Plato, in the Timaeus, accounts not only for the generation of men, of animals, of plants, and of the elements, but even of the heavens and of the gods themselves, by images reflected or extracted from the divine Creator; which images, by an harmonic movement, are arranged in the most perfect order, according to the properties of number.  The universe, he says, is a copy of the Deity; time, space, motion, and matter, are the images or representations of his attributes; and secondary and particular causes are results of the numeric and harmonic qualities of these images:  The world, from its excellency, is the most perfect animated being.  To give the world complete perfection, it was necessary that it should contain all the other animals, or all the possible forms and representations of the creative power.  Man is one of these forms.  The essence of all generation consists in the unity and harmony of the number Three, or of the Triangle, namely, that which generates, that in which generation is performed, and the result, or that which is generated.  The succession of individuals in the [64] species, is only a fugitive image of the immutable eternity of this harmonic triangle, a universal prototype of all existences, and of all generations.

This philosopher paints only ideas.  Disengaged from matter, he flies into the regions of abstraction; and, losing sight of sensible objects, he contemplates those of intellect alone.  One cause, one end, one mean, compose the whole of his perceptions:  God is the cause, perfection the end, and harmonic representation the means.  This idea is sublime; the mode of philosophisizing is noble and full of simplicity; but it is perfectly vacant, and affords no objects for speculation.  We are not pure intelligences.  We are unable to give real existence to our ideas.  Chained to matter, or rather depending on the causes of our sensations, it is impossible that we should realise [sic] abstractions.  To Plato I might reply in his own manner, “The Creator realises [sic] every thing he conceives; his perceptions beget existence:  The created being, on the contrary, conceives nothing but by retrenching from reality; and annihilation is necessary to bring forth his ideas.” 

Let us, without regret, therefore, confine ourselves to a philosophy more humble and more material; and, keeping within the sphere which nature has allotted us, let us examine those rapid and daring spirits who attempt, though in vain, to fly beyond the limits of humanity.  The whole [65] of this Pythagorean philosophy, which is purely intellectual, depends upon two principles, the one false, and the other uncertain; namely, the real power of abstraction, and the natural existence of final causes.  To apprehend numbers to be real beings; to say that unity is a general individual, which not only represents all individuals, but even communicates existence to them; to pretend that unity exercises the actual power of engendering another unity nearly resembling itself, and of creating two individuals, two sides of a triangle, that can have no connection or perfection without a third side, which is necessarily produced by the other two; in fine, to regard numbers, geometrical lines, and metaphysical abstractions, as real and efficient physical causes, by which the elements are formed, plants and animals regenerated, and all the phaenomena of nature produced, appears to be the greatest and most absurd abuse of human reason, and an invincible obstacle to the advancement of knowledge.  Besides, nothing can be more fallacious than such chimeras.  Supposing we should agree with Plato and Malbranche, that matter has not existence, that external objects are only ideal images of the creative power, and we see every thing in the Deity himself; does it follow, that our ideas are of the same order with those of the Creator, and that they can produce real existences?  Are we not dependent on our sensations?  Whether the [66] objects which excite sensations be real or imaginary, whether they exist without or within, whether it be God or matter that we every where behold, is to us of little importance:  We are not less certain of being uniformly affected in the same manner by the same causes.  The relations between our senses and the objects which affect them, are necessary and invariable.  It is upon this basis alone that the principles of philosophy ought to be founded, otherwise our knowledge must be useless and fallacious.  Can an harmonic triangle create the substance of the elements?  Is fire, as Plato affirms, an acute triangle, and light and heat two properties of this triangle?  Are water and air rectangular and equilateral triangles?  Is the form of the element of earth a square, because, being the least perfect of the four elements, it recedes as far as possible from a triangle, without departing altogether from its essence?  Do males and females embrace each other, for no other purpose but to complete the triangle of generation?  These Platonic ideas have two different aspects:  In speculation, they seem to proceed from sublime principles; but the application of them in practice leads to nothing but false and childish conclusions.

