MAEINE BIOLOGICAL STATION ON PUFFIN ISLAND. 17 



conditions carefully noted. The experiments were repeated 

 several times, the general results being that: — 



In the A jar, at the end of twelve hours all the specimens 

 had crept up and were sticking to the under surface of the 

 muslin ; at the end of thirty-six hours, they had all fallen 

 from the muslin, and were lying in various positions at the 

 bottom of the jar; while at the end of the third day one or 

 two were dead or djdng, and most of the others seemed to 

 be unwell. As the water in this jar had now gone bad, 

 this experiment was not continued any further. Whether 

 the sickly condition of the specimens in this jar was due 

 merely to being kept immersed in sea-water for three days, 

 or was caused by the water having become impure through 

 the accidental {i.e. from some other, unknown, cause) 

 death of one of the molluscs, it is impossible to say from a 

 few experiments; but, at least, there is no doubt that the 

 effect of putting closed up specimens of Littorina rudis 

 into clean sea-water, out of which they cannot escape, is 

 that they at once expand, become active, crawl as near 

 as they can get to the surface of the water, and after 

 remaining there for a time relax their hold and drop to 

 the bottom. 



.m 



Fig. 3. — Experimental Jar containing Littorina kept in the water. 



In B (fresh water), all the specimens remained during 

 the three days lying at the bottom of the jar in a tightly 

 closed up condition, but were apparently perfectly healthy 

 at the end of that time. The jar was kept under 



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