NUCLEOPLASMIC RELATIONS IN ARCELLA 25 



Change from binucleaic to uninucleate condition (fig. 22) : One peculiar 

 departure from the normal occurred in this line. A binucleate speci- 

 men (with 14 spines and a diameter of 34 units) gave rise to a small 

 uninucleate offspring (with 11 spines and a diameter of 28 units). 

 The latter gave rise to a small uninucleate specimen and then formed 

 an empty shell and became binucleate; whereas, the parent passed 

 through empty shell formation and nuclear doubling immediately, and 

 then gave rise to binucleate progeny, normal in diameter and spine 

 number. The fact that empty shell formation and nuclear doubling 

 occurred at once in the parent and was delayed in the offspring sug- 

 gests that this process is initiated by the cytoplasm and takes place as 

 soon as a sufficient quantity of c^^toplasm is present. The normal size 

 of the progeny of the parent after nuclear doubling was probably pos- 

 sible because of the large capacity of the shell, and indicates that the 

 gradual increase in the size of specimens after nuclear doubling may be 

 due, as previously suggested, to the limited capacity of the shell, rather 

 than to the inability of the nucleus and cytoplasm to build up a suffi- 

 cient quantity of protoplasm. 



11-28(1) 11-28(1): 



14-34(2) — 12-S8 E 



^12-33(2) 



Fig. 22 Arcella dentata. Pedigree of part of the specimens reared in line 

 161a showing a change from the binucleate to the uninucleate condition and back 

 again. 



Experiment 4, line 162a. Progenitor: Uninucleate specmien from 

 line 161a; spines, 10; diameter, 26 units (fig. 21, C). 



Descendants: The 21 uninucleate descendants, 5 binucleate descend- 

 ants, and 2 empty shells recorded in this line were similar to those de- 

 scribed in line 158a. 



Experiment 5, line 164a. Progenitor: Uninucleate specimen from 

 line 162a; spines, 10; diameter, 26 units (fig. 21, D). 



Descendants: The 10 uninucleate specimens, 5 binucleate specimens, 

 and 3 empty shells recorded in this line were similar to those described 

 in line 158a. 



Change from binucleate to uninucleate condition: A binucleate specimen 

 (with 12 spines and a diameter of 29 units) gave rise to a larger binu- 

 cleate offspring (with 14 spines and a diameter of 31 units) and then to 

 a large uninucleate offspring (with 16 spines and a diameter of 35 units). 

 The parent retained only one nucleus, but immediately threw an empty 

 shell, regained the binucleate condition, and gave rise subsequently to 

 binucleate progeny. The large uninucleate offspring likewise immedi-. 



