NOTES ON THE REACTIONS OF BIVALVE MOLLUSKS 



TO CHANGES IN LIGHT INTENSITY: 



IMAGE FORMATION IN PECTEN 



D. H. WENRICH 



Contributions from the Zoological Laboratory of the Museum of Comparative 

 Zoology at Harvard College. No. 277 



Contributions from the Bermuda Biological Station for Research. No. 47 



PAGE 



I. Introduction 297 



II. Results with Anadonta 298 



A. Methods 298 



B. Results 299 



1. Kind and degree of sensitivity 300 



2. Variations in sensitivity 300 



a. Variations in a single individual 300 



b. Variations among different individuals 303 



3. Comparative measurements of sensitivity 303 



III. Results with Marine Species 304 



A. Qualitative tests with different species 305 



1. Classification based on sensitivity 30 S 



2. Relation of sensitivity to presence or absence of pigment 306 



3. Differences in reactions to increase and decrease of light in- 



tensity 306 



B. Results with Pecten 307 



1. Sensitivity to increase and decrease 307 



a. Methods 307 



b. Results 308 



2. Reactions toward a moving object 309 



a. Experiments 309 



b. Discussion 311 



IV. Summary 316 



V. List of Papers Cited 317 



I. INTRODUCTION 



During the summer of 1913, while enjoying the privileges of 

 the Bermuda Biological Station for Research, the writer became 

 interested in the reactions of bivalve mollusks to changes in 

 light intensity. Little more was done, however, than to observe 

 the constancy with which the various species tested responded 

 to shadows, that is, to decreases in the intensity of the light. 

 Further observations were made in the Harvard Zoological 

 Laboratory during the first half of the 1913-14 school year, when 

 a few hours each week were devoted to a study of the reactions 

 to changes in light intensity of one of the common fresh-water 



