Hamitton, Dzviston of Cells in Nervous System. 313 
ScHaPer. He too considers that the offspring of the germinal 
cells are indifferent, and may either develop into nerve cells or 
supporting cells or remain indifferent. Paron’s work was on 
the brain of pig embryos. His description of the indifferent 
cells agrees with that of ScHAPER, but he finds them undergo- 
ing division almost invariably in the ependyma, not in the man- 
tle layer. In all stages of development except the very early, 
Paton finds two kinds of germinal cells, one large with a well 
developed cell body, and one small with almost no cell body, 
but he thinks this difference is unimportant as both alike pro- 
duce indifferent cells. Development proceeds first in the epen- 
dyma which grows rapidly and is filled with germinal cells, 
indifferent cells and the spongioblasts of His. The indifferent 
cells which are to become neuroblasts pass to the outer layer of 
the ependyma, and here or in the nerve fiber layer are trans- 
formed into neuroblasts and pass out to form the cortical cell 
layer. As for the supporting cells, they are at first represented 
by the spongioblasts of His—transformed ependymal cells 
which diminish in size and number as they wander away from 
the ventricle, persisting in higher vertebrates around the ventri- 
cle only. As they disappear, the glia cells appear, being the 
result of division of the indifferent cells. 
It is evident that there is nothing in the literature on the 
development of the central nervous system which points to the 
occurrence of large extra-ventricular dividing cells such as are 
found in the brain and cord of the white rat, nor does any 
theory of the process of cell formation allow for the presence 
of such cells. 
The germinal cells of His are described as always situated 
on the ventricular surface or separated from it by one layer of 
cells only. They have no large granular cytoplasmic body, and 
never have processes. SCHAPER has been already quoted as 
mentioning dividing cells in the gray matter, but these cells are, 
according to his description, invariably devoid of cytoplasm. 
Moreover, according to SCHAPER and to Patron, all of the new 
cells formed during the growth of the cord and brain are de- 
rived from the division of indifferent cells, which are of one 
