ABRIDGMENT OF THE CONTEMPLATION OF NATURE
BY Mr. Bonnet, of GENEVA

CHAPTER VII
OF ANIMAL ECONOMY

    1. The nerves, which extend themselves into all parts from the brain, are distinguished into several principal divisions, that are more or less numerous, or more or less extended. Each division reaches to the part for which it is destined, and whose structure corresponds with the functions appointed for it to exercise.

Feeling, sight, hearing, taste and smell, are five kinds of senses, which contain under them an almost infinite number of-species. The shaking which the mediate or immediate impression ok objects pro­duces on the nerves, give birth to those different kinds of sensations, which may all be reduced to feeling, of which they are properly only modifications. The organs of the senses are the instruments of these modifications. The number, extent and delicacy of the senses. constitute the degree of animal perfection.

The nerves, which seem to resemble the strings of a musical instru­ment, are not stretched like them. Some animals are endowed with an exquisite sensation, that are themselves little otherwise than a thick jelly: how then can we admit of elastic strings in this jelly? While the foetus is altogether gelatinous, it regulates at that time its mem­bers. With what amazing swiftness then must the impressions of objects communicate themselves to the soul! and with what won­derful celerity must the members obey the will! Thus we are led to suppose in the nerves a very subtle and elastic fluid, whose motions, being analogous to those of light, or electrical fluid, produce all the phenomena of sight. The animal spirits are this fluid, which the brain extracts and prepares, and continually conveys into the nerves, and by the nerves into all parts, which it nourishes, moves and animates.

2. An animal had in vain received senses, by means of which it can distinguish between what is useful or hurtful, if it were not able to give itself any motion for the attaining the one, and avoiding the other. It is therefore furnished with organs that procure to it this faculty, These organs are the muscles, which by the dilitation and contraction, and by the lengthening and shor­tening of the fibres that compose them, communicate to all parts the motions which are suited to the wants of the animal.

It is evident, from experiments, that the nerves contribute to the exercise of the muscles. The spirits which they disperse therein, insinuate themselves into all the vesicles, dilate them, and by that means put the organ into action.

One property of the muscular fibre, whose effects are diversified a thousand ways, the cause of which is concealed from us, is that, by virtue whereof it contracts itself on the touch of any body, either solid or liquid. This is called irritability. By means of this, different parts of the animal continue to move, after they have been separated from the entire body; and the heart, when detached from the breast, performs a number of pulsations, which cease as soon as the blood in the cavity is evacuated.

3. From that part which gives admittance to the food, to that from whence issues the remains of the grosser aliment, there is one continual canal, which is formed differently in different parts of its extent. There are three principal parts distinguished in it: the oesophegas, the stomach, and the intestines. All these are formed of various membranes laid on each other, and which are themselves composed of fibres differently interwoven. The mus­cles, wherewith one or several of these membranes are furnished, impress divers motions on the organ, the principal of which, called the peristaltic motion, bruises the aliment, and forces it from place to place.

The oesphagus receives the grosser nourishment, and transmits it to the stomach, that prepares it : it afterward passes into the intestines, where it undergoes new preparation. From thence it enters into some very small vessels, that convey it to those of circulation, where it assumes the name of blood.

Whilst the most delicate part of the aliment is subject to all these preparations, the grosser part is evacuated by different ways. Some times the animal discharges it as a sediment sometimes, being trans formed into a subtle liquour, it is carried to the surface of the skin by an infinite number of very fine vessels, whose exterior apertures are sometimes so small that a grain of sand is capable of covering several thousands of them.

Other vessels, which, like them, communicate with the surface of the skin, pump in the vapours that float in the air, and convey them into the blood.

4. Circulation is that perpetual motion by which the blood is con­veyed from a point internally to the extremities, and flows back again from the extremities to the same point. The point from whence the blood springs, is called the heart. It has two motions, one of con. traction, or systole, by means of which it forces out the blood con­tained in its cavity; the other of dilation, or diastole, by which it receives the blood again.

Two kinds of vessels join to the heart: the arteries, which convey the blood to the extremities; and the veins, which carry it back from the extremities to the heart.

