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.
Fig. 49.
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 [1845] 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.