MARINE BIOLOGICAL STATION ON PUFFIN ISLAND. 19 



invariably in the hollows, either in rows along the lines of 

 crevices, or singly at the bottom of the httle rounded 

 holes. They are never seen to move, they are attached to 

 the dry rock, and with the exception of the dark coloured 

 lichen Lichina pijgmcea growing in patches, they have no 

 visible means of subsistence. 



It has been suggested that possibly they descend to the 

 seaweed-covered rocks during the night and feed there ; 

 so to settle the matter as far as possible, I chose six 

 fairly representative individuals, and without in the least 

 disturbing them, I marked the shell and the hollow in 

 which it was lying in such a way that it would be easy to 

 detect any movement on the part of the mollusc. The 

 first three were marked respectively with one, two, and 

 three dots of red oil-paint on the shell, and one, two, and 

 three rings round their hollows ; while the remaining three 



Fig 4. — Marked Littorina on the Rocks. 



were similarly marked with blue paint (fig. 4). These 

 marked molluscs were examined by myself at intervals of 

 from six to nine hours for three days and nights (24th to 

 26th May), and during that time none of them changed 

 their positions. After that they were watched for me by 

 Mr. Eutherford until I returned to Puffin Island on the 

 7th June, when I found them unchanged. A second set 

 of six molluscs, on the rocks at the north-east end, were 

 marked with rings of paint as before by Mr. Eutherford, 

 on 21st June, and were inspected every day, and remained 

 in the same position until they were washed away on the 



2-2 



