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 
gccidentalis, 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 7’. 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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