lace-winged fly, _Chrysopa perla_. If you had seen one of these (or
more) at the instant of its creation, you would have seen a tiny oval
body placed at the extremity of an elastic footstalk half-an-inch in
length, and as fine as a hair, standing erect from the surface of a
leaf. This thread is composed of a gummy secretion, evolved in a gland
attached to the oviduct of the female Lace-fly. When she deposits an
egg, she first exudes a drop of this gum on the surface of a leaf, and
then, elevating her abdomen, the viscid substance is drawn out in a
thread, which presently hardening in the air, the egg is left at the tip
of the filament. An experienced entomologist, on seeing this object,
would have no hesitation in declaring the origin of the footstalk to be
the gum-gland of the female _Chrysopa_; and yet he would certainly have
drawn a false inference in the case that I am supposing.
[Illustration: LACE-FLY AND EGGS.]
Many Spiders enclose their eggs in an envelope, the produce of their own
bowels. Take an interesting example, as narrated by the eloquent Mr.
Kirby. "There is a Spider common under clods of earth (_Lycosa
saccata_), which may at once be distinguished by a white globular silken
bag, about the size of a pea, in which she has deposited her eggs,
attached to the extremity of her body. Never miser clung to his treasure
with more tenacious solicitude than this spider to her bag. Though
apparently a considerable incumbrance, she carries it with her
everywhere. If you deprive her of it, she makes the most strenuous
efforts for its recovery; and no personal danger can force her to quit
the precious load. Are her efforts ineffectual? a stupefying melancholy
seems to seize her; and, when deprived of this first object of her
cares, existence itself appears to have lost its charms. If she succeeds
in regaining her bag, or you restore it to her, her actions demonstrate
the excess of her joy. She eagerly seizes it, and with the utmost
agility runs off with it to a place of security.
"The attachment of this affectionate mother is not confined to her eggs.
After the young spiders are hatched, they make their way out of the bag
by an orifice which she is careful to open for them, and without which
they could never escape; and then, like the young of the Surinam toad
(_Rana pipa_), they attach themselves in clusters upon her back, belly,
head, and even legs; and in this situation, where they present a very
singular appearance, she carries them about with her, and feeds them
until their first moult, when they are big enough to provide their own
subsistence."[94]
I waive the argument derived from the fact of the apparent necessity of
the mother's care for the new-born young. But the mother's care is
indispensable to the appearance of the young at all; not only because
the eggs are the produce of her ovary, but also because the envelope
which protects them is the produce of her spinning-glands.
There is a furry moth, by no means uncommon, known to collectors as the
Gipsy (_Hypogymna dispar_), the eggs of which require to be protected by
an elaborate covering, either from extremes of temperature, from light,
or from certain electric conditions of the atmosphere. The protection is
afforded at the expense of the hair which clothed the mother herself.
Her ovipositor is furnished with a pair of nippers, by means of which
she plucks off her own hairs, and makes with them a flat cushion on the
surface of a leaf. On this she deposits her eggs in successive layers;
and when the full number is laid, she covers them with a roof of hair,
slanting downwards and outwards from an apex, so artfully arranged, like
the thatch of a cottage, as effectually to throw off water; each layer
of hairs overlapping the preceding, and all preserving the same
direction, so that, when finished, the work resembles a smooth and well
brushed piece of fur.
If, then, a patch of eggs newly-created had been subjected to our
inspection, we should have found them snugly protected by their conical
roof of thatch; and when we came to examine the thatch microscopically,
we should have found it composed of the hairs of _Hypogymna_. And thus
again we should have an indubitable and yet deceptive record of a
preceding existence.
The numerous species of the genus _Coccus_, to which we are indebted for
cochineal, lac, and other products valuable in commerce, afford me an
illustration of my argument, more striking than any of the above. In the
case of the lac insect (_C. lacca_), for example, the female resembles a
little hemispherical scale on the twig of a tree. At a certain period
of her life, a pellucid, glutinous substance begins to exude from the
margins of her body, which by and by completely covers it, cementing her
firmly to the branch, from which she never afterwards moves. She now
proceeds to lay her eggs, which one by one as they are extruded are
thrust under her, between her abdomen and the surface of the branch. The
result of this is, that when the whole are laid, they occupy pretty
nearly the same position in relation to the mother as they did before,
with this exception, that the abdominal integuments, which before were
beneath them, are now above them, and are in close contact with those of
the back, so that both together make a double, but still a thin, arched
roof over the heap of eggs, which are thus protected till the hatching
of the young, when they eat their way out of their long dead mother.
