During the month of July, 1921, I had the opportunity of working with Dr. Annandale on the molluscs of Loch Lubnaig and Loch Vennachar in Perthshire, Scotland; and I was able to study carefully the two cercariæ infecting Limnæa peregra Müll. The material was examined in the living condition. Some of it was fixed in sublimate acetic and preserved in alcohol for subsequent study in sections.