Blackwood's Edinburgh Magazine, Volume 57, No. 354, April 1845

by Various

But, 1. In order to derive any thing like an argument here, surely the whole human embryo, and not the brain only, ought to undergo these changes. But not only in man, in the other mammalia to which allusion is made, it is never the entire animal which passes through these transformations.

2. If the embryo of one of the mammalia pass through the fœtal stages of the fish and the bird, the embryo fish bears the same transitory resemblance to the fœtal condition of the bird or the mammal. So that the order here is reversed, and nothing appears proved but that some deviations of form are in all cases assumed before the final shape is adopted. And,

3. The physiologists who have made this branch of their science an especial study, tell us, as the result of their microscopic observations, that the embryo of the higher animals pursues a different course of development, from the very earliest stages, to that of the lower animals. It cannot be, therefore, according to the diagram that the author presents to us, that the same germ which is nourished up to a certain point to be fish, would, if transferred to other care and a better system of nutrition, be nourished into a bird or a mammal. If it is to be a mammal, it must be fashioned accordingly from the very beginning.

We will content ourselves with quoting, as our authority for these assertions, a passage from Dr Carpenter's work on Comparative Physiology; and we cite this author the more willingly, because he is certainly not one who is himself disposed to damp the ardour of speculation, and because the very similarity of some of his views, or expressions, renders him, at all events, an unexceptionable witness on this occasion.

"Allusion has been made to the correspondence which is discernible between the transitory forms exhibited by the embryos of the higher beings, and the permanent conditions of the lower. When this was first observed, it was stated as a general law, that all the higher animals, in the progress of their development, pass through a series of forms analogous to those encountered in ascending the animal scale. But this is not correct, for the entire animal never does exhibit such resemblance, except in a few particular cases to which allusion has already been made, (the case of the frog, and others, who undergo what is commonly called a metamorphosis.) And the resemblance, or analogy, which exists between individual organs, has no reference to their forms, but to their condition or grade of development. Thus we find the heart of the mammalia, which finally possesses four distinct cavities, at first in the condition of a prolonged tube, being a dilatation of the principal arterial trunk, and resembling the dorsal vessel of the articulated classes; subsequently it becomes shortened in relation to the rest of the structure, and presents a greater diameter, whilst a division of its cavity into two parts—a ventricle and an auricle—is evident, as in fishes; a third cavity, like that possessed by reptiles, is next formed by the subdivision of the auricle previously existing; and lastly, a fourth chamber is produced by the growth of a partition across the ventricle; and in perfect harmony with these changes are the metamorphoses presented by the system of vessels immediately proceeding from the heart. In like manner, the evolution of the brain in man is found to present conditions which may be successively compared with those of the fish, reptile bird, lower mammalia, and higher mammalia; but in no instance is there an exact identity between any of these. It is to be remembered, that every animal must pass through some change in the progress of its development, from its embryonic to its adult condition; and the correspondence is much closer between the embryonic fish and the fœtal bird, or mammal, than between these and the adult fish."—(P. 196.)

And take, also, the following short passage from the preface of the same work, where the author has been speaking of the latest discoveries of physiologists on the development of the embryo.

"Thus, when we ascend the scale of being, in either of the two organized kingdoms, we observe the principle of specialisation remarkably illustrated in the development of the germ into the perfect structure. In the lowest of each kind, the first-formed membranous expansion has the same character throughout, and the whole enters into the fully-developed structure. In higher grades the whole remains, but the organs evolved from the centre have evidently the most elevated character. In the highest none but the most central portion is persistent; the remainder forming organs of a temporary and subservient nature."

The fact that the animal kingdom exhibits a gradual progression from forms the most simple to forms the most complex, is, of course, appropriated by our author as a proof of his theory of successive development. It is well known, that whilst this scale of being is an idea which occurs to every observer, the naturalist finds insuperable difficulties in arranging the several species of animals according to such a scale. To relieve himself from these, the author has taken under his patronage what, in honour of its founder, he calls the Macleay System, in which the animal kingdom is "arranged along a series of close affinities, in a circular form;" into which circles we will excuse ourselves from entering. It is a system as confused as it is fantastic; and our author, who writes in general in a clear and lucid manner, in vain attempts to present us with an intelligible exposition of it. Arrange the animal creation how you will, in a line or in circles, there is one fact open to every observer, that however fine may be the gradations amongst the lower animals, the difference between the higher animals is very distinctly marked. It is a difference which does not at all accord with the hypothesis of our author, "that the simplest and most primitive type gave birth to the type next above it, and this again produced the next higher, and so on to the very highest, the stages of advance being in all cases very small—namely, from one species only to another; so that the phenomenon has always been of simple and modest character." Whilst he confines himself to mollusks, and suchlike obscure creatures, the phenomenon he supposes may not be very startling; but when he ascends to the higher and larger animals, whose forms and habits are well known to us—when he has to find a father for the horse, the lion, the rhinoceros, the elephant—his phenomenon, we are sure, will no longer retain its "simple and modest character."

Naturalists have observed, that there is a striking uniformity of plan even amongst animals of very different habits, and which, perhaps, inhabit different elements; they have remarked, that this uniformity is adhered to even when it appears to answer no specific purpose, as when in the fin of a whale the unbending bone bears the semblance of the jointed hand. This, too, is pressed into the service of our author's hypothesis. It is a curious fact. But if we say of it, that it appears to hint the existence of some law, and to tempt the investigation of the physiologist, we assign to it all the scientific importance that it can possibly deserve.

Some physiologists, we must be permitted to observe, have rather amused themselves by a display of ingenuity, than profited science by their discoveries of a unity of structure in animals of the most opposite description. It is easy to surprise the imagination by pointing out unexpected resemblances, if all cases of diversity are at the same time kept out of view. These writers will mention, for instance, that all quadrupeds have uniformly seven bones in the neck. The giraffe has no more than the pig. But they refuse to mention at the same time, that in birds the number varies from nine to twenty-three, and in reptiles from three to eight. Sometimes the merest fancy is indulged. We are told that in the pulpy substance of a certain mollusk there are lines drawn presenting a sketch of a vertebrated animal, and it is gravely intimated that nature seems to have made a rough design of the next work of art she was about to produce.