The arteries have, like the heart, their systole and diastole, and divide and subdivide themselves, as do the veins, into an infinite number of branches, which diminish in diameter in proportion to their distance from their origin. The perpetual motion of circulation pre­vents the corruption and extravasation of the nutricious fluid, rectifies it more and more, and disposes it insensibly to renew the nature of the animal.

5. Respiration comprehends two alternate motions; one of inspi­ration, which gives admittance to the air within ; the other, of expi­ration, which expels it, filled with the vapours of the animal.

The lungs are the principal instruments of respiration.- They are principally formed of a collection of cartilaginous and elastic vessels. which, after being divided and subdivided into a prodigious number of branches, meet in different parts, and terminate at one or more com­mon trunks, called trachae, or air vessels, whose aperture is on the outside of the body. The ramifications of the air vessels are con­nected with the vessels of circulation, and accompany them in their passage through the lungs.

6. The blood is that rich fund from whence nature derives that diversity of materials she employs with so much art in the construction of her wonderful edifice. This, as it goes from the heart, meets here and there on its passage, with certain organical, and as it were knot­ted masses. in which it is deprived of part of its principles.

We cannot yet penetrate the true mechanism of secretions: we can only faintly perceive,, that they may operate by a gradual diminu­tion of the vessels which proportions them to the smallness of the par­ticles that are to be separated. They may likewise bear some affinity to the configuration of these particles, and favour the extraction of them by means of the slackening which their folds and various circum­volutions occasion to the circulation. Thus it is, that by causing the aliment to pass through an infinite number of strainers, nature is ena­bled to assimilate it to the animal, and incorporate it into his flesh. This is then neither chyle nor blood ; it is a much more refined liquor, and known by the vague name of lymph.

We cannot sufficiently admire the prodigious apparatus of vessels which perform the secretions of different kinds. The kidneys, the liver, the pancreas, &c. are labyrinths in which the most consummate anatomist is bewildered. We can only discover an inconceivable mass of white tubes, of an extreme minuteness, folded together in thousands of different ways, which do not admit of any injection, though adhering to the blood vessels, and being placed end to end by imagination, would have formed a chain of several leagues in length. This is all that art has discovered in the secretory organs. But what a number of inter­esting particles do these minute, hollow cylinders contain, which have escaped our notice and instruments! What varieties should we not discover in their structure, functions and exercise, were we permitted to descend to the bottom of this abyss, which conceals from us one of the greatest mysteries of nature! All the animal liquors are more or less mixed, and these small tubes no doubt sufficiently diversify them­selves to separate the various molecules that must necessarily enter into- the composition of every liquor. What then must be the struc­ture and fineness of those that filter this so subtle fluid, compared to ether or light, whose operations are diversified almost to infinity,

7. If we knew how a single fibre grows, we could tell how the animal grows; for his whole body is only an assemblage of fibres. differently formed and combined. Growth always operates by nutrition. This incorporates into the fibre molecules of an heterogeneous nature, which extend in every part. The fibre incorporates into itself the heterogeneous molecules according to its own nature. A. fibre is itself composed of other fibres: these of still other fibres of which there would be no end. But the fibre is formed of mole­cules or elements, whose nature, proportions, and arrangement, re­spectively determine the species of the fibre, and adapt it to such or such a function. Thus the elements of the fibre ultimately effect assimilation, which by uniting with the nutricious molecules, that have an affinity with them, give them at the same time an arrangement like that which they have in the fibre. The extension of the fibres sup. poses that its elements may separate more or less from each other: but this separation hath its bound, and these bounds are those of the growth. In proportion as the fibre grows, it acquires more solidity. for the number of incorporated molecules increases every day, since it only grows by the successive incorporation of molecules of a fo reign nature. The more the solidity augments, the more the supple ness diminishes. There are more molecules, more coherence, and more attraction under the same foldage. The fibre then tends to a state of hardness, and the last term of its hardening is the last term of its growth. When therefore the fibre has acquired its full growth, it is a little organized whole, composed of its elementary molecules, and of all such as nutrition has incorporated with them during the time of their growth. If then we could separate from the fibre all those molecules which it has assimilated, we should restore itto its pri­mitive state. This may be applied to all organized bodies. They are, if we choose to term them so, net-work. A secret force impels the ailment into the meshes. It increases them in bulk, and supplies them by little and little. It likewise insinuates itself into the elements of the solid mass itself. The net-work stretches, thickens, and at length becomes hard.

