GEOTROPISM OF THE MARINE SNAIL, LITTORINA LITTOREA. 75 



"B" covers the activity of those animals which were still 

 below the surface at the end of one minute. 



After the first minute, twenty-six individuals at the angle of 

 90, twenty-three at 45, and one at nJ/ were found to have 

 crawled upward through the surface-film of sea-water. Eighteen 

 individuals at the angle of 90, eleven at 45 and thirteen at 11% 

 were just beneath the film of sea- water. And after another half- 

 minute, sixteen individuals at the angle of 90 out of the eighteen, 

 which were beneath the film of sea-water at the end of one minute, 

 nine at 45 out of the eleven, ten at n% out of the thirteen, and 

 one at the same angle which was crawling horizontally at the 

 end of one minute, had crawled upward through the film of sea- 

 water. This is significant. At the time of second observation, 

 also, at the angle of 90 two individuals out of six, which were 

 crawling upward in sea-water at the end of one minute, at 45 

 five out of six, and at il% one out of ten which were crawling 

 horizontally at the end of one minute, had crawled upward 

 through the film. But at the angle of 90 two individuals out of 

 eighteen which w T ere beneath the film at the end of the first 

 period, at 45 two out of eleven, and at n% three out of thirteen, 

 that is, only seven individuals altogether out of 150, still remained 

 beneath the film even at the end of the second period. This is 

 decidedly contrary to the surface-film theory. And at the angle 

 of 90 two individuals out of six, which were crawling upward in 

 sea- water at the end of the first period, at u% four out of five, 

 and at the same angle one which crawled downward in the first 

 period, were beneath the film at the end of the second period. 



Referring again to the observation of Haseman that "during 

 a falling tide, some snails are crawling down beneath the surface, 

 some with the surface, and some above the surface" (4, p. 120), 

 and which Haseman claims is "due to the action of the film of 

 water," but not "to either geotropism or phototaxis," the writer 

 is inclined to draw the conclusion based on the results of the series 

 of the experiments above, that the movements of the snails in 

 question are not due, directly, if at all, "to the action of the film 

 of water," but to geotropism and heliotropism. In nature, 

 especially in the daytime when the sun is shining, a considerable 

 part would be played by heliotropism, as Mitsukuri already 

 observed. 



