ova through the fatal laceration or dissolution of the parent's
body, is most commonly observed in the well-fed _Polygastria_,
which crowd together as their little ocean evaporates; and thus
each leaves, by the last act of its life, the means of perpetuating
and diffusing its species by thousands of fertile germs. When the
once thickly tenanted pool is dried up, and its bottom converted
into a layer of dust, these inconceivably minute and light ova will
be raised with the dust by the first puff of wind, diffused through
the atmosphere, and may there remain long suspended; forming,
perhaps, their share of the particles which we see flickering in
the sunbeam, ready to fall into any collection of water, beaten
down by every summer shower into the streams or pools which receive
or may be formed by such showers, and, by virtue of their tenacity
of life, ready to develope themselves wherever they may find the
requisite conditions for their existence.
"The possibility, or, rather, the high probability, that such is
the design of the oviparous generation of the _Infusoria_, and such
the common mode of the diffusion of their ova, renders the
hypothesis of equivocal generation, which has been so frequently
invoked to explain their origin in new-formed natural or artificial
infusions, quite gratuitous. If organs of generation might, at
first sight, seem superfluous in creatures propagating their kind
by gemmation and spontaneous fission, equivocal generation is
surely still less required to explain the origin of beings so
richly provided with the ordinary and recognized modes of
propagation."--pp. 31, 32.
Recent accounts show, that the dust collected from the atmosphere at
sea, many miles from land, generally contains some of these dried
animalcules and their ova. Many of these germs can be developed only in
particular localities, or under certain conditions which are rarely
fulfilled. Consequently, if there were but few of them, the species
might perish, because those few might not find their appropriate home.
But such an accident is guarded against by the vast multiplication of
these germs and their wide dispersion; for, unlike all the higher tribes
of beings except man, the same species is often found in all regions of
the globe. Very few, in comparison with the whole number, may find a
proper _nidus_; but these few then propagate with such marvellous
rapidity, as fully to replenish, if not to increase, the original stock.
Thus they have been enabled, as species, to survive even those
destroying causes which exterminated all the higher forms of animals.
Several species still exist, which were in being at the time of the
cretaceous formation, though all the other animated races belonging to
that period have perished. "These animalcules," says Ehrenberg,
"constitute a chain, which, though in the individual it be microscopic,
yet in the mass is a mighty one, connecting the organic life of distant
ages of the earth."
In view of facts like these, we may surely say, that the existence of
the infusory animalcules, and even of the entozoa, is conceivable,
supposing they could only have been produced by parents of their own
kind, and without having recourse to the anomalous and hypothetical
doctrine of equivocal generation. We may not be able to trace their line
of parentage, for our imperfect vision cannot follow the motes which
play in the sunbeam, nor track them from their birth-place to their
final home. But we know that they must be deposited in every layer of
dust that falls from the atmosphere, that they must be inhaled with
every breath which an animal draws, and be swallowed with every morsel
and drop of its food. The experiments which seem to prove that living
beings may be produced from pure inorganic matter are all explicable on
the supposition, that adequate precautions were not taken to exclude
every animal and germ capable of development from the substances
experimented upon, and from the air which was admitted into the
apparatus. On this ground, the experiments of Crosse and Weekes, cited
by our author, have been quite generally rejected by scientific men, as
hardly deserving of notice. We learn that the former was "discouraged by
the reception of his experiments," and "soon discontinued them";--with
good reason, for it does not appear from our author's account, that he
adopted any precautions at all. Mr. Weekes seems to have been a little
more cautious, and the consequence was, that he did not observe any
appearance of life among the substances experimented upon for "eleven
months," at the end of which time we may reasonably suppose, that his
precautions ceased to have perfect effect. The only experiment, in which
adequate means to guard against causes of error were taken, was that of
Professor Schulze, of Berlin, which had a contrary result. We extract
Mr. Owen's account of it.