Is it difficult to perceive that our ideas originate from our senses alone; that the objects we regards as real existence, are those concerning which the senses uniformly give the same testi- [67] mony; that the objects we apprehend as having a real existence, are those which are invariably presented to us in the same manner; that the mode in which they present themselves has no dependence upon our will or inclination; that, of course, our ideas, instead of being the causes of things, are only particular effects, which become less similar to the objects themselves, in proportion as they are rendered more general; and, lastly, that mental abstractions are only negative beings, which derive their intellectual existence from the faculty we possess of considering objects, without regarding their sensible qualities?

Is it not, therefore, apparent, that abstract ideas can never be the principles of existence, or of real knowledge?  On the contrary, all our knowledge is derived from comparing and arranging the results of our sensations.  These results are known by the appellation of experience, the only source of genuine science. The employment of any other principle is an abuse; and every edifice founded upon abstract ideas, is a temple erected to Error.

In philosophy, error has a more extensive influence than in morals.  A thing may be false in morals solely because it is misrepresented. But falsehood in metaphysics consists not in misrepresentation alone, but in taking for granted what has no existence at all.  It is into this most pernicious species of error that the Platonists and [68] the Sceptics have fallen.  Their false suppositions have obscured the natural light of truth, bewildered the reasoning faculties of men, and retarded the progress of philosophy.

Final causes are employed as a second principle by Plato and other theorists.  This principle has even been adopted by the vulgar, and by some modern philosophers.  A moment’s reflection, however, will be sufficient to reduce this principle to its proper value.  To say that light exists because we have eyes, and that sounds exist because we have ears; or to say that we have eyes and ears, because light and sounds exist; is not this precisely the same thing?  Or, rather, are we any wiser by this kind of reasoning?  Will we ever make any discoveries by such a mode of explication?  Is it not apparent, that final causes are only arbitrary relations and moral abstractions, which ought to have less influence than abstractions in metaphysics, because the origin of the former is less noble and worse imagined?  And, though Leibnitz has endeavoured to give an elevation to final causes, under the appellation of the reasonabless and eternal fitness of things, [raison suffisante], and Plato has represented them under the flattering picture of absolute perfection; all these efforts are insufficient to cover their native insignificance and precariousness.  Are we better instructed in the operations of Nature, because we are told that nothing exists without a reason, or that every [69] thing is created with a view to the perfection of the whole?  What is reasonableness or fitness?  What is perfection?  Are they not moral beings created solely by the human intellect? Are they not artibrary relations which we have contrived to generalise [sic]?  They have no foundation but in moral affinities, which, so far from producing any physical or real existence, change the nature of truth, and confound the objects of our sensations, of our perceptions, and of our understandings, with those of our sentiments, of our passions, and of our wills.* [70]

Much more might be said upon this subject. But I pretend not to write a treatise on philosophy; and shall therefore return to physics, from which the ideas of Plato, concerning universal generation, have diverted my attention.  Aristotle, who was as great a philosopher as Plato, and a better physician, instead of wandering in the regions of theory, collects facts, and speaks in a language more intelligible.

Matter, he remarks, which is only a capacity of receiving forms, assumes, in generation, a figure similar to the individual which furnishes it:  And, with regard to animals which generate by the intervention of sexes, he imagines, that the prolific principle proceeds solely from the male.*  For though, in another place, when speaking of animals in general, he says, that the female [71] sheds a seminal fluid within the body, it appears, that he regards not this fluid as a prolific principle; and yet he tells us, that the menstrual blood serves for the formation, nourishment, and growth of the foetus; but that the efficient principle exists alone in the seminal fluid of the male, which acts not as matter, but as a cause.  Averrhoes, Avicenna, and other philosophers who embraced this opinion of Aristotle, have endeavoured to prove that females have no prolific fluid.  They alledge [sic], that, as females are furnished with a menstrual fluid, which is both necessary and sufficient for the purposes of generation, it is unnatural to suppose them possessed of any other, especially since it begins to appear, like that of the male, at the age of puberty.  Besides, they continue, if females really have a prolific seminal fluid, why do they not produce without the intercourse of the male, since they contain the prolific principle, as well as the matter necessary for the growth and expansion of the embryo?  This last reason is the only one which merits attention.  The menstrual blood appears to be necessary for the growth and nourishment of the foetus; but still it may contribute nothing to its first formation, which requires the mixture of both prolific fluids.  Females, therefore, like males, may have a prolific fluid for the formation of the embryo, as well as menstrual blood for its growth and nourishment.  The imagination is not unnatu- [72] ral, that, as the female possesses both a prolific fluid extractef from all parts of her body, and likewise the means of expanding and nourishing, she should produce females without any communication with the male.  It must be allowed, that this metaphysical argument used by the Aristotelians for proving that females are destitute of a prolific fluid, may be urged as the strongest argument against every system of generation, and, in particular, against that which I am endeavouring to establish.

