Part 14

b. Tail of Ichthyosaurus Tenuirostris, (Buckland.)]

In illustration of this view, I would fain recommend to the reader a simple experiment. Let him procure the tail of a common dog-fish, (fig. 48, a,) and cutting it across about half an inch above where the caudal fin begins, let him boil it smartly for about half an hour. He will first see it swell and then burst, all around those thinner parts of the fin that are traversed by the caudal rays,—wholly mucoidal, as shown by this test, in their texture, and which yield to the boiling water, as if formed of isinglass. They finally dissolve, and drop away, with the surrounding cuticular integument; and then there only remains, as the insoluble framework of the whole, the bodies of the vertebræ, with their neural and hœmal processes. The tail has now lost much of its ichthyic character, and has acquired, instead, a considerable degree of resemblance to the reptilian tail, as exemplified in the saurians. I have introduced into the wood-cut, for the purpose of comparison, the tail of the ichthyosaurus, (b.) It consists, like the other, of a series of gradually diminishing vertebræ, and must have also supported, says Professor Owen, a propelling fin, placed vertically, as in the shark, which, however, from its perishable nature, has in every instance disappeared in the earth, as that of the dog-fish disappears in the boiling water. It will be seen that its processes are comparatively smaller than those of the fish, and that the bodies of its vertebræ are shorter and bulkier; but there is at least a general correspondence of the parts; and were the tail of the crocodile, of which the vertebral bodies are slender and the processes large, to be substituted for that of the enaliosaur here, the correspondence would be more marked still. After thus developing the tail of the reptile out of that of the fish,—as the cauldron-bearing Irish magician of the tale developed young ladies out of old women,—simply by boiling, let the reader proceed to a second stage of the experiment, and see whether he may not be able still further to develope the reptilian tail so obtained, into that of the mammal, by burning. Let him spread it out on a piece of iron hoop, and thrust it into the fire; and then, after exposure for some time to a red heat has consumed and dissipated its merely cartilaginous portions, such as the neural and hœmal processes, with the little pieces which form the sides of the neural arch, and left only the whitened bodies of the vertebræ, let him say whether the bony portion which remains does not present a more exact resemblance to the mammiferous tail—that of the dog, for example—than any thing else he ever saw. The Lamarckians may well deem it an unlucky circumstance, that one special portion of their theory should demand the depreciation of the heterocercal tail, seeing that it might be represented with excellent effect in another, as not merely a connecting link in the upward march of progression between the tail of the true fish and that of the true reptile, but as actually containing in itself—as the caterpillar contains the future pupa and butterfly—the elements of the reptilian and mammiferous tail. If there be any virtue in analogy, the heterocercal tail is, I repeat, of a decidedly higher type than the homocercal one. It furnishes the first example in the vertebrata of the coccygeal vertebræ diminishing to a point, which characterizes not only all the higher reptiles, but also all the higher mammals, and which we find represented by the Os coccygis in man himself. But to this special point I shall again refer.

With regard to that rudimentary state of the occipital framework of the Placoids to which the author of the “Vestiges” refers, it may be but necessary to say that, notwithstanding the simplicity of their box-like skulls, they bear in their character, as cases for the protection of the brain, at least as close an analogy to the skulls of the higher animals, as those of the osseous fishes, which consist usually of the extraordinary number of from sixty to eighty bones,—a mark—the author of the “Vestiges” himself being judge in the case—rather of inferiority than the reverse. “Elevation is marked in the scale,” we find him saying, “by an animal exchanging a multiplicity of parts serving one end, for a smaller number.” The skull of a cod consists of about thrice as many separate bones as that of a man. But I do not well see that in this case the fact either of simplicity in excess or of multiplicity in excess can be insisted upon in either direction, as a proper basis for argument. Nearly the same remark applies to the maxillaries as to the skull. The under jaw in man consists of a single bone; that of the thornback—if we do not include the two suspending ribs, which belong equally to the upper jaw—of two bones, (the number in all the mammiferous quadrupeds:) that of the cod of four bones, and, if we include the suspending ribs, of twelve. On what principle are we to hold, with one as the representative number of the highest type of jaw, that two indicates a lower standing than four, or four than twelve? In reference to the further statement, that in many of the ancient fishes “traces can be observed of the muscles having been attached to the external plates, strikingly indicating their low grade as vertebrate animals,” it may be answer enough to state, that the peculiarity in question was not a characteristic of the most ancient fishes,—the Placoids of the Silurian system,—but of some Ganoids of the succeeding systems. The reader may remember, as a case in point, the example furnished by the nail-like bone of Asterolepis, figured in page 111, in which there exists depressions resembling that of the round ligament in the head of the quadrupedal thigh-bone. And as for the remark that the opening of the mouth of the Placoid, “on the under side of the head,” is indicative of a low embryonic condition, it might be almost sufficient to remark, in turn, that the lowest family of fishes—that to which the supposed worms of Linnæus belong—have the mouth not under, but at the anterior termination of the head,—in itself an evidence that the position of the mouth at the extremity of the muzzle, common to the greater number of the osseous fishes, can be no very high character, seeing that the humblest of the Suctorii possess it; and that many osseous fishes, whose mouths open, not on the under, but the upper side of the snout, as in the distorted and asymmetrical genus Platessa, are not only in no degree superior to their bony neighbors, and far inferior to the placoid ones, but bear, in direct consequence of the arrangement, an expression of unmistakable stupidity. The objection, however, admits of a greatly more conclusive reply.

PORT JACKSON SHARK, (Cestracion Phillippi.)]

