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and he knew the shells of the country pretty well. Had I ever seen it? I told him I had, rather ! and I told him and the native the mischief they would do, and the intruder, being condemned to death, was promptly "crunched" under my foot. Then came the question, how got it there? I told Wright how it got to the Cape, and went off in a spirit of inquiry (seasoned with diplomacy) to Mons. Luguier the French chief official, or Résident as he is called ; a little manoeuvring brought round the question, did he like escargots ? "Ah, yes !” and he had lately had a stroke of luck; a French man-of-war had called in and given him a nice lot of them; he had eaten the large ones and had distributed the small ones about the place, and when they grew bigger and had large families, he would always have a dish at command. So thus the introduction of the pest into two widely remote countries is most distinctly traced to French men-of-war.”

SLUGS.

The naked molluscs, as Mr. Hedley remarks to me, seem to have roamed further and faster than shellsnails; in their race to the antipodes, at least, as recently pointed out by him, European kinds “have far outstripped their shell-bearing relatives," I and this is certainly a surprising result, for, as we have seen, the creatures clearly seem less fitted than snails for accidental dispersal under nature. In all probability, how

· C. Hedley, “ Ann. and Mag. Nat. Hist.,” (6), ix. (1892), p. 170.

ever, they have been widely scattered by man, being carried, no doubt, for the most part, along with consignments of plants, shrubs, etc. Many kinds, indeed, seem eminently suited for such transportal; of Testacella haliotidea, for instance, Mr. Jeffreys writes :

“A usual habitat of this kind of Testacella is at the roots of flower-plants, or under heaps of dead leaves in gardens; and if a plant were imported into this country from the botanic garden at Montpellier with the native soil or a compost made of leaf-mould, either the snailslug or its eggs would perhaps accompany it.” 1

The presence of T. maug ei in this country is usually attributed to transportal with plants. Many kinds must annually travel in safety from one country to another in Wardian cases, etc. Observed facts proving dispersal in this way, however, are probably scarce, but this is explained perhaps by the fact that the creatures, probably travelling chiefly as ova, are not likely to be often noticed. Tasmanian specimens of the great grey slug (Limax maximus) have been observed to be infested with an acarus, and if this proves to be identical with the European parasite, the fact will argue, as Mr. Hedley remarks, that the animals migrated in the adult rather than in the egg state. The United States National Museum, it is interesting to find, once “received a specimen of the peculiar slug Veronicella which had been found by the giver in a bunch of bananas;

»3 and

1 “British Conchology," i. (1862), p. 146.

C. Hedley, “ Ann. and Mag. Nat. Hist.,” (6), ix. (1892), p. 170. 3 R, E, C, Stearns, “West American Scientist,” vii. (1891), p. 108.

it is worthy of note also that a couple of “ splendidly grown Parmacella”_slugs foreign to our fauna-no doubt introduced accidentally with plants, are said to have been detected on one occasion in a garden near Newcastle.

· H. B. Tristram, “ Zoologist,” (3), i. (1877), pp. 260-1.

CHAPTER IX.

ON THE FRESH-WATER AND LAND MOLLUSCA

IN

TRODUCED INTO THE BRITISH ISLES BY HUMAN

AGENCY.

MAN's agency, as Forbes long ago remarked, “may materially affect a fauna, and has affected that of Britai n.” Of the forty-six fresh-water species included in the Conchological Society's list of 1883, however, only two, the zebra mussel (Dreissena polymorpha) and an American coil-shell (Planorbis dilatatus), can be reasonably regarded as human importations ; and, as far as I know, only one other, Sphærium ovale, has ever been looked upon as even doubtfully indigenous.

Sphærium ovale, which is local in this country, happens to occur in company with Planorbis dilatatus in canals at Gorton, Pendleton, etc., so that Mr. Jeffreys was led to suggest, in 1869, that it might possibly be the S. transversum of Say introduced, like P. dilatatus, from America ; but he observed that it had long been known in this country, and that he possessed a specimen which was in Dr. Turton's collection of British shells more

Edward Forbes, “Report, 9th meeting, British Association, 1839,” (1840), p. 130.

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than forty years previously. It has been further suggested that shells regarded as pertaining to a form of Planorbis glaber Jeff., found associated with P. dilatatus in a water-lodge at Burnley, may be Say's P. parvus also introduced from America ; P. glaber, however-often regarded as identical with P. parvusthough local, ranges widely in Europe, extending in this country “from the Shetland Isles to Land's End," and its right to rank as a native is not doubted.”

A short account of what is known of D. polymorpha and P. dilatatus in Britain, and of the manner in which they were probably introduced, may be of interest; and it is worth while, perhaps, to add a note on an exotic pondsnail, Physa acuta, which, though not referred to in the Conchological Society's list, is known to live, under artificial conditions, in two localities in England, and one in Scotland, and has in all probability been introduced unintentionally by man.

DREISSENA POLYMORPHA Pall. On 2nd November, 1824, the Linnean Society, as appears by an extract from their minute-book, received from Mr. J. De C. Sowerby, specimens of a fresh-water shell,“ probably the Mytilus polymorphus Gmel., 3363,” which had been found in abundance, attached to shells and timber, in

* J. G. Jeffreys, "Ann. and Mag. Nat. Hist.," (4), iv. (1869), pp. 341-2; and see also W. C. Hey,“ Journ, of Conch.,” iii. (1882), p. 271; T. Rogers, “ Journ. of Conch.," v. (1887), p. 220 ; R. Standen, Naturalist,” 1887, p. 157.

* T. Rogers, "Journ. of Conch.," v. (1887), p. 219; Jeffreys, “ British Conchology," i. (1862), p. 86; Rimmer,

“ Land and Freshwater Shells,” 1880, p. 40.

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