At the Fourneaux or Northern end of the tunnel--owing to increased difficulties peculiar to the locality--the perforation of the gallery was much delayed. A totally different system of mechanism for the compression of air was necessitated; and it was not before the 25th of January, 1863, that the boring-machine was in _successful_ operation on this side, or two years later than at Bardonneche. The experience, however, gained at this latter place, and the transfer of a few skilful workmen, soon raised the advance {65} made per day to an amount equivalent to that effected at the Southern entrance. Thus, on the South side (omitting the first year, 1861) since the beginning of 1862, and on the North side since the beginning of 1863, the new system of mechanical tunnelling may be said to have been in regular and _successful_ operation.

In the beginning of September of this year were completed in all three thousand five hundred and seventy metres of gallery. From this we deduct sixteen hundred metres done by manual labor, leaving, for the work done by the machines, a length of nineteen hundred and seventy metres. From this we can make a further deduction of the one hundred and seventy metres executed in the first year of experiment and trial at Bardonneche, so that we have eighteen hundred metres in length excavated by the machines in a time dating from the beginning of 1862 at the South end, and from the beginning of 1863 at the North end of the tunnel. Thus, up to the month of September, 1864, we have in all four years and six months; and eighteen hundred metres divided by 4.5 gives us four hundred metres as the rate of progress per year at each side, or in total, eight hundred metres per year. Basing our calculation, then, on this rate, we find that the eight thousand six hundred and fifty metres yet to be excavated will require about ten and a half more years; so that we may look forward to the opening of the Mont Cenis tunnel at about the year 1875. The directing engineers, who have given good proof of competency and skill, are, however, of opinion that this period may be considerably reduced, unless some totally unlooked-for obstacles are met with in the interior of the mountain. As has been indicated above, sixteen hundred metres in length of the tunnel was completed by manual labor before the introduction of the mechanical boring-engines, in a period of five years at the North and three years at the South side, equal to four years at each end; and eight hundred metres in four years gives us two hundred metres per year, or just one-half excavated by the machine in the same period.

In using the machines, up to the present time, a perfect ventilation of the tunnel has been secured by the compressed air escaping from the exhaust of the boring-engines; or by jets of air expressly impinged into the lower end of the gallery to clear out rapidly the smoke and vapor formed by the explosion of the mine. It should be remembered, moreover, that in working a gallery of this kind, where vertical shafts are impossible, by manual labor, a powerful and costly air-compressing apparatus would have been necessary for the ventilation of the tunnel alone, so that the economy of the system, as applied at the Mont Cenis over the general system of tunnelling in hard rock, is evident. I propose, in the second portion of this article, to give a short description of the machinery employed and the system of working adopted, both at the South and North ends of the Mont Cenis gallery.

II.

Travellers who are given to pedestrian exercises may easily visit the works being carried on for the perforation of the tunnel through the Alps, both at Bardonneche and at Modane, pa.s.sing from one mouth of the tunnel to the other by the Colle di Frejus; and in fine weather, the tourist would not repent the eight hours spent in walking from Bardonneche to Susa--a distance of about twenty-five miles. The road descends the valley of the Dora Ripari, and abounds in beautiful scenery. The railway to be constructed along this narrow defile will be found to tax the skill of the engineer as much as any road yet attempted. Its total length, from the terminus at Susa to the mouth of the Mont Cenis tunnel, will be forty kilometres, {66} or about twenty-four miles; and the difference of level between these two points is about two thousand five hundred feet, the line having a maximum gradient of one in forty, and a minimum of one in eighty-four.

There will be three tunnels of importance, having a total length of about ten thousand feet; three others of lesser dimensions, having a total length of five thousand five hundred feet; and twelve other small tunnels, of lengths varying from two hundred and twenty to eight hundred and fifty feet, their total length being five thousand four hundred feet. Thus, the total length of tunnel on these twenty-four miles of railway will be nearly twenty-one thousand feet, or about four miles--just one-sixth of the whole line. There will also be several examples of bridges and retaining walls of unusual dimensions.