8. We may easily comprehend, that all the parts of an animal have such strict and indissoluble connexions between them, that they must necessarily .have always co-existed together. The arteries imply veins; both of these imply nerves; the latter the brain ; this the heart; and all of them suppose a multitude of other organs.

in the germ of a chick there is at first perceived a vital point, whose constant motion attracts the attention of the observer. The alternate and quick contractions and dilatation of the living point, sufficiently indicate that it is the heart. But this heart seems to be without any covering, and to be placed on the outside of the body. instead of appearing in the form of a minute pyramidical mass, it bears the resemblance of a semicircle. The other viscera appear successively, and range themselves after each other, round the living speck. We cannot as yet discover any general folding; all is transparent or nearly so; and we only perceive by little and little those teguments which are appointed to cover all the parts.

In its first beginnings the animal is almost entirely fluid. It assumes by degrees the consistence of a jelly. All the parts have at that time situations, forms, and proportions that differ greatly from those they will afterward acquire. Their minuteness, softness, and transparency, serve to strengthen the illusion. We persuade ourselves that a bowel is naked, because the transparency of its coverings prevent our see­ing them.

Would you have a short and easy demonstration of this? When the lungs of the chick are first perceivable, their size is but the thou­sandth part of an inch. It would have been visible at the fourth part of these dimensions, were it not endued with the most perfect transpa­rency. The liver is much greater at its first appearance ; its transparency alone renders it invisible. It is the same with respect to the kidneys whilst they do not appear even to exist, they separate the urine. The heart forces the blood into the arteries sooner than we could imagine, and it can only be perceived by the growth of the embryo, which is never more accelerated than at the very beginning.

Many other facts concur with these to establish the pre-existence ­of organical wholes. We are now sensible that many insects multiply, like plants, by slips. We cut them into pieces, and each piece rege­nerates, and becomes a perfect animal. Earth worms are ranked in the number of those insects that are reproduced from their disjoined parts; and being very large, the phenomena of their regeneration is very perceptible. The piece that is cut off never acquires any growth; it always remains as the section left it; only it falls away in a greater or lesser degree. But aftersome time there appears a very small whitish pimple at its extremity, which increases by degrees in bulk and length. There are soon discovered rings, which are at first very small and very close. They spread themselves insensibly every way. New lungs, a new heart, a new stomach, disclose themselves, and with them a number of other organs. This piece, which is newly produced, is extremely slender, and altogether disproportioned to the part on which it grew. We may imagine that we see a worm growing, that it is grafted at the end of this stump, endeavouring to lengthen it. This little vermiform appendage unfolds itself slowly. At length it equals in thickness the piece from which it was cut, and exceeds it in length. It can no longer be distinguished from it but by its colour. which is somewhat fainter.

Here then is a new organical whole, which grows from an ancient one, and constitutes the same body: there is an animal slip that grows and expands itself on the stump of an animal, as a vegetable slip does on the trunk of a tree. Remark that the flesh of the piece cut off does not in the least contribute to the formation of the part regene­rated; the stump only nourishes the bud; it being the soil in which the latter vegetates. The part then that is reproduced passes through all the degrees of growth, by which the entire animal itself had before passed. It is a real animal, which pre-existed in a very minute form in the great animal that served it for a matrix.

Vegetable productions exhibit to us the same consequences. If a tree be topped, that does not lengthen the trunk of it; but it sends forth a multitude of buds, in each of which a little tree is comprised for the bud or branch that springs from it is a tree that is grafted on the trunk that nourishes it.

Every seed, in like manner, comprises a plant in miniature. On a very slight inspection, we may very easily discover the stalk, leaves, and root of this little plant. But the curious rise much higher, and distinguish in a bulbous root or growing bud those flowers that do not blow till the ensuing year.

