376 



ELECTRO-PHYSIOLOGY 



CHAP. 



fact that the electrical organs of Gymnotus extend to the tip of 

 the tail, we find ganglion-cells of the electrical type as far as the 

 end of the spinal cord, but they gradually diminish in number 

 and size, and more nearly resemble in form the ordinary motor 

 cells of the anterior horn. 



While in these cases we have in Torpedo and Gymnotus 

 electrical organs of such high differentiation that even the most 



powerful effects seem ab 

 initio to be accounted for, 

 there are in the tail of the 

 common Skate (Raja), as well 

 as in the species of Mor- 

 myrus, organs that in struc- 

 ture and arrangement are 

 unmistakably allied with the 

 electrical, but of which the 

 effects are so slight that they 

 have only recently been de- 

 termined. These du Bois- 

 Iteymond named " pseudo- 

 electric " organs. This dis- 

 tinction is, however, obsolete, 

 seeing that both Mormyrus and the various species of Raja belong 

 to the true electrical fishes, so that, as Babuchin expresses it, 

 " there are no pseudo- electrical fishes, but only large and strong, 

 or small and weak, electrical fishes, severally." 



As James Stark was first to discover, the electrical organs in 

 the tail of Raja lie on either side, near the vertebral column, as 

 two cylindrical, grayish, transparent bodies, pointed anteriorly and 

 posteriorly. "They begin at the centre of the sacro-lumbalis 

 muscle, near the junction of the anterior and second thirds of the 

 tail, become gradually thicker, and, after completely displacing 

 the muscle, lie close under the skin, where they are as thick as 

 the muscle itself, and extend as far as the extreme end of the 

 tail " (Fig. 245, a, &). Their position is shown even better in 

 transverse than in longitudinal section (Fig. 246). Here the com- 

 position out of single, concentric " columns," running parallel with 

 the axis of the tail, and separated, as in Torpedo or Gymnotus, by 

 septa of connective tissue (M. Schultze's "primary partition 

 walls," 31 a\ is very obvious. Each column again breaks up by 



FIG. 244. T.S. through the spinal cord of Gymnotus 

 electricus. (Fritsch.) 



