104 Miss M. V. Lebour on 



size of tl e encysted form and possess both suckers, plinrynx, 

 txcrotoiy sjic, and tail. 



It is reinavknble thai the cercaria sliouhl possess a tail 

 vhen it cncvsts in the sporocyst, as the organ must be quite 

 nseless. Tlie encysting withiTi the sporocyst is not usual, 

 but Filippi states that the Tremalode whicli he describes as 

 Cercaria ecfn'natoides encysts in the same Paludina in wiiich 

 it was developed trom redije without quitting that mollusk, 

 and it lia> a tail which it throws off before encysting (Ann. 

 des Sci. Nat. 4' ser., Zool. 1S54. p. 255). 



The above-mentioned Trematode from the cockle is not 

 common — one infested specinnn occurring from Budle Bay 

 in March 1905 out of two hundred examined, one found 

 by Mr. James Johnstone from Morecambe Bay in A.pril 1906, 

 and one out of one hundred examined from Holy Island in 

 October 1*J06. In the two tirst-mentioned specimens found 

 in March and April no tailed cercaria; were seen. They were 

 found only in the cockle from Holy Island in October. 

 Possibly examination of many cockles in the summer months 

 may show us younger stages of the worm. 



The second Trematode to be der^cribed is from the common 

 wlielk, Ptirjyura lapiVus, from Holy Island and also on the 

 siiores of Loch Ryan to the west of Stranraer. Two hundred 

 and eight specimens from the Mussel Scaup, Holy Island, 

 were examined in October 1906, and the liver in two of these 

 was found to be infested by a Trematode. At Stranraer at 

 the beginning of September 1906 it occurred more abun- 

 dantly, five specimens out of thirteen containing it. The 

 liver in healthy specimens of Purpura lapdlus is a bright 

 yellow, but when this parasite is present it is a yellowish 

 white ar.d is full of long and not very active redise, which are 

 transparent and colourless, with the exception of the sac-like 

 intestine, which is coloured yellow from granules of food- 

 material (PI. YIII. B). Each redia is about 1*8 mm. long, 

 ■with a conspicuous ))liarynx and intestine, and is full of 

 rather opaque cercarise in various stages of development. 

 The cercaria (see PI. VIII. A) is tailed, and when full-grown 

 is about 0'45 mm. in length without its tail, which is about 

 two thirds the length of the body. The head-region is more 

 trans[iarent than the rest of the body, atid is separated from 

 it by a slight constriction ; the body is criarsely granular and 

 opaque and is covered (but only in fully developed si)ecimens) 

 with blunt spines. The tail is blunt, not so opaque as the 

 body, and, as usual, comes off at the slightest touch. A large 

 anterior sucker leads into a short oesophagus, which is often 

 obscured by contraction, and this leads by a thick-lipped and 



