THE AMERICAN NATURALIST [Vol. LV 



out our work as a measure of cytoplasmic mass, hence it 

 appears from the results of our measurements that an 

 increase in mass per nucleus represented by an increase 

 in area within the limits of 8.9 sq. mm. is the stimulus 

 that initiates nuclear division. The exact mass of cyto- 

 plasm represented by this increase in area of 8.9 sq. mm. 

 might easily be obtained under more favorable cir- 

 cumstances. 



2. When we compare the measurements of the 10 speci- 

 mens with 4 nuclei, one of which is dividing (Fig. 3) with 

 13 specimens of the stage immediately following, with 3 

 large nuclei and two that have just reorganized after 

 division (Fig. 4), we find that although the latter average 

 111.6 sq. mm. larger per specimen the average area per 

 nucleus is 14.7 sq. mm. less. Thus there has been an 



