Abstract
In 1933 Mr C. Machattie, F.R.C.V.S., D.V.S.M., very kindly sent me a small portion of a specimen of Lymnaea tenera euphratica Musson, collected in Iraq, infected with a cercaria belonging to the heterogeneous Gymnocephalic group. Sections were cut and it was found that most of the cercariae had been fixed during various stages of encystment. An excellent opportunity was thus afforded for observing this process, particularly the initial stages.