Hamitton, Deveson of Cells in Nervous System. 307 
more and more to lie at the dorsal and ventral ends of the canal, 
at the points, in other words, where the spongioblasts persist 
after they have disappeared from the remainder of the epen- 
dyma. No such long pointed dividing cells are found in the 
ependyma of the brain, the mitoses here are all found in round 
or oval cells, and lie usually in the layer directly bordering on 
the ventricle. Inthe brain of the foetus the ependyma con- 
sists of many layers of cells, and it is not uncommon to find 
germinal cells at quite a distance from the ventricle, but in the 
brain of the new-born rat the ependyma is reduced to two 
layers, and the typical germinal cells, now much diminished in 
number, are found only in these two layers. 
The dividing cells in the gray matter of both cord and 
brain are more numerous in the later specimens, but the same 
types are found in all. It is here in the gray matter that the 
greatest variations are found; variations in the size of the nu- 
cleus and the character of the chromosomes, in the amount of 
cytoplasm and the shape of the cell-body. These cells may be 
roughly divided into two groups, those with no visible cell 
body, and those with a well developed cell body. 
The cells of the first class are very numerous in the later 
specimens, more so than in the foetus. They are compara- 
tively small, measuring about 6 X 3 y (Fig. 8b), but even in 
the largest there is no visible cel!-body, and the chromosomes 
are comparatively delicate (Figs. 8, 9, (0). 
A much greater variety of cells belong the second class, 
the cells with a well developed cytoplasmic body. These are 
numerous in the gray matter of both cord and brain at birth 
and after, but less abundant in the foetal brain and cord. They 
therefore increase in number as the development of the gray 
matter proceeds. Their size varies from 10 X 7 » (Fig. 11, A) 
to 18 X 12y (Fig. 12, A). They are round or oval usually 
but may be pear shaped (Fig. 12) or spindle shaped (Fig. 13). 
_ The chromosomes are thick and heavy, the cytoplasm is gran- 
ular, staining deeply with saffranin or erythrosin, but often 
showing a clear zone around the nucleus. They lie among the 
neuroblasts in the foetal cord and brain and among the multi- 
