78 THE AMERICAN NATURALIST [Vol. LIV 



periment, the total time necessary for all the water- 

 striders to reach the pool was 2 minutes and 14 seconds, 

 and the average time consumed in finding the water was 

 26f seconds. In the second group of experiments the 

 total time used by the water-striders to reach the pool 

 was 3 minutes and 6 seconds. The average time required 

 to reach the water was thirty-one seconds. In the third 

 group of experiments the total amount of time that 

 elapsed before all the gerrids had reached the water was 

 17 minutes and 55 seconds. The average time necessary 

 for individuals to find the pool was 2 minutes and 30 

 seconds. The gerrid used in Experiment XXVI did not 

 reach the pool and it was observed for 15 minutes and 

 25 seconds. If this experiment is omitted the total 

 amount of time for all the water-striders to reach the 

 pool was found to be 2 minutes and 30 seconds, while the 

 average time required for the gerrids to find the water 

 was thirty seconds. The results of these experiments 

 are typical of many others. A large majority of the 

 gerrids were successful in reaching the water, only two 

 individuals out of eighteen failing to do so. There were 

 a number of random and trial movements, but in the main, 

 the gerrids returned to the surface-film with consider- 

 able promptness. 



In the fourth, fifth, and sixth groups of experiments, the 

 initial position of the gerrids was facing the water. With 

 respect to the fourth group of experiments, all the water- 

 striders consumed a total amount of time of 2 minutes 

 and 40 seconds in reaching the surface-film. The average 

 time necessary to return to the water was 26^ seconds. 

 The gerrid used in Experiment XXXIV consumed ninety 

 seconds of time before it succeeded in finding the pool. 

 Omitting this experiment the total amount of time re- 

 quired by all the water-striders to return to the brook 

 was 1 minute and 10 seconds, while the average time 

 neecssary to reach the water was fourteen seconds. In 

 the fifth group of experiments, the total amount of time 

 required by all the gerrids to find the pool was 1 minute 



