Among living voracious reptiles we have examples of stomachs equally capacious; we know that whole human bodies have been found within the stomachs of large Crocodiles; we know also, from the form of their teeth, that the Ichthyosauri, like the Crocodiles, must have gorged their prey entire; and when we find, imbedded in Coprolites derived from the larger Ichthyosauri, bones of smaller Ichthyosauri, of such dimensions, (see Pl. 15, Fig. 18. And Geol. Trans. 2, S. vol. iii., Pl. 29, Figs, 2, 3, 4, 5,) that the individuals from which they were derived, must have measured several feet in length; we infer that the stomach of these animals formed a pouch, or sac, of prodigious size, extending through nearly the entire cavity of the body, and of capacity duly proportioned to the jaws and teeth with which it co-operated.

Spiral Disposition of Small Intestines.

As the more solid parts of animals alone, are usually susceptible of petrifaction, we cannot demonstrate by direct evidence the form and size of the small intestines of the Ichthyosauri, but the contents of these viscera are preserved in such perfection in a fossil state, as to afford circumstantial evidence that the bowels in which they were moulded, were formed in a manner resembling the spiral intestines of some of the swiftest and most voracious of our modern fishes.

We shall best understand the structure of these intestines by examining the corresponding organs of Sharks and Dog-fish, animals not less peculiarly rapacious among the inhabitants of our modern seas, than the Ichthyosauri were in those early periods to which our considerations are carried back. We find in the intestines of these fishes, (see Pl. 15, Figs. 1, and 2,) and also in those of Rays, an arrangement resembling that of the interior of an Archimedes screw, admirably adapted to increase the extent of internal

surface for the absorption of nutriment from the food, during its passage through a tube containing within it a continuous spiral fold, coiled in such a manner, as to afford the greatest possible extent of surface in the smallest space. A similar contrivance is shown by the Coprolites to have existed in the Ichthyosaurus. See Pl. 15, Figs. 3, 4, 6.*

Impressions of the Mucous Membrane on Coprolites.

Besides the spiral structure and consequent shortness of

* These cone-shaped bodies are made up of a flat and continuous plate of digested bone coiled round itself whilst it was yet in a plastic state. The form is nearly that which would be assumed by a piece of riband, forced continually forward into a cylindrical tube, through a long aperture in its side.. In this case, the riband moving onwards, would form a succession of involuted cones, coiling one round the other, and after a certain number of turns within the cylinder, (the apex moving continually downwards,) these cones would emerge from the end of the tube in a form resembling that of the Coprolites, Pl. 15, Figs. 3, 5, 7, 10, 11, 12, 13, 14. In the same manner, a lamina of coprolitic matter would be coiled up spirally into a series of successive cones, in the act of passing from a small spiral vessel into the adjacent large intestine. Coprolites thus formed fell into soft mud, whilst it was accumulating at the bottom of the sea, and together with this mud, (which has subsequently been indurated into shale and stone,) they have undergone so complete a process of petrifaction, that in hardness, and beauty of the polish of which they are susceptible, they rival the qualities of ornamental marble.

Fig. 6, shows a longitudinal section through the axis of a coprolite, from the inferior chalk, in which this involute conical form is well defined. Fig. 4, is the transverse section of another Coprolite from the lias, showing the manner in which the plate coils round itself, till it terminates externally in a broken edge (at b.) In all the figures the letter b, marks the transverse section of this plate, where it is broken off near the termination of its outer coil; the sections at b, show also the size and form of the flattened passage through the interior of the screw.

A lamina of tenacious plastic substance pressed continually forwards from the interior of such a screw, into the cavity of the large intestine, would coil up spirally within it, until it attained the largest size admitted by its diameter; from this coil successive portions would be broken off abruptly, (at b,) and descending into the cloaca would be thence discharged into the

sea.

the small intestine, we have additional evidence to show even the form of the minute vessels and folds of the mucous membrane, by which it was lined. This evidence consists in a series of vascular impressions and corrugations on the surface of the Coprolite, which it could only have received during its passage through the windings of this flat tube.* Specimens thus marked are engraved at Pl. 15, Figs, 3, 5, 7, 10, 12, 13, 14.

If we attempt to discover a final cause for these curious provisions in the bowels of the extinct reptile inhabitants of the seas of a former world, we shall find it to be the same that explains the existence of a similar structure in the modern voracious tribes of Sharks and Dog-fish.t

As the peculiar voracity of all these animals required the stomach to be both large and long, there would remain but little space for the smaller viscera; these are therefore reduced, as we have seen, nearly to the state of a flattened tube, coiled like a corkscrew around itself; their bulk is thus materially diminished, whilst the amount of absorbing

* These impressions cannot have been derived from the membrane of the inferior large intestine, because they are continued along those surfaces of the inner coils of the Coprolite, which became permanently covered by its outer coils, in the act of passing from the spiral tube into this large intestine.

