Geology and Mineralogy considered with reference to Natural Theology/Chapter 15
CHAPTER XV.
Proofs of Designs in the Fossil Remains of Mollusks.[1]
SECTION I.
FOSSIL UNIVALVE AND BIVALVE SHELLS.
We are much limited in our means of obtaining information as to the anatomical structure of those numerous tribes of extinct animals which are comprehended under Cuvier's great division of Mollusks. Their soft and perishable bodies have almost wholly disappeared, and their external shells, and, in a few cases, an internal apparatus of the nature of shell, form the only evidence of the former existence of the myriads of these creatures that occupied the ancient waters.
The enduring nature of the calcareous coverings which these animals had the power of secreting, has placed our knowledge of Fossil Shells almost on a footing with that of recent Conchology. But the plan of our present inquiry forbids us here to take more than a general review of the history, and economy of the creatures by which they were constructed.
We find many and various forms, both of Univalve and Bivalve shells, mixed with numerous remains of Articulated and radiated animals, in the most ancient strata of the Transition period that contain any traces of organic life. Many of these shells agree so closely with existing species, that we may infer their functions to have been the same; and that they were inhabited by animals of form and habits similar to those which fabricate the living shells most nearly resembling them.[2]
All Turbinated and simple shells are constructed by Mollusks of a higher Order than the Conchifers, which construct, Bivalves; the former have heads and eyes; the Conchifers, or constructors of bivalves, are without either of these important parts, and possess but a low degree of any other sense than touch, and taste. Thus the Mollusk, which occupies a Whelk, or a Limpet shell, is an animal of a higher Order than the Conchifer enclosed between the two valves of a Muscle or an Oyster-shell.
Lamarck has divided his Order of Trachelipods[3] into two great sections, viz. herbivorous and carnivorous; the carnivorous are also divisible into two families of different office, the one attacking and destroying living bodies, the other eating dead bodies that have perished in the course of nature, or from accidental causes; after the manner of those species of predaceous beasts and birds, e. g. the Hyænas and Vultures, which, by preference, live on carrion. The same principle of economy in nature, which causes the dead carcasses of the hosts of terrestrial herbivorous animals to be accelerated, in their decomposition, by forming the food of numerous carnivore, appears also to have been applied to the submarine inhabitants of the most ancient, as well as of the existing seas; thus converting the death of one tribe into the nutriment and support of life in others.
It is stated by Mr. Dillwyn, in a paper read before the Royal Society, June 1823, that Pliny has remarked, that the animal which was supposed to yield the Tyrian die, obtained its food by boring into other shells by means of an elongated tongue; and Lamarck says, that all those Mollusks whose shells have a notch or canal at the base of their aperture, are furnished with a similar power of boring, by means of a retractile proboscis.[4] In his arrangement of invertebrate animals, they form a section of the Trachelipods, which he calls carnivorous. (Zoophages.) In the other section of Trachelipods, which he calls herbivorous (Phytiphages) the aperture of the shell is entire, and the animals have, jaws formed for feeding on vegetables.
Mr. Dillwyn further asserts, that every fossil Turbinated Univalve of the older beds, from the Transition lime to the Lias, belongs to the herbivorous genera; and that the herbivorous class extends through every stratum in the entire series of geological formations, and still retains its place among the inhabitants of our existing seas. On the other hand, the shells of marine carnivorous Univalves are very abundant in the Tertiary strata above the Chalk, but are extremely rare in the Secondary strata, from the Chalk downwards to the Inferior oolite; beneath which no trace of them has yet been found.
Most collectors have seen upon the sea shore numbers of dead shells, in which small circular holes have been bored by the predaceous tribes, for the purpose of feeding upon the bodies of the animals contained within them a similar holes occur in many fossil shells of the Tertiary strata, wherein the shells of carnivorous Trachelipods also abound; but perforations of this kind are extremely rare in the fossil shells of any older formation. In the Green-sand and Oolite, they have been noticed only in those few cases where they are accompanied by the shells of equally rare carnivorous Mollusks; and in the Lias, and strata below it, there are neither perforations, nor any shells having the notched mouth peculiar to perforating carnivorous species.
It should seem, from these facts, that in the economy of
submarine life, the great family of carnivorous Trachelipods,
performed the same necessary office during the Tertiary
period, which is allotted to them in the present ocean. We have further evidence to show, that in times anterior to, and
during the deposition of the Chalk, the same important functions
were consigned to other carnivorous Mollusks, viz. the
Testaceous Cephalopods;[5] these are of comparatively rare
occurrence in the Tertiary strata, and in our modern seas;
but, throughout the Secondary and Transition formations,
where carnivorous Trachelipods are either wholly wanting,
or extremely scarce, we find abundant remains of carnivorous
Cephalopods, consisting of the chambered shells of Nautili
and Ammonites, and many kindred extinct genera of
polythalamous shells of extraordinary beauty. The Molluscous
inhabitants of all these chambered shells, probably possessed
the voracious habits of the modern Cuttle Fish, and
by feeding like them upon young Testacea and Crustacea,
restricted the excessive increase of animal life at the bottom
of the more ancient seas. Their sudden and nearly total
disappearance at the commencement of the Tertiary era,
would have caused a blank in the "police of nature," allowing
the herbivorous tribes to increase to an excess, that
would ultimately have been destructive of marine vegetation,
as well as of themselves, had they not been replaced
by a different order of carnivorous creatures, destined to
perform in another manner, the office which the inhabitants
of Ammonites and various extinct genera of chambered
shells then ceased to discharge. From that time onwards,
we have evidence of the abundance of carnivorous Trachelipods,
and we see good reason to adopt the conclusion of
Mr. Dillwyn, that "in the formations above the Chalk, the
vast and sudden decrease of one predaceous tribe has been
provided for by the creation of many new genera, and new
species, possessed of similar appetencies, and yet formed for
obtaining their prey by habits entirely different from those
of the Cephalopods."[6]
The design of the Creator seems at all times to have been, to fill the waters of the seas, and cover the surface of the earth with the greatest possible amount of organized beings enjoying life; and the same expedient of adapting the vegetable kingdom to become the basis of the life of animals, and of multiplying largely the amount of animal existence by the addition of Carnivora to the Herbivora, appears to have prevailed from the first commencement of organic life unto the present hour.
Mr. De la Beche has recently published a list of the specific
gravities of living shells of different genera, from which
he shows that their weight and strength are varied in accommodation
to the habits and habitation of the animals by
which they are respectively constructed; and points out
evidence of design, such as we discover, in all carefully
conducted investigations of the works of nature, whether
among the existing or extinct forms of the animal creation.[7]
SECTION II.
FOSSIL REMAINS OF NAKED MOLLUSKS, OENS, AND INK-BAGS OF LOLIGO.
It is well known that the common Cuttle Fish, and other living species of Cephalopods,[8] which have no external shell, are protected from their enemies by a peculiar internal provision, consisting of a bladder-shaped sac, containing a black and viscid ink, the ejection of which defends them, by rendering opaque the water in which they thus become concealed. The most familiar examples of this contrivance are found in the Sepia vulgaris, and Loligo of our own seas. (See Pl. 28, Fig. 1.)
It was hardly to be expected that we should find, amid the petrified remains of animals of the ancient world, (remains which have been buried for countless centuries in the deep foundations of the earth,) traces of so delicate a fluid as the ink which was contained within the bodies of extinct species of Cephalopods, that perished at periods so incalculably remote; yet the preservation of this substance is established beyond the possibility of doubt, by the recent discovery of numerous specimens in the Lias of Lyme Regis,[9] in which the ink-bags are preserved in a fossil state, still distended, as when they formed parts of the organization of living bodies, and retaining the same juxta-position to a horny pen, which the ink-bag of the existing Loligo bears to the pen within the body of that animal. (Pl. 28, Fig. 1.)
Having before us the fact of the preservation of this fossil ink, we find a ready explanation of it, in the indestructible nature; of the carbon of which it was chiefly composed. Cuvier describes the ink of the recent Cuttle Fish, as being a dense fluid of the consistence of pap, "bouillie," suspended in the cells of a thin net-work that pervades the interior of the ink-bag; it very much resembles common printers' ink. A substance of this nature would readily be transferred to a fossil state, without much diminution of its bulk.[10]
Pl. 28, Fig. 5, represents an ink-bag of a recent Cuttle Fish, in which the ink is preserved in a dessicated state, being not much diminished from its original volume. Its form is similar to that of many fossil ink-bags (Pl. 29, Figs. 3—10,) and the indurated ink within it differs only from the fossil ink, inasmuch as the latter is impregnated with carbonate of lime.
In a communication to the Geological Society, February 1829, I announced that these fossil ink-bags had been discovered in the Lias at Lyme Regis, in connection with horny bodies, resembling the pen of a recent Loligo.
These fossil pens are without any trace of nacre, and are composed of a thin, laminated, semi-transparent substance, resembling horn. Their state of preservation is such as to admit of a minute comparison of their internal structure with that of the pen of the recent Loligo; and leads to the same result which we have collected from the examination of so many other examples of fossil organic remains; namely, that although fossil species usually differ from their living representatives, still the same principles of construction have prevailed through every cognate genus, and often also through the entire families under which these genera are comprehended.
The petrified remains of fossil Loligo, therefore, add another link to the chain of argument which we are pursuing, and aid us in connecting successive, systems of creation which have followed each other upon our Planet, as parts of one grand and uniform Design. Thus the union of a bag of ink with an organ resembling a pen in the recent Loligo, is a peculiar and striking association of contrivances, affording compensation for the deficiency of an external shell, to an animal much exposed to destruction from its fellow tenants of the deep; we find a similar association of the same organs in the petrified remains of extinct species of the same family, that are preserved in the ancient marl and limestone strata of the Lias. Cuvier drew his figures of the recent Sepia with ink extracted from its own body. I have drawings of the remains of extinct species prepared also with their own ink; with this fossil ink I might record the fact, and explain the causes of its wonderful preservation. I might register the proofs of instantaneous death detected in these ink-bags, for they contain the fluid which the living sepia emits in the moment of alarm; and might detail further evidence of their immediate burial, in the retention of the forms of these distended membranes (Pl. 29. Figs. 3—10.) since they would speedily have decayed, and have spilt their ink, had they been exposed but a few hours to decomposition in the water The animals must therefore have died suddenly, and been quickly buried in the sediment that formed the strata, in which their petrified ink and ink-bags are thus preserved. The preservation also of so fragile a substance as the pen of a Loligo, retaining traces even of its minutest fibres of growth, is not much less remarkable than the fossil condition of the ink-bags, and leads to similar conclusions.[11]
We learn from a recent Germari publication (Zeiten's Versteinerungen Württembergs. Stuttgart, 1832, Pl. 25 and Pl. 37,) that similar remains of pens and, ink-bags are of frequent occurrence in the Lias shale of Aalen and Boll.[12] Hence it is clear that the same causes which produced these effects during the deposition of the Lias at Lyme Regis, produced similar and nearly contemporaneous effects, in that part of Germany which presents such identity in the character and circumstances of these delicate organic remains.[13]
Paley has beautifully, and with his usual felicity, described the Unity and Universality of Providential care, as extending from the construction of a ring of two hundred thousand miles diameter, to surround the body of Saturn, and be suspended, like a magnificent arch, above the heads of his inhabitants, to the concerting and providing an appropriate mechanism for the clasping and reclasping of the filaments in the feather of the Humming-bird. The geologist descries at no less striking assemblage of curious provisions, and delicate mechanisms, extending from the entire circumference of the crust of our planet, to the minutest curl of the smallest fibre in each component lamina of the pen of the fossil Loligo. He finds these pens uniformly associated with the same peculiar defensive provision of an internal ink-bag, which is similarly associated with the pen of the living Loligo in our actual seas; and hence he concludes, that such a union of contrivances, so nicely adjusted to the wants and weaknesses of the creatures in which they occur, could never have resulted from the blindness of chance, but could only have originated in the will and intention of the Creator.
SECTION III.
Proofs of Design in the Mechanism of Fossil Chambered Shells.
NAUTILUS.
I shall select from the family of Multilocular, or Chambered shells, the few examples which I shall introduce from mineral conchology, with a view of illustrating certain points that have relation to the object of the present Treatise.
I select these, first, because they afford proofs of mechanical contrivances, more obviously adapted to a definite purpose, than can be found in shells of simpler character. Secondly, because the use of many of their parts can be explained, by reference to the economy and organization of the existing animals, most nearly allied to the extinct fossil genera and species with which we are concerned. And, thirdly, because many of these chambered shells can be shown, not merely to have performed the office of ordinary shells, as a defence for the body of their inhabitants; but also to have been hydraulic instruments of nice operation, and delicate adjustment, constructed to act in subordination to those universal and unchanging Laws, which appear to have ever regulated the movement of fluids.
The history of Chambered shells illustrates also some of those phenomena of fossil conchology, which relate to the limitation of species to particular geological Formations;[14] and affords striking-proofs of the curious fact, that many genera, and even whole families, have been called into existence, and again totally annihilated, at various and successive periods, during the progress of the construction of the crust of our globe.
The history of Chambered Shells tends further to throw light upon a point of importance in physiology, and shows that it is not always by a regular gradation from lower to higher degrees of organization, that the progress of life has advanced, during the early epochs of which geology takes cognisance. We find that many of the more simple forms have maintained their primeval simplicity through all the varied changes the surface of the earth has undergone; whilst, in other cases, organizations of a higher order preceded many of the lower forms of animal life; some of the latter appearing, for the first time, after the total annihilation of many species and genera of a more complex character.[15]
The prodigious number, variety, and beauty, of extinct
Chambered shells, which prevail throughout the Transition
and Secondary strata, render it imperative that we should
seek for evidence in living nature, of the character and habits
of the creatures by which they were formed, and of the
office they held in the ancient economy of the animal world.
Such evidence we may expect to find in those inhabitants of
the present sea, whose shells most nearly resemble the 'extinct
fossils under consideration, namely, in the existing Nautilus
Pompilius, (See Pl. 31, Fig. 1,) and Spirula, (Pl. 44
Figs. 1, 2.)[16]
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 Erst scientific description ever given of the animal by which this long-known shell is constructed.[17] 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 further 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 avast tribe of organized beings, whose fossilized remains testify their existence at a remote period, and in another order of things.[18]
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.
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 Boat near the surface of the sea, or sink to the bottom.
It will be seen by reference to Pl. 31, Fig. 1,[19] 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. By means of this pipe, the animal has power to increase or diminish its specific gravity, as Fishes do, by distending their membranous air bladder with air, or by causing it to collapse. When the pipe of the Nautilus is filled with any fluid, the weight of that fluid, being added to the body and shell, renders the mass specifically heavier than water, and the animal sinks. When it is inclined to rise, it withdraws the fluid from the pipe, and thus again, becoming specifically lighter, rises upwards to the surface.