“This fish, to speak in the technical language of Agassiz,” says the Edinburgh Reviewer, in reference to the ancient ichthyolite of the Wenlock Shale, “undoubtedly belongs to the Cestraciont family of the Placoid order,—proving to demonstration that the oldest known fossil fish belongs to the highest type of that division of the vertebrata.” I may add, that the character and family of this ancient specimen was determined by our highest British authority in fossil ichthyology, Sir Philip Egerton. And it is in depreciation of Professor Sedgwick’s statement regarding its high standing that the author of the “Vestiges” refers to the supposed inferiority indicated by a mouth opening, not at the extremity of the muzzle, but under the head. Let us, then, fully grant, for the argument’s sake, that the occurrence of the mouth in the muzzle is a sign of superiority, and its occurrence under the head a mark of great inferiority, and then ascertain how the fact stands with regard to the Cestracion. “The Cestracion sub-genus,” says Mr. James Wilson, in his admirable treatise on fishes, which forms the article ICHTHYOLOGY in the “Encyclopædia Britannica,” “has the temporal aperture, the anal fin, and rounded teeth, of Squalus Mustelus; but the mouth is TERMINAL, or AT THE EXTREMITY OF THE POINTED MUZZLE.” The accompanying figure, (fig. 49,) taken from a specimen of Cestracion in the collection of Professor John Fleming, may be recorded as of some little interest, both from its direct bearing on the point in question, and from the circumstance that it represents, not inadequately for its size, the sole surviving species (Cestracion Phillippi) of the oldest vertebrate family of creation. With this family, so far as is yet known, ichthyic existence first began. It does not appear that on the globe which we inhabit there was ever an ocean tenanted by living creatures at all that had not its Cestracion,—a statement which could not be made regarding any other vertebrate family. In Agassiz’s “Tabular View of the Genealogy of Fishes,” the Cestracionts, and they only, sweep across the entire geologic scale. And, as shown in the figure, the mouth in this ancient family, instead of opening, as in the ordinary sharks, under the middle of the head, to expose them to the suspicion of being creatures of low and embryonic character, opened in a broad, honest-looking muzzle, very much resembling that of the hog. The mouths of the most ancient Placoids of which we know any thing, did not, I reiterate, open under their heads.

But why introduce the element of embryonic progress into this question at all? It is not a question of embryonic progress. The very legerdemain of the sophist—the juggling by which he substitutes his white balls for black, or converts his pigeons into crows—consists in the art of attaching the conclusions founded on the facts or conditions of one subject, to some other subject essentially distinct in its nature. Gestation is not creation. The history of the young of animals in their embryonic state is simply the history of the fœtal young; just as the history of insect transformation, in which it has been held by good men, but weak reasoners, that there exists direct evidence of the doctrine of the resurrection, is the history of insect transformation, and of nothing else. True, the human mind is so constituted that it converts all nature into a storehouse of comparisons and analogies; and this fact of the metamorphosis of the creeping caterpillar, after first passing through an intermediate period of apparent death as an inert aurelia, into a winged image, seemed to have seized on the human fancy at a very early age, as wonderfully illustrative of life, death, and the future state. The Egyptians wrapped up the bodies of their dead in the chrysalis form, so that a mummy, in their apprehension, was simply a human pupa, waiting the period of its enlargement; and the Greeks had but one word in their language for butterfly and the soul. But not the less true is it, notwithstanding, that the facts of insect transformation furnish no legitimate key to the totally distinct facts of a resurrection of the body, and of a life after death. And on what principle, then, are we to trace the origin of past dynasties in the changes of the fœtus if not the rise of the future dynasty in the transformations of the caterpillar? “These [embryonic] characters [that of the heterocercal tail, and of the mouth of the ordinary shark type] are essential and important,” remarks the author of the “Vestiges,” “whatever the Edinburgh Reviewer may say to the contrary;—they are the characters which, above all, I am chiefly concerned in looking to, for they are the features of embryonic progress, and embryonic progress is the grand key to the theory of development.” Yes; the grand key to the theory of fœtal development; for embryonic progress is fœtal development. But on what is the assertion based that they form a key to the history of creation? Aurelia are not human bodies laid out for the sepulchre, nor are butterflies human souls; as certainly gestation is not creation, nor a life of months in the uterus a succession of races for millions of ages outside of it. On what grounds, then, is the assertion made? Does it embody the result of a discovery or announce the message of a revelation? Did the author of the “Vestiges” find it out for himself, or did an angel from heaven tell it him? If it be a discovery, show us, we ask, the steps through which you have been conducted to it; if a revolution produce, for our satisfaction, the evidence on which it rests. For we are not to accept as data, in a question of science, idle comparisons or vague analogies, whether produced through the intentional juggling of the sophist, or involuntarily conjured up in the dreamy delirium of an excited fancy.

It is one of the difficulties incident to the task of replying to any dogmatic statement of error, that every mere annunciation of a false fact or false principle must be met by elaborate counter-statement or carefully constructed argument and that prolixity is thus unavoidably entailed on the controversialist who labors to set right what his antagonist has set wrong. The promulgator of error may be lively and entertaining, whereas his pains-taking confutator runs no small risk of being tedious and dull. May I, however, solicit the forbearance of the reader, if, after already spending much time in skirmishing on ground taken up by the enemy,—one of the disadvantages incident to the mere defendant in a controversy of this nature,—I spend a little more in indicating what I deem the proper ground on which the standing of the earlier vertebrata should be decided. To the test of brain I have already referred, as all-important in the question: I would now refer to the test of what may be termed homological symmetry of organization.

THE PROGRESS OF DEGRADATION. ITS HISTORY.

