10 ALBERT KUNTZ 
but that ‘these primordia are small or entirely absent in segments 
in which the remnant of the neural tube is small and represents 
only the most ventral portion of the central nervous system, 
even though ventral nerve-roots are present.’ 
Further experimental evidence indicates that the majority 
of the cells which enter the primordia of the ganglia of the sym- 
pathetic trunks are derived from those portions of the neural 
tube which give rise to the lateral cell-columns, and that some 
cells are also contributed by the spinal ganglia. A further con- 
tribution of cells from the motor niduli of the ventral nerve- 
roots is not precluded, but such contribution, if 1t occur, must 
be relatively unimportant. Figures 3, 4 and 2 constitute a pro- 
gressive series and illustrate well the results which follow the 
early destruction of the neural crests and increasingly larger 
portions of the neural tube in embryos of the chick. In the 
embryo (1) from which figure 3 was taken, the neural crest and 
less than the dorsal half of the neural tube were destroyed unilat- 
erally throughout a series of segments. In these segments, as 
illustrated in the figure, the dorsal nerve-roots are absent on the 
side involved, the ventral nerve-roots are relatively large, and 
the primordia of the ganglia of the sympathetic trunks are of 
approximately the same size as chose on the opposite side. In 
the embryo (3) from which figure 4 was taken, the neural crests 
and in excess of the dorsal half of the neural tube were destroyed 
throughout a series of not: less than six successive segments in 
the lower thoracic and upper lumbar regions. In these segments, 
as illustrated in the figure, ventral nerve-roots of nearly normal 
size and small primordia of the ganglia of the sympathetic trunks 
are present. In the embryo (14) from which figure 2 was taken, 
the cerebrospinal nervous system was completely or almost com- 
pletely destroyed throughout the greater part of the trunk re- 
gion. At the level of the section illustrated in the figure, a rem- 
nant of the ventral portion of the neural tube persists from which 
a slender ventral nerve-root (fig. 2, vr) has grown out. This 
nerve-root contains no visceral efferent fibers. It contains 
cells of medullary origin, but none deviate toward the aorta and 
there is complete absence of the primordium of the correspond- 
