136 G. E. COGHILL 



definitely correlated with the developmeDt of nervous function 

 simply because that feature arose simultaneously with the first 

 reactions to stimulation of the sensory field. In the attempt to 

 correlate cytomorphosis with function one should first be sure of 

 the physiological value of the particular nerve center with which 

 he is concerned. Certainty on this point can be established only 

 by intensive studies of systems of neurones in their relation to 

 each other and in relation to the development of particular bodily 

 activity; and the observations presented here, it is hoped, may 

 contribute something towards that end. 



3. The primitive nature of the primary motor colwnm 



The discovery that the primary ventral root fibers are col- 

 laterals of neurones of a longitudinal tract places the motor 

 system at once in the same class with the primary sensory sys- 

 tem of the aquatic vertebrates, namely, the giant ganglion cell 

 system of fishes and Amphibia. As is well known the primary 

 sensory fibers in these forms are dendritic branches of central 

 cells. This sensory system is generally conceded to be primitive 

 and, since the primary motor system is identical with it in the 

 general plan of organization, this motor system must also repre- 

 sent a primitive condition in the nervous system. While the 

 giant ganglion cell system is known to be transitory in the life 

 history of the individual it is impossible to say whether the 

 primitive condition of the motor system becomes obliterated or 

 simply obscured by the later development of the definitive ventral 

 roots. 



The theory of nerve components 



This analysis of the primary motor column and the demon- 

 stration of its primitive nature afford new and positive conforma- 

 tion of the central idea of the American theory of nerve compo- 

 nents, namely, that the primary and most fundamental divisions 

 of the vertebrate nervous system are longitudinal and differen- 

 tiated upon the basis of unity of function within each division. 

 These divisions are regarded as somatic sensory, visceral sensory. 



