PHYSIOLOGICAL INTERPRETATIONS 81 



as this concept has been developed by Sherrington. If the activated 

 motor pool is large, with wide distribution of the efferent fibers, com- 

 plicated integrated mass movement may result. If the pool is small, 

 with a single final common path, a local reflex may follow. If the out- 

 let comprises a number of open channels with different connections 

 and physiological properties, there is provision for discriminative 

 response, the selection being made (presumably) in terms of the 

 central excitatory state of the components of the system ('42, p. 295). 



It has been objected that the preceding comments on the limita- 

 tions of current doctrines of reflexology are based upon the amphibi- 

 an organization, which is aberrant and degenerate and therefore not 

 typical or significant in the interpretation of the behavior of higher 

 animals. But, even so, the Amphibia live well-ordered lives, and their 

 behavior conforms in basic patterns with that of other vertebrates. 

 We want to know how they behave as they do. Accepting the cur- 

 rent view that Amblystoma is a retrograde descendant of some more 

 highly specialized ancestor now extinct and that some of its char- 

 acters are aberrant, yet the evidence seems to me adequate that such 

 retrogression as may have occurred has been toward a generalized 

 form ancestral to modern amphibians and mammals. 



Conclusion. — I have assembled in these pages some factual de- 

 scription of observed structure, together with speculative interpre- 

 tations of its probable physiological significance. The organic struc- 

 ture here under consideration is not something vague and ill-defined. 

 Its anatomical distribution, histological organization, and fibrous 

 connections can be described with precision. Not until this has been 

 done can our imperfect knowledge of its functions be advanced by 

 experiments designed to reveal its physiological properties. 



In a discussion of "localized functions and integrating functions" 

 more than a decade ago ('34a), the significance of neuropil in the 

 evolution of cerebral structure was summarized in these words : 



"The neuropil is the mother tissue from which liave been derived both the spe- 

 cialized centers and tracts which execute the refined movements of the local re- 

 flexes and the more general web which binds these local activities together and 

 integrates the behavior. It retains something of embryonic plasticity and so is avail- 

 able as a source of raw material for two very dift'erent lines of specialization — first, 

 toward the structural heterogeneity requisite for the execution of localized reflex 

 and associational functions, and, second, toward the more generalized and dis- 

 persed apparatus of total or organismic functions of tonicity, summation, reinforce- 

 ment, facilitation, inhibition, 'spontaneity,' constitutional disposition and tempera- 

 ment, and extra-reflex activities in general." 



