Xo. G29] HABITAT BKsroXsKS OF W A TKlr sT ItlDKIl 497 



pens not because of any direct or detinite response or re- 

 sponses to the body of water per se, bnt rather is due 

 more to the fact that many of their locomotor responses 

 are spontaneous ones, modified frequently as to direction 

 and speed, mainly, by contact stimulus, many of these 

 movements probably being due not to some very i-ecent 

 stimulus or stimuli which have any direct relation to the 

 body of water, but tliat they, more probably, are due, as 

 Jennings (1906, p. 285) suggests, 



tbo channels provided by its structure. 



3. Role of Moisture. — Undoubtedly it is true that water- 

 striders, Gerris remigis, are sensitive and responsive to 

 moisture. The fact that the greater portion of their lives 

 is passed on the surface-film of brooks and streams would 

 seem to be sufficiently indicative of this. Then, also, the 

 ability to find their way back to the stream in the spring, 

 having left it in the fall. lV(M,u("nllv I'loiii distan.M's of 

 three and four yards, and snincl iiiio l"r<iiii urcatci' dis- 

 tances, after passing seNcral iiiMntii- iii li i hci iial i. >n. is 

 further indication that they arc -cn-itixc to <(»iiic -i iimihis 

 or stimuli, the response to which ic-uli> in hnnmiii:' tiicm 

 back to the water. 



That the miu-ration of tlu-e u.mm.K Imn, t^- ^'tr of a 



that form"<)f ic^iInuM- i- uMialh nitc,,„clrd, I lMlic^c to 

 he cxlfctnelv ,l..ul.tfnl. I lovvvcr. it is not my intcnti.m 



th<- cc.MH.,,i> ,.r ihc^.. uat.M Mildc. \\xx\ I <lo lint i)e- 

 lievc that tlie movements of the uci'ri.U iii tlic drv l,cd of 

 the brook afford any definite^ iiuhcation that thcv are 

 direct I'csponses to moisture. It i- \'cr\ ituprohaltic liiat, 

 <hii-in<i- severe droughts and hiu'h tcni|icratu!c>. nKM-iure, 

 diffiisiiio- thi-onuh the atmosphere, rmm Midi rompara- 



