THE FRESH- WATER LOCHS OF SCOTLAND. 
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seemed quite at home. There was in no instance any trace of a stalk. 
These facts led to the supposition that perhaps the lacustrine form may 
be a permanent pelagic race, or even a distinct species. Or it may be 
that the animal is attached when young, and becomes free when adult. 
There are difficulties in the way of accepting either hypothesis. If it be 
a true plankton form, we have to explain the absence of living animals 
from so many of the Scottish lochs in which the skeletons occur, and 
some of which have been examined at all seasons of the year. If it be 
a littoral form, and only casual in the plankton, it is still unexplained 
why the skeletons are, as a rule, only in large lakes. 
