ped cae JouRNAL OF CoMPARATIVE NEUROLOGY. 
ScHAPER (6) has gone very exhaustively into this subject, 
and takes a stand midway between ViGNAL and the majority of 
observers. The original epithelial elements, according to ScHa- 
PER, undergo one of two changes, either they are transformed 
to ependymal cells, which in higher vertebrates persist only 
around the ventricles, or they change to ‘“‘indifferent”’ cells. As 
the ependymal cells are incapable of further multiplication, all 
increase in supporting cells and nerve cells must be through the 
division of these indifferent cells. At first these cells divide 
actively: around the ventricles and the new cells wander out into 
the mantle layer. They are now the cells which by His were 
called neuroblasts, but SCHAPER considers them transition forms, 
not yet differentiated, capable of developing immediately into- 
either supporting cells or nerve cells, or of dividing again and 
again without losing their indifferent character. Later on the 
formation and division of germinal cells around the ventricle 
gradually lessens and these indifferent cells in the mantle layer 
begin to divide. We have now inthe mantle layer three kinds 
of cells: first the true neuroblast, with a large clear nucleus, 
darker nucleolus and axone; second the glia cells, small with 
no visible cytoplasm, darker nucleus with thick chromatin gran- 
ules ; third, larger cells with bubble-like nucleus, finely gran- 
ular chromatin, no nucleolus and no visible cytoplasm. These 
last are the indifferent: cells and are the only ones capable of 
multiplication. They persist up to a late period perhaps even 
imto adult life, and it is by the division of these cells alone that 
nerve cells and also neuroglia cells are formed. In his descrip- 
tion of the: process of formation of the neuroblasts, SCHAPER 
follows His, but on the question of the development of the 
neuroglia he is not quite so clear. Some of the cells are ac- 
counted for in the way given by WEIGERT and SALA y Pons, the 
migration and transformation of ependymal cells—others are 
formed by the division of the indifferent cells But SCHAPER 
says that it is hard to account for the enormous number found 
in the adult, as the fully formed neuroglia cells are incapable of 
dividing. 
In a recent article Paron (7) elaborates this theory of 
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