304 ALBERT KUNTZ 



crest. In early stages of embryos of torpedo, he has observed 

 cell-chains connecting the neural crest with cell-aggregates in 

 the ventral nerve-roots. He concludes, therefore, that the neural 

 crest represents the sole source of the cells giving rise to sympa- 

 thetic neurones. I have found no evidence of cells migrating from 

 the neural crest into the ventral roots of the spinal nerves in em- 

 bryos of birds and mammals. Cell-chains connecting the neural 

 crest with the cell-aggregates in the ventral nerve-roots, doubtless, 

 do occur in embryos of the lower vertebrates. I have observed 

 such cell-chains in embryos of Amblystoma. This does not, how- 

 ever, preclude the possibility of cells migrating from the neural 

 tube directly into the ventral nerve-roots. In the same embryos 

 in which these cell-chains were observed, I was able to trace 

 medullary cells from the ventral part of the neural tube directly 

 into the ventral nerve-roots. 



As has already been pointed out, the cells migrating peripherally 

 from the neural tube and the cerebro-spinal ganglia along the 

 spinal nerves and along the vagi are the descendants of the " germ- 

 inal" cells of His; viz., the "indifferent" cells and the "neuro- 

 blasts" of Schaper. They are, therefore, homologous with the 

 cells giving rise to the neurones and the neuroglia cells in the 

 central nervous system. Inasmuch as some of these cells give 

 rise to the sympathetic nervous system, the latter bears a direct 

 genetic relationship to the central nervous system, and the sym- 

 pathetic neurones are homologous with the afferent and the effer- 

 ent components of the other functional divisions of the nervous 

 system. The histogenetic relationships of the sympathetic neu- 

 rones were considered at some length in my paper on the develop- 

 ment of the sympathetic nervous system in mammals. They will, 

 therefore, not be considered further at this point. 



A comparative study of the morphogenesis of the sympathetic 

 nervous system in birds and in mammals reveals some striking 

 points of difference which evidently have phylogenetic signifi- 

 cance. Two pairs of sympathetic trunks arise in the course of 

 ontogeny in birds, while in mammals a single pair of sympathetic 

 trunks is developed. In the early stages in mammalian embryos, 



