344 Proceedings of the Royal Society of Edinburgh. [Sess. 
from the spinal cord and intervertebral ganglia downwards through the 
mesentery to the gut. From these cells are formed the various divisions 
and synapses of the autonomic system. That these cells are not the sheath 
cells described by Harrison as growing from the posterior root in the 
tadpole is indicated by some of their number subsequently forming the 
cells from which the two plexuses in the intestinal wall develop. 
In comparing my results with those of other histologists, I find that in 
many points they coincide with those described by His junior (14). The 
application of more modern methods of staining has, in my hands, con- 
firmed the main facts recorded by him. As regards the fate of some 
portions of the sympathetic chain and mode of development of nerve fibres 
in the abdominal sympathetic, our results do not, however, agree. 
1. His described the formation of a secondary sympathetic chain in the 
lower cervical and thoracic regions, the primary structure being wholly 
utilised in forming visceral ganglia. With this observation I do not agree, 
as I fail to find the dwindling of the sympathetic chain described in these 
positions, neither do I find that the reaction of the nerve elements of the 
sympathetic chain to the silver-nitrate stain in the cervical and thoracic 
regions showed any variation from the steady improvement seen in the 
abdominal portion of the structure. It would seem unlikely that an 
absolutely fresh formation, such as a secondary sympathetic chain occurring 
so late as the sixth day, could be overlooked, more especially with the 
Ramon y Cajal method, to which nerve structures show so much sensitive- 
ness. The fact that His used a hsematoxylin-eosin stain, which is not, like 
the silver nitrate, a peculiar nerve stain, seems to make his conclusion still 
more doubtful. Further, the fact that His illustrated the various stages 
of development of the sympathetic chain by diagrammatic drawings 
influences, I think, adversely the value of the evidence brought forward 
by him on this point. 
2. As regards the character of the outgrowths from the sympathetic 
chain to the gut, His stated that a cellular chain of nerve cells was formed 
between the spinal cord and the gut, and that this was replaced about the 
sixth day by outgrowing nerve fibres from cells in the spinal cord. My 
results do not support the second part of this statement. 
I find the first connection between the spinal cord and gut to be com- 
posed of chains of nerve cells. These chains are often very well developed, 
and form conspicuous structures in the mesentery (PI. II. fig. 1) up to the 
fifth or sixth days of development. At the sixth, but more especially at 
the seventh, days definite nerve fibres appear and gradually replace the 