The works being carried on at Bardonneche are on a larger scale than at Modane; so we will, with our readers' permission, suppose ourselves arrived in company at the former place, and the first point which we will visit together will be the large house containing the air-compressing machinery. Before entering, however, we will throw a glance at the exterior of the building. We find before us, as it were, _two_ houses, in a direct line one with the other--one situated at the foot of a steep ascent; and the other at about seventy or eighty feet above it, on the side of the mountain. These two houses are, however, but _one_, being joined by ten rows of inclined arch-work. Along the summit of each row of arches is a large iron pipe, more than a foot in diameter. These ten pipes, inclined at an angle of about forty-five degrees, come out of the side of the upper house, and enter the side of the lower house, and serve to conduct the water from the large reservoir above to the air-compressing machinery, which is arranged in the house below, exerting in this machinery the pressure of a column of water eighty-four feet six inches in height. On entering the compression-room, we have before us ten compressing-machines, precisely the same in all their parts--five on the right hand, and five on the left, forming, as it were, two groups of five each. In the centre of these two groups are two machines, in every respect like a couple of small steam-engines, only they are worked by compressed air instead of steam, and which we will call _aereomotori_. Each of these aereomotori imparts a rotary motion to a horizontal axis extending along the whole length of the room, and on which are a series of cams, which regulate the movements of the valves of the great compressors.

This axis we will call the "main shaft." One group of five compressors is totally independent of the other, and has its aereomotore with its main shaft; but still, with one single aereomotore, by means of a simple connecting apparatus, it is possible to work one or the other group separately, or both together; also, any number of the ten compressors can be disconnected for repairs without affecting the action of the rest, or may be injured without conveying any injury to the others. In front of each of the ten compressors are placed cylindrical recipients, in every respect like large steam-boilers, except that they have no fire-grate or flues, each having a capacity of seventeen cubic metres, or five hundred and eighty-three cubic feet. These recipients are put into communication one with the other by means of a tube similar to a steam-pipe connecting a series of steam-boilers; and each connection is furnished with a stop-valve, so that any one recipient can be isolated from the rest.

