RHYTHMICAL MOVEMKNT5 OF I.ITOR1NA. 115 



\\cre -ubjt/cted i" ini'.ch greater cluing - of tempcrat ure than 

 ir alon^ tin- coast and no ol>-er\al>le effect- were detected. 



D. Pressure. Severs.] individual- of Litorina litorca were-ul>- 

 mer.ucd in cages, which contained MM -hore rock-. in a depth uf 

 ."-. !>> and .V feel of \\atcr. T\\o week- l.lUT the -nail- appeared 

 to l>e perfectly normal. 



L ! .:!inn. Litorina litor*;: i- \ ery -en-iti\e \ -lisjit chaiio - 

 in aeration and e, >n-e(|iiently it i- \ er> 'difficult to arrange t IK- 

 Condition in an aquarium SO that tlu-\ l>eha\c normal 1> . 



I . \o direi ot li-hi ( ,n the di-irilunion of Li.'orina 



(ould IM- drif. icl citht-r IA Miifiit or din-ri observations 



made in nal i; 



I i :' \\hen indixiduaU ol . :<[ litotn: are \ioleiitl\ 

 >pla-hed l'\ \\a\i--.lln-\ 1 ( -me t |llie-cell t . 



II CharG lndi\ idual- of Litorina litor,,i are 

 raiel\ toimd on either -and or mini, due in part to the alienee 

 ot tood ill -in h plai - and in par I to the difficult \ eiicountereil in 

 <ra\\!iiiK over -in h -urfa. . - I hi- i- e-|ieciall\ true \\lu-n the 

 waves ton^taiiiK < han^e the |io-ition oi the -aim- and hence 

 lumlde the -nail- al-out at ramloin. 



I Mm-!:, Litorina litorca doe- not craul on dr\ -in la. 



II. FACTORS WHICH DETERMINI i HI M< >\ i \n \ i- >i 



It a|>|>eai - ( \ ideiil Inun the preceding data that thecharai 

 lei o| the -urlaie. nioi-iure and I ..... I are the chief ta tors vliich 

 detei'tnine the litoral di-t t il nit ion of the-e -nail-. Hut a- I hope 

 to demon-uale in the tollouin^ pai;e- the-e three factor- pro- 

 duce landom mo\emeiit- ol the -nail- and -Inuild not he con- 

 ton nded \\ ith the tai tor- \\ Inch direct l\ [irodm e rh\ ! limit al mo\ r- 

 nieni- cori-e-poinlin^ to the rise and fall of the tide-. 



The lollo\\ in^ experiments and ol>-ei \ at ion- \\ j||, | think, deter- 

 mine \\hat the "lirecii\e lone" ot riuthmiial movement- is. 1 



I. I'he -nail- \\hich are located on Mat hori/oiital -urLc 

 ln't\\eeii tin- tidal mark- do not -how rhythmical moxement- 

 \\hich corre-poilil to tho-e of the tide. The -nail- \\hi.h are 

 iled or placed l>e!o\v the low-tide m. irk on i-ilhrr a \erti<al 

 or a hori/ontal surface do not -how rhythmical mo\ nnrnt-. 



MM m.uiiiiiv ! t In \]" -niiii-iH - riin-il ali.ni; tin- -i-a-lmn- \>\ 



inaikin.n tin- -nail- an-l tin- 



