22 ALBERT KUNTZ 
mordia of the sympathetic trunks are present. These findings, 
though not conclusive by reason of the early stage of develop- 
ment represented by the embryos, are in full accord with the 
findings in embryos of the chick set forth above. 
DISCUSSION 
The experimental data set forth in the preceding pages prove 
conclusively that the sympathetic primordia are made up both 
of cells which arise in the neural tube and the cerebrospinal 
ganglia. Furthermore, they prove conclusively that the contri- 
bution of cells from the neural tube to the primordia of the 
sympathetic trunks and the prevertebral plexuses is much greater 
than that from the spinal ganglia. They strongly suggest also 
that the major portion of the cells coming from the neural tube 
arises in the intermediate portions of its walls, i.e., the portions 
which give rise to the lateral cell-columns. Likewise, they demon- 
strate the genetic relationship to the vagi of the oesophageal, 
the pulmonary, the cardiac, and the enteric plexuses, except 
in the aboral portions of the digestive tube, and indicate that 
the major portion of the cells which enter the primordia of 
these plexuses arises in the portions of the walls of the hindbrain 
which give rise to the visceral efferent components of the vagi. 
An experimental determination of the exact sources of the 
cells which give rise to the cranial sympathetic ganglia was not 
attempted. The writer (’20) has previously presented evidence 
which indicates that these ganglia arise both from cells which 
advance from the medullary tube and certain of the sensory 
cerebral ganglia. Doubtless, the differentiation of nervous 
tissue is governed by the same fundamental principles through- 
out the entire body. Therefore, the experimental data regard- 
ing the histogenesis of the other portions of the sympathetic 
nervous system presented in this paper lend support to the 
view that the cranial sympathetic ganglia also comprise both 
cells of medullary and ganglipnic origin. 
The sympathetic system is essentially an efferent system. 
Doubtless, all the neurons in the ganglia of the sympathetic trunks 
and the prevertebral plexuses are efferent in character. The 
