« AnteriorContinua »
that part, extend the anterior rings, and so proceed successively with a kind of undulating motion.
3. We are next to notice a tribe of Annelidans, many of which, in one respect, make some approach to the Testaceous Molluscans. Though truly annulated and furnished with a kind of false legs, they are defended by a shell resembling in its substance, that of the class just alluded to, but often by its irregular convolutions proving that it belongs to an Annelidan and not to a Molluscan; some indeed approach to the spiral convolutions of a Trachelipod shell; others form a membranous sac, and cover it with agglutinated particles of sand, as the common Sabella; others again, likewise inhabit a tube, but they fix it in the rocks. The testaceous animals of this class, particularly the worm-shells' inhabit a tortuous tube. which they form, probably with more ease and celerity than the Molluscans form their shells-for they appear almost to do this as they move, since the shape of the shell imitates the sinuous windings of a worm, and that of the Serpula adheres to the substances on which it is formed. We see it often upon the shells of bivalves, to which it adheres by the lower surface, looking like a little worm creeping upon them; and forming convolutions; I have a specimen on a valve of the cock's-crest oyster, which is bound down by a process issuing apparently from the disk of the oyster-shell itself, how produced and thrown over the Serpula it seems not easy to conjecture. Dif ferent species of these worm-shells are often found, embracing each other with their convolutions, on the same shell; whereever the sea is or has been, they abound either in a recent or fossil state; they are found on rocks, and sea-weed as well as on marine shells, and those of lobsters. The Serpulidans, in general, imitate the spiral structure of the Trachelipod and other Molluscans, as is particularly evident in Siliquaria and Vermetus, if indeed the last genus is not itself a Molluscan, as Lamarck makes it.
Other species of this Order are taught to establish themselves in fissures of rocks, which serve them instead of a shell to protect the membranous tubes into which they retract their petaliform tentacles, which together represent a beautiful radiated
2 S. Triquetra.
3 Ostrea Crista-galli. Since the above was written, in the collection of the late Peter Collinson, I have seen two specimens of this oyster, which had produced from the back of their shell a double series of processes, with which, as with so many fingers, they had taken fir:n hold of a piece of stick.
blossom, or the nectarium of a passion-flower. Of this kind is the Magnificent Amphitrite, figured in the Linnean Transactions.1 It is found in the rocks of various parts of the coast of Jamaica. When alarmed, it retracts its tentacles within its tube, and the tube itself into the rock. How it excavates its rocky burrow has not been ascertained.
The Sabella, which pass under various names in different authors, inhabit the sandy parts of the shore, and like certain case-worms form a covering for their tube of selected grains of sand, mixing sometimes other substances that suit their purpose, which, by some secretion at their disposal, they glue pretty firmly together so as to form a neat case tapering towards the tail. The animal buries itself and case in the sand, with its head towards the surface, so, probably, as to enable it to protrude it and expand its tentacles to collect its food when covered by the water. The bristles of the legs in some species resemble burnished gold.
The functions of a large proportion of the animals of this order seem to correspond with those of the bivalve shell-fish; they undermine the sands and the rocks, bore into sponges and corallines, and other submarine substances, and some probably, into submerged wood: like them, also, they seem to feed on animalcules brought within their reach by the tide. The Serpulidans, whose food is similar, are directed by the will of their Creator to affix themselves externally to any submerged bodies that come in their way, whether mineral or animal. All they require seems to be something to attach themselves to, on which they can protrude their tentacular gills, and seize their prey. They must contribute largely, as well as the mining Annelidans of this order, to the production of calcareous matter. Mr. Sowerly suspects that their proboscis may be instrumental in forming the shell, but it seems not properly a proboscis, but merely an operculum on a long footstalk, which was requisite that it might be protruded so far as not to interfere with the action of the gills.
