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1903] STUDIES {N SPINDLE FORMATION 89 
ward, the nuclear membrane disappears rapidly, and the ends of 
the fibrils at the base of the cones become attached to the 
chromosomes. 
The sequence of events which leads to the bipolar condition 
of the spindle is essentially the same as that described for Iris. 
Upon the breaking down of the nuclear membrane the apices of 
certain of the cones move toward each other and form several 
groups of cones. These in turn unite still further, until we have 
the characteristic so-called multipolar spindle. Fig. 16 shows 
a stage approaching the bipolar condition. The connective fibers 
which attach themselves to the chromosomes become more 
sharply defined than the other fibrils, and appear to be thicker 
in the region of the chromosomes, as if they had already 
begun to contract. By the time the chromosomes have arranged 
themselves at the equatorial plate, the cones have united into 
two groups, which are the poles of the bipolar spindle. The 
mature spindle does not show the free mantle fibers which are 
so characteristic of Cobaea, Gladiolus, Iris, and many other 
forms. There are a few delicate continuous fibrils, which extend 
from pole to pole. The connective fibrils are much coarser than 
the continuous ones, stain more deeply, and are much more 
clearly defined. In the bipolar stage of the spindle, these fibrils 
appear to be much thicker in the region of the chromosomes, 
which suggests that they have not begun to contract, but that 
the chromosomes imparted the stimulus to contract. This con- 
dition of the fibrils is shown in fig. 77. 
As the chromosomes (eight in polar view) approach the poles, 
the connective fibrils shorten and thicken, and by the time they 
have reached the poles the connective fibrils have disappeared 
entirely; the continuous fibrils, however, have increased in 
numbers, Having reached the poles, the chromosomes unite 
and form a mass of chromatin at each end of the spindle. 
Nuclear sap is now secreted, and a membrane is formed about 
each daughter nucleus. 
The daughter nuclei are small, and the various stages in the 
development of the spindle of the second division were difficult 
to follow. The early weft stage, however, was observed, as well 
