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I must enter at some length into the natural history of these shells, because the conclusions to which I have been led, by a long and careful investigation of fossil species, are at variance with those of Cuvier and Lamarck, as to the fact of Ammonites being external shells, and also with the prevailing opinions as to the action of the siphon and air chambers, both in Ammonites and Nautili.
Mechanical Contrivances in the Nautilus.
The Nautilus not only exists at present in our tropical seas, but is one of those genera which occur in a fossil state in formations of every age; and the molluscous inhabitants of these shells, having been among the earliest occupants of the ancient deep, have maintained their place through all the changes that the tenants of the ocean have undergone.
The recent publication of Mr. R. Owen's excellent Memoir on the Pearly Nautilus, (Nautilus Pompilius Lin.) 1832, affords the first scientific description ever given of the animal by which this long-known shell is constructed.* This Memoir is therefore of high importance, in its relation to geology; for it enables us to assert, with a confidence we could not otherwise have assumed, that the animals by which all fossil Nautili were constructed, belonged to the existing family of Cephalopodous Mollusks, allied to the common Cuttle Fish. It leads us farther to infer, that the infinitely more numerous species of the family of Ammonites, and other cognate genera of Multilocular shells, were also constructed by animals, in whose economy they held an office analogous to that of the existing shell of the Nautilus Pompilius. We therefore entirely concur with Mr. Owen, that not only is the acquisition of this species peculiarly acceptable, from its relation to the Cephalopods of the present creation; but that it is, at the same time, the living type of a vast tribe of organized beings, whose fossilized remains testify their existence at a remote period, and in another order of things.*
ther the Sepia found within this shell be really the constructor of it, or a parasitic intruder into a shell formed by some other animal not yet discovered. Mr. Broderip, Mr. Gray, and Mr. G. Sowerby, are of opinion, that this shell is constructed by an animal allied to Carinaria.
* It is a curious fact, that although the shells of the Nautilus have been familiar to naturalists, from the days of Aristotle, and abound in every collection, the only authentic account of the animals inhabiting them, is that by Rumphius, in his history of Amboyna, accompanied by an engraving, which though tolerably correct, as far as it goes, is yet so deficient in detail that it is impossible to learn any thing from it respecting the internal organization of the animal.
I rejoice in the present opportunity of bearing testimony to the value of Mr. Owen's highly philosophical and most admirable memoir upon this subject ; a work not less creditable to the author, than honourable to the Royal College of Surgeons, under whose auspices this publication has been so. handsomely conducted.
By the help of this living example, we are prepared to investigate the question of the uses, to which all fossil Chambered shells may have been subservient, and to show the existence of design and order in the mechanism, whereby they were appropriated to a peculiar and important function, in the economy of millions of creatures long since swept from the face of the living world. From the similarity of these mechanisms to those still employed in animals of the existing creation, we see that all such contrivances and adaptations, however remotely separated by time or space, indicate a common origin in the will and design of one and the same Intelligence.
* A farther important light is thrown upon those species of fossil Multilocular shells, e. g. Orthoceratites, Baculites, Hamites, Scaphites, Belcmnites, &c. (See PI. 44,) in which the last, or external chamber, seems to have been too small to contain the entire body of the animals that formed them, by Peron's discovery of the well-known chambered shell, the Spirula, partially enclosed within the posterior extremity of the body of a Sepia (PI. 44, Figs. 1, 2.) Although some doubts have existed respecting the authenticity of this specimen, in consequence of a discrepance between two drawings professedly taken from it (the one published in the Encyclopedic Methodiquc, the other in Peron's Voyage,) and from the loss of the specimen itself before any anatomical examination of it had been made, the sub. sequent discovery by Captain King of the same shell, attached to a portion of the mutilated body of some undescribed Cephalopod allied to the Sepia, leaves little doubt of the fact that the Spirula was an internal shell, having its dorsal margin only exposed, after the manner represented in both the drawings from the specimen of Peron. (See PI. 44, Fig. 1.)
We enter then upon our examination of the structure and uses of fossil Chambered shells, with a preliminary knowledge of the facts, that the recent shells, both of N. Pompilius and Spirula, are formed by existing Cephalopods; and we hope, through them, to be enabled to illustrate the history of the countless myriads of similarly constructed fossil shells whose use and office has never yet been satisfactorily explained.
