PHOTOTACTIC REACTIONS AND THEIR REVERSAL 

 IN THE MAY-FLY NYMPHS HEPTAGKMA 

 INTEKIM'NCTATA (SAY 



J. E. WODSEDALEK. 



REACTION-, n> LH.IIT. 



\\"ln-n nymphs of the may-fly Hcptu^cnia interpunctota are 

 placed in a Ion- :Ja di-h i.f water near a window, they im- 

 mediately -uim away from the light, and upon reaching the end 

 of tin- di-h they repeatedly collide \\ith and cla\\ against the 

 invisible ob-iructioii. The-e nio\emeiit- may le kept up, \vith 

 interval- <if rest, for a uhole da\\ \\"heii (|tiiet. the n\ni]ih- do 

 imi alua\- face a \\.iy IPUU the li:cht, nor \\hen they -\\iin do 

 the\ alu.i iii a -trai^ht liiu- aua\ from it. (Mini if there 



are lar^e dark ol;e(t^ in the room, lhe\- \\ill > \\ini a^ain^t the 

 -ide o| the di-h in the direction o| the olijci-t^. 



A- ihe lieha\ior o| die nxnipli-, i- often much allertcd |i\- 

 olijcct^ iii tin- nei'Jiltorhood. nio-t of the experiment-, on the 

 reactions to li;^ht \\en- pcrtormed in a dark room in a la r 



evenly colored box constructed of white cardboard, thu^ >lnn t in^ 



o|| all oliject^ and unde-iiaMi li'Jit. The liv.lit u-liall\- emplo\ed 

 \\a^ deri\ed liom an onlinar\ -ivterii laiulle pourr incainle-ceiit 

 lamp attached t<. a uire and movable about at \\ill. Alnio-t 

 \\iihoiit , Aceptioii, the n\ni])h- -\\.im a\\a\ from the li-ht. ' - 

 ca-ioiiall\ . -oine -pn inieii- alter repeatedly clauin^ a^ain-l the 

 transparent barrier and not -e ( uriii;^ a hold \\ould fall down on 

 their back- uith their le.i^ >tickinv; up, remaining in that po>iti<m 

 Munetime^ for hour-,. If a -tone \\a- placed in the end of the 

 ba-in neare-t to the li'Jit, the n\ niph would attach it-elf and 

 remain there for days. When tin- li.^ht \\ a- brought near the 

 -tone and m-.\ ed about, the- iii-ec'l would -i-ek the -haded area. 

 but liijn i-\en much more inieii-e would >eldom lorce it to de-ert 

 the -tone entirely. 



When a piece of white cardboard i- placed on the water in a 

 small ija-- di-h. the nymph- -ooii attach ihem-el\e- to the lowi-r 



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