Part 7

The shores of both the upper and lower divisions of the lake were strewed, at the time I passed, by a line of wrack, consisting, for the first few miles from where the lower loch opens to the sea, of only marine plants, then of marine plants mixed with those of fresh-water growth, and then, in the upper sheet of water, of lacustrine plants exclusively. And the fauna of the loch is, I was informed, of as mixed a character as its flora,—the marine and fresh-water animals having each their own reaches, with certain debatable tracts between, in which each kind expatiates with more or less freedom, according to its specific nature and constitution,—some of the sea-fish advancing far on the fresh water, and others, among the proper denizens of the lake, encroaching far on the salt. The common fresh-water eel strikes out, I was told, farthest into the sea-water; in which, indeed, reversing the habits of the salmon, it is known in various places to deposit its spawn. It seeks, too, impatient of a low temperature, to escape from the cold of winter, by taking refuge in water brackish enough, in a climate such as ours, to resist the influence of frost. Of the marine fish, on the other hand, I found that the flounder got greatly higher than any of the others, inhabiting reaches of the lake almost entirely fresh. I have had an opportunity elsewhere of observing a curious change which fresh water induces in this fish. In the brackish water of an estuary, the animal becomes, without diminishing in general size, thicker and more fleshy than when in its legitimate habitat, the sea: but the flesh loses in quality what it gains in quantity;—it grows flabby and insipid, and the margin-fin lacks always its strip of transparent fat. But the change induced in the two floras of the lake—marine and lacustrine—is considerably more palpable and obvious than that induced in its two faunas. As I passed along the strait, through which it gives admission to the sea, I found the commoner fucoids of our sea-coasts streaming in great luxuriance in the tideway, from the stones and rocks of the bottom. I marked, among the others, the two species of kelp-weed, so well known to our Scotch kelp-burners,—Fucus nodosus and Fucus vesiculosus,—flourishing in their uncurtailed proportions; and the not inelegant Halidrys siliquosa, or “tree in the sea,” presenting its amplest spread of pod and frond. A little farther in, Halidrys and Fucus nodosus disappear, and Fucus vesiculosus becomes greatly stunted, and no longer exhibits its characteristic double rows of bladders. But for mile after mile it continues to exist, blent with some of the hardier confervæ, until at length it becomes as dwarfish and nearly as slim of frond as the confervæ themselves; and it is only by tracing it through the intermediate forms that we succeed in convincing ourselves that, in the brown stunted tufts of from one to three inches in length, which continue to fringe the middle reaches of the lake, we have in reality the well-known Fucus before us. Rushes, flags, and aquatic grasses may now be seen standing in diminutive tufts out of the water; and a terrestrial vegetation at least continues to exist, though it can scarce be said to thrive, on banks covered by the tide at full. The lacustrine flora increases, both in extent and luxuriance, as that of the sea diminishes; and in the upper reaches we fail to detect all trace of marine plants: the algæ, so luxuriant of growth along the straits of this “miniature Mediterranean,” altogether cease; and a semi-aquatic vegetation attains, in turn, to the state of fullest development any where permitted by the temperature of this northern locality. A memoir descriptive of the Loch of Stennis, and its productions, animal and vegetable, such as old Gilbert White of Selborne could have produced, would be at once a very valuable and curious document, important to the naturalist, and not without its use to the geological student.

I know not how it may be with others; but the special phenomena connected with Orkney that most decidedly bore fruit in my mind, and to which my thoughts have most frequently reverted, were those exhibited in the neighborhood of Stromness. I would more particularly refer to the characteristic fragment of Asterolepis, which I detected in its lower flagstones, and to the curiously mixed, semi-marine, semi-lacustrine vegetation of the Loch of Stennis. Both seem to bear very directly on that development hypothesis,—fast spreading among an active and ingenious order of minds, both in Britain and America, and which has been long known on the Continent,—that would fain transfer the work of creation from the department of miracle to the province of natural law, and would strike down, in the process of removal, all the old landmarks, ethical and religious.