The motion of the Nautilus, when floating, 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 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 Pl. 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 brachyurus 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, further evidence that the existing Nautilus has the power of digesting hard shells.[20]
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. (Pl. 31, 5—11,) to the calcareous portions of the beak of the Cephalopod, inhabiting the N. Pompilius, that many of these Rhyncholites 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.[21]
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 sometimes moved and fed at the bottom of deep seas, and at other times rose and floated upon the surface.
The Nautili (see Pl. 31. Fig. 1. and Pl. 32. Figs. 1. 2.) constitute a natural genus of spiral discoidal shells divided internally into a series of chambers that are separated from each other by a transverse plates; these plates are perforated by a tube or siphon, passing through the transverse plates, either at their centre, or towards their internal margin. (Pl. 1. Fig. 31. Pl., 32. Fig. 2. and Bl. 33.)
The external open chamber is, very large, and forms the
receptacle of the body of the animal. The internal close
chambers are void, and have no communication with the
outer chamber, excepting for the passage of a membranous
tube, which descends through an aperture in each plate to
the innermost extremity of the shell, (Pl. 31, y. y. a. b. c. d.
e. and Pl. 32, a. b. d. e. f.) These air chambers are destined
to counterbalance the weight of the increasing body and
shell of the animal, and thereby to render the whole so nearly
of the weight of water, that the difference arising from the
membrane of the siphuncle being either empty, or filled with
a fluid, may cause the mass to swim or sink.[22]
As neither the siphuncle, nor the external shell have any kind of aperture through which a fluid could pass into the close chambers,[23] it follows that these chambers contain nothing more than air, and must consequently be exposed to great pressure when at the bottom of the sea. Several contrivances are therefore introduced to fortify them against this pressure.
First, the circumference of the external shell is constructed every way upon the principles of an Arch, (see Pl. 31, Fig. 1, and Pl. 32, Fig 1.) so as to offer the greatest resistance to pressure tending to force it inwards in all directions.
Secondly, this arch is further fortified by the addition of numerous minute Ribs, which are beautifully marked in the fossil specimens represented at Pl. 32, Fig 1. In this fossil the external shell exhibits line wavy lines of growth, which, though individually small and feeble, are collectively of much avail as ribs to increase the aggregate amount of strength. (See Pl. 32, Fig. 1. a. to b.)
Thirdly, the arch is rendered still stronger by the position of the edges of the internal Transverse plates, nearly at right angles to the sides of the external shell, (See Pl. 32, Fig. 1, b. to c.) The course of the edges of these transverse plates beneath the ribs of the outer shell is so directed, that they act as cross braces, or spanners, to fortify the sides of the shell against the inward pressure of deep water. This contrivance is analogous to that adopted in fortifying a ship for voyages in the Arctic Seas, against the pressure of ice-bergs, by the introduction of an extraordinary number of transverse beams and bulk heads.[24]
We may next notice a fourth contrivance by which the apparatus that gives the shell its power of floating, is progressively maintained in due proportion to the increasing weight and bulk of the body of the animal, and of the external chamber in which it resides; this is effected by successive additions of new transverse Plates across the bottom of the outer chamber, thus converting into air chambers that part, which had become too small for the body of the Sepia. This operation, repeated at intervals in due proportion to the successive stages of growth of, the outer shell, maintains its efficacy as a float, enlarging gradually and periodically until the animal has arrived at full maturity.[25]
A fifth consideration is had of mechanical advantage, in disposing the Distance at which these successive transverse Plates are set from one another. (See Pl. 31. Fig. 1. and Pl. 32, Fig. 1, 2.) Had these distances increased in the same proportion as the area of the air chambers, the external shell would have been without due support beneath those sides of the largest chambers, where the pressure is greatest: for this a remedy is provided in the simple contrivance of placing the transverse plates proportionally nearer to one another, as the chambers, from becoming larger, require an increased degree of support.
Sixthly, The last contrivance, which I shall here notice, is that which regulates the ascent and descent of the animal by the mechanism of the Siphuncle. The use of this organ has never yet been satisfactorily made out; even Mr. Owen's most important Memoir leaves its manner of operation uncertain; but the appearances which it occasionally presents in a fossil state, (see Pl. 32, Fig. 2, 3. and Pl. 33,)[26] supply evidence, which taken in conjunction with Mr. Owen's representation of its termination in a large sac surrounding the heart of the animal, (P. 34, p, p, a. a.) appears sufficient to decide this long disputed question. If we suppose this sac (p, p.) to contain a pericardial fluid, the place of which is alternately changed. from the pericardium to the siphuncle, we shall find in this shifting fluid an hydraulic balance or adjusting power, causing the shell to sink when the pericardia fluid is forced into the siphuncle, and to become buoyant, whenever this fluid returns to the pericardium. On this hypothesis also the chambers would be continually filled with air alone, the elasticity of which would readily admit of the alternate expansion and contraction of the siphuncle, in the act of admitting or rejecting the pericardia fluid.
The principle to which we thus refer the rising and sinking of the living Nautilus, is the same which regulates the ascent and descent of the Water Balloon: the application of external pressure through a membrane that covers the column of water in a tall glass, forces a portion of this water into the cavity, or single air-chamber of the balloon, which immediately begins to sink; on the removal of this pressure, the elasticity of the compressed air causing it to return to its former volume, again expels the Water, and the balloon begins to rise.[27]
I shall conclude this attempt to illustrate the structure and economy of fossil Nautili by those of the living species, by showing in what manner the chambers of the pearly Nautilus, supposing them to be permanently filled only with air, and the action of the siphuncle, supposing it to be the receptacle only of a fluid secretion, interchanging its place alternately from the siphuncle to the pericardium, would be subsidiary to the movements of the animal, both at the surface, and bottom of the sea.
First, The animal was seen and captured by Mr. Bennett, floating at the surface, with the upper portion of the shell raised above the water, and kept in a vertical position by means of the included air (see Pl. 31. Fig. 1.); this position is best adapted to the retrograde motion, which a Sepia derives from the violent ejection of water through its funnel (k); thus far, the air-chambers, serve to maintain both the shell and body of the animal in a state of equilibrium at the surface.
Secondly, The next point to be considered is the mode
of operation of the siphuncle and air-chambers, in the act of sinking
suddenly from the surface to the bottom. These
are explained in the note subjoined.[28]
Thirdly, It remains to consider the effect of the air, supposing
it to be retained continually within the chambers,
at the bottom of the sea. Here, if the position of the moving
animal be beneath the mouth of the shell, like that of a
snail as it crawls along the ground, the air within the
chambers would maintain the shell, buoyant, and floating
over the body of the animal in a vertical position, with
little or no muscular exertion, and leave the creature at
ease to regulate the movements of its tentacula (p) in
crawling and seizing its prey.[29]
Dr. Hook considered (Hook's Experiments, 8vo. 1726, page 308) that the air chambers were filled alternately with air or water; and Parkinson (Organic Remains, vol. iii. p. 102,) admitting that these chambers were not accessible to water, thinks that the act of rising or sinking depends on the alternate introduction of air or water into the siphuncle; but he is at a loss to find the source from which this air could be obtained at the bottom of the sea, or to explain "in what manner the animal effected those modifications of the tube and its contained air, on which the variation of its buoyancy depended."[30] The theory which supposes the chambers of the shell to be permanently filled with air alone, and the siphuncle to be the organ which regulates the rising or sinking of the animal, by changing the place of the pericardia fluid, seems adequate to satisfy every hydraulic condition of a Problem that has hitherto received no satisfactory solution.
I have dwelt thus long upon this subject, on account of
its importance, in explaining the complex structure, and
hitherto imperfectly understood functions, of all the numerous
and widely disseminated families of fossil chambered
shells, that possessed siphunculi. If, in all these families, it
can be shown that the same principles of mechanism, under
various modifications, have prevailed from the first commencement
of organic life unto the present hour, we can
hardly avoid the conclusion which would refer such unity
of organizations to the will and agency of one and the same
intelligent First Cause, and lead us to regard them all as
"emanations of that Infinite Wisdom, that appears in the
shape and structure of all other created beings."[31]
SECTION IV.
AMMONITES.
Having entered thus largely into the history of the Mechanism of the shells of Nautili, we have hereby prepared ourselves for the consideration of that of the kindred family of Ammonites, in which all the essential parts are so similar in principle to those of the shells of Nautili, as to leave no doubt that they were subservient to a like purpose in the economy of the numerous extinct species of Cephalopodous Mollusks, from which these Ammonites have been derived.
Geological Distribution of Ammonites.
The family of Ammonites extends through the entire series of the fossiliferous Formations, from the Transition strata to the Chalk inclusive. M. Brochant, in his Translation of De la Beche's Manual of Geology, enumerates 270 species; these species differ[32]according to the age of the strata in which they are found, and vary in size from a line to more than four feet in diameter.[33]
It is needless here to speculate either on the physical, or final causes which produced these curious changes of species, in this highest order of the Molluscous inhabitants of the seas, during some of the early and the middle ages of geological chronology; but the exquisite symmetry, beauty, and minute delicacy of structure, that pervade each variation of contrivance throughout several hundred species, leave no room to doubt the exercise of Design and Intelligence in their construction; although we cannot always point out the specific uses of each minute variation, in the arrangement of parts fundamentally the same.
The geographical distribution of Ammonites in the ancient world, seems to have partaken of that universality, we find so common in the animals and vegetables of a former condition of our globe, and which differs so remarkably from the varied distribution that prevails among existing forms of organic life. We find, the same genera, and, in a few cases, the same species of Ammonites, in strata, apparently of the same age, not only throughout Europe, but also in distant regions of Asia, and of North and South America.[34]
Hence we infer that during the Secondary and Transition periods a more general distribution of the same species, than exists at present, prevailed in regions of the world most remotely distant from one another.
An Ammonite, like a Nautilus, is composed of three essential parts: 1st. An external shell, usually of a fiat discoidal form, and having its surface strengthened and ornamented with ribs (see Pl. 35, and Pl. 37.) 2d. A series of internal air chambers formed by transversed plates, intersecting the inner portion of the shell, (see Pl. 36 and 41.) 3d. A siphuncle, or pipe, commencing at the bottom of the outer chamber, and thence passing through the entire series of air chambers to the innermost extremity of the shell, (see Pl. 36, d. e. f. g. h. i.) In each of these parts, there are evidences of mechanism, and consequently of design, a few of which I shall endeavour briefly to point out.
External Shell.
The use and place of the shells of Ammonites has much perplexed geologists and conchologists. Cuvier and Lamarck, guided by the analogies afforded by the Spirula, supposed them to be internal shells.[35] There is, however, good reason to believe that they were entirely external, and that the position of the body of the animal within these shells was analogous to that of the inhabitant of the Nautilus Pompilius. (See Pl. 31, Fig. 1.)
Mr. De la Beche has shown that the mineral condition of the outer chamber of many Ammonites, from the Lias at Lyme Regis, proves that the entire body was contained within it; and that these animals were suddenly destroyed and buried in the earthy sediment of which the lias is composed, before their bodies had either undergone decay, or been devoured by the crustaceous Carnivora with which the bottom of the sea then abounded.[36]
As all these shells served the double office of affording
protection, and acting as floats, it was necessary that they
should be thin, or they would have been too heavy to rise
to the surface: it was not less necessary that they should
be strong, to resist pressure at the bottom of the sea; and
accordingly we find them fitted for this double function, by
the disposition of their materials, in a manner calculated to
combine lightness and buoyancy with strength.
First, The entire shell, (Pl. 35,) is one continuous arch, coiled spirally around itself in such a manner, that the base of the outer whorls rests upon the crown of the inner whorls, and thus the keel or back is calculated to resist pressure, in the same manner as the shell of a common hen's egg resists great force if applied in the direction of its longitudinal diameter.
Secondly, besides this general arch-like form, the shell is further strengthened by the insertion of ribs, or transverse arches which give to many of the species their most characteristic feature, and produce in all, that peculiar beauty which invariably accompanies the symmetrical repetition of a series of spiral curves. (See Pl. 37, Fig. 1—-10.)
From the disposition of these ribs over the surface of the external shell, there arise mechanical advantages for increasing its strength, founded on a principle that is practically applied in works of human art. The principle I allude to, is that by which the strength and stiffness of a thin metallic plate are much increased by corrugating, or applying flutings to its surface. A common pencil-case, if made of corrugated or fluted metal, is stronger than if the same quantity of metal were disposed in a simple tube. Culinary moulds of tin and copper are in the same way strengthened, by folds or flutings around their margin, or on their convex surfaces. The recent application of thin plates of corrugated iron to the purpose of making self-supporting roofs, in which the corrugations of the iron supply the place, and combine the power of beams and rafters, is founded on the same principle that strengthens the vaulted shells of Ammonites. In all these cases, the ribs or elevated portions, add to the plates of shell, or metal, the strength resulting from the convex form of an arch, without materially increasing their weight; whilst the intermediate depressed parts between these arches, are suspended and supported by the tenacity and strength of the material. (See Pl. 37, Figs. 1—10.[37])
The general principle of dividing and subdividing the ribs, in order to multiply supports as the vault enlarges, is conducted nearly on the same plan, and for the same purpose, as the divisions and subdivisions of the ribs beneath the groin work, in the flat vaulted roofs of the florid Gothic Architecture.
Another source of strength is introduced in many species
of Ammonites by the elevation of parts of the ribs into little
dome-shaped tubercles, or bosses, thus super adding the
strength of a dome to that of the simple arch, at each point
Where these bosses are inserted.[38]
The bosses thus often introduced at the origin, division,
and termination of the ribs, resemble those applied by architects
to the intersections of the ribs in Gothic roofs, and are
much more efficient in producing strength.[39] These tubercles
have the effect of little vaults or domes; and they are
usually placed at those parts of the external shell, beneath
which there is no immediate support from the internal transverse
plates (see Pl. 37, Fig. S. Pl. 42, Fig. 3. c. d. e. and
Pl. 40, Fig. 5.)[40]
Similar tubercles are introduced with the same advantage of adding Strength as well as Beauty in many other cognate genera of chambered shells. (Pl. 44, Fig. 9. 10. 14. 15.)
In all these cases, we recognise the exercise of Discretion and Economy in the midst of Abundance; distributing internal supports but sparingly, to parts which, from their external form, were already strong, and dispensing them abundantly beneath those parts only, which without them, would have been weak.
