288 ALBEKT KUNTZ 



could be observed apparently on their way from the dorsal part 

 of the neural tube into the dorsal nerve-roots. It is not probable, 

 however, that many cells wander out from the dorsal region of the 

 neural tube along the fibers of the dorsal nerve-roots. Migra- 

 tion of cells from this region of the neural tube is probably only 

 a transient process which may play some part in the development 

 of the spinal ganglia. 



At the close of the thirteenth day of incubation the anlagen of 

 the sympathetic trunks appear to be somewhat more widely scat- 

 tered than in the preceding stage. The communicating rami have 

 assumed no greater prominence and their fibers cannot yet be 

 traced beyond the anlagen of the sympathetic trunks. In many 

 sections cell-strands may be observed pushing out from the 

 spinal nerves proximal to the origin of the communicating rami 

 toward the anlagen of the sympathetic trunks. These cell-strands 

 are similar to those described by Held ('09) in embryo of Emj^s 

 europea. 



From the region of the suprarenals posteriorly cells move 

 ventrally from the anlagen of the sympathetic trunks and build 

 up cell-aggregates along the ventro-lateral aspects of the aorta 

 which, as will be shown later, constitute the anlagen of the pre- 

 vertebral plexuses. 



Cells still migrate peripherally both from the spinal ganglia 

 and from the ventral part of the neural tube along the paths of the 

 spinal nerves. The marginal veil in the neural tube, however, is 

 becoming wider and cells are apparently migrating into the ven- 

 tral nerve-roots less rapidly than in the preceding stages. 



During the seventeenth day of incubation the anlagen of the 

 sympathetic trunks are still more widely scattered than in the 

 preceding stage (fig. 4, Sy.). The communicating rami have not 

 increased in size appreciably nor is there much evidence that cells 

 still continue to wander along their paths into the sympathetic 

 anlagen. The cell-strands which at the close of the thirteenth 

 day were observed pushing out from the spinal nerves proxi- 

 mal to the origin of the communicating rami now appear as irreg- 

 ular cellular tracts extending diagonally through the mesenchyme 

 toward the dorso-lateral aspects of the aorta where they become 



