SYMPATHETIC SYSTEM IN TURTLES 



291 



The accompanying diagrams (figs. 6 and 7) have been intro- 

 duced to illustrate successive stages in the process by which the 

 primary communicating rami are shifted proximally along the 

 spinal nerve-trunks until they fuse with the secondary tracts 

 growing mesially from the proximal parts of the spinal nerves. 



After the twenty-fourth day of incubation but a single tract 

 may be recognized connecting the sympathetic anlage with the 



u IS 3,6 n n 



Fig. 5 Curve designed to indicate the relative length of the intervals between 

 the origin of the ventral nerve-root and the origin of the primary communicating 

 ramus in embryos of Thalassochelys caretta in successive stages of development. 

 For explanation see text. 



spinal nerve. This tract is distinctly fibrous, but still contains 

 numerous accompanying cells. Most of the cells present in the 

 communicating rami in these later stages, doubtless, have wan- 

 dered out from the spinal ganglia. There is no longer any evi- 

 dence of the peripheral migration of cells from the ventral part of 

 the neural tube, except as an individual cell occasionally passes 

 through the external limiting membrane. 



The development of the sympathetic trunks in embryos of 

 the turtle proceeds comparatively slowly. After cells cease to 



