178 Gardner — Studies on Grozvt/i and Cell 



stages of its formation, as one would expect, are vciy difficult 

 to find, for the deeply stained chromosomes obscure the first 

 traces of the nucleolus. That the chromosomes employ their 

 chromatin to form the nucleolus is easily demonstrable in 

 slightly later stages. As the chromosome coil gives up its 

 chromatin elements, it loses its dark color gradually. At first 

 these chromosomes are full of the dark chromatin granules ; 

 these become fewer and fewer as the nucleolus becomes 

 larger and more distinct. The chromosome coil or skein now 

 appears crimson. Many stages can be found (Figs. 17, 18, 

 19), where a few deeply stained chromatin granules can still 

 be seen in the thread. 



Finally nearly all the chromatin is passed from the crimson 

 thread to the nucleolus. The thread soon loses its evident 

 connection with the nucleolus, and spreads out to form the 

 nuclear reticulum. The nuclear membrane reappears during 

 the time the nucleolus is being formed. When the nuclear 

 membrane reappears, the first traces are always on the outer 

 poles of the differentiating nucleus. 



Often instead of forming one nucleolus, the chromosomes 

 empty their contents so as to form two nucleoli (Fig. 19). 

 The two nucleoli may fuse before the resting stage is reached 

 or as perhaps more frequently occurs, they never fuse, but 

 exist as two nucleoli in the resting cell. 



The daughter nuclei becoming complete, division of the cell 

 is completed. This occurs by a pushing in of the protoplasm 

 from the two opposite walls of the cell until these inpushings 

 meet in the center. The spindle becomes fainter and gradu- 

 ally is lost. The division wall becomes distinct, the daughter 

 nuclei perfectly formed and division is complete. 



Function of the Nnclcolus. — From the above observations 

 it is impossible to regard the nucleolus as a nutritive centre. 

 The nucleolus is, at least in large part, a mass of chromatin 

 material, packed together in a rounded form, during the resting 