Let us now examine the end and action of this machinery. As the aereomotori which work the valves of the machines for forcing air into the recipients are themselves worked by compressed air coming from the recipients, it is evident that before we can put the compressing-machines in motion, we must have already some supply of compressed air in the {67} cylindrical vessels. This supply of air, compressed to a pressure of six atmospheres, is obtained in the following manner: Each group of five recipients, filled with air at the ordinary atmospheric pressure, is put in communication with a large pipe which enters into a cistern placed in the side of the mountain at about one hundred and sixty-two feet above the floor of the compressing-room. The first operation, then, is to open the equilibrium valves placed at the bottom of the two pipes (one from each group of recipients); water then rushes into the vessels, compressing the ordinary air therein contained to about a pressure of six atmospheres. A communication is now opened between this compressed air and the cylinders of the aereomotori, which commence their action precisely as a steam-engine would do on the admission of steam; a rotary motion is given to the main shaft; and the equilibrium valves, placed in chambers at the bottom of each of the ten pipes coming from the cistern of water placed in the house above, are opened. We will observe the operation in one of the ten lines of action, as it were, consisting of the pipe conducting the water from the cistern, the compressing-machine, and the cylindrical recipient. The equilibrium valve at the bottom of the pipe being opened in the manner above explained, the water, with its head of eighty-four feet six inches, rushes past it, along a short length of horizontal pipe (in which is an exhaust valve, now closed), and begins to mount a vertical column or tube of cast-iron about ten feet high and two feet in diameter: the air in this column undergoes compression until it has reached a pressure sufficient to force open a valve in a pipe issuing from the summit of the tube, and connecting it with the recipient. This valve being already weighted with the pressure of the air compressed to six atmospheres by the means previously explained, a certain quant.i.ty of air is thus forced into the vessel; at this moment, another revolution of the main shaft causes the equilibrium valve at the bottom of the conducting-pipe to be shut, and at the same time opens the exhaust valve at the foot of the vertical column. The head of water being now cut off, and the exhaust open, the water in the vertical column begins to sink by its own gravity, leaving a vacuum behind it, if it were not for a small clack-valve opening inward in the upper part of the compressing column, which opens by the external pressure of the air, so that by the time all the water has pa.s.sed out of the exhaust valve, the compressor is again full of atmospheric air; the valve in connection with the recipient being closed by the compressed air imprisoned in the vessel. The aereomotori continue their motion, another revolution of the main shaft shuts the exhaust and opens the equilibrium or admission valve; the column of water is again permitted to act, and the same action is repeated, more air being forced into the recipient at each round or _pulsation_ of the machine. Now, supposing no consumption of the compressed air to take place beyond that used for driving the aereomotori, it seems evident that the water in the vessels would be gradually forced out, owing to the growing pressure of the air inside, above the pressure of the column of water coming from the higher cistern; but the communication with this higher cistern is always kept open, the column of water acting, in fact, as a sort of moderator or governor to the compressing-machine, rising or falling according to the consumption of the compressed air, and always insuring that there shall be a pressure of six atmospheres acting against the valve at the summit of the vertical column. A water-tube placed on the outside of each group of recipients, with a graduated scale marked on it, indicates at a glance the consumption of air. If the perforating-machines in the tunnel cease working, the pressure augments in the recipients, and the water in them falls until an equilibrium is established, {68} between the pressure of the column of water and the force of the compressors, until, in fact, these work without being able to lift the valve at the summit of the vertical compressing column. On the other hand, if more air than usual be used for ventilating the tunnel, or by an accidental leakage in the conducting-pipes, the water rises rapidly in the recipients, and consequently in the water-gauge outside, and in thus creating an equilibrium, indicates the state of things. By this means a continual compensation of pressure is kept up, which prevents any shock on the valves, and causes the machine to work with the regularity and uniformity of a steam-engine provided with a governor. In every turn of the main shaft, a complete circle of effects take place in the compressors; and experience has shown that three turns a minute of the shaft--that is, three _pulsations_ of the compressing-machine per minute--are sufficient. It will thus be seen that a column of water, having the great velocity due to a head of eighty-four feet six inches, acts upon a column of air contained in a vertical tube; the effect of this velocity being to inject, as it were, a certain quant.i.ty of air into a recipient at each upward stroke of the column, and at each downward stroke drawing in after it an equivalent quant.i.ty of atmospheric air as a fresh supply. The ten recipients charged with air compressed to six atmospheres (ninety pounds on the square inch) in the manner above explained, serve as a reservoir of the force required for working the boring-engines in the tunnel, and for ventilating and purifying the gallery. The air is conducted in pipes about eight inches in diameter, having a thickness of metal of about three-eighths of an inch. Much doubt had previously been expressed as to the possibility of conveying compressed air to great distances without a very great and serious loss of power. The experience gained, however, at the Mont Cenis has shown that, conveyed to a distance of thirteen English miles, the loss would be but one-tenth of the original force; and that the actual measured loss of power in a distance of six thousand five hundred feet, a little more than a mile and a quarter, was less than 1-127th of the original pressure in the recipients.

The mouth of the tunnel is but a few hundred yards from the air-compressing house--we will now proceed thither. For nearly a mile in length the gallery is completed and lined with masonry. At the first view, we are struck with the bold outline of its section and its ample dimensions. Excepting, perhaps, the pa.s.sage of an occasional railway-truck, laden with pieces of rock and rubbish, we find nothing to remind us of the numbers of busy workmen and of the powerful machines which are laboring in the tunnel. All is perfectly quiet and solitary. Looking around us as we traverse this first and completed portion, we observe nothing very different from an ordinary railway-tunnel, with the exception of the great iron pipe which conveys the compressed air, and is attached to the side of the wall.

At the end of about a quarter of an hour we begin to hear sounds of activity, and little lights flickering in the distance indicate that we are approaching the scene of operations. In a few moments we reach the second division of the tunnel, or that part which is being enlarged from the comparatively small section made by the perforating-machine to its full dimensions, previously to being lined with masonry. In those portions where the workmen are engaged in the somewhat dangerous operation of detaching large blocks of stone from the roof, the tunnel is protected by a ceiling of ma.s.sive beams, under which the visitor pa.s.ses--not, however, without hurrying his pace and experiencing a feeling of satisfaction when the distance is completed.

