MARINE BIOLOGICAL STATION ON PUFFIN ISLAND. 15 



with various species, and I have no doubt his results will 

 be laid before us on some future occasion. 



Experiments on Molluscs. 



Scattered over the rocks at Puffin Island, above high- 

 water mark, and above any of the sea-weeds, in the region 

 of the little incrusting Lichina pijgmcea, the region which 

 Vaillant has called the subterrestrial or zero zone, we find 

 numerous specimens of the small periwinkle Littoi'ina 

 rudis, and it is difficult to see how this mollusc manages 

 to live, and why it has migrated so far up the shore. It feeds 

 upon the lichen, and is very sluggish in its habits, often 

 remaining for days — perhaps months — without moving 

 from the one spot. Like its relations further down the 

 shore, it is a branchiferous mollusc fitted for breathing in 

 water, and yet we find it living and apparently flourishing 

 in the air : possibly it may be in process by becoming 

 adapted to a terrestrial mode of life. We know that some 

 of these molluscs can shut themselves up in their shells so 

 tightly as not to allow any water to pass in or out. Gosse 

 has told how Purpura lapillus is able in this way to 

 withstand the action of fresh water for eighteen hours. 

 This may help us to understand how it is that some 

 marine molluscs upon the rocks are not injured by 

 drenching showers of rain, but it will scarcely solve the 

 difficulty in regard to the specimens of Littorina which 

 stick to the dry rock for many days, unless they have 

 become adapted to breath in air, and some experiments 

 which I have made render it probable that this modi- 

 fication has taken place. 



I collected some specimens from the rocks above high- 

 water mark, and after keeping them perfectly dry in a 

 cardboard box in the laboratory for six days, during which 

 time they showed no signs of life, I put ten of them into a 