When the evolution commences in an organized whole, its form differs so prodigiously from that which it will afterward assume, that should be apt to mistake it, were it not to accompany it in all its Progress. Observe how the parts of a plant are folded together, entwined. or concentred in the seed or bud; Is this that majestic tree which will ere long overshadow a large space of ground? This the flowers that will so gracefully display itself? This the fruit that will assume such a regular figure? You can now only perceive an uniform ed mass of knotted filaments; yet this little chaos may already contain in it a world, where all is organized and symmetrical.

You have seen frogs in their first state. They appear at that time to consist only of a large head and a long tail. Such is the chick when it begins to expand itself. A very slender tail, stretched in a straight line, is joined to a large head; and the tail contains all the rudiments of the composition; nay, is the very composition itself; and the transparent fluid in which it floats, constitutes the whole of those soft parts with which it is afterward covered.

The same revolutions, therefore, which occasion the heart of the chick to be transformed from its semicircular shape to that of a pyramid, bring the chick itself to a state of perfection. If we were permitted to penetrate to the foundation of the mechan­ism whereby these successive changes are effected, what a degree of certainty would our knowledge of animal economy acquire? We should contemplate in an egg, the mysteries of the two kingdoms. And how greatly would our imagination of that adorable wisdom be increased, which by the simplest means ever attains the most noble ends?

9 Thus the more we ascend to the origin of organized beings, the more we are persuaded of their having pre-existed before their first appearance; not such as they first appear to us, but disguised; and were it possible for us to trace them still higher, we should un­doubtedly find them stilt more disguised, and should be at a loss to conceive how they could afterward acquire that form under which they present themselves to our view.

We can then form no idea of the primitive state of organized beings; that state which I conceive to be given them by the hand of Him who has ordained all things from the beginning.

The forms of vegetables and animals, which are so elegantly varied, are, in the system of this admirable pre-ordination, only the last results of that multitude of successive revolutions, they have been liable to, and which perhaps commenced at their first creation. How great would be our astonishment. could we penetrate into these depths, and pry into the abyss! We should there discover a world very different from ours, whose strange decorations would infinitely embarrass us. The state, in which we conceive all organized bodies to have been at first, is the germ state; and the germ contains in miniature all the parts of the future animal or vegetable. It does not then acquire organs which it had not before: but those organs which did not hitherto appears begin now to be visible. We do not know the utmost limits 0f the division of matter; but we see that it has been divided in a prodigious degree. From the elephant to the mite, from the globe of the sun to a globule of light, what an inconceivable multitude of inter­mediate degrees are there! This animalcule enjoys the light; it pene­trates into its eye ; it there traces the image of objects; how extremely minute must this image be! And bow much more minute must that of a globule of light be, when several thousands, and perhaps millions, enter attbe same time into this eye! But great and small are nothing in them­selves, and have no reality but in our imagination, it is possible, that all the germs of the same kind were originally joined or linked into each other, and that they are only unfolded from generation to generation, according to that progression which geometry endeavours to assign them.

10. A barren egg has a yolk as well as a fruitful egg. And a ray of light has lately sprung, which has greatly brightened the shades in which the mystery of generation is yet involved.

Bestow your whole attention on this; you will then discover an important truth. A membrane clothes the inside of the yolk of an egg: and this membrane, which is only a continuation of that which clothes the slender intestine of the chick, is common to the stomach, pharynx, mouth, skin, and epidermis. Another membrane enfolds the yolk externally, and this membrane is only a continuation of that which covers the intestine; it unites with the mesentery and perito­neum. The arteries and veins that gently move in the egg, derive their origin from the mesenteric arteries and veins of the embryo. The blood which circulates in the yolk receives the principle of its motion from the heart.

The yolk then is essentially a dependance of the intestines of the embryo, and together with that composes one and the same organized whole. So that at its primary period, it is in some measure an animal with two bodies: the head, trunk, and extremities, compose one of these bodies; the intestines and yolk the other. At the end of the incubation, the second body connects with the first, and both together form only one.