Gradually leaving behind us the bee-like crowd of busy miners, with the eternal ring of their boring-bars against the hard rock, we find the excavated gallery {69} getting smaller and smaller, and the difficulties of picking our way increasing at every step; the sounds behind us get fainter and fainter, and in a short time we are again in the midst of a profound solitude.

The little gallery in which we are now stumbling our way over blocks of stone and rubbish, only varied by long tracts of thick slush and pools of water, is the section excavated by the boring-machine--in dimension about twelve feet broad by eight feet high. The tramway which has accompanied us all the way is still continued along this small section. In the middle portion underneath the rails is the ca.n.a.l, inclined toward the mouth of the tunnel, for carrying off the water; and in this ca.n.a.l are now collected the pipes for conveying the compressed air to the machines, and the gas for illuminating the gallery. At the end of a few minutes, a rattling, jingling sound indicates that we are near the end of our excursion, and that we are approaching the perforating-machines. On arriving, we find that nearly the whole of the little gallery is taken up by the engine, the frame of which, mounted upon wheels, rests upon the main tramway, so that the whole can be moved backward or forward as necessary. On examining the arrangement a little closely, we find that in reality we have before us nine or ten perforators, completely independent of one another, all mounted on one frame, and each capable of movement in any direction. Attached to every one of them are two flexible tubes, one for conveying the compressed air, and the other the water which is injected at every blow or stroke of the tool into the hole, for the purpose of clearing out the debris and for cooling the point of the "jumper." In front, directed against the rock, are nine or ten tubes (according to the number of perforators), very similar in appearance to large gun-barrels, out of which are discharged with great rapidity an equal number of boring-bars or jumpers. Motion is given to these jumpers by the direct admission of a blast of compressed air behind them, the return stroke being effected by a somewhat slighter pressure of air than was used to drive them forward. We will suppose the machine brought up for the commencement of an attack. The points most convenient for the boring of the holes having been selected, the nine or ten perforators, as the case may be, are carefully adjusted in front of them. The compressed air is then admitted, and the boring of the holes commences. On an average, at the end of about three-quarters of an hour, the nine or ten holes are pierced to a depth of two feet to two feet six inches. Another ten holes are then commenced, and so on, until about eighty holes are pierced. The greater number of these holes are driven toward the centre of the point of attack, and the rest round the perimeter. The driving of these eighty holes to an average depth of two feet three inches, is usually completed in about seven hours, and the second operation is then commenced.

The flexible tubes conveying the compressed air and the water are detached from the machines, and placed in security in the covered ca.n.a.l. The perforating-machine, mounted on its frame or truck, is drawn back on the tramway behind two ma.s.sive folding-doors of wood.

Miners then advance and charge the holes in the centre with powder, and adjust the matches; fire is given, and the miners retire behind the folding-doors, which are closed. The explosion opens a breach in the centre part of the front of attack. Powerful jets of compressed air are now injected, to clear off the smoke formed by the powder. As soon as the gallery is clear, the other holes in the perimeter are charged and fired, and more air is injected. Then comes the third operation. Gangs of workmen advance and clear away the debris and blocks of stone detached by the explosion of the mine, in little wagons running on a pair of rails placed by the side of the main tramway. This done, the main line is {70} prolonged to the requisite distance, and the perforating engine is again brought forward for a fresh attack. Thus, we have three distinct operations--first, the mechanical perforation of the holes; secondly, the charging and explosion of the mine; and thirdly, the clearing away of the debris.

By careful registers kept since the commencement of the work, it is found that the mean duration of each successive operation is as follows: for the perforation of the holes, seven hours thirty-nine minutes; for the charging and explosion of the mine, three hours twenty-nine minutes; for the clearing away of the debris, two hours thirty-three minutes; or, in all, nearly fourteen hours. Occasionally, however, the three operations may be completed in ten hours, all depending upon the hardness of the rock. It has been found practically more expeditious to make two series of operations in twenty-four hours.

