Mucous Membrane in the Human Embryo. 525 
Kreuter states that there is no reason to believe that the vacuoles 
are areas of degeneration for he was nowhere able to demon- 
strate evidences of a degeneration of cells followed by resorp- 
tion. There can be seen, nevertheless, a few nuclei lying within 
certain vacuoles which stain less intensely and are more indistinct 
than the nuclei of the epithelium. It does not appear, however, 
that these occasional degenerating nuclei are responsible for the 
production of the vacuoles. It seems obvious from the arrange- 
ment and crowded condition of the surrounding nuclei that the 
vacuoles increase in size. As they become larger the epithelium 
between the vacuoles and the lumen, and between adjacent vac- 
uoles becomes reduced to a thin partition. This partition 
eventually breaks through and makes the cavity of the vacuole 
and the lumen continuous. 
Measurements of the thickness of the epithelial wall of the 
cesophagus are interesting in connection with the vacuoles. Ata 
time when vacuoles begin to form, the epithelial wall of the 
cesophagus is composed of apparently three or four layers of low 
columnar cells. While vacuoles are present the number of cell 
layers varies from one to four. By a breaking through of the 
vacuoles into the lumen and a disappearance (or migration) of 
the more superficial cells, the epithelium is reduced in thickness. 
At 19 mm. and 22.8 mm. the epithelium averages .051 mm. while 
at 30 mm. only .030 mm. in thickness. This loss in thickness is 
soon compensated by a growth in the height of the individual 
cells, for at 42 mm. there are only two layers of cells, the aver- 
age thickness of the epithelium being .043 mm. Two results of 
vacuolation are, therefore, a destruction of the more superficial 
layers of cells, and an increase in the size of the lumen of the 
cesophagus. This increase in the size of the lumen is propor- 
tionately great in the early stages but less in the older ones. 
Folds. At an early stage the epithelium of the cesophagus be- 
comes thrown into large longitudinal folds which are usually 
four in number. Later smaller folds develop at the bases of, or in 
between, the larger ones. These folds give to the cesophagus in 
cross section the appearance of a Maltese cross as was first noted 
by Koelliker (’61). Certain of the folds make their appearance 