"He filled a glass flask half full of distilled water, in which
were various animal and vegetable substances: he then closed it
with a good cork, through which were passed two glass tubes, bent
at right angles, the whole being air-tight: it was next placed in a
sand bath, and heated until the water boiled violently. While the
watery vapor was escaping by the glass tubes, the Professor
fastened at each end an apparatus which chemists employ for
collecting carbonic acid: that at the one end was filled with
concentrated sulphuric acid, and the other with a solution of
potash. By means of the boiling heat, it is to be presumed that
every thing living, and all germs in the flask or in the tubes were
destroyed; whilst all access was cut off by the sulphuric acid on
the one side, and by the potash on the other. The apparatus was
then exposed to the influence of summer light and heat; at the same
time, there was placed near it an open vessel, with the same
substances that had been introduced into the flask, and also after
having subjected them to a boiling temperature. In order to renew
constantly the air within the flask, the experimenter sucked with
his mouth several times a day the open end of the apparatus, filled
with the solution of potash, by which process the air entered his
mouth from the flask through the caustic liquid, and the
atmospheric air from without entered the flask through the
sulphuric acid. The air was of course not at all altered in its
composition by passing through the sulphuric acid in the flask; but
all the portions of living matter, or of matter capable of becoming
animated, were taken up by the sulphuric acid and destroyed. From
the 28th of May until the beginning of August, Professor Schulze
continued uninterruptedly the renewal of the air in the flask,
without being able, by the aid of the microscope, to discover any
living animal or vegetable substance; although, during the whole of
the time, observations were made almost daily on the edge of the
liquid; and when, at last, the Professor separated the different
parts of the apparatus, he could not find in the whole liquid the
slightest trace of _Infusoria_ or _Confervae_, or of mould; but all
three presented themselves in great abundance a few days after he
had left the flask standing open. The vessel which he placed near
the apparatus contained on the following day _Vibriones_ and
_Monads_, to which were soon added larger Polygastric _Infusoria_,
and afterwards _Rotifera_."--pp. 32, 33.
For readers who are not familiar with these subjects, it may be well to
mention, that the weight of authority is decidedly against this doctrine
of spontaneous generation. It is rejected by Mueller, who ranks among
the first physiologists of Germany; by Ehrenberg, one of the most
distinguished microscopists in the world; and by Owen, who stands at the
head of the school of comparative anatomy in England, if not in Europe.
The remark made by Cuvier, more than thirty years ago, is still true at
the present day, that, "although the impossibility of spontaneous
generation cannot be absolutely demonstrated, yet all the efforts of
those physiologists who believe in the possibility of it have not
succeeded in showing us a single instance."
Passing over, then, our author's theory of the origination of life from
inorganic matter as utterly untenable, we come to the next point in his
system,--the most chimerical of all,--the gradual development of the
higher orders of being out of those next beneath them in the scale. It
is not pretended, that there is _any known instance_ of the
transmutation of species, or of the evolution, in the ordinary way, of
any being specifically different from its parents. The same animal,
indeed, may pass through different grades of development; but these
changes affect only the individual, not the race. The progeny of this
animal must begin at the same point where its parent did, and run
precisely the same cycle. The tadpole becomes a frog, but the young of
that frog are tadpoles; the worm becomes a winged insect, but the eggs
of that insect are hatched into nothing but worms. These changes in the
life of the individual, like the successive periods of the embryotic
state, of infancy, and manhood in the human being, are perfectly
consistent with persistence of type in the race, and do not indicate
even the possibility that a new species may be developed out of an old
one. On the contrary, the germ must be considered as _potentially_
equivalent to the whole future being, for it is invariably developed
into that being. If there be any one fact unquestionably established by
observation, it is that each species invariably produces its like. "All
the phenomena," says Mueller, "at present observed in the animal kingdom,
seem to prove that the species were originally created distinct, and
independent of each other. There is no remote possibility of one species
being produced from another."
The doctrine of our author, then, is confessedly a pure hypothesis, and,
as such, it might be summarily dismissed into the region of cloud-land
and dreams, where it had its origin. The burden of proof is upon him,
and as he has failed to produce a single instance in which his theory is
exemplified, he may be rightfully debarred the privilege of discussion.
But waiving this point, if we look into the grounds of his conjecture,
we find bold assumptions more than once substituted for the plain
statement of facts, which would destroy every shade of credibility in
his doctrine. True, there is an appearance, both in the animal and
vegetable kingdoms, of an ascending scale of being, from simply
organized forms and imperfect developments up to the complex
arrangements and nice adaptations of the advanced tribes. But the
progress is not regular, nor are the intervals of constant length. The
line is often broken and doubled, and, in fact, the individuals are far
more naturally arranged in a number of parallel lines, beginning
successively at a somewhat lower point, than in a single series. Man, of
course, is placed at the head of the animal tribes; but the interval
which separates him from the chimpanzee cannot easily be cleared at one
bound. He forms but one genus, and that genus is the only one of its
order. But even if the line of gradation were single and perfect, the
fact would be of no service to the hypothesis we are now considering;
for the interval between two species most nearly allied to each other
seems to be quite as impassable as the broadest gulf of separation.
