6 



K. MITSÜKÜBI. 



thè aquarium. Tt was intended that water poured drop by drop from 

 above should gradually submerge them and their action under the condi- 

 tion was to be observed. But the aquarium and the glass-plates 

 being somewhat wet, the shells all began to march up the inclined plane, 

 as soon as placed there, toward the dark side and was only stopped 

 by the third glass-plate C. 



[In another experiment (Exp. 9) with exactly the same arrangements 

 as the above, every thing was thoroughly dried and the shells were also 

 dried in the sun. 200 individuals were placed at 11 : 80 A. M. (Aug. 8) 

 at the point / and water was poured to a slight depth. At 4 P. M. 

 distribution was as follows : — 



Remaining at / 12 ( The L se , ™ r 1 fJZ^ll) 



ö J I weak Itali ileail ones./ 



At the corner d 3 



At the corner e 5 



At the vertical back-wall c 13 (J-JJ-g ft^Jj) 



Crept up the incline and stopped at ab ... 1(37 



Total 200 



This shows that an overwhelming majority goes up the incline toward 

 the dark side.] 



On the next morning (Aug. 8) the position of the aquarium was 

 reversed, bright light being made to strike on the abc side. This induced 

 some that were at ab to move down the incline and to creep across the 

 depth of water and to gain the de side. It was noticed that in coming 

 down, as soon as they struck water, most of them hesitated and crawled 

 horizontally along the water's edge. They showed reluctance to enter 

 deep water, and seemed only driven by negative phototaxis which 

 appeared to be a stronger instinct with them. Some indeed crawled 

 straight across to the de side. Some others, while crawling horizontally 

 at the water's edge got unfortunately on the under side of the inclined 

 glass-plates. Most of the individuals, however, did not stir and held on 

 to the abc side. Even the bright sun-rays induced only few to move down. 