Let me now make my usual application. You say the _Coccus_ was created
not an adult insect, which would involve the prochronic stages of its
metamorphosis, but as a germ, that is an egg (for the germ of an insect
is an egg, and nothing else): well, here is a batch of Coccus-eggs just
created, covered with the scaly roof which is necessary to their
existence. But this scale is not a record of the mother, but the mother
herself, _a prochronic mother_, of course!
Other genera of this wonderful class of animals yield us evidences of a
somewhat different character, in the structures which the parents form
for the reception of their eggs.
One of the most complex and elaborate pieces of mechanism found in any
animal organ is the ovipositor of the Sawflies (_Tenthredinidae_). I
cannot here describe it at length; it may suffice to say that it
consists of two saw-plates, working separately and in opposite
directions, the teeth of which are cut into finer teeth; and two
supporting plates, very similar to the saws in shape and appearance. The
whole flat side of the saw is, moreover, covered with minute sharp
points, which give the action of a rasp to the instrument, in addition
to that of saw.
By means of this complicated apparatus the parent fly cuts a groove in
the twig of the proper shrub, say, a rose-bush. When it is made, the
plates are slightly separated, and an egg is laid in the groove. The saw
is now withdrawn, and a frothy secretion is deposited, which appears to
be intended, by its hardening, to prevent the growth of the wood from
closing upon the egg, before the time of hatching arrives.
If, then, any of the species of _Tenthredo_ had been called into primal
existence as an egg, it must have been within such a groove as this; and
the groove, if carefully examined, would have presented evidences of
having been formed and filled by the curious implement of the parent
fly.
Those obscure and obscene Insects, the Cockroach tribe (_Blattadae_),
secrete an extraordinary covering for the protection of their eggs.
"Instead of being laid separately, the eggs are, when deposited,
enclosed in a horny case, or capsule, variable in its form in different
species but generally of a more or less compressed oval shape,
resembling a small bean. There is a longitudinal slit in the margin of
the capsule, each side of which is defended by a narrow serrated plate,
fitting closely to its fellow. The inside of this egg-case is divided
into two spaces, in each of which is a row of separate compartments,
every one enclosing an egg, so that the whole resembles the pod of some
leguminous vegetable. This capsule, with its precious contents, is
constantly carried about by the female for a week or a fortnight, and is
then fastened, by means of a glutinous fluid, in some safe locality.
The slit of the capsule is strongly coated with cement, so as to be even
stronger than the other parts. In this capsule the young larvae are
hatched, and immediately discharge a fluid which softens the cement, and
enables them to push open the slit, through which they escape; after
their exit the slit shuts again so closely, that it appears as entire as
before. In some species it would seem that the females themselves
liberate their offspring by seizing the capsule when the larvae are fit
for escape, and tearing it with the aid of their forelegs from end to
end, by which means the enclosed larvae are set at liberty."[95]
It is impossible to read this description without being reminded of the
manner in which the bean or other leguminous seed links itself with a
former generation by means of the dehiscent legume, itself a production
of the parent plant. And the same reasoning applies to this case, as to
the other;--the egg, if the _Blatta_ was created in that stage, would
triumphantly show in the pod with which it was covered, a record of past
processes.
So, once more, with the immense tribes of solitary Bees, Wasps, and
Spheges. I shall mention but one example, from my own experience. It is
the Dirt Dauber (_Pelopoeus flavipes_) of North America. The female of
this elegant fly, when about to lay her eggs, builds up a tubular nest
of cells with fine mud, which she makes by mingling and kneading
road-dust with her saliva. Each tube consists of several cells,
separated by transverse partitions of the mortar; and in each, before
she closes it up, she lays a single egg, which she then covers with
spiders which are to constitute the food of the grub when hatched, and
to last it during the whole period of its larval growth. Dead spiders
would not do, for their bodies would either dry up, or become putrescent
long before the young grub could devour them. On the other hand, if a
number of these fierce and carnivorous creatures were immured, in
health, they would soon destroy one another. To obviate this, the
parent-fly ingeniously stings every spider just sufficiently to
paralyse, without killing it. Thus nearly a score of living spiders are
packed away in a cell scarcely larger than a lady's thimble; and thus
they remain fresh and succulent food for the larva, not only till it is
ready to begin its eating task, but even to the close of its repast.
