76 SAKYO KANDA. 



Furthermore, in the above experiment, even the seven individ- 

 uals, that still remained beneath the film at the end of the second 

 period, and whose failure to penetrate the film seems to favor the 

 surface-film action theory, may be considered in a different way. 

 The effect of light having been excluded, their failure to emerge 

 might be due to the susceptibility of these individuals to buoyancy 

 when they had to crawl out of sea-water. This must be taken 

 into consideration as has been shown. It might also in com- 

 bination with the effect of light explain the behavior of those 

 animals that crawled horizontally beneath the film, or that 

 "hesitated" there, as shown in a number of the preceding tables. 

 Whatever may be the explanation and even if one attributes the 

 slight hesitation to the film itself, it is evident that it has very 

 little effect in determining the total behavior of the animals. 



6. The Effect of Chemicals. 



Besides the above experiments, attempts were made to control 

 the negative geotropism of the snails by chemicals, especially by 

 salts and acids. But all were unsuccessful, except possibly an 

 alcohol experiment. Five snails were placed in a finger bowl 

 containing 100 or 150 c.c. sea- water, to which about 10 c.c. of 

 95 per cent, alcohol were added without stirring. The finger 

 bowl was shaded. The animals crawled upward on the vertical 

 wall of the bowl, but as soon as they reached the upper layers they 

 turned round, and crawled downward. The negative geotropism 

 was thus apparently reversed. But if the alcohol and sea-water 

 were well mixed by stirring, the reversal was not definite and the 

 experiment was not followed further. 



IV. DISCUSSION. 



That Littorina littorea is negatively heliotropic was first shown 

 by Bohn (i), and this fact has been confirmed by the present 

 writer. Morse, however, has published puzzling conclusions 

 from his observations on this species. He states: "During the 

 days of June, they were, as a rule, negatively phototactic, and as 

 night approached, they became positively phototactic. However 

 after July 18, the preponderance of positive phototataxis during 

 the day was very noticeable. This period of transition corre- 



