Geology and Mineralogy considered with reference to Natural Theology/Chapter 16
|←Chapter 15|| Geology and Mineralogy considered with reference to Natural Theology by
Proofs of design in the Structure of Fossil Articulated Animals.
The third grand division in Cuvier's arrangement of the animal kingdom, viz. the articulated animals, comprehends four classes.
- The Annelidans, or worms with red blood.
- Crustaceans, most familiar to us under the form of Crabs and Lobsters.
- Arachnidans, or Spiders.
First Class of Articulated Animals.
However numerous may have been the ancient species of Annelidans without a shelly covering, naked worms of this class can have left but slight traces of their existence, except the holes they perforated, and the little accumulations of sand or mud cast up at the orifice of these perforations; in a preceding chapter we have noticed examples of this kind. We have also abundant evidence of the early and continued prevalence of that order of Annelidans, which formed shelly calcareous tubes, in the occurrence of fossil Serpulæ in nearly all formations, from the Transition periods to the present time.
Second Class of Articulated Animals.
The history of fossil Crustaceans has been hitherto almost
untouched by Palaeontologists, and their relations to the existing
Genera of this great Class of the Animal Kingdom
are too little known to admit of discussion in this place.
We may judge of their extent in certain Formations, from the fact, that in the cabinet of Count Munster, there are nearly sixty species collected from a single stratum of the Jurassic Limestone of Solenhofen. A rich harvest, therefore, remains in store for the Naturalist who will trace this interesting subject through the entire series of Geological formations.
The analogies between existing species, and certain fossil
remains of Crustaceans have been beautifully illustrated by
the investigations of M. Desmarest. From him we learn,
that all the inequalities of the external shell in the living
specie shave constant relation to distinct compartments in
their internal organization. By the application of these distinctions
to fossil species, he has pointed out a method of
comparing them with living Crustaceans in a new and unexpected
manner, and has established satisfactory analogies
between the extinct and existing members of this very numerous
Class, in cases where the legs and other parts on
which generic distribution shave been founded, were entirely
Referring my readers to these valuable commencements of the history of fossil Crustaceans, I proceed to select one very remarkable family, the Trilobites, and to devote to them that detailed consideration, to which they seem peculiarly entitled, from their apparently anomalous structure, and from the obscurity in which their history has been involved.
The great extent to which Trilobites are distributed over the surface of the globe, and their numerical abundance in the places where they have been discovered, are remarkable features in their history; they occur at most distant points, both of the Northern and Southern Hemisphere. They have been found all over Northern Europe, and in numerous local ties in North America; and in the Southern Hemisphere they occur in the Andes, and at the Cape of Good Hope.
No Trilobites have yet been found in any strata more recent than the Carboniferous series; and no other Crustaceans, except three forms which are also Entomostracous, have been noticed in strata coeval with any of those that contain the remains of Trilobites; so that, during the long periods that intervened between the deposition of the earliest fossiliferous strata and the termination of the Coal formation, the Trilobites appear to have been the chief representatives of a class which was largely multiplied into other orders and families, after these earliest forms of marine Crustaceans became extinct.
The fossil remains of this family have long attracted attention, from their strange peculiarities of configuration. M. Brongniart, in his valuable History of Trilobites, 1822, enumerated five genera, and seventeen species; other writers (Dalman, Wahlenberg, Dekay, and Green,) have added five more genera, and extended the number of species to fifty-two; examples of four of these genera are given in Plate 46. Fossils of this family were long confounded with Insects, under the name of Entomolithus paradoxus; after many disputes respecting their true nature, their place has now been fixed in a separate section of the class Crustaceans, and although the entire family appears to have been annihilated at so early a period as the termination of the Carboniferous strata, they nevertheless present analogies of structure, which place them in near approximation to the inhabitants of the existing seas.
The anterior segment of the Trilobites (Pl. 46, a, passim,) is composed of a large semi-circular, or crescent-shaped shield, succeeded by an abdomen, or body (c,) composed of numerous segments folding over each other, like those in a Lobster's tail, and generally divided by two longitudinal furrows into three ranges of lobes, from which they have derived the name of Trilobites. Behind this body, in many species, is placed a triangular or semi-lunar tail or post-abdomen (d,) less distinctly lobated than the body. One of these Genera, the Calymene, has the property of rolling itself up into a ball like a common Wood-Louse. (See Pl. 46, Figs. 1, 3, 4, 5.)
