16 



K. MITSUKUK1. 



D. Here the depth of water was about 15 cm., but considerably deep3r 

 at the very base of the bank at y. while it was shallower in the direction 



of X : — 



1 went up in the direction of x. 



3 started toward the land in spite of a greater depth of water. 1 of 

 these crossed the deepest part to the side y. The second went 

 as far as the deepest part. The third to a somewhat shallower 

 place. 



2 did not stir at all. 



Several individuals that were moving upwards at A were placed at 

 B and C several inches deep in water. There was a deep cut abut 2 feet 

 deep in the rock between B and C. B was 2 feet from the bank. In- 

 dividuals placed at B did not stir at all. Of those placed at C, one went 

 in the direction of the bank. The others did not stir at all. 



I take it that in this experiment, A w 7 as out of the influence of the 

 shade of the high bank, at least from the molluscan standpoint. Hence 

 they went up in the direction that must have appeared darkest to them 

 i. e. in the direction of the highest point of that rock, although this was 

 no more than a few inches in height. B, C, and especially D are 

 in the shade of the bank : hence most of those that stirred at all went 

 landward, even if they had to cross water considerably deeper than that in 

 which they were placed. In B, the darkest part was toward the high 

 bank but water being very deep must have influenced the molluscs in soaie 

 way so that they did not stir at all. 



Once a lot of Littorina sitchana var. brevicula kept in a glass-bottle 

 for about ten days showed positive phototaxis for several days conti- 

 nuously. This I can not account for in any way, as this species also is 

 ordinarily negatively phototaxic. Nor could I induce other lots to act 

 in the same way by subjecting them to a similar treatment. 



CONCLUSIONS. 



1. Littorina cxigua shows a strong negative phototaxis under ordinary 

 circumstances. That it is not negative hydrotaxis is shown 

 by Exp. 3. 



