SOMATIC MOTOR COLUMN OF AMBLYSTOMA 137 



visceral motor and somatic motor. The latter division, in its 

 primary and primitive condition is now found to be, not a 'pile' 

 of discrete metameric divisions more or less indefinitely asso- 

 ciated by means of longitudinal connectives, but a 'column' in 

 the strict sense of a continuous, functional unit. The metameric 

 arrangement of the motor roots, as suggested above, is probably 

 determined by regulation and accordingly is not paralleled by a 

 metameric arrangement of neurones within the column. The 

 neuromeric organization of the spinal cord, therefore, in so far 

 as it exists, is a secondary acquisition. 