The nearest approach among living animals to the external
form of Trilobites is that afforded by the genus
Serolis in the class Crustacea. (See Pl. 45, Figs. 6, 7.)
The most striking difference between this animal, and the
Trilobites, consists in there being a fully developed series of crustaceous legs and antennae in the Serolis (Pl. 45, Fig. 7.,) whilst no traces of either of these organs have yet been discovered in connexion with any Trilobite. M. Brongniart explains the absence of these organs, by conceiving that the Trilobites hold precisely that place in the class Crustaceans (Gymnobranchia,) in which the antennæ become very small, or altogether fail; and that the legs being transformed to soft and perishable paddles (pattes,) bearing branchiæ, (or filamentous organs for breathing in water,) were incapable of preservation.
A second approximation to the character of Trilobites
occurs in the Limulus, or King crab (Lamarck, T. 5, p.
145,) a genus now most abundant in the seas of warm
climates, chiefly in those of India, and the coasts of America
(see Pl. 45, Figs. 1. 2.) The history of this genus is important,
on account of its relations, both to the existing and
extinct forms of Crustaceans; it has been found fossil in
the Coal formation of Staffordshire and Derbyshire; and
in the Jurassic limestone of Aichstadt, near Pappenheim,
together with many other marine Crustaceans of a higher
A third example of this disposition, in an animal belonging to the same class of Crustaceans, whereby the legs are reduced to soft paddles, and combine the functions of respiration with those of locomotion, is afforded by the Branchipus stagnalis, (Cancer stagnalis, Lin.,) of our English ponds, (see Pl. 45, Figs. 3, e. 4, e. 5, e.)
In the comparison here made between four different families of Crustaceans, for the purpose of illustrating the history of the long extinct Trilobites, by the analogies we find in the Serolis, Limulus, and Branchipus; we have a beautiful example, taken from the extreme points of time of which Geology takes cognisance, of that systematic and uniform arrangement of the Animal Kingdom, under which every family is nearly connected with adjacent and cognate families. Three of the families under consideration are among the present inhabitants of the water, while the fourth has been long extinct, and occurs only in a fossil state. When we see the most ancient Trilobites thus placed in immediate contact with our living Crustaceans, we cannot but recognise them as forming part and parcel of one great system of Creation, connected through its whole extent by perfect unity of design, and sustained in its minutest by uninterrupted harmonies of organization.
We have in the Trilobites an example of that peculiar, and, as it is sometimes called, rudimentary development of the organs of locomotion in the Class Crustaceans, whereby the legs are made subservient to the double functions of paddles and lungs, The advocate for the theory of the derivation of existing more perfect species, by successive changes from more simple ancient forms, might imagine that he sees in the Trilobite the extinct parent stock from which, by a series of developments, consecutive forms of more perfect Crustaceans may, during the lapse of ages, have been derived; but according to this hypothesis, we ought no longer to find the same simple condition as that of the Tribolite still retained in the living Branchipus, nor should the primeval form of Limulus have possessed such an intermediate character, or have remained unadvanced in the scale of organization, from its first appearance in the Carboniferous Series, through the midway periods of the secondary formations, unto the present hour.
Eyes of Trilobites.
Besides the above analogies between the. Trilobites and certain forms of living Crustaceans, there remains a still more important point of resemblance in the structure of their eyes. This point deserves peculiar consideration, as it affords the most ancient, and almost the only example yet found in the fossil world, of the preservation of parts so delicate as the visual organs of animals that ceased to live many thousands, and perhaps millions of years ago. We must regard these organs with feelings of no ordinary kind, when we recollect that we have before us the identical instruments of vision, through which the light of heaven was admitted to the sensorium of some of the first created inhabitants of our planet.
The discovery of such instruments in so perfect a state of preservation, after having been buried for incalculable ages in the early strata of the Transition formation, is one of the most marvellous facts yet disclosed by geological researches; and the structure of these eyes supplies an argument, of high importance in connecting together the extreme points of the animal creation. An identity of mechanical arrangements, adapted to the construction of an optical instrument, precisely similar to that which forms the eyes of existing insects and Crustaceans, affords an example of agreement that seems utterly inexplicable without reference to the exercise of one and the same Intelligent Creative power.
