Size of Nucleus 179 



body sizes were fully attained before fission occurred. 

 If cut just before fission, then the fission proceeded 

 at the location already determined for it, in each of the 

 two instances studied. In these individuals also the 

 nuclei did not shrink, and the cytoplasms underwent 

 prolonged growth in the next generation. That the 

 nuclei shrank during regenerations of cytoplasm in 

 in Bursariae was believed by Sokoloff ('24), but ac- 

 curate measurements were impossible in this species. 

 It is also stated by Dembowska ('25) that the nuclei 

 of Stylonychiae shrank during regeneration, but no 

 measurements were given. 



Studies upon Ameba have been carried out repeated- 

 ly. Removal of cytoplasm led, according to Gruber 

 ('12), to shrinkage of nuclei; and, although measure- 

 ments of the nuclei were not published, the relative 

 numbers of individuals which showed shrinkage and 

 which did not, were reported. The fact that the cut 

 Amebae did not survive and reproduce in most cases, 

 may mean that cultural conditions were unfavorable. 

 These experiments were repeated by Phelps ('26), 

 measurements being given for one individual in which 

 the nucleus diminished in diameter after three days. 

 But the shape and proportions of the nucleus also 

 changed in that time. Moreover, the diminution was 

 greater after five days than after the first three, show- 

 ing that regeneration was not going on. Any respon- 

 sive adjustment of nuclear volume should be looked 

 for in the first few hours, one would suppose. In an- 

 other experiment by Phelps ('26) cytoplasm was cut 

 away on successive days, until the organism had only 

 about one-eightieth of the usual adult volume. But 

 in this instance the data regarding the size of the nu- 

 cleus show that the nucleus was then absolutely some- 

 what larger than in the average full-sized Ameba. 

 With the use of favorable and controllable cultural 



