100 
THE ORGANIC CELL 
differences which, however, do not affect the final result ; this 
in all cases consists of the equal longitudinal division of the 
chromosomes of the parent nucleus between the two daughter 
nuclei. 
The process of Mitosis includes three parallel sets of changes, 
affecting the nucleus, centrosome, and cytoplasm respectively. 
It is usual for descriptive purposes to divide it into a series of 
phases, which, it must be remembered, are not separated from 
one another by any sharp lines, but graduate gently one into 
the other. 
Phases of Cell Division by Mitosis or Karyokinesis : — 
[ 1. Resting nucleus. 
I. Prophases. j 2. Skein stage of chromatin, 
i 3. Segmented skein. 
4. Equatorial plate, and splitting of 
chromosomes. 
5. Movement of chromosomes to poles, 
and formation of 
6. Segmented daughter skeins. 
7. Reconstruction of nucleus. 
8. Division of cytoplasm. 
II. Metaphase. 
III. Anaphases. 
IV. Telophases. 
I. Prophases, (a) The Nucleus. — As a preparatory measure 
to division, the nuclear substance becomes altered both 
physically and chemically. There is a resolution of the chro- 
matin substance into a convoluted thread, known as the skein 
or spireme. On its first appearance, this skein is closely con- 
voluted, the ‘ close spireme ’ : shortly, however, there is a 
distinct shortening and thickening to form the * open spireme.’ 
The substance of the spireme now stains intensely, and for 
this reason can very easily be distinguished from the reticulum. 
The thread now segments transversely, forming a series of rod- 
like bodies called chromosomes. (See diagram, p. 102.) The 
chromosomes, though very often rod-like in shape, may assume 
other forms — they may be spherical, or even in the form of 
rings. At this stage of cell-division the chromatin possesses its 
maximum staining capacity. The membrane surrounding the 
nucleus fades away, the nuclear ground substance becomes 
