MARINE BIOLOGICAL STATION ON PUFFIN ISLAND. 53 
observation for some time longer; the molluscs only began 
to die on the thirteenth day—a marked contrast to jar A. 
Consequently these ‘‘marine”’ molluscs can live longer in 
fresh water than in sea-water. 
In C some of the specimens remained, in the contracted 
state, where they were put; while others crawled slowly 
about on the sides of the jar, a piece of glass over the 
top prevented their escape. None died: apparently, then, 
they can live best in the air. 
Of the twenty specimens in the aquarium (D) seven had 
crawled out of the water in fifteen minutes; at the end of 
twelve hours fifteen had crept up the slate sides out of the 
water, and at the end of twenty-four hours nineteen had 
emerged from the water, and had travelled to distances of 
from one to four feet from the aquarium over the stone 
floor and painted plaster walls of the laboratory. I 
marked pencil rings round the five which had crawled 
farthest at the end of the second day, and found they went 
no farther after that during the two months they were 
under observation. 
This experiment has been repeated several times with 
the same general result. All the specimens of Littorina 
rudis put in a contracted state into an open aquarium 
become active, and in the course of a day or two find 
their way out of the water, and after crawling for a little 
distance come to rest and remain there indefinitely. I 
have not noticed any specimens crawling downwards again 
into the water, even after being for days in the air. 
Next, I made some observations on the specimens at 
the shore under their natural conditions. The rocks at 
Puffin Island are reefs and masses of carboniferous 
limestone, broken up by the waves and worn into crevices 
and crannies of all sizes and shapes. The Littorinas 
above high-water mark on these rocks are, I find, almost 
