the amount of kindred or relative phenomena which the public mind already
possesses and acknowledges, to which the new can be assimilated. A
novelty, however true, if there be no received truths with which it can
be shewn in harmonious relation, has little chance of a favourable
hearing. In fact, as has been often observed, there is a measure of
incredulity from our ignorance as well as from our knowledge, and if the
most distinguished philosopher three hundred years ago had ventured to
develop any striking new fact which only could harmonize with the as yet
unknown Copernican solar system, we cannot doubt that it would have been
universally scoffed at in the scientific world, such as it then was, or
at the best interpreted in a thousand wrong ways in conformity with ideas
already familiar. The experiments above described, finding a public mind
which had never discovered a fact or conceived an idea at all analogous,
were of course ungraciously received. It was held to be impious, even to
surmise that animals could have been formed through any instrumentality
of an apparatus devised by human skill. The more likely account of the
phenomena was said to be, that the insects were only developed from ova,
resting either in the fluid, or in the wooden frame on which the
experiments took place. On these objections the following remarks may be
made. The supposition of impiety arises from an entire misconception of
what is implied by an aboriginal creation of insects. The
experimentalist could never be considered as the author of the existence
of these creatures, except by the most unreasoning ignorance. The utmost
that can be claimed for, or imputed to him is that he arranged the
natural conditions under which the true creative energy—that of the
Divine Author of all things—was pleased to work in that instance. On the
hypothesis here brought forward, the _acarus Crossii_ was a type of being
ordained from the beginning, and destined to be realized under certain
physical conditions. When a human hand brought these conditions into the
proper arrangement, it did an act akin to hundreds of familiar ones which
we execute every day, and which are followed by natural results; but it
did nothing more. The production of the insect, if it did take place as
assumed, was as clearly an act of the Almighty himself, as if he had
fashioned it with hands. For the presumption that an act of aboriginal
creation did take place, there is this to be said, that, in Mr. Weekes’s
experiment, every care that ingenuity could devise was taken to exclude
the possibility of a development of the insects from ova. The wood of
the frame was baked in a powerful heat; a bell-shaped glass covered the
apparatus, and from this the atmosphere was excluded by the constantly
rising fumes from the liquid, for the emission of which there was an
aperture so arranged at the top of the glass, that only these fumes could
pass. The water was distilled, and the substance of the silicate had
been subjected to white heat. Thus every source of fallacy seemed to be
shut up. In such circumstances, a candid mind, which sees nothing either
impious or unphilosophical in the idea of a new creation, will be
disposed to think that there is less difficulty in believing in such a
creation having actually taken place, than in believing that, in two
instances, separated in place and time, exactly the same insects should
have chanced to arise from concealed ova, and these a species heretofore
unknown.
HYPOTHESIS OF THE DEVELOPMENT
OF THE
VEGETABLE AND ANIMAL KINGDOMS.
IT has been already intimated, as a general fact, that there is an
obvious gradation amongst the families of both the vegetable and animal
kingdoms, from the simple lichen and animalcule respectively up to the
highest order of dicotyledonous trees and the mammalia. Confining our
attention, in the meantime, to the animal kingdom—it does not appear that
this gradation passes along one line, on which every form of animal life
can be, as it were, strung; there may be branching or double lines at
some places; or the whole may be in a circle composed of minor circles,
as has been recently suggested. But still it is incontestable that there
are general appearances of a scale beginning with the simple and
advancing to the complicated. The animal kingdom was divided by Cuvier
into four sub-kingdoms, or divisions, and these exhibit an unequivocal
gradation in the order in which they are here enumerated:—Radiata,
(polypes, &c.;) mollusca, (pulpy animals;) articulata, (jointed animals;)
vertebrata, (animals with internal skeleton.) The gradation can, in like
manner, be clearly traced in the _classes_ into which the sub-kingdoms
are subdivided, as, for instance, when we take those of the vertebrata in
this order—reptiles, fishes, birds, mammals.
