No. 639] GROWTH AND NUCLEAR DIVISION 337 



considerable accuracy the exact relation between cyto- 

 plasmic mass and nuclear division. For example, among 

 the specimens with four nuclei, there were a few with 

 three ''resting" nuclei and one nucleus in division (Fig. 

 3) ; obviously one of the four nuclei is undergoing divi- 

 sion before its three sisters. If the sum of the areas of 

 a number of specimens in which there are four nuclei of 

 equal size (Fig. 2) is divided by the total number of 

 nuclei, a fairly accurate idea may be ol)tained of the 

 amount of cytoplasm associated with each nucleus. Ac- 

 cording to the nucleo-cytoplasmic relation theory^ an 

 increase in the amount of cytoplasm as compared with 

 the amount of nuclear material furnishes the stimulus 

 which initiates nuclear division. A comparison between 

 specimens with four equal nuclei, and specimens with 

 four nuclei one of which is undergoing division, should 

 reveal approximately the increase of cytoplasmic sub- 

 stance necessary to inaugurate nuclear division. A num- 

 ber of cases of this sort were available in our material 

 and were studied with the following results. 



Table II shows the relations between area, and number, 

 volume and surface of the nuclei in the 207 specimens that 

 could be used for this purpose. The measurements were 

 made of camera-lucida drawings at a magnification of 

 650 diameters. Beginning with the group of 15 at the 

 top of the table w^e can make the following comparisons. 



1. Fifteen specimens, each with 4 equal nuclei (Fig. 

 2), have an average area per nucleus of 176.1 sq. mm. ; 10 

 specimens, each with 3 equal nuclei and a fourth nucleus 

 in division (Fig. 3), have an average area per nucleus of 

 185.0 sq. mm. The specimens in which division lias been 

 initiated hav<- .-ni nv.-rauv -Arm p.>r nucleus S.!) ...i. mm. 

 greater tlinii lliosc with ciju.-il niiinbci- u\' nuclei. iKuie 

 of which arc in .livlsi.ui. Wr li;iv,. u.d ilic ;nvn thi-ou-h- 



