170 ALBERT KUNTZ 



municating rami rather than along the compact fibrous paths of 

 the latter. 



The differences of opinion above set forth regarding the method 

 by which cells which take part in the development of the sympa- 

 thetic nervous system are displaced peripherally may be ac- 

 counted for in part by fundamental differences in the morpho- 

 genesis of the sympathetic trunks in the several classes of 

 vertebrates. The primordia of the sympathetic trunks arise in 

 the Elasmobranchii as ganglionic enlargements on the spinal 

 nerves (Balfour, 77; van Wijhe, '89; Hoffmann, '99). They 

 arise in the Amphibia as aggregates of cells lying along the dorso- 

 lateral aspects of the aorta after fibers are present in the com- 

 municating rami (Hoffmann, '02; Neumayer, '06). In birds the 

 primary sympathetic trunks arise as a pair of cell-columns lying 

 along the dorsolateral aspects of the aorta. These early give 

 way to the secondary sympathetic trunks, the primordia of which 

 arise as aggregates of cells just mesial to the ventral roots of the 

 spinal nerves (His, Jr., '97). In mammals the primordia of the 

 sympathetic trunks arise as cell-columns lying along the dorso- 

 lateral aspects of the aorta (His, '90; Kohn, '05, '07). With 

 these observed differences in the morphogenesis of the sympa- 

 thetic trunks in mind, it is appai'ent that the theory advanced 

 by Onodi was based on his findings in the Elasmobranchii, while 

 the theory of the active migration of cells into the sympathetic 

 primordia was based primarily on observations made on embryos 

 of birds and mammals. 



A few investigators, notably Kohn ('05, '07) and Neumayer 

 ('06), do not admit that active cell migration occurs, but account 

 for the aggregates of cells which constitute the primordia of the 

 sympathetic trunks by the prohferation of elements which are 

 differentiated in situ in the spinal nerves. Obviously, the views 

 of these authors are influenced by their allegiance to the theory 

 of local differentiation and the multicellular nature of nerve-fibers. 



Froriep, who like a number of investigators before him, had 

 previously observed that cells of medullary origin advance pe- 

 ripherally along the ventral roots of the spinal nerves, in 1907 

 presented evidence which indicates that some of these cells enter 



