THE DEVELOPMENT OF REFLEX MECHANISMS IN 
AMBLYSTOMA 
C. JUDSON HERRICK AND GEORGE E. COGHILL 
From the Anatomical Laboratories of the University of Chicago and 
the University of Kansas 
TEN FIGURES 
The vertebrate nervous system consists very largely of reflex 
mechanisms of various grades of complexity with innumerable 
interrelationships, all of which are integrated by a system of 
higher correlation centers. In approaching the problem of the 
analysis of these mechanisms, we are accustomed to use the con- 
cept of a simple reflex arc (fig. 1) as our point of departure and 
to think of the more elaborate systems in terms of this type of 
unit. As a matter of pedagogic convenience, this method of 
procedure of course finds abundant justification; but if we con- 
sider the problem from the genetic standpoint, the question 
arises, whether this type of a simple two-neurone reflex arc 
represents the beginning or the end of the developmental sequence. 
It is generally conceded that the earliest form of nervous 
system to appear in animal evolution was probably a diffuse 
system, similar to that of the coelenterates and that the central 
nervous system of higher forms arose by a process of condensa- 
tion within this diffuse nervous reticulum in the interest of the 
correlation and integration of the nervous control of the separate 
organs. <A certain amount of such integration can be effected 
in a multicellular organism without the aid of any nervous 
system whatever, as illustrated by the sponges, by Volvox and 
by the higher plants; and nervous protoplasm appears to have 
been differentiated at first very gradually out of the protoplas- 
mic strands concerned with this type of correlation. 
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