558 Franklin P. Johnson. 
Most of these disappear by becoming incorporated in the walls 
of the developing villi, but some may persist. A large persistent 
diverticulum was found in an embryo of 134 mm. 
3. The vacuoles of the csophagus, stomach and duodenum, 
and the pockets of the duodenum, jejunum, and the ileum are 
related structures. They are all the result of a similar process 
of growth, which for some undetermined reason, manifests itself 
differently in different parts of the digestive tube. 
5. In the upper part of the duodenum, in the jejunum, 
and in the upper part of the ileum, the villi originate singly as 
thickenings of the epithelium which are not preceded by longitudi- 
nal folds. These thickened plates of epithelium are invaginated, 
and later reduced to a single layer of cells. 
5. In the remainder of the duodenum (approximately the 
lower two-thirds) the villi are developing while vacuoles are pres- 
ent, but are not recognizable because of the ‘‘solid’’ condition 
of the duodenum. The apices of the villi of one wall are adherent 
to those of the opposite wall. The spaces in between the adjacent 
fused villi are the vacuoles. By a separation of the apices, the 
individual villi appear, and the vacuoles become confluent with 
one another to form a continuous lumen. 
6. In the lower part of the ileum low longitudinal folds occur. 
These folds, varying from two to five in number, are irregular in 
height and position. Their presence is probably due to the fact 
that the outer coats of the gut do not grow as rapidly as the epi- 
thelium. The irregularities along the tops of the folds are develop- 
ing villi. Later the folds disappear by an expansion of the epi- 
thelial tube or by being absorbed by the rapidly growing villi. 
7. As the villi develop they become arranged in longitudinal 
rows of varying regularity. 
8. Additional villi develop as separate growths, either forming 
new rows between those already present, or arising in the older 
rows. 
9. The growth of the younger villi, up to the size of the larg- 
est, is more rapid than that of the older ones. 
10. Intestinal glands develop as separate hollow outgrowths 
of the epithelium. They were first seen in an embryo of 55 mm. 
