218 PISCES. 



of Sheat-fish, and occurs in the Nile, as also in other rivers in 

 Africa, as the Niger. 



In the European Electric Rays, the Electric organs are situated 

 upon both sides of the head, occupying the space between the skull, 

 gills, and pectoral fins, and covered only by the fascia and skin, 

 through which they can be distinguished glistening both upon the 

 dorsal and ventral aspects. The electric organ of one side is com- 

 pletely separated from that of the other, is of a flattened form, i. e., 

 compressed from above downward, obovate in contour, being broader 

 in front where it extends nearly to the anterior edge of the body, 

 but narrower behind where it abuts against the gills. Upon both 

 the upper and under surface the electric organs present the appear- 

 ance of a tessellated pavement, divided into irregular obtusely- 

 angular, polygonal or hexagonal spaces. This depends upon each 

 organ itself being formed of a great number of triangular or hexan- 

 gular membranous prisms or columns passing into those of a globu- 

 lar form, and thus resembling basaltic crystallizations ; they may be 

 compared to so many galvanic columns ; each column is divided 

 into compartments by numerous transversely-disposed horizontal 

 lamellae, which can with difficulty be separated from each other. 

 Each column is moreover separated from the others by a tendinous 

 membrane or aponeurotic partition, which isolates the several col- 

 umns in a manner similar to that whereby artificial galvanic bat- 

 teries are carefully isolated by lateral glass rods. The number 

 of these columns differs in individuals of the same species, and 

 probably according to their age ; in young specimens only some hun- 

 dreds may be counted, while old animals, which attain a length of 

 four feet, number above a thousand. Upon the posterior edge of 

 the galvanic apparatus lesser rows of columns are to be observed ; 

 these are probably in a nascent condition. Each column may per- 

 haps contain 150 to 500 plates or septa, that may be compared with 

 the metallic plates of a galvanic pile ; the depth of the columns and 

 the number of their contained plates (?) varies according to age and 

 the position of the part itself, the middlemost columns being the 

 deepest (six to seven lines), while those upon the edges are more 

 depressed, and in small animals measure only about a line in depth. 

 The partitions between the columns are composed of fasciculi of 

 fibres, similar in character to elastic tissue. The transverse plates 

 or septa consist of a very thin and delicate prolongation inward of 

 the fibrous membrane composing the intercolumnar partitions, which 

 forms the basement membrane, invested upon both its free surfaces 



