ORIGIN OF GASTRIC GLANDS OF ACANTHIAS 365 
at the 133-mm. stage, and as shown in figure 2, all of the epi- 
thelial cells still reach to the surface. There are, however, 
considerable changes in the staining reactions of small groups 
of them. ‘These changes are very significant, for they show 
that, in spite of their morphological similarities, not all of the 
epithelial cells are endowed with the same specificities for fur- 
ther differentiation. Small groups of them will remain as epi- 
thelial cells, while other groups change their staining reactions, 
and the shape of their nuclei, and finally form a bottle-like plug 
which is embedded in the epithelium (fig. 3). All of these 
changes were considered in detail in connection with figures 
2 and 3. 
Since Peterson maintains that the gastric glands grow out 
from portions of the epithelium whose cells do not reach the 
surface, it would be interesting to know how he would account 
for certain nuclear variations. In figure 5 the nuclei are numer- 
ous in the glandular outgrowth. On comparing one of them 
with the epithelial nucleus on the left-hand side of the same 
figure it is apparent that there are fundamental differences 
with reference to their form, and also in the amount and distribu- 
tion of their chromatin material. These differences were also 
mentioned in connection with figures 2 and 3. How would 
Peterson explain such differences? As far as the nuclear dif- 
ferences in figures 2 and 3 are concerned, he woud be unable 
to give any logical explanation, because he failed to find similar 
stages in his material. Now, if the gastric glands in Selachians 
really arise by means of epithelial outgrowths, as Peterson 
holds, one would naturally expect to find similar nuclei in both 
the outgrowths and the general epithelium. Figures 4 and 5, 
however, show that this is not the case. They are very dif- 
ferent in their form, size, and in their arrangement of chro- 
matin material. This is precisely what one would anticipate 
after studying stages similar to the ones depicted in figures 2 
and 3 of this paper. 
stomach lumen. Griffini and Vassale found many such groups with lumina 
apparently shut in on all sides, but reconstructions always demonstrated con- 
tinuity with the stomach lumen from the first.’’ 
