Gland-Cells of Internal Secretion in Spinal Cord of Skates. 25 
In addition to the increase of granular material demonstrated in the 
stimulated skates, a study of the sections was valuable in furnishing 
other evidence that the cells were of a glandular nature. The whole 
general appearance of the cells suggested this. WVacuoles inside and 
outside the cells were much more numerous than in normal skates. 
These vacuoles were usually filled with some precipitate or granular 
material or both. In some cases, however, they were entirely clear, 
filled with nothing but a fluid. Most noticeable of all, especially in the 
animals stimulated by electricity, was the presence of exceedingly fine 
granules; these appeared to originate in vacuoles, a large number of 
them being present in a single vacuole. The vacuoles were originally 
spherical or oval in shape, but in some cases were very irregular in out- 
line. Figure 25, taken from a skate stimulated electrically for 2 min- 
utes, is a typical example. The whole central part of the cell is filled 
with a huge irregular vacuole. At one end of this vacuole is some pre- 
cipitate that does not stain with the iron hematoxylin. It has not yet 
been built up into granular secretion. The central part of the vacuole 
is filled both with lightly staining precipitate and with very fine gran- 
ules arranged along this precipitate—granules which stain deeply with 
the hematoxylin. At the other end of this vacuole is a densely packed 
group of the fine, deeply staining granules. The conclusion is obvious. 
The lightly staining precipitate is gradually changed or gives rise to the 
fine granules as the process of secretion progresses. Down near the 
ventral edge of the spinal cord are two vacuoles filled with small gran- 
ules that have become entirely separated from the cell which produced 
them, a very common occurrence. The smaller oval vacuole inside the 
cell shows, besides some very small granules, several larger ones, some 
of them evidently in process of fusing. In this vacuole the process of 
secretion has progressed farther than in the other vacuoles. This one 
cell, therefore, shows several stages in the process of secretion of granu- 
lar material. It is typical of the stimulated skates that vacuoles filled 
with precipitate and fine granules should be present in much greater 
numbers than in the normal skates, and for that reason it is believed 
that they are a direct result of the stimulus applied. This evidence 
supports the theory that the cells are gland-cells. 
Plate 8 (figs. 26 to 41) shows a series of vacuoles representing succes- 
sive changes that occur in the process of secretion. All the figures 
except 36, 37, and 38 were taken from skates of the stimulation experi- 
ments, as those afforded the best examples. Figures 26 to 30 illus- 
trate how the vacuoles may grow in size. Figures 29 to 32 show the 
appearance of a precipitate in the vacuole—precipitate which stains 
practically like the cell cytoplasm. Figures 33 to 36 show this pre- 
cipitate becoming more thread-like, with fine granules arranged along 
the threads. In this precipitate appear granules which stain deeply 
with iron hematoxylin. Figure 36 is inserted here to show the definite 
