No. 630] HABITAT RESPONSES OF WATER STRIDER 79 



and 52 seconds, and the average time consumed was 18§ 

 seconds. In considering the sixth group of experiments, 

 it was found that 1 minute and 24 seconds elapsed before 

 all the gerrids were back on the surface-film and that the 

 average time necessary to reach the water was fourteen 

 seconds. The results of these experiments are, in the 

 main, very similar to many others not recorded here. Out 

 of a total of eighteen gerrids not one failed to get back 

 to the water. The water-strider used in Experiment 

 XXXIV was the only one that took an unusual amount of 

 time to reach the pool. On the average, the gerrids used 

 in the second three groups of experiments required, ap- 

 proximately, only about one half the amount of time 

 that was required by the water-striders in the first three 

 groups of experiments in order to reach the pool of 

 water. The gerrids in the second three groups of ex- 

 periments made fewer mistakes and a less number of 

 random movements in finding the water than was the 

 case in the first three groups of experiments. 



Just a brief statement will be made with reference to a 

 series of experiments in which the bodies of the gerrids 

 were placed parallel to the shore of the pool. In other 

 respects the experiments were similar to the groups of 

 experiments, one to six inclusive, the results of which 

 already have been recorded. In general, the results were 

 very much like those obtained in the second group of ex- 

 periments, with the exception that a little more time was 

 required by the gerrids in reaching the water. There was 

 not quite so much promptness, on the part of the water- 

 striders, in moving toward the pool. They evinced a few 

 more trial directions before arriving at the water and 

 occasionally a gerrid did not succeed in reaching the pool. 



A series of experiments was carried out in which the 

 gerrids were not oriented, specifically, with reference to 

 the pool of water. The individual responses were not 

 considered in these experiments, as the water-striders 

 were used in large numbers, but records were made of the 

 number of gerrids that reached the pool and records also 



