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, 1912) 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 