Professor Müller and Mr. Straus have ably and amply illustrated the arrangements, by which the eyes of Insects and Crustaceans are adapted to produce distinct vision, through the medium of a number of minute facets, or lenses, placed at the extremity of an equal number of conical tubes, or microscopes; these amount sometimes, as in the Butter-fly, to the number of 35,000 facets in the two eyes, and in the Dragon-fly to 14,000.
It appears that in eyes constructed on this principle, the image will be more distinct in proportion as the cones in a given portion of the eye are more numerous and long; that, as compound eyes see only those objects which present themselves in the axes of the individual cones, the limit of their field of vision is greater or smaller as the exterior of the eye is more or less hemispherical.
If we examine the eyes of Trilobites with a view to their principles of construction, we find both in their form, and in the disposition of the facets, obvious examples of optical adaptation.
In the Asaphus caudatus (see Pl. 45, Figs. 9 and 10.,) each eye contains at least 400 nearly spherical lenses fixed in separate compartments on the surface of the cornea. The form of the general cornea is peculiarly adapted to the uses of an animal destined to live at the bottom of the water: to look downwards was as much impossible as it was unnecessary to a creature living at the bottom; but for horizontal vision, in every direction the contrivance is complete. The form of each eye is nearly that of the frustum of a cone (see Pl. 45, Figs. 9 and l0.,) incomplete on that side only which is directly opposite to the corresponding side of the other eye, and in which if facets were present, their chief range would be towards each other across the head, where no vision was required. The exterior of each eye, like a circular bastion, ranges nearly round three-fourths of a circle, each commanding so much of the horizon, that where the distinct vision of one eye ceases, that of the other eye begins, so that in the horizontal direction the combined range of both eyes was panoramic.
If we compare this disposition of the eyes with that in the three cognate Crustaceans, by which we have been illustrating the general structure of the Trilobites, we shall find the same mechanism pervading them all, modified by peculiar adaptations to the state and habits of each; thus in the Branchipus (Pl. 45, Fig. 3, b, b',) which moves with rapidity in all directions through the water, and requires universal vision, each eye is nearly hemispherical, and placed on a peduncle, by which it is projected to the distance requisite to effect this purpose. (See Pl. 45, Fig. 3, b, and b'.)
In the Serolis (Pl. 45, Fig. 6. b'.), the disposition of the eye, and its range of vision, are similar to those in the Trilobite; but the summit of the eye is less elevated; as the flat back of this animal presents little obstruction to the rays of light from surrounding objects.
In the Limulus (PL 45, Fig. 1.), where the side eyes (b, b') are sessile, and do not command the space immediately before the head, two other simple eyes (b″) are fixed in front, compensating for the want of range in the compound eyes over objects in that directions.
In the above comparison of the eyes of Trilobites, with
those of the Limulus, Serolis, and Branchipus, we have
placed side by side, examples of the construction of that
most delicate and complex organ the eye, selected from
each extreme, and from a midway place in the progressive
series of animal creations. We find in Trilobites of the
Transition rocks, which were among the most ancient forms
of animal life, the same modifications of this organ which
are at the present time adapted to similar functions in the
living Serolis. The same kind of instrument was also employed
in those middle periods of geological chronology
when the Secondary strata were deposited at the bottom of
a warm sea, inhabited by Limuli, in the regions of Europe
which now form the elevated plains of central Germany.
The results arising from these facts are not confined to animal Physiology; they give information also regarding the condition of the ancient Sea and ancient Atmosphere. and the relations of both these media to Light, at that remote period when the earliest marine animals were furnished with instruments of vision, in which the minute optical adaptations were the same that impart the perception of light to Crustaceans now living at the bottom of the sea.
With respect to the waters wherein the Trilobites maintained their existence throughout the entire period of the Transition formation, we conclude that they could not have been that imaginary turbid and compound Chaotic fluid, from the precipitates of which some Geologists have supposed the materials of the surface of the earth to be derived; because the structure of the eyes of these animals is such, that any kind of fluid in which they could have been efficient at the bottom, must have been pure and transparent enough to allow the passage of light to organs of vision, the nature of which is so fully disclosed by the state of perfection in which they are preserved.
