THE GEOTROPISM OF FRESHWATER SNAILS. 1 



SAKYO KANDA. 



CONTENTS. 



I. Introductory 85 



II. Materials 86 



III. Experimental 87 



1. Heliotropism of Physa gyrina Say 87 



2. Geotropism of Physa and Other Species, with the Lung Empty and 



with the Lung Filled with Air 88 



(a) Observations on Physa 88 



(6) Observations on Planorbis and Limnaa 89 



3. Geotropism of Physa with Lung Empty and Filled with Air, in Pres- 



ence of Food 92 



4. Geotropism of Physa at the Different Angles of Inclination of the 



Supports in the Air and in Total Darkness 92" 



(a) Experiments with a Plain Glass Plate 92 



(6) Experiments with a Ground Glass Plate 94 



5. Summation of Gravity and Light Stimuli 95 



IV. Summary and Conclusion 96 



V. Bibliography 97 



I. INTRODUCTORY. 



Walter (10) and Dawson (2) have investigated the geotropic 

 reactions of Physa and other freshwater snails in connection 

 with their respiratory phenomena. However, their observations 

 do not agree on certain points. Walter (10, p. 26) and Dawson 

 (2, p. 93) agree with each other that freshwater snails are nega- 

 tively geotropic, "when their lungs are empty." The snails 

 being air-breathing forms, it is, of course, necessary for them to 

 crawl up to the surface of water for their air supply, "although 

 their specific gravity is meanwhile gradually increasing through 

 exhaustion of the air," as Walter expresses it. For this upward 

 crawling, the pull of gravity would be expected to act as a 

 "directive force." 



Walter and Dawson, however, depart from each other when 

 they come to consider positive geotropism in these snails. The 

 former states that, "after filling the lung with air, they are 



1 From the Physiological Laboratory of the University of Minnesota, Minnea- 

 polis. 



8.5 



