axis, and its motion upwards is restrained within certain defined limits. We shall have occasion to recur to this mechanism so admirably adapted to secure that position of the germ which is most favorable for its receiving the nutrient warmth of the mother, at the same time preventing its tender structures from being bruised by rough contact with the shell or lining membranes. The form of the cicatricula, or rudiment of the future chick, changes from a spherical to a more longitudinal shape, and the progress of its organization is seen by a blood-vessel coming out from either side of it, branching into numerous smaller vessels, which unite at their termination, forming a marginal boundary on the covering of the yolk. The chick is the centre of this network of vessels, and as the embryo increases so do these vessels multiply, covering daily a larger space until they nearly pervade the membrane of the yolk. It appears from a beautiful experiment of Mr. Towne's, that at the first formation of these vessels, and probably before them, each branch is accompanied by a vessel carrying yolk into the body of the chick, which no doubt supplies the pabulum for its sustenance and growth. Between the third and fourth day a remarkable change is visible in the contents of the shell. The yolk suddenly becomes flattened, and a portion of the white or albumen is found to have penetrated the yolk bag. At about the same period a vascular membrane, termed by Sir E. Home, the vesicle, has so far become developed as to have passed from the body of the chick to the lining membrane of the shell. The increase of this membrane is proportioned to the growth of the embryo. It continues to enlarge over the surface of the membrane of the shell, which towards the end of incubation it entirely surrounds, thus forming an external covering to the yolk. This vesicle, or chorion, is full of bloodvessels-a system of arteries and veins-carrying livid red blood from the body of the chick, and returning it a bright red colour, fitted for the elimination of the structures of the chick. If an egg be opened between the twelfth and thirteenth day of incubation, this membrane will be prominently apparent; the pulses of the numerous blood-vessels will be seen propelling their contents, and presenting to the eye of the observer so animating and interesting a sight as to have been declared by Blumenbach to be the most beautiful spectacle in the organic creation. The progressive evolution of the chick is evinced by the development of its several organs. At about the sixth day its bare wings and legs are fully seen; the eyes are large and prominent, the brain and bill are clearly distinguished, and its organization is going on to completion. A few days additional growth discovers the wings and body covered with short feathers; and that which a week or ten days before was but an amorphous mass, is now furnished with shape, proportion, and organic life. About the fifteenth

day the yolk-bag begins to be taken up into the abdomen of the chick. The albumen has now disappeared from admixture with the yolk, and in this state, towards the completion of the chick's residence in the shell, it is found to have been gradually received into the chick's abdomen. We may here mention, that there is a small reservoir of air, called the folliculus aeris, enclosed between two membranes at the larger end of the shell, which increases in the progress of incubation. At the nineteenth day the vocal organs come into play, consequently respiration is established; the large blood-vessels which connect the chick with the chorion-any one of which if left open would prove fatal to the embryo-begin to be sealed and shrink, and every thing is combining to aid the chick in breaking its shell, and emerging into independent existence. The preparations necessary for completing this purpose are very remarkable. The package of the chick is so arranged, that while the body and appendages are enclosed in the smallest possible space, there is yet a passage left free in the long axis of the chick's head, to allow sufficient impetus to be gained by the recession of the head and neck, as to collect force enough by repeated blows, to break the shell and make its escape. The head itself is confined between the hip on one side and the wing on the other, which passes over the head as represented by Mr. Towne, in just contradiction of Sir E. Home's engraving. By this means anv lateral movement of the head is prevented, and the instinctive b.ows of the chick are directed to one spot, and not diffused and enfeebled as would be the result were its power of motion in this direction unrestrained. The tip of the upper mandible is supplied with a thick, hardened, horny point expressly for the purpose of breaking the shell, as it drops off after the chick has gained its liberty.

In preparing, at the request of the Treasurer of Guy's Hospital, a series of models to illustrate the changes in the hen's egg during incubation, Mr. Towne thought he had little else to do than to fix on some standard work, say Sir Everard Home's, and follow the author; or, as Mr. T. expresses it, 'place myself under his (Sir E. Home's) guidance, follow his track, and arrive at his results. 'I soon found (adds Mr. T.) that either I must consent implicitly 'to adopt the opinions of others, or determine to look and judge 'for myself.' And the results of this unshackled investigation are embodied in the paper which we now propose to consider.

We find that the first position, in the order of his observations that Mr. Towne has attacked, is the prevailing theory of the decarbonization of the blood. The chorion, as we have mentioned, is developed immediately beneath the lining membranes of the shell, in order, as was universally supposed, that the blood should be decarbonized by the air penetrating the porous shell, and that the folliculus aeris was a provisionary arrangement for the inter

val of time before the chorion had sufficiently grown. This theory has had the sanction of time, authority, analogy, concurrent testimony, and the confirmation of experiment. Mr. Towne first entertained a doubt of the correctness of the theory from observing that the lining membrane of the shell became uniformly thicker as incubation advanced, thus opposing a greater obstacle to the accession of air to the chorion, where it was evidently most needed. Frequent observation placed this fact beyond doubt, which Mr. Towne, with praiseworthy zeal, ascertained to exist also in the eggs of the linnet, sparrow, blackbird, moorhen, partridge, turkey, duck, and goose. The experiment on which the theory rested was, that the death of the chick followed on rendering the shell impervious to air by a coat of varnish.

'Now it seemed to me (says Mr. T.), that unless a perfectly innocent varnish had been employed, this was not a satisfactory experiment, inasmuch as admitting the shell to be pervious to air, so would it certainly be to any smell which might attach to a substance thus employed.' 'I then determined to repeat the experiment in my own way.'

