Part 14

Let the reader now mark the use which has been made, by the author of the “Vestiges,” of the name and authority of Linnæus. “Linnæus,” he states, “was so impressed by the low character of many of this order, (the _Chondropterygii_,) that he actually ranked them with worms.” Now, what is the fact here? Simply that Linnæus had no such general order as the _Chondropterygii_ in his eye at all. Though chiefly remarkable as a naturalist for the artificialness of his classifications, his estimate of the cartilaginous fishes was remarkable—though carried too far in its extremes, and in some degree founded in error—for an opposite quality. It was an estimate formed, in the main, on a natural basis. Instead of taking their cartilaginous skeleton into account, he looked chiefly at their standing as animals; and, struck with that extent of front which they present, and with both their superiority on the extreme right, and their inferiority on the extreme left, to the ordinary fishes, he erected them into two separate orders, the one lower and the other higher than the members of the osseous line. And so far was he from regarding the true Placoids—those _Chondropterygii_ which to an internal skeleton of cartilage add external plates, points, or spines of bone—as low in the scale, that he actually raised them above fishes altogether, by erecting them into an order of reptiles,—the older _Amphibia Nantes_. Surely, if the name of Linnæus was to be introduced into this controversy at all, it ought to have been in connection with _this_ special fact; seeing that the point to be determined in the question under discussion is simply the place and standing of that very order which the naturalist rated so high,—not the place and standing of the order which he degraded. It so happens that there is one of the _Chondropterygii_ which, so far from being a true Placoid, does not possess a single osseous plate, point, or spine: it is a worm like creature, without eyes, without movable jaws, without vertebral joints, without scales, always enveloped in slime, and greatly abhorred by our Scotch boatmen of the Moray Frith, who hold that it burrows, like the grave-worm, in the decaying bodies of the dead. And this creature, “the glutinous hag,” or, according to north-country fishermen, the “ramper-eel,” or “poison-ramper,” was regarded by Linnæus as belonging, not to the class of fishes, but to the Vermes. Now, _this_ is the special fact with which, in the development controversy, the author of the “Vestiges” connects the name of the Swedish naturalist! All the fish of the Silurian System belonged to that true Placoid order which Linnæus, impressed by its high standing, erected into an order, not of worms, but of reptiles. He elevated A, the true Placoid, while he degraded B, the glutinous hag. But it was necessary to the argument of the author of the “Vestiges” that the earliest existing fish should be represented as fish low in the scale; and so he has cited the name and authority of Linnæus in its bearing against the glutinous hag B, as if it had borne against the standing of the true Placoid A. The Patagonians are the tallest and bulkiest men in the world, whereas their neighbors, the Fuegians are a slim and diminutive race. And if, in some controversy raised regarding the real size of the more gigantic tribe, they were to be described as the “very _tallest_ types of their class,” any statement in reply, to the effect that some trustworthy voyager had examined certain races of the extreme south of America, and had found that they were both short and thin, would be neither relevant in its facts nor legitimate in its bearing. But if the controversialist who thus strove to strengthen his case by the voyager’s authority, was at the same time fully aware that the voyager had seen not only the diminutive Fuegians, but also the gigantic Patagonians, and that he had described these last as very gigantic indeed, the introduction of the statement regarding the smaller race, when he wholly sank the statement regarding the larger, would be not merely very irrelevant in the circumstances, but also very unfair. Such, however, is the style of statement to which the author of the “Vestiges” has (I trust inadvertently) resorted in this controversy.

