PSYCHIC ADAPTATION 97 



species of neurona arises an order probably parallel 

 to that which phylogenic evolution shows us : at 

 first the motor and sensitive apparatus (cells of the 

 early asta and bipolar spinal cells with their direct 

 passages) ; later is differentiated the apparatus of 

 association (elements of the cords or funicular cells 

 of the medulla and brain) ; and of all systems of 

 association, the cerebral, which is the most modern 

 phylogenically considered, is also the last to appear. 

 Such must have been also the order of function of 

 the central nerve -apparatus in the phylogenic series ; 

 the first invertebrates endowed with a distinct 

 nervous system only had to possess sensitive and 

 motor passages connected with one another by 

 direct cylindric axes ; further, the collateral expan- 

 sions would shoot out, and the associating passages 

 would be opened (similar funicular cells of the 

 medulla by which a single sensitive impression 

 could excite the co-ordinated actions of the motor 

 nerve-corpuscules). " 



From these comparative studies Cajal draws the 

 following most important conclusion : 



"There exists, then, one nervous system, the 

 sensory and sensitive (peripheric ganglia), which 

 has terminated its development by differentiation, 

 increasing only by extension ; and another nervous 

 system, the cerebral, which continues its progress 

 in the animal series, as well by extension or 



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