45 
infection of mussels by these cercarhe from the periwinkle, and for 
this purpose procured a lot of periwinkles from Stranraer, where 
the parasite abounded in August and September ; I was, however, 
much disappointed to find no parasite of this kind in them 
(January). Specimens examined from Budle in January had 
young rediae in two of them, and one had a small number cf full- 
grown cercarire in it. It seems clear that the time for the 
migration of this parasite into another host must be tbe autumn, 
and the young larva would go into the periwinkle most likely in the 
early Winter and Spring. From these observations it appears 
that the right time to make infection experiments would be the 
Summer months, and I hope to carry on some of these experiments 
at the first opportunity. These Trematodes were found in the 
periwinkles from the Holy Island scaup, but not in those from any 
of the other mussel beds. 
The mussel is not materially affected by the encysted worm. 
The foot is made up of a central glandular mass surrounded by 
muscular tissue, and the worm encysts in both parts, but more 
frequently in the muscular portion. Sections through the foot 
show a multiplication of nuclei in the tissue immediately sur- 
rounding the cysts (see Fig. VI — section of foot of mussel stained 
