Imágenes de página
PDF

worm to have no higher genealogy than the element which is the lightning of heaven, and too mnch honour to the subtle chemistry of the earth to be the father of a crawling subject, of some bag, or sack, or imperceptible globule of animal life? No ; we have no recoil against this generation of an animaleule by the wonderful chemistry of God; our objection to this doctrine is, that it is not proved.

But, proved or not, our author has still the most difficult part of his task to accomplish. From his animated globule he has to develop the whole creation of vegetable and animal life. We shall be contented with watching its development through one branch, that of the animal kingdom.

The idea of the development of the animal creation from certain primary rndiments or simple forms of life, is due, we believe, to Lamarck; and although his peculiar theory has met, and deservedly, with ridicule, we do not hesitate to say that it is far more plausible, and substantially far more rational, than that which our author has sub

stituted. Geology reveals to us a gradual extinction of species, accompanied by a successive appearance of new species;* it reveals to us also that the surface of the earth has undergone great mutations; that land and sea have frequently changed places; and that the climate of the several regions of the world, owing to many causes, has greatly varied. Natural history is replete with striking accounts of the modifications produced in a race of animals by the change of climate, diet, and the enforcement of new habits; and linking all these facts together, it docs not appear a very violent supposition, nor one that departs from the frequent analogies of nature, to say, that the causes which have brought about the extinction of certain species may have also operated to the development of new species. The manifest error of Lamarck was an egregious exaggeration of certain well-known truths. Because external circumstances may do much in directing the inherent power of development pos

* "In tracing the series of fossiliferous formations, from the most ancient to the more modern, the first deposits in which we meet with assemblages of organic remains having a near analogy to the Fauna of certain parts of the globe in our own time, are those commonly called tertiary. Even in the Eocene, or oldest subdivision of these tertiary formations, some few of the testacea belong to existing species, although almost all of them, and apparently all the associated vertebrata, are now extinct. These Eocene strata are succeeded by a great number of modern deposits, which depart gradually in the character of their fossils from the Eocene type, and approach more and more to that of the living creation. In the present state of science, it is chiefly by the aid of shells that we are enabled to arrive at the results; for, of all classes, the testacea are the most generally diffused in a fossit state, and may be called the medals principally employed by nature in recording the chronology of past events. In the Miocene deposits, which succeed next to the Eocene, we begin to find a considerable number, although still a minority, of recent species intermixed with some fossils common to the preceding epoch. We then arrive at the Pliocene strata, in which species now contemporary with man begin to preponderate, and in the newest of which nine-tenths of the fossils agree with species still inhabiting the neighbouring sea.

"In thus passing from the older to the newer members of the tertiary system, we meet with many chasms ; but none which separate entirely, and by a broad line of demarcation, one state of the organic world from another. There are no signs of an abrupt termination of one Fauna and Flora, and the starting into life Of new and wholly distinct forms. Although we are far from being able to demonstrate geologically an insensible transition from the Eocene to the recent Fauna, yet we may affirm that the more we enlarge and perfect our survey of Europe, the more nearly do we approximate to such a continuous series, and the more gradually are we conducted from times when many of the genera and nearly all the species were extinct, to those in which scarcely a single species flourished which we do not know to exist at present."—Ltell's PrincipUt of Geology. Vol. i. p. 283.

sessed by a given organization, he resolved that it should do every thing. The camelopard was to get his long neck by stretching for his food; and the dock her web-foot by paddling in the water. But the author before us breaks loose entirely from the region of facts; or rather he announces to us, on his own responsibility, an entirely new fact—that it is the law of animal life that each species should, from time to time, produce a brood of the species next in order of perfection or complexity of organization. With him, this development is the result merely of a law of generation which he himself has devised to meet the emergency.

Amongst the laws of life, the most conspicuous and undoubted is this— that each species reproduces itself, that like begets like. This law our author cannot of course gainsay; but he appends to it another overruling law, that from time to time, at long intervals, the like does not beget the like, but the different and superior form of organization. In other words, the old law changes from time to time. Of this novel description of law he boiTows the following illustration of Mr Babbage:—

"Unquestionably, what we ordinarily see of nature is calculated to impress a conviction that each species invariably produces its like. But I would here call attention to a remarkable illustration of natural law, which has been brought forward by Mr Babbage in his Ninth Bridgewater Treatise. The reader is requested to suppose himself seated before the calculating machine and observing it. It is moved by a weight, and there is a wheel which revolves through a small angle round its axis, at short intervals, presenting to the eye successively a series of numbers engraved on its divided circumference. "Let the figures thus seen, be the series 1, 2, 3, 4, 5, &c. &c., of natural numbers, each of which exceeds its immediate antecedent by unity.

"Now, reader,"' says Mr Babbage," let me ask you how long you will have counted before you are firmly convinced that the engine has been so adjusted that it will continue, whilst its motion is maintained, to produce the same series of natural numbers .' Some minds are so constituted, that after passing the first hundred terms they will be satisfied

that they are acquainted with the law. After seeing five hundred terms, few will doubt; and after the fifty thousandth term, the propensity to believe that the succeeding term will be fifty thousand and one, will be almost irresistible. That term will be fifty thousand and one, and the same regular succession will eontinue; the five millionth, and the fifty millionth term will still appear in their expected order, and one unbroken chain of natural numbers will pass before your eyes from one up to one hundred million.

