14 ALBERT KUNTZ 
paths of the visceral rami turn ventrally and enter the primordia 
of the prevertebral plexuses without having become incorporated 
in the cell aggregates which give rise to the ganglia of the sym- 
pathetic trunks. Consequently, the sources of the cellular ele- 
ments in the prevertebral plexuses are identical with those of 
the cellular elements in the sympathetic trunks. These find- 
ings are corroborated by the findings in the experimental em- 
bryos in the present series. The evidence that cells advance 
farther peripherally from the primordia of the sympathetic 
trunks and become incorporated in the primordia of the pre- 
vertebral plexuses is conclusive. Furthermore, the number of 
cells in the latter, as observed in sections of experimental em- 
bryos of the chick (figs. 5 and 6, pp), bears a definite relation- 
ship to the number of cells in the former; i.e., if by reason of the 
destruction of a relatively large portion of the neural tube the 
primordia of the sympathetic trunks receive but a small number 
of cells, the number of cells which become incorporated in the 
primordia of the prevertebral plexuses is correspondingly small. 
Yet in no instance was complete absence of the primordia of the 
prevertebral plexuses observed in the presence of even very 
small primordia of the sympathetic trunks in the corresponding 
segments. On the other hand, the primordia of the preverte- 
bral plexuses do not arise in the absence of the primordia of the 
sympathetic trunks. 
THE NEURILEMMA OF THE EFFERENT FIBERS OF THE SPINAL 
NERVES is 
As observed above, cells of medullary origin advance periph- : 
erally along the fibers of the ventral roots of the spinal nerves 
in embryos of the chick in segments in which but a remnant of 
the neural tube persists and the primordia of the sympathetic 
trunks fail to arise. Such cells also advance along the somatic 
efferent fibers: of the spinal nerves distal to the point at which 
the visceral ramus deviates from the ventral ramus in segments 
in which the primordia of the sympathetic trunks are present, 
although the spinal ganglia and dorsal nerve-roots are absent. 
Such cells may be recognized in portions of the spinal nerves dis- 
