xi ELECTRICAL FISHES 



organ of Raja, with its distinct series of cases. Closer inspection 

 reveals in sections parallel with the surface of the skin, or 

 with the axis of the fish, a delicate lattice-work of fibres, which 

 cross at an acute angle, the intermediate spaces appearing grayish 

 and semi-transparent. After treatment with a hardening reagent 

 (alcohol, chromic acid) these structural relations are seen still 

 more plainly. The lattice-work (" sieve," Bilharz) is then found 

 to correspond with the cross-sections of innumerable fine mem- 

 branes of connective tissue, which run vertical to the axis of the 



FIG. 259. Portion of T.S. through epidermis of Malapterurus. (Fritsch.) 



fish, separated by small intermediate spaces. These pass externally 

 into the mass of fibres of the corium, while they unite internally 

 into the so-called tendinous integument. In this way the organ 

 is composed of innumerable partition-walls, running parallel with 

 each other, but at right angles, collectively, to the axis of the fish, 

 and divided into a number of small, hollow spaces, of approxi- 

 mately the same size, with no internal communication (Fig. 260). 

 The axes of these compartments, which are mostly lens-shaped, or 

 double pyramidal, all lie parallel with the axis of the fish. Their 

 equatorial planes are thus vertical to the same, so that the one 

 wall is turned to the head-, the other to the tail-end. Within 



