52 H. V. NEAL 



By his discovery of a 'ventral neural crest' in Ammocoetes 

 Kupffer was led to abandon the cell-process theory of nerve 

 development and to adopt the cell-chain hypothesis. Accord- 

 ing to Sagemehl ('82) and Held ('09), however, somatic motor 

 nerves in Petromyzon are primarily fibrillar. Consequently, von 

 Kupffer's inference may be regarded erroneous as the result of 

 defective observation. 



Schultze ('04-'07) has adopted a modified form of the cell- 

 chain hypothesis from his observation of the growth of nerves 

 in amphibian embryos, in which he finds the nerves primarily 

 cellular. He consequently regards the nerves as a syncytium of 

 peripheral neuroblasts, on the assumption that the cells are the 

 formative ones which secrete a nerve. Thus Schultze regards 

 the neurilemma as ectodermal in origin. 



According to Held ('09), however, Schultze has failed to see 

 the earlier stages of nerve histogenesis before the anlagen have 

 acquired a cellular character. Held ('09) regards the cells which 

 find their way into embryonic nerves as 'Leitzellen,' and holds 

 that they have nothing to do with the formation of nerve fibers 

 more than to furnish the paths in which the neurofibrils are 

 driven forth from the neuroblasts. But Schultze claims that the 

 fibril-free cells (Held's Leitzellen) are as much neuroblasts as 

 muscle-forming but primarily fibril-free cells are myoblasts. 



The writer ('03) argued on the following grounds that the 

 cells of somatic motor nerve anlagen have nothing whatever to 

 do with the formation of neuraxons: 



1. In the earliest stages of histogenesis, when the number of 

 fibers increases most rapidly in the nerve anlage, the cells of 

 the anlage are distinctly peripheral in relation to the fibrillar 

 bundles (Bardeen, '03, has also emphasized this point). 



2. None of the ventral nerve cells at any stage of histogenesis , 

 show the deeply-staining properties of neuroblast cells such as 

 appear in the ganglia of the dorsal (somatic sensory) nerves. 

 Without exception the cells of the somatic motor nerve anlagen 

 are vacuolated, granular and lightly stained. 



3. While marked changes in size and shape (correlated with 

 the growth of the neuraxons) appear in the neuroblasts of the 



