The story has its origin in the peculiar formation of the little mollusc which inhabits the multivalve shell, the _Pentalasmis anatifera_, which by a fleshy peduncle attaches itself by one end to the bottoms of ships or floating timber, whilst from the other {224} there protrudes a bunch of curling and fringe-like cirrhi, by the agitation of which it attracts and collects its food. These cirrhi so much resemble feathers, as to have suggested the leading idea of a bird's tail: and hence the construction of the remainder of the fable, which is thus given with grave minuteness in _The Herbal, or General Historie of Plants_, gathered by John Gerarde, Master in Chirurgerie: London, 1597: "What our eyes have seen, and our hands have touched, we shall declare. There is a small island in Lancashire called the Pile of Foulders, wherein are found the broken pieces of old and bruised ships, some whereof have been cast thither by shipwreck; and also the trunks or bodies, with the branches of old and rotten trees, cast up there likewise, whereon is found a certain spume or froth, that in time breedeth unto certain shells, in shape like those of a mussel, but sharper pointed, and of a whitish colour; wherein is contained a thing in form like a lace of silk finely woven as it were together, of a whitish colour; one end whereof is fastened unto the inside of the shell, even as the fish of oysters and mussels are; the other end is made fast unto the belly of a rude mass or lump, which in time cometh to the shape and form of a bird. When it is perfectly formed, the shell gapeth open, and the first thing that appeareth is the foresaid lace or string; next come the legs of the bird hanging out and as it groweth greater, it openeth the shell by degrees, till at length it is all come forth, and hangeth only by the bill. In short space after it cometh to full maturity, and falleth into the sea, where it gathereth feathers, and groweth to a fowl, bigger than a mallard, and lesser than a goose; having black legs, and a bill or beak, and feathers black and white, spotted in such manner as our magpie, called in some places a Pie-Annet, which the people of Lancashire call by no other name than a tree-goose; which place aforesaid, and all those parts adjacent, do so much abound therewith, that one of the best may be bought for threepence. For the truth hereof, if any doubt, may it please them to repair unto me, and I shall satisfy them by the testimony of credible witnesses."--Page 1391. Gerarde, who is doubtless Butler's authority, says elsewhere, that "in the north parts of Scotland, and the islands called Orcades," there are certain trees whereon these tree-geese and barnacles abound.