THE REFLEX ARC 261 



changes. The segmented animal does not represent 

 the simple axial gradient of the lower forms, but is the 

 result of a repetitive process of reproduction (p. 131). 

 In early development a partial breaking up of the 

 primary individual occurs and reintegration takes place 

 only gradually as the segments successively become 

 less active and the head region regains some degree of 

 dominance. Under such conditions the relations of the 

 different axial regions and of the different segments 

 become much more complex than in the simple indi- 

 vidual, and the possibility of impulses from posterior 

 regions reaching the head is much greater. Segmenta- 

 tion of the body is then also a factor in the development 

 of the more complex and more flexible type of physio- 

 logical integration characteristic of the vertebrates. 



THE PROBLEM OF THE ORIGIN AND DEVELOPMENT OF THE 



CEREBRAL CORTEX 



It appears probable that the conditions determining 

 the increase in number and functional significance of 

 the upward paths in the central nervous system in the 

 higher animals are in some way and to some degree 

 concerned in the origin and development of the cerebral 

 cortex. The cortex is not simply a central or adjuster 

 organ for the receptors of the head region, as the cephalic 

 ganglia of the invertebrates appear in large measure to 

 be. It does not properly belong to the original reflex 

 arcs at all, but represents functionally an additional arc 

 superimposed upon the adjustor portion of the original 

 arc. It may be termed a super-adjustor, but it is not 

 simply that, for super-adjustors exist in the subcortical 

 correlation centers. The cortex is in fact the supreme 



