790 MORPHOGENESIS 



ments were also incapable of dividing. In the case of U. setigera, nor- 

 mally with one micronucleus, only one of the two halves of a bisected 

 cell was able to divide, although form regeneration occurred in both. In 

 U. hinucleata, with two micronuclei, both halves were successful in 

 regeneration and division. It appears from these observations that while 

 form regeneration is possible in amicronucleate Uronychia fragments 

 under special conditions, the micronucleus is indispensable for ultimate 

 physiological regeneration. Dembowska (1926) was unable to find evi- 

 dences of regeneration in amicronucleate pieces of either U. setigera or 

 U. transfuga. 



Euplotes patella does not live longer than a few days or divide more 

 than twice, in the absence of the micronucleus. Using a mercury micro- 

 pipette, Taylor and Farber (1924) demonstrated that portions of the 

 cytoplasm or macronucleus could be removed without serious conse- 

 quences, whereas the removal of the micronucleus with only a small vol- 

 ume of the surrounding cytoplasm ultimately proved fatal. In several 

 of their experiments on E. patella, the micronuclei were completely with- 

 drawn from the organism and then immediately replaced. The animals 

 so treated subsequently gave rise to vigorous cultures. They concluded 

 that the micronucleus plays more than a germinal role in the life his- 

 tory of Euplotes. 



A majority of the publications bearing on regeneration in ciliate frag- 

 ments contain casual references to the nonviability of amacronucleate 

 pieces, but very few have treated the matter at length. 



The vegetative individuals of Blepharisma undulans (Moore, 1924) 

 are incapable of regenerating in the absence of macronuclear material. 

 However, if cuts are made during the early phases of division, such 

 pieces sometimes regenerate. Moore found that regeneration was fol- 

 lowed by immediate dedifferentiation in all of these cases; the dedif- 

 ferentiated fragments ultimately disappeared without dividing, in spite 

 of the fact that some of them were known to contain as many as six 

 micronuclei. According to the evidence presented, there appears to be 

 no doubt that the restoration of external organelles may proceed in the 

 absence of the macronucleus // the initial steps in the division process 

 are under way at the time of cutting. From a posterior fragment possess- 

 ing only a part of the developing membranelles, an organism of nearly 

 perfect form may arise. The peristome, adoral zone, and undulating 



