436 
Marine Cercariae 
intestinal caeca reaching to the posterior end of the ventral sucker. 
Genital opening on the left of the ventral sucker. Nicoll (ix. 1907, p. 255) 
considers this as very likely to be the larval form of Spelotrema 
claviforme (Brandes) from the dunlin Tringa alpina and the ringed 
plover Aegialites hiaticula. 
The intermediate host is not known. 
Cercaria oocysta mihi (1907 c, p. 445). 
(PI. XXVII, figs. 8, 9.) 
Occurs encysted in sausage-shaped sporocysts in Paludestrina 
stagnalis from Fenham Flats and Loch Ryan. It occupies the digestive 
gland in 50 per cent, of those from Fenham Flats and two percent, from 
Loch Ryan. The sporocysts are colourless and verj' thin-walled enclosing 
cercariae in all stages. The younger cercariae are tailed but the tail is 
soon lost and the worm settles down to encyst. 
The cyst is thin-walled and a long oval 0T2 x 0'07 mm. The cast¬ 
off tails are to be seen moving about within the sporocyst. When all 
the cercariae are encysted the wall of the sporocyst dwindles and 
disappears. 
The cercaria measures 0'24 mm. in length when pressed out of the 
cyst and is about times as long as it is broad. The body is covered 
all over with spines. Oral sucker 0'026 mm. across, pharynx almost 
mid-way between the oral sucker and the bifurcation of the intestine 
but slightly further forward. Intestinal caeca reaching to about the 
level of the centre of the ventral sucker. Ventral sucker 0'019 mm. 
across. Lateral excretory canals can be made out faintly in the live 
worm. A cirrus sac opens on the left of the ventral sucker. Vitellaria 
and testes developed. 
This cercaria was found in August at Loch Ryan and in the winter 
from Fenham Flats. 
Further life-history not known, perhaps it is a species of Maritrema. 
Cercaria pirum mihi (1907 c, p. 446). 
(PI. XXVII, figs. 10, 11.) 
Occurs in the digestive gland of Paludestidna stagnalis in about 
four per cent, from Fenham Flats in July, October and December. The 
cercaria occurred in cysts all over the digestive gland and in those 
specimens examined in July the remains of the walls of the sporocysts 