THE DEVELOPMENT HYPOTHESIS, AND ITS CONSEQUENCES.

Every individual, whatever its species or order, begins and increases until it attains to its state of fullest development, under certain fixed laws, and in consequence of their operation. The microscopic monad develops into a fœtus, the fœtus into a child, the child into a man; and, however marvellous the process, in none of its stages is there the slightest mixture of miracle; from beginning to end, all is progressive development, according to a determinate order of things. Has Nature, during the vast geologic periods, been pregnant, in like manner, with the human race? and is the species, like the individual, an effect of progressive development, induced and regulated by law? The assertors of the revived hypothesis of Maillet and Lamarck reply in the affirmative. Nor, be it remarked, is there positive atheism involved in the belief. God might as certainly have originated the species by a law of development, as he maintains it by a law of development; the existence of a First Great Cause is as perfectly compatible with the one scheme as with the other; and it may be necessary thus broadly to state the fact, not only in justice to the Lamarckians, but also fairly to warn their non-geological opponents, that in this contest the old anti-atheistic arguments, whether founded on the evidence of design, or on the preliminary doctrine of final causes, cannot be brought to bear.

There are, however, beliefs, in no degree less important to the moralist or the Christian than even that in the being of a God, which seem wholly incompatible with the development hypothesis. It, during a period so vast as to be scarce expressible by figures, the creatures now human have been rising, by almost infinitesimals, from compound microscopic cells,—minute vital globules within globules, begot by electricity on dead gelatinous matter,—until they have at length become the men and women whom we see around us, we must hold either the monstrous belief, that all the vitalities, whether those of monads or of mites, of fishes or of reptiles, of birds or of beasts, are individually and inherently immortal and undying, or that human souls are not so. The difference between the dying and the undying,—between the spirit of the brute that goeth downward, and the spirit of the man that goeth upward,—is not a difference infinitesimally, or even atomically small. It possesses all the breadth of the eternity to come, and is an infinitely great difference. It cannot, if I may so express myself, be shaded off by infinitesimals or atoms; for it is a difference which—as there can be no class of beings intermediate in their nature between the dying and the undying—admits not of gradation at all. What mind, regulated by the ordinary principles of human belief, can possibly hold that every one of the thousand vital points which swim in a drop of stagnant water are inherently fitted to maintain their individuality throughout eternity? Or how can it be rationally held that a mere progressive step, in itself no greater or more important than that effected by the addition of a single brick to a house in the building state, or of a single atom to a body in the growing state, could ever have produced immortality? And yet, if the spirit of a monad or of a mollusc be not immortal, then must there either have been a point in the history of the species at which a dying brute—differing from its offspring merely by an inferiority of development, represented by a few atoms, mayhap by a single atom—produced an undying man, or man in his present state must be a mere animal, possessed of no immortal soul, and as irresponsible for his actions to the God before whose bar he is, in consequence, never to appear, as his presumed relatives and progenitors the beasts that perish. Nor will it do to attempt escaping from the difficulty, by alleging that God at some certain link in the chain might have converted a mortal creature into an immortal existence, by breathing into it a “living soul;” seeing that a renunciation of any such direct interference on the part of Deity in the work of creation forms the prominent and characteristic feature of the scheme,—nay, that it constitutes the very nucleus round which the scheme has originated. And thus, though the development theory be not atheistic, it is at least practically tantamount to atheism. For, if man be a dying creature, restricted in his existence to the present scene of things, what does it really matter to him, for any one moral purpose, whether there be a God or no? If in reality on the same religious level with the dog, wolf, and fox, that are by nature atheists,—a nature most properly coupled with irresponsibility,—to what one practical purpose should he know or believe in a God whom he, as certainly as they, is never to meet as his Judge? or why should he square his conduct by the requirements of the moral code, farther than a low and convenient expediency may chance to demand?

