No. 630] HABITAT RESPONSES OF WATER STRIDER 71 



the water, or perhaps the reflections from it, and yet not to 

 obstruct the diffusion of moisture from the brook did not 

 produce results sufficiently definite from which to draw 

 conclusions. There is much doubt as to the role played by 

 moisture in influencing water-striders to move toward the 

 brook. 



VII. Discussion of Experiments at Sykacuse 

 1. Role of Vision. — The experiments conducted near 

 the large pool in the brook at Syracuse added little infor- 

 mation to what has been stated concerning the work near 

 White Heath. I believe that vision was the main factor 

 in assisting the gerrids to reach the large pool of water. 

 There were no obstacles to obstruct the view of the ger- 

 rids, the surface of the ground being smooth and flat. The 

 water-striders facing toward the pool and also those 

 having the longitudinal axis of the body parallel with its 

 margin found the water very promptly and with consider- 

 able directness, again suggesting the probability that they 

 reached the pool according to the same principle involved 

 in the case of Vanessa antiopa in finding the areas of 

 bright sunlight. It must be recalled that the pool of 

 water was, comparatively, of large size and that reflec- 

 tions of light from its surface would be more readily seen 

 than from such a narrow brook as the one near White 

 Heath. It is true that, in the experiments in which the 

 gerrids faced away from the water, there was a little less 

 promptness in reaching the surface of the pool and also 

 some random movements. However, in this series of ex- 

 periments, also, I believe that the sense of sight was the 

 chief factor involved in assisting the gerrids to reach the 

 water. 



In the experiments when forty gerrids were used in 

 each trial, I believe that vision played the chief role in 

 directing them to the water, at distances both of one yard 

 and of three yards. It is difficult to see what other factor 

 could have served as a stimulus in assisting the water- 

 striders to reach the pool with such directness and prompt- 

 ness as was displayed. 