Whatever may be the nature of the rock, if it is very hard, the depth of the holes is reduced; that is, the perforation is only continued for a certain given time--about six and a half hours--which, for the eighty holes with ten perforaters, gives us about three-quarters of an hour for each hole. The rock is generally of calcareous schist, crystallized, and exceedingly hard, traversed by thick veins of quartz, which often break the points of the boring-tools after a few blows. Each jumper gives about three blows per second, and makes one-eighteenth of a revolution on its axis at each blow, or one complete revolution every six seconds. Thus, in the three-quarters of an hour necessary to drive a single hole to the depth of twenty-seven inches, we have four hundred and fifty revolutions of the bar, and eighteen hundred violent blows given by the point against the hard rock, and that under an impulse of about one hundred and eighty pounds. These figures will give us some idea of the wear and tear of the perforating-machines. It is calculated that on an average one perforating-machine is worn out for every six metres of gallery, so that more than two thousand will be consumed before the completion of the tunnel. The total length completed at the Bardonneche side at the present time is just two thousand three hundred metres, or nearly a mile and a half.

At the north or Modane end, the mechanical perforators are precisely the same as at Bardonneche, as also is the system of working in the gallery. The machinery for the compression of air, however, is very different, more simple, and in every way an improvement upon that at the South end. Not finding any convenient means of obtaining a head of eighty-four feet of water sufficient in quant.i.ty for working a series of compressors, as at Bardonneche, there has been established at Modane a system of direct compression, the necessary force for which is derived from the current of the Arc. Six large water-wheels moved by this current give a reciprocating motion to a piston contained in a large horizontal cylinder of cast iron. This piston, having a column of water on each side of it, raises and lowers alternately these two columns, in two vertical tubes about ten feet high, compressing the air in each tube alternately, and forcing a certain quant.i.ty, at each upward stroke of the water, to enter into a cylindrical recipient.

There is very little loss of water in this machine, which in its action is very like a large double-barreled common air-pump. It is a question open to science whether the employment of compressed air for driving the perforating engines in a work such as is in operation at the Mont Cenis, could not be advantageously and economically exchanged for the employment of a direct hydraulic motive force, the ventilation of the tunnel being provided for by other means. The system, however, employed at Modane has many advantages, which it is impossible to overlook, and its complete success has given a marked and decided impulse to the modern science of tunnelling through hard rock.

{71}

Translated from the Civilta Cattolica.

ON THE UNITY OF TYPE IN THE ANIMAL KINGDOM.

I.

The generation of a human creature takes place neither by the development of a being which is found in the germ, sketched as it were like a miniature, nor by a sudden formation or an instantaneous transition from potential to actual existence. It is effected by the true production of a new being, which pre-exists only virtually in the activity of the germ communicated by the conceiver, and the successive transformation of the potential subject.

This truth, an _a priori_ postulate of philosophy, and demonstrated by physiology _a posteriori_, was ill.u.s.trated by us in a preceding article. Here we must discard an error which has sprung from this truth. For there have been materialists who maintained that there was but one type in the whole animal kingdom, that is, _man_, as he unites in himself in the highest possible degree perfection of organism and delicacy of feelings; and that all the species of inferior animals were so many stages in the development of that most perfect type. This opinion is thus expressed by Milne-Edwards in his highly esteemed lectures on the Physiology and Comparative Anatomy of Man and Animals:

"Every organized being undergoes in its development deep and various modifications. The character of the anatomical structure, no less than its vital faculties, changes as it pa.s.ses from the state of embryo to that of a perfect animal in its own species. Now all the animals which are derived from the same type move during a certain time in the same embryonic road, and resemble each other in that process of organization during a certain period of time, the longer as their zoological relationship is closer; afterward they deviate from the common road and each acquires the properties belonging to it. Those that are to have a more perfect structure proceed further than those whose organization is completed at less cost. It results from this that the transitory or embryonic state of a superior animal resembles, in a more or less wonderful manner, the permanent state of another animal lower in the same zoological series. Some authors have thought right to conclude from this that the diversity of species proceeds from a series of stages of this kind taking place at different degrees of the embryonic development; and these writers, falling into the exaggerations to which imitators are especially liable, have held that every superior animal, in order to reach its definitive form, must pa.s.s through the series of the proper forms of animals which are its inferiors in the zoological hierarchy; so that man, for instance, before he is born, is at first a kind of worm, then a mollusk, then a fish, or something like it, before he can a.s.sume the characters belonging to his species. An eminent professor has recently expressed these views in a concise form, saying that the embryology of the most perfect being is a comparative transitory anatomy, and that the anatomic table of the whole animal kingdom is a fixed and permanent representation of the movable aspect of human organogeny."

