Xo. 629] HABITAT RESPONSES OF WATER-STRJDER 493 



V. Discussion of Observations at White Heath 

 1. Initial Locomotor Responses.— \t is an iiitorestinp; 

 fact that, just previous to the drying up of the ])oo], in 

 wliic'h the water-striders were livins:, there were no re- 

 sponses on the part of the gerrids which indicated any 

 attempt to escape from the unfavorable surroundings. 

 Not until the water had disappeared entirely was there 

 any tendency to leave tlic pUice. Soon after it l)ecanie 

 dry the water-striders began to move away from the site 

 of the former pool. What the immediate stimukis was, it 

 is difficult to say. A cliange in the physiological condi- 

 tion of the body, wliicli might have been induced by tht 

 drying uj) of the i)ool, would be sufficient to account for 

 the kx'omotor reN]K)n^e^. Whatever the stimulu'^ was, the 

 gerrids began to walk and jump away in different direc- 

 tions. But as Jennings (llXMi, pp. 284, 285) has pointed 

 out: 



Th,Mvh,iT. It i. not in.,M...nv t.. a^Mn.u that 



moxciiiciit i^ ihw to ^oMu- x.'i> icrrht ^timnl;iti..n. 

 Whatexei- the e\ph-iiinth.ii h.'. \hv u atcr-M i iders 



moved off in the diiv.-tinii m ^^hu■U tii.Mi h.-.-uK Nvere 

 pointed. They contimuMl alonu' tlic >aiiie line of proo-ress 

 until they arrived at sotiu^ ohsiach^ in thcii- pathway. 

 Such an obstacle miiilit be a lump of di'ied mud, a stone, 

 or a piece of driftwood, ^riien IIicn UMiall> turned to the 

 ridit oi- h'ft. as tlie case mla-ht he. thus "hciim- deflected 

 from their former direction of mov<Miient. They con- 

 tinued along the new path uiiti! tlics w<'re dethM-ted aa-;iin, 



2. Boir of Trial ,nu/ i:nn>. s,,. I, i,-pon^(- a^ juvvi- 



