No. 6.— CONTRIBUTIONS FROM THE ZOOLOGICAL LABORATORY 
OF THE MUSEUM OF COMPARATIVE ZOOLOGY AT HARVARD 
COLLEGE, E. L. MARK, DIRECTOR. No. 227. 
The effect of colored light on pigment-migration in the eye of the crayfish. 
By Epwarp C. Day. 
CONTENTS. 
Paas. 
I. Introduction RET ST PL SER WL, MPR T EER LO Camm gn Mens np Mee? =: 
Il. Historical review . . U8 RR IEP NA ial EE I RR MT Va pee? 8 
III. Experimental Eestieetons ae ite gh Ly dai nie rch eens Sutetee NE ae, eran 
Mery SIADLETS, oj ee sk ee ge a se te BAO 
i. eapparavs . Pl Ce Oe al ey eee hie er ee MeRrEREL) 
2. Anatomical Beit leit “hls ales Nae Dads tr rai Ed bd Nima 
merece | 0 ETE CAT, Sa ae it eee ie 
Se rrcer vinti@rise tt! TAMA ELISE REM TS EO Md tat LT Ek PR 
PU SCOhOM MeL NOU | MM ated hie Ry aT Rs RY, BS 
a. Procedure ee Piw witties sth) eo) Ciiihitdaodaie tls 
Fas elvesalts:, (pce ua. os Avehtenpay cote lite Capa: ty ee 
2. Direct-observation Bethods tical: aie < dete Moet iuiek deel 
SCP NER OMEOOR YOR IGIOW (fa Be TBR) eet ad ah bie ek 
EET ES CE ae nea ane Dg OY Vane OA nT 5. 
Gc, Prelitinary tests , ... . Sy (Nl hate) Whe ae aces 
d. Effects of blue-violet and ta er sani ace Rh A 
(i). atcenatby Varicd "so Mr eo Se ee ew gas 
(2). ‘Time ‘of exposure varied 0) OM oe PP go6 
TVs Dis@ussion |). °\'. ARDY) Why Ge as ae a Net NR ee 
A. Methods and debts aniployea TMT ARLE, HELP) PET TYE IG 
bayeammary afobservations lt) Wyiniiini yaa aod Veonvoe tee! 24888 
C. The function of the pigment oy eae cel? grb ciated deiladias 
1. Direct response of the pigment... sie. aoG 
a. Evidence for an intracellular Conaating fords a ial oy ev 
b. Evidence for an extracellular or chemotropic force . 337 
2 ladirecn) response, ,Lhroughjareliex yr... .) . . ws Bot 
V. Bibliography MR ce ee Reh lis a | at ate a ehh tal eee 
Pee ee et Bg ere ae, Mth Ca 
I. Introduction. 
Untit recently no very critical investigations have been made upon 
the effects of colored light on pigment-migration in the eye. Through- 
out the work which has been done on this problem heretofore there 
runs an error which, although recognized by a few, has been either 