With regard to the Atmosphere also we infer, that had it differed materially from its actual condition, it might have so far affected the rays of Light, that a corresponding difference from the eyes of existing Crustaceans would have been found in the organs on which the impressions of such rays were then received.
Regarding Light itself also, we learn from the resemblance of these most ancient organizations to existing eyes, that the mutual relations of Light to the Eye, and of the Eye to Light, were the same at the time when Crustaceans endowed with the faculty of vision were first placed at the bottom of the primeval seas, as at the present moment.
Thus we find among the earliest organic remains, an Optical instrument of most curious construction, adapted to produce vision of a peculiar kind, in the then existing representatives of one great Class in the Articulated division of the Animal Kingdom. We do not find this instrument passing onwards, as it were, through a series of experimental changes, from more simple into more complex forms; it was created at the very first, in the fulness of perfect adaptation to the uses and condition of the class of creatures, to which this kind of eye has ever been, and is still appropriate.
If we should discover a microscope, or telescope, in the hand of an Egyptian Mummy, or beheath the ruins of Herculaneum, it would be impossible to deny that a knowledge of the principles of Optics existed in the mind by which such an instrument had been contrived. The same inference follows, but with cumulative force, when we see nearly four hundred microscopic lenses set side by side, in the compound eye of a fossil Trilobite; and the weight of the argument is multiplied a thousand fold, when we look to the infinite variety of adaptations by which similar instruments have been modified, through endless genera and species, from the long-lost Trilobites, of the Transition strata, through the extinct Crustaceans of the Secondary and Tertiary formations, and thence onward throughout existing Crustaceans, and the countless hosts of living Insects.
It appears impossible to resist the conclusions as to Unity
of Design in a common Author, which are thus attested by
such cumulative evidences of Creative Intelligence and
Power; both, as infinitely surpassing the most exalted
faculties of the human mind, as the mechanisms of the natural
world, when magnified by the highest microscopes, are
found to transcend the most perfect productions of human art.
Third Class of Articulated Animals.
Under the relations that now subsist between the animal and vegetable kingdoms, the connexion of terrestrial Plants with Insects is so direct and universal, that each species of plant is considered to afford nutriment to three or four species of insects. The general principle which we have traced throughout the Secondary and Tertiary formations, ever operating to maintain on the surface of the earth the greatest possible amount of life, affords a strong antecedent probability that so large a mass of terrestrial vegetables as that which is preserved in the Carboniferous strata of the Transition series, held the same relation, as the basis of nutriment to Insect families of this early date, that modem vegetables do to this most numerous class of existing terrestrial animals.
Still further, the actual provisions for restraining this Insect class within due bounds, by the controlling agency of the carnivorous Arachnidans would lead us to expect that Spiders and Scorpions were employed in similar service during the successive geological epochs, in which we have evidence of the abundant growth of terrestrial vegetables.
Some recent discoveries confirm the argument from these
analogies, by the test of actual observation. The two great
families in the higher order of living Arachnidans (Pulmonariæ)
are Spiders and Scorpions; and we have evidence
to show that fossil remains of both these families exist in
strata of very high antiquity.
Although no Spiders have been yet discovered in any rocks so ancient as the Carboniferous series, the presence of Insects in this series, and also of Scorpions, renders it highly probable that the cognate family of Spiders was coordinate with Scorpions, in restraining the Insect tribes of this early epoch, and that it will ere long be recognised among its fossil remains.
The existence of Spiders in the Jurassic portion of the
Secondary formations has been established, by Count Munster's
discovery of two species in the lithographic limestone
of Solenhofen. M. Marcel de Serres and Mr. Murchison
have discovered fossil Spiders in Freshwater Tertiary strata
near Aix in Provence. (See Pl. 46″, Fig. 12.)
The address of my friend Count Sternberg to the members of the National Museum of Bohemia (Prague, 1835,) contains an account of his discovery of a fossil Scorpion in the ancient Coal formation at the village of Chomle, near Radnitz, on the S. W. of Prague. This most instructive fossil (the first of its kind yet noticed) was found in July, 1834, in a stone-quarry, on the outcrop of the Coal measures, near a spot where coal has been wrought since the sixteenth century. In the same quarry were found four erect trunks of trees, and numerous vegetable remains, of the same species that occur in the great Coal formation of England.
