by their shooting out in that direction; and thus the uniform circulation of the blood is established, and the heart, or punctum saliens, as in this part of the development it is called, begins to exercise its functions, as is testified by its quick and regular pulsations. It is still only a lengthened tube, but it soon shows three protuberances, which are the cavities of the future auricle, ventricle, and bulb of the aorta. Afterward it assumes a rounded shape, by the folding of its parts, the whole of which are coiled, as it were, into a knot; by which means the heart gradually takes the form it is permanently to retain.

When the circulation of the blood is thus established, the digestive organs begin next to appear. Two laminæ are formed from the folds of the innermost of the pellicles which invests the embryo, and these, uniting, form a tube, which gradually expands into several dilated portions, to be afterward converted into the stomach, crop, gizzard, &c. These new organs, even in this rudimental state, very soon begin to exercise their proper office, by receiving into their cavities, through a tube, temporarily provided for that purpose, the fluid of the yolk, which they prepare into nourishment.

Aëration, as it is called, or an internal communication with the atmosphere, is essential to animal life. This is first provided for by a set of temporary vessels spread over the membrane of the egg, and communicating with the blood-vessels, which receive the oxygen of the air through the pores of the shell, and convey this necessary influence to the blood. The lungs, not being required to exercise their functions till the chick is excluded from the shell, are among the last organs that are formed. The rest of the apparatus necessary for aëration is also tardily constructed, for a similar reason. The construction of the heart, in its early stages, resembles this simple organ in fishes, because the fœtus is placed in circumstances analogous with those of aquatic animals; but, by degrees, the heart is divided into two

compartments; the auricle also, by a different process, becomes double, as well as the main artery, which last is afterward separated into two distinct vessels, the one forming the aorta, and the other the pulmonary artery; and thus a foundation is laid for the double circulation, which the future condition of the animal is to require.

It is not necessary, in a work like this, and might be tedious, to follow the rest of these wonderful processes through the development of the bony skeleton, the flesh, and the skin, with the various organs of sense and of motion, till the perfect animal is formed.

Enough has

been said to introduce the reader to a new world of wonders, in which the adaptations and contrivances are not less striking indications of creative skill and forethought, than in any other part of the operations of Nature. Dr Roget concludes his elaborate account of organic development, with the following sensible remarks, which, in few words, express the views naturally arising from the contemplation of these astonishing operations, and which seem appropriately to sum them up :

"We cannot but be forcibly struck with the numerous forms of transition through which every organ has to pass before arriving at its ultimate, and comparatively permanent condition. We cannot but wonder at the vast apparatus which is provided and put in action, for effecting all these changes; nor can we overlook the instances of express contrivance, in the formation of so many temporary structures, which are set up, like the scaffold of an edifice, in order to afford the means of transporting the materials of the building in proportion as they are wanted; nor refuse to recognize the evidence of Provident Design, in the regular order in which the work proceeds; every organ growing at its appointed time, by the addition of fresh particles, brought to it by the arteries, while others are carried away, by the absorbents, and are gradually acquiring the form which is to qualify it for the performance of its proper office in this vast and complicated system of animal life.”

* Roget's Bridgewater Treatise, p. 617, 618.

"

FIFTH WEEK-SATURDAY.

REPRODUCTION OF BIRDS.-PROSPECTIVE CONTRIVANCES.

"ON contemplating," says Dr Roget, "the infinitely diversified chain of means and ends, and of causes and effects, which, during the construction and assemblage of the numerous parts composing the animal machine, are in constant operation, adapting them to their various purposes, and combining them into one efficient and harmonious system, it is impossible not to be deeply impressed with the extent and the profoundness of the views of Providence, which far exceed the utmost boundaries of our vision, and surpass even the powers of the human imagination."

"

The truth of this remark must appear striking and obvious, even in the very slight, but, I believe, correct view which I yesterday gave of the progress of animal development, as exhibited in the chick, while yet enclosed in the shell. If we follow the process a little ́farther, we shall add still more to the proofs of Creative Intelligence, and beneficent intention.

