He ALBERT KUNTZ 
as large as that which constitutes the primordium of the sym- 
pathetic trunk on the opposite side, although on that side both 
dorsal and ventral nerve-roots show normal development. Un- 
mistakable evidence of active migration of cells directly from 
the intermediate portion of the wall of the neural tube on the 
operated side may be observed in several successive sections 
through this segment. In the absence both of the spinal ganglion 
and the ventral portion of the wall of the neural tube on this 
side, practically all the cells which have entered the primordium 
of the sympathetic trunk must have advanced peripherally from 
the portion of the wall of the neural tube which normally gives 
rise to the lateral cell-column. 
Figure 6 illustrates the conditions observed in a section a few 
segments farther caudad in the same embryo. At this level the 
major portion of the neural-crest material escaped destruction. 
The spinal ganglion is represented by an aggregate of cells from 
which fibers of the dorsal nerve-root emerge. The ventral por- 
tion of the wall of the neural tube was less completely destroyed 
in this than in the segment described above, but the intermediate 
portion suffered more extensive destruction and contains rela- 
tively few cells. A very small ventral nerve-root, doubtless, 
composed both of somatic and visceral efferent fibers accompanied 
by few cells, joins the dorsal nerve-root as the latter emerges from 
the spinal ganglion. Small groups of cells, the majority of 
which apparently have advanced from the spinal ganglion, are 
present along the course of the spinal nerve. The primordium 
of the sympathetic trunk in this segment contains relatively 
few cells (fig. 6, sy) and is markedly less conspicuous than its 
fellow on the opposite side. ‘The phenomena observed in suc- 
cessive sections in this segment justify the conclusion that cells 
advance from the spinal ganglia into the primordia of the sym- 
pathetic trunks. However, the number of cells in the sym- 
pathetic primordium on the operated side in this segment is 
small as compared with the number of cells in the primordium 
of the sympathetic trunk on the opposite side and on the same 
side in the segment considered: above. In the latter segment 
practically all the cells in the sympathetic primordium must 
