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.[28]
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.
[Illustration: Fig. 50.
TAIL OF OSTEOLEPIS.]
[Illustration: Fig. 51.
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,[29] 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.[30]
[Illustration: Fig. 52.
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.[31]