308 JOURNAL OF CoMPARATIVE NEUROLOGY. 
polar and pyramidal cells in the later specimens, and may be 
found anywhere in the gray matter from the outer edge of the 
ependyma to the outer edge in the gray matter. A comparison 
of the size of these dividing cells with the large nerve cells in 
their immediate neighborhood gives the following results: 
Dividing cell in the anterior horn of the spinal cord at 
birth (shown in Fig. 12) 18 & 124. 
Multipolar cell (Fig. 12, B) 19 X IIT yp. 
Dividing cell in cortex of brain at birth (Fig. 16, A) 11 
x Sp. 
Nerveicell (Fic.16,°B)212 27m: 
The size of these large dividing cells, therefore, corres- 
ponds very closely to that.of the nerve cells in their neighbor- 
hood, while no other cell in the gray matter approaches them 
in size. The thin granular protoplasm staining deeply with 
erythrosin increases the resemblance to nerve cells. 
In rare instances mitotic figures are found in cells which 
resemble in every way multipolar ganglion cells and which lie 
in the anterior horns of the gray matter in close proximity to 
the ganglion cells. Three such cells, from the three levels of 
the cord are shown in Figs. 18, 19 and 20. In Fig. 20 the 
chromosomes are not typicaland the possibility of some degen- 
erative change must be admitted, but the same cannot be said 
. of those shown in Figs. 18 and 19. Here the arrangement of 
the chromosomes is perfectly normal. In size, shape, pro- 
cesses and cytoplasm, these dividing cells resemble the multi- 
polar cells in these regions. It is only in the cord that these 
dividing cells with processes are seen. The mitoses in the cor- 
tex of the brain are found in cells which are not as large as the 
largest dividing cells of the cord (Figs. 15, 16, 17), are usually 
round or oval and in no instance in this region was a cell with 
processes found undergoing division. 
The nerve fiber tracts are narrow in the cord of the foe- 
tus and in the hemispheres where they form a very narrow 
layer between the wide ependyma and slightly narrower cortex 
(Figs. 1 and 3). At birth the tracts in the cord have increased 
appreciably both anteriorly and laterally while in the brain they 
