100 A. r. THOMAS. 



pa tic a, there was reason to believe that here also an alternation 

 of generations existed, and that one or more molluscs served as 

 intermediate host for the asexual forms. Many attempts had 

 been made to discover the intermediate host by various eminent 

 biologists, including Professor Leuckart, von Linstow, Ercolani, 

 &c., but all had proved fruitless, and notwithstanding its im- 

 portant practical bearing the problem remained unsolved.^ 



Very many suggestions had been made as to the nature of the 

 intermediate host. Moulinie^ had found in Limax cinereus 

 and Arion rufus (ater) sporocysts containing cercarise with a 

 rudimentary tail, and suggested that these miglit have some 

 connection with the liver-fluke. I met with this species in 

 Arion ater early in the course of my investigations, and was 

 able to disprove experimentally the conjecture that this was 

 the cercaria of Fasciola hepatica. Willemoes-Suhm^ had 

 drawn attention to the fact that liver-rot was very prevalent in 

 the Faroe Islands, the molluscan fauna of which was restricted 

 to eight species, viz. Arion ater, A.cinctus, Limaxagrestis, 

 L. marginatus, Vitrina pellucida, Hyalina alliaria, 

 Limnseus pereger, and L. truncatulus. Of these Limax 

 agrestis, our common grey slug, was by far the commonest 

 and most injurious, and he suggested that this slug might act 

 as intermediate host. Von Linstow* had mentioned Planorbis 

 vortex as being possibly the host. Weinland^ had found the 

 liver ofL. truncatulus infested with nurse forms. The 



' A statement lias been published in several text -books, English and 

 American, to the effect that Cercaria cystophora inhabitiog Planorbis 

 marginatus is tlie larva of Fasciola hepatica. This, of course, is erroneous, 

 and the mistake appears to have been copied from an abstract in the 

 ' Zoological Record ' for 1872 of a paper by Willemoes-Suhm. The suggestion 

 really made in the original paper was that C. cystophora is the larval form 

 of Distoma lanceolatum. This species is known on the Continent as the 

 small liver-flnke, and is far less formidable than the larger, F. hepatica, the 

 true liver-fluke. It appears not to exist in England. 



- ' Mcmoircs de I'lnstitut Genevois,' vol. iii, p. 207. 



' ' Zeitschrift fiir wisscntschafiliche Zoolog'e,' 1873, vol. xxiii, p. 339. 



* 'Arch, fur Naturgcschichle,' 1875, p 194. 



* Abstract in 'Archiv fiir Naturgeschichte,' 1874, vol. ii, p. 423. 



