GEOTROPISM OF THE MARINE SNAIL, LITTORINA LITTOREA. 8l 



snails being negatively geotropic, the direction and intensity 

 of sunlight were not at the time of this experiment presumably 

 in favor of the reversal of negative geotropism. Therefore, 

 "the snails continued to crawl" "upward instead of downward." 

 This is, of course, reasoned upon the results which were obtained 

 by the writer. At any rate, Haseman seems not to have checked 

 the counteracting forces of gravity and light and consequently 

 all his experiments are unreliable. 



One afternoon from four to six o'clock, Dr. Irving A. Field and 

 the writer made special observations of tidal (rising) influence 

 upon the snails at the south shore of Ram Island. The animals 

 were found in large numbers covering a pair of long square beams 

 which formed an inclined railway. These beams presented 

 both vertical and sloping surfaces. In this vicinity there were 

 also rocks and stones of various shapes, their surfaces sloping at 

 many different angles on which numerous snails oriented with 

 their heads upward were exposed in dim sunlight. When the 

 tide rose higher and higher with no waves and reached to the 

 areas where the animals had been exposed so long that their 

 outer surfaces were completely dried, nearly all of them, if not 

 the entire number, gradually turned head downward and crawled 

 in that direction; some of them moved downward several inches 

 from the original spots, while some others moved about "at 

 random" as if they were seeking food; and still others turned 

 downward when the surface-film of sea-water came in contact 

 with them, while many did so after the surface-film had passed 

 over them to the extent of 0.5 or i cm., more or less. If the 

 snails follow "the direction of motion of the film of water," and 

 also, if light has no influence on the rhythmical movements of 

 Littorina, as Haseman claims, why did not the snails "crawl 

 upward instead of downward"? Thus considered, it becomes 

 evident that Haseman's observation, or experiment, was not 

 accurate, while Mitsukuri's is, in this respect, confirmed by the 

 writer. 



It is very strange to note that Haseman has no notion of the 

 influence of gravity on the snails, although he has observed phe- 

 nomena which would naturally remind one of it. "When 

 individuals are left high and dry on vertical surfaces during low 



