occupy a large portion of the 

 lower and lateral parts of the body, and are covered externally only by the 

 common integuments. The smaller pair are covered also by the muscles of 

 the caudal fin. Both pairs of organs are somewhat angular in their trans- 

 verse section, truncated anteriorly, tapering towards the tail. In a Gymno- 

 tus of average length the larger organ of one side is about one inch and 

 one-quarter in breadth at its thickest part, and in this space there are thirty- 

 four longitudinal septa. The smaller organ is about half an inch in breadth, 

 and contains fourteen septa, which are slightly waved. These septa prob- 

 ably answer the same purpose as the columns in Torpedo. 



The nerves of the electrical organs are derived from the spinal marrow 

 alone. They are large, numerous, and divided into fine twigs on the cells of 

 the organs (Coldstream.) 



Measurements. 5' to 5' 3" long. 



Habitat. Amazon River, S. A. 



Malapterurus electricus (raasch, thunder-fish). This fish belongs to the 

 Siluridae (cat-fishes). 



Malapterurus. Only one dorsal fin, which is adipose, and situated be- 

 fore the caudal ; anal of moderate length, or short ; caudal rounded ; ventrals 

 six-rayed, inserted somewhat behind the middle of the body ; pectorals with- 

 out pungent spine. Barbels six ; one to each maxillary, and two on each 

 side of the mandible. Both jaws with bands of villiform teeth ; palate eden- 

 tulous. The entire head and body covered with soft skin. Eyes small. Gill 

 opening very narrow, reduced to a slit before the pectoral. An electric 

 organ extends over the whole body, and is situated between two aponeu- 

 rotic membranes below the external integument. 



M. electricus. Description. Rays to anal fin 10-13. Eye rather small, 

 the diameter being less than one-third its distance from the upper end of the 

 gill opening. The length of the head is contained four times and a third in 



