22 



ROBERT W. HEGNER 



successfully on 6 uninucleate specimens, the operations con- 

 sisting in the bisection of the specimens so that one part con- 

 tained the nucleus. In every case the piece without a nucleus 

 died, but that with the nucleus lived and gave rise to uninucleate 

 offspring. 



16-36 



13-30 E 



13-33(2) 



14-31(2) 



-13-29(1) 



9-27(1) 



16-34(2) 



Fig. 20 Arcella dentata. Pedigree of part of the specimens reared in one of 

 the microdissection experiments (exp. 4). Note the reversion from the binucleate 

 to the uninucleate condition in the case of the fourth offspring of the original 

 progenitor. 



Experiment 1, line 158a. Progenitor: Fourth offspring (uninu- 

 cleate) of specimen 150.2b; spines, 10; diameter, 26 units (fig. 21, .4). 



Descendants: Uninucleates, 38; empty shells, 3; binucleates, 11. 



Reproduction: As rapid as before the operation. 



Immediate pror/eny: vSmaller than original progenitor and with fewer 

 spines; 7 in number, with mean spine number of 9 and mean diameter 

 of 23.14. 



Uninucleate descendants: These increased gradually in diameter and 

 in spin(^ numb(n- for three or four generations until the normal condition 



