2 ALBERT KUNTZ 
certain investigators to regard the sympathetic as the most 
primitive part of the vertebrate nervous system, having its 
prototype in the primitive nerve net of lower invertebrate ani- 
mals. In keeping with this theory, there have been isolated 
attempts to demonstrate the independent origin of the sympa- 
thetic nervous system by a process of local differentiation of meso- 
dermal elements. This lack of agreement regarding the most 
fundamental aspects of a problem which is essentially analytic 
emphasizes the desirability of a more exact method of investi- 
gation. ‘Therefore, following extensive studies based on normal 
embryonic material, the writer has employed the experimental 
method. 
Inasmuch as the literature bearing on the development of the 
sympathetic nervous system was reviewed by the writer in a 
recent paper (’20), no systematic review will be attempted at 
this time. The several papers which have appeared more re- 
cently, as well as many of the earlier ones, will be referred to in 
connection with the data presented in this paper. 
MATERIAL AND METHODS 
The material upon which this paper is based consists of a 
series of embryos of the chick and the frog which were early 
subjected to operative procedures and allowed to live for vary- 
ing periods following operation. ‘The operative technique em- 
ployed on the embryos of the chick, as indicated in an earlier 
paper (720), consisted in the destruction of tissue by means of 
electrolysis. The electrodes were applied through a circular 
opening in the egg-shell which was closed after operation by 
sealing a piece of mica over it. The egg was then returned to 
the incubator. This operative technique does not differ essen- 
tially from that which was described by Clark (20) and need 
not be described in greater detail at this time. The operative 
procedure to which the embryos of the frog were subjected con- 
sisted in the extirpation of portions of the cerebrospinal nervous 
system by means of careful dissection. This technique has 
been employed so frequently that a detailed description of it 
would be superfluous. 
