Cytology and Movements oj the Cyanophycee. 297 
the poles as in the spindles of higher plants, but each seems 
to end loosely in the cytoplasm. The spindle might, there- 
fore, be termed “open,” in the sense that for the time each 
chromosome appears to be independent. After the forma- 
tion of the above spindle, the chromosomes divide in the 
middle, half of the chromatin retreating towards each end, 
but they retain the bead-like appearance for some time, and 
leave a linin thread connecting the two daughter chromo- 
somes (Figs. 10 and 70). At this stage in the division 
there is formed, around the equator of the cell, a collar-like 
ingrowth of microsomata which gradually grows inward and 
constricts the linin connective threads (Fig. 71), which 
after they have been pressed to the centre, separate, but leave 
a pore connecting the two cells. Evidently the chromosomes 
are here divided in a transverse direction. The fact that 
they usually retain the bead-like structure until after they 
have separated into daughter chromosomes militates against 
the view that the chromatin has mixed, and that in this 
way a qualitative as well as quantitative division is effected 
as has been supposed to be necessary in the higher plants. 
The number of nuclear segments is not constant. There 
may be several (Fig. 9) rather fine chromosomes, or they 
may consolidate into two or more heavy segments (Fig. 
II), often looking like heavy bars of chromatin without 
any beaded appearance. These heavier segments divide in 
the same way as the lighter ones, revealing the linin thread 
between the divided portions (Fig. 13). The ingrowing 
cell wall soon reaches the linin connectives between the 
separate portions of the segments of the chromosomes, con- 
stricting them (Fig. 13) and finally separating them en- 
tirely. The chromatin then becomes diffuse and later forms 
the vesicles or the network, according as the cell continues 
to divide or enters upon a period of rest. The ingrowing 
collar which finally forms the division wall, in the earlier 
stages is composed of very fine microsomata of cellulose. 
These gradually fuse to form the wall (Figs. 4, 5, 7 and 
