356 Echinostonmm secundum , Nicoll 
Although infection experiments on the birds are almost impossible, 
I have been able to prove the infection of the mussel from the 
periwinkle. In experiments of this kind there is always a risk of 
the second host being already infected, but in this case great care was 
taken and a control experiment carried on at the same time. 
Experimental Infection . 
Two tanks A and B were used for the experiment. Sea water from 
Cullercoats Bay ran into these continually. The water was evidently 
free from the parasite as this worm has never been found at Cullercoats 
and almost certainly does not occur there. 
The mussels (350) were procured from Blyth Harbour. They were 
specially gathered from wood-work and piers at least fifteen feet from 
the ground and from a locality where the mussels have never been 
known to harbour the parasite. Of these mussels, 50 were opened 
and examined microscopically and were found to be free from the 
parasite. The remaining 300 were divided into two portions, one of 
which was put into Tank A and the other into Tank B. Into Tank B 
were also put 300 periwinkles from Budle Bay, and one periwinkle 
which had been cracked open to show that it contained the parasite. 
These experiments were started on October 19th, 1908. Mud and a 
little seaweed from Cullercoats Bay were from time to time put into 
both tanks. 
At intervals of about a week mussels from each of the tanks were 
forwarded to me at Leeds for examination, with the result that out of 
30 mussels from each tank, 24 from Tank B contained the encysted 
worm but none of those from Tank A were infected. The number of 
cysts in each infected specimen varied from one to five and all were in 
the foot with one exception when the parasite occurred in the liver. 
As the mussels of the control experiment in Tank A were in no case 
infected it seems clear that the source from which the parasites came 
was the periwinkles, and that the Echinostonmm encysted in the 
mussel’s foot is a later larval stage of the cercai’ia contained in the 
periwinkle. The life history of Echinostonmm secundum may therefore 
be summed up as follows:— 
First Host 
Littorina littorea 
Second or 
Intermediate Hosts 
/Mytilus eclulis 
I Cardium edule 
- Mya arenaria 
Tapes pullastra 
,Mactra stultorum 
Final Hosts 
Hcematopus ostralegus. 
- Larus ridibundus. 
L. argentatus. 
