306 ROBERT T. HANCE 



believe that this fact interfered with any of the above state- 

 ments, as the variabihty of individuals may readily account 

 for this. In general all of the results indicate that extra vacuoles 

 appear as a rule when the rate of fission is relatively slow. Chart 

 6 compares graphically the division rate with the percentages 

 of two, three and four-vacuoled, animals. 



There are, however, enough exceptions to the general rule to 

 suggest the probability of some other factors playing a part 

 and very likely, not an unimportant part in determining the 

 number of vacuoles. As yet, I am not certain what this factor 

 or these factors may be, but Experiment B, 4 gives at least the 

 basis of a working hypothesis. In this particular experiment 

 although the division rate was high the number of two-vacuoled 

 paramoecia developed was 43.5 per cent under the number pro- 

 duced in Experiment A, 2 where the rapidityof division was ap- 

 proximately the same. The difference between the experiments 

 lay in that the fluid used in Experiment B, 4 contained many times 

 the amount of metabolic waste products present in Experiment A, 

 2. From this result the tentative suggestion may be made that 

 although the rate of division seems to be the primary agent in 

 influencing the vacuole number, the presence of waste products 

 in the environment has an activating effect on the production 

 of extra vacuoles. Indeed if the amount of the waste products 

 of metabolism is sufficient it may in part offset the effect of a 

 rapid division rate. 



Merely slowing down the rate of division is not sufficient, as 

 this was tried by placing six paramoecia in a constant tempera- 

 ture room at 12°C. In four days two had divided only once 

 and the rest not at all while the controls at room temperature 

 had each divided three times. When the animals in the cold 

 room were examined it was found that the vacuole number had 

 not increased at all. Under these conditions although division 

 did not occur for four days, the temperature lowered the metabolic 

 activities of the paramoecia and made the production of extra 

 vacuoles either impossible or unnecessary. 