Though all animals be fitted by nature for the life which their instincts teach them to pursue, naturalists have learned to recognize among them certain aberrant and mutilated forms, in which the type of the special class to which they belong seems distorted and degraded. They exist as the monster families of creation, just as among families there appear from time to time monster individuals,—men, for instance, without feet, or hands, or eyes, or with their feet, hands, or eyes grievously misplaced,—sheep with their fore legs growing out of their necks, or ducklings with their wings attached to their haunches. Among these degraded races, that of the footless serpent, which “goeth upon its belly,” has been long noted by the theologian as a race typical, in its condition and nature, of an order of hopelessly degraded beings, borne down to the dust by a clinging curse; and, curiously enough, when the first comparative anatomists in the world give their readiest and most prominent instance of degradation among the denizens of the natural world, it is this very order of footless reptiles that they select. So far as the geologist yet knows, the Ophidians did not appear during the Secondary ages, when the monarchs of creation belonged to the reptilian division, but were ushered upon the scene in the times of the Tertiary deposits, when the mammalian dynasty had supplanted that of the Iguanodon and Megalosaurus. Their ill omened birth took place when the influence of their house was on the wane, as if to set such a stamp of utter hopelessness on its fallen condition, as that set by the birth of a worthless or idiot heir on the fortunes of a sinking family. The degradation of the Ophidians consists in the absence of limbs,—an absence total in by much the greater number of their families, and represented in others, as in the boas and pythons, by mere abortive hinder limbs concealed in the skin; but they are thus not only monsters through defect of parts, if I may so express myself, but also monsters through redundancy, as a vegetative repetition of vertebra and ribs, to the number of three or four hundred, forms the special contrivance by which the want of these is compensated. I am also disposed to regard the poison-bag of the venomous snakes as a mark of degradation;—it seems, judging from analogy, to be a protective provision of a low character, exemplified chiefly in the invertebrate families,—ants, centipedes, and mosquitos,—spiders, wasps, and scorpions. The higher carnivora are, we find, furnished with unpoisoned weapons, which, like those of civilized man, are sufficiently effective, simply from the excellence of their construction, and the power with which they are wielded, for every purpose of assault or defence. It is only the squalid savages and degraded boschmen of creation that have their feeble teeth and tiny stings steeped in venom, and so made formidable. Monstrosity through displacement of parts constitutes yet another form of degradation; and this form, united, in some instances, to the other two, we find curiously exemplified in the geological history of the fish,—a history which, with all its blanks and missing portions, is yet better known than that of any other division of the vertebrata. And it is, I am convinced, from a survey of the progress of degradation in the great ichthyic division,—a progress recorded as “with a pen of iron in the rock for ever,”—and not from superficial views founded on the cartilaginous or non-cartilaginous texture of the ichthyic skeleton, that the standing of the kingly fishes of the earlier periods is to be adequately determined. Any other mode of survey, save the parallel mode which takes development of brain into account, evolves, we find, nothing like principle, and lands the inquirer in inextricable difficulties and inconsistencies.

In all the higher non-degraded vertebrata we find a certain uniform type of skeleton, consisting of the head, the vertebral column, and four limbs; and these last, in the various symmetrical forms, whether exemplified in the higher fish, the higher reptiles, the higher birds, the higher mammals, or in man himself, occur always in a certain determinate order. In all the mammals, the scapular bases of the fore limbs begin opposite the eighth vertebra from the skull backwards, the seven which go before being cervical or neck vertebræ; in the birds,—a division of the vertebrata that, from their peculiar organization, require longer and more flexible necks than the mammals,—the scapulars begin at distances from the occiput, varying, according to the species, from opposite the thirteenth to opposite the twenty-fourth vertebra; and in the reptiles—a division which, according to Cuvier, “presents a greater diversity of forms, characters, and modes of gait, than any of the other two,”—they occur at almost all points, from opposite the second vertebra, as in the frog, to opposite the thirty-third or thirty-fourth vertebra, as in some species of plesiosaurus. But in all,—whether mammals, birds, or undegraded reptiles,—they are so placed, that the creatures possess necks, of greater or less length, as an essential portion of their general type. The hinder limbs have also in all these three divisions of the animal kingdom their typical place. They occur opposite, or very nearly opposite, the posterior termination of the abdominal cavity, and mark the line of separation between the vertebræ of the trunk (dorsal, lumbar, and sacral) and the third and last, or caudal division of the column,—a division represented in man by but four vertebræ, and in the crocodile by about thirty-five, but which is found to exist, as I have already said, in all the more perfect forms. The limbs, then, in all the symmetrical animals of the first three classes of the vertebrata, mark the three great divisions of the vertebral column,—the division of the neck, the division of the trunk, and the division of the tail. Let us now inquire how the case stands with the fourth and lowest class,—that of the fishes.

In those existing Placoids that represent the fishes of the earliest vertebrate period, the places of the double fins,—pectorals and ventrals,—which form in the ichthyic class the true homologues of the limbs, correspond to the places which these occupy in the symmetrical mammals, birds, and reptiles. The scapular bases of the fore or pectoral fins ordinarily begin opposite the twelfth or fourteenth vertebra; but they range, as in man and the mammals, in a forward direction, so that the fins themselves are opposite the eighth or tenth. The pelvic bases of the ventral fins are placed nearly opposite the base of the abdomen, so that, as in all the symmetrical animals, the vent opens between, or nearly between, those hinder limbs which the bases support. In the Rays, which, so far as is yet known, did not appear in creation until the Secondary ages had begun, the bases of the fore limbs, i. e. pectoral fins, are attached to the lower part of a huge cervical vertebra, nearly equal in length to all the trunk vertebræ united; and in the Chimeridæ, which also first appear in the Secondary division, they are attached, as in the osseous fishes, to the hinder part of the head. But in the representatives of all those Silurian Placoids yet known, of which the family can be determined, or any thing with safety predicated, the cervical division is found to occur as a series of vertebræ: they present in this, as in the hinder portion of their bodies, the homological symmetry of organization typical of that vertebral sub-kingdom to which they belong.

