SYMPATHETIC SYSTEM IN MAMMALS 249 



shown that migrant medullary cells actually develop into cells 

 of the neurilemma in the abducent and the oculomotor nerves in 

 the chick. 



Proof of the medullary and the ganglionic origin of the cells 

 giving rise to the neurilemma was difficult only until it could be 

 demonstrated that cells actually migrate peripherally from the 

 neural tube and the cerebro-spinal ganglia along both the spinal 

 and the cranial nerves. The present series of observations pre- 

 sents conclusive evidence on this point. We may here repeat 

 what has already been stated with regard to the cells taking part 

 in the development of the sympathetic system. We are not to 

 suppose that all the cells taking part in the development of the 

 neurilemma actually migrate as such from the neural tube and 

 the cerebro-spinal ganglia. Doubtless, many arise by the mitotic 

 division of "indifferent" cells along the course of migration. Ac- 

 cording to this interpretation, the cells of the neurilemma are 

 homologous with the neuroglia cells in the central nervous sys- 

 tem. 



(c) Sympathetic excitatory and sympathetic sensory neurones. — 

 The problem of the histogenetic relationships of the sympathetic 

 excitatory and the sympathetic sensory neurones presents peculiar 

 difficulties. The presence of sympathetic sensory neurones in the 

 sympathetic trunks and prevertebral plexuses has not been demon- 

 strated. Froriep, like Langley, Kolliker, and P. Schultz, denies the 

 existence of sympathetic sensory neurones entirely. There can 

 be little doubt, however, that sympathetic sensory neurones are 

 present in the sympathetic plexuses in the walls of the digestive 

 tube. According to Bayliss and Starling ('99), the peristaltic 

 contractions of the small intestine are true coordinated reflexes 

 carried out by the local nervous mechanism (myenteric plexus). 

 The later experimental work of Cannon ('06) and of Auer ('10) 

 lends support to this view by showing that the peristaltic contrac- 

 tions of the stomach and the intestine may be carried on more or 

 less regularly for a considerable length of time after both the vagi 

 and the splanchnic nerves have been severed. These phenomena 

 seem to indicate the existence of true sensory neurones in the 

 sympathetic plexuses in the walls of the digestive tube. 



