276 DEAN A. PACK. 



with less dense media, was evident in other general movements. 



The feeling cirri on the ciliates from the saturated medium 

 were between 17 and 20 microns long, while the feeling cirri on 

 equally large ciliates from a medium with density 1.030 were 

 between 10 and u microns long. The two inside feeling cirri 

 of the ciliate in saturated medium were thus reduced by dilution 

 to nearer the length of the two outside ones and the ventral 

 creeping cirri. That is, our ciliate has practically replaced the 

 two specialized feeling cirri by the less specialized cirri. 



The physiological and reproductive processes were accom- 

 plished in less time in the less dense solutions. With increased 

 dilution; the protozoans ingested more food, the waste vacuole 

 discharged more often, and the contractile vacuole hurried up 

 in a like manner. Reproduction occurred more rapidly and 

 more often as the foregoing processes were speeded up. 



The bodies of both protozoans became markedly less rigid as 

 dilution went on. In normal lake water the bodies of both forms 

 were not known to contract any appreciable amount. Prorodon 

 utahensis could bend its body through an angle of 30, while the 

 Uroleptus packii was never found in a bent position. At the 

 density of 1.06 the Prorodon utahensis was seen to bend through 

 an angle of 180: or until the anterior part of the body folded on 

 the posterior part. At the density 1.03 the Uroleptus packii 

 was seen to bend through an angle of 150. Both forms in the 

 lower densities could shorten and lengthen the body at will. 

 The Prorodon utahensis seemed to have lost all rigidity of body, 

 assuming readily a spherical or a cylindrical form. 



These protozoans responded definitely toward light. This 

 fact was demonstrated, first with active and second with en- 

 cysted forms. The active forms after an exposure to darkness 

 for 12 hours, swam 66 microns in 10 seconds; while after an 

 exposure to darkness for only 6 hours, they swam 100 microns 

 in 10 seconds. The same forms after being exposed to darkness 

 for 12 hours followed by exposure to light for 4 hours swam 300 

 microns in 10 seconds. These figures show: first, that exposure 

 to darkness was accompanied by decreased activity; second, the 

 longer the exposure to darkness the greater the inactivity; and 

 third, that light was necessary for maximum activity. The 