+ Paley, in his chapter on mechanical compensations on the structure of animals, mentions a contrivance similar to that which we attribute to the Ichthyosaurus, as existing in a species of Shark, (the Alopecias, Squalus Vulpes, or Sea Fox.) "In this animal, he says, the intestine is straight from one end to the other: but, in this straight, and consequently short intestine, is a winding, cork-screw, spiral passage, through which the food, not without several circumvolutions, and in fact by a long route, is conducted to its exit. Here the shortness of the gut is compensated by the obliquity of the perforation."

Dr. Fitton has called my attention to a passage in Lord King's Life of Locke, 4°. p. 166, 167, from which it appears that the importance of a spiral disposition within the intestinal canal, which he observed in many preparations in the collection of anatomy at Leyden, was duly appreciated by that profound philosopher.

surface remains almost the same, as if they had been circular. Had a large expansion of intestine been superadded to the enormous stomach and lungs of the Ichthyosaurus, the consequent enlargement of the body would have diminished the power of progressive motion, to the great detriment of an animal which depended on its speed for the capture of its prey.

The above facts which we have elicited from the coprolitic remains of the Ichthyosauri, afford a new and curious contribution to our knowledge both of the anatomy and habits of the extinct inhabitants of our planet. We have found evidence which enables us to point out the existence of beneficial arrangements and compensations, even in those perishable, yet important parts which formed their organs of digestion. We have ascertained the nature of their food, and the form and structure of their intestinal canal; and have traced the digestive organs through three distinct stages of descent, from a large and long stomach, through the spiral coils of a compressed ilium, to their termination in a cloaca; from which the Coprolites descended into the mud of the nascent lias. In this lias they have been interred during countless ages, until summoned from its deep recesses by the labours of the Geologist, to give evidence of events that passed at the bottom of the ancient seas, in ages long preceding the existence of man.

Intestinal Structure of Fossil Fishes.

Discoveries have recently been made of Coprolites derived from fossil fishes. Mr. Mantell has found them within the body of the Macropoma Mantellii, from the chalk of Lewes, placed in contact with the long stomach of this voracious fish: the coats of its stomach are also well preserved.* Miss Anning also has discovered them within

* See Mantell's Geol. of Sussex, Pl. 38. I learn from Mr. Mantell,

the bodies of several species of fossil fish, from the lias at Lyme Regis. Dr. Hibbert has shown that the strata of fresh-water limestone, in the lower region of the coal formation, at Burdie House, near Edinburgh, are abundantly interspersed with Coprolites, derived from fishes of that early era; and Sir Philip Egerton has found similar fœcal remains, mixed with scales of the Megalichthys, and freshwater shells, in the coal formation of Newcastle-underLyne. In 1832, Mr. W. C. Trevelyan recognised Coprolites in the centre of nodules of clay ironstone, that abound in a low cliff composed of shale, belonging to the coal formation at Newhaven, near Leith. I visited the spot, with this gentleman and Lord Greenock, in September, 1834, and found these nodules strewed so thickly upon the shore that a few minutes sufficed to collect more specimens than I could carry; many of these contained a fossil fish, or fragment of a plant, but the greater number had for their nucleus, a Coprolite, exhibiting an internal spiral structure; they were probably derived from voracious fishes, whose bones are found in the same stratum. These nodules take a beautiful polish, and have been applied by the lapidaries of Edinburgh to make tables, letter presses, and ladies' ornaments, under the name of Beetle stones, from their supposed insect origin. Lord Greenock has discovered, between the laminae of a block of coal, from the neighbourhood of Edinburgh, a mass of petrified intestines distended with Coprolite, and surrounded with the scales of a fish, which Professor Agassiz refers to the Megalichthys.

This distinguished naturalist has recently ascertained that

that the form of the Coprolites within the Macropoma most nearly resemble those engraved, Pl. 15, Figs. 8, 9, of the present work: he also conjectures that the more tortuous kinds, (Pl. 15, Figs. 5, 7,) long known by the name of Juli, and supposed to be fossil fir cones, may have been derived from fishes of the Shark family, (Ptychodus) whose large palatal teeth (Pl. 27. f) abound in the same localities of the chalk formation with them, at Steyning and Hamsey.