Let us suppose, it may be said, that the superfluous organic particles are sent from every part of the body into the testicles and seminal vessels of the male, why do they not, by means of your imaginary attracting forces, form small organized bodies similar to the whole?  Why are not similar bodies generated in the female, without any intercourse with the male?  If you answer, that the male fluid contains only males, that the female fluid contains only females, that both perish for want of the circumstances necessary for expansion, and that, for the procreation of an animal, a mixture of both is requisite; may it not be demanded, why this most complicated, difficult, and less fertile mode of generation, is so invariably preferred by Nature, that all animals, with a few trifling exceptions, generate by the mutual commerce of sexes?

I shall content myself, at present, with replying, that this is the mode actually employed by [73] Nature; and, therefore, however complicated it may appear, it is, in fact, the most simple; because, as I formerly remarked, whatever most frequently happens, is, in itself, however it may seem to us, the most simple.

Besides, the notion of the Aristotelians, that females have no seminal fluid, cannot receive our assent, if we consider the strong resemblance of children to their mothers, and that mules, mulattoes, and mongrels of every kind, uniformly resemble the mother more than the father; and, if it be farther considered, that the generating organs of the female, like those of the male, are properly formed for preparing and receiving a seminal fluid, we shall be easily induced to believe the existence of such a fluid, whether it resides in the spermatic vessels, the testicles, or the ovaria, or proceeds, by irritation, from the lacunae of De Graaf, which are situated at the neck and near the orifice of the uterus.

But we must examine Aristotle’s ideas more fully, as, of all the antients, this great philosopher has treated the subject of generation in the most extensive manner.  He distinguishes animals into three classes:  1.  Those that have blood, and, with few exceptions, propagate by copulation; 2.  Those that have no blood, and, being hermaphrodites, produce of themselves without copulation; and, 3.  Those that proceed from putrefaction, and have no parents of any kind.  I shall first remark, that this division is exceed- [74] ingly improper:  Though it be true, that animals having blood are distinguished into male and female, it is by no means equally true, that bloodless animals are, for the most part, hermaphrodites:  For the only hermaphrodites we know, are land-snails and worms; but we are uncertain whether all shell-animals, and all those which have no blood, be also hermaphrodites.  This must be learned from the particular histories of these animals.  And, with regard to those that are alledged [sic] to proceed from putrefaction, as Aristotle gives no enumeration of them, many objections occur; for most species which the antients believed to proceed from putrefaction, have, by the moderns, been discovered to proceed from eggs.

Aristotle makes a second division of animals, namely, into those who have the faculty of progressive motion, and those who have no such faculty.  All animals who move, and have blood, are distinguished by sexes:  But those which, like oysters, adhere to one place, or hardly move at all, have no sexes, and, in this respect, resemble plants; and it is only, he observes, from difference in bulk that they have been distinguished into male and female.  It must be acknowledged, that we are still uncertain whether shell-animals have sexes:  Among oysters, some individuals are fertile, and others not.  The fertile individuals are distinguished by a delicate edging or border which surround their bodies, [75] and they are called males.*  Our observations on this subject are extremely limited.

