26 ROBERT W. HEGNER 



ately passed through the nuclear doul^hng process. This case is some- 

 what different from those recorded above, but the same hypotheses 

 regarding the relation between shell size, cytoplasmic mass, and nuclear 

 doubling may be applied successfull^^ 



Experiment 6, line 165a. Progenitor: Uninucleate specimen from 

 Hne 164a; spines, 11; diameter, 25 units (fig. 21, E). 



Descendants: 15 uninucleates. 1 binucleate, and 2 empty shells. 

 Specimens were kept until nuclear doubling occurred. 



Discussion of experiments: The experiments described above 

 show very clearly that there is a rather definite mass relation 

 between the nuclei and the cytoplasm in these organisms. They 

 also throw light upon the influence of this nucleocytoplasmic 

 relation upon cell division, and emphasize the fact that the 



14-31 (2 ) 14-32 f 2 ) 



16-35fl): 



12-29(2) 



13-32(2) 



Fig. 23 Arcella dentata. Pedigree of part of the specimens reared in line 

 164a showing change from the binucleate to the uninucleate condition and back 

 again. 



removal of the chromidia, Avhich were embedded in the cytoplasm 

 that was cut away, has no efTect upon the characteristics of the 

 family. Among these characteristics are the binucleate condi- 

 tion, a mean spine number of about 14, and a mean diameter 

 of about 34 units. Modifications may occur and parts of the 

 organism may be removed generation after generation, but as 

 long as part of a shell remains, containing a nucleus and a small 

 quantity of cytoplasm, the line is capable of regaining its normal 

 characteristics. 



