AN AMICRONUCLEATE OXYTRICHA 485 



trichous forms and may be succeeded by the entire state, usual 

 at times of high reproductive activity. Essentially the same 

 cytoplasmic and nuclear conditions are revealed by a study of 

 the two pairs shown in figures 5 and 6. In figure 5 the animals 

 are united by the peristomial membranelles, while in figure 6 

 is shown the typical method of fusion closely resembling an early 

 stage of conjugation. An evident cytoplasmic connection is 

 seen between the two animals. 



Pathological specimens, an example of which is shown in figure 

 7, were obtained when culture A was dying and also in old mass 

 cultures. In these animals both cytoplasm and nuclei stained 

 more lightly than in the typical animal. Except for a slight 

 vacuolization of the macronuclei, there is little difference between 

 the structure of this specimen and of those described previously. 



In regard to the question of the presence or absence of micro- 

 nuclei, a most thorough and long-continued examination of 

 many specimens has been made. As already mentioned, these 

 specimens were prepared during all phases of the life-history of 

 the cultures ; during the early period of culture A, when the high 

 division rate indicated that the animal was in good physiological 

 condition; in cultures where there was no doubt that the organisms 

 were in a depressed state, and during the different stages when 

 numerous cases of attempted conjugation occurred. In none of 

 these specimens have any structures been seen which could be 

 interpreted as micronuclei. 



4. CANNIBALISM 



From the beginning of the experiments on O. hymenostoma 

 the appearance of giant specimens in stock and mass cultures 

 was noted. Stained preparations of these giants suggested that 

 such forms had arisen as a result of one animal devouring its sister 

 cells, or, in view of the observations of previous writers, what 

 may be termed cannibalism. 



Apparently the earliest account of cannibalism in ciliates was 

 given by Haime ('53) in a short paper on the so-called 'Meta- 

 morphosis of Trichoda lynceus.' He- figured an Oxytricha of 