I think this a particularly instructive example. The _Pelopoeus_ was
indubitably created; for it exists. As indubitably it was created in
some stage of its cyclical life-history. If as an imago, then I press
the argument from the necessity of its previous metamorphoses. If as a
pupa, or a larva, or an egg, each of these conditions of life was
entirely passed as an inmate of the mud-walled cottage; which, cottage
was built and stocked with food by the industry and skill of the
parent-fly. The grub could not have lived without the stored spiders;
the spiders could not have been stored (_normally_) without the agency
of the fly.
In some other instances the connexion between germ and parent is patent
to the eye. The beautiful Star-fish, _Cribella_, passes through all its
infant metamorphoses, changing from an ovum to an Infusory, thence to a
Pluteus (or what is analogous to it), thence to a Star-fish, all in the
marsupium provided for the occasion, by the drawing together of the arms
of the patient mother. The female _Brachionus_ carries its deposited
eggs attached to the hinder part of its body; and thus we can trace,
through their transparent coats, the gradual development of the organs
of the embryo,--the coloured eye, the rotatory cilia, the complex
mastax,--and even detect the vigorous movements of these and other
parts, while yet carried hither and thither by the parent.
[Illustration: FEMALE BRACHIONUS, WITH EGGS.]
But further, in the class from which I have taken this last
illustration--that of the ROTIFERA--there are examples of viviparous
genera; and these, because of the perfect transparency of all the
integuments, are peculiarly instructive and germane to my argument.
In _Rotifer macrurus_ the ovary with its germinal vesicles is distinctly
seen occupying one side of the animal. From this one of the vesicles
enlarges, until it becomes a long-oval translucent sac, nearly filling
the whole left side of the visceral cavity. A kind of spasmodic movement
is suddenly observed in this oblong ovum, and instantly we see, in its
place, a well-developed living young; as distinctly visible as if it
were excluded. It lies in a bent position, with its foot upturned; is
nearly half the length of the parent; is furnished with a proboscis,
with a pair of crimson eyes, with ciliary wheels, with a mastax whose
toothed hemispheres frequently work vigorously, and with all the viscera
proper to the species.
[Illustration: PREGNANT ASPLANCHNA.
_a._ _Unborn young._]
In the beautiful, comparatively large, and economically singular genus,
_Asplanchna_, the same process of development can be watched with
perfect facility through every stage.
In the body of the female parent, as transparent as the clearest glass,
the band-like ovary is seen floating in the visceral cavity, with
several ova in various degrees of advancement. We trace one of these
till it becomes a manifestly living young in the ovisac, lying along at
the bottom of the parental cavity, more than one-third of whose volume
is occupied by it:--supposing it to be a female infant. All its
organs,--the eyes, the jaws, the stomach, the pancreatic glands, _the
ovary with its nuclei_, the muscles, the rotatory cilia, &c. can be
traced with the utmost distinctness long before birth, and its motions
are strong and voluntary.
Neither in this case, nor in that of _Rotifer_, does the young animal
pass through any metamorphosis; the unborn young has the full
development of the parent, in every respect but size. In each case, the
_visible_ life-history of the individual commences not at birth, but at
a period long antecedent, if indeed it can be said to commence at all,
where we see it gradually developed from a nucleus, which was an
integral part of the parental ovary, _even before that parent's birth_.
In the case of the amusing little Water-fleas (_Daphnia_), we have
another example of viviparous generation, which, owing to the same cause
as in the ROTIFERA,--the transparency of the integument, can be followed
through all its stages by the eye of the observer. The eggs of this
little Crustacean are deposited in a special chamber within the valves
of the parent, where they are hatched. The young remain in their
receptacle for a period, which varies according to the temperature, but
long enough for them to undergo important changes in structure, and to
pass their first moult.[96]
Here, again, it is impossible to select a condition which does not take
hold of a pre-existence; for the youngest independent stage is dependent
on earlier stages; and these are passed in visible connexion with the
parent.
