796 MORPHOGENESIS 



to correspond with the size of the resulting cell, instead of showing any 

 constant relation with the number of segments prior to the onset of 

 reorganization. If all but one or two of the macronuclear segments are 

 surgically removed, those remaining increase their surface values by 

 elongation or deformation. In other instances the requisite equilibrium 

 of surface relations between cytoplasm and nucleus is attained by nuclear 

 coalescence or fragmentation (Schwartz, 1935). Previously Burnside 

 ( 1929) made an unsuccessful attempt to set up divers biotypes by micro- 

 dissection methods. In some of his experiments the quantity of nuclear 

 material in one individual was two to three times greater than in another. 

 Regulatory processes ensued, such that individuals with little nuclear 

 material increased that amount; and individuals with large proportions 

 of nucleus to cytoplasm decreased that proportion within a few genera- 

 tions. 



Looper (1928) took advantage of the reincorporation phenomenon in 

 Actinophrys sol as an approach to the K/P problem. By mechanical 

 means, several individuals may be fused into temporary syncytia, and 

 non-nucleated individuals may be fused with each other or with intact 

 individuals. In this way he altered K/P either by increasing or decreas- 

 ing the cytoplasmic volume. The division rate in this species was ac- 

 celerated and the amount of nuclear material ultimately increased when 

 fragments of cytoplasm were added to the cytosome. Removal of cyto- 

 plasm retarded the division rate. The same method was employed by 

 Burch (1930) in studying the possible role of the karyoplasmic rela- 

 tionship as an inciting cause of cell division in pedigreed races of Arcella 

 vulgaris and A. rotunda. Following Hegner's (1920) hypothesis that 

 additional cytoplasm outside the sphere of influence of a single nucleus 

 in rhizopods may stimulate that nucleus to divide, Burch made daily 

 additions to or reductions in the volume of cytoplasm for different lines 

 of his pedigreed strains. Trauma alone was found to have little effect 

 upon the daily division rate. In general, the division rate varied directly 

 with volumetric alterations of the cytoplasm, but these variations were 

 not proportional to the volumes of cytoplasm gained or lost. As Wood- 

 ruff (1905), Gregory (1909), Conklin (1912), Moody (1912), and 

 others have suggested, Burch assumed that other intrinsic factors affect 

 the division rate to a great degree. Our inability to distinguish between 

 cause and effect further clouds the dying issue of the Kernplasmaver- 

 haltnis theory. 



