86 SAKYO KANDA. 



positively geotropic," so that "they tend to climb down." The 

 latter, on the other hand, states that when the snails "have suf- 

 ficient air they become indifferent to gravity and crawl in all 

 directions." 



Moreover, they do not agree concerning the behavior of the 

 snails from which "the air supply is cut off." According to 

 Walter, "after reaching the highest point in the flask," which 

 was in an inverted position in water, "and finding themselves 

 unable to renew their supply, their ordinary behavior, to which 

 there were some exceptions, was to let go and drop like dead 

 weights " (10, p. 27). Dawson denies this statement of Walter 

 as follows: "Physa, after they have been denied atmospheric 

 air for some time, manifest indifference to the influence of gravity, 

 and scatter over the sides and bottom of the bottle. They have 

 never been observed to let go and drop like dead weights upon 

 being denied atmospheric air" (2, pp. 104, 105). 



In this paper an attempt has been made to compare certain 

 experimental results obtained by the writer with those of his 

 predecessors. A comparison is also made with other results 

 obtained by the writer with marine snails. 



The experimental work was done in the physiological labora- 

 tory of the University of Minnesota, under the direction of 

 Professor E. P. Lyon, during the academic year of 1913-1914, 

 while the writer was holding a Shevlin Fellowship. The writer 

 expresses his appreciation of the interest and suggestions of 

 Professor Lyon throughout the course of the work. To Professor 

 John M. Holzinger, the principal of the State Normal School of 

 Winona, Minn., the writer acknowledges indebtedness for the 

 identification of the forms experimented upon. 



II. MATERIALS. 



Common freshwater snails, Physa gyrina Say, Planorbis 

 trivolvis, Limn&a stagnalis, and Limncea Columella, were used for 

 the work. The snails were kept in glass aquaria together with 

 green algae. They seemed to be perfectly healthy, and were 

 observed to grow. 



