84 Regulation of Size in Unicellular Organisms 



multiple progeny were maintained for several genera- 

 tions, but usually this was true in only one of the pro- 

 geny of each fission. In the instances investigated, 

 the unusual individuals either regulated back to nor- 

 mal by multiple fissions, or died. There are no exact 

 measurements of size in such progeny. Kiihn ('16) 

 noted that in a general way the cytoplasm was dis- 

 tributed proportionally to the number of nuclei in mul- 

 tiple Amebse. 



Sometimes the fission of the cytoplasm is absent 

 while nuclear division occurs. Blochmann ('88) de- 

 scribed the rejection of mitotically produced half- 

 nuclei in Euglypha, and remarked on its resemblance 

 to the formation of polar bodies in eggs. In Euglypha 

 a new shell was also formed, the rejected half-nucleus 

 being deposited within it. Hegner ('20) described the 

 formation and rejection of shells alone in Arcella. This 

 was observed to occur only in individuals which had 

 been deprived of one nucleus, the binucleate condition 

 being usual. The rejection of a shell always accom- 

 panied the formation and retention of two nuclei from 

 the single one. That cytoplasm and nucleus together 

 should go through such a partial process is striking. 



Among some heliozoa and a few other multinucleate 

 species, all numbers of nuclei between one and several 

 hundred nuclei per individual can be found. The fac- 

 tors that determine when the cytoplasm shall divide 

 are apparently here wholly unrelated to the factors 

 for nuclear division, except of course for the limitation 

 that no cytoplasmic portions separate without nuclei. 

 It is usual in these species for both cytoplasm and nuclei 

 to divide into two equal or nearly equal aggregates. 



Chamber progression. Some data upon the relative 

 volumes of individuals exist in the instances of what 

 may be interpreted as a very interesting variety of in- 

 hibition of fission occurring normally in the shelled 



