1

attached for some little time, for the toe had been chafed, and the observer heard from boys in the neighbourhood that the bird had been seen about for several days, and it seems, therefore, that the shell “had not released its grasp even when the duck lit upon the water, as it must frequently have done in the intervals of time between observation." In the same year Mr. H. V. Chapman submitted to the Field the foot of a snipe, with a shell of Sphærium corneum attached to the hind toe, stating that the bird had been shot by him, while "sailing over my head with apparently a leg down." The foot and shell have since been presented to the British Museum, and are now exhibited in the British-room at Cromwell road; the bird is said to have been shot near Rye, Sussex.

It is clear, I think, from these cases that bivalves may be occasionally carried to vast distances by birds, which, of all highly organized animals, are the least confined by geographical barriers; many annually migrate over large tracts both of land and sea, and they are occasionally blown far over the ocean by violent gales. It may be objected, perhaps, that shells are likely to drop off during long journeys, but I do not think this will often happen, for when bivalves once firmly close upon an object they generally hold on for a considerable time. But it is certain, of course, that

1

J. W. Fewkes, "Ducks transporting fresh-water clamp." Auk, i. (1884), 195-6.

2 H. V. C [hapman], "Accident to a snipe," Field, lxiv. (1884), 597, and see also p. 760,

1

they must often chance to be set down in unsuitable spots; it is true, as Mr. Darwin has remarked, that a bird, such as a duck or heron, "if blown across the sea to an oceanic island or to any other distant point, would be sure to alight on a pool or rivulet," but probably a bivalve would generally remain attached for some time after the bird had landed even if kept much under water. Sooner or later, however, the valves would have to be opened, and this is more likely to happen in water than on land. It may be seriously objected, I admit, that the transplantation of a shell full of fry or ova must be a comparatively rare occurrence, and it is even doubtful, perhaps, whether a single individual in this condition would have much chance of establishing a colony in a new home. Occurrences of the kind dealt with in this chapter are perhaps, after all, chiefly significant when viewed in connection with anomalies in local distribution, and it can scarcely be doubted but that they go far towards explaining the almost mysterious presence of bivalves in isolated ponds, between which and other waters a more or less constant communication is kept up by animals of many kinds, especially by flying water-insects and aquatic birds.

Many creatures, other than those above referred to, are doubtless occasionally entrapped by bivalves. Three cases of which I have heard are perhaps worth giving, but they are not of much importance for us.

1 46 Origin," p. 345.

A dead water vole with one of its feet firmly held between the valves of an Anodonta, four inches in length, was once found by Mr. Hardy on the banks of Mere Mere, Cheshire.

A snapping turtle (Chelydra), with a Unio (complanatus?), about three inches in length, clinging to its lower jaw, was caught by Mr. J. E. Todd, in 1882, while on an excursion along Rock River, near Beloit, Wisconsin. The animals, which were out of the water several rods from the river, were taken home and kept in a box, and the reptile was seen to make frequent and vigorous attempts to push off the clam with its fore legs, but without success, for when it escaped from confinement after two or three days it carried away the shell still attached to its jaw. The end of the jaw probably reached to about the middle of the inside of one of the valves, so that the mollusc would no doubt be considerably injured, but, ultimately releasing its grasp in a suitable place, it might possibly recover.'

In 1855-6 Professor Girard found numbers of small bivalves attached to crayfishes (Astacus fluviatilis) in ponds in the environs of Brie-Comte-Robert, Seine-etMarne. Every crayfish taken from a pond called "la mare à l'Anglais" had shells upon its toes; another pond, close by, also contained individuals similarly encumbered, and a man living at Brunoy, who was in

1 J. E. Todd, "Chelydra versus Unio," American Naturalist, xvii. (1883), 428; see also " Nachrichtsblatt der Deutschen Malakozoologischen Gesellschaft," 1883, p. 93; and I am indebted to Mr. Todd for having communicated some additional particulars,

the habit of procuring these animals for the market, informed the observer that he had noticed the same phenomenon in some other ponds in the neighbourhood. Sometimes every one of the eight ambulatory legs had a shell clinging to it, so that the animal appeared as if wearing clogs. The shells in question are spoken. of as " Cyclas fontinalis," but as Mr. Heynemann, who had the kindness to draw my attention to these

FIG. 6.

"Astacus fluviatilis & Cyclas fontinalis." After Girard, "Annales de la Société entomologique de France," (3), vii. (1859), pl. 4, fig. 1.

observations, points out, M. Girard describes and figures a much larger shell (Fig. 6).1

Professor Rossmässler2 mentions that zebra mussels (Dreissena polymorpha) have frequently been found attached, by the byssus, to the tails of crayfishes.

1 Professor Girard, "Annales de la Société entomologique de France," (3), vii. (1859), 137-142.

As quoted in "Ann, and Mag. Nat. Hist.," (3), xviii. p. 494.

CHAPTER IV.

TRANSPLANTATION OF UNIVALVES.

OPERCULATE water-snails, it seems possible, may sometimes be transported while clinging by closure of the operculum to the legs of aquatic creatures of certain kinds. Water-beetles and other such animals, walking amongst the branches of aquatic weeds or upon the mud at the bottoms of pools and slow-flowing rivers, must occasionally insert their legs into the mouths of these shells, and, if the operculum be quickly closed, the mollusc may possibly cling firmly, and may be carried about by a sufficiently strong animal for a considerable time. A large and strong-flying waterbeetle, in such a case, might obviously carry a shell of small size from one piece of water to another. One little observation, more or less apposite, has been made. the aquatic larva of a dragon-fly having been seen by Mr. Hardy in May, 1890, with one foot firmly held between the operculum and lip of a specimen of Bythinia tentaculata, and it is interesting to find, also, that a humble-bee has been seen with an operculate land-shell holding on to one of its legs in a similar