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and the narrow intestine leading from the pharynx branches here 
into two lobes ; a large pear-shaped excretory sac is conspicuous. 
The cuticle is covered with small spines which are particularly 
marked near the head end, and as they are arranged in rows give 
this part of the body a transversely striated appearance. A thin 
tail occurs but it is so easily separated from the worm that the 
latter is more often seen without it. Yillot (Ann. des Sci. Nat., Ser. 
G, Zool. Tom. VIII., 1878) describes a cercaria, C. miijocera, very like 
this, but differing slightly in the tail. This he found occurring in 
sporocysts in Scrobicularia tenuis. If it be the same species it is 
curious that it should occur both in a gasteropod and a lamellibranch. 
In Macoma balthica from opposite the scaup a sporocyst occurred 
which was pale yellow, had two eyes, and was ciliated (see Plate 
III., fig. VII.) It moved fast and had nothing but small granules in 
its body. In the intestine some simple yellow sporocysts were 
found, without eyes, not ciliated, and with only small granules 
inside. These were also present in Macoma balthica from Budle. 
In conclusion I might mention a cercaria which occurred in 
Tell in a tenuis and Donax vittatus although these were not from any 
mussel bed but from the Alnmouth sands. It is very transparent, 
oval, with a conspicuous curved excretory apparatus isee Plato III., 
fig. VII.) A large oral sucker leads into an intestine with two 
very broad and short lobes, and there is a large median sucker. 
The body is covered with spines and a very small tail occurs. This 
is probably the species allied to Brachyccelium htteiun described by 
Giard (Comptes rendus hebdomadaires des seances de la Soc. de 
Biologie, 1897). He thinks it may possibly be the same species as 
P>. luteum as it only differs from it in the relative size of the suckers. 
The tail in my specimens is evidently not fully developed. 
