78 ALBERT KUNTZ 



the rhombencephalon along the several divisions of the trigeminal 

 nerve. They are obviously cells which wander out from the 

 mantle layer in the wall of the mesencephalon along the rootlets 

 of the oculomotor nerve. In the early stages of development, 

 as may be observed in parasagittal sections, medullary cells push 

 out from the mantle layer in cone-shaped masses into the rootlets 

 of the oculomotor nerve until they come into close proximity 

 with the external limiting membrane. Continuous lines of med- 

 ullary cells extending from the mantle layer into the proximal 

 parts of the oculomotor nerve could never be observed. How- 

 ever, cells identical in appearance with the medullary cells are 

 always present in the nerve-roots outside the external limiting 

 membrane as well as throughout the entire length of the growing 

 nerve. That these elements are cells of medullary origin which 

 have wandered out from the mantle layer in the mesencephalon 

 can not be doubted. They can not be traced from any other 

 source. My observations on this point substantially confirm the 

 observations of Carpenter ('06) on embryos of the chick and of 

 other investigators on embryos of various types of vertebrates. 



Migrant cells 



As indicated above, the cells which advance peripherally from 

 the semilunar ganglion and from the walls of the mesencephalon 

 and rhombencephalon along the oculomotor nerve and the several 

 divisions of the trigeminal nerve are identical, in the early stages 

 of development, with the majority of the cells in the cerebro- 

 spinal ganglia and the mantle layer in the neural tube. In well 

 stained preparations, these cells may be distinguished from the 

 cells of the surrounding mesenchyme by the somewhat larger 

 size, the more intense staining reactions and the characteristic 

 chromatin structure of their nuclei. The great majority of them 

 are characterized by very little cytoplasm and by a large rounded 

 or elongated nucleus showing a very delicate chromatin structure. 

 These cells are identical with the great majority of the cells 

 which, as was previously pointed out by Carpenter and Main 

 ('07) and as was shown by the writer in an earlier paper, ^ advance 



' Anatomical Record, vol. 3, pp. 158-165. 



