18 ALBERT KUNTZ 
primordia of the sympathetic trunks, there would remain no 
source from which cells of nervous origin could advance into 
the primordia of the sympathetic plexuses associated with and 
within the walls of the visceral organs except the vagus ganglia 
and the walls of the hindbrain. If, in such embryos, the pri- 
mordia of any of the peripheral sympathetic plexuses should 
arise, either they would arise by a process of local differentiation 
or from cells of cerebrospinal origin which advance peripherally 
along the paths of the vagi. On the other hand, if the primordia 
of the vagus ganglia and the portions of the walls of the hind- 
brain from which the vagi arise could be destroyed or extirpated 
early, these nerves would be eliminated. If such embryos 
should continue to develop with normal primordia of the sym- 
pathetic trunks, but the primordia of the sympathetic plexuses 
associated with and within the walls of the visceral organs should 
fail to arise, we would be forced to conclude that these plexuses 
are genetically related to the vagi, and that they normally arise 
from cells of nervous origin which advance peripherally along 
the paths of these nerves. 
Both methods outlined above were attempted in embryos of 
the chick and the frog. The complete elimination of the neural 
crests and the neural tube throughout the trunk region in em- 
bryos of the chick which are subjected to operation as early as 
the close of the second day of incubation involves the destruc- 
tion of so much tissue that few embryos survive. Fortunately, 
as pointed out in an earlier section of this paper, the primordia 
of the sympathetic trunks fail to arise in segments in which a 
remnant of the ventral portion of the neural tube persists, even 
though small ventral nerve-roots without visceral efferent fibers 
may grow out from it (fig. 2). In one embryo of the chick (14) 
which was subjected to operation at the close of the second day 
and killed at the close of the fifth day of incubation, the neural 
crests were completely and the neural tube almost completely 
destroyed from the lower cervical to the sacral region. In the 
upper half of the thorax, the neural tube and spinal nerves are 
entirely absent. In the lower thoracic segments, an asymmetri- 
cal remnant of the ventral portion of the neural tube persists 
