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 Edward C. Day. 

 CONTENTS. 



Page. 



I. Introduction 305 



II. Historical review 306 



III. Experimental investigations » 310 



A. Preliminary matters 310 



1. Apparatus 310 



2. Anatomical orientation 315 



3. Technique 317 



B. Observations 318 



1. Section method 318 



a. Procedure 318 



b. Results 318 



2. Direct-observation method 321 



a. Phenomenon of glow 321 



b. Procedure 322 



c. Preliminary tests 323 



d. Effects of blue- violet and red compared 323 



(1). Intensity varied 323 



(2). Time of exposure varied 326 



IV. Discussion 329 



A. Methods and checks employed 329 



B. Summary of observations 333 



C. The function of the pigment 333 



1. Direct response of the pigment 336 



a. Evidence for an intracellular activating force . . . 336 



b. Evidence for an extracellular or chemotropic force . 337 



2. Indirect response through a reflex 337 



V. Bibliography 339 



Explanation of plates 343 



I. Introduction. 



Until 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 



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