TWO CILIATA OF GREAT SALT LAKE. 



275 



and also with respect to division, conjugation, and encystment. 

 Dilution of the culture medium was accompanied by increased 

 size, increased activity, shortening of the feeling cirri, more 

 active physiological and reproductive processes, and more 

 flexible and contractile bodies. 



In changing the density of the culture from i.no to 1.040 

 the Uroleptus packii increased in length from .07* mm. to .11 mm. 

 and the Prorodon utahensis increased in length from .06 mm. to 

 .08 mm. The Uroleptus packii cysts increased in diameter from 

 .025 mm. to .03 mm., and the Prorodon utchensis cysts increased 

 in diameter from .023 mm. to .027 mm. Like changes were also 

 noted among other protozoans. 



The protozoans showed an increased activity as the medium 

 became less dense. All estimates of speed were made by means 

 of stopwatch, camera, lucida, and a dial made of concentric rings 

 reading to .01 mm. and .05 mm. The rate given for each pro- 

 tozoan is the average of ten records for each of ten individuals. 

 These rates are given in the following table. 



This increased activity was also very interestingly demon- 

 strated by the rate of vibration of the feeling cirri on the Uroleptus 

 packii. These ciliates, in the densities below 1.030, moved 

 their feeling cirri hundreds of times faster than the same ciliates 

 moved their feeling cirri when in the saturated densities. At a 

 density of 1.22 one single stroke of the feeling cirrus occupied 

 15 seconds. One stroke of a feeling cirrus at the density 1.150 

 occupied I second. In the density i.n there were at least five 

 strokes per second, while in the densities below 1.030 not even 

 an estimate could be given. The increased activity, that came 



