1909-10.] Nervous Mechanism of Alimentary Canal of the Bird. 343 
and the sympathetic chain to the plexiform nerve network in the gut wall. 
A difference in the degree of staining of the various nerve elements was 
also clearly evident. All were clearly stained, hut the plexuses in the wall 
of the gut were distinctly lighter than the nerve cells in front of the aorta 
or in the mesentery. 
The conclusions arrived at from the foregoing results, together with the 
special evidence derived from the peculiar property of the silver-nitrate 
stain of affecting tissue in accordance with their degree of development, 
will be dealt with in the next section. 
Tabulation of Results. 
1. At the end of the second day the posterior spinal ganglia were 
recognised, and from them a few nerve cells were seen to have broken 
away, and to lie somewhat ventral to the ganglia. 
2. At the middle and end of the third day nerve cells similar in type 
to those described at the end of the second day were found lying in the 
tissue near the notochord and behind the aorta. 
3. At four and a half days the sympathetic chain was readily recognised 
lying behind the aorta. Chains of cells were traced from it round the 
aorta down the mesentery to the gut wall, in which a plexiform arrange- 
ment was seen. The vagus nerve was found in the stomach wall at this 
stage of development. 
4. At the fifth day the sympathetic chain and the connections between 
it and the plexiform arrangement in the gut wall were found better 
developed. The vagus branches in the stomach were well marked. 
5. At the sixth day improvement was noted in the development of 
the structures mentioned at the fifth day, and in addition the nervi 
erigentes were recognised. 
6. At the seventh day the sympathetic chain and its connections with 
the anterior and posterior spinal nerves, and with the visceral ganglia in 
the intestine, were easily traced. The vagus and nervi erigentes were 
found to he even better developed than at the sixth day. 
Conclusions. 
1. The descriptions of the various stages of development of the 
embryonic chick from the second to the seventh days show that the 
whole sympathetic system is secondary in formation to, and directly 
derived from, the central nervous system. 
2. The abdominal sympathetic is produced by the migration of cells 
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