The animals included in Mr. Savigny's first Order, the Nereideans bring us very near to the Condylopes. They have a distinct head, jointed organs like antennæ, eyes, a proboscis armed with maxillæ, and spurious legs. They have also certain dorsal scales, which M. Savigny calls elytra, and deems analogous to the organs of flight in insects. These animals seem to afford the first example of the conversion of organs of
1 Tubularia magnifica. Shaw.
locomotion into others, employed for a different purpose. I do not mean by this, that, in the progress of the animal's growth, one organ is really converted into another, but that analogous organs, in different tribes or genera, are employed for different purposes. Thus, what in most Annelidans are locomotive organs, in Lycoris, Phyllodoce, and some other Nereideans become a kind of tentacle. The marine Scolopendra of Aristotle. most probably belonged to this Order, and many species make a near approach to the terrestrial ones. Like them they are long and often flat, consisting of a great number of segments, some having between two and three hundred, furnished according to the species, with one, two, or three pairs of legs in each; like them also they twist about in all directions when handled, they conceal themselves in close places where they lie in wait for their prey. In one respect some of them add the instinct of the spider to that of the centipede, for they line and sometimes cover the cavities of the rocks which they inhabit with a slight silken web, and thus concealed they watch the approach of some animal, and, suddenly thrusting out the anterior part of their body, seize and devour it.
My late indefatigable and talented friend, the Rev. L. Guilding, once found a land species, in an ancient wood in the Island of St. Vincent's, which from its soft body he regarded as a Molluscan, but from its figure, and annulose structure, its jointed antennæ, and seemingly jointed legs crowned with bristles, it3 certainly belongs, as Mr. Gray has remarked, to the present class. Though it has scarcely a distinct head, its resemblance to the cylindrical myriapods is very striking. Other species of this Order resemble the Isopod Crustaceans, and some even roll themselves up like one tribe of them.
These animals have their haunts sometimes in deep burrows and passages under the sea-weed or in the sea-sand. They are so fierce in their habits that some have been styled the tigers of the worms. Some fishes in their turn make them their prey. Many of them, as the sea-mouse, are remarkable for the brilliancy of their metallic hues. Perhaps these dazzling splendours, as in the case of some insects, may be of use to them in preventing the escape of their prey. Their forms and instruments of locomotion seem particularly adapted to .he situation and circumstances in which they are placed; their
1 Savigny, Syst. des. Annel. 9, 12, 13.
3 PLATE VIII. FIG. 1. Mr. G. calls it Peripatus juliformis.
4 Julus. L.
6 Aphrodita aculeata.
2 PLATE VIII. FIG. 4.
5 Nereis Armadillo.
7 Introd. to Ent. ii. 221.
legs, which approach the jointed legs of crustaceans and insects, fit them for moving on the surface of the bed of the sea, their oars for swimming in the water, and the long form of many for threading the sinuous paths and burrows in which they have their habitation and place of refuge. So exactly are they fitted by the skilful hand of the almighty and benevolent Architect of all animal forms to live and move in the place he has assigned to them,
Functions and Instincts. Cirripedes and Crincïdeans.
1 Lat. Cirri.
THERE is a class of animals defended by multivalve shells, separated from the Molluscans not only by the more complex structure of their shells, but also by very material differences in the organization of the creatures that inhabit them. These Linné considered as forming a single genus, which he named Lepas, a word derived from the Greek lexicographers, and explained by Hesychius as meaning a kind of shell-fish that adheres to the rocks. In this country these animals are known by the general name of Barnacles. Lamarck, I believe, was the first who regarded them as entitled to the rank of a class, which he denominated Cirrhipeda, not conscious, that by the insertion of the aspirate, he made his term, like Monoculus, half Greek and half Latin: later writers who have adopted the class, to avoid this barbarism, have changed the term to Cirrhopoda, but as this gives a different meaning to the word, changing fringed or tendril-legs, very happily expressing the most striking character of the animals intended, into yellow-legs, which does not indicate any prominent feature, I shall, after Dr. Leach and Mr. W. S. Mac Leay, omitting the aspirate, call them Cirripeda, or Cirripedes.
These animals have a soft body, protected by a multivalve shell. They are without eyes, or any distinct head; have no powers of locomotion, but are fixed to various substances. Their body, which has no articulations, is enveloped in a kind of mantle, and has numerous tentacular arms, consisting of many joints, fringed on each side, and issuing by pairs from jointed pedicles: their mouth is armed with transverse toothed jaws in pairs, which, like the mandibles of the Crustaceans, are furnished with a feeler; they have a knotty longitudinal spinal chord; gills for respiration; and for circulation, a heart and vascular system.
2 Gr. Hippos.