674 Graham.— N lie lear Division of Preissia commutata. 
the earlier prophases. After the segmentation of the spireme, the nucleolus 
disappears, but the manner of its disappearance was not determined. In 
sections showing the chromosomes in process of formation no fragments of 
the nucleolus were found. Fragmented nucleoli in some of the Liverworts 
have been observed. Farmer (’ 95 ) describes a fragmented nucleolus while 
the chromosomes were being formed in the spore mother-cell of Fossombronia 
Dumortieri He also describes a fragmented nucleolus at the time when 
the spireme splits longitudinally in Fegatella conica [Conocephalum conicum). 
Davis (’ 99 ) also found that the nucleolus in Anthoceros fragmented after 
synapsis. In Pellia epiphylla vacuolization and fragmentation of the 
nucleolus take place, according to Farmer (’ 95 ), during the formation of 
the chromosomes, and he thinks that it furnishes some material for the 
formation of the spireme and chromosomes. The fact that the central 
portion of the nucleolus stains less deeply in Preissia commutata prior to 
and during the segmentation of the chromosomes possibly indicates that 
some of its substance goes to the formation of the latter. But, as the 
greater part of it disappears after the formation of the chromosomes, it 
would seem that it contributes also to the formation of the spindle, if we 
accept the view of Strasburger (’ 05 ), Miyake (’ 05 ), Chamberlain (’ 03 ), and 
others on this point. It is to be regretted, however, that no direct evidence 
was obtained on this point in Preissia commutata , and that the way in 
which the nucleolus disappears was not observed. It apparently disappears 
quickly. 
After the second contraction, the spireme segments (Fig. 10). The line 
of the longitudinal splitting observed in sections illustrated by Figs. 8 and 
9 persists in the segments of the spireme (Fig. 10). The segments curve 
somewhat, sometimes throughout their entire length, sometimes at one end, 
in very much the same manner as was noted for the chromosomes in the 
somatic cells. The nucleolus shows no further change in its appearance 
than was noted at the second contraction. 
The segments of the spireme next shorten and thicken (Fig. 11). At 
this stage the chromosomes stain very deeply, and the split shown so clearly 
in Fig. 10 is now more difficult to see. It may sometimes be seen through- 
out the length of the segment, but the free ends show it plainly. As the 
chromosomes shorten and thicken they bend and twist in various directions 
(Fig. 11). The nucleolus has disappeared completely and the nuclear 
membrane is still intact. At a late stage of this prophase the split may be 
seen only at the free ends of the chromosomes. 
The achromatic spindle appears so quickly, its mode of formation was 
not determined. The results of efforts made to observe its formation will 
be given later. 
At metaphase the chromosomes are arranged on the equator of the 
spindle (Fig. 13), but thoar method of splitting was not clearly made out. 