But to proceed.  The male, according to Aristotle, contains the principle of motion, and the female the material part of generation.  The organs destined for this purpose are different in different animals.  Of these the testicles are the chief in males, and the uterus in females.  Quadrupeds, birds, and cetaceous animals, have testicles; fishes and serpents are deprived of them; but they have two canals for the reception and maturation of the semen:  These parts, so essential to generation, are always double both in males and females; and, in the male, they retard the motion of that part of the blood which goes to the formation of semen.  This he proves from the example of birds whose testicles swell considerably during the season of their amours, but afterwards diminish so greatly that they can hardly be discovered.

All quadrupeds covered with hair, and the cetaceous fishes, as whales and dolphins, are viviparous:  But vipers and cartilaginous animals are not properly viviparous; because they produce an egg within their own bodies, previous to the exclusion of the live animal.  Oviparous animals are of two kinds; those which produce perfect eggs, as birds, lizards, turtles, &c. and those which produce imperfect eggs, as fishes, whose eggs augment and come to perfec- [76] tion after they have been deposited in the water by the female:  And, in every species of oviparous animals, except birds, the females are larger than the males, as in fishes, lizards, &c.

After remarking these general varieties in the animal kingdom, Aristotle begins with examining the opinion of the antient philosophers, that the semen, both of the male and the female, was extracted from all parts of the body; and he dissents from this opinion; because, says he, though children often resemble their fathers and mothers in the voice, in the hair, in the nails, and in the gate and manner of walking.  Now, he proceeds, it is impossible for the semen to come from the hair, from the voice, from the nails, or from any external quality, as that of the mode of walking.  Infants, therefore, resemble not their parents, because the semen proceeds from all parts of the body, but for other reasons.  I will not expose the weakness of these arguments; but shall only remark, that this great man appears to have been anxious to differ from the sentiments of former philosophers:  And I am persuaded, that, whoever peruses his treatise on generation, will discover, that a strong passion for establishing a system different from that of the antients, obliges him uniformly to prefer arguments of little probability, to the [77] force of proofs, when they stand in opposition to the general principles of his philosophy. 

The seminal liquor of the male, according to Aristotle, is secreted from the blood; and the menstrual fluid of the female is likewise a secretion from the blood, and the only matter which contributes to generation.  Females, he continues, have no other prolific fluid; no mixture, therefore, of male and female fluid takes place:  This he attempts to prove by observing, that some women conceive without pleasure; that few emit any fluid during the time of copulation; that, in general, those who are brown, and have a masculine air, have no emission; and yet their powers of procreation are not less than those of a fairer complection [sic] and more delicate appearance, who emit copiously.  Thus, he concludes, women furnish nothing for the purposes of generation, but the menstrual blood.  This blood is the matter of generation, and the male fluid contributes nothing but the form:  The male fluid is the efficient cause, and the principle of motion; it is to generation what the sculptor is to a block of marble:  The seminal fluid is the sculptor, the menstrual blood the marble, and the foetus the figure.  The menstrual blood receives from the male semen a kind of soul, which gives it life and motion.  This sould is neither material nor immaterial, because it can neither act upon matter, nor augment the menstrual blood, which is the only matter neces- [78] sary to generation.  It is a spirit, says our philosopher, similar to that of the element of the stars.  The heart is the first production of this soul, which is the cause of its own growth, and of the growth and disposition of all the other members.  The menstrual blood contains the capacities of all the parts of the foetus; the soul or spirit of the male semen makes the heart begin to act, and communicates to it the powers of bestowing action on the other viscera; and, in this manner, the different parts of the animal are successively unfolded.  All this appears clear and luminous to the philosopher.  He has only one doubt, namely, whether the blood or the heart is first realized.

Thus have I given a short view of what Aristotle has delivered on the subject of generation, and shall leave the reader to consider whether any system of the antients be more obscure, or more absurd, than that which he has endeavoured to establish.  His system, however, has been adopted by most men of learning. Harvey has borrowed many of Aristotle’s notion; but he has also adopted some of his own, which are by no means better founded.  It is not surprising that Aristotle’s theory of generation, [79] which was a result of his system of philosophy, where form and matter are the great principles, where vegetable and sensitive souls are the agents of nature, and where final causes are real objects, should have been received in the schools:  But it is not a little astonishing to see a physician and an acute observer, like Harvey, carried down the stream, while, at the same time, most philosophers followed the sentiments of Hippocrates and Galen, which we shall afterwards take notice of. 

