PARAMOECIUM POSSESSING EXTRA VACUOLES S19 



of vacuoles and the line carried on with them. The last exami- 

 nation of this cultm-e showed the percentages to be as follows: 



per cent 



Two-vacuoled paramoecia 13 



Three-vacuoled paramoecia . 78 



Four-vacuoled paramoecia 9 



Experiments B and C were carried on with selection for animals 

 with the most contractile vacuoles. 



Experiment B started with a three-vacuoled paramoecium gave 

 rise to : 



per cent 



Two-vacuoled paramoecia 31 



Three-vacuoled paramoecia 69 



Experiment C started with a four-vacuoled paramoecium 

 produced: 



per cent 



Two-vacuoled paramoecia 43 



Three-vacuoled paramoecia 57 



In Experiment A where the selection was for the animals 

 having the least number of vacuoles the percentage of multi- 

 vacuoled paramoecia produced was greater than in B and C. 

 It might seem that the two-vacuoled animals of Experiment A 

 were possessed of a potentiality to produce more multi-vacuoled 

 offspring than were the paramoecia of B and C. As far as is 

 known the culture conditions in all three experiments were the 

 same. As has been stated several times before, the extensive 

 data that have been gathered on this race under all conditions 

 leads me to feel confident that in experiments such as A the 

 greater number of multi-vacuoled animals were produced be- 

 cause of some characteristic of the culture medium which either 

 slowed down the division rate (allowing more time for vacuoles 

 to develop) or had some other influence on the animals which 

 produced extra vacuoles and which as yet I have been unable to 

 discover. In B and C this factor was presumably absent or 

 was not so potent. 



