Front matter (continued 3)

All animals, both male and female, and all vegetables whatsoever, it is therefore evident are composed of living organic parts. These organic parts are in the greatest abundance in the seminal liquor of animals, and in seeds of vegetables. It is from the union of these organic parts returned from all parts of the animal or vegetable body, that reproduction is performed, and is always like the animal or vegetable in which it operates; because the union of these organic parts cannot be made but by the means of an internal mould, in which the form of an animal or vegetable is produced. It is in this also the essence of the unity and continuity of the species consists, and will so continue while the great Creator permits their existence.

But before I draw general conclusions from the system I am establishing, I must endeavour to remove some objections which might be made, and mention some other circumstances which will serve to place this matter in a better light.

It will be asked, why I deny those moving substances in the seminal liquors to be animals, since they have constantly been regarded as such by Leeuwenhoek, and every other naturalist, who has examined them? I may also be told, that living organic particles are not perfectly intelligible, if they are to be looked upon as animalculæ; and to suppose an animal is composed of a number of small animals, is nearly the same as saying that an organized being is composed of living organic particles. I shall therefore endeavour to answer these objections in a satisfactory manner.

It is certain that almost all naturalists agree in looking on the moving substances in seminal liquors as real animals; but it is no less certain, from my own observations, and those of Mr. Needham, on the seed of the calmar, that these moving substances are more simple and less organized beings than animals.

The word animal, in the acceptation we commonly receive it, represents a general idea formed of particular ideas drawn from particular animals. All general ideas include many different ones, which approach, or are more or less distant from each other, and consequently no general idea can either be exact or precise. The general idea which we form of an animal may be taken principally from the particular idea of a dog, a horse, and other beasts, which appear to us to act and move according to the impulse of their will, and which are besides composed of flesh and blood, seek after their food, have sexes, and the faculty of reproduction. The general idea, therefore, expressed by the word animal, must comprehend a number of particular ideas, not one of which constitutes the essence of the general idea, for there are animals which appear to have no reason, will, progressive motion, flesh nor blood, and which only appear to be a congealed substance: there are some which cannot seek their food, but only receive it from the element they live in: there are some which have no sensation, not even that of feeling, at least in any sensible degree: there are some have no sexes, or are both in one; there only belongs, therefore, to the animal a general idea of what is common also to the vegetable, that is, the faculty of reproduction.

The general idea then is formed from the whole taken together, which whole being composed of different parts, there is consequently between these parts degrees and links. An insect, in this sense, is something less of an animal than a dog; an oyster still less than an insect; a sea-nettle, or a fresh-water polypus, still less than an oyster; and as nature acts by insensible links, we may find beings which are still less animated than a sea-nettle, or a polypus. Our general ideas are only artificial methods to collect a quantity of objects in the same point of view; and they have, like the artificial methods we shall speak of, the defect of never being able to comprehend the whole. They are likewise opposite to the walk of nature, which is uniform, insensible, and always particular, insomuch that by our endeavouring to comprehend too great a number of particular ideas in one single word, we have no longer a clear idea of what that word conveys; because, the word being received, we imagine that it is a line drawn between the productions of nature; that all above this line is animal, and all below it vegetable; another word, as general as the first, and which is used as a line of separation between organized bodies and inanimate matter. But as we have already said, these lines of separation do not exist in nature; there are beings which are neither animals, vegetables, nor minerals, and which we in vain might attempt to arrange with either. For example, when Mr. Trembly first observed the polypus, he employed a considerable time before he could determine whether it was an animal or a plant; and possibly from this reason that it is perhaps neither one nor the other, and all that can be said is, that it approaches nearest to an animal; and as we suppose every living thing must be either an animal or a plant, we do not credit the existence of an organized being, that cannot be referred to one of those general names; whereas there must, and in fact are, a great number of organized beings which are neither the one nor the other. The moving substances perceived in seminal liquors, in infusions of the flesh of animals, in seed, and other parts of plants, are all of this kind. We cannot call these animals, nor can we say they are vegetables, and certainly we can still less assert they are minerals.

We can therefore affirm, without fear of advancing too much, that the grand division of nature's productions into Animals, Vegetables, and Minerals, do not contain every material being; since there are some that exist which cannot be classed in this division. We have already observed, that nature passes by insensible links from the animal to the vegetable, but from the vegetable to the mineral the passage is quick, and the distance considerable; from whence the law of nature's passing by imperceptible degrees appears untrue. This made me suppose that by examining nature closely we shall discover intermediate organized beings, which without having the power of reproduction, like animals and vegetables, would nevertheless have a kind of life and motion; other beings which, without being either vegetables or animals, might possibly enter into the composition of both, and likewise other beings which would be only the assemblage of the organic molecules I have spoken of in the preceding chapters.

In the first class of these kind of beings eggs must be placed; those of hens, and other birds, are fastened to a common pedicle, and draw their nourishment and growth from the body of the animal, but when fastened to the ovary, they are not then real eggs, but only yellow globules which separate from the ovary as soon as they have attained a certain growth. Their internal organization is such that they derive nourishment from the lymph, the matrix of the hen, and by which they form the white membranes, and at last the shell. The egg therefore has a kind of life and organization, a growth, expansion, and a form which it assumes by its own powers. It does not live like an animal, nor vegetate like a plant, nor is possessed of the power of reproduction; nevertheless it grows, acts externally, and is organized. Must we not then look upon it as a being of a separate class, and which ought not to be ranked either with animal or mineral? for if it is pretended that the egg is only an animal production, destined for the nutriment of the chicken, and should be looked upon as a part of the hen; I answer, that the eggs, whether impregnated or not, will be always organized after the same mode: that impregnation only changes an almost invisible part; and that it attains its perfection and growth, as well externally as internally, whether it contains the chicken or not, and that consequently it ought to be considered as a separate being.

What I have said will appear more clear, if we consider the formation and growth of the eggs of fish; when the female deposits them in the water they are only the outlines of eggs, which being separated from the body of the animal, attract and appropriate to themselves the particles which agree the best for their nourishment, and grow thus by intussusception. In the same manner as the hen's egg acquires the white and membranes in the matrix, wherein it floats, so the eggs of fish acquire their membranes and white in the water; and whether the male impregnates them, by emitting on these the liquor of its roe, or whether they remain unimpregnated, they do not the less attain their entire perfection. It appears to me, therefore, that the eggs should be considered as organized bodies, which being neither animals nor vegetables, are a genus apart.

A second class of beings, of the same kind, are the organized bodies found in the semen of all animals, and which, like those in the milt of a calmar, are rather natural machines than animals. These are properly the first assemblages which result from the organic molecules we have so much spoken of, and they are, perhaps, the parts which constitute the organized bodies of animals. They are found in the semen of all animals, because the semen is only the residue of the organic molecules that the animal takes in with its aliment, and which, as we have already observed, are those parts most analogous to the animal itself, and most organic; it is those particles which compose the matter of the semen, and consequently we must not be astonished to find organized bodies therein.

To be perfectly convinced that these organized bodies are not real animals, we need only reflect on the preceding experiments. The moving bodies in the seminal liquor have been taken for animals, because they have a progressive motion, and are thought to have a tail; but if we consider, on one hand, the nature of this progressive motion, which finishes in a very short time without ever renewing its motion; and on the other, the nature of these tails, which are only threads which the moving bodies draw after them, we shall begin to hesitate; for an animal goes sometimes slow, sometimes fast, and sometimes remains in a state of rest; these moving bodies, on the contrary, always continue the same motion, and I have never seen them stop and renew their movement again. I ask, whether this kind of continued motion, without any rest, is common to animals, and if that ought not to make us doubt these moving bodies being real animals? An animal of any kind must also have a constant form and distinct limbs; but these moving bodies vary, and change their forms every moment, have no distinct limbs, and their tails appear as a part which does not belong to the individual. Can we then imagine these bodies to be real animals? In seminal liquors filaments are seen which lengthen and appear to vegetate; after which they swell and produce moving bodies. These filaments may be kinds of vegetables, but the moving bodies which spring from them cannot be animals, for a vegetable has never yet been seen to produce an animal. These moving bodies are found in all vegetable and animal substances; they are not produced by the modes of generation, they have no uniformity of species, and therefore can neither be animals nor vegetables. They are to be met with in the flesh of animals, and in the substance of vegetables, but are most numerous in their seeds; is it not therefore natural to regard them as living organic particles which compose the animal or vegetable; as particles which having motion and a kind of life, ought, by their union, to produce moving and living beings, and so form animals and vegetables?