We mean not to convey a disadvantageous idea of Aristotle by the account we have given of his theory of generation.  We might, with equal propriety, judge of Descartes by his treatise on man.  What these two philosophers have remarked concerning the formation of the foetus should rather be considered in the light of detached observations, or as consequences which each of them drew from their principles of philosophy, than as compleat [sic] systems.  Aristotle admits, as with Plato, final and efficient causes:  The latter are the sensitive and vegetable souls, that give form to matter, which, in itself, is only a capacity of receiving forms:  And as, in generation, the female furnishes the greatest quantity of matter, and as it was repugnant to his system of final causes, that any effect should be produced by two causes, when one was sufficient for the purpose, he concludes, that the woman alone contains the matter necessary for procrea- [80] tion:  Again, another of his principles was, that matter, in itself, has no form, and that form is a being distinct from matter; he therefore maintains, that the male furnishes the form, and, of course, that he contributes nothing material.

Descartes, on the contrary, admitted into his philosophy only a few mechanical principles. By these he attempted to explain the formation of the foetus; and he imagined, that he understood, and was able to communicate to others, the manner in which a living organized body could be formed by the laws of motion alone.  The principles he employed were different from those of Aristotle.  But both of them, instead of directing their inquiries to the thing itself, in place of examining it with impartiality, only considered it in relation to their philosophic principles, which could never be applied with success to the nature of generation, because it depends, as has been already shown, upon very different principles.  Descartes, however, admits the existence and necessary concurrence of the seminal fluids of both sexes.  He allows that both furnish something material for the purposes of generation; and that the fermentation occasioned by a mixture of the two fluids, is the cause of the formation of the foetus.

Hippocrates, who lived about five or six hundred years before Aristotle, taught an opinion, which was adopted by Galen, and by most physicians, for many ages.  He maintained the ex- [81] istence of a female fluid; and even that both male and female had two fluids, the one strong and active, the other weaker and more inactive.*  A concurrence of the two stronger fluids produced a male child, and, of the two weaker, a female.  Thus, according to Hippocrates, there exist two kinds of seminal fluids both in the male and in the female.  This notion he supports in the following manner:  Several women, who produced only girls by their first husband, have had boys by their second; and the same thing has often happened to men who have had two wives.  Supposing this to be fact, it admits of an easy explanation, without having recourse to two different fluids peculiar to each sex; for the women who had girls only by the first husband, and boys by the second, furnished a greater quantity of particles proper for generation during the first, than the second marriage; or the second husband furnished a greater quantity of generating particles during the time of the second marriage, than the first.  If, at the moment of conception, the organic particles of the male are more abundant than those of the female, a male child is the result; and, when the organic particles of the female most abound, a female child is the consequence:  It is not, therefore, surprising, that the husband should be foiled with some women, and have the superiority over others.  [82]

It is farther alledged [sic] by Hippocrates, that the male semen is secreted from the strongest and most essential fluids of the body; and he thus explains the manner in which the secretion is performed:  “Venae et nervi,” says he, “ab omni corpore in pudendum vergunt, quibus dum aliquantulum teruntur, et calefcunt ac implentur, velut pruritus incidit, ex hoc toti corpori voluptas ac caliditas accidit; quum vero pudendum teritur et homo movetur, humidum in corpore calescit ac diffunditur, et a motu conquassatur ac spumescit, quemadmodum alii humores omnes conquassati spumescunt.

