404 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 
chromosomes in its body cell. Bearing in mind the description which 
has just been given of the organization of the chromatin material we 
may follow the steps involved in mitosis as they are outlined in this 
figure. In the “resting” cell at A the chromatin is scattered through- 
out the nucleus in clumps or knots loosely strung together to form an 
irregular network. As the cell prepares for division the chromatin 
elements appear in more definite form until at B the chromomeres have 
E 
Fic. 71.—Diagram of mitosis in a species having four chromosomes in its 
cells. A, the “resting” cell; B, formation of the spireme thread; C, longitudinal 
division of the spireme thread and transverse segmentation into four chromosomes; 
D, separation of the daughter chromosomes formed by longitudinal splitting 
of spireme thread; E, beginnings of nuclear reconstruction and division of the cell 
body; F, cell division complete and daughter nuclei in the “resting” stage. 
(From Babcock and Clausen.) 
arranged themselves in a single row in a long continuous spireme- 
thread. This spireme-thread may be considered to be made up of the 
four chromosomes united end to end with the chromomeres arranged 
in a linear series. As mitosis progresses to the next stage represented 
at C, each chromomere of the spireme-thread divides into two, so that 
a double spireme-thread results from the longitudinal splitting of the 
original thread. Both parts of the thread are quantitatively and quali- 
tatively equal, for, by the splitting of all the chromomeres both of the 
