Cytology and Movements of the Cyanophycece. 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 Biitschli 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 thespiremeandsubsequentlystoring 

 it up again, are probably to be looked upon as pathological. 

 Zacharias also argued that the central bodymight 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 Cyanophyceae, 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- 