In the second great period of ichthyic existence,—that of the Old Red Sandstone,—we find the first example, in the class of fishes, of “monstrosity through displacement of parts,” and apparently also—in at least two genera, though the evidence on this head be not yet quite complete—of “monstrosity through defect of parts.” In all the Ganoids of the period, with (so far as we can determine the point) only two exceptions, the scapular bases of the fore limbs are brought forward from their typical place opposite the base of the cervical vertebræ, and stuck on to the occipital plate. There occurs, in consequence, in one great order of the ichthyic class, such a departure from the symmetrical type as would take place in a monster example of the human family in whom the neck had been annihilated, and the arms stuck on to the back of the head. And in the genera Coccosteus and Pterichthys we find the first example of degradation through defect. In the Pterichthys the hinder limbs seem wanting, and in the Coccosteus we find no trace of the fore limbs. The one resembles a monster of the human family born without hands, and the other a monster born without feet. Ages and centuries pass, and long unreckoned periods come to a close; and then, after the termination of the Palæozoic period, we see that change taking place in the form of the ichthyic tail, to which I have already referred, (and to which I must refer at least once more,) as singularly illustrative of the progress of degradation. Yet other ages and centuries pass away, during which the reptile class attains to its fullest development, in point of size, organization, and number; and then, after the times of the Cretaceous deposits have begun, we find yet another remarkable monstrosity of displacement introduced among all the fishes of one very numerous order, and among no inconsiderable proportion of the fishes of another. In the newly-introduced Ctenoids, (Acanthopterygii,) and in those families of the Cycloids which Cuvier erected into the order Malacopterygii sub-brachiati, the hinder limbs are brought forward, and stuck on to the base of the previously misplaced fore limbs. All the four limbs, by a strange monstrosity of displacement, are crowded into the place of the extinguished neck. And such, at the present day, is the prevalent type among fishes. Monstrosity through defect is also found to increase; so that the snake-like apoda, or feet-wanting fishes, form a numerous order, some of whose genera are devoid, as in the common eels and the congers, of only the hinder limbs, while in others, as in the genera Muræna and Synbranchus, both hinder and fore limbs are wanting. In the class of fishes, as fishes now exist, we find many more evidences of the monstrosity which results from both the misplacement and defect of parts, than in the other three classes of the vertebrata united, and knowing their geological history better than that of any of the others, we know, in consequence, that the monstrosities did not appear early, but late, and that the progress of the race as a whole, though it still retains not a few of the higher forms, has been a progress, not of development from the low to the high, but of degradation from the high to the low.

The reader may mark for himself, in the flounder, plaice, halibut, or turbot,—fishes of a family of which there appears no trace in the earlier periods,—an extreme example of the degradation of distortion superadded to that of displacement. At a first glance the limbs seem but to exhibit merely the amount of natural misarrangement and misorder common to the Acanthopterygii and Sub-brachiati;—the base of the pectorals are stuck on to the head, and the base of the ventrals attached to that of the pectorals. From the circumstance, however, that the creature is twisted half round and laid on its side, we find that at least one of the pairs of double fins—the pectorals—perform the part of single fins,—one projecting from the animal’s superior, the other from its inferior side, in the way the anal and dorsal fins project from the upper and under surfaces of other fishes; while its real dorsal and anal fins, both developed very largely, and—in order to preserve its balance—in about an equal degree, and wonderfully correspondent in form, perform, from their lateral position, the functions of single fins. Indeed, at a first glance they seem the analogues of the largely-developed pectorals of a very different family of flat fishes,—the Rays. It would appear as if single and double fins, by some such mutual agreement as that which, according to the old ballad, took place between the churl of Auchtermuchty and his wife, had agreed to exchange callings, and perform each the work of the other. The tail, too, possesses, in consequence of the twist, not the vertical position of other fish-tails, but is spread out horizontally, like the tails of the cetacea. It is however, in the head of the flounder and its cogeners that we find the more extraordinary distortions exemplified. In order to accommodate it to the general twist, which rendered lateral what in other fishes is dorsal and abdominal, and dorsal and abdominal what in other fishes is lateral, one half its features had to be twisted to the one side, and the other half to the other. The face and cranium have undergone such a change as that which the human face and cranium would undergo, were the eyes to be drawn towards the left ear, and the mouth towards the right. The skull, in consequence, exhibits, in its fixed bones, a strange Cyclopean character, unique among the families of creation: it has its one well-marked eye orbit opening, like that of Polyphemus, direct in the middle of the fore part of its head; while the other, external to the cranium altogether, we find placed among the free bones, directly over the maxillaries. And the wry mouth—twisted in the opposite direction, as if to keep up such a balance of deformity as that which the breast-hump of a hunchback forms to the hump behind—is in keeping with the squint eyes. The jaws are strangely asymmetrical. In symmetrical fishes the two bones that compose the anterior half of the lower jaw are as perfectly correspondent in form and size as the left hand or left foot is correspondent, in the human subject, to the right hand or right foot; but not such their character in the flounder. The one is a broad, short, nearly straight bone; the other is larger, narrower, and bent like a bow; and while the one contains only from four to six teeth, the other contains from thirty to thirty-five. Scarcely in the entire ichthyic kingdom are there any two jaws that less resemble one another than the two halves of the jaw of the flounder, turbot, halibut, or plaice. The intermaxillary bones are equally ill matched: the one is fully twice the size of the other, and contains about thrice as many teeth. That bilateral symmetry of the skeleton which is so invariable a characteristic of the vertebrata, that ordinary observers, who have eyes for only the rare and the uncommon, fail to remark it, but which a Newton could regard as so wonderful, and so thoroughly in harmony with the uniformity of the planetary system, has scarce any place in the asymmetrical head of the flounder. There exists in some of our north country fishing villages an ancient apologue, which, though not remarkable for point or meaning, at least serves to show that this peculiar example of distortion the rude fishermen of a former age were observant enough to detect. Once on a time the fishes met, it is said, to elect a king; and their choice fell on the herring. “The herring king!” contemptuously exclaimed the flounder, a fish of consummate vanity, and greatly piqued on this occasion that its own presumed claims should have been overlooked; “where, then, am I?” And straightway, in punishment of its conceit and rebellion, “its eyes turned to the back of its head.” Here is there a story palpably founded on the degradation of misplacement and distortion, which originated ages ere the naturalist had recognized either the term or the principle.

