452 C. JUDSON HERRICK 



exhibit this type of brain. The more diversified conditions of 

 Ufe on land appear to require far more complex centers of higher 

 correlation than those possessed by any fish, and it seems prob- 

 able that of all known forms of morphological pattern of the 

 forebrain only that which possesses widely evaginated thin- 

 walled cerebral hemispheres capable of indefinite expansion 

 without undue thickening of the wall is adequate to form the 

 foundation on which the complexity of higher brains could be 

 elaborated. 



Mention has been made of the high efficiency on the reflex 

 plane of solid cerebral masses of teleostean type. In higher 

 vertebrates with fully evaginated cerebral hemispheres local 

 thickenings of a different sort appear in the lateral walls of the 

 hemispheres themselves in reptiles and especially in birds. Here 

 again this structural form is correlated with the predominance 

 of stable, heritable, reflex and instinctive behavior patterns. 

 In mammals, on the other hand, where individually modifiable 

 behavior of the intelfigent type is the most characteristic feature, 

 so extensive solid thickenings of the walls of the hemispheres 

 do not appear, but instead the highest correlation tissue of the 

 brain is spread out in thin sheets as cerebral cortex (Kappers, 

 '13, '14). 



From a general survey of what is known regarding the corre- 

 lation of forebrain patterns with behavior patterns, it appears 

 that solid masses of cerebral tissue may be structurally well 

 adapted for the performance of the most complex types of 

 reflex and instinctive activity whose patterns are inherited and 

 relatively stable, as illustrated in teleosts and birds. High 

 speciafization in this direction, however, seems to have precluded 

 the possibility of any great development of the more labile 

 individually modifiable sorts of behavior and especially of the 

 culmination of this kind of behavior as manifested by capacity 

 for rapid learning by individual experience and intelligence in 

 general. 



Conversely, the development of the labile functional type 

 goes hand in hand with the extensive elaboration of thin sheets 

 of correlation tissue, as exempUfied in the cerebral cortex, in 