Thus, according to this opinion, man is the only type of animal life; and every inferior species is but an imitation, more or less perfect, of the same; an inchoation stopped in its course at a greater or shorter distance from the term to which the work of nature tends in its organization of the human embryo. In short, an {72} _entoma in difetto_, to use the language of Dante.

The doctrine is not new in the scientific world. It was proclaimed in the last century by Robinet, who held that all inferior beings are but so many proofs or sketches upon which nature practises in order to learn how to form man. In the beginning of the present century Lamarck, in Germany, following Kielmayer, reproduced the same theory.

According to him all the species of animals inferior to man are but so many lower steps at which the human embryo stops in its gradual development. Man, on the contrary, is the last term reached by nature after she has travelled all through the zoological scale, to fit herself for that work. About the same time the celebrated naturalist, Stephen Geoffroy Saint Hilaire, began to disseminate in France a.n.a.logous ideas under the name of _stages of development_ (_arret de developpement)_; and these ideas, exaggerated by some of his disciples, amounted in their minds to the same doctrine of Lamarck, just alluded to. Among them Professor Serres holds the first rank, and it is to him that Milne-Edwards alludes in the pa.s.sage just cited. He expresses himself thus:

"Human organogeny is a comparative transitory anatomy, as comparative anatomy is the fixed and permanent state of the organogeny of man; and, on the contrary, if we reverse the proposition, or method of investigation, and study animal life from the lowest to the highest, instead of considering it from the highest to the lowest, we shall see that the organisms of the series reproduce incessantly those of the embryos, and fix themselves in that state which for animals becomes the term of their development.

The long series of changes of form presented by the same organism in comparative anatomy is but the reproduction of the numerous series of transformations to which this organism is subjected in the embryo in the course of its development. In the embryo the pa.s.sage is rapid, in virtue of the power of the life which animates it; in the animal the life of the organism is exhausted, and it stops there, because it is not permitted to follow the course traced for the human embryo. Distinct stages on the one hand, progressive advance on the other, here is the secret of development, the fundamental difference which the human mind can perceive between comparative anatomy and organogeny. The animal series thus considered in its organisms is but a long chain of embryos which succeed each other gradually and at intervals, reaching at last man, who thus finds his physical development in comparative organogeny."

Thus speaks Serres. And in another place:

"The whole animal kingdom appears only like one animal in the course of formation in the different organisms. It stops here sooner, there later, and thus at the time of each interruption determines, by the state in which it then is, the distinctive and organized characters of cla.s.ses, families, genera, and species."

II.

THIS OPINION REFUTED BY PHILOSOPHICAL REASONS.

The futility of the above doctrine is manifest, in the first place, from the weakness of the foundation on which it rests. That foundation is no other than a kind of likeness which appears at first sight between the rudimental forms which, in the first steps of its development, are a.s.sumed by the human embryo, and the forms of some inferior animals. For the germ, by the very reason that it has not, as it was once believed, all the organism of the human body in microscopic proportions, but in order to acquire it must pa.s.s from potential to actual existence--by that very reason, is {73} subjected to continual metamorphoses, that is, to successive transformations, which give it different aspects, from that of a little disc to the perfect human figure. Now, it is clear that, in this gradual transition from the mere power to the act of perfect organization, a kind of a.n.a.logy or likeness to some of the numberless forms of inferior organizations of the animal kingdom may, and must, be found in its intermediate and incomplete state.

But, evidently, between a.n.a.logy and ident.i.ty there is an immense difference; and the fact of there being an a.n.a.logy with some of those forms, gives us no right to infer that there is one with all. Hence this theory is justly despised by the most celebrated naturalists as the whim of an extravagant fancy.

"According to Lamarck," says Fredault, in speaking of this, theory, "all the animals are but inferior grades at which the human germ stopped in its development, and man is but the result of the last efforts of a nature which has pa.s.sed successively through the grades of its novitiate, and has arrived at the last term of its perfection.

