434 Dr. Johnston on Entozoa. 



a penis ; but this I am certain is an erroneous view of their 

 nature ; and it seems, on the contrary, to be rendered at least 

 probable, by my observations on the Udonella caligorum (Mag. 

 Nat. History, vol. viii. p. 497)> that the organ is a vesicle con- 

 taining ova or embryo young, which the Phylline lays and at- 

 taches to the fish by means of the filament. The round gra- 

 nular viscus connected with it (c) may be that in which the 

 ova are invested with their capsules ; and the didymous organs 

 in the centre of the body appear to be ovaries in which the 

 ova are themselves produced. From the researches of Nord- 

 mann in analogous worms, we may suspect that there are two 

 sets of blood-vessels and a true circulation, but I could see one 

 set only, ^uch as they are delineated in our figure ; and in this 

 respect the circulating system resembles that of the Planarice 

 as described by Duges. 



Phylline Hippoglossi has not been previously recorded as a 

 native of our seas. It lives parasitically on the Holibut (Hip- 

 poglossus vulgaris) ; and about two years since I found nume- 

 rous specimens on a large individual that had been captured 

 in Berwick Bay. Following the older authors, Cuvier and 

 Lamarck have arranged it among the Leeches, but they were 

 well aware of the unnaturalness of this allocation, for its 

 nigher relations with the Polystomce and Planarice are too ob- 

 vious to be overlooked ; and, though living on the external 

 surface, the structure proves that, in the system of nature, it 

 forms one of a family (Trematoda, Bud., Sterelmintha, Owen,) 

 of which the greater number live within the intestines of other 

 animals. 



Plate XV. fig. 1, 2, Phylline Hippoglossi of the natural size ; the 1 a 

 view of the dorsal, the 2 of the ventral surface. Fig. 3. The same magnified. 



Fasciola anguill^e. Plate XV. fig. 4 — 6. 



Generic character. " Corpus molle, oblongum, depressum, 

 interdum teretiuscidum ; ports duobus remotis : altero antico 

 subterminali ; altero ventrali, later ali ant infer o. — Os : porus 

 anticus. Anus : porus ventralisP Lamarck. 



Specific character. u F. depressiuscula, subovata, crenata, 

 postice emarginata ; pori antiei margine tumido, ventralis ma- 

 joris recto." Lam. Anim. s. Vert. iii. 182. Turt. Gmel. iv. 36. 



