Origin of Electric Tissues of Gymnarchus Niloticus. 189 



Tschermak and another by Bethe go to show that the electric discharge of 

 Torpedo and other fishes is produced by different concentrations of sodium 

 chloride in the electroplaxes and in the intervening electric connective tissue. 

 Since there is a long series, theoretically, of these alternate segments of 

 higher and lower degrees of concentration of the electrolyte, and since all the 

 higher concentrations are presumably equal, and all the lower concentra- 

 tions are equal, we would have a series of equal potentials alternately 

 opposed to each other, and the result would be zero or else only the strength 

 of one concentration current, in case there was one more or one less of 

 either of the concentrations. 



To obviate this dilifiiculty a membrane has been imagined, on one surface 

 of each electroplax, presumably the electric or nerve-ending surface (pos- 

 terior surface in this case), which will be permeable only to one kind of 

 the ions, either negative ions or positive ions, and by which the current is 

 thus rendered integral in one direction. 



Two things remain to be proved in connection with the above theory 

 the fact of different concentrations and the presence of such a membrane. 

 This can be done in any fish in which it is possible to effectively separate 

 the segments in a fresh state, so as to submit them to delicate chemical 

 tests. In Gymnarchus we have a fish whose elements are larger than those 

 in any other one of the seven electric types large enough to be cut apart, 

 I believe, and analyzed separately in the chemical laboratory; also large 

 enough to submit anterior and posterior surfaces to physical tests that may 

 show its permeability to either positive or negative ions and its imperme- 

 ability to the other kind in one direction. This experimental work can 

 most certainly be done if the proportion between the bulk of electric con- 

 nective tissue and electroplax remains the same in the adult as in the larva 

 (see fig. 23, plate 9). Fritsch shows much less of the electric connective- 

 tissue segments in his figures of the adult organ. 



Numerous other anatomical features of Gymnarchus have caused it to 

 be classed with the other mormyrid fishes. This fact makes it of interest 

 to compare its electroplax with the very different electroplax in these 

 fishes. 



That found in Mormyrus oxyrhynchus will serve as a type and its general 

 plan has been well shown by OgnefT (25) and Schlichter (30). Here it is 

 evident that a number of consecutive and entire myotomes have been 

 converted into electroplaxes and that the middle layer of each electroplax 

 is composed of unaltered and clearly striated myofibril bundles. The large 

 number of these fibril bundles, and their distribution, indicate that the 

 whole electroplax in Mormyrus is a syncytium composed of all or most of 

 the cells which would otherwise have gone to make up the single myotome. 

 In this we find an agreement with the electroplax of Gymnarchus which is 

 also formed from several cells. In the one case, however, all the cells in 

 the myotome have been used {Mormyrus) ; in the latter only those lying in 

 eight particular localities {Gymnarchus). (See paper by Dahlgren (36).) 



