No. 629] HABITAT RESPONSES OF WATER-STRIDER 499 



definiteness recorded in the experiments of Weiss with 

 individuals of Gerris marginatum. I infer from the little 

 description recorded, that the responses of individuals of 

 the same species, when placed on the ground ten yards 

 away from the water, were more of the character of those 

 of Gerris remigis at such a distance from a pool of water. 

 While I have not observed gerrids of this species make 

 their way to a body of water quite so far away as fifteen 

 yards distant, as did Weiss in some of his experiments 

 with Gerris marginatus, yet I am not prepared to state 

 that they can not do so. However, if they are able to find 

 water at such a distance, I believe that the achievement 

 is one purely of chance, or the result of a blundering sort 

 of trial and error. On one occasion, I observed individ- 

 uals of Gerris remigis leave the site of a former pool in 

 the bed of a stream and although I watched them for an 

 entire afternoon, only one, out of a. group of thirty, had 

 reached an isolated pool fourteen yards distant, when I 

 discontinued my observations at dusk. On another occa- 

 sion, SIX water-striders onlv, out of a group of forty indi- 

 viduals, were successful m finding a bodv of water four- 

 teen \ ikK tiom the ^tc of tin i^ool m wliuh tlie\ for 

 mcih hhlliN..] I x\.>nl.l <\pM! tinin ii,N ol)serva- 

 tioiis (.1 ^ry//,s n ui/fiis, the fc- 1 m ni -cs ol aiitcroiis Gerris 

 wairnuilH It (li-t m(( ^ ol tlnit\ nulloit\ \aid-, tobe 

 iiiurli a- (li'x'i-ibed })V A\ eiss, although I have recorded no 

 nl)M'i \ ai loiis of the responses of i>-errids at such distances 



1 believe that alate iiidivulunls of (n-rn.^ murninafus. 

 (luring migration bv fliulil, tiiid IkkIio ct \vat>'i- maiiilv 

 through the sense ot \i>iivii. a- i> |irMl)al)l\ true m the 

 (•as(^ of manv different >|ici'ic- oi a(|uati<- llcnuiUcra. a 

 Mil)I<( t to x\liuh Kill I, l\ ( 1- "> I nil iH 1 MtiK I unt. 

 haw (iiivct.Ml attmlioii. IJ.rnil wurk on pholntaxi- 



( liohui^ I't.l , , , ,11, hiM I'lli: p,. IMI H.l ) (( nl 1 Ml7 



].p I I nlH 1 11 . p tiiin ,n<l < L'lh \ Ms ) 



i.^p>n<l poMlix.lx to luht ln>!, ,1 nu\ h.) I ,n , u. 

 spond to liglit diiriiiu' migration. In the fall of 11>()S, at 



