114 THE BIOLOGY OF STENTOR 



manner. The macronucleus increases substantially as a rule only 

 during cell division ; therefore pre-division stentors, as they grow, 

 will come to have a decreased nucleo-cytoplasmic ratio or the 

 need for more nuclear material, which will be redressed only 

 during subsequent fission. If regeneration is then brought about, 

 a stentor can take this opportunity of primordium formation to 

 make up its lack and increase the number of macronuclear nodes. 

 Then he found that when this happened and the stentor was caused 

 to re-regenerate there was now not an increase in nodal number 

 because the normal nucleo-plasmic ratio had already been 

 achieved; and if substantial parts of the cytoplasm had been 

 removed there might even be a decrease in number or coalescence 

 of nodes. However, in all this Schwartz doubted that there was an 

 actual change in macronuclear volume and believed it more likely 

 that the adjustment was largely an increase or decrease in the 

 effective surface of the nucleus. Yet, in grafts of two stentors 

 sharing but one macronuclear node I found an indubitable increase 

 in nuclear mass at the end of regeneration (see Fig. 86b). 



When a stentor is transected across the longitudinal axis the 

 macronucleus is distributed about proportionally; the posterior 

 fragment has to regenerate a new set of feeding organelles, while 

 the anterior does not and serves as a control. Comparing these two, 

 Weisz (1949a) found that in the posterior piece only does macro- 

 nuclear coalescence occur, as an accompaniment of primordium 

 formation. More recently, Guttes and Guttes (1959) have found 

 that mitotic division also occurs only in the posterior fragment, 

 or at least this was demonstrable in 17 out of 125 cases. No mitoses 

 could be found in either the anterior fragments or in uncut 

 controls not undergoing fission. If the exact time of mitosis is 

 somewhat variable, this could account for their not always finding 

 it. They noted the similarity between their results and those of 

 Schwartz, who deduced that micronuclear multiplication occurs 

 during reorganization along with macronuclear increase. The 

 results showed that mitotic multiplication of micronuclei, as well as 

 increase in the number of macronuclear nodes (see above) can take 

 place in regeneration ; for only the posterior fragments would have to 

 form an oral primordium to replace the missing feeding organelles. 

 This is in accord with demonstrations of mitosis in other ciliates 

 during regeneration (Lewin, 191 1 ; Suzuki, 1957; and Yow, 1958). 