While the external forms of all these various animals are so different,
it is very remarkable that the whole are, after all, variations of a
fundamental plan, which can be traced as a basis throughout the whole,
the variations being merely modifications of that plan to suit the
particular conditions in which each particular animal has been designed
to live. Starting from the primeval germ, which, as we have seen, is the
representative of a particular order of full-grown animals, we find all
others to be merely advances from that type, with the extension of
endowments and modification of forms which are required in each
particular case; each form, also, retaining a strong affinity to that
which precedes it, and tending to impress its own features on that which
succeeds. This unity of structure, as it is called, becomes the more
remarkable, when we observe that the organs, while preserving a
resemblance, are often put to different uses. For example: the ribs
become, in the serpent, organs of locomotion, and the snout is extended,
in the elephant, into a prehensile instrument.
It is equally remarkable that analogous purposes are served in different
animals by organs essentially different. Thus, the mammalia breathe by
lungs; the fishes, by gills. These are not modifications of one organ,
but distinct organs. In mammifers, the gills exist and act at an early
stage of the fœtal state, but afterwards go back and appear no more;
while the lungs are developed. In fishes, again, the gills only are
fully developed; while the lung structure either makes no advance at all,
or only appears in the rudimentary form of an air-bladder. So, also, the
baleen of the whale and the teeth of the land mammalia are different
organs. The whale, in embryo, shews the rudiments of teeth; but these,
not being wanted, are not developed, and the baleen is brought forward
instead. The land animals, we may also be sure, have the rudiments of
baleen in their organization. In many instances, a particular structure
is found advanced to a certain point in a particular set of animals, (for
instance, feet in the serpent tribe,) although it is not there required
in any degree; but the peculiarity, being carried a little farther
forward, is perhaps useful in the next set of animals in the scale. Such
are called rudimentary organs. With this class of phenomena are to be
ranked the useless mammæ of the male human being, and the unrequired
process of bone in the male opossum, which is needed in the female for
supporting her pouch. Such curious features are most conspicuous in
animals which form links between various classes.
As formerly stated, the marsupials, standing at the bottom of the
mammalia, shew their affinity to the oviparous vertebrata, by the
rudiments of two canals passing from near the anus to the external
surfaces of the viscera, which are fully developed in fishes, being
required by them for the respiration of aerated waters, but which are not
needed by the atmosphere-breathing marsupials. We have also the peculiar
form of the sternum and rib-bones of the lizards _represented_ in the
mammalia in certain white cartilaginous lines traceable among their
abdominal muscles. The struphionidæ (birds of the ostrich type) form a
link between birds and mammalia, and in them we find the wings
imperfectly or not at all developed, a diaphragm and urinary sac, (organs
wanting in other birds,) and feathers approaching the nature of hair.
Again, the ornithorynchus belongs to a class at the bottom of the
mammalia, and approximating to birds, and in it behold the bill and
web-feet of that order!
For further illustration, it is obvious that, various as may be the
lengths of the upper part of the vertebral column in the mammalia, it
always consists of the same parts. The giraffe has in its tall neck the
same number of bones with the pig, which scarcely appears to have a neck
at all. {195} Man, again, has no tail; but the notion of a
much-ridiculed philosopher of the last century is not altogether, as it
happens, without foundation, for the bones of a caudal extremity exist in
an undeveloped state in the _os coccygis_ of the human subject. The
limbs of all the vertebrate animals are, in like manner, on one plan,
however various they may appear. In the hind-leg of a horse, for
example, the angle called the hock is the same part which in us forms the
heel; and the horse, and all other quadrupeds, with almost the solitary
exception of the bear, walk, in reality, upon what answers to the toes of
a human being. In this and many other quadrupeds the fore part of the
extremities is shrunk up in a hoof, as the tail of the human being is
shrunk up in the bony mass at the bottom of the back. The bat, on the
other hand, has these parts largely developed. The membrane, commonly
called its wing, is framed chiefly upon bones answering precisely to
those of the human hand; its extinct congener, the pterodactyle, had the
same membrane extended upon the fore-finger only, which in that animal
was prolonged to an extraordinary extent. In the paddles of the whale
and other animals of its order, we see the same bones as in the more
highly developed extremities of the land mammifers; and even the serpent
tribes, which present no external appearance of such extremities, possess
them in reality, but in an undeveloped or rudimental state.