I begin by observing, in general, that the whole animal apparatus is formed in the egg, not for immediate, but prospective use. At first there is a mere jelly, or what appears to be so; a little farther advanced, and there are bones, and muscles, and nerves. But these lie quite inactive for a long term; the nerve excites no action; the muscles do not move; the joints are not exercised, and are perfected slowly. The period of full development is not arrived; they have not yet received their stimulus to activity. The whole, then, is in a state of preparation. Conduit-pipes without their fluids; glands and ducts without their secretions; sensibilities dormant;

*Roget's Bridgewater Treatise, vol. ii. p. 600.

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and a mechanism quite inoperative; a whole animal system beautifully contrived, but only in prospective contrivance.* Paley applies a similar mode of reasoning to the single organs of the eye and of the lungs. Adverting to the latter, he says, in his own graphic style, Composed of air-vessels where there is no air, elaborately constructed for the alternate admission and expulsion of an elastic fluid, where no such fluid exists, this great organ, with the whole apparatus belonging to it, lies collapsed in the foetal thorax; yet in order and in readiness for action, the first moment that the occasion requires its service. This is having a machine locked up in store for future use; which incontestably proves that the case was expected to occur in which this use might be experienced; but expectation is the proper act of intelligence. Considering the state in which an animal exists before its birth, I should look for nothing less in its body than a system of lungs. It is like finding a pair of bellows in the bottom of the sea, of no sort of use in the situation in which they are found; formed for an action which was impossible to be exerted; holding no relation or fitness to the element which surrounds them, but both to another element, in another place."+

The temporary contrivances noticed in the previous paper, which are intended to answer the purposes of life in the foetus, while it remains enclosed in the egg, and which are absorbed and disappear as soon as they have accomplished their object, form a kind of counterpart to those which are prospective, and are no less indicative of Design. They are like the wooden frame of an arch, which is necessary for carrying on the work, yet is to be taken down, as no longer of use, but the contrary, when the structure is finished. A temporary contrivance of this kind exists in the bill-scale, as it is called, of the chick, which is intended, evidently, for no other purpose than that of enabling the imprisoned bird to break

* Sir Charles Bell's Note in Paley's Natural Theology, vol. i. pp. 317, 318. + Paley's Natural Theology, vol. i. pp. 315, 316.

open the door of its jail, and drops off a few days after it is hatched. This instrument, is a small, sharp, and hard protuberance on the bill of the chick, which is of itself then too soft to answer this important end, being, at this ståge, left in such a state, doubtless, for some object connected with the welfare of the bird. It is curious to remark an instance of the striking uniformity of instincts, in the manner in which the chicks of all species employ this temporary instrument for their extrication. M. Reaumur found, that all chickens chip the shell in the direction from left to right; and that the circle in which they chip invariably cuts the egg at right angles to its transverse axis, and never obliquely.

Another remarkable provision, with relation to the welfare of the chick, immediately before and after its extrusion from the shell, is found in the yolk. The white, or albumen of the egg, goes to the nourishment of the chick while the process of development of organs is proceeding; but the yolk is embraced in the body of the young bird, before it arrives at a state which fits it for living in the open air, and a duct leads from the membrane enclosing this mass of nutriment into the first intestine; and thus is the chick nourished during its first feeble existence, the yolk being to it, what milk is to the offspring of the mammalia.

Add to all this, the formation of a kind of down over the greater part of the body of the chick, while it is yet enclosed in the shell, to serve as a temporary protection to its body when first exposed to the weather, and to afford time for the production of the feathers, which could not conveniently be produced within the narrow and compact bounds of the egg.

All these circumstances, which relate to organic reproduction in the first stages of a bird's existence, are so obviously proofs of Divine wisdom, that they require no further comment; but the argument which they furnish derives particular interest and force from the instincts with which these developments are connected in the