Hatal, Centrosome in Nerve Cells. 31 
sometimes sparingly arranged but never regularly placed. The 
above structure of the sphere coincides with that found in other 
cell groups of the adult rat. 
Fig. 2 was drawn from a large pyramidal cell in the cere- 
bral cortex of the adult white rat. Fig. 5 is from a PURKINJE 
cell of the adult white rat. It is clear from these figures of the 
two different cells that the structure of the sphere in them is 
similar to that in the adult spinal ganglion cell. 
Fig. 3 represents a large pyramidal cell in a young white 
rat. This specimen was preserved with the writer’s new mix- 
ture followed by toluidin blue and eosin. If we compare this 
figure (3) with the figure 2. which was taken from the same 
locality of an adult white rat, the structural difference of the 
centrosphere is plainly seen. In the former case (Fig. 3) the 
radial arrangement of the microsomes is very conspicuous and 
unlike the latter case (Fig. 2) in which the internal structure 
presents a more homogeneous appearance. 
Curiously enough, when the centrosome consists of a 
greater number of corpuscles, then the radial structure of the 
microsomes within the centrosphere is not clear but rather 
presents the homogeneous appearance as in the case of the 
centrosphere of an adult animal. This condition is shown in 
_ Figs. 4, 6, 11. The relation existing between the radial struc- 
ture of the microsomes and the central corpuscles requires 
further study. 
IV. HISTORICAL REVIEW OF THE CENTROSOMES IN NERVE CELLS. 
The presence of the centrosomes in nerve cells was first 
announced by von Lrenuossik! in the spinal ganglion cells of 
the frog. It had been previously noticed by several investiga- 
tors that many spinal ganglion cells, especially the cells in which 
the nucleus occupied an eccentric position, showed a somewhat 
concentric arrangement of the protoplasm on the side toward 
the axone hillock. Von LENHOssEK noticed the minute cor- 
puscles which are located in the center of this protoplasmic area 
1 Von LENHOSSEK.—Centrosome und Sphire in den Spinal Ganglienzellen 
des Frosches. Arch. fir Mikr. Anat., Band XLVI, pp. 345-368. 
