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THE PHYSICAL BASIS OF HEREDITY. 157 
to decide (Fig. 5, #). Arrived at the poles the V- 
shaped chromosomes become grouped in a star-shaped 
figure, the “aster,” their outer ends become again 
joined together in the form of a tangled skein, the in- 
dividual chromatin granules separate somewhat along 
the threads of the linin network, their deeply staining 
quality is decreased, and a new nuclear membrane devel- 
ops around each group of chromosomes. Simultaneous- 
ly with this the cytoplasm constricts across the middle 
of a somewhat elongated cell, resulting in complete di- 
vision in the equatorial plane of the spindle, and two 
separate daughter cells result. Each of these is made 
up of cytoplasm containing a centrosome and a nucleus, 
similar in all respects to the parent cell from which it 
-has arisen. 
A simple tabulation of the changes just described is 
as follows: 
Phases of Cell Division by Karyokinesis. 
I. Prophases.... Skein stage of chromatin. 
1. Resting nucleus. 
2; 
3. Segmented skein. 
4. 
II. Metaphase.... | Equatorial plate and splitting of 
chromosomes. 
5. Movement of chromosomes to poles 
III. Anaphases.... and formation of 
6. Segmented daughter skeins. 
IV. Telophases.... ) 7: Reconstruction of nucleus. 
8. Division of cytoplasm. 
It is readily seen that the culmination of the process 
lies in the splitting of the chromosomes and the separa- 
tion of their component halves to form the two new 
daughter nuclei. 
In the foregoing description of the changes typ- ° 
ically passed through by an animal cell in division, 