Nor does the purely Christian objection to the development hypothesis seem less, but even more insuperable than that derived from the province of natural theology. The belief which is perhaps of all others most fundamentally essential to the revealed scheme of salvation, is the belief that “God created man upright,” and that man, instead of proceeding onward and upward from this high and fair beginning, to a yet higher and fairer standing in the scale of creation, sank and became morally lost and degraded. And hence the necessity for that second dispensation of recovery and restoration which forms the entire burden of God’s revealed message to man. If, according to the development theory, the progress of the “first Adam” was an upward progress, the existence of the “second Adam”—that “happier man,” according to Milton, whose special work it is to “restore” and “regain the blissful seat” of the lapsed race—is simply a meaningless anomaly. Christianity, if the development theory be true, is exactly what some of the more extreme Moderate divines of the last age used to make it—an idle and unsightly excrescence on a code of morals that would be perfect were it away.

I may be in error in taking this serious view of the matter; and, if so, would feel grateful to the man who could point out to me that special link in the chain of inference at which, with respect to the bearing of the theory on the two theologies—natural and revealed—the mistake has taken place. But if I be in error at all, it is an error into which I find not a few of the first men of the age,—represented, as a class, by our Professor Sedgwicks and Sir David Brewsters,—have also fallen; and until it be shown to be an error, and that the development theory is in no degree incompatible with a belief in the immortality of the soul—in the responsibility of man to God as the final Judge—or in the Christian scheme of salvation—it is every honest man’s duty to protest against any ex parte statement of the question, that would insidiously represent it as ethically an indifferent one, or as unimportant in its theologic bearing, save to “little religious sects and scientific coteries.” In an address on the fossil flora, made in September last by a gentleman of Edinburgh to the St. Andrew’s Horticultural Society, there occurs the following passage on this subject: “Life is governed by external conditions, and new conditions imply new races; but then as to their creation, that is the ‘mystery of mysteries.’ Are they created by an immediate fiat and direct act of the Almighty? or has He originally impressed life with an elasticity and adaptability, so that it shall take upon itself new forms and characters, according to the conditions to which it shall be subjected? Each opinion has had, and still has, its advocates and opponents; but the truth is, that science, so far as it knows, or rather so far as it has had the honesty and courage to avow, has yet been unable to pronounce a satisfactory decision. Either way, it matters little, physically or morally, either mode implies the same omnipotence, and wisdom, and foresight, and protection; and it is only your little religious sects and scientific coteries which make a pother about the matter,—sects and coteries of which it may be justly said, that they would almost exclude God from the management of his own world, if not managed and directed in the way that they would have it.” Now, this is surely a most unfair representation of the consequences, ethical and religious involved in the development hypothesis. It is not its compatibility with belief in the existence of a First Great Cause that has to be established, in order to prove it harmless; but its compatibility with certain other all-important beliefs, without which simple Theism is of no moral value whatever—a belief in the immortality and responsibility of man, and in the scheme of salvation by a Mediator and Redeemer. Dissociated from these beliefs, a belief in the existence of a God is of as little ethical value as a belief in the existence of the great sea-serpent.

Let us see whether we cannot determine what the testimony of Geology, on this question of creation by development, really is. It is always perilous to under-estimate the strength of an enemy; and the danger from the development hypothesis to an ingenious order of minds, smitten with the novel fascinations of physical science, has been under-estimated very considerably indeed. Save by a few studious men, who to the cultivation of Geology and the cognate branches add some acquaintance with metaphysical science, the general correspondence of the line of assault taken up by this new school of infidelity, with that occupied by the old, and the consequent ability of the assailants to bring, not only the recently forged, but also the previously employed artillery into full play along its front, has not only not been marked, but even not so much as suspected. And yet, in order to show that there actually is such a correspondence, it can be but necessary to state, that the great antagonist points in the array of the opposite lines, are simply the law of development versus the miracle of creation. The evangelistic Churches cannot, in consistency with their character, or with a due regard to the interests of their people, slight or overlook a form of error at once exceedingly plausible and consummately dangerous, and which is telling so widely on society, that one can scarce travel by railway or in a steamboat, or encounter a group of intelligent mechanics, without finding decided trace of its ravages.