We find an infinity of variations in the form and sculpture of the external shell, and a not less beautiful variety in the methods of internal fortification, all adapted, with architectural advantage, to produce a combination of Ornament with Utility. The ribs also are variously multiplied, as the increasing space demands increased support; and are variously adorned and armed with domes and bosses, wherever there is need of more than ordinary strength.
Transverse Plates, and Air Chambers.
The uses of the internal air chambers will best be understood
by reference to our figures. Pl. 36 represents a longitudinal
section of an Ammonite bisecting the transverse
plates in the central line where their curvature is most simple.
On each side of this line, the curvature of these plates
become more complicated, until, at their termination in the
external shell, they assume a beautifully sinuous, or foliated
arrangement, resembling the edges of a parsley leaf, (Pl.
3S,) the uses of which, in resisting pressure, I shall further
illustrate by the aid of graphic representations.
At Pl. 35, from d. to e. we see the edges of the same transverse
plates which, in Pl. 36, are simple curves, becoming
foliated at their junction with the outer shell, and thus distributing
their support more equally beneath all its parts, than
if these simple curves had been continued to the extremity
of the transverse plates. In more than two hundred known
species of Ammonites, the transverse plates present some
beautifully varied modifications of this foliated expansion at
their edges; the effect of which, in every case, is to increase
the strength of the outer shell, by multiplying the subjacent
points of resistance to external pressure. We know that
the pressure of the sea, at no great depth, will force a cork
into a bottle filled with air, or crush a hollow cylinder or
sphere of thin copper; and as the air chambers of Ammonites
were subject to similar pressure, whilst at the bottom
of the sea, they required some peculiar provision to preserve
them from destruction,[41] more especially as most zoologists
agree that they existed at great depths, "dans les grandes
profondeurs des mers."[42]
Here again we find the inventions of art anticipated in the works of nature, and the same principle applied to resist the inward pressure of the sea upon the shells of Ammonites, that an engineer makes use of in fixing transverse stays beneath the planks of the wooden centre on which he builds his arch of stone.
The disposition of these supports assumes throughout the family of Ammonites a different arrangement from the more simple curvature of the edges of the transverse plates within the shells of Nautili; and we find a probable cause for this variation, in the comparative thinness of the outer shells of many Ammonites; since this external weakness creates a need of more internal support under the pressure of deep water, than was requisite in the stronger and thicker shells of Nautili.
This support is effected by causing the edges of the transverse
plates to deviate from a simple curve, into a variety
of attenuated ramifications and undulating sutures. (See
Pl. 38. and Pl. 37, Figs. 6, 8.) Nothing can be more beautiful
than the sinuous windings of these sutures in many species,
at their union with the exterior shell; adorning it with
a succession of most graceful forms, resembling festoons of
foliage, and elegant embroidery. When these thin septa are
converted into iron pyrites, their edges appear like golden
filigrane work, meandering amid the pellucid spar, that fills
the chambers of the shell.[43]
The shell of the Ammonites Heterophyllus (Pl. 38, and
Pl. 39,) affords beautiful exemplifications of the manner in
which the mechanical strength of each transverse plate is so
disposed, as to vary its support in proportion to the different
degrees of necessity that exist for it in different parts of the
same shell.[44]
At Plate 41. we have a rare and most beautiful example of the preservation of the transverse plates of the Ammonites giganteus converted to chalcedony, without the introduction of any earthy matter into the area of the air chambers.
This shell is so laid open as to show the manner in which each transverse plate forms a tortuous partition between the successive air-chambers. By means of these winding plates, the external shell, being itself a continuous arch, is further fortified with a succession of compound arches, passing transversely across its internal cavity; each arch being disposed in the form of a double tunnel, vaulted not only at the top, but having a corresponding series of inverted arches along the bottom.
We can scarcely imagine a more perfect instrument than this for affording universal resistance to external pressure, in which the greatest possible degree of lightness is combined with the greatest strength.
The form of the air-chambers in Ammonites is much
more complex than in the Nautili, in consequence of the
tortuous windings of the foliated margin of the transverse
plates.[45]
Siphuncle.
It remains to consider the mechanism of the Siphuncle,
that important organ of hydraulic adjustment, by means of
which the specific gravity of the Ammonites was regulated.
Its mode of operation as a pipe, admitting or rejecting a
fluid, seems to have been the same as that we have already
considered in the case of Nautili.[46]
The universal prevalence of such delicate hydraulic contrivances in the Siphuncle, and of such undeviating and systematic union of buoyancy and strength in the air-chambers, throughout the entire family of Ammonites and Nautili, are among the most prominent instances of order and method, that pervade these remains of former races that inhabited the ancient seas; and strange indeed must be the construction of that mind, which can believe, that all this order and method can have existed, without the direction and agency of some commanding and controlling Intelligence.
Theory of Von Buch.
Besides the uses we have attributed to the sinuous arrangement
of the transverse septa of Ammonites, in giving
strength to the shell to resist the pressure of deep water, M.
Von Buch has suggested a further use of the lobes thus formed around the base of the outer chamber, as affording
points of attachment to the mantle of the animal, whereby
it was enabled to fix itself more steadily within its shell.
The arrangement of these lobes varies in every species of
Ammonite, and he has proposed to found on these variations,
the specific character of all the shells of this great
family.[47]
The uses ascribed by Von Buch to the lobes of Ammonites in affording attachment to the base of the mantle around the margin of the transverse plates, would in no way interfere with the service we have assigned to the same lobes, in supporting the external shell against the pressure of deep water. The union of two beneficial results from one and the same mechanical expedient, confirms our opinion of the excellence of the workmanship, and increase our admiration of the Wisdom in which it was contrived.
Conclusion.
On examining the proofs of Contrivance and Design that
pervade the testaceous remains of the family of Ammonites,
we find, in every species, abundant evidence of minute and
peculiar mechanisms, adapting the shell to the double purpose
of acting as a float, and of forming a protection to the
body of its inhabitant.
As the animal increased in bulk, and advanced along the outer chamber of the shell, the spaces left behind it were successively converted into air-chambers, simultaneously increasing the power of the float. This float, being regulated by a pipe, passing through the whole series of the chambers, formed an hydraulic instrument of extraordinary delicacy, by which the animal could, at pleasure, control its ascent to the surface, or descent to the bottom of the sea.
To creatures that sometimes floated, a thick and heavy shell would have been inapplicable; and as a thin shell, inclosing air, would be exposed to various, and often intense degrees of pressure at the bottom, we find a series of provisions to afford resistance to such pressure, in the mechanical construction both of the external shell, and of the internal transverse plates which formed the air-chambers. First, the shell is made up of a tube, coiled round itself, and externally convex. Secondly, it is fortified by a series of ribs and vaultings disposed in the form of arches and domes on the convex surface of this tube, and still further adding to its strength. Thirdly, the transverse plates that form the air-chambers, supply also a continuous, succession of supports, extending their ramifications, with many mechanical advantages, beneath those portions of the shell which, being weakest, were most in need of them.
If the existence of contrivance proves the exercise of
mind; and if higher degrees of perfection in mechanism are
proof of more exalted degrees of intellect in the Author from
whom they proceeded; the beautiful examples which we
find in the petrified remains of these chambered shells, afford
evidence coeval and coextensive with the mountains wherein
they are entombed, attesting the Wisdom in which such
exquisite contrivances originated, and setting forth the Providence
and Care of the Creator, in regulating the structure
of every creature of his hand.
SECTION V.
NAUTILUS SYPHO, AND NAUTILUS ZIC ZAC.
The name of Nautilus Sypho[48] has been applied to a very curious and beautiful chambered shell found in the Tertiary strata at Dax, near Bourdeaux; and that of Nautilus Zic Zac to a cognate shell from the London clay. (See Pl. 43, Figs. 1, 2, 3, 4.)
These fossil shells present certain deviations from the ordinary characters of the genus Nautilus, whereby they in some degree partake of the structure of an Ammonite.
These deviations involve a series of compensations and peculiar contrivances, in order to render the shell efficient in its double office of acting as a float, and also as a defence and chamber of residence to the animal by which it was constructed.
Some details of these contrivances, relating to the Nautilus
Sypho will be found in the subjoined note.[49]
As the place of the syphon in 'this species is upon the internal
margin of the transverse plates (Pl. 43; Fig. 2 b1, b2, b3,) it
had less power than the more central siphuncle of the Nautilus
to attach the mantle of the animal to the bottom of the
outer chamber. For this defect we find a compensation,
resembling that which Von Buch considers to have been
afforded by the lobes of Ammonites to the inhabitants of
those shells. This compensation will be illustrated by a
comparison of the lobes in N. Sypho (Pl. 43, Fig. 2.,) with
a similar provision in the Nautilus Zic Zac (Pl. 43, Figs.
3, 4)[50]
A still more important use of the lobes formed by the transverse plates both of the N. Sypho and N. Zic Zac, may be found in the strength which they impart to the sides of the external shell (see Pl. 43, Figs. 1, 2, 3, 4.,) under propping their flattest and weakest part, so as to resist pressure more effectually than if the transverse plates had been curved simply, as in N. Pompilius. One cause which rendered some such compensation necessary, may be found in the breadth of the intervals between each transverse plate; the weakness resulting from this distance, being compensated by the introduction of a single lobe, acting on the same principle as the more numerous and complex lobes in the genus Ammonite.
The N. Sypho and N. Zic Zac seem, therefore, to form
Links between the two great genera of Nautilus and Ammonite,
in which an intermediate system of mechanical
contrivances is borrowed, as it were, from the mechanics
of the Ammonite, and applied to the Nautilus. The
adoption of lobes, analogous to the lobes of the Ammonite,
compensating the disadvantages, that would otherwise
have followed from the marginal position of the
siphuncle in these two species, and the distances of their
transverse plates.[51]
It is a curious fact, that contrivances, similar to those which existed in some of the most early forms of Ammonite, should have been again adopted in some of the most recent species of fossil Nautili, in order to afford similar compensation for weakness that would otherwise have been produced by aberrations from the normal structure of the genus Nautilus. All this seems inexplicable on any theory which would exclude the interference of controlling Intelligence.
SECTION VI.
CHAMBERED SHELLS ALLIED TO NAUTILUS AND AMMONITES.
We have reason to infer, from the fact of the recent N. Pompilius being an external shell, that all fossil shells of the great and ancient family of Nautili, and of the still more numerous family of Ammonites, were also external shells, inclosing in their outer chamber the body of a Cephalopod. We further learn, from Peron's discovery of the shell of a Spirula partially enclosed within the body of a Sepia
[52] (see Pl. 44, Fig. 1, 2,) that many of those genera of fossil chambered shells, which, like the Spirula, do not terminate externally in a wide chamber, were probably internal, or partially enclosed shells, serving the office of a float, constructed on the same principles as the float of the Spirula. In the class of fossil ash ells thus illustrated by the discovery of the animal in closing the Spirula, we may include the following extinct families, occurring in various positions from the earliest Transition strata to the most recent Secondary formations:—Orthoceratite, Lituite, Baculite, Hamite, Scaphite, Turrilite, Nummulite, Belemnite.[53]
Orthoceratite, Pl. 44, Fig. 4.
The Orthoceratites (so called from their usual form,—that of a straight horn) began their existence at the same early period with the Nautili, in the seas which deposited the Transition strata; and are so nearly allied to them in structure, that we may conclude they performed a similar function as floats of Cephalopodous Mollusks. This genus contains many species, which abound in the strata of the Transition series, and is one of those which, having been called into existence amongst the earliest inhabitants of our planet, was at an early period also consigned to almost total destructions.[54]
An Orthoceratite (see Pl. 44, Fig. 4) is, like the Nautilus, a multilocular shell, having its chambers separated by transverse plates, concave externally, and internally convex; and pierced, either at the centre or towards the margin, by a Siphuncle, (a.) This pipe varies in size, more than that of any other multilocular shell, viz. from one-tenth to one-half of the diameter of the shell; and often assumes a tumid form, which would admit of the distension of a membranous siphon. The base of the shell beyond the last plate presents a swelling cavity, wherein the body of the animal seems to have been partly contained.
The Orthoceratites are straight and conical, and bear the same relation to the Nautili which Baculites (see Pl. 44, Fig. 5) bear to Ammonites; the Orthoceratites, with their simple transverse septa, resembling straight Nautili; and the Baculites, with a sinuous septa, having the appearance of straight Ammonites. They vary considerably in external figure, and also in size; some of the largest species exceeding a yard in length, and half a foot in diameter. A single specimen has been known to contain nearly seventy air chambers. The body of the animal which required so large a Hoat to balance it, must have greatly exceeded, in all its proportions, the most gigantic of our recent Cephalopods; and the vast number of Orthoceratites that are occasionally crowded together in a single block of stone, shows how abundantly they must have swarmed in the waters of the early seas. These shells are found in the greatest numbers in blocks of marble, of a dark red colour, from the transition Limestone of Oeland, which some years ago was imported largely to various parts of Europe for architectural purposes.[55]
Lituite.
Together with the Orthoceratite, in the Transition Limestone of Oeland, there occurs a cognate genus of Chambered shells, called Lituites. (Pl. 44, Fig. 3.) These are partially coiled up into a spiral form at their smaller extremity, whilst their larger end is continued into a straight tube, of considerable length, separated by transverse plates, concave outwards, and perforated by a siphuncle (a.) As these Lituites closely resemble the shell of the recent Spirula (Pl. 44, Fig. 2,) their office may have been the same, in the economy of some extinct Cephalopod.
Baculite.
As in rocks of the Transition series, the form of a straight Nautilus is presented by the genus Orthoceratite, so we find in the Cretaceous formation alone, the remains of a genus which may be considered as a straight Ammonite. (See Pl. 44, Fig. 5.)
The baculite (so called from its resemblance to a straight staff) is a conical, elongated, and symmetrical shell, depressed laterally, and divided into numerous chambers by transverse plates, like those in the Ammonite, are sinuous, and terrninated by foliated denotations at their junction with the external shell; being thus separated into dorsal, ventral, and lateral lobes and saddles, analogous to those of Ammonites.[56]
It is curious, that this straight modification of the form of Ammonites should not have appeared, until this Family had arrived at the last stage of the Secondary deposites, throughout which it had occupied so large an extent; and that, after a comparatively short duration, the Baculite should have become extinct, simultaneously with the last of the Ammonites, at the termination of the Chalk formation.
Hamite.
