72 H. V. NEAL 



from the midbrain or from the mesocephaUc ganglion — are neuro- 

 blast cells which form the fibers of the oculomotor; that the 

 cells of the anlage form the neurilemma; that they contribute 

 to the formation of the ciliary ganglion; and that those which 

 migrate from the midbrain, if not also those that are derived 

 from the mesocephalic ganglion, have both fates. 



Taking up these views in turn, we find that Dohrn ('91) is 

 the only one who has attempted to support the cell-chain hy- 

 pothesis on the basis of evidence derived from the study of the 

 development of the oculomotor nerve, but as he has wholly 

 repudiated ('07) the considerations which earlier led him to advo- 

 cate the cell-chain hypothesis, it seems inadvisable to discuss 

 his arguments in favor of the former theory. 



Gast ('09) asserts that some of the migrant medullary cells 

 become located in the 'root ganglion' of the oculomotor, where 

 they become differentiated as neuroblasts, but the evidence upon 

 which he bases his statement is far from convincing. It would 

 seem necessary, even were one prejudiced in favor of such a 

 view, to be able to demonstrate in its favor more convincing 

 evidence than the presence of spindle-shaped or even multipolar 

 cells in the cell mass which Gast calls a ganglion, especially in 

 preparations made according to the usual embryological methods 

 which do not differentiate the distinctive histological elements 

 of ganglion cells. In a section made by usual embryological 

 methods, how can Gast tell whether a spindle-shaped cell is a 

 nerve cell or a sheath cell? Even multipolarity is no decisive 

 criterion of a ganglion cell. Therefore, while there may be no 

 theoretical reasons why the migrant medullary elements may 

 not be expected to form ganglion cells, it would seem that some 

 more critical evidence than form is to be taken as proof that 

 such is their fate. None of the methods used in the present 

 investigation upon Squalus embryos demonstrate the presence 

 of neuroblasts or ganglion cells among the cells in the roots of 

 the oculomotor. Whatever multipolar cells appear in close prox- 

 imity to the nerve appear to be similar to adjacent cells of the 

 mesenchyma. 



