8 ALBERT KUNTZ 
nerves and the neural tube are entirely absent. This condition 
is illustrated microphotographically in figure 7 which is taken 
from a section through an anterior thoracic segment of an em- 
bryo which was subjected to operation about the close of the 
second day of incubation. Small primordia of the sympathetic 
trunks (fig. 7, sy) are present, in this embryo, in the absence of 
spinal nerves and complete or almost complete absence of the 
neural tube in six successive segments. In the posterior tho- 
racic and lumbar regions, the primordia of the sympathetic trunks 
aré absent in at least seven successive segments. 
The peripheral migration of’ nervous elements is initiated 
somewhat earlier in the anterior thoracic segments than farther 
posteriorly in embryos of the chick. Obviously, in the embryo 
cited above, migration was going on in the anterior, but not in 
the posterior portion of the trunk, at the time of operation. The 
presence of the small primordia of the sympathetic trunks in 
the anterior thoracic segments in the absence of the cerebro- 
spinal nervous system does not indicate the local origin of the 
former. The experimental evidence here presented can only 
be interpreted as demonstrating the direct genetic relationship 
of the sympathetic to the cerebrospinal nervous system. 
THE HISTOGENESIS OF THE SYMPATHETIC TRUNKS AND THE 
PREVERTEBRAL PLEXUSES 
The sympathetic trunks 
According to the teaching of the older investigators who ad- 
vocated the theory of the ectodermal origin of the sympathetic 
nervous system, the ganglia of the sympathetic trunks arise 
exclusively from cells which become displaced peripherally from 
the spinal ganglia. Cells which arise in the neural tube had 
previously been traced along the ventral roots of the spinal 
nerves and into the sympathetic primordia, but the earliest 
evidence that cells of medullary origin play a major réle in the 
development of the sympathetic nervous system was presented 
by Froriep (07), who traced such cells along the paths of the 
ventral roots of the spinal nerves and the visceral rami into the 
primordia of the sympathetic trunks in embryos of Torpedo 