A series of drawings of this Scorpion was submitted to a
select committee at the meeting of Naturalists and Physicians
of Germany, in Stutgard, 1834; and from their report
the subjoined particulars are taken. All our Figures,
(Pl. 45'.) are copied from those attached to this Report, in
the Transactions of the Museum of Bohemia, April, 1835.
As far as we can argue from the analogy of living species, the presence of large Scorpions is a certain index of the warmth of the climate in which they lived; and this indication is in perfect harmony with those afforded by the tropical aspect of the vegetables with which the Scorpion, found in the Bohemian coal-field, is associated.
Fourth Class of Articulated Animals.
Altough the numerical amount of living Insects forms so vast a majority of the inhabitants of the present land, few traces of this large class of Articulated animals have yet been discovered in a fossil state. This may probably result from the circumstance, that the greatest portion of fossil animal remains are derived from the inhabitants of salt water, a medium in which only one or two species of Insects are now supposed to live.
Had no indications of Insects been discovered in a fossil state, the presence in any strata, of Scorpions or Spiders, both belonging to families constructed to feed on Insects, would have afforded a strong a priori argument, in favour of the probability, of the contemporaneous existence of that very numerous class of animals, which now forms the prey of the Arachnidans. This probability has been recently confirmed by the discovery of two Coleoptera of the family Curculionidæ in the Iron-stone of Coalbrook Dale, and also of the wing of a Corydalis, which will be noticed in our description of Pl. 46″.
It is very interesting and (important, to have discovered in the Coal formation fossil remains, which establish the existence of the great Insectivorous Class Arachnidans, at this early period. It is no less important to have found also in the same formation the remains of Insects, which may have formed their prey. Had neither of these discoveries been made, the abundance of Land plants would have implied the probable abundance of Insects, and this probability would have involved also that of the contemporaneous existence of Arachnidans, to control their undue increase. All these probabilities are now reduced to certainty, and we are thus enabled to fill up what has hitherto appeared a blank in the history of animal life, from those very distant times when the Carboniferous strata were deposited.
The Estuary, or Freshwater formation of those strata of the Corboniferous series which contain shells of Unio, in Coalbrook Dale, and in other Coal basins, renders the presence of Insects and Arachnidans in such strata, easy of explanation; they may have been drifted from adjacent lands, by the same torrents that transported the terrestrial vegetables which have produced the beds of Coal.
The existence of the wing-covers of insects in the Secondary Series, in the Oolitic slate of Stonesfield, has been long known; these are all Coleopterous, and in the opinion of Mr. Curtis many of them approach most nearly to the Buprestis, a genus now most abundant in warm latitudes. (See Pl. 46″. Figs. 4. 5. 6. 7. s. 9. 10.)
Count Munster has in his collection twenty-five species of fossil insects, found in the Jurassic Limestone of Solenhofen; among these are five species of the existing Family of Libellula, (See Pl. 1, Fig. 49,) a large Ranatra, and several Coleoptera.
Numerous fossil Insects have recently been discovered in
the Tertiary Gypsum of Freshwater formation at Aix, in
Provence. M. Marcel de Serres speaks of sixty-two
Genera, chiefly of the Orders Diptera; Hemiptera, and
Coleoptera; and Mr. Curtis refers all the specimens he has
seen from Aix to European forms, and most of them to
existing Genera. Insects occur also in the tertiary Brown
coal of Orsberg on the Rhine.
We have seen from the examples cited in the last four sections, that all of the four existing great Classes of the grand Division of Articulated animals, viz. Annelidans, Crustaceans, Arachnidans, and Insects, and many of their Orders, had entered on their respective functions in the natural world, at the early Epoch of the Transition Formations. We find evidences of change in the Families of these Orders, at several periods of the Secondary and Tertiary series, very distant from one another; and we further find each Family variously represented during different intervals by Genera, some of which are known only in a fossil state, whilst others (and these chiefly in the lower Classes,) have extended through all geological Eras unto the present time.
