562 THE PHYSIOLOGY OF ELECTRICAL ORGANS. 



man. The term " pseudo-electric " has now been abandoned, and is 

 obviously misleading, since the structures in question, though diminut- 

 ive and less highly differentiated than those of Torpedo, are fundament- 

 ally the same as these, both as regards structure and functional activity. 



All electric organs possess a characteristic structure which deter- 

 mines the peculiar features of their functional activity, and they all 

 have an unmistakable appearance when examined in the fresh state. 

 This is well displayed in the recently killed Torpedo, when the ventral 

 or dorsal skin is removed. Two large masses now come into view placed 

 between the gill slits and the margin of the fish. Each has a concave 

 inner border, and consists of a semi-transparent material, of the con- 

 sistency of jelly, in which may be seen connective tissue septa and 

 numerous nerve branches. The septa are so arranged as to divide the 

 mass into hexagonal columns, the ends of which lie immediately beneath 

 the dorsal and ventral skin, so that the skin surface of the whole organ 

 presents an appearance resembling the tops of basaltic columns. On 

 making a transverse section of the fish, the organs are seen to extend 

 from the ventral to the dorsal surface, and to contain a number of closely 

 packed columns arranged side by side ; as these run from the ventral to 

 the dorsal skin, some of them are displayed in the section, which has 

 cut them in the direction of their length. 



In G-ymnotus, the dissection of the fish shows four such organs, 

 two dorsal and two ventral, the former being the larger. These 

 present a similar transparent appearance in the fresh state, and con- 

 sist of columns of jelly-like material separated and bounded by con- 

 nective tissue septa. The organs extend from the neighbourhood of 

 the cephalic to that of the caudal end of the fish, and the columns run 

 for variable distances in the same direction. A section at right angles 

 to the spinal canal thus reveals organs and columns in cross-section. 



In Mormyrus there are four slender organs situated between the 

 muscles, with their long diameter parallel to the spinal column, thus 

 resembling in general disposition the arrangement present in Gymnotus. 



The organs found in the skate (Raia latis) are situated one on each 

 side of the caudal portion of the spinal column. Each is a slender 

 body tapering at its two ends, and exhibits in the fresh state the 

 characteristic transparent material enclosed within connective tissue 

 septa. A cross-section of the tail at right angles to the spinal column 

 shows that each organ consists of columns which lie closely packed 

 with their long axes parallel to the spinal column ; they are thus dis- 

 played in such a section as translucent masses, bounded by hexagonal 

 walls. 



Finally, in Malapterurus, the organ attains a high degree of differen- 

 tiation. Unlike those just described, it is situated within the skin, which 

 is correspondingly thickened. The organ is imperfectly divided into 

 two halves by a connective tissue septum upon the ventral surface, and 

 enwraps the whole body except the fins and a small portion of the 

 cephalic end. It has not been developed at the expense of any of the 

 muscles used in locomotion, and hence the rapid movements which 

 characterise these fish are in striking contrast with the sluggish motions 

 of the Torpedo and Gymnotus. The jelly-like organ is bounded exter- 

 nally by the surface layers of the skin, and internally by a strong layer 

 of connective tissue, which is loosely connected with the subjacent 

 muscles. On making sections through the organ, the characteristic 



