Origin of Electric Tissues of Gymnarchus Niloticus. 187 



The nerve-process, carrying its connective- tissue sheath until it actually 

 reaches the surface of the electroplax, ends in a blunt and somewhat thick- 

 ened knob which is embedded in a hollow or invagination in the substance 

 of the posterior cytoplasmic or electric layer of that structure (see figs. 18 

 and 19, plate 6; also fig. 16, plate 5; also figs. 24 and 25, plate 9). This knob 

 may be quite elongate in form and in some cases appears to be branching. 

 The nerve fiber becomes very narrow and apparently dense just before 

 entering the cavity, but it quickly broadens out, to as much as or more than 

 its previous width, to fill the cytoplasmic cavity of the electroplax. Its 

 substance becomes very light-staining, more so than any other part of its 

 length is, and this light-staining quality is most apparent at its extreme 

 distal end in the cavity. The nerve-fibrils, faintly visible in the outer 

 courses of the axon and rather more so in the denser neck just before entering 

 the cavity, can be seen in the light-colored club-shaped ending to be running 

 in an irregular reticulum instead of in their previously almost straight and 

 parallel manner. They could not be traced into the protoplasmic bridges 

 between the club-shaped nerve-ending and the surface of the protoplasmic 

 cavity in which it lies. In very few instances did the nerve-substance fill 

 the recess in the electric layer tightly, probably owing to some shrinkage in 

 both of the tissues. The small space between the two surfaces is crossed 

 by the numerous fine processes or strands, mentioned above, of some of the 

 nerve-tissue remnants, probably of an original closer contact. 



The question now arises as to whether the cavity or depression which 

 the nerve-ending occupies is to be considered as an invagination of the 

 surface of the electric layer or as a real penetration of the electroplax by 

 the nerve. I shall consider it as the former, because the surface of the 

 electroplax appears not to be interrupted by the opening but to continuously 

 follow the inner edge of the cavity all the way around. 



The presence of a perceptible cell-membrane or electrolemma would 

 assist in the solution of this question, but such an organ could not be 

 demonstrated. The edge of the cytoplasm was sharp and definite, but no 

 membrane was visible, either by its staining properties or by refrangibility. 

 It possibly will be found in the adult organ. Nor was it possible to see the 

 "Stabchen" or rodlets which have been described in other electric organs 

 by Ballowitz (3, 5) and his pupils (30). Some striated arrangement of 

 the granular electrochondria or granules described previously was observ- 

 able, but this constituted a fibrillar secretory striation, such as is seen in 

 the surfaces of most cells that are undergoing exchanges of any kind. Here, 

 again, we must await examinations of the adult electroplax before we can 

 say if such "Stabchen" are present; also if they are homologous with the 

 well-defined rodlets found by Ballowitz in Torpedo and in Raja, and whether 

 they are specific structures of any importance in the production of electricity. 



Returning to the relation of nerve-ending to electroplax, we have 

 practically decided that the nerve-club is embedded in an invagination of 

 the surface rather than in a cavity in the substance of the electric layer. 



