74() 



A. SUBBA llAU AND P. U. JOHNSON ON THE NEUVOUS 



60 hrs. Text-fig. 4 is drawn from a section of sucli an embryo. 

 It shows neuroblasts isolated between spinal cord and aorta 



Text-fio-ure 4. 







r^7'' 





0mm. 





>^a 



Transverse section of chick of 1\ days (Bielschowsky preparation), showing auiid 

 tlie niescnchymo cells isolated neuroblasts (iV.C.) between spinal cord (S.C.) 

 and aorta (Ao.). 



possessing distinct nervous processes. The neuroblast has a large 

 oval nucleus, and its processes are directed towards the aorta. 



C. Relations with the Ventral Boots. 



- "Whilst all investigators are not agreed as to the origin of 

 sympathetic cells from the neural crest before its differentiation 

 into the dorsal root ganglia, most are agreed that the ganglia 

 when formed give origin to the sympathetic cells. Held (7) goes 

 so far as to derive the whole of the sympathetic ganglia from the 

 dorsal root ganglia. His evidence is based on the examination 

 of Selachian material, but he is so satisfied with those observa- 

 tions that he applies his deductions to the case of chick embryos, 

 although he confesses that he has not been able to discriminate 

 the roots satisfactorily in them. 



Kuntz (11, 12), on the other hand, attaches by far the greater 

 importance to the ventral roots as the path by which the cells 

 migrate, a view \vhich he supports by both morphological and 

 experimental evidence. 



