and other arms of shell-fish, would imagine that their object is defence, yet when he is told that those which are most remark able for them, are themselves predaceous animals; and that the herbivorous shell-fish are usually not distinguished by any thing of the kind, he seems to hesitate as to what conclusion he shall draw. It may be observed, however, that the tribemost distinguished for these arms, the rock-shells, are not so. remarkable for their size as many others which live by prey,. as the strombs, the helmet-shells, and the tritons, so that their armour may sometimes prevent one of these from boring their shells, and inserting its proboscis into them. The tribe we are now considering, the rock-shells, were in high esteem from the earliest ages on account of the dye that some of them afforded, and cloths dyed with it bore a higher price than almost any other: more than one species, however, yielded anciently a dye; one, according to Bochart, a glaucous or azure colour, as he interprets it, and the other purple. But Tyrian purple is no longer in request. I could say much, observes the author just named, upon the finding, fishing, and method of dyeing of the purpura, about the price, formerly enor mous, nearly equalling that of pearls, a single shell, according to Aristotle, selling for a mina or about 31., concerning the timeat which it began gradually to grow out of fashion, and at length to be wholly neglected: so that now it is never used, and no one knows the method of preparing it. In fact, the cochineal seems to have supplanted it, but it would surely be an object of great interest to re-discover the Tyrian rock-shell, as well as that which yielded the azure colour, and ascertain how far they deserved, especially the former, the high encomiums bestowed upon them, and to deck imperial shoulders. The shells are probably still in existence on the coast of Palesfine. It was the custom to crush the shell as soon as taken, for if kept the animal was wont to vomit its flower, as the purple dye was called by Aristotle. This great philosopher thought the purpura lived six years, as the adult animal had six whirls in its shell, and he supposed one to be formed annually. He gives a detailed history of these animals, of their congregating in the spring, and of their forming a kind of comb, like bees; he also mentions several kinds of them, that the small shells were bruised, and the animal extracted from the large ones; that the dye lies between the neck and what he denominates the poppy. It is found, by Cuvier, to be placedabove the neck by the side of the stomach. Plumier relates. that a shell-fish of this genus squirts out its fluid in a stream, whenever molested, which renders it probable that its object is defence. Aristotle mentions the operculum of the purple, and also the proboscis, or tongue as he calls it, which he describes as longer than the finger, and protruded from under the operculum: with this it feeds, and with it can pierce shells, and will attack even those of its own kind; this agrees with modern observations, adding that the tongue is terminated by a sucker armed with short tentacles. Aristotle also observes, an observation confirmed likewise by modern investigators, that these animals bury themselves in the sand like the pectens. This learned naturalist also states that shell-fish at certain seasons hide themselves, snails in the winter, and the purples and whelks for a month during the dog days. The dye of the purple is mentioned in Scripture as well as that of the coccus, and was used as such in the time of Moses. It is said also to be used at this time in India and America to dye small pieces of stuff, but in no place is it an important object. Having given so long an account of the rock-shells or purples, I shall not have occasion to dilate upon any of the remaining genera, but shall merely notice a few peculiarities that some of them exhibit. The Cowries are a tribe long kuown and admired for their beauty and polish, and one species1 forms the current coin in many parts of Africa, and many Asiatic Islands. Some remarkable facts distinguish their history; from the form of their shell and of its aperture, its increment could not take place in the usual way, these animals, therefore, are furnished by their Creator with a remarkably ample mantle, the wings of which cover half the shell, and thus it is gradually thickened, and changes and variations in the colour take place that have puzzled conchologists to distinguish a species from a variety. At certain times the animal is also stated to quit its shell, and form itself a new one more appropriate to its size, a circumstance related by Aristotle of the Buccinum," Volutes are another polished tribe of shells, which are probably formed by the mantle as in the Cowries-they are particularly distinguished by having no operculum. The jet volute is viviparous, and its young when excluded are said to have shells an inch long. These probably are more exposed to enemies than the young of other shell-fish. They form an important article of food to some African nations. 1 Cypræa Moneta. 2 Kapu, Arist. Before I close this account of these predaceous Molluscans, I must observe, that they have two distinct sexes, and consequently male and female shells. The genuine hermaphrodites are confined to the bivalves, for in the univalve hermaphrodites two individuals are necessary for reproduction, and therefore those form a distinct link between the true hermaphrodites that impregnate themselves, and those that have distinct sexes. So gradual are the steps by which the Creator passes from low to high. First, animals are reproduced without sexual intercourse, as in the polypes; then the two sexes are united in one body, and suffice for their own impregnationnext follow two sexes in the same body, which cannot impregnate themselves, bringing us at last two distinct sexes, or unisexual individuals. 