748 



A. SUBBA RAU AND 1'. U, JOHNSON ON TlIK NERVOUS 



root ganglia, bvit tliey lead us to attach somewhat more im- 

 poi'tance to that source of origin than Kuntz would seem to 

 allow. 



Text-fig. 5 shows the ventral root of a Sparrow embryo, No. 11 

 (= 78-hr. chick). The ventral roots are well developed, and 

 the one figured shows a group of cells close to the origin of the 

 root, and evidently in course of migration. That the migration 

 is outwards seems clear from the observation of a later stage, 

 such as is reproduced in text-fig. 6 of SpaiTow 51 (= 84-hr. 

 chick). Hei-e we find some of these migrating cells leaving the 

 ventral root and making their way to the dorso-lateral angle of 

 the aorta, at which point they join the previously described 



Text-figure 6. 



{3n.-..-.w 



3.C. 



1^ 





v./?. 





CS. 



Transverse .section of Siiarrow 51 (= 84-lir. chick), showing- cells loaviuf^ ventral 

 root in the direction of the dorso-lateral angle of the aorta. 

 O.S. Cell strand. S.C. Spinal cord. F.B. Ventral root. 



(Sp. 51, 3, 2, 4.) 



sympathetic cells, and with them form diffuse masses of cells, 

 which are the primordia of the primary sympathetic chains. 

 At this stage the chains are not formed, but the difi'use cell 

 masses occur metamerically at intervals corresponding with the 

 somites. 



This migration of cells along the ventral roots, and thence to 

 the dorso-lateral angle of the aorta, is visible to a greater or less 

 extent in all the embryos examined at about this stage (= 3-3^- 

 day chick). Owing to the curvature of the embryo it is obvious 

 that the occurrence of a transverse section passing along one of 

 these migratory paths is quite fortuitous, though it can always 