If we imagine a Baculite to be bent round near its centre, until the smaller extremity became nearly parallel to its larger end, it would present the most simple form of that cognate genus of chambered shells, which, from their frequently assuming this hooked form, have been called Hamites. At Pl. 44, Fig. 9, 11, represent portions of Hamites which have this most simple curvature; other species of this genus have a more tortuous form, and are either closely coiled up, like the small extremity of a Spirula, (Pl. 44, Fig. 2,) or disposed in a more open spiral. (Pl. 44, Fig. 8.)[57]
It is probable that some of these Hamites were partly internal, and partly external shells; where the spines are present, the portion so armed was probably external. Nine species of Hamites occur in the single formation of Gault or Speeton clay immediately below the chalk, near Scarborough. (See Phillips' Geology of Yorkshire.) Some of the larger species equal a man's wrist in diameter.[58]
Scaphite.
The Scaphites constitute a genus of Elliptical chambered shells, (see Pl. 44, Fig. 15, 16,) of remarkable beauty, which are almost peculiar to the Chalk formation; they are so rolled up at each extremity, whilst their central part continues nearly in a horizontal plane, as to resemble the ancient form of a boat; whence the name of Scaphite has been applied to them.[59]
It is remarkable that those approximations to the structure of Ammonites which are presented by Scaphites and Hamites, should have appeared but very rarely, and this in the lias and inferior oolite,[60] until the period of the cretaceous formations, when the entire type of the ancient and long continued genus Ammonite was about to become extinct.
Turrilite.
The last genus I shall mention, allied to the family of Ammonites, is composed of spiral shells, of another form, coiled around themselves in the form of a winding tower, gradually diminishing towards the apex (Pl. 44, Fig. 14.)[61]
The same essential characters and functions pervade the Turrilites, which we have been tracing in the Scaphites, Hamites, Baculites, and Ammonites. In each of these genera it is the exterior form of the shell that is principally varied, whilst the interior is similarly constructed in all of them, to act as a float, subservient to the movements of Cephalopodous Mollusks. We have seen that the Ammonites, beginning with the Transition strata, appear in all formations, until the termination of the Chalk, whilst the Hamites and Scaphites are very rare, and the Turrilites and Baculites do not appear at all, until the commencement of the Cretaceous formations. Having thus suddenly appeared, they became as suddenly extinct at the same period with the Ammonites, yielding up their place and office in the economy of nature to a lower order of Carnivorous mollusks in the Tertiary and existing seas.
In the review we have taken of genera in the family of
Chambered shells, allied to Nautilus, and Ammonite, we
have traced a connected series of delicate and nicely adjusted
instruments, adapted to peculiar uses in the economy
of every animal to which they were attached. These all
attest undeviating Unity of design, pervading many varied
adaptations of the same principle; and afford cumulative
evidence, not only of the exercise of Intelligence, but also
of the same Intelligence through every period of time, in
which these extinct races inhabited the ancient deep.
SECTION VII.
Belemnite.
We shall conclude our account of chambered shells with a brief notice of Belemnites. This extensive family occurs only in a fossil state, and its range is included within that series of rocks which in our section are called Secondary.[62] These singular bodies are connected with the other families of fossil chambered shells we have already considered; but differ from them in having their chambers inclosed within a cone-shaped fibrous sheath, the form of which resembles the point of an arrow, and has given origin to the name they bear.
M. de Blainville, in his valuable memoir on Belemnites, (1827) has given a list of ninety-one authors, from Theophrastus downwards, who have written on this subject. The most intelligent among them agree in supposing these bodies to have been formed by Cephalopods allied to the modern Sepia. Voltz, Zeiten, Raspail, and Count Münster, have subsequently published important memoirs upon the same subject. The principal English notices on Belemnites are those of Miller, Geol. Trans. N. S. London, 1826, and that of Sowerby, in his Min. Conch. vol. vi. p. 169, et seq.
A Belemnite was a compound internal shell, made up of three essential parts, which are rarely found together in perfect preservation.
First, a fibro-calcareous cone-shaped shell, terminating at
its larger end in a hollow cone (Pl. 44, Fig. 17. and Pl. 44',
Fig. 7, 9, 10, 11, 12.[63]
Secondly, a conical thin horny sheath, or cup, commencing from the base of the hollow cone of the fibro-calcareous sheath, and enlarging rapidly as it extends outwards to a considerable distance. Pl. 44', Fig. 7, b, e, e', e″. This horny cup formed the anterior chamber of the Belemnite, and contained the ink-bag, (c,) and some other viscera.[64]
Thirdly, a thin conical internal chambered shell, called the Alveolus, placed within the calcareous hollow cone above described. (Pl. 44, Fig. 17, a. and Pl. 44', Fig. 7, b, b'.)
This chambered portion of the shell is closely allied in form, and in the principles of its construction, both to the Nautilus and Orthoceratite. (See Pl. 44, Fig. 17, a, b. and Fig. 4.) It is divided by thin transverse plates into a series of narrow air-chambers, or areolæ, resembling a pile of watch-glasses, gradually diminishing towards the apex. The transverse plates are outwardly concave, inwardly convex; and are perforated by a continuous siphuncle, (Pl. 44, Fig. 17, b.), placed on the inferior, or ventral margin.
We have already (Ch. XV. Section II.) described the
horny pens and ink-bags of the Loligo, found in the Lias at
Lyme Regis. Similar ink-bags have recently been found in
connexion with Belemnites in the same Lias. Some of
these ink-bags are nearly a foot in length, and show that the
Belemno-sepiæ,[65] from which they were derived, attained
great size.
The fact of these animals having been provided with so
large a reservoir of ink, affords an à priori probability that
they had no external shell; the ink-bag, as far as we yet
know, being a provision confined to naked Cephalopods,
which have not that protection from an external shell,
which is afforded by the shell of the N. Pompilius to its
inhabitant, that has no ink-bag. No ink, or ink-bags have
been ever seen within the shell of any fossil Nautilus or
Ammonite: had such a substance existed in the body of the
animals that occupied their outer chamber, some traces of
it must have remained in those beds of lias at Lyme Regis,
which are loaded with Nautili and Ammonites, and have
preserved the ink of naked Cephalopods in so perfect a condition.
The young Sepia officinalis, whilst included within
the transparent egg, exhibits its link-bag distended with ink,
provided beforehand for use as soon as it is excluded; and
this ink-bag is surrounded by a covering of brilliant nacreous matter, similar to that we find on certain internal membranes
of many fishes.[66]
Comparing the shell of Belemnite, with that of Nautilus,
we find the agreement of all their most important parts to
be nearly complete;[67] and the same analogies might be
traced through the other genera of chambered shells.[68]
Eighty-eight species of Belemnites have already been discovered;[69] and the vast numerical amount to which individuals of these species were extended, is proved by the myriads of their fossil remains that till the Oolitic and Cretaceous formations. When we recollect that throughout both these great formations, the still more numerous extinct family of Ammonites is co-extensive with the Belemnites; and that each species of Ammonite exhibits also contrivances, more complex and perfect than those retained in the few existing cognate genera of Cephalopods; we cannot but infer that these extinct families filled a larger space, and performed more important functions among the inhabitants of the ancient seas, than are assigned to their few living representatives in our modern oceans.
Conclusion.
It results from the view we have taken of the zoological affinities between living and extinct species of chambered shells, that they are all connected by one plan and organization; each forming a link-in the common chain, which unites existing species with those that prevailed among the earliest conditions of life upon our globe; and all attesting the Identity of the design, that has affected so many similar ends through such a variety of instruments, the principle of whose construction is, in every species, fundamentally the same.
Throughout the various living and extinct genera of Chambered shells, the use of the air-chambers and siphon, to adjust the specific gravity of the animals in rising and sinking, appears to have been identical. The addition of a new transverse plate within the conical shell added a new air-chamber, larger than the preceding one, to counterbalance the increase of weight that attended the growth of the shell and body of all these animals.
These beautiful arrangements are, and ever have been,
subservient to a common object, viz. the construction of
hydraulic instruments of essential importance in the economy
of creatures destined to move sometimes at the bottom, and
at other times upon or near the surface of the sea. The
delicate adjustments whereby the same principle is extended
through so many grades and modifications of a single type,
show the uniform and constant agency of some controlling
Intelligence; and in searching for the origin of so much
method and regularity amidst variety, the mind can only
rest, when it has passed back, through the subordinate
series of Second causes, to that great First Cause, which is
found in the will and power of a common Creator.
SECTION VIII.
FORAMINATED POLYTHALAMOUS SHELLS.
Nummulites.
If the present were a fit occasion for such minute inquiries, the investigations of the various known species of Microscopic shells would unfold a æries of contrivances having relation to the economy of the minute Cephalopods by which they were constructed, not less striking than those we have been examining in the shells of extinct Genera and species of larger Cephalopods. M. D'Orbigny has noticed from 600 to 700 species of these shells, and has prepared magnified models of 100 species, comprehending all the Genera.[70]
The greater number of these shells are microscopic, and swarm in the Mediterranean and Adriatic. Their fossil species abound chiefly in the Tertiary formations, and have hitherto been noticed principally in Italy. (See Soldani, as quoted at page 97 of this volume.) They occur also in the Chalk of Meudon, in the Jura Limestone of the Charente inférieure, and the Oolite of Calne. They have been found by the Marquis of Northampton in Chalk Hints from the neighbourhood of Brighton.
The Nummulite is the only Genus I shall select on the present occasion from this Order. It is included in M. D'Orbigny's Section Nautiloids.
Nummulites (Pl. 44, Fig. 6, 7,) are so called from their resemblance to a piece of money, they vary in size from that of a crown piece to microscopic littleness; and occupy an important place in the history of fossil shells, on account of the prodigious extent to which they are accumulated in the later members of the Secondary, and in many of the Tertiary strata. They are often piled on each other nearly in as close contact as the grains in a heap of corn. In this state they form a considerable portion of the entire bulk of many extensive mountains, e. g. in the Tertiary limestones of Verona and Monte Bolca, and in secondary strata of the Cretaceous formation in the Alps, Carpathians, and Pyrenees. Some of the pyramids and the Sphinx, of Egypt, are composed of limestone loaded with Nummulites.
It is impossible to see such mountain-masses of the remains
of a single family of shells thus added to the solid materials
of the globe, without recollecting that each individual
shell once held an important place within the body of a
living animal; and thus recalling our imagination to those
distant epochs when the waters of the ocean which then
covered Europe were filled with floating swarms of these
extinct Mollusks, thick as the countless myriads of Beröe
and Clio Borealis that now crowd the waters of the polar
seas.[71]
The Nummulites, like the Nautilus and Ammonite, are divided into air-chambers, which served the office of a float: but there is no enlargement of the last chamber which could have contained any part of the body of the animal. The chambers are very numerous, and minutely divided by transverse plates; but are without a siphuncle.[72] The form of the essential parts varies in each species of this genus, but their principles of construction, and manner of operation, appear in all to have been the same.
The remains of Nummulites are not the only animal bodies which have contributed to form; the calcareous strata of the crust of the earth; other, and more minute species of Chambered shells have also produced great, and most surprising effects. Lamarck (Note, v. 7. p. 611,) speaking of the Miliola, a small multilocular shell, no larger than a millet seed, with which the strata of many quarries in the neighbourhood of Paris are, largely interspersed, notices the important influence which these minute bodies have exercised by reason of their numerical abundance. We scarcely condescend, descend, says he, to examine microscopic shells, from their insignificant size; but we cease to think them insignificant, when we reflect that it is by means of the smallest objects, that Nature every where produces her most remarkable and astonishing phenomena. Whatever she may seem to lose in point of volume in the production of living bodies, is amply made up by the number of the individuals, which she multiplies with admirable promptitude to infinity. The remains of such minute animals have added much more to the mass of materials which compose the exterior crust of the globe, than the bones of Elephants, Hippopotami, and Whales.
- ↑ See note, p. 56.
- ↑ See Mr. Broderip's Introduction to his Paper on some new species of Brachipoda, Zool. Trans., vol. I., p. 141.
- ↑ This name is derived from the position of the foot, or locomotive apparatus, on the lower surface of the neck, or of the anterior part of the body. By means of this organ Trachelipods crawl like the common garden snail (Helix aspersa.) This Helix offers also a familiar example of the manner in which they have the principal viscera packed within the spiral shell.
- ↑ The proboscis, by means of which these animals are enabled to drill holes through shells, is armed with a number of minute teeth, set like the teeth of a file, upon a retractile membrane, which the animal is enabled to fix in a position adapted for boring or filing a hole from without, through the substance of shells, and through this hole to extract and feed upon the juices of the body within them. A familiar example of this organ may be seen in the retractile proboscis of Buccinum Lapillus, and Buccinum Undatum, the common whelks of our own shores. A valuable Paper on this subject has recently been published by Mr. Osler (Phil. Trans., 1832, Part 2, P. 497,) in which he gives an engraved figure of the tongue of the Buccinum Undatum, covered with its rasp, whereby it perforates the shells of animals destined to become its prey. Mr. Osler modifies the rule or the distinction between the shells of carnivore and herbivore, by showing that, although it is true that all beaked shells indicate their molluscous inhabitant to have been carnivorous, an entire aperture does not always indicate an herbivorous character.
- ↑ See explanation of the term Cephalopod, in note at p. 230.
- ↑ Mr. Dillwyn observes further, that all the herbivorous marine Trachelipods of the Transition and Secondary strata were furnished with an operculum, as if to protect them against the carnivorous Cephalopods which then prevailed abundantly; but that in the Tertiary formations, numerous herbivorous genera appear, which are not furnished with opercula, as if no longer requiring' the protection of such a shield, after the extinction of the Ammonites and of many cognate genera of carnivorous Trachelipods, at the termination of the Secondary period, i. e. after the deposition of the Chalk formation.
- ↑ "It can scarcely escape the observation of the reader, that, while the specific gravities of the land shells enumerated are generally greatest, the densities of the floating marine shells are much the smallest. The design of the difference is obvious; The land shells have to contend with all changes of climate, and to resist the action of the atmosphere, while, at the same, time, they are thin for the purpose of easy transport, their density is therefore greatest. The Argonaut, Nautilus, and creatures of the like habits require as light shells as may be consistent with the equisite strength; the relative specific gravity of such shells is consequently small. The greatest observed density was that of a Helix, the smallest, that of an Argonaut. The shell of the Ianthina, a floating Molluscous creature, is among the smallest densities. The specific gravity of all the land shells examined was greater than that of Carara marble; in general more approaching to Arragonite. The freshwater and marine shells, with the exception of the Argonaut, Nautilus, Ianthina, Lithodomus, Haliotis, and great radiated crystalline Teredo from the East Indies, exceeded Carara marble in density. This marble and the Haliotis are of equal specific gravities."—De la Beche's Geological Researches, 1834, p. 76
- ↑ The figure of the common Calmar, or Squid (Loligo Vulgaris Lam.—Sepia loligo of Linnæus,) see Pl. 28, Fig. 1, illustrates the origin of the term Cephalopod, a term applied to a large family of molluscous animals, from the fact of their feet being placed around their heads. The feet are lined internally with ranges of horny cups, or suckers, by which the animal seizes on its prey, and adheres to extraneous bodies. The mouth, in form and substance resembles a Parrot's beak, and is surrounded by the feet. By means of these feet and suckers the Sepia octopus, or common Poulpe (the Polypus of the ancients,) crawls with its head downwards, along the bottom of the sea.
