PARAMOECIUM POSSESSING EXTRA VACUOLES 309 



Common two-vacuoled race 



progressive lessening of rate of pulsation from anterior to pos- 

 terior end. This is not so e\ddent in the records of the two- 

 vacuoled race as both vacuoles appear to beat in almost idenfical 

 rate. While the observations were not taken at the same tem- 

 perature, the relative frequency of the various vacuoles in each 

 case would remain approximately the same. 



An interesting condition appears in the first table by averaging 

 the average time of contraction of the vacuoles in each group. 

 The result is: 



seconds 



Two-vacuoled group 10 



Three-vacuoled group 11 



Four-vacuoled group 12 



There is a steady slowing down of the rate of pulsation as the 

 number of vacuoles increases. Whether this will be borne out 

 by more extensive studies remains to be seen. 



1 . The effect of salt solutions on the rate of contraction. The work 

 of other investigators has shown that marine protozoa seldom 

 possess contractile vacuoles and that when fresh water forms are 

 subjected to saline solutions the rate of contraction decreases 

 greatly and in some cases the vacuole disappears entirely (6). 

 This race was subjected to salt solutions of various strengths to 

 determine whether it was possible to cause some of the extra 

 vacuoles to disappear permanently. Enough sea salt was added 

 to hay infusion to bring the percentage of salt to 0.06 per cent 

 or to 0.1 per cent. The animals could not withstand an immer- 

 sion in a solution as strong as 0.5 per cent immediately but 

 they survived very well if the percentage was allowed to in- 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY. VOL. 2.3. NO. 2 