The point chiefly relied upon to show the credibility of this doctrine
is the fact, according to our author, that the higher animals pass
through a series of changes resembling the permanent forms of the lower
tribes. The first form of man himself "is that which is permanent in the
animalcule"; and thence he comes to resemble successively a fish, a
reptile, a bird, and the lower mammifers, before he attains his specific
maturity. It is held, then, that a premature birth from an animal of a
higher kind might have instituted a new race of a lower type; and that a
birth unusually delayed, permitting an embryo to be still farther
advanced in the line of organization, might have created a new species
of a higher order than the parent. Here, every thing depends on the
_absolute identity_ of the germs of all animals, in the lower stages of
their growth. General resemblances and analogies are of no weight
whatever; the essential internal organization of the ova of different
species must be the same; otherwise, however ripened into a mature
being, whether the birth be advanced or postponed, the individual must
still belong to its parents' species, of which it possesses the
distinctive peculiarity. Now, this point of _the identity of germs is a
mere assumption_; not only is it destitute of proof,--the whole evidence
is against it. There is a degree of outward resemblance, but there is no
sameness. When we trace the origin of life back to the remotest point to
which our powers of observation extend, when we come to microscopic
vesicles that can be discerned only by the highest magnifiers, general
similarity of outward shape is all that can be predicated of them. The
specific differences lie below this general resemblance of outward form;
we cannot discern them, but we _know_ that they must exist, and that
they are _essential_ differences, for each one of these vesicles is
invariably developed, if at all, into an individual of the species to
which its parent belongs. The germinal vesicles of a tree and a
quadruped are somewhat alike, outwardly; so, to the hen's eyes, there is
no difference between her own eggs and the duck's eggs which the
farmer's wife has put into her nest. But when she has hatched her brood,
part of them are found to be web-footed, and these, to her great
astonishment and distress, immediately take to the water. Our author
commits the same blunder as the poor hen. This want of consciousness
that he has got to the end of his tether, this inability to believe that
any difference can exist where he is not able to see it, though it is
invariably indicated by future consequent differences of the most
striking nature, is perfectly characteristic of the rash theorist in
science.
The assertion, that man's "first form _is_ that which is permanent in
the animalcule,"--even if we do not look to the potentiality of
development into a higher being, which experience shows to exist in the
human germ, but not in the infusorial,--is a positive misstatement. The
lowest monad has a mouth and means for propagating its kind, which do
not belong to the primitive ovum of any higher animal. About the
succeeding stages in the growth of the embryo our author's language is
more cautious. He only says, that they _resemble_, or _typify_, some of
the lower orders of being; and this is virtually admitting a specific
difference, and giving up his own theory for all the conditions
posterior to that of the germ. The brain and heart of the embryo
successively _resemble_ the corresponding organs in a fish, a reptile, a
bird, and a quadruped; but they are not identical, _even in outward
appearance_, with those organs. Of course, if arrested at any stage of
its growth, and prematurely born, the embryo would not be one of the
lower animals, but only something resembling it in outward shape; and
conversely, if it were possible for the birth of a bird to be delayed
till it had reached a higher stage of development in the same line in
which it was proceeding, it would not become a quadruped, but it would
be an anomalous creature somewhat like one. Consequently, no one species
now on the earth can have been evolved out of any other existing race;
because the germs of any two, at a very early stage in their history,
according to our author's own confession, are specifically unlike.
To avoid this difficulty, he is driven to a further supposition, still
more gratuitous and improbable; namely, that the germ destined to become
one of a different race from its parents, having advanced along its
usual line of development so far as that line coincides with the one
belonging to the new species, there diverges, and follows a different
path up to the period of its birth into a new creature; that is, the
embryo of a reptile, having grown for a certain time as if it were to be
a reptile, suddenly turns aside, like a young man changing his mind
about the choice of a profession, and for the rest of its foetal life
follows the proper line of progress in order to be developed into a
bird. This is mere dreaming, and reminds one only of the wonderful
transformations effected by enchantment in an Arabian tale. We might
just as plausibly suppose, that the reptile, after it became mature, was
suddenly transformed into a bird, as that it underwent this change
before it was hatched. All the evidence attainable goes to show, that
the law of development is as immutable before as after birth, the
several stages of progress succeeding each other in a constant order,
and affecting the individual only, not the race. A young monkey is no
more likely to be transmuted into a man than an old one; nor is such a
metamorphosis at all more probable in the course of its foetal life.
The view we have now obtained of the specific differences between
distinct races of being at separate periods of their existence is
precisely what might have been anticipated from the law of gradual
development, which holds throughout the organic kingdoms. Between two
mature animals, these differences are perfectly obvious and well
marked. As we go a step back in their history, the distinction becomes a
little more obscure; two worms may resemble each other very closely,
though the two winged insects subsequently produced from them may be
very unlike. Receding still farther, some of these specific differences
may entirely disappear, the organs or parts which should exhibit them
being not yet developed. And when we come to the primitive germs, so
minute as to be visible only through the microscope, no outward
distinction, perhaps, is any longer perceptible, and the radical
difference of their internal organization is indicated only by the fact,
to be verified by subsequent observation, that the two are invariably
developed into perfectly distinct animals, belonging respectively to the
same races with their parents. A theorist, whose whole system is based
upon the invariable operation of natural agencies, cannot reasonably
object to this conclusion.