- ↑ We owe this discovery to the industry and skill of Miss Mary Anning, to whom the scientific world is largely indebted, for having brought to light so many interesting remains of fossil Reptiles from the Lias at Lyme Regis.
- ↑ So completely are the character and qualities of the ink retained in its fossil state, that when, in 1826, I submitted a portion of it to my friend Sir Francis Chantrey, requesting him to try its power as a pigment, and he had prepared a drawing with a triturated portion of this fossil substance; the drawing was shown to a celebrated painter, without any information as to its origin, and he immediately pronounced it to be tinted with sepia of excellent quality, and begged to be informed by what colour man it was prepared. The common sepia used in drawing is from the ink-bag of an oriental species of cuttle-fish. The ink of the cuttlefishes, in its natural state, is said to be soluble only in water, through which it diffuses itself instantaneously; being thus remarkably adapted to its peculiar service in the only fluid wherein it is naturally employed.
- ↑ We have elsewhere applied this line of argument to prove the sudden destruction and burial of the whose skeletons we find entire in the same Lias that contains the pens and ink-bags of Loligo. On the other hand, we have proofs of intervals between the depositions of the component strata of the Lias, in the fact, that many beds of this formation have become the repository of Coprolites, dispersed singly and irregularly at intervals far distant from one another, and at a distance from any entire skeletons of the Saurians, from which they were derived; and in the further fact, that those surfaces only of the Coprolites, which lay uppermost at the bottom of the sea, have often suffered partial destruction from the action of water before they were covered and protected by the muddy sediment that has afterwards permanently enveloped them. Further proof of the duration of time, during the intervals of the deposition of the Lias, is found in the innumerable multitudes of the shells of various Mollusks and Conchifers which had time to arrive at maturity, at the bottom of the sea, during the quiescent periods which intervened between the muddy invasions that destroyed, and buried suddenly the creatures inhabiting the waters, at the time and place of their arrival.
- ↑ As far as we can judge from the delineations and lines of the structure in Zeiten's plate, our species from Lyme Regis is the same with that which he has designated by the name of Loligo Aalenis; but I have yet seen no structure in English specimens like that of his Loligo Bolensis.
- ↑ Although the resemblance between the pens of the Loligo and a feather (as might be expected from the very different uses to which they are applied) does not extend to their internal structure, we may still, for convenience of description, consider them as composed of the three following parts, which, in all our figures, will be designated by the same letters, A. B. C. First, the external filaments of the plume, (Pl. 28, 29, 30, A.) analogous to those of a common feather. These filaments terminate inwards on a straight line, or base, where they usually form an acute angle with the outer edges of the marginal bands. Secondly, two marginal bands, B. B., dividing the base of the filaments from the body of the shafts the surface of these bands, B., usually exhibits angular lines of growth in the smaller fossil pens (Pl. 28, Fig. 6, and Pl. 29, Fig. 2,) which become obtuse and vanish into broad curves, in larger specimens, Pl. 29, Fig. 1, and Pl. 30. Thirdly, the broad shaft, which forms the middle of the pen, is divided longitudinally into two equal parts by a straight line, or axis, C.: it is made up of a number of thin plates, of a horn-like substance, laid on each other, like thin sheets of paper in pasteboard; these thin plates are composed alternately, of longitudinal, and transverse fibres; the former (Pl. 28, Fig. 7. f. f.) straight, and nearly parallel to the axis of the shaft, the latter (Pl. 28, Fig. 7, e. e.) crossing the shaft transversely in a succession of symmetrical and undulating curves. These transverse fibres do not interlace the others, as the woof interlaces the weaver's warp, but are simply laid over, and adhering to them, as in the alternate laminæ of paper made from slices of papyrus; the strength of such paper much exceeds that made from flax or cotton, in which the fibres are disposed irregularly in all directions. The fibres of both kinds are also collected at intervals into fluted fasciculi, Pl. 30, f, and e, forming a succession of grooves and ridges fitted one into another, whereby the entire surface of each plate is locked into the surface of the adjacent plate, in s manner admirably calculated to combine elasticity with strength.
- ↑ Thus, the Nautilus multicarinatis is limited to strata of the Transition formation; the N. bidorsatus to the Muschelkalk; N. obesus, and N. lineatus, to the Oolite Formation; N. elegans, and N. undulatus, to the Chalk. The divisions of the Tertiary formations have also species of Nautili peculiar to themselves.
- ↑ The introduction, in the Tertiary periods, of a class of animals of lower organization, viz. the carnivorous Trachelipods, (See Chap. XV. Section 1,) to fill the place which, during the Secondary periods, had been occupied by a higher order, namely, the carnivorous Cephalopods, affords an example of Retrocession which seems fatal to that doctrine of regular Progression, which is most insisted on by those who are unwilling to admit the repeated interferences of Creative power, in adjusting the successive changes that animal life has undergone.
It will appear, on examination of the shells of fossil Nautili, that they have retained, through strata of all ages, their aboriginal simplicity of structure; a structure which remains fundamentally the same in the Nautilus Pompilius of our existing seas, as it was in the earliest fossil species that we find in the Transition strata. Meantime the cognate family of Ammonites, whose shells were more elaborately, constructed than those of Nautili, commenced their existence at the same early period with them in the Transition strata, and became extinct at the termination of the Secondary formations. Other examples of later creations of genera and species, followed by their periodical and total extinction, before, or at the same time with the cessation of the Ammonites, are afforded by those cognate Multilocular shells, namely, the Hamite, Turrilite, Scaphite, Baculite, and Belemnite, respecting each of which I shall presently notice a few particulars.
- ↑ I omit to mention the more familiar shell of the Argonauta or Paper Nautilus, because, not being a chambered species, it does not apply so directly to my present subject; and also, because doubts still exist whether 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 anything 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 hasbeen so handsomely conducted.
- ↑ A further important light is thrown upon those species of fossil Multilocular shells, e. g. Orthoceratites, Baculites, Hamites, Scaphites, Belemnites, &c. (See Pl. 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 (Pl. 44; Figs. 1, 2.) Although some doubts have existed respecting the authenticity of this specimen, in consequence of a discrepancy between two drawings professedly taken from it (the one published in the Encyclopédie Méthodique, the other in Peron's Voyage,) and from the loss of the specimen itself before any anatomical examination of it had been made, the subsequent 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 Pl. 44, Fig. 1.)
- ↑ The animal is copied from Pl. 1 of Mr. 0wen'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.
- ↑ In Pl. 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 same hard calcareous substance as its point; this substance is of the nature of shell.
These calcareous extremities 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, and Loligo, I have found them to contain numerous shells of small Conchifera.
- ↑ See p. 192.
- ↑ The siphuncle represented in Pl. 31, Fig. 1, illustrates the structure and uses of that organ; in the smallest whorls, from d. inwards, it is enclosed by a thin calcareous covering, or sheathr, of so soft a nature as to be readily scraped off by the point of a quill; this sheath may admit of expansion or contraction, together with the membranous tube enclosed within it. In the fossil Nautili, a similar calcareous sheath is often preserved, as in Pl. 32, Figs. 2, 3, and Pl. 33, and forms a connected series of tubes of carbonate of lime, closely fitted to the collar of each transverse plate. In four chambers of the recent shell (Pl. 31, Fig. 1, a. b. c. d.) this sheath is partially removed from the desiccated membranous pipe within it, which has assumed the condition of a black elastic substance, resembling the black continuous siphuncular pipe that is frequently preserved in a carbonaceous state in fossil Ammonites.
At that part of each transverse plate, which is perforated for the passage of the siphuncle, (Pl. 31, Fig. 1, y. y.,) a portion of its shelly matter projects inwards to about one-fourth of the distance across each chamber, and forms a collar, around the membranous pipe, thus directing its passage through the tans verse plates, and also affording to it, when distended with fluid, a strong support at each collar. A similar projecting collar is seen in the transverse plate of a fossil Nautilus. (Pl. 32, Fig. 2, e, and Fig. 3, e, i. and Pl. 33.) A succession of such supports placed at short intervals from one another, divides this long and thin membranaceous tube, when distended, into a series of short compartments, or small oval sacs, each sac communicating with the adjacent sacs by a contracted aperture or neck at both its ends, and being firmly supported around this neck by the collar of each transverse plate. (See Pl. 32, Figs, 2, 3, and Pl. 33.)
The strength of each sac is thus increased by the shortness of the distance between its two extremities, and the entire pipe, thus subdivided into thirty or forty distinct compartments, derives from every subdivision an accession of power to sustain the pressure of any fluid that may be introduced to its interior.
- ↑ We learn from Mr. Owen, that there was no possibility of the access of water to the air chambers between the exterior of this pipe and the siphonic apertures of the transverse plates; because the entire circumference of the mantle in which the siphuncle originates, is firmly attached to the shell by a horny girdle, impenetrable to any fluid.—Memoire on Nautilus Pompilius, p. 47.
- ↑ The disposition of the curvatures of the transverse ribs, or lines of growth, in a different direction from the curvatures of the internal transverse plates, affords an example of further contrivance for producing strength in the shells both of recent and fossil Nautili. As the internal transverse plates are convex inwards, (see Pl. 32, Fig. 1, b. to c.) whilst the ribs of the outer shell are in the greater part. of their course convex outwards, these ribs intersect the curved edges of the transverse plates at many points, and thus divide them into a series of curvilinear parallelograms; the two shorter sides of each parallelogram being formed by the edges of transverse plates, whilst its two longer sides are formed by segments of the external ribs. The same principle of construction here represented in our plate of Nautilus hexagon us, extends to other species of its family of Nautilus, in many of which the ribs are more minute; it is also applied in other families of fossil chambered shells; e. g. the Ammonites, Pl. 35, and Pl. 38. Scaphites, Pl. 44, Fig. 15. Hamites, Pl. 44, Fig. 8—13. Turrilites, Pl. 44-, Fig. 14, and Baculites, Pl. 44, Fig. 5.
- ↑ In a young Nautilus Pompilius in the collection of Mr. Broderip, there are only seventeen Sepia. Dr. Hook says that he has found in some shells as many as forty. A cast, expressing the form of a single air chamber, of the Nautilus Hexagonous is represented in Pl. 42, Fig. 1.
- ↑ Pl. 32, Fig. 2, represents a fractured portion of the interior of a Nautilus Hexagonus, having the transverse plates (c. c'.) encrusted with calcareous spar; the Siphuncle also is similarly encrusted, and distended in a manner which illustrates the action of this organ. (Pl. 32, Fig. 2, a.
a1. a2. a3. d. e. f, and Fig. 3, d. e. f.) The fracture at Fig. 2, b. shows the diameter of the siphuncle, where it passes through a transverse plate, to be much smaller than it is midway between these Plates (at d. e. f.) The transverse sections at Fig, 2 a. and h., and the longitudinal sections at Fig. 2, d. e. f., and Fig. 3, d. c. £, show that the interior of the siphuncle is filled with stone, of the same nature with the stratum in which the shell was lodged. These earthy materials, having entered the orifice of the pipe at a in a soft and plastic state, have formed a cast which shows the interior of this pipe, when distended, to have resembled a string of oval beads, connected at their ends by a narrow neck, and enlarged at their centre to nearly double the diameter of this neck.
A similar distension of nearly the entire siphuncle by the stony material of the rock in which the shell was imbedded, is seen in the specimen of Nautilus striatus from the Lias of Whitby, represented at Pl. 33. The Lias which fills this pipe, must have entered it in the state of liquid mud, to the same extent that the pericardial fluid entered, during the hydraulic action of the siphuncle in the act of sinking; not one of the air-chambers has admitted the smallest particle of this mud; they are all filled with calcareous spar, subsquently introduced by gradual infiltration, and at successive periods which are marked by changes in the colour of the spar. In both these fossil Nautili, the entire series of the earthy casts within the siphuncle represents the bulk of fluid which this pipe could hold.
The sections, Pl. 32, Fig. 3, d. e. £, show the edges of the calcareous sheath surrounding the oval casts of three compartments of the expanded siphuncle. This calcareous sheath was probably flexible, like that surrounding the membranous pipe of the recent Nautilus Pompilius. (Pl. 31, Fig. 1, b. d. e.) The continuity of this sheath across the air-chambers, (Pl. 32, Fig. 2, d. e. f. Fig. 3, d. e. £ and Pl. 33,) shows that there was no communication for the passage of any fluid from the siphuncle into these chambers: had any such existed, some portion of the line earthy matter, which in these two fossils forms the casts of the siphuncle, must have passed through it into these chambers. Nothing has entered them, but pure crystallized spar, introduced by infiltration through the pores of the shell, after it had undergone sufficient decomposition to be percolated by water, holding in solution carbonate of lime.
The same argument applies to the solid casts of pure crystallized carbonate of lime, which have entirely filled the chambers of the specimen Pl. 32, Fig. 1; and to all fossil Nautili and Ammonites, in which the air chambers are either wholly void, or partially, or entirely filled with pure crystallized carbonate of lime. (See Pl. 42, Fig. 1, 2, 3, and Pl. 36.) In all such cases, it is clear that no communication existed, by which water could pass from the interior of the siphon to the air chambers. When the pipe was ruptured, or the external shell broken, the earthy sediment, in which such broken shells were lodged, finding through these fractures admission to the air chambers, has filled them with clay, or sand or limestone.
- ↑ The substance of the siphuncle is a thin and strong membrane, with no appearance of muscular fibres, by which it could contract or expand itself; its functions, therefore, must have been entirely passive, in the process of admitting or ejecting any fluid to or from its interior.—See Owen's Memoir, p. 10.
- ↑
It appears from the figure of the animal, Pl. 34, with which I have been favoured by Mr. Owen, that the upper extremity of the siphuncle marked by the insertion of the probe b., terminates in the cavity of the pericardium p, p. As this cavity may contain a fluid, more dense than water, excreted by the glandular follicles d. d., and is apparently of such a size that its contents would suffice to fill the siphuncle, it is probable that this fluid forms the circulating medium of adjustment, and regulates the ascent or descent of the animal by its interchange of place from the pericardium to the siphuncle.
When the arms and body are expanded, the fluid remains in the pericardium, and the siphuncle is empty, and collapsed, and surrounded by the portions of air that are permanently confined within each air-chamber; in this state, the specific gravity of the body and shell together is such as to cause the animal to rise, and be sustained floating at the surface.
