256 



BIOLOGY AND ITS MAKERS 



show in resting-stages of the nucleus; their substance is 

 present, but is not aggregated into the form of chromosomes. 

 Fig. 78 shows tissue cells, some of which are in the divid- 

 ing and others in the resting-stage. The nuclei in process of 



nu/rv 



D 





G 



M 



^# 





Fig. 79. — Diagram of the Chief Steps in Cell-division. 

 (After Parker as altered from Flemming.) 



division exhibit the rod-like chromosomes, as shown at a, 

 b, and c. 



Centrosome. — The discovery (1876) of a minute spot of 

 deeply staining protoplasm, usually just outside the nuclear 



