regarding it simply as a _fœtal_ one, that indicates a certain stage
of imperfection in the creature in which it occurs, on what principle,
I ask, are we to infer that what is a sign of immaturity in the young
of one set of animals, is a mark of inferior organization in the adult
forms of another set? The want of eyes in any of the animal families, or
the want of organs of progression, or a fixed and sedentary condition,
like that of the oyster, are all marks of great inferiority. And yet,
if we admit the principle, that what are evidences of immaturity in
the young members of one family are signs of inferior organization in
the fully-grown members of another, it could easily be shown that eyes
and legs are defects, and that the unmoving oyster stands higher in the
scale than the ever-restless fish or bird. The immature _Tubularia_
possess locomotive powers, whereas in their fully developed state they
remain fixed to one spot in their convoluted tubes. The immature _Lepas_
is furnished with members well adapted for swimming, and with which it
swims freely; as it rises towards maturity, these become blighted and
weak; and, when fully grown,—fixed by its fleshy pedicle to the rock or
floating log to which it attached itself in its transition state,—it is
no longer able to swim. The immature _Balanus_ is furnished with two
eyes: in its state of maturity these are extinguished, and it passes its
period of full development in darkness. Further, it is not generally held
that in the human family a white skin is a decided mark of degradation,
but rather the reverse; and yet nothing can be more certain than that
the Negro fœtus has a white skin. Since eyes, and organs of progression,
and a power of moving freely, and a white skin, are mere embryonic
peculiarities in the _Balanus_, the _Lepas_, the _Tubularia_, and the
Negro, and yet are in themselves, when found in the mature animal,
evidences of a high, not of a low standing, on what principle, I ask are
we to infer that the peculiarity of a heterocercal tail, embryonic in the
salmon, is, when found in the mature Placoid, an evidence, not of a high
standing, but of a low? Every true analogy in the case favors an exactly
opposite view. In the heterocercal or one-sided tail, the vertebral
joints gradually diminish, as in the tails of the _Sauria_ and _Ophidia_,
till they terminate in a point; whereas the homocercal tail common to the
osseous fishes exhibits no true analogy with the tails of the higher
orders. Its abruptly terminating vertebral column, immensely developed
posterior processes, and broadly expanded osseous rays, seem to be simply
a few of the many marks of decline and degradation which fishes, the
oldest of the vertebrata, exhibit in this late age of the world, and
which, in at least the earlier geologic periods, when they were greatly
younger as a class, they did not betray.
[Illustration: Fig. 48.
a. _Tail of Spinax Acanthias._
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.
[Illustration: 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.
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;[27]
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.