The same law of development presides over the vegetable kingdom. Amongst
phanerogamous plants, a certain number of organs appear to be always
present, either in a developed or rudimentary state; and those which are
rudimentary can be developed by cultivation. The flowers which bear
stamens on one stalk and pistils on another, can be caused to produce
both, or to become perfect flowers, by having a sufficiency of
nourishment supplied to them. So also, where a special function is
required for particular circumstances, nature has provided for it, not by
a new organ, but by a modification of a common one, which she has
effected in development. Thus, for instance, some plants destined to
live in arid situations, require to have a store of water which they may
slowly absorb. The need is arranged for by a cup-like expansion round
the stalk, in which water remains after a shower. Now the _pitcher_, as
this is called, is not a new organ, but simply a metamorphose of a leaf.
These facts clearly shew how all the various organic forms of our world
are bound up in one—how a fundamental unity pervades and embraces them
all, collecting them, from the humblest lichen up to the highest
mammifer, in one system, the whole creation of which must have depended
upon one law or decree of the Almighty, though it did not all come forth
at one time. After what we have seen, the idea of a separate exertion
for each must appear totally inadmissible. The single fact of abortive
or rudimentary organs condemns it; for these, on such a supposition,
could be regarded in no other light than as blemishes or blunders—the
thing of all others most irreconcilable with that idea of Almighty
Perfection which a general view of nature so irresistibly conveys. On
the other hand, when the organic creation is admitted to have been
effected by a general law, we see nothing in these abortive parts but
harmless peculiarities of development, and interesting evidences of the
manner in which the Divine Author has been pleased to work.
We have yet to advert to the most interesting class of facts connected
with the laws of organic development. It is only in recent times that
physiologists have observed that each animal passes, in the course of its
germinal history, through a series of changes resembling the _permanent
forms_ of the various orders of animals inferior to it in the scale.
Thus, for instance, an insect, standing at the head of the articulated
animals, is, in the larva state, a true annelid, or worm, the annelida
being the lowest in the same class. The embryo of a crab resembles the
perfect animal of the inferior order myriapoda, and passes through all
the forms of transition which characterize the intermediate tribes of
crustacea. The frog, for some time after its birth, is a fish with
external gills, and other organs fitting it for an aquatic life, all of
which are changed as it advances to maturity, and becomes a land animal.
The mammifer only passes through still more stages, according to its
higher place in the scale. Nor is man himself exempt from this law. His
first form is that which is permanent in the animalcule. His
organization gradually passes through conditions generally resembling a
fish, a reptile, a bird, and the lower mammalia, before it attains its
specific maturity. At one of the last stages of his fœtal career, he
exhibits an intermaxillary bone, which is characteristic of the perfect
ape; this is suppressed, and he may then be said to take leave of the
simial type, and become a true human creature. Even, as we shall see,
the varieties of his race are represented in the progressive development
of an individual of the highest, before we see the adult Caucasian, the
highest point yet attained in the animal scale.
To come to particular points of the organization. The brain of man,
which exceeds that of all other animals in complexity of organization and
fulness of development, is, at one early period, only “a simple fold of
nervous matter, with difficulty distinguishable into three parts, while a
little tail-like prolongation towards the hinder parts, and which had
been the first to appear, is the only representation of a spinal marrow.
