144 
Charles E. Allen 
Cytokinesis. 
Düring the anaphases (PI. VII, Figs. 50 — 53), a considerable number 
of connecting spindle fibers are present in the region between the separat- 
ing ehromosome groups. Some of the fibers are separate, others are 
gathered into a small number of bundles — perhaps, as Timberlake (1900) 
has suggested, because of the crowding of the fibers into the small spaces 
between adjacent ehromosomes. These bundles of fibers, as already 
noted, are different from those which were seen in the equatorial plate 
and metaphase stages (Figs. 35 — 37, 49), each of which consisted of fibers 
attaehed to a single ehromosome. The latter-mentioned fiber elusters 
are still visible in the early anaphases (Fig. 50), between the daughter 
ehromosomes and the respective spindle poles. Often, particularly in the 
later androgonial divisions (Figs. 52, 53) when the cells are smaller and 
the mitotic figure is consequently more compact, it is difficult to determine 
whether eertain spindle elements are single coarse fibers or elusters of 
fine ones. A few fibers, as in the prophases and metaphases, diverge 
from the poles in the general direction of the equatorial region, ending 
freely in the cytoplasm, or oecasionally upon the plasma membrane. 
The clustered arrangement of the fibers persists until the chromo- 
somes reach the poles (Figs. 54, 55) ; but soon (Figs. 57, 58) the individual 
fibers become more uniformly distributed, much as they were just previous 
to the completion of the equatorial plate (Figs. 31, 32, 34). The fibers are 
now (Fig. 58) more numerous than before, and their number continues 
for some time to increase (PI. VIII, Figs. 59 — 61). Of the new ones, many 
appear at the periphery of the spindle, whose equator therefore approaches 
more closely to the cell boundary. Others of the newly-formed fibers, 
however, are evidently inserted between those already present, so tliat 
the spindle as a whole grows gradually denser (PI. VII, Figs. 57, 58; 
PI. VIII, Figs. 59—61). 
A stage follows at which most of the spindle fibers become shorter, 
their ends pulling away from the ehromosomes (Fig. 59), so that a relatively 
clear space is left between each ehromosome group and the bodv of the 
spindle; through this clear space, how'ever, a few* fibers still run, apparently 
into contact with the ehromosomes. Figure 55, Plate VII, shows that this 
shortening of the fibers mav occur relatively early; but usually, as in the 
cell represented in Figure 59, Plate VIII, it is not observable until after 
a considerable increase has occurred in the number of the fibers con- 
stituting the spindle. It is commonly soon after this contraction that the 
daughter nuclear membranes are formed (Fig. 61), and after their appear- 
