106 THE BRAIN OF THE TIGER SALAMi\NDER 



even in the lowest members of the class, are in larger measure indi- 

 vidually learned. And enhancement of learning ability goes hand in 

 hand with cortical differentiation. 



It is impossible to define a primordial boundary between pallial 

 and subpallial territory ('27, p. 316; '33a). There is apparently no 

 primitive (palingenetic) distinction between the pars pallialis and the 

 pars subpallialis of the cerebral hemisphere; cortical types of struc- 

 ture and function may be differentiated out of such raw materials as 

 are available, and the locations of these indefinite boundaries will 

 vary from species to species. Even in the human brain the boundary 

 is in some places obscure and controversial. 



This, in outline, seems to be the history of the origin and evolution 

 of the cerebral cortex. The details have not yet been filled in, and this 

 can be done only by experimental methods, checked and controlled 

 at every step by accurate histological analysis of the tissue operated 

 upon. When the facts about the sequences of the evolution of cortical 

 structure and function are colligated with experimental studies of 

 behavioral capacities of the animals in question, we shall have a 

 secure foundation upon which to build a sound comparative psychol- 

 ogy, and this, in turn, will clarify much that is now obscure in human 

 experience. 



PHYSIOLOGY AND PSYCHOLOGY 



Returning, now, to a general survey of the factors involved in the 

 differentiation and normal operation of the central nervous system, 

 we find that these fall into two categories. Some of them conform 

 perfectly with well-known laws of traditional mechanics of the in- 

 organic realm, as formulated in the Newtonian system and its mod- 

 ern derivatives. Others have not been successfully fitted into this 

 frame of reference. From the beginning of inquiry into this problem, 

 there has been a tendency to set these refractory components apart 

 from the natural order in some mystic realm of vitalism. To the nat- 

 uralist this solution is not acceptable, for the two classes of phe- 

 nomena are empirically indissociable. 



That the operations of nature are not bound by the man-made 

 rules of Newtonian mechanics is now evident. It has been shown that 

 the formulas of Newtonian mechanics, Euclidean geometry, and 

 Aristotelian logic are not universals. They are valid in a restricted 

 field but not in the realm opened up by current conceptions of rela- 

 tivity and quantum mechanics. In view of this situation, the field of 

 neurological inquiry is immeasurably enlarged and complicated. 



