MORPHOLOGY OF EYE MUSCLE NERVES 95 



the neurilemma cells as they penetrate among the fibers in ad- 

 vanced stages of histogenesis. 



There appears to be no reason for doubting the identity of 

 the fibers differentiated by the Vom Rath method with those 

 which appear in Cajal and Bielschowsky-Paton preparations. 

 They have practically identical appearance, form and relations, 

 both in cross and longitudinal sections. So that if it be granted 

 that the coarse fibrils seen in preparations made by the latter 

 methods are genetically related to the neurofibrils of the adult 

 nerve, the reasons apply with equal force to those which appear 

 in Vom Rath preparations. 



d. Is the individual neuraxon of the abduceris anlage multicellu- 

 lar in origin or is it the process of a single cell? Reasons have 

 aheady been stated why the abducens fibers may be regarded 

 as products of protoplasmic movement and not of cell chains, 

 and it seems unnecessary to repeat them. All the evidence 

 favoring this conclusion for spinal somatic motor nerves and 

 for the oculomotor and trochlearis may be advanced for the 

 abducens. ,The proof is even more convincing in the case of 

 the abducens, since development is simplified by the absence 

 of connection with a ganglionated nerve. 



e. By what means does the increase in length of the constituent 

 neuraxons take place? This question may be answered in the 

 same way as in the case of the other somatic motor ne^-ves de- 

 scribed, and has already been stated above. The evidence upon 

 which the hypothesis of the plasmodesmatous origin of the nerve 

 anlage is based is no less equivocal and unconvincing than that 

 offered by its most recent exponent. Held ('09). 



/. What is the source of origin of the cells of the abducens anlage? 

 Since the abducens makes no connection with a ganglionic nerve 

 and therefore receives no cells from that source, the cells of the 

 anlage must either be derived from the mesenchyma or from the 

 medulla or from both. Neal ('98) and Belogolowy ('10) were 

 unconvinced of the medullary origin of the cells, which both 

 derived from the mesenchyma. But Dohrn ('91) was undoubt- 

 edly correct in inferring the medullary origin of some of the 

 abducens cells. The evidence of migration is quite as convinc- 