But since the yolk exists in eggs that have not been fecundated, it necessarily follows that the germ existed before fecundation. This consequence is self-evident: you have lately seen that the yolk is an essential part of the chick: you have observed the strict communication between them. The chick then has never existed without it. The membranes and vessels of the former, are only a continuation of the membranes and vessels of the latter. And what a number of other things are there which are common to both, and which prove that they have never existed separately! The chick was then entire in the egg before fecundation. It does not therefore owe its origin to the liquor furnished by the male, but was sketched in miniature in the egg, previous to it. Consequently the germ belongs solely to the female. Such is the grand conclusion which immediately flows from facts.

1. The yolk has its liquors, which are conveyed to it by the arte­ries belonging to it. They circulate, and without veins there is no circulation. But the arteries and veins of the yolk take their origin from the mesenteric arteries and veins of the foetus; the heart of this latter therefore is the principle of that circulation which is performed in the yolk. At the time of fecundation the foetus does not weigh the hundredth part of a grain. The yolk at that time weighs a dram. It has vessels proportioned to its size. Now if the germ existed entire before fecundation that which we style generation is not the same thing with it; but is only the beginning of an evolution, which will by degrees bring to open day such parts as were before hid in impenetrable darkness.

But the germ cannot be unfolded in an egg which has not been fecundated, and incubation would only accelerate its eruption: What does it then want to enable it to continue to grow ? It has all the organs necessary for evolution. It has even already attained to a certain degree of growth, for eggs grow in young pullets ; their ovaries contain them of all sizes. The germ grows there likewise. Why cannot it enfold itself more than it does ? What secret force retains it within the limits of invisibility ?

Growth depends on the impulsion of the heart. A greater degree of growth depends on a greater impulsion. T his degree of impulsion, consequently, is wanting in the heart of the germ that has not been fecundated.

This demonstrates a certain resistance in the parts of the germ. As it grows, this resistance augments in proportion. Some resist more than others ; the bony parts, or such as will hereafter become so, more than the membranous, or those that always must remain so.

The heart of the germ then hath need of a determinate strength to surmount this resistance. Its strength is in its irritability, or in the power it has of contracting itself on the touch of some liquid. Wherefore to augment the irritability of the heart, is to augment its impulsive force.

Fecundation, without doubt, increases this force, and that can alone increase it; since it is only by the intervention. of it that the germ passes over the narrow limits that it retained jfl its first state.

12. The fecundating liquor then is a true stimulus, which being conveyed to the heart of the germ, excites it in a powerful man­ner, and communicates to it a new activity. Herein consists what we call conception. Motion being once impressed on the little moving body, is there preserved solely by the energy of its admi­rable mechanism.

But it is not sufficient that the heart should acquire a force suffi­cient to surmount the resistance of solids ; it is likewise necessary that the fluid which it conveys to them, and which should nourish them, be proportionable to the exceeding fineness of the vessels. Such a blood as ours would not circulate in them. The blood of the embryo is at first a whitish liquor it grows yellow by degrees, and afterward red. The more the impulsion of the heart dilates the vessels, the more gross, heterogeneous, and colouring particles they admit.

The prolific liquor then is not a mere stimulus ; but is likewise a nutricious fluid appropriated to the extreme delicacy of the germ. It has already discharged the functions of a nutricious fluid in the fecundating individual; has caused its comb, spurs, &c. to grow, anti give strength to all its parts.

Being conveyed by the arteries to all its parts, it unites itself to the nature of each. From thence proceeds growth, which we do not pay a sufficient attention to.

It is not long before the chick loses the first form. Wings, thighs, legs, and feet, spring out from its long tail. Every thing is formed and disposed on a new model. The little animal, which before was stretched out in a straight line, becomes more and more curved. It is successively clothed with muscles, tendons, flesh, and feathers, and in eighteen or twenty days is a perfect chick.

13. if the chick pre-existed in the hen, it is probable the horse pre-existed in the mare. This would be more than probable, if it could be demonstrated that the young of viviparous animals are en­closed in eggs: and that all the difference between viviparous and oviparous may be reduced to this, that the former are batched in the belly of their mother, and the latter after their issuing from it.

