290 JouRNAL oF CoMPARATIVE NEUROLOGY. 
FLEMMING’S observation was soon confirmed by many in- 
vestigators and was also extended by HaAxckeEL on the germinal 
tract and urogenital cells of Cyclops; by VAN DER STRICHT on 
the Thysanozoon eggs; by v. KLINcKowsTROM on the Prosthe- 
ceraeus eggs, etc. In each case, the ‘tetrad’ formation of the 
chromosome is somewhat similar in its principle to that of the 
salamander (FLEMMING), although there occur slight morpho- 
logical differences. 
The mitotic figure in the nerve cell may be regarded as 
one of the modifications of the heterotypical mitosis. <A slight 
difference between the nerve cell and the case of the salamander 
is the following: The chromosomes in the nerve cell are always 
continuous throughout the entire course of division, while in 
the salamander the chromosomes divide into numerous seg- 
ments which are separated from one another and perform the 
dividing processes independently. For this reason, the process 
of the mitosis is more difficult to follow in the nerve cells. 
Although typically the chromosomes form a continuous 
thread, the present writer noticed occasionally somewhat V- 
shaped chromosomes which hac been separated from the con- 
tinuous group. The writer expects in the near future, to ex- 
plain these peculiar cases. 
V. Morphology of the nucleolus. 
As has been already mentioned, the nucleolus of the nerve 
cell not only plays an important role in mitosis, but also pre- 
sents a peculiar behavior when compared with that of other 
tissue as described by different authors. This peculiarity, how- 
ever, depends on the special structure of the nucleolus in the 
nerve cell. At the later stage of the telophase, the nucleolar 
substance which intimately surrounds the chromosomes with a 
thick layer is dissolved and accumulated at certain places in the 
nucleus forming small spherical masses. These isolated masses 
in most cases aggregate themselves at the center of the nucleus 
and form a large group. 
The nucleolar granules thus grouped give out one process 
from each pole. The processes fuse with one another, thus 
