PHYSIOLOGICAL VARIATIONS IN PARAMECIUM 



511 



D. Variations in Paramecium 



Jennings in 1908, from the study of statistical data came to 

 the conchision that variations in size in Paramecium are brought 

 about through amphimixis and largely from this study, he has 

 developed the argument that conjugation is for the purpose of 

 initiating variations. As this is a conclusion of fundamental 

 biological importance, the ground on which it is based must be 

 absolutely firm and beyond question of doubt. 



Jennings material (culture M) came from a small pond. From 

 this a number of pairs were isolated and allowed to multiply 

 after conjugation, seven pure line cultures being obtained from 

 single equal pairs or single ex-conjugants of the caudatum type. 

 About one month after isolation, random samples of about 100 

 individuals from each line were measured. About three weeks 

 later random samples of 100 individuals (56 in one case) from the 

 same strains were again measured. The data are contained in 

 his table 25. "Examination of this table shows that lines de- 

 rived from different conjugating pairs or different ex-conjugants 

 do differ from each other at the same periods in the life cycle 

 even though living under identical conditions. The differences 

 are fully as marked as, those found among diverse lines derived 

 from individuals not conjugating and taken without reference to 

 the life cycle in which they happen to be" (Jennings '08, p. 494). ■ 

 From the seven pure lines examined, Jennings found that four 

 types or races could be obtained accorHing to the mean length 

 of the random samples. The mean lengths for the two periods 

 are shown below: 



THE JOURN.\L OF EXPERIMENTAL ZOOLOGY, VOL. 15, NO. 4 



