FORMATION OF ASSOCIATIONS IN THE MAY-FLY 17 



Should a line be drawn through the parts of the table where 

 the letters appear most abundantly we should have a gradual 

 curve representing the reinforcement of the reactions to a given 

 stimulus as a result of the formation of associations. The 

 behavior of the three nymphs represented in the foregoing 

 table is characteristic of many other nymphs experimented 

 with. To check these results, daily observations were made in 

 regard to the position and behavior of another set of individuals 

 which had a food supply scattered in small particles at the bot- 

 toms of their dishes. Their records show that they exercised 

 no choice between the two ends of the dish, and that they 

 never swam toward me as did those in the training experiments. 

 The trained nymphs no doubt formed an association. 



Not infrequently during the work with H. inter punctata 

 nymphs did I observe specimens which behaved in an uncommon 

 manner. The most interesting individual which attracted my 

 attention was in the midst of a large number of newly collected 

 specimens in a dish of water. Its peculiar conduct led me to 

 observe it carefully, when I noticed that it skipped about among 

 its fellows, lashing its setae and occasionally making a pass 

 at one of the other nymphs with its front limb like a playful 

 kitten. 



It was placed in a separate dish and taken to my room where 

 it was observed and trained daily. After a few days I noticed 

 that its tendency to remain on the upper surface of the stone, 

 whenever the stone was inverted, became more and more pro- 

 nounced. The nymph was brought to the upper surface in that 

 manner several times each day and on every occasion it was 

 offered a particle of alga. So long as it was treated gently it 

 would remain in that position for a considerable time, but, the 

 moment it was dealt with roughly it would conceal itself under 

 the stone. Great care was taken not to frighten the insect, and 

 within a few weeks it would remain on the upper surface of 

 the rock for hours at a time facing me. Whenever I noticed 

 that the nymph had gone under I would turn the rock over. 

 In about two weeks more, it had almost completely inhibited 

 its shyness and would follow a particle of food to any part of 

 the stone. Then I removed the much coveted stone and placed 

 in the dish a stone bearing a finger-like projection about three 

 inches long. The stone was so submerged that the extreme 



