NUCLEOPLASMIC RELATIONS IN ARCELLA 81 



hence have each an equal amount of cytoplasm with which to 

 interact. This is very clearly indicated in figures 30 and 34, 

 which show the positions of the nuclei in typical specimens 

 of Arcella polypora. That the nuclei are free to move about to 

 a certain extent is shown in figure 47, which gives the positions 

 assumed by the two nuclei of a specimen of Arcella dentata 

 at intervals of about twenty-four hours. It seems clear, there- 

 fore, that they are not held in place by a network of fibers or by 

 other structures in the cytoplasm. Also, when nuclei are forced 

 out of place by pressing upon the shell with a blunt needle, 

 they become equidistant from one another again in a short 



Fig. 47 Arcella dentata. Outlines of a specimen showing the positions of 

 the two nuclei at intervals of twenty-four hours. One nucleus is represented by 

 a solid circle, the other by a dotted circle. Their positions are numbered as fol- 

 lows: 1, March 14; 2, March 15; 3, March 16; 4, March 18. X 207. 



time. The freedom of the nuclei from cytoplasmic attach- 

 ment was strikingly exhibited during the microdissection experi- 

 ments, since a slight pressure on the shell, after a break had 

 been made near them (fig. 18), was sufficient to cause them 

 to pop out through the shell opening, usually in a condition 

 entirely free from any accompanying cytoplasm. 



The principal data that have been presented in the preced- 

 ing pages in favor of the presence of a definite quantitative 

 relation between nucleus and cytoplasm may be summarized 

 briefly as follows: 



Arcella dentata. When part of the shell and a small portion 

 of the cytoplasm were remo^'ed, but both nuclei were left intact. 



