BEHAVIOR AND FUNCTIONS OF THE NUCLEUS 291 



portion of the macronucleUvS is sufficient for regeneration and 

 survival, implying that this nucleus is highly polyploid, with 

 representation of the complete genome throughout. The develop- 

 ment of internuclQSir differences as in mating type determination 

 in certain ciHates is of course a demonstrated fact. Had regular 

 intranuclear differences been confirmed, we would have been 

 provided with another and most excellent means for analyzing 

 nuclear functions. Our disappointment is however mitigated by 

 the consequence that we are now apparently free to continue 

 experiments on ciliates without having to take into consideration 

 an additional factor of varying capacities within the macronucleus. 



5. Shape, size and number of nuclear nodes 



When he removed all but a single node of the macronucleus 

 from coeruleuSy Prowazek (1904) found that the remaining bead 

 became much elongated and spindle shaped. Schwartz (1935) 

 observed the same, as well as that the remaining node may 

 become much flattened like a ribbon. Cases from my own observa- 

 tion are shown in Figs. 82A and 86c. These increases in the nodal 

 surface are as if to compensate somewhat for the great diminution 

 in nuclear volume. 



Starting from a single node, the nuclear chain is regenerated 

 during episodes of primordium formation. Two reorganizations 

 seem to be required to recover the typical nodal number from a 

 single bead. This number is quite variable and in coeruleus is 

 between 6 and 20, with a mode around 15. K. M. Moller (unpub- 

 lished) has a race with a mode of lo-ii nodes and suspects that 

 the average number may prove to be a racial characteristic. When 

 de Terra (1959) implanted into enucleate coeruleus 2 macronuclear 

 nodes labeled with adenine-Ci4 she found that the regenerated 

 nuclear chain was labeled throughout, confirming the cytological 

 picture that this regenerative growth is not accomplished by simple 

 addition of new nodes. Instead, the implanted nodes increased 

 greatly in size, coalesced, and renodulated into many nuclear beads 

 from a common pool of macronuclear material. 



Although the nucleus readily adapts by increase in size, the 

 occasions when it should decrease give an entirely different 

 impression. It appears difficult for the cell to take down or diminish 

 a too-large macronucleus. Starving stentors with decreasing 



