74 THE AMERICAN NATURALIST [Vol. LIV 



striders were entrapped. The first one to reach the pool 

 did so in 5 minutes and 30 seconds. Another gerrid re- 

 quired fifteen minutes to find the water. The last water- 

 strider to arrive at the pool completed the journey in 

 forty minutes. There was considerable variation as to 

 the time necessary to reach the pool on the part of the 

 others, the average being 14 minutes and 30 seconds. 



The direction of locomotion, of the ten water-striders 

 that did not find the pool was mainly up the dry bed of 

 the brook. Four wandered so far upstream that there 

 was little probability of their reaching water. With ref- 

 erence to the six remaining gerrids, two of them jumped 

 into a large crack in the dry mud of the brook channel: 

 two crawled under some driftwood; one worked its way 

 into a clump of dead leaves ; and one disappeared while I 

 was observing some other water-striders. The following 

 day I was unable to find any of these gerrids, although I 

 sought for them thoroughly, and had marked carefully 

 the various places where they were seen last on the previ- 

 ous evening. 



There was considerable variation, by different indi- 

 vidual water-striders, as to the amount of time consumed 

 in traversing the distance between their former abode 

 and the large pool of water downstream. None of the 

 gerrids, that reached the pool, journeyed there along a 

 straight path. Those that were among the first to com- 

 plete the journey seemed to make the least number of 

 errors in direction. All of them made deviations from 

 the most direct route, and also evinced random move- 

 ments. They found the pool of water through a blunder- 

 ing method of trial and error. The responses of the ger- 

 rids that moved downstream and found the water and 

 also of those that moved upstream and were not so suc- 

 cessful were, in the main, very similar, although the latter, 

 traveling a longer distance, made many more erratic 

 movements. In general there appeared to be a lack of 

 definiteness in orientation with reference to the direction 

 of the pool and a lack of promptness in journeying to it. 



