12 HEREDITY IN RELATION TO EUGENICS 



Fig. 2. — Diagrams showing a series of stages in the process of division of 

 the chromosomes during cell division. A. Resting cell in which the chromatic 

 material lies (apparently) scattered through the nucleus: at c is a pair of 

 recently divided central bodies (centrosomes) which come to be the centers of the 

 forces that separate the chromosomes. B. The chromatin has fallen into the 

 form of a thick ribbon or sausage-like body, outside of which lies a dark body 

 which is called the "nucleolus." The centrosomes are moving apart. C. The 

 centrosomes now lie far apart and the thin membrane around the nucleus is 

 beginning to disappear — a process completed in D, where a "spindle" is seen 

 lying between the two centrosomes. The chromosomes are beginning to move 

 under the influence of the new forces centered at the centrosomes. E. A later 

 phase in which changes of two sorts are taking place in the chromosomes; 

 first, they are moving to an equatorial position between the two poles, and, 

 secondly, they show their double nature by virtue of which the subsequent 