When, on any alarm, the arms and body are contracted, and drawn into the shell, the retraction of these parts, causing pressure on the exterior of the pericardium, forces its fluid contents downwards into the siphuncle; and the bulk of the body being thus diminished, without increasing the bulk of the shell, into whose cavities the fluid is withdrawn, the specific gravity of the whole mass is suddenly increased, and the animal begins to sink.
The air within each chamber remains under compression, as long as the siphuncle continues distended by the pericardia fluid; and returning, by its elasticity, to its former state, as soon as the pressure of the arms and body is withdrawn from the pericardium, forces the fluid back again into the cavity of this organ; and thus the shell, diminished as to its specific gravity, has a tendency to rise.
The place of the pericardia fluid, therefore, will be always in the pericardium, excepting when it is forced into and retained in the siphuncle, by muscular pressure, during the contraction of the arms and body closed up within the shell. When these are expanded, either on the surface, or at the bottom of the sea, the water will have free access to the branchiæ, and the movements of the heart will proceed freely in the distended pericardium; which will be emptied of its fluid at those times only, when the body is closed, and the access of water to the branchiæ consequently impeded.
The following experiments show that the weight of fluid requisite to be added to the shell of a Nautilus, in order to make it sink, is about half an ounce.
I took two perfect shells of a Nautilus Pompilius, each weighing about six ounces and a half in air, and measuring about seven inches across their largest diameter; and having stopped the siphuncle with wax, I found that each shell, when placed in fresh water, required the weight of a few grains more than an ounce to make it sink. As the shell, when attached to the living animal, was probably a quarter of an ounce heavier than these dry dead shells, and the specific gravity of the body of the animal may have exceeded that of water to the amount of another quarter of an ounce, there remains about half an ounce, for the weight of fluid which being introduced into the siphuncle, would cause the shell to sink; and this quantity seems well proportioned to the capacity both of the pericardium, and of the distended siphuncle.
- ↑ If the chambers, were filled with water, the shell could not be thus suspended without muscular exertion, and instead of being poised vertically over the body, in a position of ease and safety, would be continually tending to fall flat upon its side; thus exposing itself to injury by friction, and the animal to attacks from its enemies. Rumphius states, that at the bottom, He creeps with his boat above him, and with his head and barbs (tentacula) on the ground, making a tolerably quick progress. I have observed that a similar vertical position is maintained by the shell of the Planorbis corneus, whilst in the act of crawling at the bottom.
- ↑ The recent observations of Mr. Owen show, that there is no gland connected with the siphuncle, similar to that which in supposed to secrete air in the air-bladder of fishes.
- ↑ Dr. Hook's Experiments, p. 306.
- ↑ Thus one of the first forms under which this family appeared, the Ammonites Henslowi, (Pl. 40, Fig. 1,) ceased with the Transition formation; the A. Nodosus (Pl. 40, Figs. 4, 5.) began and terminated its period of existence with the Muschelkalk. Other genera and species of Ammonites, in like manner, begin and end with certain definite strata, in the Oolitic and Cretaceous formations; e. g. the A. Bucklandi (Pl. 37, Fig. 6.) is peculiar to the Lias; the A. Goodhalli to the Greensand; and the A. Rusticus to the Chalk. There are few, if any, species which extend through the whole of the Secondary periods, or which have passed into the Secondary, from the Transition period.
The following Tabular Arrangement of the distribution of Ammonites, in different geological formations, is given by Professor Phillips in his Guide to Geology, 1834, p. 77.
SUB-GENERA OF AMMONITES. LIVING SPECIES Gonia-
titesCera-
titesArie-
tesFalci-
feriAmal-
theiCapri-
corniPlanu-
latiDor-
satiCoro-
nariiMacro-
cephaliArmati Den-
tatiOrnati Fle-
xuosiIn Tertiary strata In Cretaceous system 2 4 9 4 13 2 3 In Oolitic system 22 27 12 26 5 11 11 11 4 5 3 In Saliferous system 3 12 In Carboniferous system 7 [nested 1]In Primary strata 17 Total 223 species. "It is easy to see how important, in questions concerning the relative antiquity of stratified rocks, is a knowledge of Ammonites, since whole sections of them are characteristic of certain systems of rocks."—Phillips's Guide to Geology, 8vo. 1834, sec. 82.
- ↑ Mr. Sowerby (Min. Conch. vol. iv. p. 79 and p. 81,) and Mr. Mantell speak of Ammonites in Chalk, having a diameter of three feet. Sir T. Harvey, and Mr. Keith Milnes, have recently measured Ammonites in the Chalk near Margate, which exceeded four feet in diameter; and this in cases where the diameter can have been in a very small degree enlarged by pressure.
- ↑ Dr. Gerard has discovered at the elevation of sixteen thousand feet in the Himmalaya Mountains, species of Ammonites, e. g. A. Walcoti, and A. Communis, identical with those of the Lias at Whitby and Lyme Regis. He has also found in the same parts of the Himmalaya, several species of Belemnite, with Terebutulæ, and other bivalves, that occur in the English Oolite; thereby establishing the existence of the Lias, and Oolite formations in that elevated and distant region of the world. He has also collected in the same Mountains, shells of the genera Spirifer, Products, and Terebratula, which occur in the Transition formations of Europe and America.
The Greensand of New Jersey also contains Ammonites mixed with Hamites and Scaphites, as in the green sand of England, and Captain Beechy and Lieutenant Belcher found Ammonites on the coast of Chili in Lat. 36 S. in the Cliffs near Conception; a fragment of one of these Ammonites is preserved in the Museum of Hasler Hospital at Gosport.
Mr. Sowerby possesses fossil shells from Brazil resembling those of the Inferior Oolite of England.
- ↑ The smallness of the outer chamber, or place of lodgment for the animal, is advanced by Cuvier in favour of his opinion that Ammonites, like the Spirula, were internal shells. This reason is probably founded on observations made upon imperfect specimens. The outer chamber of Ammonites is very seldom preserved in a perfect state, but when this happens, it is found to bear at least as large a proportion to the chambered part of the shell, as the outer cell of the N. Pompilius bears to the chambered interior of that shell. It often occupies more than half, (see Pl. 36. a. b. c. d.) and, in some cases, the whole circumference of the outer whorl. This open chamber is not thin and feeble, like the long anterior chamber of the Spirula, which is placed within the body of the animal producing this shell; but is nearly of equal thickness with the sides of the close chambers of the Ammonite.
Moreover, the margin of the mature Ammonite is in some species reflected in a kind of scroll, like the thickened margin of the shell of the garden snail, giving to this part a strength which would apparently be needless to an internal shell. (See Pl. 37. Fig. 3. d.) The presence of spines also in certain species, (as in A. Armatus, A. Sowerbii,) affords a strong argument against the theory of their having been internal shells. These spines which have an obvious use for protection, if placed externally, would seem to have been useless, and perhaps noxious in an internal position, and are without example in any internal structure with which we are acquainted.
- ↑ In the Ammonites in question, the outer extremity of the first great chamber in which the body of the animal was contained, is filled with stone only to a small depth, (see Pl. 36, from a. to b.); the remainder of this chamber from b. to c., is occupied by brown calcareous spar, which has been ascertained by Dr. Prout to owe its colour to the presence of animal matter, whilst the internal air chambers and siphuncle are filled with pure white spar. The extent of the brown calcareous spar, therefore, in the outer chamber, represents the space which was occupied by the body of the animal after it had shrunk within its shell, at the moment of its death, leaving void the outer portion only of its chamber, from a. to b., to receive the muddy sediment in which the shell was imbedded. I have many specimens from the lias of Whitby, of the Ammonites Communis, in which the outer chamber thus filled with spar, occupies nearly the entire last whorl of the shell, its largest extremity only being filled with lias. From specimens of this kind we also learn, that the animal inhabiting the shell of an Ammonite, had no ink-bag; if such an organ existed, traces of its colour must have been found within the cavity which contained the body of the animal at the moment of its death. The protection of a shell seems to have rendered the presence of an ink-bag superfluous.
- ↑ The figures engraved at Pl. 37, afford examples of various contrivances to give strength and beauty to the external shell. The first and simplest mode, is that represented in Pl. 35 and Pl. 37, Fig. 1 and 6. Here each rib is single, and extends over the whole surface, becoming gradually wider, as the space enlarges towards the outer margin, or back of the shell.
The next variation is that represented (Pl. 37, Figs. 2, 7, 9,) where the ribs, originating singly on the inner margin, soon bifurcate into two ribs that extend outwards, and terminate upon the dorsal keel.
In the third case, (Pl. 37. Fig. 4,) the ribs originate simply, and bifurcating as the shell enlarges, extend this bifurcation entirely around its circular back. Between each pair of bifurcated ribs, a third or auxiliary short rib is interposed, to fill up the enlarged space on the dorsal portion where the shell is broadest.
In the fourth modification, (Pl. 37, Fig. 3,) the ribs, originating singly on the internal margin, soon become trifurcate, and expand outwards, around the circular back of the shell. A perfect mouth of this shell is represented at Pl. 37, Fig. 3, d.
A fifth case is that (Pl. 37, Fig. 5,) in which the simple rib becomes trifurcate as the space enlarges, and one or more auxiliary short ribs are also interposed, between each trifurcation. These subdivisions are not always maintained with numerical fidelity through every individual of the same species, nor over the whole surface of the same shell; their use, however, is always the same, viz. to cover and strengthen those spaces which the expansion of the shell towards its outer circumference, would have rendered weak without the aid of some such compensation.
- ↑ These places are usually either at the point of bifurcation, as in Pl. 37, Figs. 2, 7, 9, 10, or at the point of trifurcation, as in Fig. 3.
- ↑ The ribs and bosses in vaulted roofs project beneath the under surface of the arch; in the shells of Ammonites, they are raised above the convex surface.
- ↑ In Pl. 37, Fig. 9 (A. varians,) the strength of the ribs and proportions of the tubercles are variable, but the general character exhibits a triple series of large tubercles, rising from the surface of the transverse ribs. Each of these ribs commences with a small tubercle near the inner margin of the shell. At a short distance outwards is a second and larger tubercle, from which the rib bifurcates, and terminates in a third tubercle, raised at the extremity of each fork upon the dorsal margin.
Many species of Ammonites have also a dorsal ridge or keel, (Pl. 37, Figs. 1. 2. 6.) passage along the back of the shell, immediately over the siphuncle, and apparently answering, in some cases, the further purpose of a cut-water, and keel (Pl. 37, Figs. 1, 2.) In certain species, e. g. in the A. lautus (Pl. 37, Fig. 7, a. c.) there is a double keel, produced by a deep depression along the dorsal margin; and the keels are fortified by a line of tubercles placed at the extremity of the transverse ribs. In the A. varians (Pl. 37, 9. a. b. c.) which has a triple keel, the two external ones are fortified by tubercles, as in Fig. 7, and the central keel is a simple convex arch.
Pl. 37, Fig. 8, offers an example of domes, or bosses, compensating the weakness that, without them, would exist in the A. catena, from the minuteness of its ribs, and the flatness of the sides of the shell. These flat parts are all supported by an abundant distribution of the edges of the transverse plates directly beneath them, whilst those parts which are elevated into bosses, being sufficiently strong, are but slightly provided with any other support. The back of this shell also, being nearly flat, (Pl. 37, Fig. 8. b. c.) is strongly supported by ramifications of the transverse plates.
In Pl. 37, Fig. 6, which has a triple keel, (that in the centre passing over the siphuncle,) this triple elevation affords compensation for the weakness that would otherwise arise from the great breadth and flatness of the dorsal portion of this species. Between these three Reels, or ridges, are two depressions or dorsal furrows, and as these furrows form the weakest portion of the shell, a compensation is provided by conducting beneath them the denticulated edges of the transverse plates, so that they present long lines of resistance to external pressure.
- ↑ Captain Smyth found, on two trials, that the cylindrical copper air tube, under the vane attached to Massey's patent log, collapsed, and was crushed quite flat under a pressure of about three hundred fathoms. A claret bottle, filled with air, and well corked, was burst before it had descended four hundred fathoms. He also found that a bottle filled with fresh water, and corked, had the cork forced at about a hundred and eighty fathoms below the surface; in such cases, the fluid sent down is replaced by salt water, and the cork which had been forced in, is sometimes inverted.
Captain Beaufort also informs me, that he has frequently sunk corked bottles in the sea more than a hundred fathoms deep, some of them empty, and others containing a fluid. The empty bottles were sometimes crushed, at other times, the cork was forced in, and the bottle returned full of sea water. The cork of the bottles containing a fluid was uniformly forced, in, and the fluid exchanged for sea water; the cork was always returned to the neck of the bottle, sometimes, but not always, in an inverted position.
- ↑ See Lamarck, who cites Bruguières with approbation on this point.—Animaux sans; Vert: vol. vii. p. 635.
- ↑ The A. Heterophyllus, (Pl. 38,) is so called from the apparent occurrence of two different forms of foliage; its laws of denotation are the same as in other Ammonites, but the ascending secondary saddles (Pl. 38; S. S.) which, in all Ammonites are round, are in this species longer than ordinary, and catch attention more than the descending points of the lobes, (Pl. 38. d. 1.)
The figures of the edge of one transverse plate are repeated in each successive plate. The animal, as it enlarged its shell, thus leaving behind it a new chamber, more capacious than the last, so that the edges of the plates never interfere or become entangled.
Although the pattern on the surface of this Ammonite is apparently so complicated, the number of transverse plates is but sixteen in one revolution of the shell; in this, as in almost all other cases, the extreme beauty and elegance of the foliations result from the repetition, at regular intervals, of one symmetrical system of forms, viz. those presented by the external margin of a single transverse plate. No trace of these foliations is seen on the outer surface of the external shell. (See Pl. 38, c.)
The figures of A. obtusus, (Pl. 35 and Pl. 36,) show the relations between the external shell and the internal transverse partitions of an Ammonite. Pl. 85 represents the form of the external shell, wherein the body occupied the space extending from a. to c., and corresponding with the same letters in Pl. E. 36.
This species has a single series of strong ribs passing obliquely across the shell of the outer chamber, and also across the air-chambers. From c. to the inmost extremity of the shell, these ribs intersect, and rest on the sinuous edges of the transverse plates which form the air chambers. These edges are not seen where the outer shell is not removed. (Pl. 35, e.) A small portion of the shell is also preserved at Pl. 35, b.
From d. inwards, these sinuous lines mark the terminations of the transverse plates at their junction with the external shell; they are not coincident with the direction of the ribs, and therefore more effectually cooperate with them in adding strength to the shell, by affording it the support of a series of various props and buttresses, set nearly at right angles to its internal surface.
