PHOTOTACTIC REACTIONS IX THE MAY-FLY. 269 



phototactic, but that the different individuals vary in the in- 

 tensity of their negative n -ponse. Also, out of about five or 

 six hundred specimens several were quite indifferent, and a tew 

 were even \\cakly positive. This obvious variability in response 

 among the different individuals, in an identical external environ- 

 ment, is apparently due to the variability in tin- internal con- 

 ditions of the various specimens. 



1.0(1,' says that in all probability light produces chemical 

 change- in the eyr <>r -kin of the animal-, and that these changes 

 are re-pon-ible for tin- heliotropic react i >n-. In a brief pre- 

 liminary communication 2 on the control of heliotnipic reactions 

 in fre-h water crustaceans by chemical-. he says that specimens 

 ol (inninmrns (nilcx, which are naturally negatively heliotropic 

 can be made po-iii\r b\ -pecilir chemical -ub-tanc. -. 1 ". -r ex- 

 ample, if carbon di"\ide i- allowed to bubble through tin- water, 

 or it ihe animal- are thrown into \\aier previously charged \\ith 

 i arlion dioxide. ihe\ ai on, , become po-itively phot, iiaclic. The 

 -a me i. nib- were obtained \\ith othei" a. id-, a- hydrochloric, 

 oxalic and aCCUC, but boracic acid produced no -ncll ettecl. 

 AIIIOII- the salts, lie found that onlv tli.-e of ammonium could 

 be ( 'impaled in their ell. < i- \\ ith tli id-. 



Ja< k-on .\pei-imeiitc.l \\ith another amphipod, //:.:.'. lid 

 knit kfr'tnx kcri, \\ hich i- al-o nev;at ivel\- phoiotactic. and obtained 

 re-ult- similar t.> tho-e ! I ..> 1,, except, that Ilynlcll.i" were made 

 p..-ili\e b\ ! id. Tartaric acid, ho\\e\er, |iroluci-d no 



change in their reaction. \Yith the -ab- and alkali.-- it \\a- 

 a-aill found that there -eenied to be no relation between the 

 cla-- "I > liemical u-ed and the reaction-. 



Ma-t' found that A ': larva' \\hich are iKirmally |>o-iti\e, 



become negative in -olutioii- coiitainiiu 1 various narcotics, at id-. 

 alkalie- or neutral -alt-, and In- claims that the sense of the re- 

 action in the-e form- -eem- to be due to the general State of the 



'Loeb, J., "Compa ' :i aini t'lUHpaial: . :.'il.,ny." 



1910, 



1 ,!,. J. Heliotropi. I< I ins, 



l.v Chemicals, especiall; uy i t'.iliiornia I'ut.li. ati-n- . "Physi- 



l'. i. i'. 

 i. II 11. 1 . 1 h> < ontrol ol I'i R tions in ll\<il,-llu l>y 



' '- 20 ^ 



' 



