124 GEORGE DELWIN ALLEN. 



it was not far from vertical as it was 1 1 130 in the morning. At 

 12:20 only 4 worms could be found in sight, 3 going up-stream 

 and one going down-stream. At 1 :3O, when it was cloudy, 40 

 worms were found going up-stream and 4 going down-stream. 

 At 3:10 a piece of raw beef was placed in the upper part of the 

 stream and fifteen minutes later 176 worms were counted going 

 up-stream and 34 going down-stream. It has frequently been 

 noted that worms in a moderate stream of water will respond 

 in this way and collect upon a piece of fresh beef and this be- 

 havior has been put to practical advantage in collecting speci- 

 mens. Worms removed from this stream and tested in a cir- 

 cular pan by the method employed in the laboratory showed 

 both the positive and the negative reactions very clearly, the 

 positive in stronger current and the negative in weaker current, 

 as described above. 



These observations show that planarians may react to currents 

 of water in nature. Pearl considered it "very improbable that 

 this reaction is of any importance in the normal activity of the 

 animal." This opinion may have been due to the difficulty which 

 he experienced in demonstrating the reaction experimentally 

 which might lead one to think that unusual conditions are neces- 

 sary for its production in nature; whereas it has been shown that 

 the reaction is given with readiness under experimental conditions 

 which are similar to those in a natural stream of water, and also 

 that it can be observed in nature. It would seem that a reaction 

 which is so characteristic of the animals in the laboratory would 

 play a part in their daily life in nature, when they live in an 

 environment which offers the appropriate stimuli for the reac- 

 tion. These animals seem to belong characteristically to stream 

 communities where these conditions are fulfilled. 



VIII. SUMMARY. 



1. Planaria dorotocephala show both positive and negative 

 reactions in a stream of water. 



2. The sign of the reaction may differ, depending upon the 

 velocity of the current. The positive reaction is then given in 

 stronger current and the negative reaction in weaker current. 



3. A negative reaction in weaker current can often be reversed 

 to the positive by increasing the velocity of the current. 



