328 Proceedings of the Royal Society of Edinburgh. [Sess. 
of an independent origin, more especially as he regards the results of 
histological research on this point as equivocal. 
The theory of Gaskell as to the homology existing between the central 
nervous system of vertebrates and the nervous system of invertebrates 
would lead to the expectation that the development of the sympathetic 
system in vertebrates must follow that of the central nervous system. 
The dubiety which still existed as to the precise mode of development of 
the nerve elements forming the autonomic nervous system of the intestine, 
and the possibility of their independent origin suggested by physiological ex- 
periment, seemed to show the desirability of again investigating the question 
from a histological standpoint, with the aid of a more modern method. 
One of the most complete histological investigations on the question 
was made by His junior (14), who used the hsematoxylin-eosin method. 
Since this is not a stain peculiarly adapted for nerve work, the desirability 
of repeating the investigation is apparent. 
The present paper is therefore an account of such an investigation 
made on the embryonic chick with the aid of the most modern of nerve 
stains — the silver-nitrate method of Ramon y Cajal. The results are illus- 
trated partly by sepia drawings for the sake of clearness, but a sufficient 
number of photographs are given to fully illustrate the various points dealt 
with. These photographs are selected from a large series used in illus- 
trating a thesis on this subject which was presented for the degree of M.D. 
at the University of Aberdeen. 
Historical. 
Histological Section. 
Remak (1) published in 1843 the results of observations made by him 
on the development of the embryonic chick. He described the whole 
nervous system as being mesoblastic in origin. The nerve network in the 
intestinal wall he regarded as developed primarily in situ from the meso- 
blastic tissue, and joined secondarily to the main sympathetic chain. 
Four years later, in a second paper (2) on this subject, Remak stated 
that the nerve network in the intestinal wall appeared at the sixth day, 
and became joined to the main sympathetic chain during the second week. 
In 1864 Hensen (3) advanced the theory that the cerebro-spinal system 
was ectodermic in origin, and suggested that all nerve structures originated 
from the ectodermic layer. 
His senior (4) in 1868 described the cerebro-spinal system as originating 
from the ectodermic layer. Further, he described the sympathetic chain as 
