THE REFLEX ARC 259 
Whether the paths from postcephalic regions upward 
are, in the higher vertebrates, parts of the main paths 
of the reflex arcs, as Pike (1909, 191 2) maintains, or are 
lateral or accessory paths not essential to the functioning 
of the arcs, as has been generally believed, is of secondary 
importance in this connection. The upward paths exist, 
and their existence suggests that the general antero- 
posterior physiological gradient in the central nervous 
system has become in some way less effective in deter- 
mining functional direction in the higher than in the 
lower animals, and that the primitive relation of domi- 
nance and subordination with the more or less complete 
autocracy of the apical region or head in flatworms or 
annelids is undergoing alteration toward a relation of 
true co-ordination in which many different arcs with 
receptors in various regions of the body are concerned 
in determining the final effect or action. The physio- 
logical dominance of the nervous system and of more 
anterior over more posterior levels is in fact departing 
from the primitive, autocratic relation and becoming 
more and more like that of a representative government. 
Such change does not mean a decrease in the degree of 
physiological integration but rather an increase in the 
complexity, flexibility, and potentialities of integration. 
It does not represent a functional degradation of the 
higher levels but a functional elevation of the lower 
levels of the gradients, and this constitutes a basis for 
relations and combinations of arcs and paths which are 
impossible in the lower forms. 
Such a decrease in functional or apparent steepness 
of the physiological gradient must be associated with 
the development and evolution of the mechanism of 
