THE FRESH- WATER LOCHS OF SCOTLAND. 333 



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. 



