has been observed to take place in insects, and perhaps points. out some analogy between the valves of the shell and the upper wings, or elytra of insects, and the mantle and their under wings. Bosc states, that the animals of the genus Venus, in calm weather, may be seen sailing on the surface of the waters, using one of their valves as a boat and the other as a sail. As these are usually rather heavy shells, they must be furnished with some means of rendering themselves lighter than the water. Pliny, of old, mentions shells dedicated to Venus, which sail and oppose their concave part to the wind. Thus we see the Creator has given even to these apparently stupid and inactive creatures means of enjoyment, that every one is not aware of; and powers of locomotion, of which, at first sight, they seem incapable. I might enlarge here on the admirable contrivance and variety observable in the hinge, as it is called, by means of which the animals are enabled to open and shut the valves of their shells; upon the sculpture and colours that distinguish many of them, particularly amongst the unimusculars, but this chapter is already too long, and enough has been said to prove that they have in no respect been neglected or overlooked by the Almighty Being who willed their existence, and who is ever watchful over the creatures of his hand, to provide them with all things necessary for their being, consistently with the ends he created them to serve. CHAPTER IX. Functions and Instincts. Univalve Molluscans. THE Univalve shells of the Swedish naturalist, a term adopted from Aristotle's Monothyra, are next to be considered; these, with the multivalve Chitons form the Gastropods, or shell-fish using their belly for a leg, of Cuvier; and with the cuttle-fish and nautilus tribe constitute Lamarck's Class of Molluscans. The latter author divides his Class into five orders, four of which belong to the tribe I am considering. 1. Pteropods (wing-footed;) furnished with organs only for swimming and sailing.' 2. Gastropods (belly-footed ;) body straight, never spirally convolved; a muscular foot for creeping under the belly. 3. Trachelipods (neck-footed;) greatest part of the body spirally convolved, always inhabiting a spirivalve shell; foot free, attached to the neck, formed for creeping. 4. Heteropods (diverse-footed ;) no coronet of arms; no subventral, or subjugular foot; fins, one or more, not disposed in pairs.2 As the Cephalopods, forming Lamarck's fourth Order, may be regarded rather as constituting a larger division or Sub-class of the Molluscans, than an Order, I shall consider them in a separate chapter. 1. Proceeding from one of the above Orders to another, I shall select such individuals, belonging to it, as appear to exemplify the great attributes of their Creator, either in their structure, forms, habits, or instincts. The animals of the first Order, like the long celebrated Argonaut and Nautilus, enliven the surface of the ocean in fine weather, where they steer their little barks through, between, and over its fluctuating waves, and spread their membranous sails to the soft breathing of the zephyrs. One of the most noted animals of the tribe is known by the appellation of the Boreal Clio, which, like the jelly-fish, has a gelatinous body, is defended by no shell, and affords food to 1 PLATE V. Fio. 6, 7. 2 Fie. 8. This the whales and other fishes, as well as to the sea-birds. animal is abundant in places that suit it, and appears only during the warmest hours of the day on the surface. Other genera of this Order are covered by a shell or shells. Of this kind is the genus Hyalaa, so named from its semitransparent shell, which wears the appearance of a bivalve with soldered valves, the upper one being the largest; this difference of size of the seeming valves causes an aperture through which the animal sends forth two large yellow and violet wings, or sails, rounded and divided at their summit into three lobes. The head in this genus is almost evanescent, so that both shell and head exhibit an easy transition from the acephalous or bivalve Molluscans to those which have a head. When its wings or sails are unfolded it moves with great velocity on the surface of the sea. The animals of this Order, both from the beautiful colouring of their filmy sails or wings, and from their number and symmetry, are better entitled to the appellation of the butterflies of the ocean, than the escallop shells which have sometimes been so called. The mantle of the bivalves becomes an organ of very different use in the Pteropods; for they, having no means of fixing themselves, like most of the bivalves, float continually in the ocean; to compensate for this want, as in innumerable other instances, their Creator has given them' the power of expanding this organ as a sail, both for motion and to give some direction to their course; it is attached to the mouth or neck, and is connected in some species with their respiration. Nothing certain is known with respect to their food: probably they absorb the animalcules swarming in the sea water. 