at first but often turn back to the hot end several times be- 

 fore finally swimming over to the cool water. Once ar- 

 rived at the cool end the Paramoecia do not stay there, but 

 turn and start back to the hot water. In this way a 

 Paramoecium may traverse the length of the tube a dozen 

 times or more before coming to rest at the cool end of the 

 tube. As the animals leave their resting place at the warm 

 meniscus in obedience to the repeated reversing of tem- 

 peratures in the tube, their movements become slower and 

 more regulated and they seldom turn more than once toward 

 the cold water before swimming in that direction. It is not 

 significant to express this modification of behavior in terms 

 of time for, although the time involved in getting away from 

 the heated end of the tube is somewhat reduced as the 

 stimulus recurs, it is the suitability of the movement to ac- 

 complish the result which characterizes the later reactions. 

 In these the actual locomotion, is slower but the random 

 movements give place to more determined ones. 



The influence of an associated past experience upon the 

 reaction to a given stimulus. Although in the following ex- 

 periments the observations gave nothing but negative results, 

 these results serve to fix the limits of educability in Para- 

 moceium. Although Paramoecium profits by experience, as 

 seen in the above sections, it does not show associative memory 

 such as Loeb would demand as the criterion of consciousness. 



The conditions of the first experiment were these. Para- 

 moecia were placed in a trough having an extremely thin 

 glass bottom and this trough was immersed in a partitioned 

 box containing hot and normally cool water on the two sides, 

 so that the bottom of the trough was kept cool on one half 

 and warm on the other. There was a distinct line, not cor- 

 responding exactly to the partition of the under box, at 

 which the Paramoecia approaching from the cool side would 

 turn back. A light was fixed above the trough and a screen 

 interposed so that a shadow fell covering the warm area and 

 a minute part of the cool area beyond the reaction line. 

 The white Paramoecium which was here used, gives no re- 



ELEVEN] 



