Hamitton, Devszon of Cells in Nervous System. 311 
he himself has abandoned it. The mesoblastic origin of the 
neuroglia cells is rejected by almost all histologists, and as the 
number of ependymal cells is not nearly large enough to ac- 
count for all these cells, it is usually assumed that they must 
jncrease by cell division. The germinal cell of His, then, is 
considered by the authors mentioned above as a simple epithe- 
lial cell in process of division. It is not in any sense a special- 
ized cell and gives rise not only to nerve cells, but also to the 
cells of the neuroglia. On the question of the exact mode of 
formation of the supporting cells, there is a difference of opin- 
ion. WEIGERT (73) and Sata y Pons (74) both describe the 
gradual transformation of ependymal cells into glia cells as 
follows: The ependymal cell elongates and sends out two pro- 
cesses to end at the ventricle and at the periphery. Then by 
a gradual shortening of the peripheral process the cell is drawn 
out, away from the ventricle, it loses its connection first with 
the ventricle, then with the periphery, develops side processes 
and is converted into a spider cell. Von LENHOSSEK (z0) ac- 
cepts this description of the formation of glia cells for some of 
the cells, but only for a few, as the number of ependymal cells 
is too small to account for all the spider cells found in the adult 
cord. Some undoubtedly are formed in this way, but the larger 
number must arise by division of the cells of the neuroglia. 
Von KOLLiKER (8) also thinks it probable that glia cells divide. 
The explation of VicnaL (5) differs from that of any other 
writer, not only by assuming a process of cell division which 
does not correspond with mitosis, nor amitosis as usually de- 
scribed, but also by denying any differentiation of cells in the 
central nervous system during the earlier stages of development. 
Thus, he considers not only the germinal cells indifferent, but 
all of the cells of the neural tube up to the time when a dis- 
tinct grouping of the multipolar cells of the anterior horns can 
be seen. Until this time—a point represented by three anda 
half months in the human embryo—the cells have all been 
alike in spite of apparent differences in size, shape and staining 
reactions. Nerve cells, he maintains, cannot be distinguished 
from supporting cells until the dendrites are formed. 
