HISTOGENESIS OF SYMPATHETIC SYSTEM mA 
bryo in which the portion of the hindbrain giving rise to the 
efferent components of the vagi was destroyed; consequently, 
small vagus ganglia and some afferent fibers are present. How- 
ever, but few cells advanced from these ganglia along the grow- 
ing afferent fibers. This observation is of interest in view of 
the experimental evidence presented above which indicates that 
the majority of the cells which become incorporated in the 
primordia of the sympathetic trunks have their origin in the 
neural tube and advance peripherally along the efferent fibers 
of the spinal nerves. It strongly suggests that, likewise, the 
majority of the cells which become incorporated in the 
primordia of the vagal sympathetic plexuses arise in the hind- 
brain and advance peripherally along the efferent fibers of 
the vagi. 
The operative procedure involved in the extirpation of the 
neural crests and the neural tube in the trunk region or the por- 
tions of the hindbrain which give rise to the vagi in embryos of 
the frog is relatively simple. A goodly number survived the 
operation and continued to develop at a somewhat retarded 
rate for several days. None survived longer than five days 
following operation. If development had not been retarded in 
these embryos, they would have been sufficiently advanced 
three or four days following operation to have afforded material 
from which conclusive evidence regarding the histogenetic re- 
lationships of the vagal sympathetic plexuses could have been 
obtained. Some of these embryos which were killed three to 
four days following operation afford some data which are worthy 
of consideration. Those in which the cerebrospinal nervous 
system was extirpated posterior to the head show complete 
absence of the primordia of the sympathetic trunks, but cells 
of nervous origin may be traced along the fibers of the vagi into 
proximity with the heart and along the walls of the oesophagus 
as far as the growing fibers have advanced. Those in which the 
vagi were eliminated by extirpation of the corresponding part 
of the hindbrain show complete absence of nervous elements 
associated with the heart and the walls of the digestive tube as 
far as the latter have become differentiated, although the pri- 
