AND OF HYBRID PIGEONS. 
23 
The large thick spindle fibers do not seem to persist at the 
equator after the chromosomes have divided. They may be 
seen extending from the chromosomes to the pole as long as 
the chromosomes are moving poleward, but when the chromo¬ 
somes have reached their goal, the fibers disappear. A system 
of distinct interzonal fibers exists, but they are plainly the linin 
filaments which have been left stretched between the separating 
chromosomes, and are not the remnant of the original spindle. 
They are much more delicate than the spindle fibers and have 
an entirely different appearance. Occasionally bits of chro¬ 
matin may be seen imbedded in their substance (Fig. 13). As 
the division proceeds these fibers gradually constrict in the 
region of the equator and acquire the well known hour-glass 
shape. They ultimately fuse at the equator and form a distinct 
band-like intermediate body (Fig. 13) which may persist even 
after the new cell walls are formed and the cells are no longer 
contiguous. 
Before the final division of the cytoplasm is completed, the 
nuclear reconstruction is well under way. A clear area between 
the centrosome and the chromosomes persists for some time, 
but it finally becomes obscured and the centrosome is lost to 
view. The new nuclear membrane forms first on the side of 
the nucleus av/ay from the centrosome. 
At times the chromosomes break up into a number of 
smaller bodies or granules while yet in transit toward the pole, 
but usually they remain intact. As soon as the chromosomes 
cease their progressive motion, and sometimes before, they fuse 
with one another (Fig. 13) into a dense mass which ultimately 
spreads about in such a way as to form the new network with 
its distribution of chromatin. None of the details of this pro¬ 
cess could be determined because, after the vesicular condition 
consequent upon the fusion of the rings, very few stages could 
be found. This fact would indicate that the process is one of 
very short duration. It is doubtful in some cases, indeed, if 
they go into a resting condition before the next division. 
While the above transformations are occurring in the nu¬ 
cleus, the cytoplasm seems to remain in a quiescent state. It 
has the general appearance of a homogeneous substance in 