But ere the Churches can be prepared competently to deal with it, or with the other objections of a similar class which the infidelity of an age so largely engaged as the present in physical pursuits will be from time to time originating they must greatly extend their educational walks into the field of physical science. The mighty change which has taken place during the present century, in the direction in which the minds of the first order are operating, though indicated on the face of the country in characters which cannot be mistaken, seems to have too much escaped the notice of our theologians. Speculative theology and the metaphysics are cognate branches of the same science; and when, as in the last and the preceding ages, the higher philosophy of the world was metaphysical, the Churches took ready cognizance of the fact, and, in due accordance with the requirements of the time, the battle of the Evidences was fought on metaphysical ground. But, judging from the preparations made in their colleges and halls, they do not now seem sufficiently aware—though the low thunder of every railway, and the snort of every steam engine, and the whistle of the wind amid the wires of every electric telegraph, serve to publish the fact—that it is in the departments of physics, not of metaphysics, that the greater minds of the age are engaged,—that the Lockes, Humes, Kants, Berkeleys, Dugald Stewarts, and Thomas Browns, belong to the past,—and that the philosophers of the present time, tall enough to be seen all the world over, are the Humboldts, the Aragos, the Agassizes, the Liebigs, the Owens, the Herschels, the Bucklands, and the Brewsters. In that educational course through which, in this country, candidates for the ministry pass, in preparation for their office, I find every group of great minds which has in turn influenced and directed the mind of Europe for the last three centuries, represented, more or less adequately, save the last. It is an epitome of all kinds of learning, with the exception of the kind most imperatively required, because most in accordance with the genius of the time. The restorers of classic literature—the Buchanans and Erasmuses—we see represented in our Universities by the Greek and what are termed the Humanity courses; the Galileos, Boyles, and Newtons, by the Mathematical and Natural Philosophy courses; and the Lockes, Kants, Humes, and Berkeleys, by the Metaphysical course. But the Cuviers, the Huttons, the Cavendishes, and the Watts, with their successors, the practical philosophers of the present age,—men whose achievements in physical science we find marked on the surface of the country in characters which might be read from the moon,—are not adequately represented. It would be perhaps more correct to say, that they are not represented at all; and the clergy, as a class, suffer themselves to linger far in the rear of an intelligent and accomplished laity—a full age behind the requirements of the time. Let them not shut their eyes to the danger which is obviously coming. The battle of the Evidences will have as certainly to be fought on the field of physical science, as it was contested in the last age on that of the metaphysics. And on this new arena the combatants will have to employ new weapons, which it will be the privilege of the challenger to choose. The old, opposed to these, would prove but of little avail. In an age of muskets and artillery, the bows and arrows of an obsolete school of warfare would be found greatly less than sufficient, in the field of battle, for purposes either of assault or defence.

“There are two kinds of generation in the world,” says Professor Lorenz Oken, in his “Elements of Physio-philosophy;” “the creation proper, and the propagation that is sequent thereupon—or the generatio originaria and secundaria. Consequently, no organism has been created of larger size than an infusorial point. No organism is, nor ever has one been created, which is not microscopic. Whatever is larger has not been created, but developed. Man has not been created, but developed.” Such, in a few brief dogmatic sentences, is the development theory. What, in order to establish its truth, or even to render it in some degree probable, ought to be the geological evidence regarding it? The reply seems obvious. In the first place, the earlier fossils ought to be very small in size; in the second, very low in organization. In cutting into the stony womb of nature, in order to determine what it contained mayhap millions of ages ago, we must expect, if the development theory be true, to look upon mere embryos and fœtuses. And if we find, instead, the full grown and the mature, then must we hold that the testimony of Geology is not only not in accordance with the theory, but in positive opposition to it. Such, palpably, is the principle on which, in this matter, we ought to decide. What are the facts?

