MORPHOLOGY OF EYE MUSCLE NERVES 35 



4. Have these protoplasmic connections a genetic relation to the 



neurofibrils? 



Paton decides adversely to the view that the protoplasmic 

 bridges are formed by the processes of neuroblasts on the ground 

 that they do not contain fibrillae. He does not deny, however, 

 that ''under certain circumstances a nerve cell may throw out a 

 process of very considerable length." But he thinks that "the 

 greatest caution should be observed in assuming that mere 

 length of process, without positive knowledge regarding the na- 

 ture of the structures contained in it, is in any sense to be con- 

 sidered a criterion as to whether a cellular prolongation is or is 

 not to be called a nerve." To "refer to an undifferentiated 

 tract as a nerve would give rise to endless confusion." 



Paton ('07, p. 560) finds that in sections fixed in sublimate- 

 acetic and stained by hematoxylin-eosin, the medullary cells 

 appear 'faintly fibrillar;' but he thinks that this 'primitive fi- 

 brillation' has no connection with the development of the neuro- 

 fibrils. 



In his opinion, the conclusions of those who claim a connection 

 between the primitive ventral root fibrils and medullary cells 

 are based upon faulty technique. "No reliable method of 

 staining has yet been employed that is capable of demonstrating 

 the presence of processes in the vicinity of the distal ends 

 of these primitive filaments." According to Paton, the first 

 neurofibrils or 'primitive fibrils' make their appearance within 

 the myotome at a point remote from the protoplasmic bridges, 

 as shown in Paton 's figure 2, plate 23, shown in outline in text- 

 figure A of this paper (p. 25). 



The primitive neurofibrils are coarse, deeply stained structures ap- 

 pearing primarily in a locality where more than in any other place the 

 ground substance, even after sublimate fixation, seems to be granular 

 in character, while the more delicate and attenuated filaments only 

 become visible at later stages. . . : . The apparent independence 

 of these primitive neurofibrils in the ventral roots from cells is one of 

 their distinguishing characteristics, but in the large cells of Beard a dif- 

 ferent arrangement exists. There the fibrils appear in the apical proc- 

 ess of the cell close to its nucleus (compare figure 2 with figure 12, 

 plate 23). 



