ORIGIN OF GASTRIC GLANDS OF ACANTHIAS 355 
does it correspond in its configuration to the long narrow epi- 
thelial nucleus contained in the cells at the extreme right and 
left of the figure. A decided change in shape is clearly seen 
in those cells which have changed both their cytoplasmic and 
nuclear staining reactions. 
If the conditions in the gastric epithelium of 133-mm. <Ac- 
anthias embryos, as I have described them in figure 2, are inter- 
preted properly, they would indicate that in this group gland 
development is of a rather primitive nature. No specialized 
cells are set apart in early embryonic life for the origin of glands, 
but the general epithelium is endowed with the capacity of 
transforming certain patches of its constituent cells into definite 
gland rudiments at the proper time. When the proper time 
is at hand, small groups of these apparently similar epithelial 
cells change their staining reactions and the shape of their nuclei, 
and differentiate in another direction. They continue to evolve 
in a very definite direction, because they are incapable of giv- 
ing rise to any other structure than the particular gland rudi- 
ment towards which their potentialities are directed. 
B. Formation of definite gland rudiments 
The characteristic changes which appear in the gastric epi- 
thelium at the 133-mm. stage are even more pronounced in 
slightly longer embryos. In 137-mm. specimens the epithe- 
lium has been modified only at those points where glands are 
to be formed. It is surprising with what regularity the ap- 
portioning of the general epithelium into glandular and non- 
glandular areas has taken place at this stage. The number of 
epithelial cells which intervene between two potential gland 
areas is practically the same in all cases. Just what factors 
determine the selection of certain groups of epithelial cells as 
the precursors of glands to the absolute exclusion of others 
obviously can no more be answered than why certain entodermal 
cells will differentiate into liver cells, while other similar cells, 
at least so in their early stages of differentiation, will give origin 
to pancreatic tissue. 
