ON THE EOT IN SHEEP. 569 



slugs, all told, out of which to choose the guilty party or parties. 

 These are, as enumerated in Siebold and Kolliker's ' Zeitschrift ' 

 for 1873 (vol. xxiii. p. 339), Limax agrestis, Limax margmatus, 

 Vitrina pellMcida, Hyalina alliaria, Limnaeus pereger, Limnaeus 

 tmncatulus, Arion ater, Arion cinctus. That the fluke of the Faroe 

 Islands sheep spends a considerable part of its life as a parasite in 

 one or more of these mollusca admits of about as much doubt as 

 the statement that the ' giddy ' disease — the ' sturdy,' as the Lake 

 District shepherds pronounce the French word etourdi — of the 

 sheep is similarly dependent upon a to-and-fro shuttlecock alterna- 

 tion of one animal between two others. I do not say that it is 

 necessarily in one, and one only, of the specified eight mollusca. 

 Undoubtedly the fluke, like other parasites, may, in its sporting 

 tour, infest many hosts. As a matter of fact, this particular fluke 

 (Fasciola hepatica) in its adult stage infests some dozen mammals 

 beside the sheep and ourselves. But, as a matter of speculation, I 

 incline to think that the fluke in its younger days is, like some 

 other animals, a little, or indeed a good deal, more particular as to 

 where it lodges than it is in later life. As a matter of practice at 

 any rate there is no need to tell farmers to be on their guard 

 against snails which do not infest their pastures, and of the eight 

 just specified they need usually in England only look to the 

 black slug and the gray slug. Willemoes-Suhm suspected the 

 gray slug, I suspect the black slug ; partly on account of its very 

 wide distribution in space (it having been found as a ' spectre noir ' 

 in Prince Jerome Bonaparte's voyage to Jan Mayen's island), 

 partly from the facts furnished to me by Mr. D. Gresswell, 

 M.R.C.V. S., of Louth, to the effect that sheep which have been 

 feeding on turnips harbouring ' black jacks ' will die of rot even 

 when shifted on to salt marshes. Any inhabitant of the Shetland 

 Islands who will inform us that sheep-rot does infest his country, 

 or any inhabitant of Siberia who will inform us that it does not 

 infest his, will settle the question, in a preliminary way at least, in 

 favour of the black slug. For ' this very common, beautiful, and 

 exceedingly variable slug,' as Forbes calls it, is not found in 

 Siberia, and the Limax agrestis is ; while in the Shetlands the case 

 of distribution is precisely reversed. Whoever will furnish us with 

 the information required will be indeed a ' true farmers' friend.' 

 Anyhow, the line of prevention indicated in my previous letter of 



