DIFFERENTIATIONS OF ECTODERM IN NECTURUS. 511 
mesenchyme cells below, and form with them a loose con- 
nective tissue, in which I am unable to distinguish the cells of 
one source from those of another, yet comparison of sections 
14 and 15 with sections 18, 16, and 17, in which the neural 
Anlage has not as yet reached the level of the motor root, 
shows most clearly that the first nuclei found in the motor 
nerve have migrated from the spinal cord through the motor 
nerve-root. Ganglion cells have frequently been observed on 
motor nerves, and although His (20) affirms that no medullary 
cell migrates permanently from the cord into a motor nerve, 
Dohrn (6), claiming to have observed the passage of such cells 
from the spinal cord to the motor nerves of the trunk, supports 
this view by observations recorded in a paper on the origin and 
development of the eye-muscle nerves in the Selachii (7). The 
description there given of the development of the trochlearis 
is at variance with observations simultaneously published by 
Froriep (13) and myself (80). Dohrn’s account of the origin 
of the oculo-motorius differs no less from the account I gave 
(loc. cit.), which has since been confirmed by Mitrophanow 
(29) and Sedgwick (34). Froriep, Mitrophanow, Sedgwick, 
and the author find that the first ganglion cells of the troch- 
learis or oculo-motorius in the Selachii are of peripheral, and 
not central origin. It is therefore with the greatest pleasure 
that I now confirm Dohrn’s observations in regard to the origin 
of the ganglion cells on the motor nerves of the trunk, and 
add this evidence in support of his view that an actual and 
permanent migration of medullary cells takes place. 
The cells of the neural crest do not immediately take part 
in forming the spinal ganglia, bnt wander in a continuous 
sheet down the sides of the spinal cord, and are there lost in a 
loose connective tissue, of which at first only those cells that 
come directly in contact with the motor nerve appear to develop 
nervous properties. Shall we then say with Goronowitsch 
(17, 18) that the cells of the neural crest have become “meso- 
derm”? By no means. I do not for a moment imagine the 
actual disparity of the cells dependent on my ability to dis- 
tinguish them. 
