74 



SAKYO KANDA. 



5. The Effect of the Surface-film of Sea-water. 



The last of this series was planned in a little different way from 

 the above, entirely excluding light. 



As a preliminary test, the snails were placed on the glass plate 

 at the angle of 56^ in the aquarium, which was half filled with 

 sea-water. When those crawling upward reached the surface- 

 film of sea-water and "hesitated," as Haseman calls it, beneath 

 the film, the whole arrangement was covered with the dark box. 

 Ten seconds later, the box was removed for observation. Nearly 

 all that had "hesitated" at the film, were found to have crawled 

 upward through the film. 1 Certain individuals at that time had 

 already crawled upward as high as 3 cm. from the film, some 2 

 cm., and others were just above the film. This experiment was 

 repeated several times and these results were readily demon- 

 strable. Judging from the results, the animals did not seem to 

 have "hesitated" long, after the light was excluded. The 

 "hesitation" of the snails at the surface of sea- water seems to the 

 writer to be due chiefly to the effect of light instead of to action 

 of the surface-film of sea-water. This point also becomes evident 

 after further consideration. 



Quantitative experiments were conducted as indicated above. 

 The results are tabulated in Table VII. and show rather compli- 

 cated conditions. 



TABLE VII. 



GEOTROPISM OF SNAILS AT THE DIFFERENT ANGLES OF INCLINATION OF A GLASS 

 PLATE IN AND OUT OF SEA-WATER IN TOTAL DARKNESS. 



At beginning of experiment each head placed pointing downward. 

 results after one minute and after another half minute. 



Table shows 



1 They change their "minds" very rapidly! 



