marine biological station at port erin. 39 



The Minute Life of the Sea-beach. 



In continuation of the observations which have been 

 recorded in the last two Reports as to the occurrence of the 

 Dinofiagellate Amphidinium operculatum, in two distinct forms, 

 from time to time, upon the beach at Port Erin, I have only 

 now to add : — 



(1) That Mr. R. D. Laurie, while at Port Erin in April, 

 made a series of observations designed to test the question, 

 raised by his observations at Hoylake,* as to whether certain 

 rhythmic movements of the patches of the organisms are due 

 to direct response to environmental stimuli or to habit. The 

 former view was supported. The patches have a daily 

 rhythm of appearance above and disappearance below the 

 surface of the sand, and the times of these movements can be 

 very fairly calculated from a knowledge of the actinic value of 

 the light and the condition of the tide. The optimum light 

 intensity is a diffused condition, a strong light is avoided. 

 The influence of the tide, apart from light, was studied 

 during the night and the organisms were seen to disappear 

 shortly before the incoming tide reached them and to 

 reappear as soon as the tide receded from their area. The 

 interaction of light and tide stimuli produce a daily and also a 

 fortnightly rhythm, very little, if any, of which is due to habit. 

 Under experimentally altered conditions a new rhythm super- 

 venes. 



(2) That during the last year our knowledge of the range of 

 distribution of Amphidinium on the British Coasts has been 

 considerably enlarged — as may be seen from the following 

 letter to " Nature," which appeared on July 31st, 1913, 

 p. 558 :— 



" Biological readers of ' Nature ' will perhaps recollect the 



*Mr. Laurie also read a paper on the Bionomics of Amp)iidi)iiiu)i before 

 Section D of the meeting of the British Association at Birmingham, in 

 September. 