It would be an easy matter for an ingenious theorist, not much disposed to distinguish between the minor and the master laws of organized being, to get up quite as unexceptionable a theory of degradation as of development. The one-eyed, one-legged Chelsea pensioner, who had a child, unborn at the time, laid to his charge, agreed to recognize his relationship to the little creature, if, on its coming into the world, it was found to have a green patch over its eye, and a wooden leg. And, in order to construct a hypothesis of progressive degradation, the theorist has but to take for granted the transmission to other generations of defects and compensating redundancies at once as extreme and accidental as the loss of eyes or limbs, and the acquisition of timber legs or green patches. The snake, for instance, he might regard as a saurian, that, having accidentally lost its limbs, exerted itself to such account throughout a series of generations, in making up for their absence, as to spin out for itself, by dint of writhing and wriggling, rather more than a hundred additional vertebræ, and to alter, for purposes of greater flexibility, the structure of all the rest. And as fishes, when nearly stunned by a blow, swim for a few seconds on their side, he might regard the flounders as a race of half-stunned fishes, previously degraded by the misplacement of their limbs, that, instead of recovering themselves from the blow given to some remote parent of the family, had expended all their energies in twisting their mouths round to what chanced to be the under side on which they were laid, and their eyes to what chanced to be the upper, and that made their pectorals serve for anal and dorsal fins, and their anal and dorsal fins serve for pectorals. But while we must recognize in nature certain laws of disturbance, if I may so speak, through which, within certain limits, traits which are the result of habit or circumstance in the parents are communicated to their offspring, we would err as egregiously, did we take only these into account, without noting that infinitely stronger antagonist law of reproduction and restoration which, by ever gravitating towards the original type, preserves the integrity of races, as the astronomer would, who, in constructing his orrery, recognized only that law of propulsion through which the planets speed through the heavens, without taking into account that antagonist law of gravitation which, by maintaining them in their orbits, insures the regularity of their movements. The law of restoration would recover and right the stunned fish laid on its side; the law of reproduction would give limbs to the offspring of the mutilated saurian. We have evidence, in the extremeness of the degradation in these cases, that it cannot be a degradation hereditarily derived from accident. Nature is, we find, active, not in perpetuating the accidental wooden legs and green patches of ancestors in their descendants, but in restoring to the offspring the true limbs and eyes which the parents have lost. It is, however, not with a theory of hereditary degradation, but a hypothesis of gradual development, that I have at present to deal; and what I have to establish as proper to the present stage of my argument is, that this principle of degradation really exists, and that the history of its progress in creation bears directly against the assumption that the earlier vertebrata were of a lower type than the vertebrata of the same ichthyic class which exist now.

The progress of the ichthyic tail, as recorded in geologic history, corresponds with that of the ichthyic limbs. And as in the existing state of things we find fishes that nearly represent, in this respect, all the great geologic periods,—I say nearly, not fully, for I am acquainted with no fish adequately representative of the period of the Old Red Sandstone,—it may be well to cast a glance over the contemporary series, as illustrative of the consecutive one. In those Placoids of the shark family that to a large brain unite homological symmetry of organization, and represent the fishes of the first period, we find, as I have already shown, that the vertebræ gradually diminish in the caudal division of the column, until they terminate in a point,—a circumstance in which they resemble not merely the betailed reptiles, but also all the higher mammiferous quadrupeds, and even man himself. And it is this peculiarity, stamped upon the less destructible portions of the framework of the tail,—vertebræ and processes,—rather than the one-sided or heterocercal form of the surrounding fin, composed of but a mucoidal substance, that constitutes its grand characteristic; seeing that in some Placoid genera, such as Scyllium Stellare, the terminal portion of the fin is scarce less largely developed above than below, and that in others, as in most of the Ray family, the under lobe of the fin is wholly wanting. In the sturgeon,—one of the few Ganoids of the present time,—we become sensible of a peculiar modification in this heterocercal type of tail: the lower lobe is, we find, composed, as in Spinax and Scyllium, of rays exclusively; while through the centre of the upper lobe there runs an acutely angular patch of lozenge-shaped plates, like that which runs through the centre of the double fins of Dipterus and the Cœlacanths. But while in the sharks the gradually diminishing vertebræ stand out in bold relief, and form the thickest portion of the tail, that which represents them in the sturgeon (the angular patch) is slim and thin,—slimmer in the middle than even at the sides;—in part a consequence, no doubt, of the want, in this fish, of solid vertebræ, but a consequence also of the extreme attenuation of the nervous cord, in its prolongation into the lobe of the fin. Further, the rays of the tail—its peculiarly ichthyic portion, which are purely mucoidal in Spinax, Scyllium, and Cestracion—have become osseous in the sturgeon. The fish has set and become fixed, as cement sets in a building, or colors are fixed by a mordant. And it is worthy of special remark that, correspondent with the peculiarly ichthyic development of tail in this fish, we find the prevailing ichthyic displacement of the fore limbs. Again, in the Lepidosteus, another of the true Ganoids which still exist, the internal angle of the upper lobe of the tail wholly disappears, and with the internal angle the prolongation of the nervous cord. Still, however, it is what the tail of the sturgeon would become were the angular patch to be obliterated, and rays substituted instead,—it is a tail set on awry. And in this fish also we find the ichthyic displacement of fore limb. One step more, and we arrive at the homocercal or equal-lobed tail, which seems to attain to its most extreme type in those fishes in which, as in the perch and flounder, the last vertebral joint, either very little or very abruptly diminished in size, expands into broad processes without homologue in the higher animals, on which the caudal rays rest as their bases. And in by much the larger proportion of these fishes all the four limbs are slung round the neck;—they at once exhibit the homocercal tail in its broadest type, and displacement of limb in its most extreme form.

TAIL OF OSTEOLEPIS.]

TAIL OF LEPIDOSTEUS OSSEUS.]

