8 



K. MIÏSUKUltI. 



The dotted line marks the level of water, and the black dots show the 

 positions in which the molluscs settled down. 



uneventiesses on the glass-plates A and B, and how the molluscs settled 

 themselves on this first day. It will be noticed that they are most 

 abundant in valleys and were more numerous in the lower half. 



On the next day no spontaneous changes were visible : so the level 

 of the water was raised to that indicated by the dotted line in Fig. 5, B. 

 All the molluscs that were threatened with submergence marched upward 

 again ; a few were finally left at the water's edge but none below it. 

 On the third day, the level of water was raised to that given in Fig. 5, C. 

 The molluscs shifted their positions upward for the third time. A 



