PLATE 1 
EXPLANATION OF FIGURES 
All of the figures of plate 1 were drawn with camera lucida to the same scale of 
magnification (x 390). 
1 Dahlgren cell from the spinal cord of the mackerel, Scomber scombrus. 
The nucleus is almost spherical and a plasmosome is present. The diameter of 
this cell is about twice that of an ordinary muscle motor nerve-cell in the same 
animal. This cell and the cells of figures 2, 3, and 4 were all present in the same 
cross-section. 
2 Dahlgren cell from the spinal cord of the mackerel, Secomber scombrus. 
The nucleus is slightly elongated and lobulated. A plasmosome is present, but is 
not shown in the section represented. 
3 Dahlgren cell from the spinal cord of the mackerel, Scomber scombrus. 
The nucleus has three lobes. 
4 Dahlgren cell from the spinal cord of the mackerel, Scomber scombrus. 
This section shows the nuclear material enclosing a central core of cytoplasm. 
5 Dahlgren cell from the spinal cord of the butterfish, Rhombus tricanthus. 
The nucleus is more highly branched than in the mackerel, and in this section it 
appears to be multiple. Two plasmosomes may be seen. The size of the cell is 
also somewhat larger than in the mackerel. : 
6 Dahlgren cell from the spinal cord of the tautog, Tautoga onitis. Note the 
two greatly elongated nuclear masses. These are, however, in reality parts of a 
single nucleus. 
7 Dahlgren cell from the spinal cord of the sandshark, Carcharias littoralis. 
Note the increase in lobulation of the nucleus. Note also the vacuole at the edge 
of the cell containing some fine granular material. Apparently the vacuole has 
just burst and discharged most of its contents. Plasmosomes are not distinguish- 
able in this cell nor in any of the cells of the succeeding figures. 
8 Dahlgren cell from the spinal cord of the sting-ray, Dasyatis. This shows 
further increase in size of the cell and size and lobulation of the nucleus. 
9 Dahlgren cell from the spinal cord of the skate, Raia ocellata. Both the 
cell body and nucleus are of enormous size. Note especially the characteristic 
groups of granules of various sizes at the ends of the cell. Each group of granules 
represents the original content of a single vacuole. Only a small percentage of 
the granular secretion is shown in the section represented, most of it being present 
in the sections near the ends of the cell (anterior and posterior ends). 
10 Dahlgren cell from the spinal cord of the summer flounder, Paralichthys 
dentatus. The size of the cell is about the same as that of the skate, Raia ocellata 
No large granules, however, have ever been found associated with these cells of 
the flounder, such as are present in the skate. 
11 Typical vacuole sometimes found associated with the cells of the summer 
flounder, Paralichthys dentatus. This vacuole contains a fine granular or thread- 
like precipitate which is apparently elaborated by the cell. It is similar in 
appearance to the vacuoles containing fine secretion material which are often 
found associated with the Dahlgren cells of the skate (both inside the cell and 
outside). 
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