It is true there is in this genus, another mode of reproduction, by
means of eggs which are thrown off enveloped in an organic covering,
called the ephippium. If this condition be selected for the argument of
my supposed opponent, I reply that it amounts to nearly the same thing;
only the case will then come into the category of those animals whose
earliest stages are protected by coverings formed from the body of the
parent,--like the _Hypogymna_, and the Cockroach, already alluded to.
Where then, in these species, can we possibly select a stage of life,
which is not inseparably and even visibly connected with a previous
stage?
If we come to the vertebrate creatures, the argument becomes assuredly
not less convincing. The formidable Shark, which we considered as a
well-toothed adult ready for slaughter, let us suppose to have been
created in the harmlessness of infancy. It is a slender thing, some ten
or twelve inches long, bent upon itself, inclosing in the ring thus
made, the vitellus or yelk-bag, the contents of which are in process of
being absorbed into the abdomen. But the whole,--Shark, yelk-bag, and
all--is imprisoned in a brown horny capsule, that looks like a
pillow-case, with long tapes appended to the four corners.
This very peculiar protecting capsule points clearly to a peculiar
structure in the parent. The embryo was not inclosed in the pillow-case,
at its first formation; but, in the course of its descent from the ovary
through the oviduct, it had to pass a region of the latter, where was a
thick glandular mass,--the nidamental gland,--whose office it was to
secrete a dense layer of albumen, with which, the embryo became
invested. This substance took the form of the flattened purse, or
pillow-case, with produced angles, above described, and on its exclusion
from the duct assumed a very tough horny consistence, and a dark
mahogany colour.
The comparative anatomist would, therefore, without the least
hesitation, refer the origin of the investing capsule to the nidamental
glands of the female Shark; but supposing the embryo to be but just
created, his physiological science would only lead him to a false
conclusion.
If the Tree-frog afforded us evidence of pre-existent time, in the
metamorphosis which it must naturally have experienced from the tadpole
to the reptilian condition, what shall we say to that strange and
uncouth member of the same class,--the Surinam Toad (_Pipa_)? Little
would be gained by selecting the germ-stage, as the presumed epoch of
creation in this case; for, according to the extraordinary economy of
this genus, the male acts as midwife, and the female as wet-nurse, to
the hopeful progeny.
"As fast as the female deposits her eggs, the male who attends her
arranges them on her broad back, to the number of fifty or upwards. The
contact of these eggs with the skin appears to produce a sort of
inflammation; the skin of the back swells, and becomes covered with pits
or cells, which enclose each a single egg, the surface of the back
resembling the closed cells of a honeycomb. The female now betakes
herself to the water; and in these cells the eggs are not only hatched,
but the tadpoles undergo their metamorphosis, emerging in a perfect
condition, though very small, after a lapse of _eighty-two days_ from
the time in which the eggs were placed in their respective pits."
To a tyro in animal physiology it might seem that the smooth rounded egg
of a bird or a lizard, presents an example of an organism in the
simplest possible condition, and in a stage which, if any can be, is
independent of anything that went before.
But is it so? Let us see. Here is the egg of the common Fowl. I take it
in my hand, and perceive nothing but an uniform, smooth, hard, white
surface. This I break, and find that it is a thin layer of calcareous
substance, which, on microscopical examination, proves to be composed of
minute polygonal particles, so agglutinated as to leave open spaces in
the interstices of their contiguous angles.
Below this calcareous shell I find a membrane (_membrana putaminis_),
which seems, from its thinness in most parts, to be single, but which is
separated into two layers at the large end of the egg.
[Illustration: HEN'S EGG.]
Within this membrane there is another (_the chalaza_) which, closely
enveloping the yelk, passes off from it towards each extremity of the
egg in the form of a twisted cord.
Then comes a delicate membrane (_memb. vitelli_) in close contact with,
and enveloping the orange-coloured yelk; which latter carries, on one
point of its globular surface, the thin _blastoderm_, or germinal
membrane.
