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The singular structure of the genus Pleuronectes, or Flat-fish, accords as well with its habits and economy, as contrivance does with use, in the general works of nature. The flat form, the situation of the eyes, the absence of the air-bladder, sufficiently point out the ocean site it is designed to occupy. The defenceless creatures which
genus reside either at the bottom of the sea, or in the estuaries of the larger rivers, imbedded in their sandy pastures, for the evident purpose of avoiding the attack of rapacious aquatic animals. Here they feed on such marine insects and shell-fish, as the sands abound with ; and here also they evade, by their superior activity, the pursuits of their voracious enemies.
The fins of the Black Goby coalesce, and form a sort of funnel, by means of which this otherwise unprotected animal fixes itself immoveably to the rocks. In like manner, the Jura Sucker is furnished with strong membranes, that answer the same purpose. A similar construction is also obvious in the Unctious Sucker, which derives its name from the soft and unctuous nature of its body, resembling that of the common Snail. It is found in the sea, at the mouth of great rivers, where the waters generally rush forward with such rapidity as to carry every thing before them.
The peculiarity of its construction, and the agitated character of the surrounding element, naturally lead us to expect some compensatory contrivance adapted to its mode of life; or rather, that the defect of one part or organ, should be supplied by the structure of another. We find, accordingly, that the body is nearly round, and covered in every part with a slippery secretion, for the evident purpose of protecting it from the friction of the water; that the pectoral fins are broad, thin, transparent, nearly uniting under the throat, in order to assist it in stemming the most rapid torrents ; that the orifices of the gills are remarkably small, doubtless to prevent the water from entering too rapidly; and that further, beneath the throat is a circular depression, resembling that made by a seal; this is surrounded with twelve small, pale, yellow tubes, by means of which it can readily attach itself to rocks and stones. But how is this effected! Reasoning from the structure of the Echinus, a creature furnished in like manner with numerous absorbing tubes, for securing the shell fish on which that species of Crustaceæ most generally prey, we may conjecture that the pale yellow tubes of the Unctious Sucker own a similar construction. That they are hollow, furnished at the termination with a plate provided with muscles, and one or more absorbents, for the evident purpose of close adhesion to any extraneous substance; and that by the aid of these they not only fix themselves to the sides of the rocks, and thus resist the violence of the waves, but also secure the shell-fish, and floating insects, or suck out the juices of the surrounding fuci and sea-weeds.
A still more extraordinary configuration is obvious in the Occellated Sucker, and in its relative the Lump Sucker, one of the numerous family of Rock-fish, which derive their name from fixing themselves immoveably to the surface of the rocks. In the former, a very singular appendage is observable on the head : in the second, the pectoral fins are large and broad, nearly uniting at the base, in such a manner as to form a kind of funnel. An oval aperture is situated beneath, surrounded with a soft muscular substance, beautifully edged with small thread-like appendages, which act the part of numerous claspers, and enable it tenaciously to adhere to rocks and stones. Nay, such are its powers of adherence, that when thrown into a pail of water, it has attached itself so firmly to the bottom, that on taking it by the extremity, the whole pail, though capable of containing several gallons, has been lifted up without removing the fish from its hold. The utility of these appendages to an animal inhabiting the rocky shores and turbulent seas of Greenland, and generally diffused throughout the Northern Ocean; their inutility, and consequent omission, in such as frequent still lakes and inland seas, is so obvious, that I am at a loss to conjecture how any one can admit the fact, and discredit the design.
The head of this singular species is provided with an oval shield or disk, resembling in its construction, and obvious purposes, such as are assigned to the common Scuttle-fish. This disk is varied with eighteen striæ, the interstices of which are capable of being inflated or contracted, so as to produce a vacuum, at the pleasure of the animal. Now let it be remembered, that by this simple and admirable contrivance, the Remora is enabled to adhere with great tenacity to any flat surface. It is, therefore, often found on the sïdes of vessels, and has been fabled to impede their progress ; it is even also seen occasionally on aquatic animals. A cod-fish was recently taken up at Scarborough, with a Remora clinging to its back.
In many species, a different organization is discoverable, varying in accordance with their respective habits. The mouths of the Lesser, and Sea Lampreys are formed in such a manner as to admit of their closely adhering to the rocks. For this purpose, the mouth in each is round, and placed rather obliquely below the end of the snout; the edges are jagged, and the teeth disposed in a circular order, at a considerable distance from the margin, evidently, lest they should interfere with the action of the mouth. But in order to obviate any inconvenience that might result from the necessity of retaining a portion of salt water, after adhering to the stones, the Creator has placed on the summit of the head a small orifice,