STUDIES ON THE GEOTROPISM OF THE MARINE 

 SNAIL, LITTORINA LITTOREA. 1 



SAKYO KANDA. 



CONTENTS. 



I. Introduction 57 



II. Material and Methods 58 



III. Experiments 61 



1. Preliminary Experiments with Gravity and Light 61 



2. The Relation between the Pressure of Gravity and the Precision of 



Orientation 63 



3. What Determines whether the Head End will be Directed Up or 



Down? 66 



4. The Effects of Light and Surface-Film of Seawater 71 



5. The Effect of the Surface-Film of Sea- water 74 



6. The Effect of Chemicals 76 



IV. Discussion 76 



V. Summary and Conclusions 82 



VI. Bibliography 83 



I. INTRODUCTION. 



In 1888, Loeb pointed out that "Die Schwerkraft der Erde, 

 wenn sie senkrecht gegen die ventrale Seite der Schabe gerichtet 

 ist, wirkt als Reiz, der dieselbe zu Bewegungen veranlasst" 

 (8, p. 9). Since then, with modifications of his method, Daven- 

 port and Perkins (2) and Frandsen (3) have investigated the 

 same problem on a slug, Limax maximus. The former drew the 

 conclusions that, "the precision of orientation of the slug varies 

 directly with the active component of gravity" (2, p. 105) and 

 that "this tendency (to go either up or down) must be ascribed 

 to some internal condition of the individuals, for it varies in 

 different individuals and in the same individuals at different 

 times" (2, p. no). The latter reached rather different con- 

 clusions, thus: 'The different geotactic response, on a glass 

 plate, of different individuals is due mainly to two factors: (a) The 

 quantity and quality of the slime secreted, which is a very im- 

 portant factor; (6) the relative proportions of the length of the 



1 From the Marine Biological Laboratory, Woods Hole, Mass., and the Physio- 

 logical Laboratory, University of Minnesota, Minneapolis, Minn. 



57 



