OF THE LEPAS ANATIFERA OR BARNACLE.[101]
[Plate XIII.] Fig. 1 and 2.
This is a tender and brittle shell-fish of a very peculiar species; its length is about an inch, and its diameter about three quarters of an inch. The shell is not composed of two pieces or valves, as in others, but of five; two of these are larger than the rest, to which are affixed two smaller ones; the fifth piece is long, slender, and crooked, running down length-ways, and covering the joinings of the other pieces. The shell part is of a pale red, variegated with white; it adheres to a neck or pedicle of an inch long, and about a fifth of an inch in diameter; by which means it affixes itself to old wood, to stones, to sea-plants, or any other solid substance that lies under water. It can shorten or extend this neck at pleasure, which resembles a small gut, and is usually full of a glareous liquor; it is composed of two membranes, an external one, hard and brown, an internal one, soft and of an orange colour. The large portions of the shell open and shut in the manner of the bivalves; the others, being moveable by means of their membranaceous attachments, give way to the opening of these, and to the motions of the body of the fish in any direction. It is furnished with a cluster of filaments or tentacida, placed in a row on each side, usually twelve, sometimes fourteen in number. They are a kind of arms appropriated for catching its prey, and therefore placed so as to surround the mouth of the animal, which is situated between them, and consequently easily receives what they thrust towards it. By the motion of these arms, which may be exerted in such a manner as to play either within or without the cavity of the shell, it forms a current of water, which brings with it the prey it feeds upon. Fig. 1 represents two of these arms as magnified by the microscope; Fig. 2, the natural size of those from which these drawings were made. Each arm consists of several joints, and each joint is furnished on the concave side of the arm with a brush of fibrillæ or long hairs. The arms, when viewed in the microscope, seem rather opake; but they maybe rendered transparent, and form a most beautiful object, by extracting out of the interior cavity a bundle of longitudinal fibres, which runs the whole length of the arm. Mr. Needham[102] thinks the motion and use of these arms illustrates the nature of that rotatory motion which some writers have thought they discovered in the wheel animal.
[101] This animal is classed by Linnæus among the Vermes Testaceæ. Its generic character is: Animal, resembling a triton; Shell, consisting of several unequal valves; affixed by its base. Specific character: Pedunculated Barnacle, with compressed shell consisting of five valves. Syst. Nat. p. 1107, 1109. Edit.
[102] Needham’s Microscopical Observations.
In the midst of the arms is a hollow trunk, consisting of a jointed fibrous or hairy tube, which incloses a long round tongue or proboscis, that the animal can push occasionally out of the tube or sheath, and retract at pleasure. The mouth of this animal is singular in its kind, consisting of six laminæ, which go off with a bend, indented like a saw on the convex edge, and by their circular disposition are so ranged, that the teeth in the alternate elevation and depression of each plate, act against whatever intervenes between them. The plates are placed together in such a manner, that to the naked eye they form an aperture not much unlike the mouth of a contracted purse.
The western isles of Scotland, and some other parts of the British dominions, are abundantly stored, at certain times of the year, with a bird of the goose kind, commonly known in those places by the name of the brent goose or barnacle. These birds rarely breed with us, but seek, for their sitting season, islands less frequented than those where we find them in common. The seeing the birds so frequent, and yet never finding any of their nests, induced ignorant people to believe they never had any, and that they were not bred like other birds.
About the very shores where these birds are most common, the lepas anatifera is also found in great abundance. The fishermen, who observed vast quantities of these shells affixed to rotten wood, or dead trees that were floating in the water, or lodged by it on the shore, were soon led to imagine that the fibrous substances that hung out of them resembled feathers, and persuaded themselves that the geese, whose origin they could before by no means make out, were bred from them, instead of being hatched, like other birds, from eggs.[103] It was afterwards affirmed, that the shells themselves originally grew on the trees, in the manner of their fruit; and that the young bird, having in the shell obtained its plumage, dropt from thence into the water. From this arose the opinion that the barnacle or brent goose was the produce of a tree.[104]
[103] Hill’s Natural History of Animals.