82 SAKYO KANDA. 



tide," he says, "they come to rest 'directed upward,' i. e., with 

 their heads toward the sky. This is true for all sides of the stones 

 and is obviously due to the shape of the apertures of the shells 

 which makes it far easier for exposed individuals to cling thus to 

 vertical surfaces" (4, p. 117). How does he know that "the 

 shape of the aperture of the shells" makes it easier to cling to 

 vertical surfaces? Is it not rather true that the natural tendency 

 of negative geotropism of the snails, favored by the heavier 

 posterior region of the shells instead of the shape of the aperture, 

 "makes it far easier for exposed individuals to cling thus to 

 vertical surfaces"? This sounds more reasonable and nearer 

 to the fact than Haseman's supposition. 



V. SUMMARY AND CONCLUSIONS. 



1. Littorina littorea crawls up the vertical (inside) wall of a 

 beaker in a dark aquarium, though the sea-water be better sup- 

 plied with oxygen at the bottom than at the top. It is negatively 

 geotropic. 



2. This snail is negatively heliotropic. 



3. The posterior region of the snail has a greater specific 

 gravity than the anterior region. 



4. In sea-water, the larger the angle of inclination (to the 

 horizontal) of the surface on which the animals move the larger 

 is the number of negatively geotropic animals; and the smaller 

 the angle of inclination, the larger the number of animals which 

 move downward and are perhaps positively geotropic. 



5. In the air, the number of animals showing negative geo- 

 tropism is always higher than that in the sea-water. 



6. On a ground glass plate, the animals are less negatively 

 geotropic than on a plain glass plate. 



7. On a dry plain glass plate, a number of individuals oriented 

 positively and crawled downward even at the angle of 90 (ver- 

 tical) though this never happens on the moist plate. This is 

 more striking on a dry wooden plate. 



8. When the animals are placed with their heads down on a 

 dry wooden plate, the highest percentage of positive geotropism 

 is obtained. 



9. The snails "hesitate" at the surface-film of sea-water, when 

 light is not excluded. 