The oldest organism yet discovered in the most ancient geological system of Scotland in which vertebrate remains occur, seems to be the Asterolepis of Stromness. After the explorations of many years over a wide area, I have detected none other equally low in the system; nor have I ascertained that any brother-explorer in the same field has been more fortunate. It is, up to the present time, the most ancient Scotch witness of the great class of fishes that can in this case be brought into court; nay, it is in all probability the oldest ganoid witness the world has yet produced; for there appears no certain trace of this order of fishes in the great Silurian system which lies underneath, and in which, so far as geologists yet know, organic existence first began. How, then, on the two relevant points—bulk and organization—does it answer to the demands of the development hypothesis? Was it a mere fœtus of the finny tribe, of minute size, and imperfect, embryonic faculty? Or was it of at least the ordinary bulk, and, for its class, of the average organization? May I solicit the forbearance of the non-geological reader, should my reply to these apparently simple questions seem unnecessarily prolix and elaborate? Peculiar opportunities of observation, and the possession of a set of unique fossils, enable me to submit to our palæontologists a certain amount of information regarding this ancient ganoid, which they will deem at once interesting and new; and the bearing of my statements on the general argument will, I trust, become apparent as I proceed.

THE RECENT HISTORY OF THE ASTEROLEPIS. ITS FAMILY.

It had been long known to the continental naturalists, that in certain Russian deposits, very extensively developed, there occur in considerable abundance certain animal organisms; but for many years neither their position nor character could be satisfactorily determined. By some they were placed too high in the scale of organized being; by others too low. Kutorga, a writer not very familiarly known in this country, described the remains as those of mammals;—the Russian rocks contained, he said, bones of quadrupeds, and, in especial, the teeth of swine: whereas Lamarck, a better known authority, though not invariably a safe one,—for he had a trick of dreaming when wide awake, and of calling his dreams philosophy,—assigned to them a place among the corals. They belonged, he asserted, as shown by certain star-like markings with which they are fretted, to the Polyparia. He even erected for their reception a new genus of Astrea, which he designated, from the little rounded hillock which rises in the middle of each star, the genus Monticularia. It was left to a living naturalist, M. Eichwald, to fix their true position zoologically among the class of fishes, and to Sir Roderick Murchison to determine their position geologically as ichthyolites of the Old Red Sandstone.

Sir Roderick, on his return from his great Russian campaigns, in which he fared far otherwise than Napoleon, and accomplished more, submitted to Agassiz a series of fragments of these gigantic Ganoids; and the celebrated ichthyologist, who had been introduced little more than a twelvemonth before to the Pterichthys of Cromarty, was at first inclined to regard them as the remains of a large cuirassed fish of the Cephalaspian type, but generically new. Under this impression he bestowed upon the yet unknown ichthyolite of which they had formed part, the name Chelonichthys, from the resemblance borne by the broken plates to those of the carapace and plastron of some of the Chelonians. At this stage, however, the Russian Old Red yielded a set of greatly finer remains than it had previously furnished; and of these casts were transmitted by Professor Asmus, of the University of Dorpat, to the British and London Geological Museums, and to Agassiz. “I knew not at first what to do,” says the ichthyologist, “with bones of so singular a conformation that I could refer them to no known type.” Detecting, however, on their exterior surfaces the star-like markings which had misled Lamarck, and which he had also detected on the lesser fragments submitted to him by Sir Roderick, he succeeded in identifying both the fragments and bones as remains of the same genus and on ascertaining that M. Eichwald had bestowed upon it, from these characteristic sculpturings, the generic name Asterolepis, or star-scale, he suffered the name which he himself had originated to drop. Even this second name, however, which the ichthyolite still continues to bear, is in some degree founded in error. Its true scales, as I shall by and by show, were not stelliferous, but fretted by a peculiar style of ornament, consisting of waved anastomosing ridges, breaking atop into angular-shaped dots, scooped out internally like the letter V; and were evidently intermediate in their character between the scales which cover the Glyptolepis and those of the Holoptychius. And the stellate markings which M. Eichwald graphically describes as minute paps rising out of the middle of star-like wreaths of little leaflets, were restricted to the dermal plates of the head.

