SYMPATHETIC SYSTEM IN TURTLES 305 



the sympathetic trunks into the anlagen of these plexuses after 

 the latter have become connected wih the former by sympathetic 

 nerves. Such connections of the vagal sympathetic plexuses with 

 the sympathetic trunks must, however, be looked upon as of only 

 secondary importance in their development. 



The cells which migrate peripherally from the walls of the hind- 

 brain and from the vagus ganglia along the paths of the vagi in 

 embryos of the turtle, like the cells which migrate peripherally 

 from the cerebro-spinal nervous system in the trunk region, are 

 characterized by very little cytoplasm and by large rounded or 

 elongated nuclei showing a delicate chromatin structure. They 

 are, therefore, cells of the same character; viz., the 'indifferent' 

 cells of Schaper. Inasmuch as thses cells give rise to the vagal 

 sympathetic plexuses, these plexuses also bear a direct genetic 

 relationship to the cerebro-spinal nervous system. Mitotic 

 figures occur frequently along the paths of the vagi and in the 

 anlagen of the vagal sympathetic plexuses. We are not to suppose, 

 therefore, that all the cells which take part in the development 

 of the vagal sympathetic plexuses actually migrate as such from 

 their sources in the hind-brain and in the vagus ganglia. As in 

 the case of the sympathetic trunks, doubtless, many of these 

 cells arise by the mitotic division of 'indifferent' cells along the 

 course of migration. 



DISCUSSION 



The observations set forth in the preceding pages have shown 

 that in turtles the sympathetic nervous system bears a direct 

 genetic relationship to the central nervous system. The cells 

 giving rise to the anlagen of the sympathetic trunks and of the 

 prevertebral plexuses have their origin in the spinal ganglia or 

 the neural crest and in the ventral part of the neural tube and mi- 

 grate peripherally either through the mesenchyme or along the 

 paths of the spinal nerves and of the communicating rami. The 

 vagal sympathetic plexuses; viz., the cardiac plexus and the sym- 

 pathetic plexuses in the walls of the visceral organs, are not de- 

 rived from the same sources, but arise from cells which have their 



