408 



THE AMERICAN NATURALIST [Vol. LIII 



The wanderings of two water-striders, out of the group 

 of five, have not yet been traced. Attention already has 

 been directed to the fact that, when they first left the site 

 of the former pool, they wandered toward the right bank 

 of the brook. After reaching this point, they turned 

 downstream. I lost sight of one of them, while observing 

 some of the other gerrids, and I was not able to find it 

 again. The other water-strider proceeded downstream, 

 but frequently deviated from a straight path, and often 

 paused with its body in contact with various obstacles. 

 After wandering downstream for three yards, it made a 

 complete turn and its head thus pointed up=.tream. Thi> 

 occurred as the insect was making a jump, it appearing to 

 lose control of the orientation of its body. The water- 

 strider moved upstream for two feet and tlien turned to 

 the left, walking in that direction for four feot. The 

 geri'id made a wide turn to the left, so that its liead wa^ 

 directed downstream. After much erratic wandering, it 

 eventually blundered upon the large pool of water, having 

 consumed forty minutes in completing the journey. It 

 was a task of coTisiderable ditficulty to keep all the gerrids 

 uiidc!' ol)S('i'\Mtioii, because, being almost the color of the 

 backui-ouiid. tlicy were very inconsyiicuous. 



I records of a niirn[)er of other instances, treating' 



of iii\ ol)-('rv;!tion=^ on tlie re^])on^e< of \vater-^triders 

 after the di'ving up of several othei- stream ])oo]s, at 

 different times and during different >easons. Some of 

 tliese pools were at distances of less than ten yards, while 

 others were eleven, twelve, and fourteen yards distant 

 from the original pool on which the water-striders lived. 

 It is true that, on the particular occasion to which atten- 

 tion has been directed and which has been described in 

 some detail, half of the liwrlds entrapped on the surface 

 of the pool escaped when ii l)iM-;ime dry— to another and 

 larger body of water niaki n-' t heir way overland. But 

 in all the other in-l.iiirc. th;it wen- recorded in my field 

 notes of similar i)he]ioinon;i. ;i vrw tnneh <nialh'r ])ercent- 

 age of the entrapped -crrid- -uce.-M'ul in ranching 



