HISTOGENESIS OF SYMPATHETIC SYSTEM 19 
which is large enough to give rise to small ventral nerve-roots 
unilaterally. In two or three of these segments, small visceral 
rami and small sympathetic primordia are also present unilater- 
ally. Neither the primordia of the sympathetic trunks nor 
those of the prevertebral plexuses are present in the lumbar 
region. The peripheral migration of cells of cerebrospinal origin 
was effectively prevented throughout the thoracic and lumbar 
regions in this embryo, following operation, except unilaterally 
in a few lower thoracic segments. Nevertheless, the primordia 
of the esophageal, the pulmonary, the cardiac, and the enteric 
plexuses are present and apparently contain as many cellular 
elements as in unoperated embryos representing the same stage 
of development. Figure 10 is a camera-lucida sketch taken 
from a section of this embryo at the level of the heart. The 
stippled areas represent branches of the vagi, the solid areas 
represent aggregates of cells of nervous origin which are incor- 
porated in the primordia of the oesophageal, the pulmonary, and 
the cardiac plexuses. Unless these cells were differentiated in 
situ, they must have advanced peripherally along the fibers of 
the vagi. Branches of the vagi may be traced along the wall 
of the stomach and the upper portion of the small intestine. 
Cell aggregates representing the primordia of the enteric plexuses 
are present in the wall of the stomach and the intestine as far 
as vagus fibers can be traced. No aggregates of cells represent- 
ing the primordia of the coeliac plexus are present. The findings 
in this embryo demonstrate conclusively that the oesophageal, 
the pulmonary, the cardiac, and the enteric plexuses may arise 
in the absence of the primordia of the sympathetic trunks or 
any pathways except those of the vagi along which cells of cere- 
brospinal origin could migrate peripherally. 
The elimination of the vagi by the destruction of the primordia 
of the vagus ganglia and the portions of the walls of the hind- 
brain from which these nerves arise is also a drastic operation 
which few embryos of the chick survive. This operation was 
not wholly successful in the hands of the writer. However, 
one embryo survived in which the portions of the hindbrain from 
which the vagi arise were successfully destroyed, but some of the 