Now, in this state it perfectly resembles the brain of an adult fish,
thus assuming _in transitu_ the form that in the fish is permanent. In a
short time, however, the structure is become more complex, the parts more
distinct, the spinal marrow better marked; it is now the brain of a
reptile. The change continues; by a singular motion, certain parts
(_corpora quadragemina_) which had hitherto appeared on the upper
surface, now pass towards the lower; the former is their permanent
situation in fishes and reptiles, the latter in birds and mammalia. This
is another advance in the scale, but more remains yet to be done. The
complication of the organ increases; cavities termed _ventricles_ are
formed, which do not exist in fishes, reptiles, or birds; curiously
organized parts, such as the corpora striata, are added; it is now the
brain of the mammalia. Its last and final change alone seems wanting,
that which shall render it the brain of MAN.” {201} And this change in
time takes place.
So also with the heart. This organ, in the mammalia, consists of four
cavities, but in the reptiles of only three, and in fishes of two only,
while in the articulated animals it is merely a prolonged tube. Now in
the mammal fœtus, at a certain early stage, the organ has the form of a
prolonged tube; and a human being may be said to have then the heart of
an insect. Subsequently it is shortened and widened, and becomes divided
by a contraction into two parts, a ventricle and an auricle; it is now
the heart of a fish. A subdivision of the auricle afterwards makes a
triple-chambered form, as in the heart of the reptile tribes; lastly, the
ventricle being also subdivided, it becomes a full mammal heart.
Another illustration here presents itself with the force of the most
powerful and interesting analogy. Some of the earliest fishes of our
globe, those of the Old Red Sandstone, present, as we have seen, certain
peculiarities, as the one-sided tail and an inferior position of the
mouth. No fishes of the present day, in a mature state, are so
characterized; but some, at a certain stage of their existence, have such
peculiarities. It occurred to a geologist to inquire if the fish which
existed before the Old Red Sandstone had any peculiarities assimilating
them to the fœtal condition of existing fish, and particularly if they
were small. The first which occur before the time of the Old Red
Sandstone, are those described by Mr. Murchison, as belonging to the
Upper Ludlow Rocks; _they are all rather small_. Still older are those
detected by Mr. Philips, in the Aymestry Limestone, being the most
ancient of the class which have as yet been discovered; _these are so
extremely minute as only to be distinguishable by the microscope_. Here
we apparently have very clear demonstrations of a parity, or rather
identity, of laws presiding over the development of the animated tribes
on the face of the earth, and that of the individual in embryo.
The tendency of all these illustrations is to make us look to
_development_ as the principle which has been immediately concerned in
the peopling of this globe, a process extending over a vast space of
time, but which is nevertheless connected in character with the briefer
process by which an individual being is evoked from a simple germ. What
mystery is there here—and how shall I proceed to enunciate the conception
which I have ventured to form of what may prove to be its proper
solution! It is an idea by no means calculated to impress by its
greatness, or to puzzle by its profoundness. It is an idea more marked
by simplicity than perhaps any other of those which have explained the
great secrets of nature. But in this lies, perhaps, one of its strongest
claims to the faith of mankind.
