ORIGIN OF GASTRIC GLANDS OF ACANTHIAS 369 
5. The presence and further differentiation of the gland rudi- 
ments in the epithelium play an important part in causing the 
proximal free ends of the epithelial cells to be laterally com- 
pressed. As a result of compression, the epithelial cells inter- 
vening between two gland rudiments are forced to take on a 
fan-shaped arrangement in cross-section (fig. 3). 
6. Acanthias embryos 137 mm. in length show that many of 
the gland rudiments are growing out into the underlying meso- 
dermic tissue to form the future gastric glands (figs. 4, 5, and 6). 
In the course of a very short time all the gland rudiments have 
given origin to glandular outgrowths. Peterson recognized 
similar outgrowths, but he thinks that they arise from certain 
epithelial cells which do not reach to the free surface—lumen 
side of the stomach. His interpretation is obviously incorrect 
because, on the basis of it, he is unable to account for all the glands 
in older specimens. Peterson failed to discover stages similar 
to those shown in figures 2 and 3, and these are the critical stages 
in establishing the number of glands for any given specimen. 
7. As the glandular outgrowths invade the mesodermic tissue 
there is an actual rotation of their cells (fig. 6 and 7). In many 
outgrowths it is not possible to distinguish cell boundaries, but 
in instances where they are evident, it is apparent that the 
shifting movements of the nuclei are but a rotation of the cells 
that contain them (Scammon, 715). The rotation processes 
are confined chiefly to the cells at the lower two-thirds of the 
glandular outgrowth. The fundic portion of the gland takes 
on a flask-like form as a direct result of these rotation proc- 
esses (figs. 6 and 7). 
8. With the completion of rotation, the cells at the fundic 
portion of the gland are placed, with reference to their long 
axes, at right angles to the lumen of the gland (fig. 7). 
9. The fully differentiated gastric gland of Squalus acanthias 
is an unbranched, flask-shaped structure. The differentiation 
of the two cell-types does not occur. 
