222 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY, 
More theoretical and farther from the truth Rabl could scarcely be, yet 
several investigators have in essential respects confirmed his theory, 
that the oculomotorius is a derivative of the neural crest. Dohrn’s 
(91) observations, however, differ fundamentally from those of his 
predecessors, He sees the beginnings of the oculomotorius in em- 
bryos intermediate between Balfour's stages I and K. At first cells in 
the base of the brain assume a more transparent appearance, and later 
migrate into the “ Randschleier,” where they send out processes which 
unite in a network just outside the base of the brain to form the stem of 
the nerve. Immediately at the beginning of the outflow of the plasma 
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Ficurr G. 
cells are seen half in and half out of the wall of the tube, and later, 
but before the oculomotorius has any connection with the mesocephalic 
ganglion, large deeply staining nuclei are seen in the protoplasmic net- 
work which forms the root of the nerve. Dohrn does not lay great 
stress on the fact that these nuclei are larger than those of the surround- 
ing mesenchyma cells, but from the fact that similar nuclei lie nearer 
the medullary wall, from which they appear to emerge in’ increasing 
numbers during the course of development, he holds the opinion to be 
permissible, that the nuclei of the early network are emerged medullary 
elements, and not mesoderm cells. which press close to the medullary 
Fic. G. A portion of the same section as that shown in Figure F. X 240. 
The fibrillar nature of the oculomotorius is clearly shown. ax-cyl., axis cylinder 
process; cl. n’bl., neuroblast cell ; oc-mot., oculomotorius. 