On the two sides of viviparous females there is a body resembling a small bunch of grapes, whose berries are bladder full of a limpid liquor. These are the ovaries. They communicate with the matrix by two canals which they call tubes. The prolific liquor penetrates in the matrix, and passes through the tubes into the ovaries. Thus fecundation is performed. Foetuses have more than once been found in the ovaries itself. Nay more, there has been found in the vesicle of the ovary a complete foetus sketched in miniature.

The vesicles of the ovary are real eggs, which after fecundation descend through the tubes into the matrix, and are there in some measure brooded on. In a short time they send forth small roots’ which convey the nourishment to the embryo. The suppleness of their membranes admits of their extending, and making way for the growth of the little animal. It is true, the growing of eggs is familiar to us; but the history of insects furnishes us with many examples of it. It even exhibits to us insects that are at one time viviparous, and another oviparous. The young were in that case at first lodged in eggs; sometimes the mother lays her eggs; and at another brings forth living young ones, which were hatched from these eggs whilst they were yet in the matrix.

It is therefore the same with respect to the vesicles of the ovary, as the eggs of the hen; a germ pre-exists in them, but its transparency conceals it from us; fecundation renders it visible.

14.  But if an ass cover a mare, there will be produced from this commerce an animal that will not properly be a horse, but a mule. Nevertheless a horse was delineated in miniature in the egg of a mare: how then was it transformed into a mule? Whence did it acquire these long ears and slender tail so different from those of the horse? Dissection increases the difficulty ; that informs us that this kind of transformation does not only effect the exterior part of the animal, but the interior likewise. The voice of the mule is very like that of the ass, and does not at all resemble the neighing of a horse. The organ of the ass’s voice is an instrument that is very much com­pounded. A drum of a singular structure, lodged within the larynx, is the principal part of this instrument. This drum does not exist in the horse, hut is found in the mule.

The liquor furnished by the male consequently penetrates the germ, since it there produces such great changes. But these rela­tions of the prolific liquor to the male that furnishes it, must necessa­rily depend on the organs that prepare it.

There are then in these organs vessels that separate the molecules relative to different parts of the great whole. These molecules are carried to the corresponding parts of the germ, since these parts are modified by the action of the prolific liquor. Therefore it incor­porates itself with the germ, and is the first aliment of it, as I said above.

The organs of generation in the ass have then a relation to his ears and larynx ; for they prepare a liquor which modifies the ears and larynx of the little horse enclosed in the egg. The prolific liquor creates nothing, but it may change what already exists. It does not engender the chick, which existed before fecundation.

Growth depends on nutrition; the latter on incorporation. At the dame time that a part grows, it acquires solidity. An excess of growth in a part, then, supposes a superabundance of nutricious juices or such as are more active. The excessive growth which the ears of the horse acquire by the influence of the liquor of the ass, indicates that this liquor contains more molecules, appropriated to the unfolding of the ears, than that of the horse, or that the molecules of the first are more active than those of the second.

The extreme softness, I should rather say, fluidity of the germ, renders every part of it extremely modifiable. Those changes which you cannot conceive in an adult, depend here on the slightest causes.

But if the fecundating liquor modifies the germ, this latter in its turn, modifies the action of that liquor. By virtue of its organi­zation, it tends to preserve its primitive stale, resist more or less every new arrangement, and never gives way without always retaining something of its primitive form.

15. Every organical production, which has more or less parts than the species requires, or constructed otherwise, is a monster. The male, which doth not engender, is therefore a monster.

The object of inquiry in a celebrated dispute, was, whether cer­tain monsters were such originally or by accident?

It is evident, that the mule is not a monster from its origin. Mon­sters do not exhibit so much constancy and uniformity. Does an egg, of which the mule is formed, offer itself in the ovary of the mare just at the instant in which the ass fecundates it?

Two branches, fruits, or leaves, graft themselves accidentally, and afterward compose but one and the same whole. Art performs other more extraordinary engraftings, in all of which there is nothing originally monstrous.

