74 THE BRAIN OF THE TIGER SALAMANDER 



reflexology. But reflexes can be conditioned, and this name for a 

 well-known physiological fact is for the neurologist scarcely more 

 than a symbol of complete ignorance of the mechanisms actually 

 employed. 



The several reflexes have been so closely colligated with specific 

 details of central architecture that the reflex arc came to be regarded 

 as the primary unit of nervous organization, and it was assumed that 

 the increasing complexity of the upper levels of the brain in higher 

 vertebrates has been brought about by progressively more intricate 

 interconnections among these elementary units. The integrative ac- 

 tion of the nervous system was conceived in terms of the definition of 

 mathematical integration — "the making up or composition of a 

 whole by adding together or combining the separate parts or ele- 

 ments." This conception leaves unexplained how any additive proc- 

 ess of this sort can result in such a unique centrally controlled unitary 

 organization as we actually observe, capable of conditioning the 

 reflexes in terms of individual experience (learning), of abstracting 

 some common features of mixed experience and synthesizing these 

 into quite original patterns of response, and of maintaining some 

 measure of "spontaneous" or self-determined directive control. 



A far more serious charge against traditional doctrines of re- 

 flexology is the observed fact that in the development of Ambly stoma 

 the early responses to external stimulation are not local reflexes but 

 total movements of the entire available musculature. The integrated 

 total pattern precedes in time the appearance of the partial patterns. 

 These are individuated within the total pattern; they are integral 

 parts of it, and for an appreciable time they are subordinate to it. 

 Even in the adult animal the local partial patterns are not completely 

 emancipated from control by the body as a whole. It is, indeed, im- 

 possible to find in this brain any sharply defined, well-insulated reflex 

 arcs. 



What happens during the emergence of specific reflexes from the 

 total reactions is, first, the development of an increasing number of 

 collateral branches of the primary axons and the central linkage of 

 sensory and motor pathways in ever more complicated patterns. 

 Then, second, in the adjusting centers additional neurons are dif- 

 ferentiated, the axons of which take longer or shorter courses, branch- 

 ing freely and participating in the formation of a nervous feltwork of 

 extraordinary complexity. These neurons are not concerned pri- 

 marily with specific reflexes but with the co-ordination and Integra- 