4. Lamarck's fifth family, the Heteropods, I introduce here because, being univalves, they appear to connect that tribe with the Cephalopods forming his fourth order, but which from the discovery of the animal of Nautilus Pompilius, so admirably described by Mr. Owen, being farther removed from the other Molluscans, and the animal of the Heteropods having a proboscis and only two tentacles, seems intermediate between the Zoophagan Trachelipods and the Cephalopods. They have four swimming organs. There seems a considerable affinity between this tribe and the Pteropods in these organs, which indicates a circular arrangement in the univalve Molluscans. The Carinaria vitrea is one of the rarest shells that is known, arising probably from its extremely fragile conch, which is nearly as transparent as glass. A model of it in wax may be seen in the British Museum. The animal is a sailor like the Argonaut, to which it comes near. It is found in the South Seas. There are two other species known, one of which frequents the Mediterranean. Some genera without shells are placed in this order by Lamarck. They swim horizontally. like fishes, which circumstance, in conjunction with their fins or swimming organs, induced him to place them at the end of the Molluscans as near the fishes; several authors consider them as belonging to the Pteropods, to which they are certainly related.. CHAPTER X. Functions and Instincts. Cephalopods. We have now taken leave of what may be called the proper Molluscans, including the Bivalves, and Univalves1 of Aristotle and Linné, or the Conchifers and Molluscans of Lamarck, and are arrived at a Class remarkable, not only for their organization, form and habits, but also for their position in the animal kingdom; for in their composition they seem to include elements from both the great divisions of that kingdom: from the Vertebrates-the beak, the eye, the tongue, an organ for hearing, the crop, the gizzard, and an analogue of the spine, with several other parts enumerated by Cuvier; and from their own sub-kingdom, many of their remaining organs. We may descend to the very basis of the animal kingdom for the first draught of their nervous system, for it is discoverable in the wheel-animals in which Ehrenberg detected pharyngal ganglions and a nuchal nervous collar; the sucker-bearing arms seem to have their first outline in the fresh water polypes ;3 indeed if the mouth of the cuttle-fish with its suckers, be separated from the head, leaving behind the long arms, we see immediately an analogue of a radiary, particularly of a star-fish,. with its rays bearing suckers below, and its central mouth.. The lamellated tentacles observed by Mr. Owen in his work, before quoted, on the animal of the Pearly Nautilus,' above and below the eyes, seem to lead to the antennæ of Crustaceans and Insects, and numerous Molluscan characters are obvious to every one. From these circumstances it seems evident that the Creator has placed this tribe in a station which leads to very different and distant points in the animal' kingdom, and that their is scarcely any but what may recog nise in it one or more of its own peculiar features-yet at the same time it exhibits many characters, both in its most extraordinary outward form and its internal organization, that are quite 1 Διθυρα. Μονοθυρα. 2 Ganglia nervea pharyngea. Annulus nerveus nuchalis. Ehren. peculiar and sui generis, of which no animal at present known exhibits the slightest traces. To mention only its muscular apparatus adapted to its unparalleled form; its system of circulation, carried on in the first Order by three distinct organs instead of one heart; and the wonderful complication of their tentacles, of the nerves that move them, and the vascular system that animates them. This singular Class, which Cuvier denominated Cephalopods, or having their feet attached to their head, appears to follow very naturally the Trachelipods and Heteropods, lately described, which have not only eyes furnished with iris, and pupil, but also distinct sexes, and are of predaceous habits, all characters which they possess in common with the Cephalopods or Cuttle-fish. There is, however, an animal amongst the naked Gastropods-called by the ancients, from its tentacles representing the ears of a hare, the sea-hare,' a name it still bears in Italy, which Linné named Laplysia, in which he was followed by Lamarck, but modern writers after Gmelin have called it Aplysia, a name used by Aristotle for a very different animal, a kind of sponge, and, therefore, improperly applied-this animal has many characters that are found in some of the Cephalopods, particularly in its circulating and nervous systems; in having internal solid parts, and in discolouring the water with an inky fluid, so that there seems also a connexion between this genus, and the Cephalopods, amounting to something more than a mere analogical resemblance. The Mr. Owen has divided this Class into two Orders, from the composition of their respiratory organs, namely, those that have two branchiæ,3 or gills, and those that have four. first includes those that have no shell, and the second those that have one. The last is farther divisible into those whose shell has many chambers, as the Nautilus, and those where it has only one, as the Argonaul, or paper nautilus. 5 To the first of these Orders belongs the Cuttle-fish, one of the most wonderful works of the Creator. Its mouth is surrounded by eight long fleshy arms, or rather legs, somewhat conical in shape, and acute at the end, moved by innumerable nerves, furnished from numerous ganglions: these legs can bend in every direction with the utmost vigour and activity, their surface is furnished with many suckers, by which they can fix themselves strongly to any thing they wish to lay hold 1 Lepus marinus, Plin. 3 Dibranchiata. 2 Hist. An. 1. v. c. 16. 4 Tetrabranchiata. 5 Sepia. |
