NUCLEOPLASMIC RELATIONS IN ARCELLA 83 



uninucleates, half of the shell with its contained cytoplasm was 

 removed from certain specimens, yet in each case the uninucleate 

 progeny regained after a few generations the normal size of 

 the uninucleates of the line, and the binucleates later derived 

 from these subsequently reached the dimensions of normal 

 binucleates of the line. 



Confirmative data were obtained from the experiments per- 

 formed on the uninucleate half-specimen that appeared in the 

 cultures, and also from the microdissection experiments during 

 which one nucleus but no cytoplasm was removed. Most of 

 the specimens from which the nucleus only was removed assumed 

 the binucleate condition immediately, and as suggested on a 

 preceding page, this was probably due to the fact that the single 

 nucleus that remained was associated with a mass of cytoplasm 

 that extended beyond its sphere of influence. The normal 

 condition could be regained either by the acquisition of a second 

 nucleus or by a decrease in the mass of the cytoplasm. The 

 former process occurred in all cases. 



Arcella polypora. The observations and experiment on 

 Arcella polypora demonstrate that a constant mass relation 

 exists between cytoplasm and nucleus in these organisms even 

 more clearly than do those on A. dentata. 



In family ap. 5 the coefficient of correlation between diameter 

 and nuclear number was 0.752 ± 0.018 (table 15) even at a 

 time when selection was being practiced for large and small 

 diameters within the groups containing certain numbers of 

 nuclei. Later during a non-selection period the correlation 

 with respect to these characteristics within this family rose to 

 0.818 ± 0.023 (table 17). In family ap. 34 the coefficient of 

 correlation between the diameter of the shell and nuclear number 

 was 0.699 ± 0.020 (table 21). It is assumed that the diameter 

 of the shell is a reliable index of the size (mass) of the organism, 

 and hence it follows that in any particular family a large number 

 of nuclei is accompanied by a greater mass of cytoplasm than 

 a smaller number of nuclei. This relation between the num- 

 ber of nuclei and the cytoplasmic mass is also illustrated by 

 the data collected at the time when changes in the number of 



