HISTOGENESIS OF SYMPATHETIC SYSTEM 5) 
have given the work of the advocates of the theory of the meso- 
dermal origin of the sympathetic nervous system serious consid- 
eration because the genetic relationship of the latter to the cere- 
brospinal nervous system was regarded by them as an established 
fact. However, as late as 1912, Camus, a student of Goette, 
once more revived this theory. Furthermore, it has very re- 
cently been advanced in a somewhat modified form by Dart 
and Shellshear (21) as an integral part of their ‘‘new interpre- 
tation of the morphology of the nervous system.” 
The writer is one of those who have regarded the genetic re- 
lationship of the sympathetic to the cerebrospinal nervous sys- 
tem as an established fact. However, in view of the recent 
arguments to the contrary, and inasmuch as the material on 
which the present study is based affords conclusive evidence 
regarding the genetic relationship of the sympathetic nervous 
system, a brief discussion of this problem at the present time 
may be justified. 
Embryos of the chick and the frog in which the neural crests 
and the neural tube were destroyed throughout a series of seg- 
ments by operation before cells of nervous origin had advanced 
peripherally show complete absence of the primordia of the 
sympathetic trunks and the prevertebral sympathetic plexuses 
in these segments.. The same absence of the sympathetic pri- 
mordia may be observed also in segments in which a remnant of 
the ventral portion of the neural tube persists, even though small 
ventral nerve-roots including no visceral efferent fibers may be 
present. ‘These facts are illustrated microphotographically in 
figures 1 and 2, which are taken from sections of an 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 in- 
cubation. Figure 1 is taken from a section through a lumbar 
segment in which the cerebrospinal nervous system is entirely 
absent. The mesenchymal tissue around the aorta presents a 
relatively homogeneous appearance. There are no aggregates 
of cells or condensations of tissue along the dorsolateral aspects of 
1 Figures introduced in this manner indicate the number of the embryo in the 
experimental series. 
