340 Proceedings of the Royal Society of Edinburgh. [Sess. 
small clusters, with delicate, faintly-stained outgrowths. In the inner 
layer the nerve cells were not arranged in clusters, but formed a delicate 
network with their interlacing fibres. At several points a delicate chain 
of nerve cells could be traced from the outer to the inner layer. The 
vagus fibres were widely scattered and very numerous in the stomach wall. 
A small cluster of cells, similar in type to those forming the two nerve 
layers in the stomach wall, was found lying against the outer margin of 
the stomach wall, just where the vagus entered. A few were recognised 
further up the trunk of the vagus, and apparently represent a route 
followed by some sympathetic cells along the course of the vagus branches 
to the stomach (PL III. fig. 3). In the lower intestine a cylindrical band 
of nerve cells and fibres was recognised lying on the dorsal side of the gut. 
This corresponds to a similar band described as the intestinal nerve of 
Remak by His junior in his paper on the development of the abdominal 
sympathetic. At this stage no direct communication could be demonstrated 
between this band of nerve tissue and the nerve elements in the pelvic 
region. A very few nerve cells were found in the wall of this portion of 
the intestine, but no true plexus was recognised. This stage of develop- 
ment confirmed the observations made at the previous stage. It also 
showed the effect of the silver-nitrate stain on the various portions of the 
sympathetic system. The best stained part was the sympathetic chain, 
which was the oldest of the sympathetic nerve structures, while from it 
to the plexuses in the intestinal wall the nerve elements showed a 
decreasing degree of pigmentation. This fact and its significance will be 
dealt with fully in the next section. 
At the sixth day of incubation the sympathetic chain was still more 
sharply defined, and delicate fibro-cellular connections were seen between 
it and the spinal nerves (line drawing). At the upper abdominal region 
and downwards a well-marked plexiform arrangement of sympathetic 
nerve cells and fibres was seen in front of the aorta (PI. III. fig. 4). 
In the pelvic portion the plexiform arrangement of nerve cells described 
at the fifth day was better marked, while outgrowths from the lower 
portion of the spinal cord in the position of nervi erigentes were traced 
to the lower gut. The mesenteric bands of nerve cells and fibres were 
better developed (PI. II. fig. 1), and at several points a complete scheme of 
sympathetic nerve cells and fibres was seen extending from the pre-aortic 
plexus to the gut wall. In the stomach and small intestine the double 
layers of nerve cells and fibres were better marked. The number of cells 
in both the inner and outer layers had increased, and with their out- 
growths formed a more complicated network (PI. IV. fig. 1). The 
