156 FOOT-NOTES TO EVOLUTION. 
each segment receives a series of fibrils from each pole 
of the amphiaster, the two series being attached along 
opposite sides of the chromosomes, Under the influence 
of these fibres, probably by direct pulling, the chromo- 
somes, now bent into V- or U-shaped loops, tend to place 
themselves in a circle around the centre of the spindle, 
transversely to its long axis, and form the “ equatorial 
plate” (Fig. 5, 2). 
The changes thus far constitute the “ prophases ” of 
the division. The “metaphases” following these con- 
sist primarily in the longitudinal splitting 
of each chromosome and the moving 
apart of the halves. This longitudinal 
splitting of theechromosome into two equivalent parts 
forms the most important act of the whole cell division, 
and is of the greatest theoretical significance. By it 
the chromatin substance of the original nucleus is equally 
distributed between the two daughter nuclei, so that 
each receives a half of each original chromosome. The 
elaborate mechanism and consequent expenditure of 
energy involved in this careful longitudinal division of 
each chromosome, rather than a simple mass division, 
such as might be brought about by far less complicated 
means, indicates clearly that the distribution of the defi- 
nite organization of the chromatin to the daughter cells 
is of primary importance, a conclusion which is further 
strengthened by much evidence too extended to be en- 
tered upon here. 
In the ““anaphases” and “telophases,” which in- 
clude the closing stages of division, the daughter chro- 
mosomes migrate along the fibres of the central spindle 
toward its poles, perhaps through the direct contraction 
of the mantle fibres under the influence of the centro- 
some, though this and many other points regarding the 
forces at work must be left for future investigation 
Splitting of the 
chromosomes. 
