Il8 J. D. IIA-I.MAN. 



in a<|uaria to test the effect of -urface icn~i.ui. I'ndcr these 

 < onditions the -nail- had ci m-iderablc difficulty in breaking the 

 -urface tilni and alwa\- he-itated ,n the surface pii-hin^ them- 



selves to the right and to the left until their bodie- wen elevated 



-ufticieiilly to break the -urface tension. Their lieha\ior under 

 the above condition -hovxed that the lu'sitation on entering and 

 lea\ ini^ the -urface wa- due to tin- -urface til in and noi to photo- 

 taxis, hydrotaxi- <r clieniotaxis. 



M. \\'lien individuals of LitnriiHi litorca, nidis and pxilliata 

 \\ere placed in a -mall round a(|iiariuin e<|iial areas of \\ Inch were 

 painted brown, yellow and dark olive, they as a rule came to 

 re-t on the dark olive sector, rareh' stopped on the bn>\\ n sector 

 and still more- rarely on the yellow sector. When the same 

 -naiK \\ere |>laced in a similar unpainted ai|iiarium before a 

 window, about one half of them came to rest on the lighter >ide 

 and half on the darker side. The position of the aquaria were 

 interchanged and the -.a me results were obtained. Various 

 -hading experiments were tried and neither positive or negative 

 phoiota\i> could be detected. In nature one sees snails crawling 

 at random from lighter areas into shaded areas and \ ice 

 \ ersa. 



The writer wa^ unable to dc-tect \\h\- the snails stopped on 

 the dark olive sector, but inasmuch as such conditions are not 

 met on vertical sin-face- of stones between the tidal mark, the 

 results appear to have nothing to do with the rhythmical move- 

 ment- of Liiorina. 



12. Main- -nails \\cre placed in quiet aquaria and aquaria in 

 which running water \\a- kept at a constant le\ el and they never 

 exhibited an\ -i^n- of o-cillations which corre-pondi'd to those 

 ot i he tide-. In the-e experiments. snail> \\hich were kno\\n to 

 have be.-n pre\iou-ly o-cillatin;^ with the tide- \\ere u-ed. I 

 also |)laced snail-, which had been oscillating with the tide-, 

 on \erlic.il -urface- bt lo\\ the low tide mark and an average of 

 many count- did not -how rhythmical movement- \\hich corre- 

 sponded to iho-e of the tide-. 1 ( )nly when the -nail- are touched 

 by the -urface film of water are directive movement- called 

 forth. 



1 M -nt l\ ol milai i'-Milt. 



