2s6 



BIOLOGY AND ITS MAKERS 



show in resting-stagcs 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 



chr 



D 



/ 



^^^s^S^K r 



-^ 





chr 



^A 



'Ml': 



G 



^^i. 



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

 (After Parker as altered from Fleming.) 



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

 h^ and c. 



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

 deeply staining protoplasm, usually just outside the nuclear 