Presented in this view, the doctrine of epigenesis raised against itself the most simple and scientific common sense, as being manifestly erroneous. Numerous works on the development of the germ have demonstrated that appearances were taken for realities, and that imagination had created a real romance. It has been proved that if, at certain epochs of its development, the human germ has a distant resemblance either to a worm or a reptile, such resemblance is very remote, and that on this point we must believe as much as we would believe of the a.s.sertion of a man who, looking at the clouds, should say that he could discover the palaces and gardens of Armida, with hors.e.m.e.n and armies, and all that a heated imagination might fancy."

However, laying aside all that, the opinion which we are now examining originates, with those who uphold it, in a total absence of philosophical conceptions. That strange idea of the unity of type and of its stages, in order to establish the forms of inferior animals, would never have risen in the mind of any one who had duly considered the immutability of essences and the reason of the formation of a thing. The act of making differs from the thing made only as the means differs from the end. Both belong to the same order--one implies movement, the other rest. Their difference lies only in this: that what in the term is unfolded and complete, in its progress toward the term is found to be only sketched out, and having a tendency to formation. Hence it follows that, whatever the point of view from which we consider the embryo of each animal, it is nothing else but the total organism of the same in the course of formation; and, therefore, it differs as substantially from every other organism as the term itself toward which it proceeds. And what we affirm of the whole organism must be said of each of its parts, which are essentially related to the whole and follow the nature of the whole.

The first rudiments, for instance, of the hands of man could not properly be compared to the wings of a bird. As they are hands after being made, so they are hands in the process of formation; as their structure is different, so is their being immutable.

Whatever may be the likeness between the first appearances of the human embryo and the forms of lower animals, they are not the effect of a stable existence, but of a transitory and shifting existence, which does not const.i.tute a species, but is merely and essentially a movement toward the formation of the species. On the contrary, the forms presented by animals already const.i.tuted in their being belong to a stable and permanent existence, which diversifies one species from another. The difference, then, between the former and the latter is interior and substantial, and cannot be changed into exterior and accidental, as it would be if it consisted in {74} stopping or in travelling further on. The movement or tendency which takes place in the germ to become another thing until the said germ a.s.sumes a perfect organization relative to the being it must produce, is not a quality which can be discarded, since it is intimately combined with the subject itself in which it is found. The essence itself must be changed in it in order to obtain stability and consistency. But if the essence be changed, we are out of the question, since in that case we should have, not the human embryo arrested at this or that stage on its road, but a different being subst.i.tuted for it; of a.n.a.logous exterior appearance, perhaps, but substantially different, which would const.i.tute an annual of inferior degree.

In short, each animal is circ.u.mscribed in its own species, like every other being in nature. If to reach to the perfection required by its independent existence it needs development, every step in that journey is an inchoation of the next, and cannot exist but as such. To change its nature and to make it a permanent being, is as impossible as to change one essence into another.

Again: From the opinion we are refuting it would follow that all animals, man excepted, are so many monsters, since they are nothing else but deviations, for want of ulterior development, from what nature really intends to do as a term of its action. Thus anomaly is converted into law, disorder into order, an accidental case into a constant fact.

Finally, in that hypothesis we should have to affirm not only that the inferior and more imperfect species appeared on earth before the n.o.bler and the more akin to the unique and perfect type, but also that on the appearance of a more perfect species the preceding one had disappeared; being inferior in the scale of perfection. For what other reason could be alleged for nature's stopping at a bird when it intends to make a man, but that the causes are not properly disposed, or that circ.u.mstances are not quite favorable to the production of that perfect animal? Then when the causes are ready, and the circ.u.mstances propitious, it is necessary that man be fashioned and that the bird disappear. Now all that is contrary to experience. For all the species, together with the type, are of the same date, and we see them born constantly in the same circ.u.mstances which are common to all, either of temperature or atmosphere or lat.i.tude, etc.

The theory, then, of the unity of type in the animal kingdom and of stages of development falls to the ground, if we only look at it from a philosophical point of view.

III.

IT IS REFUTED BY PHYSIOLOGICAL REASONS.

However, physiological arguments have more force in this matter than the philosophical; since they are more closely connected with the subject, and have in their favor the tangible evidence of fact.

We shall take our arguments from three celebrated naturalists as the representatives of an immense number, whom want of s.p.a.ce forbids us to quote.