Origin of Electric Tissues of Gymnarchus Niloticus.. 



183 



The electric-motor cells at this age must of course be considered as still 

 very young, and descriptions from the adult are desirable. We will begin 

 by examining the 9-day-old embryo once more to see if they have started. 

 In this cord (fig. 8, plate 2) there are but very faint traces of any nerve- 



Fig. 9. Diagram to show position and relations of 

 ^ nerve elements to electric soindles. S.C.. sninal 



nerve elements to electric spindles. S.C., spinal 

 cord, showing central canal and four motor elec- 

 tric nerve-cells. Processes from these cells pass 

 out through ventral roots, and distribution of these 

 roots to electric spindles and muscle-masses is in- 

 dicated. M, some of the muscle-masses. D, U.M., 

 L.M., and V show electric spindles on one side. 

 Sp.G., spinal ganglion; L.L.N. , lateral line nerve. 



cell development, and some neuroblast mitosis is still going on. In the 

 position to be later occupied by electric cells a little enlargement of nucleus 

 and cell-body is visible. One cell here is of great interest, and that is one 

 of the now well-known " Hinterzellen " or giant cells, first described by 

 J. Beard (37), Rohon (29), Studnitzka (33), and others, in the embryos of 

 Salmo and Raja, and later by Fritsch (21), as a different sort of cell, in the 

 adult Lophius. Still later, such cells were described by the writer (36) in the 

 embryos and adults of various Pleuronectidae and in Pterophryne, where he 

 showed it to be the same cell in both embryo and adult, and described the 

 relations of anterior and posterior branches of the neuraxon. From its 

 size, shape, and position in the present specimen, it seems that this dorsal 

 cell might be, in some way, related to the electric-motor cells, but that 

 question is easily settled when one examines the 12-day embryo and finds 

 that all of the dorsal cells have effectually disappeared before the electric- 

 motor cells begin to differentiate. Besides, the well-known fiber courses of 

 the dorsal cells as worked out by Fritsch in Lophius, the writer in Ptero- 

 phryne, Harrison in Salmo, and Johnson in Catostomus are sufficient proof 

 that the two have nothing in common. 