On these facts we may found conclusions which are of great importance in the investigation of the physical history of the Earth. If the existing Classes, Orders, and Families of Marine and terrestrial Articulated animals have thus pervaded various geological epochs, since life began upon our planet, we may infer that the state of the Land and Waters, and also of the Atmosphere, during all these Epochs, was not so widely different from their actual condition as many geologists have supposed. We also learn that throughout all these epochs and stages of change, the correlative Functions of the successive Representatives of the animal and vegetable kingdoms have ever been the same as at the present moment; and thus we connect the entire series of past and present forms oft organized beings, as parts of one stupendously grand, and consistent, and harmonious Whole.
- See note at pages 198—199.
- H. Von Meyer has recently noticed five or six extinct genera of Macrourous Decapods in the Muschelkalk of Germany. (Leonhardt and Bronn Jahrbuch, 1835.)
The subject of English fossil Astacids (Crawfishes) is at this time receiving important illustration in the able hands of Pro£ Phillips.
In a recent communication to the Geological Society (June 10, 1835,) Mr. Broderip describes some very interesting remains of Crustaceans from the Lias at Lyme Regis, in the collection of Viscount Cole. In one of these, the Lamellæ of the external Antennae, the form and situation of the eyes, and other characters, show that it was a macrorous-decapod intermediate between Palinurus and the Shrimps.
A fragment of another macrourous decapod proves the existence at this early period of a crustacean approaching to Palinurus, and as large as our common Sea Crawfish.
Two other specimens exhibit the breathing organs of another delicate Crustacean, with the tips of the four larger and four smaller branchiæ preserved, and pointing towards the region of the heart, showing that these fossil Crustaceans belonged to the highest division of the Macroura. They reminded Mr. Broderip of the living Arctic forms of the macrourous decapods.
- I learn from Mr. Pentland that M. D'Orbigny has lately found Trilobites, accompanied by Strophomena and Producta in the Greywacke slate formation of the Eastern Cordillera of the Andes of Bolivia. Freshwater shells, Melania, Melanopsis, and probably Anodon, occur also in the same rock; a fact which seems analogous to the recent discovery of similar fossils in the Transition rocks of Ireland, Germany, and the United States. The Freshwater fossils occurred near Potosi, at an elevation of 13,200 feet.
M. D'Orbigny's specimens also confirm Mr. Pentland's view, as to the analogies between the great Limestone formation of this district, and the Carboniferous limestones of England; and as to the great extent also of the Red Marl, and New red sandstone formations on the Continent of South America.
- In Scotland two genera of Entomostracous Crustaceans, the Eurypterus, and Cypris, occur in the Freshwater limestone beneath the Mid Lothian Coal Field; the Eurypterus at Kirkton, near Bathgate, and the Cypris at Burdiehouse, near Edinburgh. (Trans. Royal Soc. Edin. vol. xiii.) The third Genus, Limulus, has but recently been recognised in the Coal Formation, and will be described presently. The Entomostracans appear to have been the only representatives of the Class Crustaceans until after the deposition of the Carboniferous strata.
- Trilobites of a new species have lately been found in Ironstone from the centre of the coal measures in Coalbrook-dale. Lond. and Edin. Phil. Mag. vol. 4. 1834, p. 376.
- The names of these Genera are Calymene, Asaphus, Ogyges, Paradoxus, and Agnostus. Some of these terms are devised expressly to denote the obscure nature of the bodies to which they are attached; e.g. Asaphus, from ἀσαφης, obscure; Calymene, from κακαλυμμένη, concealed; παράδοξος, wonderful; ἀγνωστος, unknown.
- See M. Audouin's Recherches sur les Rapports naturels qui existent entre les Trilobites et les Animaux articulés.
- The Genus Serolis was first established by Dr. Leach, on the authority of specimens collected by Sir Joseph Banks, in the Straits of Magellan (or rather of Magalhaens, the proper name of the navigator, according to Captain King) during Sir Joseph's voyage with Captain Cook, and given by Sir Joseph to the Linnaean Society; and of another specimen of the same Genus from Senegal given by Mr. Dufresne to Dr. Leach. From these Dr. Leach described and named the species represented in our plate; his description of this Genus is published in the Dictionnaire des Sciences Naturelles, v. 12, p. 340. Captain King has lately collected many specimens of Serolis on the east coast of Patagonia, lat. 45. S. 80 miles from the shore, and brought up by dredging in 40 fathoms water; and also at Port Famine, in the Straits of Magalhaens, where it was thrown upon the beach by the tide; here Captain King saw the beach literally covered with them dead; he has observed them alive swimming close to the bottom among the sea-weed; their motions were slow and gradual, and not like those of a shrimp; he never saw them swimming near the surface; their legs seemed shaped for swimming and crawling on the bottom.
