No. 639] GROWTH AND NUCLEAR DIVISIOX 343 



6 (equal) 154.5 sq. mm. 



6 (one in division) 172.1 sq. mm. 17.6 sq. mm. 



7 (equal) 152.4 sq. mm. 



7 (one in division) 168.1 sq. mm. 15.7 sq. mm. 



These figures, of course, indicate only the relative in- 

 crease necessary to stimulate nuclear division; the actual 

 increase could be determined by measuring accurately the 

 mass of cytoplasm in each case. 



crease in age and the constancy of the area per nucleus. 



In looking over our camera drawings it was noticed 

 that usually only one nucleus was in division in any one 

 specimen (Figs. 3 and 6) and that in many cases two of 

 the nuclei in a specimen were smaller than the rest (Fig. 

 4), indicating that they were daughter nuclei that had 

 just emerged from mitosis. Of a total of 137 specimens 

 in which nuclei wore found in division, 109 contained one 

 division figiii-c, 1!) t'ontniiicd 2, S coiitniiu'd .'>, and 1 con- 

 tained 4. Furtlicniioro. those containin^ir more than 



