114 GEORGE DELWIN ALLEN. 



This is illustrated in Figs. I and 2. Fig. i is a photograph 

 of a lot of worms in a dish pan, reacting positively to a current 

 stirred in the clockwise direction. The conspicuous spiral 

 form of the figure is characteristic of the positive reaction. Fig. 

 2 is a photograph showing the characteristic negative reaction 

 near the center of the pan. 



These peculiar and characteristic spiral figures in a "circular 

 current" called for a more careful examination of the physical 

 conditions in the experiment, which revealed the fact that the 

 worms were subjected to a system of spiral currents instead of a 

 circular current. If a drop of a water suspension of carmine 

 is placed on the bottom of a dish in which the water has been 

 stirred in this way, the carmine in the lower layers of water close 

 to the bottom will be seen to stream inward along a spiral course 

 toward the center. Fig. 3 is a photograph of a dish pan in which 

 the water was stirred in the clockwise direction and then drops 

 of carmine were placed on the bottom at eleven points around 

 its circumference. The carmine was dragged along by the 

 currents and left streaks on the bottom of the pan which show 

 as spiral lines in the photograph. The worms were subjected 

 to this spiral system of currents. Carmine in the upper layers 

 of water was swept about the dish in a fairly circular direction, 

 and the water which flowed along the spiral lines on the bottom 

 toward the center, rose, as it neared the center, and spread out- 

 ward above. 



A comparison of Fig. 3 with Fig. I shows that the spiral lines 

 of the currents and the spiral lines of the positive reaction are 

 alike. This explains, therefore, the spiral character of the re- 

 action. The worms orient themselves to a spiral current. A 

 comparison of Fig. 2 with Fig. 3 shows that in the usual negative 

 reaction the direction taken is away from the side stimulated, 

 but rather diagonally than directly down-stream. In some cases, 

 however, when worms were distributed over the bottom and 

 were not dislodged by the stirring, they were observed to turn 

 inward and follow along the lines of the spiral current in as 

 precise a negative orientation as was often characteristic of the 

 positive reaction. 



A mixture of definitely positive and definitely negative re- 