But in order to leave this matter as little in doubt as possible, let us examine other substances. Can it be said, the active machines which Mr. Needham perceived in the milt of the calmar were animals? Can it be thought that eggs, which are active machines of another kind, are also animals? If we turn our eyes to the representation of almost all the moving bodies Leeuwenhoek saw in different matters, shall we not be convinced, even at the first inspection, that those bodies are not animals, since not one of them has any limbs, but are all either globular or oval? If we afterwards examine what this celebrated naturalist says, when he describes the motion of these pretended animals, we can no longer doubt of his being in an error when he considered them as such; and we shall be still more and more confirmed that they are only moving organic particles by the following examples: Leeuwenhoek gives[W] the figure of the moving bodies which he observed in the liquor of a male frog. This figure only represents a slender body, long, and pointed at one of its extremities; and of this he says, "Uno tempore caput (thus he calls the thickest extremity of this moving body) crassius mihi apparebat alio; plerumque agnoscebam animalculum haud ulterius quam a capite ad medium corpus, ob caudæ tenuitatem, & cum idem animalculum paulo vehementius moveretur (quod tamen tarde fiebat) quasi volumine quodam circa caput ferebatur. Corpus fere carebat motu; cauda tamen in tres quatuorve flexus volvebatur." This then is the change of form which I mentioned to have seen, the mucilage from which the moving bodies use all their efforts to be disengaged, the slowness of their motion before they are disengaged; and the animal, according to Leeuwenhoek, one part of which is in motion, and the other dead: for he afterwards says, "Movebant posteriorem solum partem, quæ ultima, morti vicinia esse judicabam." All this does not agree with an animal, but with what I have spoken of; excepting that I never saw the tail move but by the agitation of the body. He afterwards says, speaking of the seminal liquor of a cod, "Non est putandum omnia animalcula in semine aselli contenta uno eodemque tempore vivere, sed illa potius tantum vivere quæ exitui seu partui viciniora sunt, quæ & copiosiori humido innatant præ reliquis vita carentibus, adhuc in crassa materia, quam humor eorum efficit, jacentibus."

If these are animals, why have they not all life? why are they in the most fluid part of the liquor alive, while those in the thickest are not so? Leeawenhoek did not perceive that the thick matter, the origin of which he attributes to the humour of the animalculæ, is nothing but a mucilaginous matter which produces them. By diluting this mucilage with water, he would have given life to the whole of them. Even this mucilage is oftentimes only a mass of those bodies which are set in motion on being separated; and consequently this thick matter, instead of being a humour, produced by the animalcules, is only the substance of the animals themselves, or rather, as we have already observed, the matter from which they originate. Speaking of the seed of a cock, Leeuwenhoek says, in his letter to Grew, "Contemplando materiam (seminalem) animadverti ibidem tantam abundantiam viventium animalium, ut ea stuperem; forma seu externa figura sua nostrates anguillas fluviatiles referebant, vehementissima agitatione movebantur; quibus tamen substrati videbantur multi & admodum exiles globuli, item multæ plan-ovales figuræ, quibus etiam vita posset attribui, & quidem propter earundem commotiones; sed existimabam omnes hasce commotiones & agitationes pro venire ab animalcules, sicque etiam res se habebat; attamen ego non opinione solum, sed etiam ad veritatem mihi persuadeo has particulas planam & ovalem figuram habentes, esse quædam animalcula inter se ordine suo disposita & mixta vitaque adhuc carentia." Here we see in the same seminal liquor animalcules of different forms; and I am convinced, by my own experiments, that if Leeuwenhoek had closely observed these oval substances, he would have discovered that they moved by their own powers, and that consequently they were as much alive as the rest. This change perfectly coincides with what I have said, that they are organic particles which take different forms, and not constant species of animals; for in the present case, if the bodies, which have the figure of an eel, are true spermatic animalcules, each, destined to become a cock, which supposes a very perfect organization, and a very constant form, what will those be which have an oval figure, and what end do they answer? He says indeed afterwards, that these ovals maybe conceived to be the same animals, by supposing their bodies to be twisted in a spiral form; but then how shall we conceive that an animal, whose body is constrained, can move without being extended? I maintain, therefore, that these oval substances are no other than the organic particles separated from their threads, and that the eels were the separated parts which dragged those threads after them, as I have many times perceived in other seminal liquors.

Leeuwenhoek, who imagined all these moving bodies were animals, and established a system thereon; who also pretended, that spermatic animals must become men and animals, now suspected they were only natural machines, or organic particles in motion; for he does not doubt these spermatic animals contained the great animal in miniature, he says, "Progeneratio animalis ex animalculo in seminibus masculinis omni exceptione major est; nam etiamsi in animalculo ex semine masculo unde ortum est, figuram animalis conspicere nequeamus, attamen satis superque certi esse possumus figuram animalis ex qua animal ortum est, in animalculo quod in semine masculo reperitur, conclusam jacere sive esse; & quanquam mihi sæpius conspectis animalculis in semine masculo animalis, imaginatus fuerim me posse dicere, en ibi caput, en ibi humeros, en ibi femora; attamen eum ne minima quidem certitudine de iis judicium ferre potuerim, hujusque certi quid statuere supersedeo, donec tale animal, cujus semina mascula tam magna erunt, ut in iis figuram creaturæ ex qua provenit, agnoscere queam, invenire secunda nobis concedat fortuna." This fortunate chance, which Leeuwenhoek desires, presented itself to Mr. Needham. Every part of the spermatic animals of the calmar are easy to be seen without a microscope; but they are not young calmars, as Leeuwenhoek thinks, nor even animated, although they are in motion, but only machines which must be regarded as the first produce of the union of organic particles.

Although Leeuwenhoek had not such an opportunity of undeceiving himself, he nevertheless had another phenomena which ought to have had that effect; for example, he had remarked that the spermatic animals of a dog often change their figures, especially when the liquor was on the point of evaporating; that these pretended animals had a hole in the head when they were dead, and that this hole did not appear when they were alive; he had seen that the part which he looked upon as the head was full and plump when it was alive, and flaccid and flat when dead. All this ought to have led him to doubt whether these moving bodies were real animals; and consider it as agreeing better with a machine, which empties itself like that of the calmar, than with a moving animal.

I have said that these moving bodies, these organic particles, do not move like animals, nor have an interval of rest. Leeuwenhoek has observed the same: "Quotiescunque, says he, animalcula in semine masculo animalium fucrim contemplatus, attamen illa se unquam ad quietem contulisse, me nunquam vidisse, mihi dicendum est, si modo sat fluidæ superesset materiæ in qua sese commode movere poterant; et eadem in continuo manent motu, & tempore quo ipsis moriendum appropinquante, motus magis magisque deficit, usquedum nullus prorsus motus in illis agnoscendus sit." It appears difficult to conceive that animals can exist, from the moment of their birth till that of their death, in a continual rapid motion without the least interval of rest; and I cannot possibly imagine how these animals in the semen of a dog, which Leeuwenhoek saw the seventh day in as rapid motion as they were when they were first taken from the body of the animal, preserved a motion during that time so exceedingly swift, that no animal has sufficient power to move in for an hour; especially if we consider the resistance which proceeds from the density and the tenacity of the liquor. This kind of continued motion, on the contrary, agrees with the organic particles, which, like artificial machines, produce their effects in a continual operation, and which stop when that effect is over.

Among the great number of Leeuwenhoek's experiments, he, without doubt, often perceived spermatic animals without tails; and he endeavours to explain this phenomena by a supposition; for example, he says, speaking of the semen of a cod, "Ubi vero ad lactum accederem observationem, in iis partibus quas animalcula esse censebam neque vitam neque caudam dignoscere potui; cujus rei rationem esse existimabam, quod quamdiu animalcula natando loca sua perfecte mutare non possunt tam diu etiam cauda concinne circa corpus maneat ordinata, quodque ideo singula animalcula rotundum repræsentent corpusculorum."

It would have been better to have said, as it in fact is, that the spermatic animals of these fish have tails at certain times and none at others, than to suppose their tails twisted so exactly round their bodies as to give them the shape of a globule. But this must not lead us to think that Leeuwenhoek only attended to the moving bodies which he saw with tails, but rather that he did not describe the others, because, although they were in motion, he did not regard them as animals; and this is the cause that all the spermatic animals he has depicted resemble each other, and drawn with tails, since he only took them for real animals in that state; and that when he saw them under other forms, he thought them imperfect, or rather that they were dead. On the whole it appears, by my experiments, that far from displaying their tails the more as they are in a more perfect condition of swimming, as Leeuwenhoek says, they, on the contrary, lose their tails in a gradual manner, till at last these tails, which are no more than foreign bodies of the animalcules, and which they drag after them, entirely disappear.

