FORMATION OF ASSOCIATIONS IN THE MAY-FLY 3 



end of the tunnel. If the nymph, after emerging from the 

 tunnel, did not go in a straight line in the direction of the stone, 

 the stone would be brought closer at each trial until a distance 

 was obtained at which the insect would make several successive 

 straight trips to it. The stone would then be placed at the 

 same distance, but at various points in a semi-circle in front 

 of the opening, at different times. Table I shows the variations 

 in the distance at which the first definite trip was made by each 

 one of the different individuals experimented with, and also the 

 percentage of straight trips made by each individual toward 

 the stone, at the recorded distance, in 10 successive trials. 



TABLE I 



Individual Variations Among H. Interpunctata in Reactions to Objects 

 in an Evenly Illuminated Environment 



In another experiment on variations the same apparatus was 

 used, but the source of light was a 16 candle-power incandescent 

 lamp attached to one end of the basin. In order to reach the 

 stone the nymphs were obliged to swim directly toward the light. 1 



l Wodsedalek, J. E. Phototactic reactions and their reversal in the May-fly 

 nvmphs H. interpunctata (Say). Biological Bulletin, 1911. vol. XXL, pp. 

 265-272. 



