J. D. HASKMAX. 



The individual^ which \\ere previously left high and dry are 

 already directed upttard and hence lollow tin- rising tide. Be- 

 fore inaxinunn high tide is reached, the unevenness of the surface 

 alt in- with the presence and absence of food scatter the snails 

 at random because the rapidly rising tide soon submerges them 

 and then then' is no "specific directive force." 



\\ In D the tide begins to fall some of the snails are already 

 crawling downward and those that are not will be directed thus 

 by the Mirface film. I hiring a falling tide, some snails are 

 ng do\\ n beneath the surface, some with the surface, and 

 above the surface. As the tide falls lower and lower, 

 main snails lag behind more and more until they are finally left 

 on filmless surfaces under which conditions there is no specific 

 directive force and such snails are left exposed. This lagging 

 appears to be due to feeding, rough surfaces, rough sea, rapid 

 fall of the tide and the more rapid desiccation on certain days. 

 As a result of all these factors the amount of oscillation varies 

 from day to day. 



The snails on either flat horizontal surfaces between the tidal 

 marks or on any kind of a surface below the low-tide mark have 

 no ''specific directive force" and consequently do not exhibit 

 "M illatory movements synchronous with the ocean tides. 



SUMMARY. 



1. Litorina rndis, pallia! a and lilorca are found in definite 

 zones 



2. Individuals of Litorina lilnrea, located on vertical surfaces 

 I iet \\een the tidal marks, exhibit oscillatory moxeinents which 

 <Mrn-pond to those of the tide- but they do not exhibit such 

 movements \\hen they are located either on Hat hori/ontal sur- 

 face- beitteen the tidal marks or on any kind of a surface below 

 the lo\\-tide mark. 



J. The primary direct i\e force for rhythmical movements is 

 the -iirface film of water. The -econdary directive forces are 

 the r|uiesceni position of desiccated individuals, character ol the 

 moist lire and food. 



l. Liturhid litorni ha- no e-tablished rhvlhm in the absence 

 of t ida! chair 



