No. G-JS] HABITAT RESPONSES OF W ATER-^TEIDEB 413 



tlie water, that tliere was imicli evidence of lack of prompt- 

 ness in turning: towai'd the brook and of random move- 

 ments. 



5. Experhnrnts 2rifh Bn rrirr.—ln the ex])eriments that 

 have been described, I felt tliat the sense of sig-ht was tlie 

 important factor in (iii'cctiiiiz' the watcr-striders to the 

 brook. However, there wa- al\va\s the i^ossibility that 

 moisture, as a stimnhis, miuht inlhieiice tlie roponscs of 

 the gerrids. Therefore, I jtlanned a nnmhci' of cxpcii- 

 ments for the purpose of obtaining more ilctinitc int'ot- 

 mation on this subject. My idea was to ai i aiiuc a -oi l 

 of barrier, along a limited section of the hank of the hrook, 

 which was to be of such construction as to pci'iiiit dilTus- 

 ing moisture to pass through it readily, ])nt on the ot4iei' 

 hand, the barrier was to be so opariue that the retlectioii 

 from the water of either sunliglit or dilfuse daylight could 

 not ))e seen through it. The })arrier first employed was 

 made of roughly int(M'woveii leafy branches of trees. This 

 wa<^ liehl in position hx ^^o(ul("n ^take^. It \\a^ four fret 

 high and e\trnd(Ml nhum tlir hank <.r tho Miraii, for a 



fir^t. the readiiu-s 'with ^^lli(■ll tlir niatni.ii- ^ ..iiM ho 

 ol)tained; and second, Ww fart that il> a| .po;) ranee was In 

 liarmony with the genera! eii\ i roniiieiit. llo\ve\er. \\ 

 found to he practioalK inipc-^ihle t<. make It Mitlieientlv 

 tiuht a- to ])revent ivtle.-tion> tVoiii the -nrt'aee of tho 



ments were not suniciriil 1\- sat isl';u'tor> , as ;i basis for 

 dclinite (.onelii-inn.. it ni.ix he MalMj tli.ii the uvrrids 

 di.plaNed -omeuhat le.. p,nni]Un.-- in n aehinu the 



water than ua- the en-e uhni Mieh a haiiie, u,,- .-M.-ent. 

 iroxN.-Ner. in -eiieinl it ua- exi-lent that the uat<T -tii-lei^ 



;jninpe,l touaid tlie lno.,k Ullll .M.nH.lerahle eNliedltin,, 