The whole train of animated beings, from the simplest and oldest up to
the highest and most recent, are, then, to be regarded as a series of
_advances of the principle of development_, which have depended upon
external physical circumstances, to which the resulting animals are
appropriate. I contemplate the whole phenomena as having been in the
first place arranged in the counsels of Divine Wisdom, to take place, not
only upon this sphere, but upon all the others in space, under necessary
modifications, and as being carried on, from first to last, here and
elsewhere, under immediate favour of the creative will or energy. {204}
The nucleated vesicle, the fundamental form of all organization, we must
regard as the meeting-point between the inorganic and the organic—the end
of the mineral and beginning of the vegetable and animal kingdoms, which
thence start in different directions, but in perfect parallelism and
analogy. We have already seen that this nucleated vesicle is itself a
type of mature and independent being in the infusory animalcules, as well
as the starting point of the fœtal progress of every higher individual in
creation, both animal and vegetable. We have seen that it is a form of
being which electric agency will produce—though not perhaps usher into
full life—in albumen, one of those compound elements of animal bodies, of
which another (urea) has been made by artificial means. Remembering
these things, we are drawn on to the supposition, that the first step in
the creation of life upon this planet was _a chemico-electric operation_,
_by which simple germinal vesicles were produced_. This is so much, but
what were the next steps? Let a common vegetable infusion help us to an
answer. There, as we have seen, simple forms are produced at first, but
afterwards they become more complicated, until at length the
life-producing powers of the infusion are exhausted. Are we to presume
that, in this case, the simple engender the complicated? Undoubtedly,
this would not be more wonderful as a natural process than one which we
never think of wondering at, because familiar to us—namely, that in the
gestation of the mammals, the animalcule-like ovum of a few days is the
parent, in a sense, of the chick-like form of a few weeks, and that in
all the subsequent stages—fish, reptile, &c.—the one may, with scarcely a
metaphor, be said to be the progenitor of the other. I suggest, then, as
an hypothesis already countenanced by much that is ascertained, and
likely to be further sanctioned by much that remains to be known, that
the first step was _an advance under favour of peculiar conditions_,
_from the simplest forms of being_, _to the next more complicated_, _and
this through the medium of the ordinary process of generation_.
Unquestionably, what we ordinarily see of nature is calculated to impress
a conviction that each species invariably produces its like. But I would
here call attention to a remarkable illustration of natural law which has
been brought forward by Mr. Babbage, in his _Ninth Bridgewater Treatise_.
The reader is requested to suppose himself seated before the calculating
machine, and observing it. It is moved by a weight, and there is a wheel
which revolves through a small angle round its axis, at short intervals,
presenting to his eye successively, a series of numbers engraved on its
divided circumference.
Let the figures thus seen be the series, 1, 2, 3, 4, 5, &c., of natural
numbers, each of which exceeds its immediate antecedent by unity.
“Now, reader,” says Mr. Babbage, “let me ask you how long you will have
counted before you are firmly convinced that the engine has been so
adjusted, that it will continue, while its motion is maintained, to
produce the same series of natural numbers? Some minds are so
constituted, that, after passing the first hundred terms, they will be
satisfied that they are acquainted with the law. After seeing five
hundred terms few will doubt, and after the fifty thousandth term the
propensity to believe that the succeeding term will be fifty thousand and
one, will be almost irresistible. That term _will_ be fifty thousand and
one; and the same regular succession will continue; the five millionth
and the fifty millionth term will still appear in their expected order,
and one unbroken chain of natural numbers will pass before your eyes,
from _one_ up to _one hundred million_.
“True to the vast induction which has been made, the next succeeding term
will be one hundred million and one; but the next number presented by the
rim of the wheel, instead of being one hundred million and two, is one
hundred million _ten thousand_ and two. The whole series from the
commencement being thus,—
1
2
3
4
5
.
. .
. . .
99,999,999
100,000,000
regularly as far as 100,000,001
100,010,002 the law changes.
100,030,003
100,060,004
100,100,005
100,150,006
100,210,007
100,280,008
. . .
. . .
. . .
“The law which seemed at first to govern this series failed at the
hundred million and second term. This term is larger than we expected by
10,000. The next term is larger than was anticipated by 30,000, and the
excess of each term above what we had expected forms the following
table:—
10,000
30,000
60,000
100,000
150,000
. . .
. . .
being, in fact, the series of _triangular numbers_, {208} each multiplied
by 10,000.
“If we now continue to observe the numbers presented by the wheel, we
shall find, that for a hundred, or even for a thousand terms, they
continue to follow the new law relating to the triangular numbers; but
after watching them for 2761 terms, we find that this law fails in the
case of the 2762d term.
“If we continue to observe, we shall discover another law then coming
into action, which also is dependent, but in a different manner, on
triangular numbers. This will continue through about 1430 terms, when a
new law is again introduced which extends over about 950 terms, and this,
too, like all its predecessors, fails, and gives place to other laws,
which appear at different intervals.