No. 630] HABITAT EESP0N8ES OF WATER S TBI DEB 77 



in any of the previous ones. A slightly smaller percent- 

 age reached the water from a distance of four yards than 

 was the case in any of the other experiments. 



Experiments were conducted in order to discover 

 whether vision, moisture, or both of these factors func- 

 tioned as stimuli in influencing the water-striders to find 

 the brook. A barrier was constructed to shut off the view 

 of the stream, but to be so arranged as still to permit 

 moisture to pass through it. However, the barrier proved 

 to be defective in this respect. The water-striders were 

 a little less prompt in reaching the water when the barrier 

 was employed than was the case when it was not used. 

 The information that was obtained regarding the re- 

 sponses of the gerrids proved to be inconclusive. How- 

 ever, I am strongly of the opinion that vision is the impor- 

 tant factor in directing these hemipterons to find water. 



Experiments, of a character similar to those that previ- 

 ously have been described, were undertaken near a small 

 rapid brook in the vicinity of Syracuse. Near the head- 

 waters was a large pool, its approximate dimensions 

 being 55 X 17 X 2 feet, formed by an artificial dam and 

 on its surface were thousands of gerrids. It was here 

 that the experiments were performed. 



The gerrids used in the experiments were taken directly 

 from the surface-film of the pool. Different individuals 

 were employed in each experiment. In all the experi- 

 ments in which the responses of individuals were re- 

 corded, the distance from the pool to which the gerrids 

 were taken was one yard. Six experiments were grouped 

 together for convenience. 



In the first, second, and third groups of experiments, the 

 water-striders were placed on the ground facing away 

 from the large pool. In the first group of experiments 

 the total time consumed by all the gerrids in reaching the 

 water was 12 minutes and 14 seconds. The average time 

 required to find the pool was 2 minutes and 2^ seconds. 

 In Experiment VII, the gerrid had not yet reached the 

 water after ten minutes had elapsed. Omitting this ex- 



