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.
The conversion of the fish into a bird, however fabulous, would be scarcely more astonishing than the metamorphosis which it actually undergoes--the young of the little animal having no feature to identify it with its final development. In its early stage (I quote from Carpenter's _Physiology_, vol. i. p. 52.) it has a form not unlike that of the crab, "possessing eyes and powers of free motion; but afterwards, becoming fixed to one spot for the remainder of its life, it loses its eyes and forms a shell, which, though composed of various pieces, has nothing in common with the jointed shell of the crab."
Though Porta wrote at Naples, the story has reference to Scotland; and the tradition is evidently northern, and local. As to SPERIEND's Query, What could give rise to so absurd a story? it doubtless took its origin in the similarity of the tentacles of the fish to feathers of a bird. But I would add the farther Query, whether the ready acceptance and general credence given to so obvious a fable, may not have been derived from giving too literal a construction to the text of the passage in the first chapter of Genesis:
"And God said, Let the _waters bring forth abundantly_ the moving creature that hath life, and _the fowl_ that may fly in the open firmament of heaven?"
Drayton (1613) in his _Poly-olbion_, iii., in connexion with the river Dee, speaks of--
"Th' anatomised fish, and fowls from planchers sprung,"
to which a note is appended in Southey's edition, p. 609., that such fowls were "_barnacles_, a bird breeding upon old ships." In the _Entertaining Library_, "Habits of Birds," pp. 363-379., the whole story of this extraordinary instance of ignorance in natural history is amply developed. The barnacle shells which I once saw in a sea-port, attached to a vessel just arrived from the Mediterranean, had the brilliant appearance, at a distance, of flowers in bloom[1]; the foot of the _Lepas anatifera_ (Linnæus) appearing to me like the stalk of a plant growing from the ship's side: the shell had the semblance of a calyx, and the flower consisted of the fingers (_tentacula_) of the shell-fish, "of which twelve project in an elegant curve, and are used by it for making prey of small fish." The very ancient error was to mistake the foot of the shell-fish for the neck of a goose, the shell for its head, and the _tentacula_ for a tuft of feathers. As to the body, _non est inventus_. The Barnacle Goose is a well-known bird: and these shell-fish, bearing, as seen out of the water, resemblance to the goose's neck, were ignorantly, and without investigation, confounded with geese themselves, an error into which Albertus Magnus (d. 1280) did not fall, and in which Pope Pius II. proved himself infallible. Nevertheless, in France, the Barnacle Goose may be eaten on fast-days by virtue of this old belief in its marine origin.