8 ROBERT W. HEGNER 



If-. E7npty shell formation and nuclear doubling. At first it 

 appeared that a smaller, uninucleate line of Arcellas had been 

 established by the cutting experiments, but soon a most inter- 

 esting phenomenon occurred at the time of division in the case 

 of certain of these uninucleate specimens; this was the forma- 



13-35 

 (1E0.2) 



150,2a 



9-26 



150.21) 8-25 



11-26: 



10-26 



10-26- 



10-26- 



10-26 11-25- 



9-25 ll-?5- 



10-26 12-27- 



11-27 10-27- 



-12-27 



-10-26 



■10-26 



-H-26 

 -11-26 

 -10-26 

 ■11-26 



— 10-26 



Fig. 9 Arcella dentata. Part of the pedigree of the two lines, 150.2a and 

 150.2b resulting from the bisection of specimen 150.2. 



TABLE 1 



Ai'cella dentata. Table showing differences in mean spine number and in mean 

 diameter for the first four generations of lines 150.2a and 150.2b, exclusive of 

 empty shells and the progeny of binucleate specimens. The unit of measurement 

 is 4-S M 



