296 Allen . — The Early Stages of Spindle- Formation 
drawn at this stage (Fig. 14) is unusually rich in fibrous 
material, also in c extra-nuclear nucleoles.’ It is very common 
to find a relatively clear zone surrounding the developing 
spindle (Figs. 13, 15, 16); apparently on the dissolution of 
the nuclear membrane the kinoplasmic weft presses into the 
cavity, leaving a clear zone between itself and the still present 
layer of granular cytoplasm. 
5. The Completion of the Spindle. 
The further history of the spindle is essentially what has 
been described by many of the writers already cited. The 
arrangement of the fibres into bundles becomes more regular ; 
the fibres forming the bundles are straightened out ; the 
number of poles decreases, apparently as a result of this 
straightening (Figs. 15-18), until the fibres all lie approxi- 
mately parallel, forming a c multipolar diarch 5 figure. 
By the time the chromosomes are arranged on the equatorial 
plate (Fig. 19), the spindle is fully formed. Its fibres con- 
verge, not to definite points, but into two polar regions. At 
first view they seem to end in these region's ; but by careful 
examination and focusing, the fibres, here very lightly stained, 
may be traced through the polar area into the cytoplasm 
beyond, where they spread out, still less deeply stained than 
in the body of the spindle, to form a system of polar radia- 
tions. The effect is very much as though the whole bundle 
of fibres seen in Fig. 18 had been constricted at two points, 
one not far from each end, and still allowed to spread out, 
fan-like, at the ends and in the equatorial region. The fibres 
can be followed from the polar region out into the peripheral 
region of the cytoplasm, but only occasionally as far as the 
plasma-membrane. No indication of any kind of central 
body has ever been seen in the polar region. Some polar 
radiations are seen which cannot be traced as continuations 
of the spindle-fibres ; such radiations are more numerous in 
the diaster stage (Fig. 20), and here also they diverge from 
a general region rather than from a distinct point, and no 
central body is to be found. 
