The Visible Basis op Heredity 69 



adult (Plate II, p. 26). Cell division at times 

 may be a very simple process. The nucleus 

 elongates, becomes dumb-beU shaped, and 

 pinches apart to form two new nuclei. The cell 

 body goes through a similar performance, and 

 each new nucleus hes in one of the new cells. 

 But in most cases cell division is much more 

 complicated. The physical condition of the 

 cell protoplasm varies much; at times it is fluid, 

 again gelatinous, and it may assume a fibrous 

 or spongy structure with fluid materials in the 

 meshes or spaces. As the nucleus prepares for 

 division its substance assumes this latter con- 

 dition. At the points of juncture of the fibrous 

 strands there are found granules that stain 

 very deeply with certain chemical substances; 

 this deeply staining material has hence been 

 called chromatin. As the early division stages 

 come on in the cell the spongy network becomes 

 coarser and the chromatin granules unite to 

 form larger grains (Fig. 6, B and C). Many 

 strands of the fibrous mesh break, others appear 

 to contract and draw the grains of chromatin 

 closer together until finally this nuclear material 



