Alleged Rhythm in Phototaxis. 



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Alleged rhythm in phototaxis synchronous with ocean tides. 

 By MAX WITHROW MORSE. 



[From the Harpswell Biological Laboratory, South Harpswell, 



Maine.] 



A series of observations upon the periwinkles, Littorina litorea 

 and Littorina rudis, and the snail, Ilyanassa obsoleta, carried on 

 from June 18 until August 26, failed to corroborate the conclusions 

 of Bohn, 1 who describes a daily rhythm in the reaction to light in 

 specimens of Littorina litorea and Littorina rudis corresponding 

 to the times of high and low tide, even when the animals are taken 

 from the sea and placed in aquaria, exhibiting thus a sort of 

 "memory" of the tides. 



In the present experiments the reaction to light was tested 

 in each specimen, at least three times a day, and white and black 

 screens were used, as in Bohn's experiments, to determine whether 

 the forms were positively or negatively phototactic. During the 

 days of June, they were, as a rule, negatively phototactic, and as 

 night approached, they became positively phototactic. However, 

 after July 18, the preponderance of positive phototaxis during 

 the day was very noticeable. This period of transition corre- 

 sponded to the time of change from spring to neap tide, during 

 which the specimens out on the rocks were exhibiting a corre- 

 sponding change in phototaxis, for the water did not reach them; 

 their behavior tallied with the description of Mitsikuri, 2 who 

 showed that when desiccated, periwinkles became positively photo- 

 tactic, and when wet, turned negatively phototactic. In these 

 observations there is an approach to Bohn's conclusions concerning 

 rhythms in phototaxis with respect to fortnightly (spring and neap) 

 rhythms in tides, if not to his conclusions concerning daily (high 

 and low) oscillations. However, no other period was passed 

 through while these animals were under observation, during which 

 there was a return to negative phototaxis, and it is doubtful that 

 this change was anything more than a variation in laboratory 

 conditions which were not determined by suitable check. On the 



■Bohn, Georges, Compl. rend. d. I'Acad. des sciences, 1904, cxxxix, 610, 646. 

 2 Mitsikuri, K., Annol. zool. japonenses, 1901, 4. 