- In the genus Limilus (see Pl. 45, Figs. 1. 2.) there are but faint traces of antennæ, and the shield (a.,) which covers the anterior portion of the body, is expanded entirely over a series of all crustaceous legs (Fig. 2. a.) Beneath the second, or abdominal portion of the shell (c.,) is placed a series of thin horny transverse plates (Fig. 2, e. 2, e'. and 2, e″.) supporting the fibres of the branchiæ, and at the same time acting as paddles for swimming. The same disposition, of laminated branchiæ is found also in the Serolis, Fig. 7. e. Fig. 8, is a magnified representation of these laminated branchiæ, very similar to those at Figs. 3, e. and 5. e.
Thus while the Serolis (Fig. 7) presents a. union of antennas and crustaceous legs with soft paddles bearing the Branchiæ, we have in the Limulus (Fig, 2,) a similar disposition of legs and paddles, and only slight traces of antenna; in the Branchipus, (Figs. 3 and 5,) we find antennæ, but no crustaceous legs; while the Trilobite, being without antennæ, and having all its legs represented by soft paddles, as in Branchipus, is by the latter condition placed near Branchipus among the Entomostracous Crustaceans, in the order of Branchiopods, whose feet are represented by ciliated paddles, combining the functions of respiration and natation. At Pl. 45. Fig. 3. e, Fig. 4. e, Fig. 5. e, represent the soft branehia: of Branehipus, performing the double office of feet and lungs.
- The very rare fossil engraved in Martin's Petrifacata Derbiensia (Tab. 45. Fig. 4,) by the name of Entomolithus Monoculites (Lunatus) appears to be a Limulus. It was found in Iron Stone of the Coal formation on the borders of Derbyshire. A similar fossil in the collection of Mr. Anstice, of Madely, is engraved in our Plate 46″, Fig. 3. In the Secondary period, during the deposition of the Jurassic limestone, the Limulus abounded in the seas which then covered central Germany; and it still maintains its primeval intermediate form in the King Crab of the present ocean. My friend Mr. Stokes has discovered, on the under side of a fossil Trilobite from Lake Huron (Pl. 45, Fig. 12.,) a crustaceous plate (f) forming the entrance into the stomach, the shape and structure of which resemble those of the analogous parts in some recent Crabs. This organ forms another link of connexion between the Trilobite and living Crustaceans.—Geol. Trans. N. S. vol. i. p. 208, Pl. 27.
- See Lib. Ent. Knowledge, v. 12.; and Dr. Roget's Bridgewater Treatise, vol. ii. p. 486 et seq. and Fig. 422—428.
- As the Crystalline lens in the eyes of Fishes is spherical, and those in the Eye of Trilobites are nearly so, there seems to be in this form an adaptation to the medium of Water, which would lead us to expect to find a similar form of lens in the compound Eyes of all marine Crustacea, and probably a different form in the compound Eyes of Insects that live in Air.
- The facetted eyes of Bees are disposed most favourably for horizontal vision, and for looking downwards.-Lib. Ent. Knowl. v. xii. p. 130.
- Fig. 1. b'. Fig. 3. b'. and Fig. 6. b'. are magnified representations of the eyes to which these figures are respectively adjacent. Figs. 10. and 11. are differently magnified forms of the eye of Assphus caudatus, which in Fig. 9. is represented of its natural size. A few of these lenses are semi-transparent; they are still set in their original rims, or frame-work of the cornea, the whole being converted into calcareous spar.
- These eyes are placed so close together, that, having been mistaken for a single eye, they caused the name of Monoculus Polyphernus to be applied to this animal by Linnaeus.
- The animal found by Mr. W. Anstice in the Ironstone of Coalbrook Dale, and noticed by Mr. Prestwich as "apparently a Spider" (Phil. Mag. May, 1834, v. iv. p. 376,) has been subsequently laid open by me, and shown to be an Insect, belonging to the family of Curculionidæ. (Pl. 46″, Fig. 1.) At the time when it was figured, and supposed to be a Spider, its head and tail were covered by iron stone, and its appearance much resembled an animal of this kind. Mr. Prestwich announces also the discovery, in the same formation, of a Coleopterous Insect, which will be further described in our next section, as referable also to the Curculionidæ.
