SYSTEM AND SUPRARENAL BODIES IN THE SPARROW. 763 



admirably set fortli by Goormaghtigli in his recent paper. The 

 only point on which our observations lead us to dift'er from him 

 is as to the origin of the medullary substance. This is derived, 

 according to our observations, from the primary sympathetic 

 cords and not, as Goormaghtigli maintains, from the mesodermal 

 cells of the sclerotome. 



II. Discussion. 



Since Francis Balfour (2) in 1877 described tlie development- 

 of the sympathetic nervous system in the Selachii, many theories 

 have been put forward supporting, or refuting, his statement as 

 to its origin. Without going deeply into the history of the con- 

 troversy, we may summarize tlie chief suggestions as follows : — 



A. Origin ectodermal. 



a. From the medullary tube. 



b. From the spinal nerve roots. 



c. From the dorsal root ganglia only. 



d. From ventral roots chiefly. 



B. Origin mesodermal. 



Diiierentiation iii situ. 



C. Mixed origin. 



From the medullary tube and sclerotome. 



Supporters of the mesodermal origin of the sympathetic nervous 

 system have based their conclusions chiefly on the presence of the 

 sympathetic primordia, at the dorso-lateral angles of the aorta 

 and the carotids, before the appearance of the nerve roots. 

 Although we agree with them in this observation, we are yet of 

 the opinion that the cells in question have not differentiated 

 in sitih, but that they have been proliferated from the neural 

 crest (see text-fig. 1). 



We have not found a trace of support for the interpretation 

 recently put forward l\v Dart and Shollshear (4), who state that 

 " a mesodermal origin of these neuroblasts (i. e. neuroblasts in 

 relationship with mesodermal structures) must therefore be postu- 

 lated and is demonstrable." All nerve fibres which we have 

 observed could either be traced from the central nervous system, 

 or, in certain cases, from free cells closely associated with it, and 

 in no case occupying a position such as would support their 

 view. 



With regard to Goormaghtigli s (6) contention for a mixed 

 origin, we may state that we have kept a careful look out for the 

 strands, which he describes as arising from the sclerotome and 

 contributing to the formation of the primary sympathetic system, 

 and have been entirely unsuccessful in our search. The paths of 

 the migrating cells destined to form the sympathetic primordia. 

 certainly pass close to the sclerotomes, but the boundary between 

 the two structures in our material has always been clearly 

 marked, and the cells on either side of that boundary sufficiently 



