STRUCTURE AND POLARITY OF THE ELECTRIC MOTOR 

 NERVE-CELL IN TORPEDOES. 



Some time ago the writer noticed that the electric motor nerve-cell 

 of Tetronarce occidentalis, a large torpedo found on the coast of Massa- 

 chusetts in America, contained two nucleoli in its nucleus; and further, 

 that these nucleoli were different from one another in form and in 

 chemical composition, as shown by their staining properties and their 

 optical properties under the microscope. The point of greatest in- 

 terest, however, was the position of these two nucleoli, one always 

 being dorsal and the other ventral in position in the nucleus. So 

 invariable was this condition that it was decided to undertake studies 

 of these cells, and for that purpose a visit was made to the Naples 

 Station, where Torpedo marmorata and Torpedo ocellata are to be 

 had. Here it was surprising to find that the electric motor nerve-cells 

 of these two forms did not contain both the nucleoli found in Tetronarce 

 occidentalis, but only one of them, the larger of the two, which always 

 appears in the ventral position in the American form. This larger 

 nucleolus corresponds to the body known to cytologists as the plasmo- 

 some and will be spoken of by this name. It is so evidently the same 

 and shows such an evident tendency toward an orientation of its 

 position that it was decided to prepare this paper chiefly with regard 

 to the structure and position of the plasmosome in the electric motor 

 nerve-cells of Torpedo ocellata and Torpedo marmorata, reserving the 

 material already gathered upon Tetronarce occidentalis for a second 

 part of this paper when further experiments can be made upon that 

 eastern American fish. 



This work will, therefore, consist of a description of the structure of the 

 electric motor nerve-cell as found in T. marmorata and T. ocellata and an 

 account and discussion of the literature and of the experiments which 

 were performed by the writer in an effort to decide what physiological 

 and chemical or physical factors were capable of influencing the posi- 

 tion of its nucleolus or plasmosome. Incidentally, some more or less 

 interesting results of the experiments which pertain only indirectly to 

 the main point will be mentioned, as well as a few new facts concerning 

 the structure of the cytoplasm. 



I wish, at this point, to express my thanks to the Carnegie Institu- 

 tion of Washington for allowing me to occupy one of their tables at 

 the Zoological Station at Naples in 1912-13. Also to the officers of 

 that Station for many kindnesses and for the very efficient help given 

 me in the course of my work. 



As is well known, the electric organ of these fishes consists of two 

 large masses of modified muscle, lying symmetrically on each side of 

 the median line, as can be seen from the well-known figure of Fritsch 



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