It is not uninstructive to mark how slowly and gradually the naturalists have been groping their way to a right classification in the ichthyic department of their science, and how it has been that identical perception of resemblance, having _cartilage_ for its general idea, to which the author of the “Vestiges” attaches so much importance, that has served mainly to retard their progress. Not a few of the more distinguished among their number deemed it too important a distinction to be regarded as merely secondary; and so long as it was retained as a primary characteristic, the fishes failed to range themselves in the natural order;—dissimilar tribes were brought into close neighborhood, while tribes nearly allied were widely separated. It failed, as has been shown, to influence Linnæus; and though he no doubt pressed his peculiar views too far when he degraded the glutinous hag into a worm, and elevated the Sharks and Rays into reptiles, it is certainly worthy of remark, that, in the scheme of classification which is now regarded as the _most natural_,—that of Professor Muller, modified by Professor Owen,—the ichthyic worms of the Swede are placed in the first and lowest order of fishes,—the _Dermopteri_,—and the greater part of his ichthyic reptiles, in the eleventh and highest,—the _Plagiostomi_. Cuvier yielded, as has been shown, to the idea of resemblance founded on the _material_ of the ichthyic framework, and so ranged his fishes into two parallel lines. Professor Oken, after first enunciating as law that “the characteristic _organ_ of fishes is the osseous system,” confessed the “great difficulty” which attaches to the question of skeletal “texture or substance,” and finally gave up the distinction founded on it as obstinately irreducible to the purposes of a natural classification. “The cartilaginous fishes,” he says, “appear to belong to each other, and are also usually arranged together; yet amongst them we find those species, such as the Lampreys, which obviously occupy the lowest grade of all fishes, while the Sharks and Rays remind us of the Reptilia.” And so, sinking the consideration of texture altogether, he placed the family of the Lamprey, including the glutinous hag, at the bottom of the scale, and the Sharks and Rays at the top. Agassiz’s system, peculiarly his own, has had the rare merit, as I have shown, of furnishing a key to the history of the fish in its several dynasties, which we may in vain seek in any other. His divisions,—if, retaining his strongly-marked Placoids and Ganoids, as orders stamped in the mint of nature, we throw his perhaps less obviously divisible Ctenoids and Cycloids into one order,—the corneous or horn-covered,—are scarcely less representative of periods than those great classes of the vertebrata, mammals, birds, reptiles, and fishes, which we find not less regularly ranged in their order of succession in the geologic record than in the “Animal Kingdom” of Cuvier,—a shrewd corroboration, in both cases, I am disposed to think, of the rectitude of the arrangement. What seems to be the special defect of his system is, that having erected his four orders, and then finding a certain number of residuary families that, on his principle of cuticular character, stubbornly refused to fall into any determinate place, he distributed them among the others, with reference chiefly to the totally distinct principle of Cuvier. Thus the _Suctorii_, soft, smooth, slimy-skinned fishes, that do not possess a single placoid character, and are not true Placoids, he has yet placed in his Placoid order, influenced, apparently, by the “perception of resemblance that has _cartilage_ for its central idea;” and the effect has been a massing into one anomalous and entangled group the fishes of the first period of geologic history, with fishes of which we do not find a trace save in the existing scene of things, and of the highest families of their class with families that occupy the lowest place. But we live in an age in which even the benefactors of the world of mind cannot make false steps with impunity; and so, while Agassiz’s _three_ ichthyic orders will continue to be recognized by the palæontologist as the orders of three great geologic periods, the _Suctorii_ have already been struck from off his higher fishes by the classification of Muller and Owen, and carried to that lowest point in the scale (indicated by Linnæus and Oken) which their inferior standing renders so obviously the natural one. Some of my readers may perhaps remember how finely Bacon, in his “Wisdom of the Ancients,” interprets the old mythologic story of Prometheus. Prometheus, says the philosopher, had conferred inestimable favors on men, by moulding their forms into shape, and bringing them fire from heaven; and yet they complained of him and his teachings to Jupiter. And the god, instead of censuring their ingratitude, was pleased with the complaint, and rewarded them with gifts. In putting nature to the question, it is eminently wholesome to be doubting, cross-examining, complaining; ever demanding of our masters and benefactors the philosophers, that they should reign over us, not arbitrarily and despotically,

“Like the old kings, with high exacting looks, Sceptred and globed,”

but like our modern constitutional monarchs, who govern by law; and, further, that an appeal from their decisions on all subjects within the jurisdiction of Nature should for ever be open to Nature herself. The seeming ingratitude of such a course, if the “complaints” be made in a right spirit and on proper grounds, Jupiter always rewards with gifts.

Let us now see for ourselves, in this spirit, whether there may not be something absolutely derogatory, in the existence of a cartilaginous skeleton, to the creatures possessing it; or whether a deficit of internal bone may not be greatly more than neutralized, as it assuredly must have been in the view of Linnæus, Muller, and Owen, by a larger than ordinary share of a vastly more important substance.

THE PLACOID BRAIN. EMBRYONIC CHARACTERISTICS NOT NECESSARILY OF A LOW ORDER.

That special substance, according to whose mass and degree of development all the creatures of this world take rank in the scale of creation, is not _bone_, but _brain_. Were animals to be ranged according to the solidity of their bones, the class of birds would be assigned the first place; the family of the _Felidæ_, including the tiger and lion, the second; and the other terrestrial carnivora the third. Man and the herbivorous animals, though tolerably low in the scale, would be in advance of at least the reptiles. Most of these, however, would take precedence of the sagacious _Delphinidæ_; the osseous fishes would come next in order; the true Placoids would follow, succeeded by the _Sturiones_; and the _Suctorii_, _i. e._ Cyclostomi or Lampreys, would bring up the rear. There would be evidently no order here: the utter confusion of such an arrangement, like that of the bits of a dissected map flung carelessly out of its box by a child, would of itself demonstrate the inadequacy and erroneousness of the regulating principle. But how very different the appearance presented, when for _solidity of bone_ we substitute _development of brain_! Man takes his proper place at the head of creation; the lower mammalia follow,—each species in due order, according to its modicum of intelligence; the birds succeed the mammalia; the reptiles succeed the birds; the fishes succeed the reptiles; next in the long procession come the invertebrate animals; and these, too, take rank, if not according to their development of brain proper, at least according to their development of the _substance_ of brain. The occipital nervous ganglion of the scorpion greatly exceeds in size that of the earthworm; and the occipital nervous ring of the lobster, that of the intestinal Ascaris. At length, when we reach the lowest or _acrite_ division of the animal kingdom, the substance of brain altogether disappears. It has been calculated by naturalists, that in the vertebrata, the brain in the class of fishes bears an average proportion to the spinal cord of about two to one; in the class of reptiles, of about two and a half to one; in the class of birds, of about three to one; in the class of mammals, of about four to one; and in the high-placed, sceptre-bearing human family, a proportion of not less than _twenty-three_ to one. It is palpably according to development of brain, not development of bone, that we are to determine points of precedence among the animals,—a fact of which no one can be more thoroughly aware than the author of the “Vestiges” himself. Of this let me adduce a striking instance, of which I shall make further use anon.