In another part Leeuwenhoek, speaking of the spermatic animals of man, says, "Aliquando etiam animadverti inter animalcula particulas quasdam minores & subrotundas; cum vero se ea aliquoties eo modo oculis meis exhibuerint, ut mihi imaginarer eas exiguis instructas esse caudis, cogitare cœpi annon hæ forte particulæ forent animalcula recens nata; certum enim mihi est ea etiam animalcula per generationem provenire, vel ex mole minuscula ad adultam procedere quantitatem: & quis sit annoa ea animalcula, ubi moriuntur, aliorum animalculorum nutritioni atque augmini inserviant?" By this passage it appears that Leeuwenhoek had seen animals without tails in the seminal liquor of a man, and that he is obliged to suppose them to be just born, and not adult; but I have observed quite the contrary; for the moving bodies are never larger than when they separate from the filaments, and begin to move. When they are entirely disengaged from the mucilage they become smaller, and continue decreasing as long as they remain in motion. With respect to the generation of these animals, which Leeuwenhoek speaks of as certain, I am persuaded no sign of generation has ever been discovered; all he says is advanced on mere suppositions, which it is easy to prove by his own observations; for example, he says that the milt of certain fish, as the cod, fills by degrees with seminal liquor, which after the fish has emitted, the milt dries up, leaving only a membrane destitute of any liquor. "Eo tempore, says he, quo ascellus major lactes suos emisit, rugæ illæ, seu tortiles lactium partes, usque adeo contrahuntur, ut nihil præter pelliculas seu membranæ esse videantur." How then does he understand that this dry membrane, in which there is no longer either seminal liquor or animalcules, can reproduce animals of the same kind the succeeding year? if there was a regular generation in these animals, there could not be this interruption, which in most fishes lasts for a whole year. To draw himself out of this difficulty, he says, "Necessario statuendum erit, ut ascellus major semen suum emiserit, in lactibus etiamnum multum materiæ seminalis gignendis animalculis aptæ remansisse, ex qua materia plura oportet provenire animalcula seminalia quam anno proxime elapso emissa fuerant." This supposition, that there remains something in the seminal liquor in the milts to produce spermatic animals for the succeeding year, is absolutely contrary to observations, for the milt is in this interval only a thin and absolutely dry membrane. But what reply can be made to a still further opposition to this point, there being fish like the calmar, the seminal liquor of which is not only renewed every year, but even the reservoir which contains it? Can it be said, that there remains a seminal matter in the milt for the production of the animals for the succeeding year, when even the milt does not remain? it is therefore very certain that these pretended spermatic animals are not multiplied, like other animals, by the mode of generation; which alone is sufficient to make us presume, that those particles which move in the seminal liquors are not real animals. Thus Leeuwenhoek, who in the passage above quoted says, it is certain that spermatic animals multiply and propagate by generation, nevertheless owns, in another part, that the manner in which these animals are produced is very obscure, and that he leaves to others the task of clearing up this matter. "Persuadebam mihi," says he, speaking of the spermatic animals of the dormouse, "hæcce animalcula ovibus prognasci, quia diversa in orbem jacentia & in semet convoluta videbam; sed unde, quæso, primam illorum originem derivabimus? in animo nostro concipiemus horum animalculorum semen jam procreatum esse in ipsa generatione, hocque semen tam diu in testiculis hominum hærere, usquedum ad annum ætatis decimum-quartum vel decimum-quintum aut sextum pervenerint, eademque animalcula tum demum vita donari vel in justam staturam excrevisse, illoque temporis articulo generandi maturitatem adesse! sed hæc lampada aliis trado." I do not think it necessary to make any remarks on what Leeuwenhoek says on this subject: he saw spermatic animals without tails, and round, in the seed of a dormouse; "in semet convoluta," says he, because he supposes that they should have tails, and instead of being certain, as he before had been, that the animals propagate by generation, he here seems convinced of the contrary. But when he had observed the generation of pucerons, and was assured[X] that they engendered without copulation, he caught the idea to explain the generation of spermatic animals. "Quemadmodum, says he, animalcula hæc quæ pediculorum antea nomine designavimus (the pucerons) dum adhuc in utero materno latent, jam prædita sunt materia seminali ex qua ejusdem generis proditura sunt animalcula, pari ratione cogitare licet animalculæ in seminibus masculinis ex animalium testiculis non migrate seu ejici quin post se relinquant minuta animalcula aut saltem materiam seminalem ex qua iterum alia ejusdem generis animalcula proventura sunt idque absque coitu; eadem ratione qua supradicta animalcula generari observavimus." This supposition gives no more satisfaction than the preceding: for we do not understand by this comparison of the generation of these animalcules with that of a puceron, why they are not found in the seminal liquor of a man, before he has attained the age of fourteen or fifteen years; nor do we know from whence they proceed, nor how they are renewed every year in fish, &c. and it appears, that whatever efforts Leeuwenhoek made to establish the generation of spermatic animals on some probability, it still remained an entire obscurity, and would, perhaps, perpetually have remained so, if the preceding experiments had not evinced that they are not animals, but moving organic particles contained in the nutriment the animal receives, and which are found in great numbers in the seminal liquor, which is the most pure, and in the most organic extracts drawn from this nutriment.

Leeuwenhoek acknowledges that he had not always found animalcules in the seminal liquor of males; in that of the cock, for example, which he had often examined, he saw spermatic animals in the form of eels but once, and some years after he could not discover any under that form, but observed some with large heads and tails, which his designer could not perceive. He says also, that one season he could not find living animals in the seminal liquor of the cod. All these disappointments proceeded from his desire of finding tails to these animals; and although he perceived little bodies in motion, he did not consider them as animals, because they were without tails, notwithstanding it is under that form they are generally seen, either in seminal liquors, or infusions of animal or vegetable substances. He says, in the same place, that he was never able to make his designer perceive the spermatic animalcules of a cod, which he had so often seen himself.—"Non solum, says he, ob eximiam eorum exilitatem, sed etiam quod eorum corpora adeo essent fragilia, ut corpuscula passim dirumperentur; unde factum fuit ut nonnisi rare, nec sine attentissima observatione, animadverterem particulas planas atque ovorum in morem longas, in quibus ex parte caudas dignoscere licebat; particulas has oviformes existimavi animalcula esse dirupta, quod particulæ hæ diruptæ quadruplo fere viderentur majores corporibus animalculorum vivorum." When an animal of any kind ceases to live, it does not then suddenly alter its form, and from being long, like a thread, becomes round like a ball; neither does it become four times larger after its death than it was before. Nothing that Leeuwenhoek says here agrees with the nature of animals; but, on the contrary, the whole corresponds with a kind of machine, which, like those of a calmar, empty themselves after having performed their functions. But let us pursue this observation; he says, he has seen the spermatic animals of the cod in different forms, "multa apparebant animalcula sphæram pellucidam representantia;" he has also seen them of different sizes, "hæc animalcula minori videbantur mole, quam ubi eadem antehac in tubo vitreo rotundo examinaveram."

There needs nothing more to shew that there are no constant and uniform species of these animalcules; and that consequently they are not animals, but only organic particles in motion, which, by their different combinations, take different forms and sizes. These organic moving particles are found in great quantities in the extract and residue of our nutriment. The matter which adheres to the teeth, and which in healthy people has the same smell as the seminal liquor, is only a residue of the food, and a great number of these pretended animals are also found there, some of which have tails, and resemble those in the seminal liquor. Mr. Baker had four different kinds of them engraved, and which were all of a cylindrical or oval make, or globules with and without tails. I am persuaded, after having strictly examined them, that not any of them are real animals, but are like those in the seed, only living organical parts of the nutriment which present themselves under different forms, Leeuwenhoek, who did not know how to account for these pretended animals in the matter which adhered to the teeth, supposed them to proceed from certain food they were previously in, as cheese, &c. but we find them among the teeth of those who do not eat cheese, as well as in those that do; besides, they have not the least resemblance to mites, nor the other animalcules seen in rotten cheese. In another place he says, these animals of the teeth may proceed from the cistern water that is drank, because he observed animals like them in dew and rain water, especially in that which stagnates upon lead and tiles; but with which we can prove there is not the least resemblance.

Most seminal liquors dilute of themselves, and liquefy when exposed to the air or a certain degree of cold; but they thicken when a moderate degree of heat is communicated to them. I have exposed some of these liquors to a very intense cold, as water on the point of freezing, but it did no injury to these supposed animals; they continued to move with the same swiftness, and as long as those which had not been so exposed, but those which had suffered but a little warmth soon ceased to move, because the liquor thickened. If the moving bodies were animals, they were of a complexion and temperament quite different from all others, to whom a gentle and moderate heat strengthens their powers and motions, which the cold stops and destroys.

Notwithstanding it may be thought I have dwelt too long upon this subject, I cannot conclude it without making one remark, from which some useful conclusions may be drawn. These pretended spermatic animals, which are only living organic particles of the nutriment, not only exist in the seminal liquors of the two sexes, and in the residue of the nutriment which adheres to the teeth, but also in the chyle and excrements. Leeuwenhoek having met with them in the excrements of frogs, and other animals, which he dissected, was at first very much surprised, and notable to conceive from whence these animals proceeded, so entirely like those he had observed in the seminal liquors, accuses himself of having, in dissecting the animal, opened the seminal vessels, and that the seed had by that means been mixed with the excrements. But having afterwards found them in the excrements of other animals, and even in his own, he no longer knew to what to attribute them. Leeuwenhoek, it is worthy remark, never met with them in his own excrements, but when they were liquid. Every time he was disordered and the stomach did not perform its functions, and was relaxed, he discovered these animalcules; but when the concoction of the food was well performed, and the excrement was hard, there was not a single one, although it was diluted with water. This seems perfectly to agree with all we have before advanced: for when the stomach and intestines perform their functions, the excrements are only the grosser parts of the nutriment; and all that is really nutritive and organic passes into the vessels which serve to nourish the animal; whereas if the stomach and intestines are not in a condition to comminute the food, then it passes with the inanimate parts, and we find the living organic molecules in the excrements; from whence it may be concluded, that those which are often lax must have less seminal liquor, and be less proper for generation, than those of a different habit of body.