The experiment consisted in varnishing a number of fresh eggs with successive coats of thickened albumen, until the shells were completely lackered.' They were then enveloped with four coverings of paper cut like the sections of an orange, well soaked in albumen, and so critically adjusted as to bring the middle of ' each section opposite the joining in the previous coating.' 'The 'whole formed a covering so thick and horny that I felt con'vinced it was entirely impermeable.' These eggs were submitted to incubation on the 18th of April, and one of them was opened on each day between the 4th and 10th inclusive, and the 'chicks had gone through all their changes without interruption.' The venous and arterial circulation was beautifully seen at the eleventh and twelve and a half days, under the same circumstances, and one egg that was opened on the nineteenth day, exhibited a proportionate maturity. No process had been suspended, and the chick was living and vigorous, and evinced a 'strong disposition to make its escape from the shell.'

6

Mr. Towne, sensible of the extreme importance of disturbing the prevailing opinion on insufficient evidence, submitted it to a still more rigorous test, adding an extra coat of paper to the four in the other experiment, and then three coats of oil-paint com'posed of white-lead, with a large portion of sugar of lead as a drier; this I did with the double intention of offering an addi'tional obstruction to the air, and also to prove whether the 'paper was or was not entirely sufficient for the purpose: con

'cluding that if it were not, the fume from so noxious an applica'tion must inevitably prevent the progress of incubation. All 'this, however, had no effect. I opened the egg at twelve and a half days, and found that no interruption had occurred, the venous ' and arterial circulation being perfectly natural.'

We have thus given the outline of the experiments from which Mr. Towne has drawn the inference, that the blood circulating in the chorion is not decarbonized by air derived from without through the shell. The deduction is certainly most startling; but we are at a loss to see how it can be evaded. We have ourselves carefully inspected the artificial coverings which surrounded the eggs, and after the most critical examination we could give, were left without doubt of their impermeability. The experiments, however, ought to be repeated in all the various ways which ingenuity can devise, and if with a similar result-which we fully anticipate-Mr. Towne's conclusion must be acknowledged. We know the pertinacity with which scientific men oftentimes reject innovations on old established opinions, and the sort of churlish refractoriness with which they hold off from admitting truth to be contained in novelties. That sort of hesitation which a wise caution requires is merged into obstinate incredulity, and a host of quibbles, shifts, and prevarications are summoned up to protect what is virtually a fixed determination, though it be dignified by the title of philosophical doubt, obstructing the ingress of truth, tricking the judgment, and perpetuating error.

In the present case Mr. Towne has other difficulties to encounter, He has apparently crushed a fondly cherished notion, but has not supplied a new one. The principle of vitality' to which he has referred is necessarily vague, and very unlike the plain, practical, homethrusting inferences which his well authenticated observations induce. We are disposed to think that this interesting subject of inquiry is again reduced to its first elements, and however great the temptation may be to speculate and raise dim conjectures concerning it, yet steady and laborious search alone can hope successfully to surmount the difficulties which surround it. We may feel reluctant to give up that in which we confided as a sure result of scientific knowledge, but to oppose the dictates of our judgment because we cannot make up the loss, is to league ourselves with the practical promoters of philosophy falsely so called.' It may unsettle our views, wound our vanity, and mock our discernment to be thus schooled, to begin the lessons we thought we had learnt; but he who has matriculated as a disciple of science, and after the manner of her most illustrious founder, is 'as a little 'child picking up pebbles on the vast shore of truth,' will often be thus disappointed, and will find the occasional non-plus of his 'reason affords a fairer scope and opportunity for the exercise of his industry and faith." Certain it is,' says Lord Bacon, whether

'it be believed or no, that the most excellent of metals, gold, is ' of all others the most pliant, and most enduring to be wrought; 'so of all living and breathing substances the perfectest (man) is 'the most susceptible of improvement, impression, and alteration.' We wish a little more of this ductility were possessed by the class of philosophers we have been reproaching.

We have noticed already that at the larger extremity of the egg there is a reservoir or bag of air, termed the folliculus aeris. During the first days of incubation it is very small, but increases. as this process advances. The chamber in which the air is enclosed was said to be formed by the separation of the two lamina of the lining membrane of the shell (the membrana albuminis); or rather to speak more accurately, the inner lamina, which closely adheres to its fellow throughout the shell, abruptly diverges at the greater extremity in a transverse direction, leaving the outer lamina to pass over the remainder of the shell. In this way a small portion of the interior of the egg-shell is isolated which is the containing cavity of the air. In the course of Mr. Towne's dissections of the egg, he was led to regard this description as erroneous. He noticed that the lining membrane of the shell underwent considerable changes during incubation, and that these changes were so uniform in their character that there generally 'needed no surer guide as to how far the process of incubation was proceeding successfully.' The transverse septum, however, forming the floor of the folliculus aeris, did not participate in these changes, but remained thin and semi-transparent throughout the period. This was a sufficient presumption against the identity of the two; and upon inserting a blow-pipe in the larger extremity of the shell, the whole of this membrane was raised by inflation. It was thus demonstrated to be a distinct membrane, unconnected with the membrane of the shell, the two layers of which remained in close approximation with each other, and in intimate adhesion to the shell. Mr. Towne has termed this the 'inner lining membrane,' which he says, is thin and delicate, and differs from the membrana albuminis in remaining almost unchanged during incubation. As this process, however, advances, it separates from it to a considerable extent, and its use 'appears to be to hold the contents of the egg in suspension 'within the shell, and thus protect the chick from being bruised, 'which might otherwise occur when the egg was subjected to

'motion.'

In assenting to the accuracy of this description of Mr. Towne's, we assure our readers that we have tested his experiments for ourselves, and that what we advance is consequently the result of ocular demonstration. The function which Mr. T. has assigned to the inner lining membrane, is, we think, correct; and we egard it as beautifully adapted for acting as a natural hammock