FORMATION OF ASSOCIATIONS IN THE MAY-FLY 13 



food would either break or the nymphs would make an attempt 

 to attach themselves to the forceps. 



Later, I would hold a piece of alga near the head of the nymph 

 and when it made an attempt to secure the food I would with- 

 draw a little, in which case the insect would slowly crawl after 

 it. This was a difficult task, for if the food was too far away 

 the nymph would make no attempt to secure it, and again, when 

 it was brought nearer, the insect would make a quick snap at 

 it before I had time to withdraw it. For several weeks I was 

 not able to entice the nymphs to follow the food any consider- 

 able distance before they would have their claws on it. How- 

 ever, when this was done the food was not taken away, but, 

 by means of a gentle pull the insect was brought to the part 

 of the dish nearest to me where it was allowed to feed, to a 

 limited extent, undisturbed. 



After experimenting with the insects in this manner daily 

 for about four weeks I noticed that most of the specimens would 

 frequently swim after the food when it was brought near them, 

 and would often swim toward me when they happened to be 

 at the further end of the dish when I made my appearance or 

 moved my hand over them. Not all of the individuals which 

 I experimented with reacted so favorably. Some, on account 

 of their decidedly strong thigmotactic propensity, proved to be 

 entirely intractable; while others absolutely refused to eat, 

 and swam about very much agitated whenever a particle of 

 food was brought near them. However, after two and a half 

 months a large majority of the specimens plainly manifested, 

 by means of swimming toward me or clawing against the side 

 of the dish nearest to me, that my presence meant food to them. 



From table VIII, on the feeding reactions of three of the speci- 

 mens, it will be seen that not only did the insects show a growing 

 tendency to remain in the feeding portion of their field, but that 

 they learned to swim after the food. In column I, opposite the 

 number of the day of the experiment, are indicated the positions 

 of the three nymphs A, B, and C, respectively. The ( + ) sign 

 indicates that the nymph occupied the end of the dish at which 

 I always made my appearance and where the nymph was allowed 

 to feed; the ( — ) sign indicates that the specimen was at the 

 opposite end. For example, at the time of the observation on 

 the third day of the experiment, specimen A was at the (+) 



