310 ALBERT KUNTZ 



cells which wander out from the ventral part of the neural tube 

 take part in the development of the sympathetic trunks. 



2. About the eleventh day of incubation the anlagen of the 

 sympathetic trunks begin to break up and to become more or less 

 scattered. This scattering continues for a considerable period 

 until the cell-groups again become aggregated into compact 

 ganglia. 



3. About the thirteenth day of incubation cell-strands push 

 out from the spinal nerves proximal to the origin of the communi- 

 cating rami and advance toward the aorta. These cell-strands 

 increase in size and advance mesially until at the close of the six- 

 teenth day they appear as irregular cellular tracts extending from 

 the spinal nerves into the anlagen of the sympathetic trunks. 



4. As development advances, the primary communicating 

 rami are shifted proximally along the spinal nerve-trunks until 

 they fuse with the cellular tracts extending from the proximal 

 part of the spinal nerves into the anlagen of the sympathetic 

 trunks. 



5. A comparative study of the development of the sympathetic 

 trunks in embryos of the turtle and in the chick strongly suggests a 

 more or less direct phylogenetic relationship between the sympa- 

 thetic nervous system in birds and in the ancestral type of reptiles. 



6. The prevertebral plexuses arise as cell-aggregates lying 

 along the ventro-lateral aspects of the aorta. They are derived 

 from cells which migrate ventrally from the anlagen of the sym- 

 pathetic trunks. 



7. In the sacral region, cells may be traced ventrally from the 

 anlagen of the prevertebral plexuses into the mesentery where 

 they become aggregated into small cell-groups associated with the 

 rectum. These sympathetic cell-groups probably represent the 

 prototype of the ganglion of Remak in birds. 



8. In the region of the genital ridges cells migrate ventrally 

 from the anlagen of the prevertebral plexuses and become aggre- 

 gated at the lateral surfaces of the former to give rise to the genital 

 plexuses. 



9. The vagal sympathetic plexuses; viz., the cardiac plexus and 

 the sympathetic plexuses in the walls of the visceral organs, arise, 



