SYMPATHETIC SYSTEM IN TURTLES 309 



It may be pointed out, furthermore, that the theory advanced 

 above maybe applied to the peripheral migration of the cells giving 

 rise to the vagal sympathetic plexuses as well as of the cells giving 

 rise to the sympathetic trunks. In either case the direction of 

 migration is toward a region in which there is an abundant food 

 supply and which is the seat of primary vegetative processes. In- 

 asmuch as the sympathetic nervous system is concerned primarily 

 with the control of the purely vegetative functions we may suppose 

 that the sympathetic elements respond primarily to the influence 

 of hormones which are produced in these regions. 



As has already been pointed out, the cells which migrate pe- 

 ripherally from the cerebro-spinal nervous system have the same 

 genetic relationships as the cells which give rise to the neurones 

 and to the neurogla cells in the central nervous system. The sym- 

 pathetic nervous system is, therefore, homologous with the other 

 functional divisions of the peripheral nervous system and the sym- 

 pathetic neurones are homologous with their afferent and their 

 efferent components. 



SUMMARY 



1. In embryos of the turtle the anlagen of the sympathetic 

 trunks arise as cell-aggregates lying along the lateral surfaces 

 of the aorta and along the dorsal surfaces of the carotid arteries. 

 The cells which give rise to the anlagen of the sympathetic trunks 

 have their origin (a) in the spinal ganglia or in the neural crest and 

 (b) in the neural tube. Before the spinal nerves may be traced 

 peripherally, cells advance from the distal ends of the spinal 

 ganglia, directly through the mesenchyme, into the anlagen of the 

 sympathetic trunks. After the spinal nerves have grown peripher- 

 ally, cells migrate from the spinal ganglia and from the ventral 

 part of the neural tube along the paths of the spinal nerves and of 

 the communicating rami into the anlagen of the sympathetic 

 trunks. These findings agree, in regard to the sources of the cells 

 giving rise to the sympathetic trunks, with the writer's observa- 

 tions on the histogenesis of the sympathetic trunks in manamals, 

 birds, and fishes. They disagree with the findings of the earlier 

 investigators, except those of Froriep, primarily in the fact that 



