SAKYO KANDA. 



of water. The same was true in the case of Physa. But with 

 this species, as has been already pointed out, it was impossible 

 to exclude light in the experiments because it was inactive 

 in darkness. Consequently the negative heliotropism tended 

 to blur the geotropism. This disadvantage was entirely removed 

 in Planorbis and Limncea, because these forms w T ere active even 

 in total darkness. 



Observation I : Planorbis trivolvis was put in the 6oo-c.c. beaker 

 full of water. It either floated or sank, depending on the con- 

 dition of its lung as above mentioned. If it floated, i. e., was 

 lighter than water, observation on positive geotropism was made; 

 if it sank, i. e., was heavier than water, observation on negative 

 geotropism was made. Either event, therefore, was useful. At 

 about two-minute intervals, the snail was dislodged by a test- 

 tube cleaner, and then was covered by a dark-box. The results 

 are given in Table III. 



TABLE III. 



Geotropism of Planorbis trh'oh'is on a Vertical 

 Side of a Beakei Full of Water in Total Dark- 

 ness When it Was Lighter than the Water. 

 Table Shows Results Within Two Minutes. 



Geotropism of Planorbis trh'oh'is on a Vertical 

 Side of a Beaker Full of Water in Total Dark- 

 ness When it Was Heavier than the Water. 

 Table J-hows Results After Two Minutes. 



Discussion is hardly needed. A hundred per cent, in both 

 positive and negative geotropisms was obtained. The orientation 

 of positive geotropism in this snail was just as precise as that of 

 negative geotropism. 



Observation 2 : In the same manner as above, Limncea stagnalis 

 was observed in total darkness. The results are given in 

 Table IV. 



TABLE IV. 



Geotropism of Limniea stagnalis on a Vertical 

 Side of a Beaker of Water in Total Darkness 



When it Was Lighter than Water. 

 Table Shows Results After Two Minutes. 



Geotropism of Limna-a siagnalis on a Vertical 

 Side of a Beaker of Water in Total Darkness 



When it Was Heavier than Water. 

 Table Shows Results After Two Minutes. 