- ↑ Thus on the back or keel, Pl. 39, from V. to B., where the shell is narrow, and the strength of its arch greatest, the intervals between the septa are also greatest, and their sinuosities comparatively distant; but as soon as the flattened sides of the same shell, Pl. 38, assume a form that offers less resistance to external pressure, the foliations at the edges of the transverse plates approximate more closely; as in the flatter form of a Gothic root; the ribs are more numerous, and the tracery more complex, than in the stronger and more simple forms of the pointed arch.
The same principle of multiplying and extending the ramifications of the edges of the transverse plates, is applied to other species of Ammonites, in which the sides are flat, and require a similar increase of support, whilst in those species to which the more circular form of the sides gives greater strength (as in A. obtusus, Pl. 35.) the sinuosities of the septa are proportionately few.
It seems probable that some improvement might be made, in fortifying the cylindrical air-tube of Massey's Patent Log for taking soundings at great depths, by the introduction of transverse plates, acting on the principle of the transverse plates of the chambered portion of the shells of Nautili and Ammonites, or rather of Orthoceratites, and Baculites, (see Pl. 44, Figs. 4. and 5.)
- ↑ Pl. 42, Fig. 1, represents the cast of a single chamber of N. Hexagonus, convex inwards, and concave outwards, and bounded at its margin by lines of simple curvature. In a few species only of Nautilus the margin is undulated, (as in Pl. 43, Fig. 3, 4,) but it is never jagged, or denticulated like the margin of the casts of the chambers of Ammonites.
In Ammonites, the chambers have a double curvature, and are, at their centre, convex outwards (see Pl. 36. d. and Pl. 39. d. V.). Pl. 42, Fig, 2, represents the front view of the cast of a single chamber of A. excavatus; d, is the dorsal lobe enclosing the siphuncle, and e. f. the auxiliary ventral lobes, which open to receive the inner whorl of the shell. Pl. 49. Fig. 3. represents a cast of three chambers of A. catens, having two transverse, plates still retained in their proper place between them. The foliated edges of these transverse plates have regulated the foliations of the calcareous casts, which, after the shell has perished, remain locked into one another, like the sutures of a skull.
The substance of the casts in all these cases is pure crystalline carbonate of lime, introduced by infiltration through the pores of the decaying shell. Each species of Ammonite has its peculiar form of air-chamber, depending on the specific form of its transverse plates. Analogous variations in the form of the air-chambers are co-extensive with the entire range of species in the family of Nautili.
- ↑ In the family of Ammonites, the place of the Siphuncle is always upon the exterior, or dorsal margin of the transverse plates. (See Pl. 36. d. e. f. g. h. i., and Pl. 42, Fig. 3. a, b.) It is conducted through them by a ring, or collar, projecting outwards; this collar is seen, well preserved, at the margin of all the transverse plates in Pl. 36. In Nautili, the collar projects uniformly inwards, and its place is either at the centre, or near the inner margin of the transverse plates. (See Pl. 31, Fig. 1. y. and Pl. 42. 1.)
The Siphuncle represented at Pl. 36, is preserved in a black carbonaceous state, and passes from the bottom of the external chamber (d.) to the inner extremity of the shell. At e. f. g. h. its interior is exposed by section, and appears filled, like the adjacent air-chambers, with a cast of pure calcareous spar. At Pl. 42. Fig. 3. b. a similar cast fills the tube of the Siphuncle, and also the air-chambers. Here again, as in Pl. 36, its diameter is contracted at its passage through the collar of each transverse plate, with the same mechanical advantages as in the Nautilus.
The shell engraved at Pl. 4-2. Fig. 4., from a specimen found by the Marquis of Northampton in the Greensand of Earl Stoke, near Devizes, and of which Figs. 5. 6. are fragments, is remarkable for the preservation of its Siphuncle, distended and empty, and still fixed in its place along the interior of the dorsal margin of the shell. This Siphuncle, and also the shell and transverse plates, are converted into thin chalcedony, the pipe retaining in these empty chambers the exact form and position it held in the living: shell.
The entire substance of the pipe, thus perfectly preserved in a state that rarely occurs, shows no kind of aperture through which any fluid could have passed to the interior of the air-chambers. The same continuity of the Siphuncle appears at Pl. 42, Fig. 3. and in Pl. 36, and in many other specimens. Hence we infer, that nothing could pass from its interior into the air-chambers, and that the office of the Siphuncle was to be more or less distended with a fluid, as in the Nautili, for the purpose of adjusting the specific gravity, so as to cause the animal to float or sink.
Dr. Prout has analyzed a portion of the black material of the Siphuncle, which is so frequently preserved in Ammonites, and finds it to consist of animal membrane penetrated by carbonate of lime. He explains the black colour of these pipes, by supposing that the process of decomposition, in which the oxygen and hydrogen of the animal membrane escaped, was favourable to the evolution of carbon, as happens when vegetables are converted into coal, under the process of mineralization The lime has taken the place of the oxygen and hydrogen which existed in the pipe before decomposition.
- ↑ The most decided distinction between Ammonites and Nautili, is founded on the place of the siphon. In the Ammonite, this organ is always on the back of the shell, and never so in the Nautilus. Many other distinctions emanate from this leading difference; the animal of the Nautilus having its pipe usually fixed near the middle, (See Pl. 31, Fig. 1,) or towards the ventral margin (Pl. 32, Fig. 2, and Pl. 42. Fig. 1.) of the transverse plates, is thereby attached to the bottom of the external chamber, which is generally concave, and without any jagged termination, or sinuous flexure, of its margin. As the siphon in Ammonites is comparatively small, and always placed on the dorsal margin (Pl. 36, d. and Pl. 39, d.,)it would have less power than the siphuncle of Nautili to keep the mantle in its place at the bottom of the shell; another kind of support was therefore supplied by a number of depressions along the margin of the transverse plate, forming a series of lobes at the junction of this plate with the internal surface of the shell.
The innermost of these, or ventral lobe, is placed on the inner margin of the -shell (Pl. 39, V.); opposite to this, and on the external margin, is placed the dorsal lobe (D,) embracing the siphon and divided by it into two divergent arms. Beneath the dorsal lobe are placed the superior lateral lobes (L,) one on each side of the shell; and still lower, the inferior lateral lobe (l,) next above the ventral lobe.
The separations between these lobes form seats, or saddles, upon which the mantle of the animal rested, at the bottom of the outer chamber; these saddles are distinguished in the same manner as the lobes—that between the dorsal and superior lateral lobe, forming the dorsal saddle (S. d.,) that between the superior and inferior lateral lobes, forming the lateral saddle (S. L.), and that between the inferior lateral and ventral lobe, the ventral saddle (S. V.), This general disposition, variously modified, pervades all forms of Ammonites; but when, as in Pl. 39, the turn of the shell increases rapidly in width, so that the last whorl nearly, or entirely, covers the preceding whorls, the additional part is furnished with small auxiliary lobes, varying with the growth of the Ammonite to the number of three, four, or live pairs. (Pl. 39, a. 1, a. 2, a. 3, a. 4, a. 5.).
All the lobes, as they dip inward, are subdivided by numerous denotations, which afford points of attachment to the mantle of the animal; thus each lobe is flanked by a series of accessory lobes, and these again are provided with further symmetrical denotations, the extremities of which produce all the beautiful appearances of complicated foliage, which prevail through the family of Ammonites, and of which we have a striking example on the surface of Pl. 38.
The extremities of the denotations are always sharp and pointed, inwards, towards the air-chamber; (Pl. 38, d. 1.); but are smooth and rounded upwards towards the body of the animal, (Pl. 38, S. S.,) and thus the jagged terminations of these lobes may have afforded hold fasts whereby the base of the mantle could fix itself firmly, and as it were take r00t, around the bottom of the external chamber.
No such denotations exist in any species of Nautilus. In the N. Pompilius, Mr. Owen has shown that the base of the mantle adheres to the outer shell, near its junction with the transverse plate by means of a strong horny girdle; a similar contrivance probably existed also in all the fossil species of Nautili. The sides of the mantle also of the N. Pompilius are fixed to the sides of the great external chamber by two strong broad lateral muscles, the impressions of which are visible in most specimens of this shell.
- ↑ This shell has been variously described by the names of Ammonites Atun, Nautilus Sypho, and N. Zonarius. (See M. de Basterot. Mem. Geol. de Bourdeaux.)
- ↑ The transverse plates, (Pl. 43, Fig. 1, a. a1. a2,) present a peculiarity of structure in the prolongation of the collar, or siphuncular aperture entirely across the area of the air chambers, so that the whole series of transverse plates are connected in one continuous spin] chain. This union is effected by the enlargement and elongation of the collar for the passage of the siphuncle into the form of along and broad funnel, the point of which b. its closely into the neck of the funnel next beneath it, c. whilst its inner margin, resting upon the arch of the subjacent whorl of the shell, transfers to this arch a portion of the external pressure upon the transverse plates, thereby adding to their strength.
As this structure renders it impossible for the flexible siphuncle to expand itself into the area of the air-chambers, as in other Nautili and in Ammonites, the diameter of each funnel is made large enough to allow space within it for the distension of the siphuncle, by a sufficient quantity of fluid to cause the animal to sink.
At each articulation of the funnels, the diameter of the siphuncle is contracted, as the siphuncles of Ammonites and Nautili are contracted at their passage through the collars of their transverse plates. Another point in the organization of the siphuncle is illustrated by this shell, namely, the existence of a soft calcareous sheath, (Pl. 43, Fig. 1, b. c. d.) analogous to that of the N. Pompilius, (Pl. 31, Fig, 1, a. b. c. d.) between each shelly funnel and the membranous pipe or siphuncle enclosed within it. At Pl. 43, Fig. 1, b, we have a section of this sheath folding round the smaller extremity of the funnel a'. From e, to d, it lines the inside of the subjacent funnel a3; and from d, continues downwards to the termination of the funnel a3, on the inside of e. At e, and f; we see the upper termination of two perfect sheaths, similar to that of which a section is represented at b. c. d. This sheath, from its insertion between the point of the upper siphon and mouth of the lower one, (Fig. 1, c.,) must have acted as a collar, intercepting all communication between the interior of the shelly siphuncular tube and their chambers. The area of this shelly tube is sufficient, not only to have contained the distended siphuncle, but also to allow it tube surrounded with a volume of air, the elasticity of which would act in forcing back the pericardia fluid from the siphuncle, in the same manner as we have supposed the air to act within the chambers of the N. Pompilius.
- ↑ On each side of the transverse plate in both these species these is an undulation, or sinus, producing lobes (Pl. 43, Fig. 2. a1, a2, a3, Fig. 3. a. and Fig. 4. a. b.) There is also a deep backward curvature of the two ventral lobes, Fig. 4. c. c. All these lobes may have acted can jointly with the siphuncle, to give firm attachment to the mantle of the animal at the bottom of the outer chamber. The shell Fig. 1. is, broken in such a manner, that no portion of any lateral lobe is visible on the side here represented. At Fig. 2. a1, we see the projection of the lateral lobes, on each side of the convex internal surface of a transverse plate; at a2 we see the interior of the same lobes, on the concave side of another transverse plate; and at a3 the points of a third pair of lobes attached to the sides of the largest air-chamber that remains in this fragment.
- ↑ In some of the most early forms of Ammonites which we find in the Transition strata, e. g. A. Henslowi, A. Striatus, and A. Sphericus, (Pl. 40, Figs. 1, 2, and 3,) the lobes were few, and nearly of the same form as the single lobe of the Nautilus Sypho, and of N. Zic zac; like them also the margin was simple and destitute of fringed edges. The A. nodosus (Pl. 40, Figs. 4 and 5.,) which is peculiar to the early Secondary deposites of the Muschelkalk, others an example of an intermediate state, in which the fringed edge is partially introduced, on the descending or inward portions only, of the lobated edge of the transverse plates.
- ↑ The uncertainty which has arisen respecting the animal which constructs the Spirula, from the circumstance of the specimen discovered by Peron having been lost, is in some degree removed by Captain King's discovery of another of these shells, attached to a fragment of the mantle of an animal of unknown species resembling a Sepia, which I have seen in the possession of Mr. Owen, at the Royal College of Surgeons, London
- ↑ In the genus Lituite, Orthoceratite, and Belemnite, Pl. 44, f. 3, 4, 17, the simple curvature of the transverse plates resembles the character of the Nautilus. In the Baculite, Hamite, Scaphite, and Turrilite, Pl. 44, Fig. 5, 8, 12, 13, 14, 15, the sinuous foldings and foliated edges of the transverse plates resemble those of the Ammonites.
- ↑ See D'Orbigny's Tableau Méthodique des Céphalopodes.
There are, I believe, only two exceptions yet known to the general fact, that the genus Orthoceratite became extinct before the deposition of the Secondary strata had commenced. The most recent rocks in which they have been noticed, are a small and problematical species in the Lias at Lyme, and another species in Alpine Limestone of the Oolitc formation, at Halstadt, in the Tyrol.
- ↑ Part of the pavement in Hampton Court Palace, that of the hall of University College, Oxford, and several tombs of the kings of Poland in the cathedral at Cracow, are formed of this marble, in which many shells of Orthoceratites are discoverable. The largest known species are found in the Carboniferous limestone of Closeburn, near Edinburgh, being nearly of the size of a man's thigh. The presence of such gigantic Mollusks seems to indicate a highly exalted temperature, in the then existing climate of these northern regions of Europe. See Sowerby's Min. Con.
- ↑ The external chamber (a) is larger than the rest, and swelling; and capable of containing a considerable portion of the animal. The outer shell was thin, and strengthened, like the Ammonite, by oblique ribs. Near the posterior margin of the shell, the transverse plates are pierced by a Siphuncle (Pl. 44, 5b, c,). This position of the Siphuncle, and the sinuous form and denticulated edges of the transverse plates, are characters which the Baculite possesses in common with the Ammonite.
- ↑ Both these forms of Hamite bear the same relation to Ammonites that Lituites bear to Nautili; each being nearly such as shells of these genera would respectively present, if partially unrolled. See Phillips' Geol. Yorkshire, Pl. 1, Figs. 22, 29, 30.
Baculites and Hamites have two characters which connect them with Ammonites; first, the position of the Siphuncle, on the back, or outer margin of the shell, (Pl. 44, Figs. 5b, c. 8a, a. 10. 11, a. 12, a. 13, a.); secondly, the foliated character of the margin of the transverse plates, at the junction with the external shell. (Pl. 44, Fig. 5, 8, 12, 13.) The external shell of Hamites is also fortified by transverse folds or ribs, increasing the strength both of the outer chambers and of the air chambers, upon the same principles that we have pointed out in the case of Ammonites. (See Pl. 44, Fig. 8, 9, 11, 12, 13.)
