MoUusk-inf eating Trematodes. 105 



conspicuous pharynx to a narrow intestine bifurcating about 

 a tiiircl of the way down the body, eacli lobe reachinji; nearly 

 to the posterior end. Two clear excretory canals beginning 

 in the head-region run down the sides of the body, and join 

 just before tliey reach the clear excretory sac opening 

 posteriorly. The ventral sucker, which is larger than the 

 anterior, is phiced slightly behind the centre of tiie body. 

 'J'he cercaria is very contractile, and when moving uses its 

 body more tiiau its tiiil, shortening and elongating itself 

 continually. 



It is an interesting fact that these specially large and fine- 

 looking Purjtura lapiUus from Stranraer are much more 

 frequently infested with tiiis Trematode than the poor under- 

 sized specimens from Holy Island. One would imagine that 

 the reason for this is the greater ])revalence at Stranraer of 

 the host in which the adult worm lives, in all probability a 

 sea-bird. 



The third Ti-ematode is not unlike the second, but is some- 

 what slimmer in build and has a distinct double row of spines 

 round the head. It occurred in one specimen of the common 

 limpet. Patella vulgata, out of sixteen examined from the 

 shores of Locii Kyan, east of Stranraer, in September 1906, 

 completely obliterating tlie gonad and riddling the liver. 

 The worm occurred as long narrow rediai about 1'8 mm. long, 

 transpart nt and colourless (see PI. VIII. Dj. A pharynx can 

 be distinctly seen, but I could make out no enteron in any of 

 the specimens. Tailed cercarioe fill the redise and move about 

 inside them, contractinjr and elono^ating in much tlie same 

 •way as those from Purpura lapillus. The blunt tail is less 

 than half the length of the animal (see PI. VIII. C). The 

 cercaria is about 0"50 mm. long without tiie tail ; its head is 

 transparent, surrounded by a collar of two rows of fine spines, 

 and is constricted off slightly from the rest of tlie body, wliicli 

 is coarsely granular and opaque, and in fully developed 

 specimens covered with short blunt spines. A large anterior 

 sucker leads to a narrow oesophagus, which leads by a small 

 pharynx to a narrow intestine running down for about two 

 fifths of the length of the body before it branches into two 

 lobes nearly reaching to the posterior end. Two very 

 granular excretory canals begin in tiie head-region, run down 

 the sides of the body, and pass into a clear excretory sac 

 opening posteriorly. A large ventral sucker occurs behind 

 the centre of the body. Tiiis worm seems to be an Ecliiuo- 

 sloinuniy and the last species was so like this that one would 

 expect it to belong to the same subgenus; but no spines were 

 seen on the head. 



