340 



Scientific Proceedings (123). 



discovered them during division within the macronuclear mem- 

 brane, and described their emergence and activities during conju- 

 gation. He likewise was unsuccessful in obtaining a single viable 

 exconjugant. 



During the past five months we have had under observation 

 a pedigree culture of Blepharisma undulans which emphasizes 

 racial differences within the species. The animals of this race 

 possess from four to fourteen relatively conspicuous micronuclei, 

 all of which are free in the cytoplasm during every stage of the 

 life of the cell; and all the exconjugants thus far secured proved 

 to be viable. 



The main culture has attained one hundred and fifty genera- 

 tions to date, an average of about one division per day, in the 

 standard beef extract culture medium used in this laboratory. 

 At intervals, epidemics of conjugation have appeared. Exconju- 

 gants have been isolated and new lines established from their 

 progeny. Studies are in progress similar to those which have 

 been conducted on Spathidiums. 1 



The wide experience of such observers as Butschli and Calkins 

 precludes the assumption that they were in error in regard to the 

 micronuclear condition of the animals which they studied and the 

 only reasonable conclusion is that there are races of Blepharisma 

 which differ in regard to the vegetative position of the micronuclei; 

 in some it is intramacronuclear and others extramacronuclear — the 

 present pedigree race of Blepharisma undulans representing the 

 latter and therefore agreeing with the marine species, Blepharisma 

 clarissima, as described by Anigstein. 2 



The results of all previous workers are consistent in regard to 

 to the non- viability of exconjugants. Whether the intrama- 

 cronuclear position of the micronuclei bears any causal relation 

 to non-viability it is impossible to decide. Certainly there are 

 no obvious differences between the chief nuclear phenomena de- 

 scribed by Calkins in his non-viable conjugants and those which 

 occur in the viable conjugants of the pedigree race which we are 

 conducting. 



1 Woodruff and Spencer, Proc. Soc. Exp. Biol, and Med., 1921, xviii, 180, 240 



303. 



'Anigstein, Archiv. /. Protislenk., 1912, Bd. xxiv. 



