u6 



GEORGE DELWIN ALLEX. 



Table I. shows the total number of trials in which the different 

 types of reaction were given during all the experiments. 



TABLE I. 



SUMMARY OF ALL REACTIONS OBSERVED (EXCEPT THOSE GIVEN UPON INCREASING 

 THE VELOCITY OF THE CURRENT, FOR WHICH SEE TABLE II). 



The sign + indicates a positive spiral, , a negative spiral and ?, no dominant 

 spiral of either sign. The sign + indicates positive reaction in stronger current 

 and negative reaction in weaker current; (+) indicates only a few worms in 

 the positive spiral, and + ( ) only a few worms in the negative spiral. 



In the observations described above, the same individuals 

 were not observed to give both reactions because under the con- 

 ditions of the tests the same individuals are not subjected to 

 both extremes of current velocity. The earlier worms receive 

 the stronger current and the later worms receive weaker current. 

 It was readily shown, however, that the same individuals which 

 responded negatively in a weaker current would respond posi- 

 tively in a stronger current. Upon second stirring of the water 

 over a negative spiral without dislodging the worms, it was gen- 

 erally found that the worms composing the negative spiral re- 

 versed their direction of movement from negative to positive, 

 so that the negative spiral became converted into a positive 

 spiral composed of the same individuals. Out of 100 cases in 

 which second stirring of the water over a negative spiral was 

 tried, 80 cases showed reversal to positive. In some cases all 

 the individuals gave this reversal while in other cases few in- 

 dividuals, that is, only those forming the outside of the spiral 

 gave the reversal. In some cases reversal was readily induced 

 by currents of moderate velocity while in other cases reversal 

 was given only in very strong currents. 



