MARINE BIOLOGICAL STATION ON PUFFIN ISLAND, 49 
grass-green seaweed, Hnteromorpha intestinalis, and on 
this we find enormous quantities of Copepoda belonging to 
the genus Harpacticus. The condition of some of the pools 
suggested to me that these animals would probably be 
able to stand considerable variations in the salinity of 
the water, as in wet weather they are flooded with rain 
while in dry summers the pools become almost or com- 
pletely dried up. 
So, taking some sample tubes of salt water with Hntero- 
morpha and Harpacticus fulvus from the pool, I added 
to one a third of its volume of fresh water, and con- 
tinued every morning to add a little fresh water, until 
at the end of twelve days there were nineteen parts of 
fresh water to one part of the original sea-water and the 
fluid was no longer salt to the taste. The Hnteromorpha 
appeared healthy, and the Copepoda had increased greatly 
in numbers and were very active. The young ones hatched 
in the nearly fresh water were all colourless, but the 
adults had not lost their original bright red tint. 
A second sample tube of Harpacticus, Enteromorpha and 
sea-water from the pool was emptied into a shallow glass 
dish and allowed to evaporate slowly. The Copepoda in 
this case did not increase in numbers, but they did not die 
until the dish was almost dry and the salt had crystallised 
out round the edges. After evaporation had been going on 
for a few days, I noticed that the Copepoda had retreated 
into the interior of the Enteromorpha filaments, where 
their bright red bodies were distinctly visible on the green 
ground, and I think that under natural conditions they 
might in this way escape death when their pool became 
dried up, as the desiccation would not be so thorough in 
the damp atmosphere of the sea-shore as in the warm dry 
air of my laboratory. Mr. W. J. Halls is going to take 
this matter up and carry out some further experiments 
4 
