SYMPATHETIC SYSTEM IN TURTLES 281 



Neumayer's observations on embryos of Lacerta reveal nothing 

 which is characteristic of reptiles. His conception, according to 

 which the sympathetic anlagen arise from cells which are to be 

 regarded as the offspring of the dorsal and the ventral nerve-roots 

 and are differentiated in situ, is based primarily on other classes 

 of vertebrates. 



According to Held's ('09) observations on embryos of Emys 

 europea, the sympathetic trunks arise as cell-aggregates lying 

 along the lateral surfaces of the aorta at the distal ends of cell- 

 chains which grow mesially from the spinal nerves. Further- 

 more, Held has observed that in this species more than one such 

 cell-chain may grow from the spinal nerve toward the aorta. 

 According to his observations, the cell-aggregates constituting 

 the anlagen of the sympathetic trunks soon become broken up 

 into small cell-groups which become more or less scattered in the 

 mesenchyme. From these cell-groups cells migrate ventrally, 

 some of which enter the mesentery and give rise to the sympa- 

 thetic plexuses in the walls of the digestive tube. Held agrees with 

 Neumayer that the sympathetic anlagen arise as outgrowths from 

 the spinal nerves. He, however, traces the origin of the cells giv- 

 ing rise to the sympathetic nervous system to the spinal ganglia. 



OBSERVATIONS 



Sympathetic trunks 



a. Development. The earliest traces of the anlagen of the sym- 

 pathetic trunks appear in the thoracic and the dorsal region of 

 embryos of Thalassochelys caretta during the eighth day of incu- 

 bation, as loose cell-aggregates lying along the lateral surfaces of the 

 aorta just below its dorsal level. At this stage the spinal ganglia are 

 not yet completely differentiated. Traces of a few short fibers con- 

 stituting the earhest fibers of the dorsal nerve-roots appear in the 

 distal ends of the spinal ganglia, while in a few sections the rudi- 

 ments of the ventral nerve-roots appear as inconspicuous fiber- 

 bundles growing out from the neural tube. The spinal ganglia 

 are not sharply limited distally. Tracts of cells may be traced 



