406 



THE AMERICAN NATURALIST 



[Vol. LIII 



in one direction and then in another. Sometimes they 

 stopped with their bodies in contact with some obstacle 

 in their path. Frequently the direction was changed when 

 they renewed the journey. The gerrids did not turn down- 

 stream for any considerable distance during any of their 

 movements. After having observed them at intervals for 

 two hours, I decided that they were unlikely to reach the 

 water unless they eventually should wander to a pool 

 somewhere upstream. The gerrids had moved away from 

 the site of the former pool to such a distance that the 

 water-strider farthest upstream was twenty yards dis- 

 tant from the starting point. One individual crawled 

 under a piece of driftwood and had been in that situa- 

 tion for tw^enty-five minutes, when the observations were 

 discontinued. Another water-strider crawled among 

 some dead leaves and was there for twenty minutes 

 previous to the time when I left that place for observa- 

 tions elsewhere. 



Of the eight gerrids that have not yet been mentioned, 

 three of them stumbled toward the left bank and five of 

 them wandered toward the right bank of the brook. There 

 were various obstacles in their paths, such as small rocks, 

 pieces of dry mud, dead leaves and driftwood. The water- 

 striders frequently came to rest in close contact with these 

 objects— response to contact being a prominent feature in 

 the behavior of these gerrids — and at length two of those, 

 that had moved toward the left bank of the stream, 

 jumped into a large ci-ack formed in the baked mud of the 

 bed of the brook. I obsorviMl those individuals from time 

 to time — for at least tlncf hoiir^ until I left for Urbana, 

 at about 8:00 p.m., and they ucic >till in the same situa- 

 tion. I should state licrc that 1 searched for these two 

 gerrids the next day and was unable to find them ; nor was 

 I able to discover the other four water-striders— to which 

 I already have referred— that had moved uf)stream. The 

 responses of one of the three gei'i ids, that in the first in- 

 stance had moved toward the h'i't hank of the hrook, have 

 not yet been described comj)h'leIy. After reaching the 