It is scarcely possible to ascertain the precise nature of the animals, rudely figured as Spiders and Insects on Coal slate by Lhwyd, (Ichnograph. Tab. 4,) and copied by Parkinson, (Org. Rem. V. iii. Pl. 17, Figs. 3, 4, 5, 6;) but his opinion of them is rendered highly probable by the recent discoveries in Coalbrook Dale: "Scripsi olim suspicari me Araneorum quorundam icones, unà cum Lithophytis in Schisto Carbonarià observasse: hoc jam ulteriore experientià edoctus apertè assero. Alias icones habeo, quæ ad Scarabæorum genus quàm proxime accedunt. In posterum ergo non tantam Lithophyta, sed et quædam Insecta in hoc lapide investigate conabimur." Lhwyd Epist. iii. ad fin.
- This fossil Scorpion differs from existing species, less in general structure than in the position of the eyes. In the latter respect, it approaches nearest to the genus Androctonus, which, like it, has twelve eyes, but differently disposed from those of the fossil species. From the nearly circular arrangement of these organs in the latter animal, it has been ranged under a new genus, Cyclopthalmus.
The sockets of all these twelve eyes are perfectly preserved, (Pl. 46'. fig. 3.) One of the small eyes, and the left large eye, still retain their form, with the cornea preserved in a wrinkled state, and their interior filled with earth.
The jaws also are very distinct, but in a reversed position. (Pl. 46'. fig. 2. a.) Both these jaws have three projecting teeth, and one of them (Pl. 46', Figs. 4. 5.) exhibits, when magnified, the hairs with which its horny integument was covered.The rings of the thorax, (apparently eight) and of the tail, are too much dislocated for their number to be accurately distinguished, but they differ from all known species. The view of the back (Pl. 46', Fig. 1.) has been obtained by cutting into the stone from behind.
The under surface of the animal is well exposed in fig. 2, with its characteristic pincers on the right claw. Between this claw and the tail lies a fossil carbonized Seed, of a species common in the Coal formation. The horny covering of this Scorpion is in a most extraordinary state of preservation, being neither decomposed nor carbonized. The peculiar substance (Chitinr or Elytrinr) of which, like the elytra of Beetles, it is probably composed, has resisted decomposition and mineralization. It can readily be stripped off] is elastic. translucent, and horny. It consists of two layers, both retaining their texture. The uppermost of these (Pl. 46', Pig. 6. a.) is harsh, almost opaque, of a dark-brown colour, and flexible; the under skin (Pl. 46', Fig. 6. b.) is tender, yellow, less elastic, and organized like the upper. The structure of both exhibits, under the microscope, hexagonal cells, divided by strong partitions. Both are penetrated at intervals by pores, which are still open, each having a sunk areola, with a minute opening' at its centre for the orifices of the trachea. Fig 7. represents impressions of the muscular fibres connected with the movement of the legs.
- See Pl. 46″. Figs. 1. 2. & 4.—11.
- Our figures (Pl.46″. Figs. 1. 2.) represent these fossils of their natural size. See description of this Plate for further details respecting them.
- M. Aug. Odier has ascertained, that the Elytra and other parts of the horny covering of insects, contain the peculiar substance Chitine, or Elytrine, which approaches nearly to the vegetable principle Lignine, these parts of insects bum without fusion, or swelling, like horn, and without the smell of animal matter; they also leave a Coal which retains their form.
M. Odier found that even the hairs of a Scarabæus nascicornis retained their form after burning, and therefore concludes that they are different from the hairs of vertebral animals. This circumstance explains the preservation of the hairs on the horny cover of the Bohemian Scorpion.
He ascertained also that the Sinews (Nervures) of Scarabaei, are composed of Chitine, and that the soft flexible laminæ of the shell of a crab, which remain after the separation of the Lime, also contain Chitine.
Cuvier observes, that the Integuments of Entomostracons, are rather horny than calcareous, and that in this respect they approximate to the nature of Insects and Arachnidans. See Zoological Journal. London, 1825, vol. i. p. 101.
- See Edinburgh New Phil. Journ. Oct. 1829.