In all I have said, I constantly supposed the female furnished a seminal liquor, which was as necessary to generation as that of the male. I have endeavoured to establish in Chap. I. that every organized body must contain living organic particles, and I have endeavoured to prove Chap. II. and III. that nutrition and reproduction operates by the same cause; that nutrition is made by the intimate penetration of these organic particles through each part of the body, and that reproduction operates by the superfluity of these same organic particles collected together from all parts of the body and deposited in proper reservoirs. I have explained in Chap. IV. how this theory must be understood in the generation of man and animals which have sexes. Females then being organized bodies like males, they must also have some reservoirs for the superfluity of organic particles returned from every part of their bodies. This superfluity cannot come there through any other form than that of a liquor, since it is an extract of all parts of the body; and this liquor is that to which I have given the name of the female semen.

This liquor is not, as Aristotle pretends, an infecund matter of itself, which enters neither as matter nor form into the business of generation, but as essentially prolific as that of the male, containing characteristic parts of the feminine sex, which the female alone can produce, the same as the male contains particles necessary to form the masculine organs; and each of them contains every other organic particle that can be looked on as common to both sexes; which causes that, by their mixture, the daughter may resemble her father, and the son his mother. This semen Hippocrates says, is composed of two liquors; the one strong, for the production of males; and the other weak, for the production of females. But this supposition is too extended; I do not see how it is to be conceived that a liquor, which is the extract of every part of the female body, should contain particles for the formation of the male organs.

This liquor must enter by some way into the matrix of animals which bear and nourish their fœtus within the body, and in others, as oviparous animals, it must be absorbed by the eggs, which may be looked upon as portable matrixes. Each of these matrixes contains a small drop of this prolific liquor of the female, in the part that is called the cicatrice. When there has been no communication with the male, this prolific drop collects under the form of a small mole, or mass, as Malpighius observes; but when impregnated by that of the male; it produces a fœtus which receives its nutriment from the juices of the egg.

Eggs, instead of being parts generally found in every female, are therefore only instruments made use of by Nature to serve as the matrix in females which are deprived of that organ. Instead also of being active and essential to the first fecundation, they only serve as passive and accidental parts for the nutrition of the fœtus already formed by the mixture of the liquor of the two sexes in a particular part of this matrix. Instead also of being existing bodies, inclosed, ad infinitum, one within the other, eggs, on the contrary, are bodies formed from the superfluity of a more gross and less organic part of the food, than that which produces the seminal and prolific liquor; and are in oviparous females something equivalent, not only to the matrix, but even to the menstrua in the viviparous.

We should be perfectly convinced, that eggs are only destined by Nature to serve as a matrix in animals who have not that viscera, by those females producing eggs independant of the male. In the same manner as the matrix exists in viviparous animals, as a part appertaining to the female sex, hens, which have no matrix, have eggs in their room, which are successively produced of themselves, and necessarily exist in the female independently of any communication with the male. To pretend that the fœtus is pre-existing in the eggs, and that these eggs are contained, ad infinitum, within each other, is nearly the same as to pretend that the fœtus, is pre-existing in the matrix, and that the matrix of the first female inclosed all that ever were or will be produced.

Anatomists have taken the word egg in several acceptations and meanings. When Harvey took for his motto, Omnia ex ovo, he understood by the word egg, as applied to viviparous animals, the membrane which includes the fœtus and all its appendages: he thought, he perceived this egg, or membrane, form immediately after the copulation of the male and the female. But this egg does not proceed from the ovium of the female; and he has even maintained, that he did not remark the least alteration in this testicle, &c. We perceive there is here nothing like what is commonly understood by the word egg unless the figure of the bag may be supposed to have some resemblance thereto. Harvey, who dissected so many viviparous females, did not, he says, ever perceive any alteration in the ovaria; he looked on them even as small glands, perfectly useless to general ion,[Y] although they undergo very remarkable changes and alterations in them, since we may perceive in cows the glandular bodies grow from the size of a millet seed to that of a cherry. This great anatomist was led into this error by the smallness of the glandular bodies in the species of deer, to which he principally paid his attention. C. Peyerus, who also made many experiments on them, says, "Exigui quidem sunt damarum testiculi, sed post coitum fœcundum, in alterutro eorum, papilla, sive tuberculum fibrosum, semper succrescit; scrofis autem prægnantibus tanta accidit testiculorum mutatio, ut mediocrem quoque attentionem fugere nequeat."[Z] This author imagines, with some reason, that the minuteness of the testicles of does, is the cause of Harvey's not having remarked the alterations; but he is wrong in advancing that the alterations he had remarked, and which had escaped Harvey's notice, did not happen till after impregnation.

It appears that Harvey was deceived in many other essential points; he asserts, that the seed of the male does not enter into the matrix of the female, and even that it cannot; yet Verheyen found a great quantity of the male seed in the matrix of a cow, which he dissected six hours after copulation.[AA] The celebrated Ruysch asserts, that having dissected a woman who had been caught in the act of adultery, and was assassinated, he found, not only in the cavity of the matrix, but also in the trunks, a quantity of the seminal liquor of the male,[AB] Valisnieri affirms, that Fallopius and other anatomists had also discovered male seed in the matrix of many women. After the positive testimony of these great anatomists, there can remain no doubt but Harvey was deceived in this important point; especially when to these are added that of Leeuwenhoek, who found the male seed in the matrix of a great number of females of different species.

Harvey makes another error in speaking of an abortion in the second month, where the mass was as large as a pigeon's egg, but without any fœtus regularly formed; whereas, it is maintained by Ruysch, and many other anatomists, that the fœtus is perceptible, even to the naked eye, in the first month. The History of the Academy mentions a fœtus, that was completely formed in twenty-one days after impregnation. If to these authorities we add that of Malpighius, who perceived the chicken in the cicatrice, immediately after the egg was laid by the hen, we cannot doubt, but that the fœtus is formed immediately after copulation; consequently, we must not pay any credit to what Harvey says on the parts increasing one after the other by juxta-position, since they are all existent from the first, and gradually expand until the whole is complete.

De Graaf took the acceptation of the word egg in a quite different light to Harvey: he insists that the testicles of women were true ovaries, and contain eggs like those of oviparous, animals, only that they are much smaller, do not quit the body, and are never detached till after impregnation, when they descend from the ovary into the horns of the matrix. The experiments of De Graaf have contributed most to establish the existence of these pretended eggs, which yet is not at all founded; for this famous anatomist is deceived, first, by mistaking the vesicles of the ovarium for eggs, whereas they are inseparable from it, form parts of its substance, and are filled with a kind of lymph. Secondly, he is also deceived when he considers the glandular bodies to be the covering of those eggs, or vesicles; for it is certain, by Malpighius's, Valisnieri's, and my own observations, that the glandular bodies neither surround nor contain one of those vesicles. Thirdly, he is deceived still more when he supposes the glandular body is never formed till after fecundation; as they are invariably found in every female who has attained the age of puberty. Fourthly, he is no less deceived when he believes that the globules which he saw in the matrix, and which contained the fœtuses, ware the same vesicles, or eggs, which had fallen from the ovariam, and which, he remarks, were become ten times smaller than they were in the ovary. This remark alone, one would imagine, Should have made him perceive his error. Fifthly, he is wrong in saying that the glandular bodies are only the coverings of the fecundated eggs, and that the number of coverings, or empty follicles, always answer to the number of fœtuses. This assertion is entirely contrary to truth: for on the testicles of all females we find a greater number of glandular bodies, or cicatrices, than there are productions of fœtuses, and they are also found in those which have never brought forth. To this we may add, that neither he, Verheyen, nor any other person, have ever seen these eggs, much less these pretended coverings, on which they have, notwithstanding, established their system.

Malpighius, who perceived the growth of the glandular bodies in the female testicles, was deceived when he thought he had seen the egg in their cavities, since they contain only liquor; nor indeed has anything like an egg ever been discovered.

Valisnieri, who was not deceived in facts, has yet drawn false conclusions in asserting that, although neither himself, nor any anatomist in whom he could confide, ever found the egg in the cavity of the glandular body, yet it must there exist.

