PARAMOECIUM POSSESSING EXTRA VACUOLES 



297 



Chart 2 illustrates these percentages graphically. In com- 

 parison with the twos, threes and fours, the fives and sixes, and 

 especially the latter, scarcely appear above the base line. 



b. Variability in vacuole number in the life cycle of the individual 



While making the above studies it became e\'ident that the 

 time of day apparently had some influence on the various per- 

 centages. This suggested that the period in the life cycle of the 

 individual at which the observation was made might play a 

 role in determining the general percentage of the various vacuole 

 numbers. (In this paper reference to the life cycle of the para- 

 moecium always refers to the period between transverse divi- 

 sions.) A single indi\ddual showing two vacuoles was therefore 

 isolated and allowed to divide several times. Examination was 

 then made of all the offspring and each was isolated in a separate 

 watch glass. At intervals of from three to five hours the animals 

 were again examined with the following results. 



2 



22222 ,3 242 



332243242 



432243243 



As can be seen, paramoecia possessing two contractile vacuoles 

 increased this number in several cases before division. In some 

 of the individuals the number was not increased. However, 

 continued work with the two vacuoled forms has demonstrated 

 that they have not lost their power of producing multi-vacuoled 

 daughters. In one case I have followed individuals through 

 three generations (representing fifteen animals in all) without a 

 three vacuoled form appearing and then the extra vacuoled ani- 

 mals were produced in just a large percentages as in other lines. 

 This point will be more concretely illustrated under 'selection,' 

 page 316. 