Now, in tracing the geologic history of the ichthyic tail, we find these several steps or gradations from the heterocercal to the homocercal, represented by periods and formations. The Siluran periods may be regarded as representative of that true heterocercal tail of the Placoids, exemplified in Spinax, (page 172, fig. 48,) and Cestracion, (page 177, fig. 49.) The whole caudal portion of this latter animal, commencing immediately behind the ventrals, is, as becomes a true tail, slim, when compared with its trunk; the vertebræ are of very considerable solidity; the rays mucoidal; and where the spinal column runs into the terminal fin, it takes such an upward turn as that which the horse-jockey imparts, by the process of nicking, to the tails of the hunter and the racehorse. And with the heterocercal tail, so true in its homologies to the tails of the higher vertebrata, we find associated, as has been shown, the true homological position of the fore limbs. With the commencement of the Old Red Sandstone the ganoidal tail first presents itself; and we become sensible of a change in the structure of the attached fin, similar to that exemplified in the caudal rays of the sturgeon. As shown by the irregularly-angular patch of scales which in all the true Cœlacanths, and almost all the Dipterians, runs through the upper lobe of the fin, and terminates in a point, (see fig. 50,) it must have possessed the gradually diminishing vertebræ, or a diminishing spinal cord, their analogue; but the rays, fairly set, as their state of keeping in the rocks certify, exist as narrow oblong plates of solid bone; and their anterior edges are strengthened by a line of osseous defences, that pass from scales into rays. And in harmonious accompaniment with this fairly stereotyped edition of the ichthyic tail, we find, in the fishes in which it appears, the first instance of displacement of limb,—the bases of the pectorals being removed from their original position, and stuck on to the nape of the neck. It may be remarked, in passing, that in the tails of two ganoidal genera of this period,—the Coccosteus and Pterichthys,—the analogies traceable lie rather in the direction of the tails of the Rays than in those of the Sharks; and that one of these, the Coccosteus, seems, as has been already intimated, to have had no pectorals, while it is doubtful whether in the Pterichthys the pectorals were not attached to the shoulder, instead on the head. In the Carboniferous and Permian systems there occur, especially among the numerous species of the genus Palæoniscus, tails of the type exemplified by the internal angle of the tail of the sturgeon: the lozenge-shaped scales run in acutely angular patches through their upper lobes; but such is their extreme flatness, as shown by the disposition of the enamelled covering, that it appears exceedingly doubtful whether any vertebral column ran beneath;—they seem but to have covered greatly diminished prolongations of the spinal cord. In the base of the Secondary division,—another long stage towards the existing state of things,—we find, with the homocercal tail, which now appears for the first time, numerous tails like that of the Lepidosteus, (fig. 51,) of an intermediate type;—they are rather tails set on awry than truly heterocercal. The diminished cord has disappeared from among the fin rays. In the numerous Lepidoid genus, and the genera Semionotus and Tetra gonolepis,—all ganoidal fishes of the Secondary period—this intermediate style is very marked; while in their contemporaries of the genera Uræus, Microdon, and Pycnodus, we find the earliest examples of true homocercal tails. And in the Ctenoids and Cycloids of the Chalk the homocercal tail receives its fullest development. It finds bases for its rays in broad non-homological processes, that spread out behind abruptly-terminating vertebræ, (fig. 52,) in the same period in which, by a strange process of degradation, the four ichthyic limbs are first gathered into a cluster, and hung about the neck.

TAIL OF PERCH.]

I am aware that by some very distinguished comparative anatomists, among the rest Professor Owen, the attachment, so common among fishes, of the scapular arch and the fore limbs to the occipital bone, is regarded, not as a displacement, but as a normal and primary condition of the parts. Recognizing in the scapular bones the ribs of the occipital centrum, the anatomists of this school of course consider them, when found articulated to the occiput, as in their proper and original place, and as in a state of natural dislocation when removed, as in all the reptiles, birds, and mammals, farther down. We find Professor Oken borrowing support to his hypothesis from this view. The limbs, he tells us, are simply ribs, that in the course of ages have been set free, and have become by development what they now are. And it is unquestionably a curious and interesting fact, that there are certain animals, such as the crocodile, in which every centrum of the vertebral column, and of every vertebra of the head, has its ribs or rib-like appendages, with the exception of the occipital centrum. And it is another equally curious fact, that there is another certain class of animals, such as the osseous horn-covered fishes, with the Sturionidæ, Salamandroidei, and at least one genus among the Placoids, (the Chimæroidei,) in which this occipital centrum bears as its ribs the scapular bones, with their appendages the fore limbs. It is the centrum without ribs that is selected in these animals as the centrum to which the scapular ribs should be attached. Be it remembered, however, that while it is unquestionably the part of the comparative anatomist to determine the relations and homologies of those parts of which all animals are composed, and to interpret the significancy in the scale of being of the various modes and forms in which they exist, it is as unquestionably the part of the geologist to declare their history, and the order of their succession in time. The questions which fall to be determined by the geologist and anatomist are entirely different. It is the function of the anatomist to decide regarding the high and the low, the typical and the aberrant; and so, beginning at what is lowest or highest in the scale, or least or most symmetrical in type, he passes through the intermediate forms to the opposite extreme: and such is the order natural and proper to his science. It is the vocation of the geologist, on the other hand, to decide regarding the early and the late. It is with time, not with rank, that he has to deal. Nor is it in the least surprising that he should seem at issue with the comparative anatomist, when, in classifying his groupes of organized being according to the periods of their appearance, there is an order of arrangement forced upon him, different from that which, on an entirely different principle, the anatomist pursues. Nor can there be a better illustration of a collision of this kind, than the one furnished by the case in point. That peculiarity of structure which, as the lowest in the vertebral skeleton, is to the comparative anatomist the primary and original one, and which, as such, furnishes him with his starting point, is to the geologist not primary, but secondary, simply because it was not primary, but secondary, in the order of its occurrence. It belongs, so far as we yet know, not to the first period of vertebrate existence, but to the second; and appears in geologic history as does that savage state which certain philosophers have deemed the original condition of the human species, in the history of civilization, when read by the light of the Revealed Record, under the shadow of those gigantic ruins of the East that date only a few centuries after the Flood. It is found to be a degradation first introduced during the lapse of an intermediate age,—not the normal condition which obtained during the long cycles of the primal one. It indicates, not the starting point from which the race of creation began, but the stage of retrogradation beyond it at which the pilgrims who set out in a direction opposite to that of the goal first arrived.