Let us, therefore, examine what may be fairly called the real discoveries of these naturalists. Graaf was the first who perceived there were alterations in the female testicles; and he had reason to affirm, they were parts essential and necessary to generation. Malpighius demonstrated that these alterations were occasioned by the glandular bodies which grew to perfect maturity, afterwards they become flaccid, obliterated, and left only a slight cicatrice remaining. Valisnieri has placed this discovery in a very clear light; he has shewn that these glandular bodies are found in the testicles of every female; that they are augmented considerably in the season of love, that they increase at the expence of the lymphatic vesicles of the testicles, and that at the time of their maturity they were hollow and filled with liquor. This, then, is all that can be reduced to truth on the subject of the pretended ovaries and eggs of viviparous animals. What must we conclude therefrom? Two things appear very evident: the one, that there does not exist any eggs in the female testicles; the other, that there exists a liquor in the vesicles of the testicle, and in the cavity of the glandular bodies. We have demonstrated by the preceding experiments, that this last liquor is the true seed of the female, since it contains, like that of the male, spermatic animals, or rather organic moving particles.

We must, therefore, now be assured, that females have, as well as males, a seminal liquor. After all that has been advanced, we cannot doubt but the seminal liquor is the superfluity of the organic nutriment, which is sent back from all parts of the body into the testicles and seminal vesicles of the males, and into the testicles and glandular bodies of females. This liquor, which issues by the nipple of the glandular bodies, continually sprinkles the horns of the matrix, and may easily procure admission either by the suction of the membrane of these horns, or by the little opening which is at the upper extremity, and thus enter into the matrix; but in the supposition of these pretended eggs, which were ten or twenty times larger than the opening of the horns of the matrix, we cannot comprehend how they could enter therein.

The liquor emitted by females, when they are excited, and which, according to de Graaf, issues from the neck of the matrix, and the orifice of the urethra, may be a superabundant portion of the seminal liquor which continually distills from the glandular bodies on the trunks of the matrix. But, possibly, this liquor may be a secretion of another kind, and perfectly useless in generation. To decide this question observations with a microscope are requisite; but all experiments are not permitted even to philosophers. I can only say, that I am inclined to believe that the same spermatic animals would be met with in this liquor as in that of the glandular bodies. I can quote an Italian doctor on this subject, who made this observation with attention, and which is thus related by Valisnieri: "Aggiugne il lodato fig. Bono d'avergli anco veduti (animali spermatici) in questa linfa o siero, diro cosi voluttuoso, che nel tempore dell'amorosa zuffa scappa dalle femine libidinose, senza che si potesse sospettare che fossero di que' del maschio, &c." If this circumstance is true, as I do not doubt, it is certain, that this liquor is the same as that found in the glandular bodies, and that, consequently, it is the true seminal liquor: and although anatomists have not discovered the communication between the vacuities of de Graaf and the testicles, that does not prevent it being once in the matrix, from issuing out by the vacuities about the exterior orifice of the urethra.

From hence we must conclude that the most abandoned women will be the least fruitful, because they emit that liquor which ought to remain in the matrix for the formation of the fœtus. Thus we see why common prostitutes seldom have children, and why women in hot countries, where they have stronger desires than in the cold, are much less fertile; but we shall have occasion to speak of this hereafter.

It is natural to think that the seminal liquor of the male or female would not be fertile but when it contains moving bodies; nevertheless that is still a question, and I should be led to think, as there are different states of this liquor, that in which these organic particles are seen in motion is not absolutely necessary for the purpose of generation. The Italian physician, above quoted, never perceived spermatic animals in his semen till he had attained a middle age, although he was father of several children before, and continued to have them afterwards.

These spermatic bodies, which move, may be looked upon as the first assemblages of the organic molecules which proceed from every part of the body; when a quantity of them collect they may be perceived with the microscope; but if they collect only in small quantity the body which they form will be too minute to be perceived, and in this case we shall not be able to distinguish any in the seminal liquor. A very long continuance of observations would be necessary to determine what can be the cause of all the differences remarked in the states of this liquor.

I can assert, from having often tried it, that by infusing the seminal liquors in water closely corked, at the end of three or four days an infinite multitude of moving bodies will be found, although the seminal liquors had no motion on being first taken from the body of the animal. Flesh, blood, chyle, urine, nay all animal or vegetable substances, contain organic particles, which move at the end of some days in an infusion of water; they appear to act and move nearly in the same manner, and though produced from different bodies are perfectly similar, without any of them having a power peculiar to themselves. If these bodies must absolutely be termed animals, it must be allowed they are so imperfect that they ought to be looked upon as the outlines of them, or rather as bodies simply composed of particles the most essential to the existence of an animal; for natural machines, such as those found in the roe of a calmar, although they put themselves in action at certain times, are certainly not animals, although they are organized, acting, and, as I may say, living beings.

If it is once allowed, that the productions of Nature follow in an uniform order, and advance by imperceptible degrees and links, we shall have no difficulty in conceiving there are organic bodies existing, which belong neither to animals, vegetables, nor minerals.

It is certain, however, that all animals and vegetables contain an infinity of organic living molecules. These molecules successively take different forms, and different degrees of motion and activity, according to different circumstances They are in a much greater number in the seminal liquor of both sexes, and in the germs of plants, than in other parts of the animal or vegetable. There exists, then, a living substance in animals and vegetables, common to both, and which substance is necessary to their nutrition. An animal procures nutriment from an animal or vegetable substance, and the vegetable can likewise be nourished from an animal or vegetable in a decomposed state. This nutritive substance, common to both, is always living, always active, and produces an animal or vegetable, as it finds an internal mould or an analogous matrix, as we have explained in the first chapters; but when this active substance collects in great abundance, in those parts where it can unite, it forms in the animal body other living creatures, such as the tape-worm, ascarides, and worms, which are sometimes found in the veins, in the sinus of the brain, in the liver, &c. These kinds of animals do not owe their existence to the animals of the same species, and we may, therefore, suppose, they are produced by this organic matter when it is extravasated, or is too abundant for the lacteal vessels to absorb. We shall hereafter have occasion to examine more largely the nature of those worms, and many other animals which are formed in a similar manner.

When this organic matter, which may be looked on as an universal seed, is collected in any great quantity, as in the seminal liquors, and in the mucilaginous parts of the infusion of plants, its first effect is to vegetate, or rather to produce vegetating beings. These zoophytes swell, extend, ramify, and produce globules, ovals, and other small bodies, of different figures, which have all a kind of animal life, a progressive motion, which is often very swift, and sometimes very slow. These globules themselves decompose, change their figures, and become smaller; and in proportion as they diminish in size the rapidity of their motion augments.

I have sometimes thought that the venom of the viper, and other active poisons, even that of the bite of a mad dog, might possibly be this active matter too rarefied; but I have not as yet had time to make the experiments which I had projected on this matter, as well as on drugs used in medicine; all that I can at present ascertain is, that all infusions of the most active drugs swarm with moving bodies, which form therein in much less time than in other substances.

Almost all microscopic animals are of the same nature as the organized bodies which move in the seminal liquor, in the infusions of vegetables and the flesh of animals; the eel-like bodies in flour, vinegar, and water, in which lead has been soaked, are beings of the same nature as the first, and have a like origin.

CHAPTER IX.

VARIETIES IN THE GENERATION OF ANIMALS.

The matter which serves for the nutrition and reproduction of animals and vegetables is therefore the same; it is a productive and universal substance, composed of organic molecules, and whose union produces organized bodies. Nature always works on the same fund, which is inexhaustible, but the means she employs to stamp its value are different, and these differences, or general agreements, deserve attention, because it is from thence we must derive our reasons to account for exceptions and particular varieties.

In general large animals are less productive than small. The whale, elephant, rhinoceros, camel, horse, the human species, &c. only produce one, and very seldom two, at a birth; whereas small animals, as rats, herrings, insects, &c. produce a great number at a time. Does not this difference proceed from there being more food required to support a large body than to nourish a small one, and from hence the former has less superfluous organic particles, which would convert into semen, than the latter? It is certain that small animals eat more in proportion than large ones; but it is likewise probable that the prodigious multiplication of the small animals, as bees, flies, and other insects, may be attributed to their being endowed with very fine and slender limbs and organs, by which they are in a condition to chuse what is most substantial and organic in the vegetable or animal matters from whence they derive their nutriment. A bee, who lives on the purest parts of flowers, certainly receives more organic particles in proportion than a horse who feeds on the grosser parts of vegetables, hay, &c. The horse produces but one at one time, whereas the bee will bring forth three thousand.

Oviparous animals are in general smaller than the viviparous, and produce also more at a birth. The duration of the fœtus in the matrix of viviparous animals likewise opposes their increase, nor can there be any new generation take place during gestation, or while they are suckling their young; whereas oviparous animals produce at the same time both matrix and fœtuses, which they cast out of the body, and are therefore almost always in a state of reproduction; and it is well known that by preventing a hen from setting, and largely feeding, the number of her eggs will be considerably increased. If hens cease to lay when they sit, it is because they have ceased to feed; and it is the fear lest their eggs should not produce which causes them not to quit their nests but once a day, and that for a very short time, during which they take a little nutriment, but not one-tenth part of what they take at other times.

