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THE AMERICAN NATURALIST [Vol. LIV 



after having been removed from it, and also for the pur- 

 pose of observing their responses while doing so. Twenty 

 water-striders were used at each trial. They were re- 

 moved quietly from the surface-film and then carefully 

 placed on the ground at distances of one, two, three, and 

 four yards away from the brook. In some experiments 

 the gerrids faced the water, in others they were parallel 

 with the current of the brook, and in still others they 

 faced away from the stream. 



In all the experiments in which the gerrids faced the 

 brook, the majority of them regained the surface-film. 

 When they were placed on the ground one yard away 

 from the water, all those that reached the brook did so in 

 less than one minute. In no experiment were there more 

 than two gerrids that did not reach the water. When the 

 water-striders were taken two and three yards away from 

 the stream, they were back again on its surface within 

 2 minutes and 30 seconds. Those gerrids that were 

 placed on the ground four yards away from the brook dis- 

 played more random movements in reaching the water 

 than did those that were nearer to it and a slightly 

 smaller percentage succeeded in finding the brook. Those 

 that reached the water did so within four minutes. The 

 experiments with the gerrids parallel with the brook 

 showed that the majority of them reached the water at 

 distances from one to four yards inclusive. Some indi- 

 viduals required a little longer time to make the journey 

 than did those that faced the brook. Sometimes there 

 was a little delay before they began to jump toward the 

 water. Those that were taken four yards away from the 

 brook evinced more hesitancy and more random move- 

 ments than was the case with the gerrids placed on the 

 ground at points nearer the water. Experiments with the 

 water-striders facing away from the brook showed again 

 that the majority of the gerrids reached the water from 

 all distances from one to four yards inclusive. There 

 were more random movements and less promptness on 

 the part of the water-striders in these experiments than 