“Sic autem in homine ab humido spumescente id quod robustissimum est ac pinguissimum secernitur, et ad medullam spinalem venit; tendunt enim in hanc ex omni corpore viae, et diffundunt ex cerebro in lumbos ac in totum corpus et in medullam:  Et ex ipsa medulla procedunt viae, ut et ad ipsam humidum perferatur et ex ipsa secedat; postquam autem ad hanc medullam geniture pervenerit, procedit ad renes, ac enim via tendit per venas; et si renes fuerint exulcerati, aliquando etiam sanguis deserter:  A renibus autem transit per medios testes in pudendum, procedit autem non qua urina, verum alia ipsi via est illi contigua, etc.” *

It will, doubtless, be perceived by anatomists, that Hippocrates errs in tracing the route of the seminal fluid.  But this affects not his hypothesis [83] that the semen proceeds from every part of the body, and particularly from the head; because, he remarks, those who have had the veins behind their ears cut, secrete only a weak and often an unfertile semen.  The female likewise sheds a seminal fluid sometimes within the uterus, and sometimes without, when the orifice is too open.  The male semen enters the uterus and mixes with that of the female; and, as each has two species of fluid, the one strong and the other weak, if both of them furnish the strong kind, a male foetus is the consequence; and, if both furnish only the weak kind, the result is a female:  Besides, if in the mixture there are more particles of the male than of the female fluid, the child will resemble the father more than the mother; et e contra.  Here me might ask him, what would happen, when the fluid of the one was strong, and that of the other weak?  I cannot conceive what reply could be made to this question; and, therefore, we are warranted to reject the opinion of two distinct fluids in each sex as perfectly chimerical.

Let us now attend to his account of the formation of the foetus.  The seminal fluids first mix in the uterus, and gradually thicken by the heat of the mother.  The mixture extracts the spirit of heat, and when too warm, part of the heat escapes into the air.  But a cold spirit is likewise conveyed to it by the respiration of the mother:  Thus a cold and a hot spirit alternately [84] enter the mixture, give life to it, and cover its surface with a pellicle [sic], which assumes a round figure, because the spirits acting in the center, expand the matter equally on all sides.  I have seen, says this great physician, a foetus of six days old:  It was a ball of liquor inclosed [sic] in a pellicle.  The liquor was reddish; and the pellicle was interspersed with red and colourless vessels.  In the middle of it there was a small eminence, which I apprehended to be the umbilical vessels, by which the foetus receives nourishment and the spirit of respiration from the mother.  A second covering or pellicle gradually forms above the first.  Abundance of nourishment is furnished by the menstrual blood, which coagulates by degrees, and is converted into flesh.  This flesh gradually articulates as it grows; and the spirit bestows this form upon it.  Every part proceeds to take its proper place; the solid particles unite together; the moist particles associate by themselves; every thing searches for what is analogous to it; and, in fine [sic], the foetus, by these causes and means, is completely formed. 

This system is more rational, and less obscure than that of Aristotle; because Hippocrates endeavours to explain every particular appearance, and borrows only one general principle fro mthe philosophy of his times, namely, that heat and cold produce spirits, and that these spirits have the power of arranging and of bestowing [85] figure upon matter.  He treats his subject more like a physician than a philosopher; but Aristotle explains the phaenomena of generation more as a metaphysician than a naturalist.  It is for this reason that the errors of Hippocrates are particular and less apparent, and that those of Aristotle are general and evident.

These two great men have each had their followers.  Almost all the philosophers of the schools adopted Aristotle’s theory of generation, while most physicians adhered to the theory of Hippocrates; and, in this manner, 17 or 18 centuries passed without the appearance of any thing new upon this mysterious subject.

At last, upon the revival of literature, some anatomists began to investigate the nature of generation; and Fabricius ab Aquapendente was the first who thought of making a course of experiments upon the impregnation and expansion of the eggs of fowls, the substance of which we shall lay before the reader.

He distinguishes the matrix of a hen into two parts, the one superior, and the other inferior.  The superior part, which he calls the ovarium, is an assemblage of a great number of small yellow eggs, of a round figure, the sizes of which vary from that of a mustard seed to that of a walnut.  These eggs are attached to one another by foot-stalks, and the whole somewhat resembles a bunch of grapes. The smallest [86] eggs are white, and they turn yellower in proportion as they increase.

