224 Papers from the Department of Marine Biology. 
from those cases where the whole nuclear content has been piled up in a 
broken mass. Some of the best workers on the structures of the cyto- 
plasm have left us figures that give no true conception of the structures 
of the nucleus. Much careful work remains to be done upon it before 
we possess an adequate picture of its organization. 
The plasmosome is one of the most prominent contents of the nucleus. 
It is large, being usually about 7 microns in diameter when single, and 
is an almost perfect sphere. Its most prominent physical property is 
a dense refractiveness which makes it easily visible in the living cell 
even under a wide opening of the condenser diaphragm. As the dia- 
phragm opens, the outline of the plasmosome lasts a trifle longer than 
that of the nuclear membrane, and when one considers the greater 
radius of the nuclear membrane this means that the plasmosome is 
the most refractive body in the cell, excepting perhaps the karyosomes. 
No accurate measures have been taken to measure the actual refrangi- 
bility of the various organs of this cell by accurate physical means, 
but it is hoped that this will be done at another time. 
In perhaps a majority of cases the plasmosome is a single body, but 
this factor varies in the different individual fishes examined. I think 
it may be safely stated that in the oldest and largest specimens the 
plasmosome is most apt to be single, while in younger specimens it is 
most apt to be a multiple body. Also a distinct tendency to vary in 
the distribution of the plasmosome was observed in individuals of the 
same size and sex. When multiple, it is most usually found as a single 
large body with one or more smaller masses in some other (usually 
distant) part of the nucleus. Or in some cases it may be found as two 
fairly large spheres of approximately equal bulk. In one Torpedo 
ocellata of 15 em. each nucleus appeared to contain its plasmosome as 
four or more bodies of equal size, any one of which was much smaller 
than the usual size of 7 microns. In all cases of multiple plasmosome 
it appeared that the total volume of the various bodies was greater than 
that estimated in the nuclei where a single body appeared. It may be 
said here that in the large American Tetronarce occidentalis a single 
plasmosome is almost the invariable rule. 
The plasmosome is by no means a homogeneous body. In the large 
and typical forms at least three substances may be distinctly seen in it. 
One is a granular, non-refractive, and non-staining content of the 
various ‘‘vacuoles” found in this structure. The principal vacuole 
occupies a large part of the exact center or, in numerous cases, a More or 
less eccentric position in the body of the plasmosome. The usual 
diameter of this vacuole is a little more than half of that of the whole 
plasmosome, or 4 microns. It is always round and ‘‘bubble-like” and 
in some very few cases is so close to the periphery of the plasmosome 
that it has broken through and is open to the other contents of the 
nucleus. The edges of the plasmosome thus broken are rounded up as 
