HYDROTROPISMS OF FRESH-WATER INVERTEBRATES. 49 



away from the water; three, between 90 and 100 per cent.; four, 

 between 80 and 90 per cent.; five, between 70 and 80 per cent.; 

 four, between 60 and 70 per cent.; four, between 50 and 60 per 

 cent. Kvidmtly, although some individuals are undoubtedly in- 

 fluenced by water as a directive force, this is certainly not true 

 of the group as a whole. 



Near a small pond in Carondelet Park, St. Louis, Mo., there 

 is a narrow valley. The floor, which is nearly horizontal is about 

 60 feet long and 20 feet wide. About eight feet from the pond it 

 slopes, at an angle of 60 degrees to the water. On the two sides 

 the walls slope upward at an angle of from 30 to 50 degrees. This 

 valley floor was selected as the place in which to perform the 

 following experiments with water-striders which had been cap- 

 tured in a brook near Creve Coeur Lake, Mo. One at a time the 

 water-striders were placed on the ground, at a certain definite 

 di-iance from the water. They were always faced away from 

 tin- water. They were watched continuously until they had 

 rit her reached the water or had gone from the starting point, 

 in -oim- direction other than toward the water, a distance equal 

 to that from the starting place to the water. Such individuals 

 were recorded as not moving toward the water. Sometimes an 

 individual would start in a certain direction and continue in 

 that direction to the close of the experiment. More often it 

 wandered about in various directions before settling down to 

 continue in one course. Sometimes an individual would move 

 toward the water a distance of ten to twenty feet and then 

 turn about and move away from it. In a few cases an indi\ idiial 

 would move away from the water a distance of ten to til'u-en iVrt 

 and then turn, meander about, and finally reach the \\.iitr. 

 Several of those that did not reach the water rlimU-d tin- -idr- 

 of the valley for a distance of fifteen to twenty feet. If. in its 

 wanderings, an individual happened to arrive on the steep slope 

 that extended from the horizontal floor of the valley to the pond, 

 it invariably continued, sometime.-, \\iih accelerated -peed, to 

 the water. The results are recorded in Table VIII. 



These results harmonize with the conclusions l>a-rd upon ex- 

 periments with the checkerboard plate. 



