rm 
524 Franklin P. Johnson. 
of 19 mm. (series 829) similar vacuoles are found, but are less 
numerous than in the above embryo of the same length. They 
are also more numerous in the lower portion of the cesophagus 
than in the upper. 
At 22.8 mm. (series 871) the diameter of the cesophagus is 
nearly double that at 19 mm. The vacuoles are more numerous 
and, as shown in fig. 1b, communicate with one another and with 
the main lumen to a greater extent. In the upper part of the figure 
the cesophagus appears to have a double lumen. This appear- 
ance is due to the fusion of a number of vacuoles. The vacuoles 
are about the same size as those found in the preceding embryo 
but the lumen has increased in diameter. Although vacuoles 
also occur in the dorsal and ventral walls of the cesophagus, they 
are less numerous there than in the lateral walls. The few vacu- 
oles found in the dorsal and ventral walls do not show in the figures; 
they are, however, of the same general character as those described. 
In other embryos of 22 mm., 22.8 mm. (series 737) and 23 mm. 
the vacuoles are found to be less numerous in the upper half of 
the cesophagus than in the lower half. At 29 mm. and 30 mm. 
they have become very few; at 32 mm. only slight traces of them 
are found; at 37 mm. they have entirely disappeared. ‘ 
Vacuoles of the nature described were noted by Schultz in 
1897. Kreuter (05) believed that they cause a temporary occlu- 
sion of the cesophagus, but Forssner (07) showed by means of 
models that the main lumen is not obliterated. Schridde (’08) 
failed to find an occlusion at any stage and denied the presence 
of vacuoles but described epithelial bridges which arise by epithe- 
lial proliferation in circumscribed places. From a study of these 
structures by means of wax reconstructions, the writer is able to 
confirm the results of Forssner inasmuch as the lumen is not 
entirely occluded and vacuoles are present. 
The exact cause and significance of the vacuoles are difficult 
to determine. Similar vacuoles are found in the cesophagus of pig, 
rat and rabbit embryos. They have been reported by Forssner 
in the hedgehog, where in a certain stage they lead to a complete 
occlusion. Vacuoles similar to those of the oesophagus are found 
in the walls of the stomach and the duodenum of human embryos, 