Agassiz ultimately succeeded in classing the bones which had at first so puzzled him, into two divisions—interior and dermal; and the latter he divided yet further, though not without first lodging a precautionary protest, founded on the extreme obscurity of the subject, into cranial and opercular. Of the interior bones he specified two,—a super-scapular bone, (supra-scapulaire,)—that bone which in osseous fishes completes the scapular arch or belt, by uniting the scapula to the cranium; and a maxillary or upper jaw-bone. But his world-wide acquaintance with existing fishes could lend him no assistance in determining the places of the dermal bones: they formed the mere fragments of a broken puzzle, of which the key was lost. Even in their detached and irreducible state, however, he succeeded in basing upon them several shrewd deductions. He inferred, in the first place, that the Asterolepis was not, as had been at first supposed, a cuirassed fish, which took its place among the Cephalaspians, but a strongly helmed fish of that Cœlacanth family to which the Holoptychius and Glyptolepis belong; in the second, that, like several of its bulkier cogeners, it was in all probability a broad, flat-headed animal; and, in the third, that as its remains are found associated in the Russian beds with numerous detached teeth of large size,—the boar tusks of Kutorga—which present internally that peculiar microscopic character on which Professor Owen has erected his Dendrodic or tree-toothed family of fishes,—it would in all likelihood be found that both bones and teeth belonged to the same group. “It appears more than probable,” he said, “that one day, by the discovery of a head or an entire jaw, it will be shown that the genera Dendrodus and Asterolepis form but one.” As we proceed, the reader will see how justly the ichthyologist assigned to the Asterolepis its place among the Cœlacanths, and how entirely his two other conjectures regarding it have been confirmed. “I have had in general,” he concluded, “but small and mutilated fragments of the creature’s bones submitted to me, and of these, even the surface ornaments not well preserved; but I hope the immense materials with which the Old Red Sandstone of Russia has furnished the savans of that country will not be lost to science; and that my labors on this interesting genus, incomplete as they are, will excite more and more the attention of geologists, by showing them how ignorant we are of all the essential facts concerning the history of the first inhabitants of our globe.”

I know not what the savans of Russia have been doing for the last few years; but mainly through the labors of an intelligent tradesman of Thurso, Mr. Robert Dick,—one of those working men of Scotland of active curiosity and well-developed intellect, that give character and standing to the rest,—I am enabled to justify the classification and confirm the conjectures of Agassiz. Mr. Dick, after acquainting himself, in the leisure hours of a laborious profession, with the shells, insects, and plants of the northern locality in which he resides, had set himself to study its geology; and with this view he procured a copy of the little treatise on the Old Red Sandstone to which I have already referred, and which was at that time, as Agassiz’s Monograph of the Old Red fishes had not yet appeared, the only work specially devoted to the palæontology of the system, so largely developed in the neighborhood of Thurso. With perhaps a single exception,—for the Thurso rocks do not yet seem to have yielded a Pterichthys,—he succeeded in finding specimens, in a state of better or worse keeping, of all the various ichthyolites which I had described as peculiar to the Lower Old Red Sandstone. He found, however, what I had not described,—the remains of apparently a very gigantic ichthyolite; and, communicating with me through the medium of a common friend, he submitted to me, in the first instance, drawings of his new set of fossils; and ultimately, as I could arrive at no satisfactory conclusion from the drawings, he with great liberality made over to me the fossils themselves. Agassiz’s Monograph was not yet published; nor had I an opportunity of examining, until about a twelvemonth after, the casts, in the British Museum, of the fossils of Professor Asmus. Besides, all the little information, derived from various sources, which I had acquired respecting the Russian Chelonichthys,—for such was its name at the time,—referred it to the cuirassed type, and served but to mislead. I was assured, for instance, that Professor Asmus regarded his set of remains as portions of the plates and paddles of a gigantic Pterichthys, of from twenty to thirty feet in length. And so, as I had recognized in the Thurso fossils the peculiarities of the Holoptychian (Cœlacanth) family, I at first failed to identify them with the remains of the great Russian fish. All the larger bones sent me by Mr. Dick were, I found, cerebral; and the scales associated with these indicated, not a cuirass-protected, but a scale-covered body and exhibited, in their sculptured and broadly imbricated surfaces, the well-marked Cœlacanth style of disposition and ornament. But though I could not recognize in either bones or scales the remains of one ichthyolite more of the Old Red Sandstone, “that could be regarded as manifesting as peculiar a type among fishes as do the Ichthyosauri and Plesiosauri among reptiles,” I was engaged at the time in a course of inquiry regarding the cerebral development of the earlier vertebrata, that made me deem them scarce less interesting than if I could. Ere, however, I attempt communicating to the reader the result of my researches, I must introduce him, in order that he may be able to set out with me to the examination of the Asterolepis from the same starting-point, to the Cœlacanth family,—indisputably one of the oldest, and not the least interesting, of its order.

