As this facing about in the tube is repeated, the time 

 taken for each turn may be longer than for the last, the 

 animal finally dying of apparent fatigue, or, if the tube is not 

 so small that too violent an effort is required of the animal, 

 the time may gradually be shortened and a most surprising 

 aptitude of turning be developed. Paramoecia from a vig- 

 orous culture give better results than poorly nourished ones. 

 Under optimum conditions there was \found a reduction of 

 turning time, after the animals had been in the tube for 

 twelve hours or more, from four or five minutes to a second 

 or two, which is the minimum time* , in which the turn can 

 be made. 



Often the Paramoecium will rest for a long period at 

 once meniscus, slowly circling around with its buccal groove 

 resting against the air surface. When, however, the effort 

 is made to reverse, the shortening of time in the practiced 

 individuals is very apparent. 



Reactions to temperature. In these experiments a 

 capillary tube was selected large enough to allow the Para- 

 moecia to reverse their direction without touching its 

 sides, and in which two Paramoecia could pass each other 

 without difficulty. A number of individuals were taken up 

 in this tube and the tube was placed on a carriage having 

 two large glass supporting tubes through which water of 

 different temperatures was passing and on which the 

 capillary tube rested. 



While hot water was flowing through one support and 

 cold water through the other the temperatures could be re- 

 versed, so that the cold water would flow through the one 

 and the hot water through the other. Thus the distribution 

 of temperature in the capillary tube could be reversed. By 

 cold water is meant water at normal temperature to which the 

 animal gives no reaction. 



As soon as the capillary tube is heated at one end by 

 contact with the hot support, the Paramoecia at that end 

 dart about at random until they are headed toward the cool 

 end of the tube and even then do not swim to the cool end 



[TEN 



