316 JouRNAL oF CoMPARATIVE NEUROLOGY. 
they occasionally are found near the edge of the gray matter, 
and in the brain, especially in the earlier stages, they may be 
found among the neuroblasts which are passing through the fiber 
tracts to the cortex. As for the large dividing cells which lie 
in the gray matter, they have an appreciable cell body, often 
quite as large as the nerve cells in those places, and it is notice- 
able that those found among the multipolar cells of the cord are 
as much larger than those in the cortex of the brain as the 
multipolar cells are larger than the pyramidal. 
The obstacles to the assumption that fully formed nerve 
cells may divide are not only theoretical. Mitotic figures have 
been seen in the pyramidal cells of the cortex, in the neighbor- 
hood of aninjury ;' but under normal conditions, in vertebrates 
at least, the division of nerve cells has never been seen, and 
even in the cases cited above, it may be that the presence of 
mitotic figures is not a proof that the cells really were dividing, 
but simply that the nucleus had entered upon the preliminary 
stages of mitosis which would never have been completed. To 
-the division of the neuroglia cells there are no such strong ob- 
jections; indeed, if the theory of WEIGERT is accepted as to the 
dissociation of the glia fibers from the cells, there seems no 
reason why these cells should not divide. 
Assuming, then, that the large dividing cells of the gray 
matter are not either indifferent germinal cells, or fully differ- 
entiated nerve cells, what explanation remains? Might it be 
that they are not now in process of division but have already 
divided, and before the nucleus has returned to its resting con- 
dition, differentiation has proceeded and the cell is changing to 
a multipolar or a pyramidal cell? To this it must be objected 
that during mitosis all the energies of the cell are absorbed in 
this process and a further differentiation never, so far as we 
know, takes place until this is completed. 
It seems impossible to explain the different varieties of 
dividing cells in this animal except by assuming a process of 
1 CATTANI (76), MONDINO (z7), FRIEDMAN (78), COEN (79), MARINESCO 
(20), SANARELLI (27), VITZOU (22), TEDESCHI (23). 
