THE TYPICAL CELL 



13 



their divergent migration until they finally reach opposite poles- 

 of the nucleus. From these points achromatic fibrils, (astf'al rays) 

 push into the nucleus, and, by union with their fellows of the 

 opposite pole, form the achromatic spindle. 



Meanwhile changes have taken place within the nucleus. The 

 nuclear wall and nucleolus disappear, and the entire chromatin 



FIG. 13. METAPHASE AND TELOPHASE OF MITOSIS. 



G-H, metaphuse ; J-J, telophase ; e p, equatorial plate ; i/, interzonal fibres ; n, neben- 

 kern. (After Wilson.) 



mass, now even more intensely chromatic, unites to form a single 

 coarse, thread-like, convoluted fiber, the chromatic skein or spi- 

 reme. The spireme soon breaks into a definite number of seg- 

 ments or chromosomes, the number of which varies as between 

 different animal species, but, as regards the individuals of each 