“All life,” says Oken, “is from the sea; none from the continent. Man also is a child of the warm and shallow parts of the sea in the neighborhood of the land.” Such also was the hypothesis of Lamarck and Maillet. In following up the view of his masters, the author of the “Vestiges” fixes on the _Delphinidæ_ as the sea-inhabiting progenitors of the simial family, and, through the simial family, of man For that highest order of the mammalia to which the _Simiadæ_ (monkeys) belong, “there remains,” he says, “a basis in the _Delphinidæ_, the last and smallest of the cetacean tribes. This affiliation has a special support in the brain of the dolphin family, which is distinctly allowed to be, in proportion to general bulk, the greatest among mammalia next to the orang-outang and man. We learn from Tiedemann, that each of the cerebral hemispheres is composed, as in man and the monkey tribe, of three lobes,—an anterior, a middle, and a posterior; and these hemispheres present much more numerous circumvolutions and grooves than those of any other animal. Here it might be rash to found any thing upon the ancient accounts of the dolphin,—its familiarity with man, and its helping him in shipwreck and various marine disasters; although it is difficult to believe these stories to be altogether without some basis in fact. There is no doubt, however, that the dolphin evinces a predilection for human society, and charms the mariner by the gambols which it performs beside his vessel.”

Here, then, the author of the “Vestiges” palpably founds on a large development of brain in the dolphin, and on the manifestation of a correspondingly high order of instincts,—and this altogether irrespective of the structure or composition of the creature’s internal skeleton. The substance to which he looks as all-important in the case is _brain_, not _bone_. For were he to estimate the standing of the dolphin, not by its brain, but by its skeleton, he would have to assign to it a place, not only _not_ in advance of its brethren the _mammalia_ of the sea, but even in the rear of the _reptiles_ of the sea, the marine tortoises, or turtles,—and scarce more than abreast of the osseous fishes. “Fishes,” says Professor Owen, in his “Lectures on the Vertebrate Animals,” “have the least proportion of earthy matter in their bones; birds the largest. The mammalia, especially the active, predatory species, have more earth, or harder bones, than reptiles. In each class, however, there are differences in the density of bone among its several members. For example, in the fresh-water fishes, the bones are lighter, and retain more animal matter, than in those which swim in the denser sea. And in the _dolphin_, a warm-blooded marine animal, they differ little in this respect from those of the sea-fish.” Such being the fact, it is surely but fair to inquire of the author of the “Vestiges,” why he should determine the rank and standing of the _Delphinidæ_ according to one set of principles, and the rank and standing of the Placoids according to another and entirely different set? If the _Delphinidæ_ are to be placed high in the scale, notwithstanding the softness of their skeletons, simply because their brains are large, why are the Placoids to be placed low in the scale, notwithstanding the largeness of their brains, simply because their skeletons are soft? It is not too much to demand, that on the principle which he himself recognizes as just, he should either degrade the dolphin or elevate the Placoid. For it is altogether inadmissible that he should reason on one set of laws when the exigencies of his hypothesis require that creatures with soft skeletons should be raised in the scale, and on another and entirely different set when its necessities demand that they should be depressed.

