86 THE BRAIN OF THE TIGER SALAMANDER 



well separated, and in the aggregate they comprise a rather dispersed 

 collection of ascending fibers loosely assembled in several tracts, 

 which are distinguished more by their general fields of origin and 

 termination than by the functions which they serve. It is to be borne 

 in mind that this low level of functional specificity of the secondary 

 tracts is not correlated with a corresponding generalized structure 

 and function of sense organs and related peripheral nerves. These 

 organs, though different from those of higher animals, are highly 

 specialized and as sharply localized. The correlation, on the contrary, 

 is with the generalized character of the motor responses evoked. In 

 higher animals with a wider range of motor capacities the functional 

 specificity of the lemniscus tracts becomes more precise. 



During the process of differentiation of these more specific tracts 

 they retain collateral connections along the entire course, so that 

 they continue to perform integrative functions similar to those of the 

 less specialized ancestral pattern. In this connection we quote a pas- 

 sage from Dr. Papez ('36) : 



"In tracing the central connections of any one of the main afferent systems in the 

 vertebrates one gains the impression that there is a progressive pliyletic tendency of 

 each system to enter into connections with all the important segments of the central 

 organ. In this way there arises a totally integrated anatomical pattern common to 

 all the receptorial systems in spite of the wide diversity of the receptors, their indi- 

 vidual pathways and their interpolated centers. This central integration is not 

 essentially of a reflex nature and cannot be appropriately described as a chain of 

 reflex connections insomuch as each level has a highly individual structural organiza- 

 tion designed primarily for the production of distinctive organic functions." 



Papez appropriately emphasizes the integrating action of these 

 long conductors; it seems to me, however, that his conception of "a 

 progressive phyletic tendency of each system to enter into connections 

 with all the important segments" in the interest of integration is a 

 reversal of the actual course of phyletic history. These collateral con- 

 nections are more numerous and more dispersed in lower forms than 

 in higher. The integration is primary, and the analysis is secondary. 

 It is true that the primary integration is not subordinated in the 

 course of phylogeny; it is accentuated; but the apparatus employed 

 is radically changed. Dispersed nonspecific connections are progres- 

 sively replaced by localized specific structures, which are so inter- 

 related as to work together harmoniously in the performance of 

 standardized patterns of behavior. And, in addition to this, higher 

 centers are elaborated, notably in the cortex, which progressively ac- 

 quire dominant control of the total action system. 



The phylogenetic history of the differentiation of the visual-motor 



