1900] DIVISION OF CELL AND NUCLEUS IN LIVERWORTS 397 
suppose that they appear before the radiations, for in fact centro- 
somes can be recognized during the reconstruction of the 
daughter nucleus after the radiations have disappeared (fig. 17). 
The dense center of the centrosphere, or the centrosome, is best 
seen previous to the appearance of the mature spindle as a dark 
round body at the center of many distinct radiations. There is 
no reason why it should not appear as a temporary body arising 
from some specialized cytoplasm, as kinoplasm. 
As the nucleus increases in length, the radiations become 
exceedingly distinct and extend farther over the nuclear mem- 
rane (fig. 2). They also penetrate the nuclear membrane, for 
any section of the nucleus at this stage will show them in its 
interior, Before they meet at the middle from the two centro- 
somes to form the spindle, the linin threads have become more 
conspicuous with thickened or knotty portions appearing as 
chromatin (fig. 3). This forms a network filling the large cen- 
tral part of the nucleus, but does not seem to extend into the 
Pointed ends. In no case was a continuous band or spirem 
observed, but a framework of linin at whose crossings or 
thickened parts chromatin gathers. These increase rapidly in 
Size, Separate by the dissolution of the intervening linin, and 
forma number of chromosomes. The number seems to vary. 
In one instance I counted five, in another eight. These are irregu- 
larly Scattered within the nuclear cavity (fig. 4). They are 
often in the form of irregular masses, but sometimes in the shape 
of straight or bent rods varying in size (fig. 5): When arranged 
: “a the nuclear plate, however, they are generally U-shaped, and 
fach is seen to be split longitudinally. 
The spindle fibers have now extended to the =o of the 
- “quator, the nuclear membrane disappears, and the spindle - 
_°tmed. At its center the chromosomes gather, arranging cen 
Selves at the circumference of the equatorial plane. The space 
- Clongates very rapidly. It is pointed, with the ee ae 
Yet Visible at either pole. In many cases it assumes a 4 
—« Urve like an elongated letter $ (fig. 8). In almost every instance 
eM this Stage this curve may be observed. Even those that seem 
Sepa Litas 
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