AN AMICRONUCLEATE OXYTRICHA 505 



bolic change occurs than is implied by mere nutrition, consider- 

 ing that, in the present case, there is an addition of elements 

 derived from similar cytoplasmic and nuclear constituents. 



5. DISCUSSION 



The most recent researches have seemed to show conclusively 

 that, though ciliates may exist in an apparent amicronucleate 

 state at certain periods of their life-history, sooner or later a 

 micronucleus or chromatin equivalent to that contained by a 

 micronucleus takes on a definitive form. Studies on the ciliates, 

 Opalina, Trachelocerca, Ichthyophthirius, and Blepharisma, 

 have revealed that their amicronucleate condition exists only 

 during part of the life-history. However, in all the Hypo- 

 trichida studied to date a micronucleus has invariably been found 

 as a normal cell constituent, although both temporary or per- 

 manent disappearance of this organelle have been described 

 under certain conditions. Thus Maupas ('88) stated that the 

 micronucleus in pathological cultures of Onychodromus grandis 

 disappeared entirely. R. Hertwig ('89) questioned this state- 

 ment and suggested that Maupas might possibly have over- 

 looked the presence of the micronucleus, since he himself 

 had often found great difficulty in observing micronuclei in 

 Paramecium. 



Calkins ('02) made the positive statement, based on his study 

 of Paramecium, that he believed the micronucleus was present 

 at all times in the hypotrichous ciliates. Woodruff ('05) found 

 that in a culture of Oxytricha one of the two micronuclei — the 

 posterior — was not present in indiviuals from the 361st to the 

 369th generation. On the other hand, Popff ('07), working 

 with Stylonychia, found that during depression periods the 

 micronuclei increased in number. Lewin ('11), working with 

 the same form in regeneration, also found an increase in the 

 number of micronuclei. Baitsell ('12) carried a culture of Sty- 

 lonychia for 572 generations and found that micronuclei were 

 present in non-con jugants, conjugants, and ex-conjugants at 

 all stages. 