2. The series of Gastropods begins with animals that have no shell, amongst which the most remarkable seem to be the Scylla and the Tethys, both known to Linné, and by him described. The former is an oblong gelatinous animal, laterally compressed, elevated above in the middle, where it has two pair of membranous wings or fins. Its inferior surface is hollowed out longitudinally, by means of which, and its tentacles, it can embrace the stems of the fuci or sea-wrack, the flowers of which it eats. It is described as moving very slowly in the water by bending its extremities. It swims on the surface when the weather is calm, but adheres to the floating fuci when the sea is agitated, so that the kindness and foresight of its Maker-by giving it wings, for independent motion, and means to adhere to the fuci, when support is necessary to it, or it takes its food-has thus provided amply for its enjoyment and sustenance. The great peculiarity of the latter, the Tethys, is a mantle which extends above and beyond the head, like that of some marine goddess, concealing it entirely, and forming an ample veil, fringed or undulated at its margin. By the help of this veil they elevate themselves to the surface, and probably sail on the waters. This animal is nearly related to the Laplysia, a kind of sea-slug, like which it lives in muddy places, and ejects a black fluid; it is very fetid, and its flesh is poisonous. It only rises to the surface in the hot season. 1 shall next notice a tribe of Gastropods, which at first sight, considering the number of pieces of which their shelly covering is composed, seems to belong to the multivalves, amongst which Linné has placed it. It will be readily perceived that I am speaking of the Chiton, or coat-of-mail shell, but when the animal that it covers is examined, it will be found that, notwithstanding its multivalve shell, it really belongs to the Gastropods. These animals are generally found under stones, sometimes they adhere to the surface of rocks, and sometimes conceal themselves in their fissures: they often traverse vast tracts of ocean fixed to the keels of ships: like some of the limpets, they fix themselves a good way out of the water, so as only to be wetted when the tide is up, and sometimes above high water mark. Poli says that when they resist any attempt to force them from their station, they expel the air and water on all sides and produce a vacuum, so that it is very difficult to overcome the pressure of the atmosphere; and Mr. Frembly, who had an opportunity of studying their habits on the coast of Chili, states that when not apprehensive of danger their attachment is very slight, and by pushing them gently they will easily slide from the surface to which they are attached, but if a direct attempt is made to unfix them by force, they will part with a portion of their shells sooner than let go their hold. When we consider that these animals are not only often exposed to the violent action of the waves, but also to the attack of countless enemies, we see abundant reason for the coat of Imail with which their Creator has covered them. Even the fleshy or cartilaginous margin, or zone, as my lamented friend the Rev. Lansdown Guilding, in his admirable memoir on this tribe, denominated it, is defended sometimes by scales, spines, and bristles, at others rough with numerous little bony tubercles; it is also described as in general fringed, so that when the animal attaches itself to a rock or stone, it is altogether calculated, by the application of the prone part of its body, to produce a vacuum. The wing-shell and other bivalves that suspend themselves by a byssus, are sufficiently protected by their shells from the attack of their enemies, without so complete an adhesion of the body as is necessary for the coat-ofmail shell. Mr. Guilding, who had excellent opportunities of observation, informs as that these animals are night-feeders, remaining stationary as above, during the day; reasoning from analogy he suspects they feed on marine plants, the sea-wrack, &c. These creatures slide along very slowly: if accidentally reversed, they recover a prone position by the violent mottous of the ligament or zone that surrounds them, and if alarmed they sometimes roll themselves up like woodlice. Lamarck proceeds immediately from the Chitonidans to the Patellidans or Limpets,' which also fix themselves so firmly to the rock, that it requires considerable force to separate them, and sometimes in such numbers that their surface seems quite covered by them. The transition from the former tribe to this, with no intermediate links, seems at first sight violent, and their right to be associated in the same family rather problematical probably intermediate species will come to light which will render this point more evident than the shell of these animals appears to indicate. With regard to their functions and the part assigned to them in the great plan of creation, little is known; probably, from their numbers in some parts, they may help to soften the rocks, so that they may, at some destined hour, yield more readily to the force of the winds and waves; thus they may be enumerated amongst the instruments which the Creator employs to effect his purposes, and such changes in the coast of any country, as he wills shall take place. They afford a beautiful instance of the gradual progress of Creative Wisdom from form to form. If the student of the tribe looks with inquiring eye at a collection of the Patellidans, or limpets, in the flattest and most depressed of them he will find no small resemblance to one of the valves of a bivalve shell, he will soon, however, discover a prominence in it, the first tendency towards the spiral convolution, a little removed from its centre, which will prove to him that it belongs to a very different tribe; looking again at others that are more elevated and conical,' he will see the same prominence or beak forming a more striking feature, and ascertaining these shells to be univalves, he will find, upon a comparison of them with the nerit,* the snail,' or the periwinkle, that this umbo or knob is analo 1 Patella. 3 Patella vulgata. 5 Helix. 2 Umbrella indica. |