TWO CILIATA OF GREAT SALT LAKE. 277 



encysted forms for several hours before emerging exhibited 

 periods of rest followed by periods of activity. This could be 

 explained as fatigue. However it was found that they were 

 more active during the day than during the night. It was also 

 noted that individuals quieted down by exposure to darkness 

 were excited to activity in a few minutes by exposure to a 40- 

 watt light (distance 2 feet). These individuals were found to 

 be more active as the intensity of light increased within the 

 limits of photosynthesis. A suggested explanation of these 

 results is found in the fact that the protozoans possess chlorophyll, 

 probably in the form of a symbiotic alga, which gathers carbon 

 dioxide and other wastes from the ciliate, recombines them into 

 food, and liberates oxygen. The utilization of the synthesized 

 food and free oxygen by the protozoan may account for its 

 increased activity. 



The geological history tells us that a few hundred thousand 

 years ago Great Salt Lake was a body of fresh water. This 

 suggests that our present salt water forms were in the past fresh 

 water animals. The fact that these forms have withstood the 

 the great change from fresh water to a solution of 23 per cent. 

 salinity shows that they were capable of adaptation. Those 

 forms that w r ere unable to adapt themselves to the salt water 

 have been weeded out and only plastic forms left. The results 

 discussed in the foregoing part of this article show that these 

 ciliata are plastic and capable of great adaptation. They adapted 

 themselves to all densities from 1.22 down to i.oio (to date), 

 which is almost a complete reversal of a change covering thous- 

 ands of years. 



DESCRIPTION OF SPECIES. 



Uroleptus packii Calkins 1 (see Fig. i) is a pale green colored 

 ciliate with dorsal and ventral surfaces, a tapering posterior end, 

 and a blunt anterior end which bears two long and two shorter 

 feeling cirri. This form is .07 mm. long (salinity 23 per cent.). 

 The body is quite rigid; keeping the characteristic shape. The 

 ectoplasm is easily distinguished and carries three marked rows 

 of creeping cirri. These rows of cirri extend diagonally back- 



1 Prof. Gary N. Calkins has seen this form and, provisionally, named it Uroleptus 

 packii. 



