Part 17 (1/2)

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 s.p.a.ces in the interstices of their contiguous angles.

Below this calcareous sh.e.l.l 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.

[Ill.u.s.tration: HEN'S EGG.]

Within this membrane there is another (_the chalaza_) which, closely enveloping the yelk, pa.s.ses 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 (alb.u.men), which fills the s.p.a.ce between it and the _membrana putaminis_. This fluid, though apparently h.o.m.ogeneous, 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 alb.u.men 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 alb.u.men, 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 a.s.signed to any being, the more it is a.s.sisted in infancy by the parent.

”This law is remarkably exemplified in the cla.s.s 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 cla.s.s, 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 pa.s.sing 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.

The umbilical cicatrix I have already alluded to; but I may be permitted to mention it again; because, in all the higher MAMMALIA, at least, it exists, throughout life, an eloquent witness to the organic connexion of the individual with a mother, and therefore to her pre-existence. If it were legitimate to suppose that the first individual of the species Man was created in the condition answering to that of a new-born infant, there would still be the need of maternal milk for its sustenance, and maternal care for its protection, for a considerable period; while, if we carry on the suggested stage to the period when this provision is no longer indispensable, the development of hair, nails, bones, &c., will have proceeded through many stages. And, in either condition, the navel cord or its cicatrix remains, to testify to something anterior to both.

XII.

THE CONCLUSION.

”We have no experience in the creation of worlds.”

CHALMERS.

We have pa.s.sed, in review before us the whole organic world: and the result is uniform; that no example can be selected from the vast vegetable kingdom, none from the vast animal kingdom, which did not at the instant of its creation present indubitable evidences of a previous history. This is not put forth as a _hypothesis_, but as a _necessity_; I do not say that it was _probably_ so, but that it was _certainly_ so; not that it _may have been thus_, but that it _could not have been otherwise_.

I do not touch the inorganic world: my acquaintance with chemistry is inadequate for this: perhaps the same law does not extend to the inorganic elements: perhaps their developments, and combinations are not, like the economy of plants and animals, essentially and exclusively cyclical: perhaps carbon and oxygen and hydrogen could be created in conditions, which obviously did not depend on any previously existing conditions. This I do not know: I neither affirm nor deny it.