Having examined those yellow eggs immediately after a communication with the male, he could perceive no sensible difference; he saw none of the male semen in any part of the eggs: He therefore concluded, that the whole eggs, and even the ovarium itself, were rendered fertile by a subtile spirit which issues from the male semen; and, he adds, that, in order to prevent the escape of this fecundating spirit, nature has placed, at the external orifice of the vagina of birds, a membranous valve which permits the seminal spirit to enter freely into the vagina, but prevents its return.

When an egg is detached from the common pedicle, it gradually descends, though a winding canal, into the inferior part of the matrix.  This canal is filled with a liquor very similar to the white of an egg.  It is here that the egg receives its white liquor, the membrane in which it is inclosed, the two cords (chalazae) that run through the white, and join it to the yolk, and the shell which is suddenly formed immediately before exclusion.  These cords, according to our author, are the part of the egg which is impregnated by the seminal spirit of the male; and it is here also that the rudiments of the foetus first appear.  The egg is not only the true matrix, or the place where the chick is formed, but the whole business of generation depends upon [87] it.  The egg is the great agent in generation; it furnishes both the matter and the organs.  The substance of the cords is the matter of which the chick is formed; the white and the yolk afford it nourishment; and the seminal spirit of the male is the efficient cause.  This spirit communicates to the cords, first, an alterant quality, then a forming quality, and, lastly, a power of augmenting, &c.

These observations of Fabricius, it is apparent, lead not to any clear idea of generation.  At the same time that this anatomist was making his experiments, which was about the middle of the sixteenth century, the famous Aldrovandus* made some remarks upon eggs.  But, as Harvey properly observes of him, he followed more the authority of Aristotle than of experiment.  The description he gives of the chick in the egg is by no means exact.  Volcer Coiter, one his pupils, succeeded better than his master; this writer, together with Parisanus, a Venetian physician, have each given descriptions of the chick in the egg, which Harvey prefers to all the others.

This celebrated anatomist, who first discovered the circulation of the blood, has given an excellent treatise on generation.  He flourished about the middle of last century, and was physician to Charles I. of England.  As he was obliged to follow this unhappy Prince during his [88] misfortunes, he lost, among other papers, what he had written concerning the generation of insects; and it appears, that he composed from memory his treatise on the generation of birds and of quadrupeds.  I shall give a short view of his remarks, of his experiments, and of his theory. 

Harvey alledges, that men, and all other animals, proceed from eggs; that, in viviparous animals, the first produce of conception is a kind of egg; and that the only difference between the viviparous and oviparous is, that, in the former, the fetuses begin to exist, increase, and acquire their full growth in the uterus; but that, in the oviparous animals, the fetuses begin to exist in the body of the mother, where they are in the form of eggs; and it is only after their exclusion that they become real fetuses. And it deserves to be remarked, says he, that, in oviparous animals, some retain their eggs till they be perfect, as birds, serpents, and oviparous quadrupeds; and that others exclude their eggs before they are perfect, as fishes, crustaceous, and testaceous animals.  The eggs laid by those creatures are only the rudiments of eggs, which afterwards acquire membranes and a white, and attract nourishment from the matter with which they are surrounded.  There are even, he adds, insects, caterpillars, for example, which are only imperfect eggs; they search for their nourishment, and, at the end of a certain time, they ar- [89] rive at the state of a chrysalis, which is a perfect egg.  Another difference may still be remarked in oviparous animals:  The eggs of hens, and other birds, are all of different sizes; but those of fishes, frogs, &c. who lay them before they are perfect, are all of the same size.  He indeed observes, that, in pigeons, who lay two eggs, all the small eggs that remain in the ovarium are of the same bulk; and that the two only which are next to be excluded exceed the size of the rest.   The same thing happens in cartilaginous fishes, as in the ray, which only brings to maturity two eggs at a time, all the rest being of different sizes, like those of the hen.

He next describes anatomically the parts necessary to generation; and remarks, that the situation of the anus and vulva in birds differ from those of all other animals, the anus being placed before, and the vulva behind.*  And, with regard to the cock, and all small birds, he alledges, that they have no proper penis, and that they generate by rubbing, without any intromission.  But male-ducks, geese, and ostriches, are amply provided with this instrument.

