NEAL: NERVOUS SYSTEM IN SQUALUS ACANTHIAS. 223 
wall. Dohrn considers it as the punctum saliens of the evidence given 
by him, that ganglion cells and ganglia which may be traced to the 
adult are to be found in the course of the oculomotorins before this 
comes into connection with the mesocephalic ganglion, and concludes 
that such ganglion cells can have had no other source than the ventral 
horn of the midbrain. He thus takes the view of Balfour, Marshall, 
Kupffer, and others, that this ventral nerve is formed as a chain of 
medullary cells, in opposition to the views of His (89), Kölliker (92), 
von Lenhossék (92), and others, that ventral nerves are formed from 
processes of “neuroblast” cells in the ventral horn of the medullary 
tube. 
E CG He 
Fısure H. 
Miss Platt (91) comes to fundamentally different conclusions from 
those of Dohrn ('91). She finds that the oculomotorius appears first as 
a single cell proliferated from the mesocephalic (ciliary) ganglion toward 
the base of the midbrain, with which it at first has no connection. Ob- 
servations on Squalus, Raja, Pristiurus, and Torpedo convince her that 
tke oculomotorius develops after the type of a sensor nerve [Y] by a pro- 
liferation of ganglion cells toward the brain wall. Mitrophanow’s (93) 
Fio. H. Left face of a parasagittal section through the right half of the same 
embryo as that represented in Figures F and G, showing the oculomotorius in an 
early stage of development (52 somites). X 447. The relation of the nerve fibre 
with an axis-cylinder process from the neuroblast cell x seems clear. azx-cyl., axis- 
cylinder process ; oc-mot., oculomotorius ; x, neuroblast cell. 
