RHYTHMS IN BEHAVIOR 157 



the spray from the incoming tide begins to moisten them 

 they emerge and begin crawling about. Their photo taxis 

 changes with the tide, becoming negative when the tide 

 is high and positive when it is low. Bohn placed Littorina 

 in an aquarium and found that for several days they under- 

 went changes in their phototactic responses parallel with 

 those of specimens upon the rocks. Similar experiments 

 have been made by Morse on a species of Littorina on the 

 New England coast, but he failed to obtain any evidence 

 of a tidal rhythm. And more recently Haseman has in- 

 vestigated the tidal rhythms of several species of Littorina, 

 none of which showed any rythmical movements independ- 

 ent of the direct influence of the tides. 



Among actinians Bohn has found in many cases daily 

 rhythms due to the alternation of light and darkness super- 

 posed upon tidal rhythms. Both of these rhythms are 

 influenced greatly by the nature of the habitat in which the 

 anemones live. Individuals situated rather high upon the 

 rocks and living therefore under strongly contrasted con- 

 ditions in high and in low tide exhibit tidal rhythms to a 

 marked degree; whereas those which live at depths in which 

 they are little affected by the waves show little or no in- 

 fluence of the tide. Alternation of day and night affects 

 anemones to a greater or less degree in all habitats; its 

 influence is complicated by many factors, such as degree of 

 exposure to the sun, depth of water, shock of waves, tem- 

 perature, purity of the water, and various other causes. 

 The daily rhythms differ greatly in anemones from different 

 local situations, according to the influences to which the 

 animals are adapted. These rhythms with their various 

 characteristics peculiar to different habitats were found to 

 persist for several days in aquaria, but they gradually wore 

 away. 



