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MURIEL ROBERTSON. 
it. One or two points can, however, be observed. It has been 
noticed that the nucleus immediately before division 
always shows a dense staining karyosome which disappears 
during the formation of the primitive spireme (fig. 9). There 
is, of course, no proof of the converse, and it by no means 
follows that because the nucleus shows a dense kaiyosome it 
is therefore about to enter upon division. In the work on 
Clathrina a corresponding point was observed, namely, that 
cells about to divide showed a pale nucleus containing a dense 
karyosome. Another point in the life of the cell can, as it 
were, also be caught, and that is the period immediately after 
division. The young daug'hter-cells have certain characteristic 
features to be noted later, and can readily be recognised. 
The nucleus in these cells is always of the reticulate type, and 
does not show the karyosome (fig. 21). Whether this be- 
haviour on the part of the karyosome may prove of importance 
when we know more of what induces a cell to divide cannot 
be determined at present, but is worth recording in passing. 
Mitosis. 
The first alteration to be observed in a collar-cell about to 
divide is usually the disappearance of the flagellum and the 
subsequent division of the blepharoplast, which has at this 
stage lost its connection with the nucleus. The exact 
sequence of these early processes is, however, subject to 
a good deal of variation, and sometimes the flagellum is 
retained until after the division of the blepharoplast (fig. 10). 
In the nucleus itself very characteristic changes take place, 
culminating in a curious phase which is of very constant 
occurrence and which corresponds to the spireme-stage. The 
dense karyosome gradually breaks up (figs. 3-10), and there 
are formed a number of masses of chromatin which become 
increasingly definite in appearance; they are connected 
together at this stage by delicate filamentous strands which 
do not take up the chromatin stains. This condition 
corresponds to the spireme-stage, which never reaches a 
