298 ROBERT T. HANCE 



The potentiality for the higher number of contractile vacuoles 

 is maintained although several generations may be passed before 

 it exerts itself or, better, before the conditions are such that it 

 must exert itself. 



c. The number of contractile vacuoles in the offspring 



Whew normal individuals get ready to divide, and when the be- 

 ginning of the constriction has appeared, two new vacuoles are 

 added so that immediately after division the daughter cells are 

 fully equipped with excretory organs. In this new race, as a 

 rule, two vacuoles are added at this time, although cases appear 

 when only one seems to be formed. In a certain percentage, 

 apparently more than two have been added before division but 

 whether the vacuoles in excess of two were added before or after 

 division cannot be ascertained from my data, as the observations 

 were not, as a rule, made until some time after separation had 

 taken place, in which case the extra vacuoles might have been 

 formed after division. In a few cases division occurred without 

 the formation of any new vacuoles. 



For 225 animals in: 



15.11 per cent — one vacuole was added 



54.66 per cent — two vacuoles were added 



30.22 per cent — more than two vacuoles were added 



From this it is evident that in at least 50 per cent of the cases 

 the usual normal addition of two new vacuoles prevails as in the 

 common race. 



With these facts in hand, the number of vacuoles possessed 

 by the offspring of the individuals of this new race may be un- 

 derstood. It is practically impossible, however, to predict 

 with certainty what number of contractile vacuoles the offspring 

 of any particular paramoecium will have immediately following 

 division. Some of the possibilities observed up to date are 

 illustrated below. 