"True to the vast induction which has been made, the next succeeding term will be one hundred million and one; but the next number presented by the rim of the wheel, instead of being one hundred million and two, is one hundred million ten thousand and two. The law changes."

The illustration is carried through a page or two more, but we have quoted all that is essential.

Mr Babbage makes a very useless parade here of his calculating machine. A common household clock that strikes the hours, would illustrate all that his machine can possibly illustrate. If the reader seat himself before that homely piece of mechanism, he will hear it tick for sixty minutes, when the law ofthe machine will change, and it will strike.

In a scientific point of view it is absurd to talk about the law of his machine. His machine partakes only of the laws of mechanics, which, we presume, are as constant there as elsewhere. Our only definition of law is, a sequence that is constant; deny its constancy, and you deny it to be law; it is a mere contradiction in terms to speak of a law that changes.

If, therefore, our author, guided by this illustration of Mr Babbage's, proclaims a law of animal life which changes of itself from time to time, he is departing from the fundamental principle of all science—he who is so zealous to reduce all phenomenon to the formula of science! Anxioift to escape from an abrupt interposition of creative power, he introduces a sndden mutability in the laws themselves of nature! If it be said that he does not (although his words

[graphic]

imply it) insist upon a single nature that varies at interval?

contends for a variable result, produced by the law of reproduction acting under varied circumstances, and in co-operation with different laws—then was Mr Babbage's machine of no use whatever to him, nor did he stand in need of any peculiar illustration. There is not a class of phenomena which does not exhibit this variety of result by the diversified co-operation of laws constant in themselves. The frozen river becomes motionless; it ceases to flow; yet no one attributes any inconstancy to the laws of heat, or the laws of hydrostatics.

Quitting these abstractions, in which the writer before us has shown himself no very great adept, let us enquire by what arguments he attempts to support his peculiar principles of development. That on which he appears chiefly to rely is the fact, that the embryo of one of the higher animals passes through the foetal stages of the lower animals—the fish, the reptile, the bird—before it assumes its last definite shape. From this he would infer, that the germ of life is alike in all, and that it depends only on peculiarities of gestation whether it shall become a fish, a fowl, or a mammal. He lays particular stress on the circumstance, that the brain of the human embryo passes through these several stages.

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 foetal stages of the fish and the bird, the embryo fish bears the same transitory resemblance to the foetal 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 stndy, 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 anthor 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/or»u, 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 foetal 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 fullydeveloped 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 coursc, appro

Edated by our author as a proof of is 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 Macteay

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 docs 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 veryhighest, 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 mollushs, 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 bypointing 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 arc 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.

[graphic]

When Dr Carpenter tells us, in exemplifying this law of unity of composition, that "the sknll is but an expansion of the three highest vertebrae, modified to afford space for the development of the contained brain and of the organs of sense," p. 191— is he much wiser than those entomologists whom he had been previously criticising for "maintaining that the wing of an insect is a modification of its leg?" Verily we suspect that if Martinus Scriblerus had had his attention drawn to this manner of viewing things, it would have greatly excited his learned ingenuity: he would probably have begun to apply this scientific method to a variety of things, and found a unity of composition never before dreamt of. What should have prevented him from casting a philosophic glance upon the furniture of his room? With less ingenuity than certain physiologists, he would easily detect a marvellous unity of plan. He would have probably taken the table with its four legs, and the disk they support, as his great type of joinery, and would have traced a modification of this type in all the articles around him. The chair is manifestly nothing else than the table, with a development of the hinder legs commonly called the back. From the chair to the sofa the transition would be ridiculously easy; indeed the sofa can only be considered as a variety of the chair, produced by a high state of cul

tivation. In the footstool, or ottoman, the disk of the table has become thick and pulpy, while its legs have dwindled into small globular supports. This exaggeration of the upper portion at the expense of the lower, is carried a step further in the chest of drawers, where the small globular supports bear a singular disproportion to the corpulent figure they sustain. In some varieties even these knob-like legs are wanting; but precisely in these cases, he would observe, the knobs invariably re-appear in the shape of handles, which are still a sort of paw. What is the fire-screen, he would say, but a table with the disk in a vertical position? What the four-post bedstead but a reduplication of the original type, a table placed' on a table, the upper one being laid open? If he had had the advantage of reading Mr Dickens, he would have mentioned, in confirmation of this view, that young Mr Weller, when sleeping under a table, congratulates himself upon enjoying the luxury of a fourpost bedstead. The coal-scuttle might perhaps present some difficulties; but if he might be allowed to approach it through the bo-table, he would doubtless succeed in tracing here also the unity of composition. In the lootable the four legs have collapsed into a central column! The coal-scuttle is only a loo-table with the edges of the disk curled up—assuming a bonnet-like shape, the result, perhaps, of its long domesticity. In short, we believe the only insuperable difficulty Martin would encounter, would be, when, after having completed his survey, he would run off to the joiner to convince him of the unity of plan on which he had been so unconsciously working.

It was a bold step of our author's to adduce thegeographical distribution of theseveral species of animals as a proof of his law of development. To most minds it would have immediately occurred as an objection. Each region of the earth has its own peculiar fauna, and this difference is not accountable on any known influence of soil or climate. What can explain the peculiar fauna of New Holland? If all the varieties of animal life spring from one and the same germ under the uniform laws of nature, how is It that in some re

« AnteriorContinuar »