54 LIVERPOOL BIOLOGICAL SOCIETY. 
invariably in the hollows, either in rows along the lines of 
crevices, or singly at the bottom of the little 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 pygmea 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. Rutherford 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. Rutherford, 
on 21st June, and were inspected every day, and remained 
in the same position until they were washed away on the 
