254 ALBERT KUNTZ 



the neurilemma are homologous with the neuroglia cells in the 

 central nervous system. 



6. The cells taking part in the development of the sympa- 

 thetic nervous system and the neurilemma do not all actually 

 migrate as such from their sources in the cerebro-spinal system. 

 Doubtless, many arise by the mitotic division of "indifferent" 

 cells along the course of migration. 



7. The existence of sympathetic sensory neurones in the sym- 

 pathetic trunks and the prevertebral plexuses has not been demon- 

 strated. Experimental evidence, however, indicates the presence 

 of sympathetic sensory neurones in the sympathetic plexuses in 

 the walls of the digestive tube. While it is impossible, by direct 

 observation, to trace either sympathetic excitatory or sympa- 

 thetic sensory elements back to their specific source in the cere- 

 bro-spinal nervous system, indirect embryological and anatomical 

 evidence warrants the conclusion that the sympathetic excita- 

 tory neurones arise from cells which migrate from the neural tube 

 along the fibers of the motor nerve-roots, while the sympathetic 

 sensory neurones, wherever such neurones exist, arise from cells 

 which migrate from the cerebro-spinal ganglia. This interpreta- 

 tion makes the sympathetic neurones homologous with the affer- 

 ent and the efferent components of the other functional divisions 

 of the peripheral nervous system. 



8. Inasmuch as the cells migrating peripherally from the cere- 

 bro-spinal nervous system are the "indifferent" cells and the 

 "neuroblasts'" of Schaper, Schaper's conception of the develop- 

 mental relations of the neurones and the supporting elements in 

 the central nervous system, may be extended to the sympathetic 

 neurones and the cells of the neurilemma. 



9. The nervous system is a unit of which the sympathetic 

 system is a part homologous with the other functional divisions. 

 The sympathetic system may be looked upon as an accession to 

 the nervous system, which has arisen comparatively late in the 

 evolution of vertebrates in response to the conditions of the vegeta- 

 tive life. 



