SYMPATHETIC SYSTEM IN BIRDS 307 



ent" cells and the " neuroblasts" of Schaper. They are, therefore, 

 homologous with the cells which give rise to the neurones and the 

 neuroglia cells in the central nervous system, and the sympathetic 

 neurones are homologous with the afferent and the efferent com 

 ponents of the other functional divisions of the peripheral nervous 

 system. These observations agree with the author's observations 

 on mammalian embryos. 



7. Certain morphogenetic differences exist in the development 

 of the sympathetic nervous system in birds and mammals, which 

 the author interprets as indicating that the sympathetic system 

 has departed more widely from the ancestral type in birds than 

 in mammals. Such departure is no more than should have been 

 expected in the specialized avian branch of the vertebrate series. 



