M. V. Lebour 
443 
EcJdnostomum leptosorimm Creplin. 
(Villot, 1898, p. 18. Lebour, 1907 c, p. 447.) 
(PI. XXVIII, figs. 7-10.) 
Occurs in colourless or pale yellow rediae in the digestive gland 
of Paludestrina stagnalis from Fenham Flats and Loch Ryan. In 
about 26 per cent, from Fenham Flats and one per cent, from Loch 
Ryan. It occurs in spring, summer, and early autumn, most plentifully 
in marshy pools above high water mark, although also in pools left 
uncovered for several hours in the day. 
The rediae are all sorts of shapes which are constantly changing ; 
the smallest seen were 0’20 mm. long, the largest 1'4 mm. long. The 
young forms are pointed at the hind end and have two conspicuous 
ambulatory processes each side which tend to disappear in the larger 
rediae. The cuticle in all is very thick and much wrinkled anteriorly 
especially round the mouth. The pharynx is large but the intestine 
can hardly be made out. All stages of cercariae are contained within 
the rediae. The full-grown cercaria is tailed, without the tail 0‘40- 
0’50 mm. long, tail 0’3 mm. long and very thin and active. It is ex¬ 
tremely transparent, very agile and fond of bending itself backwards 
in the form of a U. Body covered with spines except at the posterior- 
end. Head end with a crown of 29 head spines arranged in a row 
round three parts of the head two at each end being below the 
others but very little smaller (long spines 0-019—0-02 mm., short spines 
O'OIG mm.), oral sucker O'OSO mm. across, prepharynx rather long, 
pharynx 0-026 mm. long, oesophagus long and narrow with intestinal 
caeca reaching nearly to the posterior end of the body. Ventral 
sucker 0-046 mm. across. Excretory vesicle roundish, with two 
much branched lateral canals filled with clear granules. Ducts of 
glands opening near anterior end. Gland cells all over body. In one 
case an encysted cercaria was found among the rediae but this is an 
exception as there is an intermediate host. The cercaria leaves the 
first host and swims about, finally getting- into Scrohicularia tenuis. 
This small bivalve is very common on Fenham Flats and the cercaria 
encysts in the foot as described by Villot. The cyst measures 0-12 mm. 
across with a thin transparent wall of two layers. 
The final host is the turnstone Strepsilas interpres in which 
Echinostomum leptosomuvi is quite common. Villot found it in the 
dunlin Tringa alpina and I have also found it in this bird. Both feed 
on Scrohicularia tenuis. 
