SYMPATHETIC SYSIEM IN TURTLES 285 



out along the ventral nerve-roots and those which wander down 

 from the spinal ganglia. As the cells advancing peripherally 

 along the paths of the spinal nerves reach the origin of the com- 

 municating rami many of them deviate from the course of the 

 spinal nerves and enter the anlagen of the sympathetic trunks 

 (fig. 2, Sy.). The cells which wander into the anlagen of the 

 sympathetic trunks along the paths of the communicating rami 

 are, doubtless, derived in part from the spinal ganglia and in part 

 from the ventral part of the neural tube. The great majority 

 of the cells present in the spinal nerves are still undifferentiated 

 and there is no reason to suppose that cells advancing peripherally 

 from the spinal ganglia enter the sympathetic anlagen while those 

 advancing peripherally from the ventral part of the neural tube 

 do not. Furthermore, the fibers growing peripherally into the 

 communicating rami are primarily ventral root fibers. If the 

 growing nerve-fibers exert any guiding influence on the peri- 

 pherally advancing cells, as, doubtless, they do, it is highly prob- 

 able that many of the cells which wander out along the fibers of 

 the ventral nerve-roots wander along these fibers into the anlagen 

 of the sympathetic trunks. 



In his work on the development of the head of Gymnophion, 

 Marcus ('10) described light areas in contact with and partly 

 surrounding the anlagen of the sympathetic trunks in the early 

 stages. These areas he interpreted as lymph spaces and ex- 

 pressed the opinion that the anlagen of the ganglia of the sym- 

 pathetic trunks grow mesially from the spinal nerves in these lymph 

 spaces or at least are surrounded by them. To quote: "Der 

 Zellstrang der Sympathicusanlage wachst medianwarts vor, gegen 

 die Dorsalseite der Aorta zustrebend. Dabei kann ich mich des 

 Eindrucks nicht erwehren, dass der Sympathicus in einem Lymph- 

 raum seitlich der Aorta hineinwachst oder dochjedenfalls, dass er 

 von Lymphgefaszen umspielt ist." 



In the early stages in embryos of the turtle, narrow spaces simi- 

 lar to those described by Marcus in embryos of Gymnophion 

 may be observed in contact with and in some cases almost sur- 

 rounding the anlagen of the sympathetic trunks as they appear 

 in transverse sections. Such spaces, however, are not present 



