98 Wisconsin Academy of Sciences , Arts and Letters . 
Distinct fibers running continuously from pole to pole can be 
easily distinguished between others, often considerably heavier, 
which end at the chromosomes (Digs. 10 and 11). In the 
metaphases, the spindle at times shows a peculiar zonated ap¬ 
pearance, a dark band running across it in one or two places 
between the equatorial plate and the poles. These dark bands 
are symmetrically placed in the two halves of the spindle and 
seem to be due to a thickening of the fibers at these regions. 
This suggests the possibility that in the living cell there may 
be waves of contraction passing over the spindle. The fact 
that such zonated spindles are not often found in fixed ma¬ 
terial does not argue strongly against this possibility, for it is 
only under an exceptionally favorable combination of circum¬ 
stances that the fixation of such “waves” could be expected. A 
more important argument against this possibility lies in the 
fact that in studies which have been made on karyokinetic fig¬ 
ures in living cells nothing has been observed, as far as I am 
aware, of waves of contraction passing over the spindle. The 
difficulty of observation here, however, discounts the conclu¬ 
siveness of a negative result. 
The chromosomes on any spindle show considerable differ¬ 
ences between themselves both in form and size, differences 
which are, if anything, even more marked in the late diakine- 
sis stages and shortly after the breaking down of the nuclear 
membrane. Equally remarkable is what may be called a phys¬ 
iological difference between the chromosomes. There are regu¬ 
larly found around the periphery of the spindle small chromo¬ 
somes whose halves separate considerably earlier than those of 
the other chromosomes, so that they are halfway to the poles 
when the halves of the others are still together at the equator 
of the spindle. It seems that for my specimens of M. quadri- 
folia this is a regular occurrence. Strasburger observed that 
in the equatorial plate stages of M. drummondii a varying num¬ 
ber of chromosome pairs separate before the others; but he 
finds this associated with a more or less abnormal course of 
division, and refers it to a diminished attraction between ho¬ 
mologous chromosomes. In its extreme case, this diminution in 
