NUCLEOPLASMIC RELATIONS IN ARCELLA 9 



tion of empty shells and the regaining of the binucleate con- 

 dition. Empty shells were formed at irregular intervals, and 

 in every case the parents, on examination, were found, after 

 empty shells were thrown off, to possess two nuclei instead 

 of a single nucleus. The next offspring produced by these 

 binucleate parents also possessed two nuclei and were always 

 larger and had more spines than their parents or the empty 

 shells (fig. 10). The offspring of these binucleate progeny were 



11-26 E 



IS. 29 f 2 ) 13-32 (2 ): 



11-27(1) 



(150. 2b. 2. 1.1) 



10-25(1); 

 (150. 2a. 1.1. 2.1) 



13-33(2) 



14-30(2) 14-34(2) —12-35(2) 16-34(2) 



13-30(2) 13-34(2) 



-10-29(2) 15-33(2) 14-34(2) 16-35(2) 



.11-25(1) 



11-25(1)- 

 (150.2a.5.3)~ 



-11-29(2) 13-30(2) 14-32(2) 13-34(2) 



Fig. 10 Arcella dentata. Parts of the pedigrees of specimens belonging to 

 family 150, showing the relative size of uninucleates, empty shells, and binu- 

 cleates, and the gradual increase in size of the binucleates imtil the 'normal' 

 dimensions are attained in the third or fourth generations. The empty shells are 

 indicated by the letter E and the number of nuclei by the numbers in parentheses. 



likewise binucleate and were again larger and had more spines 

 than their parents. Thus the members of each generation after 

 empty shell formation and nuclear doubling exceeded those 

 of the preceding generation in spine number and in diameter 

 until the specimens attained an average for these characters 

 equal to that of the line before the operation was performed. 

 The attainment of this condition required, as a rule, three or 

 four generations (fig. 11). Tables 2 and 3 give the data for 



