354 ADOLPH R. RINGOEN 
all of its constituent cells- presented similar morphological fea- 
tures and identical staiing reactions. The nuclei also pre- 
sented their own characteristic configuration and staining re- 
actions. With the establishment, however, of local changes 
in the gastric epithelium (133-mm. embryos) there appear cer- 
tain definite modifications in its cellular make up. Figure 2, 
from a 133-mm. embryo, shows a number of these modifications. 
The two cells on the extreme right and left, respectively, of this 
figure represent the typical columnar epithelial cells so char- 
acteristic of the selachian stomach. They are long and narrow, 
and are without a basement membrane. The cytoplasm stains 
a faint grayish tint with iron haematoxylin-orange G. The 
nuclei are long and slender; they present a deeper gray tint 
than does the cellular cytoplasm. The four cells just described 
are destined to remain as epithelial cells. Interpolated between, 
however, are a number of other cells which are characteris- 
tically different from the former in both their cytoplasmic and 
nuclear staining reactions. A number of these cells may still 
show a close relationship to the neighboring epithelial cells 
as exemplified by their behavior toward the iron haematoxylin- 
orange G stain. In most cases, however, the cytoplasm and 
the neuclus do not stain in the same manner as in the 
adjacent epithelial cells. The whole tendency of staining vari- 
ations in this direction is for an epithelial cell to decrease 
in its avidity for the stain as soon as it is called upon to 
assume a different rdle from that of an ordinary epithelial cell. 
At times such a change in the staining reactions of the cell body 
may precede somewhat that of corresponding changes in the 
nucleus or vice versa, and again the changes may proceed rather 
synchronously in both the cytoplasm and the nucleus. 
In addition to the above-described staining reactions, there 
is also a further change in the form of the nucleus, as shown 
in figure 2. On the right-hand side of the figure, in the third 
cell from the margin, is a nucleus which has not changed its 
staining reactions, although the cell body has progressed to 
some extent in that direction. It is apparent from the figure 
that the nucleus is undergoing a change in its shape. No longer 