We may divide these fossils into two distinct classes; the one comprising external shells, whose inhabitants resided like the inhabitant of the N. Pompilius, in the capacious cavity of their first or external chamber (PL 31, Fig. 1;) the other, comprising shells, that were wholly or partially included within the body of a Cephalopod, like the recent spirula, (PL 44, Figs. 1, 2.) In both these classes, the chambers of the shell appear to have performed the office of air vessels, or floats, by means of which the animal was enabled either to raise itself and float on the surface of the sea, or sink to the bottom.
It will be seen by reference to PL 31, Fig. 1,* that in the recent Nautilus Pompilius, the only organ connecting the air chambers, with the body of the animal, is a pipe, or siphuncle, which descends through an aperture and short projecting tube (y) in each successive transverse plate, till it terminates in the smallest chamber at the inner extremity of the shell. I shall presently attempt to show how by means of a peculiar fluid, admitted into or abstracted from this pipe, the animal has the the power to increase or diminish its specific gravity, and to sink or float accordingly; as the floating portion of that beautiful toy the Water balloon is made to descend or ascend by means of water forced into, or abstracted from its interior. (See P. 248.)
* The animal is copied from PI. 1, of Mr. Owen's Memoir; the shell from a specimen in the splendid and unique collection of my friend W. J. Broderip, Esq., by whose unreserved communications of his accurate and extensive knowledge in Natural History, I have been long and largely benefited.
The motion of the Nautilus, when swimming, with its arms expanded, is retrograde, like that of the naked Cuttle Fish, being produced by the reaction of water, violently ejected from the funnel (k.)
The position assumed during this operation is that which is best adapted to facilitate its passage through the water, as it places foremost that portion of the shell, which approaches most nearly in form to the prow of a boat. The fingers and tentacula (p, p,) are here represented as closed around the beak, which is consequently invisible; when the animal is in action, they are probably spread forth like the expanded rays of the sea Anemone.
The horny beak of this recent Nautilus (See PI. 31, Fig. 2, 3) resembles the bill of a Parrot. Each mandible is armed in front, with a hard and indented calcareous point, adapted to the office of crushing shells and crustaceous animals, of which latter, many fragments were found in. the stomach of the individual here represented. As these belonged to species of hairy brachyurous Crustacea, that live exclusively at the bottom of the sea, they show that this Nautilus, though occasionally foraging at the surface, obtains part of its food from the bottom. As it also had a gizzard, much resembling that of a fowl, we see in this organ, farther evidence that the existing Nautilus has the power of digesting hard shells.*
* In PI. 31, Fig. 3 represents the lower mandible, armed in front like Fig. 2. with a hard and calcareous margin; and Fig. 4 represents the anterior calcareous part of the palate of the upper mandible Fig. 2. formed' of the
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A similar apparatus is shown to have existed in the beaks of the inhabitants of many species of fossil Nautili, and Ammonites, by the abundance of fossil bodies called Rhyncholites, or beak-stones, in many strata that contain these fossil shells, e. g. in the Oolite of Stonesfield, in the Lias at Lyme Regis and Bath, and in the Muschelkalk at Luneville.
As we are warranted in drawing conclusions from the structure of the teeth in quadrupeds, and of the beak in birds, as to the nature of the food on which they are respectively destined to feed, so we may conclude, from the resemblance of the fossil beaks, or Rhyncholites, (PI. 31, Fig. 5—11,) to the calcareous portions of the beak of the Cephalopod, inhabiting the N. Pompilius, that many of these Rhyncolites were the beaks of the cephalopodous inhabitants of the fossil shells with which they are associated; and that these Cephalopods performed the same office in restraining excessive increase among the Crustaceous and Testaceous inhabitants of the bottom of the Transition and Secondary seas, that is now discharged by the living Nautili, in conjunction with the carnivorous Trachelipods.*
Assuming, therefore, on the evidence of these analogies, that the inhabitants of the shells of the fossil Nautili and Ammonites were Cephalopods, of similar habits to those of the animal which constructs the shell of the N. Pompilius, we shall next endeavour to illustrate, by the organization and habits of the living Nautilus, the manner in which these fossil shells were adapted to the use of creatures, that somesame hard calcareous substance at its point; this substance is of the nature of shell.
These calcarcous-extremilies of both mandibles are of sufficient strength to break through the coverings of Crustacea and shells, and as they are placed at the extremity of a beak composed of thin and tough horn, the power of this organ is thereby materially increased.
In examining the contents of the stomach of the Sepia vulgaris, Mid Loligo, I have found them to contain numerous shells of small Conchifera.
* See p. 192.