SYMPATHETIC SYSTEM IN MAMMALS 



229 



already present in the sensory and the motor nerve-roots. This 

 view seems to be quite generally accepted by the advocates of 

 the theory of local differentiation and the multicellular nature 

 of nerve-fibers. These two conceptions obviously go hand in 

 hand. It is not the writer's purpose to discuss the nature of 

 nerve-fibers. Suffice it to say that in the light of the recent inves- 

 tigations of Cajal, Harrison, and others, the neurone theory 



Fig 8. Curve designed to indicate the relative rate of migration of cells from 

 the neural tube and the spinal ganglia along the spinal nerves, in successive stages 

 of development. For explanation see text. 



seems to be firmly established. On the other hand, if the " accom- 

 panying" cells do not migrate peripherally we cannot account 

 for the rapid decrease in the number of such cells present in the 

 proximal part of the spinal nerves, which, as shown in fig. 8, 

 takes place in embryos from 9 to 13 mm. in length. Mitotic 

 figures occur occasionally in the nerve-roots as well as in the 

 nerve-trunks and in the communicating rami. Doubtless, many 



THE JOURNAL OF COMPARATIVE NEUROLOGY AND PSYCHOLOGY, VOL. 20, NO. 3. 



