Structure and Polarity of Electric Motor Nerve-Cell in Torpedoes. 221 
off from the main body by a layer of fine granular material that appears 
in figure 3, plate 2. This layer becomes visible only in a few favorable 
fixations and stains. 
The black-staining, thread-like bodies described by Solger (33) and 
the centrosomes, as well as the intercellular canals described by other 
authors in this torpedo, were not seen in the thirty or more fish whose 
brains were very carefully examined under all kinds of preparation, 
as well as in the fresh condition. Nor have the cells been studied yet 
for mitochondria. 
NUCLEUS. 
The nucleus of the electric motor nerve-cell of this fish is about 35 
microns in diameter on the average, and attains nearly its maximum 
size while the fish is still small. Thus it increases but little in size 
from the 10 cm. size of fish to the 42 cm. size. It is placed at the 
approximate center of the cell and is but rarely far from this center, 
although in a very few exceptional cases it may appear at one side or 
Fig. 3.—Diagram of nuclear content in electric motor nerve-cell of Torpedo and Tetronarce. 
in one end. In some very few cases two nuclei appear to occupy an 
extra-large cell. This appears to me to be rather a case of the cyto- 
plasmic union of two cells in early life. The nucleus is inclosed in a 
smooth, even membrane of appreciable thickness and considerable 
staining power in the basic as well as in other dyes. This membrane, 
as the experimental work will show, is of equal thickness and apparently 
of equal chemical composition at all points and offers little of interest 
with regard to our question of polarity. 
The contents of this membrane form a more highly differentiated 
mass than the contents of most other nerve-cell nuclei. This differen- 
