PARAMOECIUM POSSESSING EXTRA VACUOLES 295 



In both of these tables, and in all of the following work, the 

 three vacuoled animals show themselves to be in the excess in 

 nearly all cases. The statement made in my "first note on this 

 race that there was an apparent tendency for the vacuole num- 

 ber to settle down with three as the standard must be retracted. 

 When the note was written I was not familiar with the response 

 of the vacuole number to various conditions (rate of division, 

 age of medium, etc.)- 



The last table shows that a five-vacuoled paramoecium ap- 

 peared. Animals with five vacuoles, while not rare, seldom 

 have been found in a percentage greater than the one indicated. 

 The cause of the limited production of these extreme forms will 

 be discussed under Section VI. Recently four paramoecia have 

 been obtained with six contractile vacuoles and one with seven 

 (figs. 10 and 12). It is a striking sight to see a paramoecium 

 with six or seven vacuoles in a row all swelling and contracting 

 regularly. The six vacuoled condition is very rare and in over 

 a year I have not seen more than a half dozen animals thus 

 equipped, and the majority of these I have found recently. 

 The only cases seen in 1915 were very doubtful as the contractile 

 vacuoles were hidden by food vacuoles of similar refractiveness. 



The above results were obtained-on cultures maintained under 

 relatively similar conditions and it is interesting to compare 

 them with the average of the results obtained from a number of 

 cultures under observation for a much longer time and under 

 much more varied conditions. The data from which charts 2, 

 3, 4 and 5 were made served as a basis for these calculations. 

 These data were obtained on paramoecia under exceedingly 

 varied conditions — in cultures ranging from freshly made up 

 infusions to cultures that were very old, in cultures where plenty 

 of medium was present and in cultures that were undergoing 

 rapid evaporation, in culture during conjugation and after the 

 process had stopped. The averages given below are based on 

 an examination of 9818 animals. 