The yelk-globe, fastened by its twisted _chalazae_, is suspended in a
glairy fluid (albumen), which fills the space between it and the
_membrana putaminis_. This fluid, though apparently homogeneous, is
really composed of many layers, and the innermost of these it is which
is condensed into the _chalaza_.
Such, then, is the complex structure of this apparently simple object.
What light can it throw on our inquiry?
Each of these component parts bears witness to a succession of past
periods. The yelk with its germ was first formed, escaping naked, or
clothed only with its own excessively delicate membrane, from its ovisac
into the oviduct. Through the course of this tube it now slowly
descended, receiving successive investments as it proceeded. The albumen
was deposited layer upon layer from the mucous membrane of the upper
part of the oviduct; the first depositions condensing into the
_chalaza_. By and by it came down to a region of the oviduct where a
tenacious secretion was poured out, which, investing the albumen, soon
hardened into a substance resembling thin parchment, and formed the
_membrana putaminis_; two successive layers of this were deposited,
between which a bubble of gas, chiefly composed of oxygen generated in
the interval, was inclosed. Then it descended still farther, to a part
where the lining membrane of the duct was endowed with the power of
secreting calcareous matter, which, as above stated, was deposited in a
thin layer of polygonal atoms. And now, having received all its
components, and having arrived at the orifice of the duct, the egg was
laid.
Here, then, there is abundant evidence of successive processes, which
must have preceded the existence of this complete and perfect egg. But
there is yet one more evidence which I have reserved to the last,
because it is peculiarly distinct and palpable, even to the senses.
The _chalaza_, we see, is twisted at each pole of the yelk-globe, until
it resembles a piece of twine: what is the meaning of this? It was, as I
observed, deposited as a loosely enveloping membrane in the upper part
of the oviduct; the yelk-globe, however, was progressively descending;
and, as it descended, _it continually revolved upon its axis_; by means
of which rotation the investing membrane was gathered at each pole into
a spirally twisted cord, stretching from the yelk to the ends of the
_membrana putaminis_. Thus it presents us with an unmistakeable record
of what took place in the earlier periods of the descent.
We saw distinct traces of the past in the structure of a feather. But
the feathers have already begun to develop before the young bird leaves
the egg. And the structure of the egg carries us back to the oviduct of
the parent-fowl.
At what stage of existence, then, could a bird, by possibility, have
been created, which did not present distinct records of prochronic
development?
If we come to the MAMMALIA, the impossibility of finding such a stage
becomes only more and more obvious. For it is a law in physiology, that
the higher the grade of organization assigned to any being, the more it
is assisted in infancy by the parent.
"This law is remarkably exemplified in the class MAMMALIA, which
unquestionably ranks at the head of the animal kingdom, in respect to
degree of intelligence and general elevation of structure. It is the
universal and most prominent characteristic of this class, that the
young are retained within the body of the female parent, until they have
made considerable progress in their development; that, whilst there,
they derive their support almost immediately from her blood; and that
they are afterwards nourished for some time by a secretion which she
affords."[97]
The foetus of the Kangaroo, when expelled from the womb, is scarcely
more than an inch in length. Its limbs and its tail are indeed formed,
but the imperfect creature has been compared to an earthworm, for the
colour and semi-transparency of the integument. In this condition it is
unable to find and seize the nipple, and equally unable to draw
sustenance therefrom, by its own unaided efforts. The _milk is ejected_,
by the _muscular action of the mother_, into the throat of the foetus,
and there is a peculiar and beautiful contrivance to obviate the danger
of the injected fluid's passing into the trachea instead of the
oesophagus.
Yet, from this helpless naked condition to that of the active,
well-clothed, experienced young, able to quit the maternal pouch at
will, and flee to it for protection, there is a well-understood and
perfectly appreciable concatenation of stages, each of which looks back
to, and depends on, those previously existing. And, during the whole of
these, the mother's presence is necessary to the comfort, and, for the
greater part of them, to the very existence of the infant.
Thus, once more, there is no condition of the animal, on which we may
fix, as being so simple, as to have no retrospective history.