TREMATODES OF THE NORTHUMKJERLAND COAST 33 



figure and description of it, and for convenience have given it 

 the name of Cenaria strigata. This cercaria occurs between the 

 mantle and shell of Tellina tenuis and Donax vittahis ; its body 

 is oval and very conspicuously striated by rows of spines. 

 Length o"3o-o'4o mm., oral suckers 0.09 mm., ventral sucker 

 0*05 mm., agreeing fairly well with Giard's measurement {i.e., 

 length 0*42-05 mm., oral sucker cogS-o'io mm., ventral 

 sucker 0*052 mm.). The pharynx (0*03 mm. long) leads to a 

 short oesophagus, and this branches into two broad, clear, and 

 almost circular lobes, reaching a very little way below the 

 anterior margin of the ventral sucker. The excretory vesicle 

 is regularly and gracefully curved, somewhat in the shape of 

 a lyre. A pair of testes are occasionally seen symmetrically 

 placed, one on each side behind the ventral sucker. The hind 

 part of the body is slightly drawn out just where the excretory 

 vesicle opens, giving the cercaria the appearance of having a 

 very short tail, and in some examples this is very conspicuous. 

 This is alluded to by Giard*, and Pelseneerf figures and 

 describes evidently the same cercaria, which he considers to 

 be probably the young form of his fork-tailed Cercaria 

 syndosmyce. The latter cercaria has the suckers nearly 

 equal, which makes it unlikely that this is the same worm. 

 When I first found the cercaria in Tellina., I believed 

 it should have been tailed, but since then I have regarded 

 this as erroneous, since no tailed forms of the cercarias of 

 Gymnophalbis have ever been seen, and the only younger 

 stage known is that described by Jameson, and later found 

 abundantly by Nicoll and myself in the cockle, Cardiuni edule, 

 and in Tapes dcciissata, where the cercarias occur in simple 

 sporocysts and are tailless. The cercarice are often to be seen 

 free, having emerged from the sporocysts, and they never 

 have tails. Although Cercaria syndosmya, is in many ways 

 like a Gymnophallus, e.g. in the digestive system and excretory 

 vesicle, yet I think it is more likely to belong to some other 

 allied genus. 



* Op. cit., Comptes rendus cTes stances de la Societe do Biologie', T. LXIII., 



p. 419, 1907. 



t Op. cit., p. 173 and 185, PI. X., fig. 22. 



