ENDOMIXIS 659 



maturation "crescents" were not observed, and the elimination of chro- 

 matin bodies was found to be the typical method of macronuclear de- 

 struction. Only one among the many hundreds of endomictic animals 

 studied by Woodruff and Erdmann showed even a slight simulation of 

 the macronuclear ribbon-formation so characteristic of conjugating ani- 

 mals, and also of autogamy according to Diller. This single animal, of 

 the four-thousand-and-eighty-seventh generation, was figured as atypi- 

 cal. However, eight years later Woodruff and Spencer (1922) found, on 

 one single day in a subculture from this same pedigreed race at about 

 the eight-thousand-nine-hundredth generation, several animals with rib- 

 bon-like degenerating macronuclei. The publication of this exception 

 brought a protest from Erdmann, who was convinced that conjugation 

 must have occurred in the subculture. 



Now much of Diller's work has been done on this same Yale race, 

 and therefore it is clear that ribbon-formation does occur, other than at 

 conjugation, in this race, under certain conditions. It is not clear how 

 Diller's culture conditions differ from those in the Yale Laboratory, 

 where ribbon-formation has not been observed since the instance in 1922, 

 referred to above. A clue may be afforded by De Lamater (1939), 

 who found that different kinds of bacteria in the culture medium of this 

 same race of Paramecium had marked effects on the macronuclear 

 changes. It is possible that other types of bacteria or other environmental 

 changes may underly the differences between endomixis and autogamy. 



Periodicity of Endomixis 



Another important point is the rhythmic periodicity of endomixis ob- 

 served by Woodruff and Erdmann (1914, 1916) and Woodruff (1917a, 

 1917b), which, according to Diller, is absent in autogamy. He says: 

 "Under the conditions of my experiments, no regular periodicity in the 

 incidence of autogamy was evident." 



Woodruff and Erdmann (1914) and Woodruff (1917) definitely 

 stated that the interendomictic periods in both P. aurelia and P. caudatum 

 showed some variation in length and furthermore were somewhat modi- 

 fied by environmental factors, but nevertheless were strikingly periodic — 

 endomictic periods and interendomictic periods affording the rhythms 

 in the division rate of pedigreed cultures. And this rhythmicality has 

 appeared throughout the years in the culture of P. aurelia in the Yale 



