40 H. V. NEAL 



neurilemma cells. The cell-chain hypothesis has entirely looked upon 

 and conceived the beginning of this third stage as the actual beginning 

 of the specific formation of nervous substance. Actually, however, 

 this condition belongs to that period of the development which trans- 

 forms the embryonic type of nerve into the adult and differentiated 

 structure. 



In presenting evidence of the secondary connection of nerve 

 and muscle, and perhaps more convincingly, evidence of the en- 

 dogenous origin of the neurofibrils and their genetic relation to 

 the medullary neuroblasts, Held supports the essential points of 

 the process theory of nerve development. His conclusions, how- 

 ever, differ from those usually held by supporters of the Kupffer- 

 Bidder theory in regard to the origin of protoplasmic connections 

 of nerve center and end-organ. In this regard Held considers 

 himself an advocate of the Hertwig theory, since he holds that 

 protoplasmic coiinection of tube and myotome is formed, not 

 by the neuroblasts which form the neurofibrils, but independ- 

 ently as plasmodesms of indeterminate and multicellular origm. 



There is nothing in Held's monograph, however, to indicate 

 that he has given as careful attention to the development of 

 these plasmodesms as to the histogenesis of the neurofibrils. 

 The evidence presented by the writer ('03 and in the present 

 paper) supports the view of His, von Lenhossek, Cajal that the 

 same cells w^hich form the neurofibrils also form the protoplasmic 

 connections between tube and myotome. In other words, 

 the neuroblasts themselves form the protoplasmic connections 

 of tube and myotome. As shown in plates 1 and 2, the processes 

 of medullary neuroblasts extend along the median surface of 

 the somite between myotome and sclerotome and within these 

 processes (w'hich may be traced to their connections with med- 

 ullary cells as stated by Froriep, '04) neurofibrils make their 

 first appearance as is clearly shown in preparations made by 

 suitable methods of staining. In the light of Held's results, 

 it seems probable that a neuro-reticulum is present wdthin 

 the neuroblast cell, but no method sharpl^^ differentiates it 

 in Selachians in early stages of histogenesis. Sometimes in 

 Bielchowsky-Paton preparations a fibrillar network appears 

 in certain medullary cells in stages before protoplasmic con- 

 nection with the mvotome has been formed. That this is neu- 