That our statements in the course of this argument may not appear of the
same questionable character as those advanced by our author, we will
fortify them with a few brief citations from a work of such
unquestionable authority as the Lectures of Professor Owen.
"No doubt the minute infusoria, which seem to have their
development arrested at the first or nearest stage from the
primitive cell formation, offer close and striking analogies to the
primitive cells out of which the higher animals and all their
tissues are developed; but the very [first] step which the
infusoria take beyond the primitive cell stage invests them with a
specific character as independent and distinct in its nature as
that of the highest and most complicated organisms. No mere organic
cell, destined for ulterior changes in a living organization, has a
mouth armed with teeth, or provided with long tentacula; I will not
lay stress on the alimentary canal and appended stomachs, which
many still regard as 'sub judice'; but the endowment of distinct
organs of generation, for propagating their kind by fertile ova,
raises the polygastric infusoria much above the mere organic
cell."--pp. 25, 26.
"In comparing the several stages in the very interesting
development of the _cyanaea aurita_ to the infusoria and polypes, it
must be understood that such comparisons are warranted only by a
similarity of outward form, and of the instruments of locomotion
and prehension. The essential internal organization of the
persistent lower forms of the _zooephyta_ is entirely wanting in the
transitory states of the higher ones. A progress through the
inferior groups is sketched out, but no actual transmutation of
species is effected. The young medusa, before it attains its
destined condition of maturity, successively resembles, but never
becomes, a polygastrian, a rotifer, and a bryozoon."--p. 112.
"Thus every animal in the course of its development typifies or
represents some of the permanent forms of animals inferior to
itself; but it does not represent all the inferior forms, nor
acquire the organization of any of the forms which it transitorily
represents. Had the animal kingdom formed, as was once supposed, a
single and continuous chain of being, progressively ascending from
the monad to the man, unity of organization might then have been
demonstrated to the extent in which the theory has been maintained
by the disciples of the Geoffroyan school."--p. 370.
If these similarities of structure in the germ had any bearing on the
subject, they would indicate the possibility only of retrogression in
the scale. Of course, the immature ovum, arrested in its development,
could not form a more perfect being than its parent. There is no
pretence that the embryo, at any stage of its progress, images an animal
of a higher grade than its own family. Then what aid do these
similarities of structure afford to the theory, that all the higher
organisms have been evolved by successive steps out of the lowest monad?
At the best, you have only shown, that a _retreat_ is possible; you have
still to point out any likelihood, even the remotest, of an _advance_ in
the scale of being. There is no fact whatever to confirm the
supposition, that birth may possibly be delayed till the animal be
developed into one of a higher species; and the law of immature births
seems to be, that, if the offspring escapes at all--for there is great
risk consequent on such an accident,--it becomes as perfect as its
progenitors. Nature seems to guard the distinctions between the several
races with peculiar care; so far as we know, monsters either do not
survive their birth, or are incapable of continuing their kind, or in
the course of a single generation are reunited to the original family.
To say that these laws, distinct and invariable as far as the
observation of man has extended, may possibly have been superseded in
the lapse of ages by a higher principle, manifesting itself only at
long intervals, is again to have recourse to a blank hypothesis,
incapable alike of proof or disproof, and unsupported by the faintest
intimations from the world of experience. To build up a theory in this
way is not to account for the work of creation by the natural agencies
and inherent qualities of matter, _as at present observable_, but to fly
off to the wild supposition, that matter and life were more richly
endowed ages ago than they are in our own day. You affirm, that this
higher principle of development did not override the inferior laws at
the earlier periods in time's history, because, in the infancy of the
universe, the conditions were wanting which are requisite for its
manifestation,--because the earth was not ready, the atmosphere was not
purified, for the nobler races of being. Very well; but these conditions
are answered _now_. All things are ready at the present day for the
innate energies of matter to put forth their utmost strength. Why do not
fishes generate reptiles, and birds produce mammifers, _now_? Ah! but
"the earth being now supplied with both kinds of tenants in great
abundance, we could only expect to find the life-originating power at
work in some very special and extraordinary circumstances." It seems,
then, that these inherent qualities of matter, once supposed to be
blind, absolute, and invariable in their operation, are really very
judicious and reasonable; they suit the supply to the demand, and
actually cease working when the market is likely to be overstocked. The
results of such "_natural_ agencies" as these are very like the effects
produced by the volitions of a wise and thinking being.