Animals which produce but a small number at a time, acquire the chief part of their growth before they are fit for engendering, whereas those which multiply numerously generate before they have received half their growth. The human species, the horse, the ass, the goat, and the ram, are not able to engender until they have obtained nearly the whole of their growth. It is the same with pigeons and other birds, who lay but a few eggs; but those which produce in great numbers, as poultry, fish, &c. engender much sooner. A cock is capable of engendering at the age of three months, when he has not attained a third part of his growth; a fish, which at the end of twenty years will weigh thirty pounds, engenders in the first or second year, when perhaps it does not weigh half a pound. But exact observations on the growth and duration of the life of fish are still wanting: their age may be nearly known by examining the annual layers of their scales; but we are not certain how far that may extend. I have seen carp in the Comte de Maurepas' canals, at his castle at Pont Chartrain, which were said to be 150 years old, and they appeared as brisk and lively as the common carp. I will not say, with Leeuwenhoek, that fish are immortal, or at least can never die with age; all must perish in time, that is; all which have a beginning, a birth, must arrive to an end, or death; but fish, living in an uniform element, and being sheltered from the vicissitudes and all the injuries of the air, must live a longer time in the same state than other animals, especially if these vicissitudes of the air be, as a great philosopher asserts, the principal causes of the destruction of living beings. But what must contribute to the long duration of their life is, that their bones are softer than those of other animals, and do not harden with age. The bones of fish lengthen, and grow thick without taking any more solidity; whereas the bones of other animals continually increase in hardness and density, until at length, being absolutely full, the motion of their fluid ceases, and death ensues. In their bones the repletion or obstruction, which is the cause of natural death, is formed by such slow and insensible degrees, that fish must require much time to arrive at what we call old age.

All quadrupeds covered with hair are viviparous; all those covered with scales oviparous. May we not then believe than in oviparous quadrupeds, a much less waste is made by transpiration, than the cloathing of scales retains; whereas in animals covered with hair this transpiration is more free and abundant? and is it not partly by this superabundance of nutriment, which cannot be carried off by transpiration, that those animals multiply so abundantly, and are enabled to go so long without food? All birds and all insects that fly are oviparous, excepting some kinds of flies which bring forth their young alive. These flies have no wings at their birth, but they shoot out and grow by degrees, and which they cannot use before they are of full growth. Scaly fish are likewise oviparous; as are all reptiles which have no legs, such as snakes and different kinds of serpents; they change their skins, which are composed of small scales. The viper is only a slight exception to the general rule, for it is not truly viviparous, as it produces eggs, from which the young are hatched; it is certain this is performed in the body of the mother, who instead of casting those eggs, like other oviparous animals, she retains and hatches them in her own body. The salamander, in which eggs and young ones are found at the same time, as observed by M. de Maupertuis, is an exception of the same kind in oviparous quadrupeds.

Most animals are perpetuated by copulation; yet many birds seem only strongly to compress the females; indeed the ostrich, Crane, and some few others, are so well supplied as to leave intromission no ways equivocal. Male fish approach the female in the spawning time; they seem even to rub their bellies against each other, for the male often turns upon its back to meet the belly of the female; but the necessary part for copulation does not exist in them; and the male fish approaches the female only to emit the liquor in their milts on the eggs, which the female then deposits; and it seems rather to be attracted by the eggs than the female; for when she ceases throwing out the eggs, he instantly forsakes her, and with eagerness pursues the eggs, which the stream carries away, or that the wind disperses. Male fish may be seen to pass and repass every spot where eggs are deposited several times. It is certainly not for the love he bears the female that all these motions are made, because it is not to be presumed he always knows her; often being seen to emit his liquor on all eggs that he comes near, and that often before he has met with the female to which they belonged.

There are therefore animals, distinguished by sexes, which have proper parts for copulation, and some which are deficient in them; others, as snails, have both, and the two sexes in the same individual; others, as vine-fretters, have no sex, and engender in themselves separately; although they couple together when they please, we cannot determine whether that is a conjunction of sexes; if it is so, we must suppose that Nature has included in this small individual more faculties for generation than in any other kind of animal, and that it not only has the power of reproducing distinctly, but also the means of multiplying by the communication of another individual.

But whatever difference takes place in generation, Nature, by a new production, prepares the body for it, and which, whether manifested outwardly, or concealed internally, always precedes generation. The ovaries of oviparous animals, and the testicles of female viviparous animals, before the season of impregnation, experience a considerable change. Oviparous animals produce eggs, which at first are attached to the ovaries, by degrees they increase in size, until they fall into the canal of the matrix, where they acquire their white membranes, and shell. This production has marks of the fecundity of the female, and without which generation cannot be performed: so in viviparous females there are always one or more glandular bodies on the testicles, which by degrees grow under the membrane that surrounds them; these glandular bodies enlarge and pierce, or rather impel and lift up the membrane of the testicle; when their maturity is complete, a small slit or several small holes appear at their extremities, by which the seminal liquor escapes, and falls into the matrix: these glandular bodies are new productions that precede generation, and without which there would not be any.

In males there is also a similar change which always precedes their capacity for generating. In oviparous animals a great quantity of liquor fills a considerable reservoir, and which reservoir itself is sometimes formed every year; as in the calmar and some other fish. The testicles of birds swell surprisingly just preceding their amorous season. In viviparous males the testicles also swell considerably in those who have seasons, and in general there is a swelling and an extension of the genital members in all species, which, although it be external, must be regarded as a new production necessarily preceding generation.

In the body of every animal, male or female, new productions are formed which precede generation; and when there is no real production there is always a swelling, and considerable extension in some of the parts. There are species in which this new production is not only manifest, but even the whole body seems to be renewed before generation can be performed; as is the case with insects whose various metamorphoses seem to be only for the purpose of generating; for the growth of the animal is completed before it is transformed. It ceases from taking nutriment, has no organs for generation, no means of converting the nutritive particles, of which they abound, into eggs or seminal liquor, and therefore this superfluity unites and moulds itself at first into a form something like that of the original. The caterpillar becomes a butterfly, because, for these reasons, it is unable to produce small organized beings like itself; the organic particles, always active, take another form, by uniting, whose figure answers in part, and even in essential constitution, to that of the caterpillar, but in which the organs of generation are developed, and may receive and transmit the organic particles of the nutriment which forms the eggs, and the individuals of the species. The individuals which proceed from the butterfly ought not to be butterflies, because the nutriment, from whence the organic particles proceed, was taken while in the form of caterpillars; the produce therefore must be similar, and not butterflies, which is only an occasional production of the superabundant nutriment; a method adapted by Nature to accomplish the purposes of generation in these species, as by the glandular bodies and milts in other animals.

When the superabundant quantity of organic nutriment is not great, as in man and most large animals, generation is not made till the growth of the animal is nearly complete, and then it is confined to the production of a small number of individuals. When these particles are more abundant, as in many kinds of birds, and in oviparous fishes, generation is completed before the animal has received its full growth, and their production of individuals is very numerous. When the quantity of particles is still greater, as in insects, it first forms a large organic body, which, though retaining the essential constitution of its original, differs in many parts, as the butterfly from the caterpillar, but shortly produces an astonishing number of young, similar in form to the animal which selected the nutriment. When the superabundance is greater still, and when at the same time the animal has the necessary organs for generation, as the vine-fretter, it immediately produces a generation in every individual, and afterwards a transformation, like other insects. The vine-fretter becomes a fly, but cannot produce any thing, because it is only the remainder of the organized particles which had not been made use of in the production of the young.

Almost every animal except man has stated times for generation. Spring is marked out for birds. Carp, and many kinds of fish, spawn in June and August. Barbel, and other kinds, in spring. Cats have three seasons, in January, May, and September. Roebucks, in December. Wolves and Foxes, in January. Horses, in summer. Stags, in September and October; and almost all insects generate in autumn: these last seem to be totally exhausted by generation, and die a short time after. Other animals, though not exhausted, become extremely lean and very weak, and require a considerable time to repair the loss which is made of the organic substance. Others are exhausted still less, and are soon restored to an engendering state; while man is scarcely in the least affected; his loss is speedily repaired, and therefore may be said to be at all times in a state for propagation; all which depends solely on the particular construction of the animal organs. The grand limits Nature has placed in the mode of existence are equally conspicuous in the manner of receiving and digesting the food, in the manner of retaining it in, or excluding it from, the body, and in the means by which the organic molecules, necessary for reproduction, are extracted. In a word, we shall find throughout all nature, that all what can be, is.

