20S ALBERT KUNTZ 



appearance be accounted for by mij^ration of cells along the sen- 

 sory nerve root and local cell division alone. 



A study of Neal's paper seems to justify the inference that he 

 does not admit that cells of cerebrospinal origin either migrate 

 in advance of the growing nerve fibers or deviate from the course 

 of the latter. His observations are based largely on material 

 prepared by the method of vom Rath. Since the observations 

 referred to above were published the writer has had occasion to 

 study a series of embryos of Acanthias prepared by the vom Rath 

 method. This method brings out the early nerve fibers much 

 more distinctly than does the iron-hematoxylin method ; however, 

 it does not differentiate cells of nervous origin from cells of mes- 

 enchymal origin as clearly as does the latter method. Doubtless, 

 fibers are present in the nerve roots somewhat earlier than the 

 writer observed them in his earlier work. However, the impor- 

 tant question at issue is, do any cells of medullary and neural 

 crest origin deviate from the course of the motor and sensory 

 roots of the spinal nerves respectively as they advance peripher- 

 ally? For evidence on this point we need not depend on the 

 observations of the present writer nor on embryos of the Elasmo- 

 branchii alone. As indicated by the work of well-known investi- 

 gators referred to in this paper, the migration of cells of cerebro- 

 spinal origin in advance of the growing nerve fibers and directly 

 through mesenchymal tissue outside the paths of the growing 

 nerves has been observed repeatedly in embryos of various types 

 of vertebrates. 



At this point the writer would call attention to the very careful 

 work of Ganfini ('11) on the development of the sympathetic 

 nervous system in fishes. In early ernbryos of Amia, a ganoid 

 type, Ganfini observed that cells of medullary origin which ad- 

 vance peripherally in the motor roots of the spinal nerves deviate 

 from the path of the motor fibers and advancing toward the aorta 

 become scattered in the mesenchymal tissue along its dorsolateral 

 aspects. These cells, according to Ganfini, with cells which ad- 

 vance from the spinal ganglia along the sensory roots of the 

 spinal nerves, become incorporated in the primordia of the sym- 

 pathetic trunks. These findings in embryos of Amia corroborate 



