Cytology and Movements of the Cyanophycee. 285 
considered it to be a nucleus, but without a nuclear mem- 
brane. Zacharias based his argument against the nuclear 
nature of the central body upon the fact that the chromatin 
did not increase during division. This can be accounted 
for by the fact that there is no nucleolus present, which in 
the higher plants contains the chromatin in a changed form 
during the resting stage, but gives it out to the spireme 
during the process of division. If, on the other hand, the 
chromatin vesicles should be termed nucleoli they retain the 
chromatin in an unchanged form, and therefore there is no 
apparent increase in the amount of chromatin at the time 
of division as in the higher forms. The apparent decrease 
in the amount of nuclein at the time of division mentioned 
by Butschli may be accounted for by the fact of its becom- 
ing diffuse before forming the network, thus appearing to 
decrease, though in reality not doing so. Any hyper- or 
hypo-chromatin stages appearing in the processes of division, 
except those which come from the passing out of the chro- 
matin of the nucleolus to thespiremeand subsequently storing 
it up again, are probably to be looked upon as pathological. 
Zacharias also argued that the central body might bechanged 
by environment, though this had never been observed for 
the nuclei of higher cells. Brass was, however, able to 
bring about some very profound changes in nuclei of Infu- 
soria by varying their conditions of growth. The morpho- 
logical changes spoken of by Zacharias are, however, really 
the changes due to the different stages of division, which, in 
the Cyanophycez, present very different aspects. Zacharias, 
in his reply to Biitschli, conceded the central body to be the 
starting point of the nucleus, and that its functions might 
be the same as those of the nuclei, but he did not consider 
it to be that organ. His conceptions of what constitute the 
essentials of a nucleus do not seem to be plain from his 
writings. 
Palla considered the central body to be homogeneous, 
having no chromatin network, nucleoli or granules. Be- 
