240 



Causes and Course of Organic Evolution 



been diagrammatically but graphically figured by Edinger for 

 some groups of vertebrates, and which are here reproduced 

 (Fig. 9). In these diagrams the evolving neencephalon can 



a 



d 



^ Fig. 9 — Comparative diagrammatic stages in development of the front 

 brain or neencephalon, in (a) Selachian, (6) Amphibian, (c) Reptile, (<:/) Mam- 

 mal, in each case shown in black. (After Edinger.) 



truly be regarded as a receptor for discrete simple or result- 

 ant stimuli, as a condensor and correlator of these into complex 

 or summated perceptions, as a storage center for these per- 

 ceptions, and particularly as a great proenvironal activator, 

 from which extremely varied and often complexly summated 

 efferent stimuli proceed. 



It is not necessary therefore at present that an attempt 

 should be made further to trace examples of proenvironal 

 reaction as a great evolutionary factor that has worked through- 