In certain species of Hamites, as in certain Ammonites, the marginal Siphuncle has a keel-shaped pipe raised .over it. Others have a series of spines on each side of the back. (Pl. 44, Fig. 9, 10.)
- ↑ The Hamites grandis, (Sowerby, M. C. 593,) from the Greensand at Hythe, is of these large dimensions.
- ↑ The inner extremity of the Scaphite is coiled up like that of an Ammonite, (Pl. 44, Fig. 15, c. and 16) in whorls embracing one another; the last and outer chamber (a) is larger than all the rest together, and is sometimes (probably in the adult state) folded back so as to touch the spire, and thereby materially to contract the mouth, which is narrower than the last or outer chamber. (Pl. 44, Fig. 15, b.) in this character of the external chamber, the Scaphite differs from the Ammonite; in all other respects it essentially agrees with it; its transverse plates being numerous, and pierced by a marginal Siphuncle, at the back of the shell (Fig. 16, a.); and their edges being lobated, deeply cut, and foliated. (Fig. 15, c.)
- ↑ The Scaphites bifurcates occurs in the Lian of Wurtemburg, and Hamites annulatus in the Inferior oolite of France.
- ↑ The shells of the Turrilites are extremely thin, and their exterior is adorned and strengthened (like that of Ammonites,) with ribs and tubercles. In all other respects also, except the manner in which they are coiled up, they resemble Ammonites; their interior being divided into numerous chambers by transverse plates, which are foliated at their edges, and pierced by a siphuncle, near the dorsal margin. (Pl. 44, Fig. 14, a, a.) The outer chamber is large.
- ↑ The lowest stratum in which Belemnites are said to have been found is the Muschelkalk, and the highest the upper Chalk of Maestricht.
- ↑ This part of the Belemnite is usually called the sheath, or guard: it is made up of a pile of cones, placed one within another, having a common axis, and the largest enclosing all the rest. (See Pl. 4-4, Fig. 17.) These cones are composed of crystalline carbonate of lime, disposed in fibres that radiate from an eccentric axis to the circumference of the Belemnite. The crystalline condition of this shell seems to result from calcareous infiltrations (subsequent to interment,) into the intervals between the radiating calcareous fibres of which it was originally composed. The idea that the Belemnite was a heavy solid stony body, whilst it formed part of a living and Hosting sepia, would be contrary to all analogies afforded by the internal organs of living Cephalopods. The odour, resembling burnt horn, produced on burning this part of a Belemnite, arises from the remains of horny membranes interposed between each successive fibro-calcareous cone.
An argument in favour of the opinion that Belemnites were internal organs, arises from the fact of their surface being often covered with vascular impressions, derived from the mantle in which it was inclosed. In some species of Belemnites the back is granulated, like the back of the internal shell of Sepia officinalis.
- ↑ This laminated horny sheath is rarely preserved in connexion with the fibro-calcareous shelly sheath; but in the Lias at Lyme Regis it is frequently found without the shell. Certain portions of it are often highly nacreous, whilst other parts of the same sheath retain their horny condition.
- ↑ In 1829, I communicated to the Geological Society of London a notice respecting the probable connexion of Belemnites with certain fossil ink-bags, surrounded by brilliant nacre, found in the Lias at Lyme Regis. (See Phil. Mag. N. S. 1829, p. 388.) At the same time I caused to be prepared the drawings of fossils, engraved in Pl. 44″, which induced me to consider these ink-bags as derived from Cephalopods connected with Belemnites. I then withheld their publication, in the hope of discovering certain demonstration, in some specimen that should present these ink-bags in connexion with the sheath or body of a Belemnite, and this demonstration has at length been furnished by a discovery made by Professor Agassiz (October, 1834,) in the cabinet of Miss Philpotts, at Lyme Regis, of two important specimens which appear to be decisive of the question. (See Pl. 44', Figs. 7, 9.)
Each of these specimens contains an ink-bag within the anterior portion of the sheath of a perfect Belemnite; and we are henceforth enabled with certainty to refer all species of Belemnites to a family in the class of Cephalopods, for which I would, in concurrence with M. Agassiz propose the name of Belenmo-sepia. Such ink-bags are occasionally found in contact with traces of isolated alveoli of Belemnites: they are more frequently surrounded only by a thin plate of brilliant nacre.
The specimen (Pl. 44″, Fig. 1,) was procured by me from Miss Mary Anning in 1829, who considered it as appertaining to a Belemnite. Near its lower end we see the lines of growth of the horny anterior sheath, but no traces of the posterior calcareous sheath; within this horny sheath is placed the ink-bag. The conical form of this anterior chamber seems to have been altered by pressure. It is composed of a thin laminated substance (see Pl. 44″, Fig. 1, d.,) which in some parts is brilliantly nacreous, whilst in other parts it presents simply the appearance of horn. The outer surface of this cup is marked transversely with gentle undulations, which probably indicate stages of growth. Miss Baker has a Belemnite from the inferior Oolite near Northampton, in which one half of the fibrous cup being removed, the structure of the conical shell of the alveolus is seen impressed on a cast of iron-stone, and exhibits undulating lines of growth, like those on the exterior of the shell of N. Pompilius.
M. Blainville, although he had not seen a specimen of Belemnite in which the anterior horny conical chamber is preserved, has argued from the analogy of other cognate chambered shells that such an appendage was appertinent to this shell. The soundness of his reasoning is confirmed by the discovery of the specimen before us, containing this part in the form and place which he had predicted. 'Par analogie elle était donc évidemment dorsale et terminale, et lorsqu'elle était complèt c'est-à-dire pourvue d'une cavité, l'extremite postérieure dee viscères de l'animal (très-probablement l'organe sécréteur de la generation et partie du foie) y était renfermée."—Blainville Mem. sur les Bèlemnites. 1827. Page 28.
Count Munster (Mem. Geol. par A. Boue, 1832, V, 1, Pl. 4, Figs. 1, 8, 3, 15) has published figures of very perfect Belemnites from Solenhofen, in some of which the interior horny sheath is preserved, to a distance equal to the length of the solid calcareous portion of the Belenmite (Pl. 44', Figs. 10, 11, 12, 13,) but in neither of these are there any traces of an ink-bag.
- ↑ I would here add a few words in explanation of the curious fact, that among the innumerable specimens of Belemnites which have so long attracted the attention of naturalists, not one has till now been found entire in all its parts, having the ink within its external chamber; either the fibro-calcareous sheath is found detached from the horny sheath and ink-bag, or the ink-bag is found apart from the Belemnite, and surrounded only by the nacreous horny membrane of its anterior chamber. We know from the condition of the compressed nacreous Ammonites in the Lias-shale at Watchet, that the nacreous lining only of these shells is here preserved, whilst the shell itself has perished. This fact seems to explain the absence of the calcareous sheath and shell in almost every specimen of ink-bags at Lyme Regis, which is surrounded with iridescent nacre, like that of the Ammonites of Watchet. The matrix in these cases may have had a capacity for preserving nacreous or horny substances, whilst it allowed the more soluble calcareous matter of shells to be removed, probably dissolved in some acid.
The greater difficulty is to explain the reason, why amidst the millions of Belemnites that are dispersed indiscriminately through almost all strata of the Secondary series, and sometimes form entire pavements in beds of shale connected with the Lias and Inferior oolite, it so rarely happens that either the horny sheath, or the ink-bag, have been preserved. We may, I think, explain the absence of the nacreous horny sheath, by supposing that a condition of the matrix favourable to the preservation of the calcareous sheath was unfavourable to the preservation of horny membrane; and we may also explain the absence of ink-bags, by supposing that the decomposition of the soft parts of the animal usually caused the ink to be dispersed, before the body was buried in the earthy sediment then going on.
At the base of Golden Cap hill, near Charmouth, the shore presents two strata of marl almost paved with Belemnites, and separated by about three feet only of comparatively barren marl. As great numbers of these Belemnites have Serpulæ, and other extraneous shells attached to them, we learn from this circumstance that the bodies and ink-bags had decomposed, and the Belemnites lain some time uncovered at the bottom. These facts are explained by supposing that the sea near this spot was much frequented by Belemno-sepiæ during the intervals of the deposition of the Lias. Similar conclusions follow, from the state of many Belemnites in the chalk of Antrim, which had been perforated by small boring animals, whilst they lay at the bottom of the sea, and these perforations tilled with casts of chalk or flint, when the matter of the chalk strata was deposited upon them, in s soft and Buid state. (See Allan's Paper on Belemnite, Trans. Royal Soc. Edin., and Miller's Paper, Geol. Trans. Lond, 1826, p. 53.)
Thus of the millions of Belemnites which crowd the Secondary formations, only the fibro-calcareous sheath and chambered alveoli are usually preserved; whilst in certain shale beds this sheath and shell have sometimes entirely disappeared, and the horny or nacreous sheath or ink-bag alone remain. See Pl. 44″, Fig. 1, 2, 3, 4, 5, 6, 7, 8. In the rare case, Pl. 44′, Fig. 7, which has afforded the clue to this hitherto unexplained enigma, we have all the three essential parts of a Belemnite preserved in their respective places nearly entire. The ink-bag (c) is placed within the anterior horny cup (e, e', e″;) and the chambered alveolus, (b b') within the hollow cone of the posterior fibro-calcareous shell, or common Belemnite.
- ↑ The air-chambers and siphuncle are, in both these families, essentially the same.
In Belemnites, the anterior extremity of the fibro-calcareous shell, which forms a hollow straight cone, surrounding the transverse plates of the chambered alveolus, represents the hollow, coiled-up cone containing all the transverse plates, which make up the alveolus of the Nautilus.
The anterior horny cup, or outer chamber of the Belemnite, surrounding the ink bag, and other viscera, represents the large anterior shelly chamber which contains the body of the Nautilus.
The posterior portion of the Belemnite, which is elongated backwards into a fibrous pointed shaft, is a modification of the apex of the straight cone of this shell, to which there seems to be no equivalent in the apex of the coiled-up cone of Nautilus. The cause of this peculiar addition to the ordinary parts of shells, seems to rest in the peculiar uses of the shall of the belemnite, as an internal shell, acting like the internal shell of the Sepia Officinalis, to support the soft parts of the animals, within the bodies of which they were respectively enclosed. The fibrous structure of this shaft is such as is common to many shells, and is most obvious in the Pinnæ.
- ↑ Comparing the Belemnite, or internal shell of Belemno-sepia with the Sepiostaire, (Blainville,) or internal shell of the Sepia Officinalis, we have the following analogies. In the Sepiostaire, (Pl. 44', Fig. 2, a. e. and Figs. 4, 4', 5,) the small conical apex (a) represents the apex of the long calcareous posterior sheath of the Belemnite, (Fig. 7, a.,) and the calcareous plates, alternating with horny plates, which form the shield and shallow cup of the Sepiostaire, (Pl. 44', Fig. 2, e. and Fig. 5. e.,) represent the hollow fibro-calcareous cone or cup of the Belemnite, surrounding its alveolus.
The margin of the horny plates, interposed between the calcareous plates of the shield and cup of the Sepiostaire, (Pl. 44', Fig. 4, e, e', e″, e.,) represents the horny marginal cavity of the cone of the Belemnite, beyond the base of its hollow calcareous cone, (Pl. 44' Fig. 7, e. e'. e″.) This horny sheath of the Belemnite was probably formed by the prolongation of the horny laminæ which were interposed between its successive cones of fibro-calcareous matter.
The chambered alveolus of the Belemnite is represented by the congeries of thin transverse plates, (Pl. 44', Fig. 4, b.) which occupy the interior of the shallow cup of Sepiostaire, (e. e'.); these plates are composed of horny matter, penetrated with carbonate of lime.
The hollow spaces between them, (Fig. 5, b, b',) which are nearly a hundred in number in the full grown animal, act as air-chambers to make the entire shell permanently lighter than water; but there is no siphuncle to vary the specific gravity of this shell; and the thin chambers between its transverse plates are studded with an infinity of minute columnar, and sinuous partitions, planted at right angles to the plates, and giving them support. (Fig. 6', 6″, 6‴.)
The absence of a siphuncle renders the Sepiostaire an organ of more simple structure, and of lower office, than the more compound shell of Belemnite. - ↑ (See index to M. Brochant de Villiers' Translation of De la Beche's Manual of Geology.)
- ↑ M. D'Orbigny, in his classification of the shells of Cephalopodous Mollusks, has established three orders. 1. Those that have but a single chamber, like the shell of the sepia and horny pen of the Loligo. 2. Polythalamous shells, which have a siphuncle passing through all the internal chambers, and which terminate in a large external chamber, beyond the last partition, such as Nautili, Ammonites, and Belemnites. 8. Polythalamous internal shells, which have no chamber beyond their last partition.
Shells of this order have no siphuncle, but the chambers communicate with each other by means of one or many small foramina. On this distinction he has founded his Order Foraminiferes, containing five families and fifty-two genera.
It maybe necessary to apprise the reader that doubts have been entertained as to the cephalopodous structure of some of these minute multilocular shells; and that there are not wanting those who attribute to them a different organization.
- ↑ We have an analogy to this supposed state of crowded population of Nummulites in the ancient sea, in the marvellous fecundity of the northern ocean at the present time. It is stated by Cuvier, in his memoir the Clio Borealis, that in calm weather, the surface of the water in these seas swarms with such millions of these mollusks (rising for a moment to the air at the surface, and again instantly sinking towards the bottom,) that the whales can scarce open their enormous mouths without gulping in thousands of these little gelatinous creatures, an inch long, which, together with Medusæ, and some smaller animals, constitute the chief articles of their food; and we have a farther analogy in the fact mentioned in Jameson's Journal, vol. ii. p. 12. "That the number of small Medusæ in some parts of the Greenland seas is so great, that in a cubic inch, taken up at random, there are no less than 64. In a cubic foot this will amount to 110,592; and in a cubic mile (and there can be no doubt of the water being charged with them to that extent,) the number is such, that allowing one person to count a million in a week, it would have required 80,000 persons, from the creation of the world, to complete the enumeration."—See Dr. Kidd's admirable Introductory Lecture to a course of Comparative Anatomy, Oxford, 1824, p. 35.
- ↑ In Pl. 44, Figs. 6, 7. sections of two species of Nummulite are copied from Parkinson. These show the manner in which the whorls are coiled up round each other, and divided by oblique septa.
- ↑ The strata here termed primary are those which, in the Section, (Pl. 1,) I have included in the lower region of the transition series.