This fact of degradation, strangely indicated in geologic history, with reference to all the greater divisions of the animal kingdom, has often appeared to me a surpassingly wonderful one. We can see but imperfectly, in those twilight depths to which all such subjects necessarily belong; and yet at times enough does appear to show us what a very superficial thing infidelity may be. The general advance in creation has been incalculably great. The lower divisions of the vertebrata preceded the higher;—the fish preceded the reptile, the reptile preceded the bird, the bird preceded the mammiferous quadruped, and the mammiferous quadruped preceded man. And yet, is there one of these great divisions in which, in at least some prominent feature, the present, through this mysterious element of degradation, is not inferior to the past? There was a time in which the ichthyic form constituted the highest example of life; but the seas during that period did not swarm with fish of the degraded type. There was, in like manner, a time when all the carnivora and all the herbivorous quadrupeds were represented by reptiles; but there are no such magnificent reptiles on the earth now as reigned over it then. There was an after time, when birds seem to have been the sole representatives of the warm-blooded animals; but we find, from the prints of their feet left in sandstone, that the tallest men might have

“Walked under their huge legs, and peeped about.”

Further, there was an age when the quadrupedal mammals were the magnates of creation; but it was an age in which the sagacious elephant, now extinct, save in the comparatively small Asiatic and African circles, and restricted to two species, was the inhabitant of every country of the Old World, from its southern extremity to the frozen shores of the northern ocean; and when vast herds of a closely allied and equally colossal genus occupied its place in the New. And now, in the times of the high-placed human dynasty,—of those formally delegated monarchs of creation, whose nature it is to look behind them upon the past, and before them, with mingled fear and hope, upon the future,—do we not as certainly see the elements of a state of ever-sinking degradation, which is to exist for ever, as of a state of ever-increasing perfectibility, to which there is to be no end? Nay, of a higher race, of which we know but little, this much we at least know, that they long since separated into two great classes,—that of the “elect angels,” and of “angels, that kept not their first estate.”

EVIDENCE OF THE SILURIAN MOLLUSCS—OF THE FOSSIL FLORA. ANCIENT TREE.

After dwelling at such length on the earlier fishes, it may seem scarce necessary to advert to their lower contemporaries the mollusca,—that great division of the animal kingdom which Cuvier places second in the descending order, in his survey of the entire series, and first among the invertebrates; and which Oken regards as the division out of which the immediately preceding class of the vertebral animals have been developed. “The fish,” he says, “is to be viewed as a mussel, from between whose shells a monstrous abdomen has grown out.” There is, however, a peculiarity in the molluscan group of the Silurian system, to which I must be permitted briefly to refer, as, to employ the figure of Sterne, it presents “two handles” of an essentially different kind, and as in all such two-handled cases, the mere special pleader is sure to avail himself of only the handle which best suits his purpose for the time.

Cuvier’s first and highest class of the molluscs is formed of what are termed the Cephalopods,—a class of creatures possessed of great freedom of motion: they can walk, swim, and seize their prey; they have what even the lowest fishes such as the lancelet, want,—a brain enclosed in a cartilaginous cavity in the head, and perfectly formed organs of sight; they possess, too, what is found in no other mollusc,—organs of hearing; and in sagacity and activity they prove more than matches for the smaller fishes, many of which they overmaster and devour. With this highest class there contrasts an exceedingly low molluscous class at the bottom of the scale, or, at least, at what is now the bottom of the scale; for they constitute Cuvier’s fifth class; while his sixth and last, the Cirrhopodes, has been since withdrawn from the molluscs altogether, and placed in a different division of the animal kingdom. And this low class, the Brachiopods, are creatures that, living in bivalve shells, unfurnished with spring hinges to throw them open, and always fast anchored to the same spot, can but thrust forth, through the interstitial chinks of their prison-houses, spiral arms, covered with cilia, and winnow the water for a living. Now, it so happens that the molluscan group of the Silurian system is composed chiefly of these two extreme classes. It contains some of the other forms; but they are few in number, and give no character to the rocks in which they occur. There was nothing by which I was more impressed, in a visit to a Silurian region, than that in its ancient graveyards, as in those of the present day, though in a different sense, the high and the low should so invariably meet together. It is, however, not impossible that, in even the present state of things, a similar union of the extreme forms of the marine mollusca may be taking place in deep-sea deposits. Most of the intermediate forms provided with shells capable of preservation, such as the shelled Gasteropoda and the Conchifers, are either littoral, or restricted to comparatively small depths; whereas the Brachiopoda are deep-sea shells; and the Cephalopoda may be found voyaging far from land, in the upper strata of the sea above them. Even in the seas that surround our own island, the Brachiopodous molluscs—terebratula and crania—have been found, ever since deep-sea dredging became common, to be not very rare shells; and in the Mediterranean, where they are less rare still, fleets of Argonauts, the representatives of a highly organized family of the Cephalopods, to which it is now believed the Bellerophon of the Palæozoic rocks belonged, may be seen skimming along the surface, with sail and oar, high over the profound depths in which they lie. And, of course, when death comes, that comes to high and low, the remains of both Argonauts and Brachiopods must lie together at the bottom, in beds almost totally devoid of the intermediate forms.