That which happens between two fruits that engraft themselves, or are engrafted by force, may happen in the matrix between two eggs, or in an egg between two germs. Two foetuses that are united only by the spine, perfectly resemble two fruits that are grafted by contact. An egg sometimes contains two yolks, consequently it then contains two germs. How easy a matter is it for them to engraft themselves together as they unfold? We have seen a chicken with four feet, which undoubtedly proceeded from a like union. The germs, which are first fluid, and for a considerable time gelatinous, are very penetrable. If they come in contact, they will mix together in part. Similar organs, which at least half penetrate each other, will subsist in the other moiety. We see clearly this reciprocal penetration in a human foetus having two heads on a single body. This monster was evidently formed of two moieties of the foetus con­nected together.

If their gelatinous state renders germs very penetrable, it favours with much greater reason their union by grafting, or that of some parts to each other, either of the same germ or two or more germs.

The graft is united to its subject only by gelatinous or at least herbaceous fibres. Such fibres are proper for forming new productions, and for connecting and intermingling together. Two polypus unite together much more easily than two rinds; they are abundantly softer.

16.  Accidental grafts may give birth to monsters which we should term inexplicable, by this principle. But you have not forgot, that all organical parts have forms and situations in the germ which differ prodigiously from those they will have in the unfolded fcetus. Recal to mind the chick in its first form, its heart in that of a semicircle and you will comprehend that those conjunctions, which appear impossible to you, in the foetus may be easily effected in the germ.

The analogy of parts likewise favours their union. This analogy results from that of the elements. Two membranes are more disposed to unite than a membrane and a bone; and similar parts of the;! same organ, than parts of different organs.

Lastly, evolution is not uniform in all parts of the germ : they grow unequally, and this inequality of growth may influence the effects of contact, pressure, adhesion, &c. Thus a monster that is produced with superfluous members, may derive them from a germ that has perished, and of which only these members remained. We plainly see bow many causes may destroy such or such a part, and produce a monster by defect.

But all monsters by excess might not owe their origin to the union of two germs. Certain parts may grow excessively by the concur­rence of particular circumstances, and augment the number of similar parts in the same individual. A subject with twenty-six ribs is really a monster by excess, It has been proved that supernumerary ribs are entirely owing to the unnatural developement of a bony appendage of the transverse apophysis of one of the vertebrae. The causes which operate in the like unfoldings, act nearly as the liquor of the ass on the ears and larynx of the horse.

As supernumerary ribs unfold themselves, so two or three ribs unite themselves into a single one, and these kind of cases are not rare either in the vegetable or animal kingdom. Such parts as almost touch each other, are very apt to unite: two drops of jelly, and of the same jelly, unite very easily.

17. The principles I have laid down concerning the generation of animals, are likewise applicable to that of plants. What the prolific liquor is to the former, the dust of the stamina is to the latter. There is a wonderful analogy betwixt these two classes of organized bodies. The seed, which so nearly resembles the egg, does therefore, in all probability contain a germ, which existed in an invisible manner before fecundation, which makes it sensible to us. It appears first of all like a greenish or yellowish speck. It has been thought that a grain of the stamina dust has been perceived in this speck. The germs have en this account been placed in this dust, and introduced themselves into the seeds, which were destined to receive and nourish them. But can we discover the germ in the egg before fecundation? Not­withstanding which it pre-exists there. it is highly probable that it likewise pre-exists in the seed, and that its minuteness, together with the transparency of its parts, conceals it from our sight.. Will a philosopher argue, that because a thing is invisible to us, it does not therefore exist?

18. An exact observer has taken a good method to clear up the mystery of the generation of plants. He considered what has re­sulted from the fecundation of diverse species, by the dust of dif­ferent species. Be has seen mules that have been well described proceed from it. These mules, when combined with other species, have produced new ones. The resemblances have always been in a direct proportion to the dust. The changes and alterations have al­ways been sensible. The female has had some superiority. The privilege of fecundity has adhered more exactly to what came from her, than to that which proceed from the male. Do not these curious observations themselves indicate that in vegetables, as well as in animals, the germ originally belongs to the female?  

Chapter 8