ABSTRACT
It has been known from very early times that the liver-rot of various herbivorous mammals is a parasitic disease due to the presence of very numerous flukes in the liver of the affected animals. Amongst our domesticated animals the sheep is by far the most frequent victim. The fluke disease is always common in certain districts in England and in many parts of the world; but in consequence of a succession of wet seasons there was a serious outbreak of it in the winter 1879-80, and it is estimated that in the United Kingdom 3,000,000 sheep were then destroyed by it. Hence special attention was called to the subject, and the research summarised in the following paper was undertaken on behalf of the Royal Agricultural Society of England.
A statement lias been published in several text-books, English and American, to the effect that Cercaria cystophora inhabiting Planorbis marginatus is the 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 specieá is known on the Continent as the small liver-fluke, and is far less formidable than the larger, F. hepatica, tlie true liver-fluke. It appears not to exist in England.
‘Mémoires de I’institut Genevois,’ vol. iii, p. 267.
‘Zeitschrift für wissentschafdiche Zoologie,’ 1873, vol. xxiii, p. 339.
‘Arch, für Naturgeschichte,’ 1875, p 191.
Abstract in ‘Archiv für Naturgeschichte,’ 1874, vol. ii, p. 423.
“Dell’ Adattamento delle specie all’ ambiente,” ‘Memorie dell’ Accademia delle Scienze dell’ Istituto di Bologna,’ serie iv, tomo ii, 1881, pp. 241, 327.
‘Archiv für Naturgeschichte,’ 1882, p. 80.
‘Proceedings of the Ashmoleau Society,’ 1857.
‘Die menschliclien Parasiteu,’ p. 531.
‘Transactions ‘of the New Zealand Institute, vol. v, p. 18.
‘Geographical Distribution of Animals,’ vol. i.
‘Brit. Ass. lieport,’ 1859, p. 127.
‘Roy. Agrio. Soo. Journ.,’ 1881, p. 7.
‘Beiträge z. Entw. d. Eiogeweidewürmer,’ p. 65.
‘Zeitschrift für wissentscbaftliche Zoologie,’ x, p.272.
Diesing (‘Wien. Sitzungsberichte,’ vol. xxxi, p. 248) has described the redia of Cercaria fallax as having two short processes situated anteriorly, and two, pf thrice the length, posteriorly. De Filippi (‘Memorie della Reale Accademia delle Scienze di Torino,’ Ser. ii, tomo xviii, p. 207) has described the redia of Cercaria tuberculata as having four lateral processes, two anteriorly and two posteriorly. I have met with a species which appears to be identical with Cercaria tuberculata, and in the redia recognised a collar. The same writer has figured (ibid., vol. xvi, pl. i, fig. 13) in the young redia of Cercaria coronata four processes; the two placed in front are slightly smaller than the two posterior, but otherwise they are drawn as if exactly alike. There can be no doubt that in all these cases the structures described as anterior lateral processes are simply the projecting borders of the transparent collar, seen perhaps in the flattened redia. From comparison with the descriptions given by these distinguished observers 1 was led in my first paper (‘Roy. Agricult. Soc. Journ.,’ 1881, p. 19) to similarly misinterpret the corresponding projections in the young rediæ of Fasciola hepatica.
Prof. Leuckart (‘Zool. Anz.,’ Oct. 9th, 1882) has also found these curious bodies (which had already been described by me in the ‘Journ. Roy. Agrie. Soc.,’ for April, 1881), and as he was unable to find any spines on the cuticle of his cercariæ, he suggests that the rod-like bodies are subsequently arranged in bnndles to form the spines of the adult fluke. But I have found the spines in the most mature cercariæ, and can say that these rod-shaped bodies have no connection with them, though I am unable to suggest any probable explanation as to their nature.
Sir Charles Lyell (‘Life,’ vol. ii, p. 212), in speaking of Madeira, says that Limnaeus truncatulus was unintentionally introduced by the Portuguese thirty years before, and has spread so widely that it is now found even in the pools and ruts in the roads, so that it must have a mode of distribution which needs investigation. It will be seen from the above account that the terrestrial habits of this snail, and its power of withstanding drought, are amply sufficient to explain its spread in Madeira.
‘Journ. R. A. S.’ 1881, p. 25.
Ibid., p. 26.