The same difference exists in the time of female gestation; some, as mares, carry their young eleven or twelve months; others, as women, cows, &c. nine months; others, as foxes, wolves, &c. five months; bitches, nine weeks; cats, six weeks; rabbits, thirty-one days. Most birds come out of the egg at the end of twenty-one days; though some, as canary birds, hatch in thirteen or fourteen days. The variety is as great here as in every thing else relative to animals. The largest animals which produce only few, are those which go the longest with young; this still more confirms what we have already said, that the quantity of organic food is in proportion less in large than in small animals; for it is from the superfluity of the mother's food that the fœtus derives what is necessary to the growth and expansion of its parts, and since this expansion demands much more time in large than in small animals, it is a proof that the quantity of matter which contributes is not so abundant in the first as in the last.

There is, therefore, an infinite variety in animals, with respect to the time and manner of gestation, engendering, and bringing forth; and this variety is found even in the causes of generation; for although the general principle of production is this organic matter common to all that lives or vegetates, the manner in which the union is made, must have infinite combinations, which must all proceed from the source of new productions. My experiments clearly demonstrate, that there are no pre-existing germs, and at the same time prove that the generation of animals and vegetables is not equivocal; there are, perhaps, as many beings, either living or vegetating, which are produced by the fortuitous assemblage of organic molecules, as by a constant and successive generation. It is to those productions we should apply the axiom of the ancients, "Corruptio unius, generatio alterius." The corruption and composition of animals and vegetables produce an infinite number of organized bodies; some, as those of the calmar, form only kinds of machines, which, although very simple, are exceedingly active; others, as the spermatic animalcules, seem by their motion, to imitate animals; others imitate vegetables by their manner of growing or extending; there are others, as those of blighted corn, which may be made to live and die alternately, and as often as we please; there are still others, even in great quantities, which are at first kinds of vegetables, afterwards become species of animals, then return again to vegetables, and so on alternately. There is a great appearance, that the more we shall observe this race of organized beings, the more we shall discover varieties, always so much the more singular as they are the more remote from our sight, and from the varieties of other animals that have already become known to us.

For example, spurred barley, which is produced by an alteration or decomposition of the organic substance of the grain, is composed of an infinity of little organized bodies, like to eels. By infusing the grain for ten or twelve hours in water, we find them to have a remarkable twirling, and a slight progressive motion; when almost dry, they cease to move, but by adding fresh water their motion returns. The same effects may be produced for months, or even years; insomuch that we can make these little machines act as often and as long as we please without destroying them, or their losing any of their power or activity. Their threads will sometimes open, like the filaments of semen, and produce moving globules; we may therefore suppose them to be of the same nature, only more fixed and solid.

Eels, in paste made with flour, have no other origin than the union of the organic particles of the most essential parts of the grain: the first which appear are certainly not produced by many others; yet, although they have not been engendered, they engender others. By cutting them with the point of a lancet, we may perceive small eels come from their bodies in great numbers; the body of the animal appears to be only a sheath or bag which contains a multitude of other little animals, which perhaps are themselves only sheaths of the same kind, in which the organic matter assimilates, and takes the form of eels.

There requires a great number of observations to be made to establish classes and races between such singular beings, which are at present so little known; there are some which may be regarded as real zoophytes, which vegetate, and at the same time appear to twirl and move like animals. There are some that at first appear to be animals, which afterwards join and form kinds of vegetables. A little attention to the decomposition of a grain of wheat infused in water will elucidate all I have asserted. I could add more examples, but I have related these only to point out the varieties there are in generation. There are certainly organized beings which we regard as animals, but which are not engendered by others of the same kind; there are some which are only a kind of machines, whose action is limited to a certain effect, and which can act but once in such a certain time, as those in the calmar; and there are others, as we have just remarked, which we can cause to act as long and as often as we please. There are vegetating beings which produce animated bodies, as the filaments of the human seed, from whence the active globules spring, and which move by their own powers. In the corruption, fermentation, or rather the decomposition of animal and vegetable substances, there are organized bodies which are real animals, and can propagate their like, although they have not been so produced. The limits of these varieties are perhaps still greater than we can imagine. We may extend our ideas, and exert every effort to reduce the effects of Nature to certain points, and class her productions to certain classes, yet an infinite number of links will always escape us.

CHAPTER X.

OF THE FORMATION OF THE FŒTUS.

It appears to be clearly ascertained by the experiments of Verheyen, who in one of them found the seed of a bull in the matrix of a cow; and by those of Ruysch, Fallopius, Leeuwenhoek, and many others, who perceived the male semen in the uterus of women, and numberless other animals, that the seminal liquor of the male enters by some means into the matrix of the female. It is probable, that in the time of copulation the orifice of the matrix opens to receive the seminal liquor, but if that is not the case, the active and prolific substance of this liquor, may penetrate the membranes of the matrix; for the seminal liquor being, as we have proved, almost all composed of organic molecules, which are in great motion, and extremely minute, they may pass across the coat of the closest membranes, and penetrate those of the matrix with the greatest facility.

What proves that the active part of this liquor may not only pass through the pores of the matrix, but even penetrate its substance, is the sudden change that immediately takes place after conception. The menses are suppressed, the matrix becomes softer, swells, and appears inflamed. All these alterations can only happen by the action of an external cause; by the penetration of some part of the seminal liquor into the substance even of the matrix. This penetration not only operates on the external surface of the matrix, but on all the other parts of which this viscera is composed, like that penetration by which nutrition and expansion is produced.

We shall be easily persuaded that it is so, when we consider that the matrix, during the time of gestation, not only augments in bulk but also in quantity of matter, and that it has a kind of life or vegetation, which is continually increasing till the time of delivery; for if the matrix was only a pouch, a destined receptacle to receive the seed and contain the fœtus, it would extend and grow thin in proportion as the fœtus increased in size; but in reality the matrix not only extends in proportion as the fœtus grows larger, but receives at the same time a thickness and solidity. This augmentation is a real growth, like the expansion of the body in young animals, which can only be produced by the intimate penetration of the organic molecules analogous to the substance of the parts: and as this expansion of the matrix never happens but after impregnation, we cannot doubt its being produced by the liquor of the male, especially as the expansion takes place before the fœtus has sufficient bulk to dilate it.

It seems certain, by my experiments, that the female has a seminal liquor which commences to be formed in the testicles, and is completed in the glandular bodies: this liquor distills through the small holes, at the extremities of these bodies; and may, like that of the male, enter into the matrix in two different manners, either by these holes at the extremities, or through the membraneous coat of the matrix.

These seminal liquors are both extracts from all parts of the body, and in the mixture of them there is every thing necessary to form a certain number of males and females; and the more the animal abounds with this liquor, and the more that abounds with organic molecules, the greater is their number of young; as we have already remarked is the case with the small animals, and diminishes in the large.

But to pursue our subject with greater attention, we shall first examine the particular formation of the human fœtus, and afterwards return to the other animals. In the human species, as well as in large animals, the seminal liquors of the male and female do not contain a great abundance of organic molecules, and therefore seldom produce more than one at a time: the fœtus is a male, if the number of the organic molecules of the male predominates in the mixture, and a female if the contrary; and it resembles the father or the mother as they happen to abound in the mixture of the two liquors.

I conceive, therefore, that the seminal liquor of both are two matters equally active and necessary for generation; and this I think is sufficiently proved by my experiments, since I have seen the same moving bodies in the one as the other. I perceived that the liquor of the male enters into the matrix, where it meets with that of the female: that they have a perfect analogy, and are both not only composed of similar parts by their form, but also in their motions and actions; as we have remarked in Chap. VI.

By the mixture of these two liquors I conceive the activity of the organic molecules of each is stopped, and that the actions of one counterbalance that of the other, insomuch that each particle ceasing to move, remains in the place most analogous to itself, and that they will naturally take the same position, and will dispose themselves in the same order they held in the animal body; those that came from the head will arrange themselves in the head of the fœtus, those of the back the same, and so of every other part; consequently they will form a small organized being, in every thing like the animal from which they are extracted.

It must be observed that this mixture of organic molecules of the two sexes contains similar and different particles; the similar ones are those which have been extracted from every part common to both sexes. The different particles are those which have been extracted from the parts whereby the sexes are distinguished; thus there is, in this mixture, double the number of organic molecules to form the head, or the heart, or such other parts common to both, whereas there are only what are requisite to form the parts of the sex. Now the similar particles may act upon each other without being disordered, and collect together as if they had been extracted from the same body; but the dissimilar parts cannot act on each other, nor unite together, because they have not any relation; hence these particles will preserve their nature without mixture, and will fix of themselves the first, without the need of being penetrated by the others. Thus the molecules proceeding from the sexual parts will be the first fixed, and all the rest which are common to both, will afterwards fix indiscriminately, whether they are those of the male or female, and form an organized being which, in its sexual parts, will perfectly resemble its father, if it is a male, and its mother if a female; but which may resemble one another, or both, in all the other parts of the body.

It seems to me that if this was well understood, we shall in a great measure be enabled to answer the objections made to the sentiments pf Aristotle, and which might also be advanced against this system. The question is, Why each individual, male and female, does not produce of itself an animal of its own sex? It must be acknowledged this question seems to carry weight with it; but having reflected a long time on this subject I think I have found an answer, and which I shall endeavour to explain.

