352 
A CONTRIBUTION TO THE LIFE HISTORY OF 
ECH1NOSTOMUM SECUNDUM, NICOLL. 
By MARIE V. LEBOUR, M.Sc. 
Assistant Demonstrator in Zoology , Leeds University. 
Plate XXIV. 
In some notes on the Trematodes of Northumbria published in 
1905 a few remarks were made on a larval Trematode inhabiting the 
liver of the common periwinkle Littorina littorea. The liver in two 
per cent, of the periwinkles from Budle Bay was full of redise con¬ 
taining cercarise more or less developed, the latter agreeing in every 
way with an encysted Echinostomum larva which inhabits mussels, 
cockles and other bivalve mollusks in the same localit} 7 . So close 
was the resemblance that I had no hesitation in declaring them to 
be the same worm in different stages, but hoped for an opportunity 
of demonstrating this by experiment. In October 1908 through the 
courtesy of Professor Meek I had the opportunity of conducting 
some feeding experiments in the Dove Marine Laboratory, Cullercoats, 
which have given satisfactory results, and although it is not possible 
to state absolutely that the forms are identical yet the evidence 
is so strong that I think I am justified in regarding the young 
worm in the periwinkle as an earlier larval form of the encysted worm 
in the foot of the mussel and cockle. 
The youngest stage of this species I have seen is the redia, and I 
have never noticed miracidia or sporocysts. The liver in the infested 
periwinkles instead of being of a greenish-brown colour, as it usually is 
in healthy specimens, is a pinkish orange. On examination this is seen 
to be due to an enormous quantity of redias packed together. So 
crowded are they that very little liver substance is left and almost the 
whole of the spire of the shell is occupied by the worms. The full- 
grown redia is easily seen with the naked eye as a pinkish-yellow sac 
