1 if, J. D. HASEMAN. 



But tin- -nails which are- located mi an\ more or le-s vertical 

 -u rl act bei ween tin- tidal marks do exhibit rhythmical niovemeiu- 

 which correspond to those of the tides. 



2. \Yln-n a stone, which has snails crawling on a llat surface 

 belo\\ ihc low-tide mark, is raised and lowered in the sea, tin- 

 -nail- do not -how rhythmical movement- \\hich correspond with 

 those of the stone, /'. c., their movements were not directhe. 

 The same tv-iilts are obtained when, with the llat surface hori- 

 /ontal, the stone is raised out of and lowered into the sea. But 

 when, with the surface \eriical, the stone is raised out ol and 

 lowered into t he sea, the snails at once showed rhythmical mo\e- 

 meni - \\ hich correspond to those of the stone. These same snail- 

 were known (from observations made on snails placed bei \\een 

 tin- tidal marks and below the low-tide mark) to have shown in 

 some cases and not to have shown in other cases rhythmical 

 movements during several days prc\ ions to the experiment-. 

 Therefore an\ alleged retained rhythm has nothing to do with 

 the abo\ e results. 



Kvcn more interesting is the fact that when, with a vertical 

 -m-faiH', a stone, upon which snails were crawling at random, was 

 rai-ed out of the sea, the snails alwax- followed the vanish! M.: 

 film of water even when the vertical surface was rotated through 

 an angle of 180. In this case the rotation of the vertical surface 

 would reverse the direction of motion of the film of water and 

 the snail- would at once turn around and follow it. But if most 

 of the \\ater was previously removed from the surface ol the 

 -tone, in order that the film might entirely disappear before tin- 

 snails (which 'were crawling downward in the direction o! the 

 \ani-liing film i had reached the lower surface, and if, as the 

 film was drying up, the vertical surface was rotated through 

 an angle of lSo, tin- -nails continued to crawl tor some time- 

 in the direction in \\hich they had started. In other words, 

 the -nail- crauled upward instead of do\\ n\\ ard. They con- 

 tinued io crawl thii- until the rough -urlace, lood and moisture 

 either delleded or -lopped iheir movements. In the above ex- 

 periment, the mere turning of the moi-1 but lilmle surface 

 through an anije of I So doc- not si-em adequate to n-\er-e ai 

 once ihe n-a< lion to gr.i\il\ and light, if either ol these ha\e a 



direct inthieiice on i he rh\ ihmical movements of Litorina. 



