i68 



ARTHUR WHITE GREELEY. 



stant temperatures, ranging from i to 10 C., could be main- 

 tained. For each low temperature experiment, a control experi- 

 ment was performed at the temperature of the room, and great 

 care was taken that all the conditions, with the exception of 

 temperature, might be identical in the two cases. 



Monas is more sensitive to changes 

 in the temperature than any of the 

 other Protozoa experimented with. 

 Within a few hours after the temper- 

 ature has been lowered to 4 C. all 

 the Monads in a dish settle to the 

 bottom, and cease their progressive 

 movement. At same time the cell 

 gradually becomes spherical, the fla- 

 gellum and mouth opening disappear, 

 Fi<;. 2. A resting cell of Monas, and there is formed a resting cell like 



formed by an exposure to a tern- those alread described ih the experi- 

 perature of 4 C. during six hours. 



ments upon Stentor. These resting 



cells can be kept at a temperature of 4 to 6 C. indefinitely, 

 and will withstand partial desiccation without losing their power 

 to revert to the normal Fionas form when they are removed to 

 the temperature of the room. This 

 reversion to the motile form takes 

 place within twenty-four hours after 

 the room temperature has been 

 reached. Theflagellum first make. c 

 its appearance, and the cells be- 

 come motile while still in the spher- 

 ical conpition. They soon, how- 

 ever, assume the normal elongated 

 form of the adult Monas. 



If these resting cells of Monas FIG. 3. The formation of spores 



which have been formed at a tern- within the restin cel1 ' after an ex ' 



posure to a temperature of 1 C. for 



perature of 4 to 6 C., instead five days 

 of being returned to the temper- 

 ature of the room, be placed on ice at a temperature of i 

 C. further structural changes take place as a result of this ex- 

 treme lowering of the temperature. After remaining at a tern- 



