314 JOURNAL OF COMPARATIVE NEUROLOGY. 
type only, and it is impossible to tell whether nerve elements 
or supporting cells will result from the division of any cell. 
Fully formed neuroglia cells, spongioblasts, neuroblasts and 
nerve cells are ail, according to these two authors, incapable of 
multiplication. There is indeed practically unanimous agree- 
ment among histologists as to the impossibility of the fully 
formed nerve cells or supporting cells dividing, under normal 
conditions, whatever may be true of pathological conditions. 
ScHAPER expresses the general view when he says: ‘‘A new 
formation of nerve cells in the fully developed nervous system 
is impossible for the division and increase of such highly differ- 
entiated ganglion cells as exist in vertebrates at least, must be 
rejected. Not only is a cell which is morphologically so highly 
differentiated incapable of dividing by karyokinesis, but it is 
impossible that a nerve cell should suspend its physiological 
activity and with it that of a whole chain of neurones, during 
a period when the nuclear subscancé must be entirely devoted 
to the processes preparatory for cell division. Also during this 
period the nutrition of the processes especially the axone would 
suffer, and finally, an equal division of a cell can occur only 
when the whole cell body with all its protoplasmic contents 
takes equal parts in the division, and this in the case of a nerve 
cell, is of course, impossible’ (p. 108). 
Since the evidence is convincing that the axone is the first 
of the branches to grow off from the cell-body, the appearance 
of mitotic figures in cell bodies that exhibit dendrites would be 
open to one of two explanations only. First, that the mitotic 
appearances are not necessarily followed by a division of the 
cell-body ; or, second, that the cell-body does divide after the 
axone has been formed. If this latter were true, then we might 
expect to find two cells attached to a single axone. Those who 
have worked most with the methods which would show this 
relation if it existed, have not observed it. The first hypothesis 
therefore, appears the more probable. 
Putting aside, as rare and atypical, the dividing nerve-cells 
which are multipolar cells and the spongioblasts, which perhaps 
should not have much stress laid upon them, there still remains 