Now, the author of the “Vestiges,” in maintaining his hypothesis, suspends it on the handle furnished him by the immense abundance of the Silurian Brachiopods. The Silurian period, he says, exhibits “a scanty and most defective development of life; so much so, that Mr. Lyell calls it, par excellence, the age of Brachiopods, with reference to the by no means exalted bivalve shell-fish which forms its predominant class. Such being the actual state of the case, I must persist in describing even the fauna of this age, which we now know was not the first, as, generally speaking, such a humble exhibition of the animal kingdom as we might expect, upon the development theory, to find at an early stage of the history of organization.” The reader will at once discern the fallacy here. The Silurian period was peculiarly an age of Brachiopods, for in no other period were Brachiopods so numerous, specifically or individually, or of such size or importance; whereas it was not so peculiarly an age of Cephalopods, for these we find introduced in still greater numbers during the Liasic and Oolitic periods. In 1848, when Professor Edward Forbes edited the Palæontological map of Britain and Ireland, which forms one of the very admirable series of “Johnstone’s Physical Atlas,” the Cephalopods of the Silurian rocks of England and Wales were estimated at forty-eight species, and the Brachiopods at one hundred and fifty; whereas at the same date there were two hundred and five Cephalopods of the Oolitic formations enumerated, and but fifty-four Brachiopods. It is the molluscs of the inferior, not those of the superior class, that constitute (with their contemporaries the Trilobites) the characteristic fossils of the Silurian rocks; and hence the propriety of the distinctive name suggested by Sir Charles Lyell. But in the development question, what we have specially to consider is, not the numbers of the low, but the standing of the high. A country may be distinctively a country of flocks and herds, or a country of the carnivorous mammalia, or, like New South Wales or the Galapagos, a country of marsupial animals or of reptiles. Its human inhabitants may be merely a few hunters or shepherds, too inconsiderable in numbers, and too much like their brethren elsewhere, to give it any peculiar standing as a home of men. But in estimating the highest point in the scale to which the animal kingdom has attained within its limits, it is of its few men, not of its many beasts, that we must take note. And the point to be specially decided regarding the organisms of the Silurian system, in this question, is, not the proportion in number which the lower forms bore to the higher, but the exact rank which the higher bore in the scale of existence. Did the system furnish but a single Cephalopod or a single fish, we would yet have as certainly to determine that the chain of being reached as high as the Cephalopod or the fish, as if the remains of these creatures constituted its most abundant fossils. The chain of animal life reached quite as high on the evening of the sixth day of creation, when the human family was restricted to a single pair, as it does now, when our statists reckon up by millions the inhabitants of the greater capitals of the world; and the special pleader who, in asserting the contrary, would insist on determining the point, not by the rank of the men of Eden, but by the number of minnows or sticklebacks that swarmed in its rivers, might be perhaps deemed ingenious in his expedients, but certainly not very judicious in the use of them. It is worthy of remark, however, that the Brachiopods of those Palæozoic periods in which the group occupied such large space in creation, consisted of greatly larger and more important animals than any which it contains in the present day. It has yielded to what geological history shows to be the common fate, and sunk into a state of degradation and decline.

The geological history of the vegetable, like that of the animal kingdom, has been pressed into the service of the development hypothesis; and certainly their respective courses, both in actual arrangement and in their relation to human knowledge, seem wonderfully alike. It is not much more than twenty years since it was held that no exogenous plant existed during the Carboniferous period. The frequent occurrence of Coniferæ in the Secondary deposits had been conclusively determined from numerous specimens; but, founding on what seemed a large amount of negative evidence, it was concluded that, previous to the Liasic age, nature had failed to achieve a tree, and that the rich vegetation of the Coal Measures had been exclusively composed of magnificent immaturities of the vegetable kingdom,—of gigantic ferns and club-mosses, that attained to the size of forest trees, and of thickets of the swamp-loving horsetail family of plants, that well nigh rivalled in height those forests of masts which darken the rivers of our great commercial cities. Such was the view promulgated by M. Adolphe Brongniart; and it may be well to remark that, so far as the evidence on which it was based was positive, the view was sound. It is a fact, that inferior orders of plants were developed in those ages in a style which, in their present state of degradation, they never exemplify: they took their place, not, as now, among the pigmies and abortions of creation, but among its tallest and goodliest productions. It is, however, not a fact that they were the highest vegetable forms of their time. True exogenous trees also existed in great numbers and of vast size. In various localities in the coal fields of both England and Scotland,—such as Lennel Braes and Allan Bank in Berwickshire, High-Heworth, Fellon, Gateshead, and Wideopen near Newcastle-upon-Tyne, and in quarries to the west of the city of Durham,—the most abundant fossils of the system are its true woods. In the quarry of Craigleith, near Edinburgh, three huge trunks have been laid open during the last twenty years, within the space of about a hundred and fifty yards, and two equally massy trunks, within half that space, in the neighboring quarry of Granton, all low in the Coal Measures. They lie diagonally athwart the strata,—at an angle of about thirty,—with the nether and weightier portion of their boles below, like snags in the Mississippi; and we infer, from their general direction, that the stream to which they reclined must have flowed from nearly north-east to south-west. The current was probably that of a noble river, which reflected on its broad bosom the shadow of many a stately tree. With the exception of one of the Granton specimens, which still retains its strong-kneed roots, they are all mere portions of trees, rounded at both ends as if by attrition or decay; and yet one of these portions measures about six feet in diameter by sixty-one feet in length; another four feet in diameter by seventy feet in length; and the others, of various thickness, but all bulky enough to equal the masts of large vessels, range in length from thirty-six to forty-seven feet. It seems strange to one who derives his supply of domestic fuel from the Dalkeith and Falkirk coal-fields, that the Carboniferous flora could ever have been described as devoid of trees. I can scarce take up a piece of coal from beside my study fire, without detecting in it fragments of carbonized wood, which almost always exhibit the characteristic longitudinal fibres, and not unfrequently the medullary rays. Even the trap-rocks of the district enclose, in some instances, their masses of lignite, which present in their transverse sections, when cut by the lapidary, the net-like reticulations of the coniferæ. The fossil botanist, who devoted himself chiefly to the study of microscopic structure, would have to decide, from the facts of the case, not that trees were absent during the Carboniferous period, but that, in consequence of their having been present in amazing numbers, their remains had entered more palpably and extensively into the composition of coal than those of any other vegetable. So far as is yet known, they all belonged to the two great divisions of the coniferous family, araucarians and pines. The huge trees of Craigleith and Granton were of the former tribe, and approximate more nearly to Altingia excelsa, the Norfolk-Island pine,—a noble araucarian, that rears its proud head from a hundred and sixty to two hundred feet over the soil, and exhibits a green and luxuriant breadth of foliage rare among the Coniferæ,—than any other living tree.