a. Shagreen of the Thornback (Raja clavata.)

b. Shagreen of Sphagodus,—a placoid of the Upper Silurian.]

So far as is yet known, all the fish of the earliest fossiliferous system belonged to the placoid or “broad plated” order,—a great division of fishes, represented in the existing seas by the Sharks and Rays,—animals that to an internal skeleton of cartilage unite a dermal covering of points, plates, or spines of enamelled bone, and have their gills fixed. The dermal or cuticular bones of this order vary greatly in form, according to the species or family: in some cases they even vary, according to their place, on the same individual. Those button-like tubercles, for instance, with an enamelled thorn, bent like a hook, growing out of the centre of each, which run down the back and tail, and stud the pectorals of the thorn-back, (Raja clavata,) differ very much from the smaller thorns, with star-formed bases, which roughen the other parts of the creature’s body; and the bony points which mottle the back and sides of the sharks are, in most of the known species, considerably more elongated and prickly than the points which cover their fins, belly, and snout. The extreme forms, however, of the shagreen tubercle or plate seem to be those of the upright prickle or spine on the one hand, and of the slant-laid, rhomboidal, scale-shaped plate on the other. The minuter thorns of the ray (fig. 2, a) exemplify the extreme of the prickly type; the fins, abdomen, and anterior part of the head of the spotted dog-fish (Scyllium stellare) are covered by lozenge-shaped little plates, which glisten with enamel, and are so thickly set that they cover the entire surface of the skin, (fig. 3, b,)—and these seem equally illustrative of the scale-like form. They are shagreen points passing into osseous scales, without, however, becoming really such; though they approach them so nearly in the shape and disposition of their upper disks, that the true scales, also osseous, of the Acanthodes sulcatus, (fig. 3, a,) a Ganoid of the Coal Measures, can scarce be distinguished from them, even when microscopically examined. It is only when seen in section that the distinctive difference appears. The true scale of the Acanthodes, though considerably elevated in the centre, seems to have been planted on the skin; whereas the scale-like shagreen of the dog-fish is elevated over it on an osseous pedicle or footstalk (fig. 5, a) as a mushroom is elevated over the sward on its stem; and the base of the stalk is found to resemble in its stellate character that of a shagreen point of the prickly type. The apparent scale is, we find, a bony prickle bent at right angles a little over its base, and flattened into a rhomboidal disk atop.

a. Scales of Acanthodes sulcatus.

b. Shagreen of Scyllium stellare, (Snout.)

(Mag. eight diameters.)]

a. Scales of Cheiracanthus microlepidotus.

b. Shagreen of Spinax Acanthias. (Snout.)

(Mag. eight diameters.)]

a. Section of shagreen of Scyllium stellare.

b. Under surface of do.

c. Section of scales of Cheiracanthus microlepidotus.