It is certainly evident, from what we have said in the preceding chapters, and the experiments we have described, that reproduction is effected by the union of organic molecules returned from each part of the body of the animal, or vegetable, into one or many common reservoirs; and that they are the same molecules which serve for nutriment and expansion of the body. This appears to me to have been so clearly proved, that I apprehend no scruple can remain as to the foundation of the theory; but I admit there may be some reason to ask, Why each animal and vegetable does not produce its own likeness, since each individual returns from every part of its body, and collects in a common reservoir, all the organic molecules necessary for the formation of a small organized being? Why then is not this organized being formed? and why, in almost every animal, is a mixture of the liquors of the two sexes required to produce an animal? If I content myself with answering, that in almost all vegetables, and all kinds of animals which multiply by cutting, that it appears the design of Nature that each individual should increase its own species, and that we must regard as an exception to this rule, the use which is made of the sexes in other kind of animals; it may be said, that the exception is more universal than the rule itself. This difficulty will be very little weakened, if we were to say, that each individual perhaps would produce its like, if it had proper organs, and contained the necessary matter towards the nutriment of the embryo; because females have both this matter, and organs, and yet do not produce either male or female fœtus without the intervention of the male; which intervention of sexes in all animals is essential and absolutely necessary.

Although the testicles and seminal vesicles of a man, contain all the necessary molecules to form a male, yet the local establishment and arrangement of these molecules cannot be made, because the effect of an union is prevented by the continual circulation of the seed both by absorption, and the action of the new organic molecules which constantly come into this reservoir from all parts of the body. The same circumstances taking place with the organic molecules of the female, is an evident reason why neither can produce of themselves, because when the seminal liquors of the male and female are mixed, they have more analogy to each other, than with the parts of the body of the female where the mixture is performed. By admitting of this explication, it may be asked, Why the common mode of generation in animals does not agree with it; for, upon that supposition, each individual would produce like snails, and impregnate each other, and each individual receiving the organic molecules the other furnished, the union would be made of itself, and by the sole power of the affinity of these molecules among themselves? I own, if it was by this cause alone the organic molecules could unite it would be natural to conclude, that the shortest mode to perform the reproduction of animals, would be to give to one individual both sexes. But it is quite contrary to the general rule pursued by Nature, as this manner of generation is confined to snails, and a small number of other animals. This answer cannot be said to fully satisfy the question, as it merely supposes the male does not produce, as it cannot receive any thing from the female, and that having besides no proper viscera to contain and nourish the fœtus.

We may also suppose that the activity of the organic molecules, in the semen of one individual, has need of being counterbalanced by the activity or force of those of another individual, in order to fix and bring them into a kind of equilibrium, a state of rest highly necessary to the formation of the animal; and that this activity in the organic molecules can only be counterbalanced by there being a contrary action in those which come from the male, and those proceeding from the female; so that, in this sense, all living or vegetating beings must have two sexes, conjointly and separately, to produce their resemblances. But this answer is too general to be entirely clear; nevertheless, if we pay attention to all the phenomena, we shall find some explanation resulting therefrom. The mixture of those two liquors produces not only a male or female fœtus, but also other organized bodies, which have a kind of growth or expansion. The placenta, membranes, &c. are produced at the same time as the fœtus. There are, therefore, in the seminal liquor of the male or female, or in the mixture of both, not only organic molecules necessary for the production of the fœtus, but also those which form the placenta and membranes. We know not from whence these molecules come, since there is no part of the body, either of the male or female, from which they could be sent back. From hence it seems it must be admitted, that the molecules of the seminal liquors of each, being alike active, form organized bodies every time they can fix, by acting mutually one on the other: that the particles employed to form a male, will be those of the masculine sex, which will fix the first, and form the sexual parts; and that those common to both sexes will then fix indifferently to form the rest of the body, and that the placenta and membranes are then formed from the superabundant particles, which have not been used to form the fœtus; if, as we suppose, the fœtus is a male, then there remains to form the placenta, and membranes, all the organic particles peculiar to the feminine sex which have not been employed; and also all those of both which shall not have entered the composition of the fœtus, and which cannot be less than one half. So likewise, if the fœtus is a female, the same abundance will be left for the formation of the placenta, and membranes, and the whole effects be the same, excepting it will have the superfluity of the male, instead of that of the female.

But, it may be said, that in that case the placenta and membranes ought to become another fœtus, which would be a female, if the first was a male; and a male if the first was a female; for the first having consumed the organic molecules of the sexual parts of only one individual, and half those common to both, there remains all the molecules of the sexual parts of the other individual, and the other half of those common to both. To this I answer, that the first union of the organic molecules prevents a second, at least, under a similar form; that the fœtus, being the first formed, exercises an external power, which disorders the arrangement of the other organic molecules, prevents the formation of a second fœtus, and throws them into a state from which the form of the placenta and membranes result.

We are assured by the experiments and observations we have made, that every living being contains a great quantity of living and active molecules. The life of the animal or vegetable appears to be only the result of all the young lives (if that expression is permitted me) of each of these active molecules, whose life is primitive, and appears impossible to be destroyed. We have found these living molecules in every living or vegetating being, and are assured, that they are alike necessary for nutrition, and consequently, for the reproduction of animals or vegetables. It is not, then, difficult to conceive, that a certain number of those molecules united should compose a living being. Each of these particles possessing animation, an assemblage of them must be endowed with life, and thus these living organic molecules, being common to all living beings, they necessarily form any particular animal or vegetable, according as they are arranged. Now, this arrangement absolutely depends on the form of the individuals which furnish those molecules. If they are furnished by an animal, they will arrange under the form of an individual like to it, exactly as they were arranged when they served for the expansion of the animal itself; but must we not then suppose that this arrangement cannot be made either in animals or vegetables, but by the means of a kind of base, round which the molecules might unite to form the fœtus? Now, it is plain, this basis is furnished by particles peculiar to the different sexes, as I shall explain.

While the molecules of either sex remain by themselves, their action produces no effect, because they are without any opposition from any different kind of particles; but, when these molecules are mixed, then there are dissimilar parts, and those serve for the base and point of rest to the other molecules, and fix their activity.

In this supposition that the organic molecules, which, in the mixture of the seminal liquors of the two individuals, represent the sexual parts of the male, can alone serve for a base to the organic molecules proceeding from every part of the female, and those peculiar to the female sex as a base to them which are extracted from the male, we might conclude, that the sexual part of the male infant is formed of the organic molecules of the father, and from those of the mother, for the rest of the body: and that, on the contrary, the female partakes of its mother only in sex, and takes the rest of its body from its father. Boys, therefore, ought, excepting the parts of the sex, to have a greater resemblance to their mother than to their father, and girls more to the father than to the mother; but this consequence is not, perhaps, conformable to experience.

By considering, under this point of view, generation by sexes, we should conclude it to be the most general mode of reproduction, as it is in fact. Beings, whose organization is the most complete, as animals, whose bodies compose a whole, which can neither be separated nor divided, and whose powers are con-centered to one single point, can only reproduce by this mode; because they contain only particles which resemble each other, and whose union can only be made by different particles, furnished by another individual. Those where organization is less perfect, as that of vegetables, whose bodies may be divided and separated without being destroyed, can be reproduced by other modes. First, because they contain dissimilar particles; secondly, because their forms not being so determinate and fixed as that of animals, the particles may supply the functions of each other, and change according to circumstances; as we see roots become branches, and shoot out leaves when exposed to the air, which causes that the vegetable particles obtain a local establishment, become fixed, and are enabled to multiply, by various modes.

It will be the same with animals, whose organization is less perfect, as the fresh water polypus, and others, which can reproduce by division of their parts. These organized beings are not so much a single animal, as a number united under one common covering, as trees are composed of a multiplicity of young trees, (see Chap, II.) Pucerons, which engender singly, also contain dissimilar particles, since, after producing their young they change into flies which do not produce at all. Snails communicate mutually these dissimilar particles, and afterwards they both produce. Thus, in all known matters of generation, we see that the requisite union of organic particles, can only be made by the mixture of different particles, which serve as a basis capable of fixing their motions.

If to the idea of the word sex, we give all the extent here supposed, we shall say, that sexes are found throughout all nature; for then sex will mean only the parts which furnish the organic particles, different from the common particles, and which must serve as a fixed point for their union. But, enough of reasoning on a question that can be at once resolved, by saying, that God having created sexes, it necessarily follows that animals should reproduce by their connection. In fact, we are not made, as I have formerly said, to give a reason for every why. We are not in a state of explaining why Nature, almost throughout her works, makes use of sexes for the reproduction of animals, or why sexes exist; we ought, therefore, to content ourselves with reasoning on what is, on things as they are, since we cannot go beyond, by forming suppositions which will remove us from the sphere we ought to contain ourselves in, and to which the small extent of our knowledge is limited.