But do the Placoids possess in reality a large development of brain? I have examined the brains of almost all the common fish of our coast, both osseous and cartilaginous, not, I fear, with the skill of a Tiedemann, but all the more intelligently in consequence of what Tiedemann had previously done and written: and so I can speak with some little confidence on the subject, so far at least as my modicum of experience, thus acquired, extends. Of all the common fish of the Scottish seas, the spotted or lesser dog-fish bears, in proportion to its size, the largest brain; the gray or picked dog-fish ranks next in its degree of development; the Rays, in their various species, follow after; and the osseous fishes compose at least the great body of the rear; while still further behind, there lags a hapless class—the _Suctorii_, one of which, the glutinous hag, has scarce any brain, and one, the _Amphioxus_ or lancelet, wants brain altogether. I have compared the brain of the spotted dog-fish with that of a young alligator, and have found that in scarce any perceptible degree was it inferior, in point of bulk, and very slightly indeed in point of organization, to the brain of the reptile. And the instincts of this Placoid family,—one of the truest existing representatives of the Placoids of the Silurian System[25] to which we can appeal,—correspond, we invariably find, with their superior cerebral development. I have seen the common dog-fish, _Spinax Acanthias_, hovering in packs in the Moray Frith, some one or two fathoms away from the side of the herring boat from which, when the fishermen were engaged in hauling their nets, I have watched them, and have admired the caution which, with all their ferocity of disposition, they rarely failed to manifest;—how they kept aloof from the net, even more warily than the cetacea themselves,—though both dog-fish and cetacea are occasionally entangled;—and how, when a few herrings were shaken loose from the meshes they at once darted upon them, exhibiting for a moment, through the green depths, the pale gleam of their abdomens, as they turned upon their sides to seize the desired morsels,—a motion rendered necessary by the position of the mouth in this family; and how next, their object accomplished, they fell back into their old position, and waited on as before. And I have been assured by intelligent fishermen, that at the deep-sea white-fishing, in which baited hooks, not nets, are employed, the degree of shrewd caution exercised by these creatures seems more extraordinary still. The hatred which the fisher bears to them arises not more from the actual amount of mischief which they do him, than from the circumstance that in most cases they persist in doing it with complete impunity to themselves. I have seen, said an observant Cromarty fisherman to the writer of these chapters, a pack of dog-fish watching beside our boat, as we were hauling our lines, and severing the hooked fish, as they passed them, at a bite, just a little above the vent, so that they themselves escaped the swallowed hook; and I have frequently lost, in this way, no inconsiderable portion of a fishing. I have observed, however, he continued, that when a fresh pack of hungry dog-fish came up, and joined the pack that had been robbing us so coolly, and at their leisure, a sudden rashness would seize the whole,—the united packs would become a mere heedless mob, and, rushing forward, they would swallow our fish entire, and be caught themselves by the score and the hundred. We may see something very similar to this taking place among even the shrewder mammalia. When pig refuses to take his food, his mistress straightway calls upon the cat, and, quickened by the dread of the coming rival, he gobbles up his rations at once. With the comparatively large development of brain, and the corresponding manifestations of instinct, which the true Placoids exhibit, we find other unequivocal marks of a general superiority to their class. In their reproductive organs they rank not with the common fishes, nor even with the lower reptiles, but with the Chelonians and the Sauria. Among the Rays, as among the higher animals, there are individual attachments formed between male and female: their eggs unlike the mere spawn of the osseous fishes, or of even the Batrachians, are, like those of the tortoise and the crocodile, comparatively few in number, and of considerable size: their young, too, like the young of birds and of the higher reptiles, pass through no such metamorphosis as those of the toad and frog, or of the amphibia generally. And some of their number—the common dog-fish for instance—are ovoviviparous, bringing forth their young, like the common viper and the viviparous lizard, alive and fully formed.

“But such features,” says the author of the “Vestiges,” referring chiefly to certain provisions connected with the reproductory system in the Placoids, “are partly partaken of by families in inferior sub-kingdoms, showing that they cannot truly be regarded as marks of grade in their own class.” Nay, single features do here and there occur in the inferior sub-kingdoms, which very nearly resemble single features in the placoid character and organization, which even very nearly resemble single features in the _human_ character and organization; but is there any of the inferior sub-kingdoms in which there occurs such a _collocation_ of features? or does such a collocation occur in any class of animals—setting the Placoids wholly out of view—which is not a high class? Nay, further, does there occur in any of the inferior sub-kingdoms—existing even as a single feature—that most prominent, leading characteristic of this series of fishes,—a large brain?

But is not the “cartilaginous structure” of the Placoids analogous to the embryonic state of vertebrated animals in general? Do not the other placoid peculiarities to which the author of the “Vestiges” refers,—such as the heterocercal or one-sided tail, the position of the mouth on the under side of the head, and the rudimental state of the maxillaries and intermaxillaries,—bear further analogies with the embryonic state of the higher animals? And is not “embryonic progress the grand key to the theory of development?” Let us examine this matter. “These are the characters,” says this ingenious writer, “which, above all, I am chiefly concerned in looking to; for they are features of embryonic progress, and embryonic progress is the grand key to the theory of development.” Bold assertion, certainly; but, then, assertion is not argument! The statement is not a reason for the faith that is in the author of the “Vestiges,” but simply an avowal of it; it is simply a confession, not a defence, of the Lamarckian creed; and, instead of being admitted as embodying a first principle, it must be put stringently to the question, in order to determine whether it contain a principle at all.