VII.] 



MITOSIS OR KARYOKINESIS. 



143 



4. Monaster, Star, or 

 equatorial stage. 



5. Metakinesis or 



Divergence 



6. Dy aster or 



Double Star. 



7. Dispirem or 



Double Skein. 



8. Network or 



Reticulum. 



The achromatic spindle distinct with two poles, 

 terminating in two polar corpuscles (with 

 cytasters), nuclear membrane lost. The V-shaped 

 chromatin fibres arrange themselves in the equator 

 of the spindle. Cytoplasm separates into a clear 

 and a granular zone. 



Sister threads separate and move towards poles along 

 fibres of the spindle. 



Complete separation of the two sets of V-shaped 

 sister thread", towards the poles of the spindle. 



Open skein iu daughter nuclei passing into a close 

 skein. Nuclear membrane forming. Cell itself 

 divides. 



Kesting condition of daughter nuclei. Cytoplasm 

 divided, remains of spindle disappear. Chromatic 

 fibres more twisted. 



In the preparations one readily finds examples of these and the 

 other stages of mitosis. 



Mitosis. ])y far the best animals to use for studying the process 

 of mitosis are the larvae of the water-salamander. The young 



FlG. 106. Mitosis. A. Nuclear reticulum, resting-stage ; B. Preparing for division ; C. 

 Wreath stage ; I). Mouaster with achromatic spindle ; E. Barrel or pithode stage or 

 metakinesis, i.e., chromatin fibrils travelling along the achromatic spindle towards the 

 jioles ; F. Diaster ; G. Daughter wreath stage ; II. Daughter cells passing to resting- 



animals must be carefully'fed, else the mitotic figures are not well 

 seen. They are killed at various stages, when they vary in length 

 from | to i inch in length. They may be hardened in J per cent. 

 chromic acid. 



A very good hardening reagent is one-sixth p.c. chromic acid. 

 From a week to ten days is sufficient. If Flemming's mixture (p. 32) 

 lie used, the tissues must remain in it twenty-four hours or less. 

 Some prefer KabFs mixture (12-24 hours) (p. 31), others absolute. 

 alcohol or picric acid. After being " fixed " the tissues are placed in 