Hens produce eggs without the intervention of the cock; but, though perfect, they are fewer in number, and unfertile.  He credits not the common opinion, that a few days intercourse with the cock are sufficient to impregnant all the eggs which a hen will lay during the year; [90] but he acknowledges, that he separated a hen from the cock for 20 days, and that all the eggs she laid were fecundated.  As long as the egg remains attached to the ovarium, it is nourished by the vessels of the common pedicle; but, when it separates from this pedicle, it receives the white liquor and the shell from the matter with which the canal of the uterus is filled.

The two cords (chalazae) which Aquapendente considered to be the germ, or part produced by the male semen, are found in unimpregnated, as well as impregnated eggs; and Harvey properly observes, that these parts neither proceed from the male, nor receive the impregnation.  The part of the egg which receives the impregnation is a small white circle situated upon the membrane that covers the yolk, and has the appearance of a cicatrice about the size of a lentil.  Harvey likewise remarks, that this cicatrice is found in all eggs, whether they be fecundated or not; and that those are deceived who imagine it to be produced by the seed of the male.  It is of the same size and form in fresh eggs as in those which have been long kept.  But, as soon as the process of hatching is begun, whether by means of artificial heat, or by the heat of the hen, this small mark or cicatrice gradually augments and dilates like the pupil of the eye.  This is the first change, and it is visible after a few hours incubation. [91] 

When the egg has been heated for 24 hours, the yolk, which was formerly in the centre, rises towards the cavity at the thick end of the egg.  This cavity continues to englarge by the evaporation of the more fluid part of the white; and the heaviest part of the white falls down to the small end.  The cicatrice or speck on the membrane of the yolk, is elevated along with it, and applies itself to the membrane which lines the cavity at the thick end.  This speck is now as large as a pea; and a white point is distinguishable in the middle of it, with several circles, of which this point appears to be the common centre.

At the end of the second day, these circles are larger and more conspicuous, and they divide the speck sometimes into two, and sometimes into three parts, of different colours.  A small external protuberance likewise appears, which nearly resembles a little eye, with a white point or cataract on the pupil.  Between the circles a liquor, as transparent as crystal, is contained by means of a very thin membrane.  The speck, which is now become a kind of bubble, or liquid globe, appears as if it were situated in the white, rather than on the membrane of the yolk.  On the third day the transparent liquor, as well as the membrane in which it is inclosed, is considerably augmented.  On the 4^th, a small line of blood, of a purple colour, appears on the circumference of the bubble; and, at a little distance from the [92] centre, we perceive a dot or point, of a bloody colour, which beats like a heart.  It is visible at every diastole, and disappears during the systole.  From this animated point two small blood-vessels issue, and terminate in the membrane which contains the transparent crystalline liquor.  These blood-vessels set off from the same place, nearly in the same manner as the roots of a tree set off from the trunk; and it is in the angle which these roots form with the trunk, and in the middle of the liquor, that the animated point is situated.

Towards the end of the fourth, or beginning of the fifth day, the animated point is so much enlarged, that it has the appearance of a small bladder filled with blood; and, by its contractions and dilations, it is alternately filled and emptied.  On the same day we distinctly perceive, that this bladder is divided into two parts, each of which dilates and contracts in the same manner.  Round the shortest of the blood-vessels described above, a kind of cloud appears, which, though very transparent, obscures the view of the vessel.  Every hour this cloud becomes thicker; it attaches itself to the root of the blood-vessel, and seems to depend [sic] from it like a small globe.  This globe extends and appears to divide into three parts, one of which is globular, and larger than the other two; and here we perceive the rudiments of two eyes, and of the whole head:  And, at the end of the fifth day, we see, in the remainder of this lengthened globe, the beginnings of the vertebrae. [93]

On the sixth day, the parts of the head are more apparent.  We distinguish the coats of the eyes, the thighs, and wings; and then the liver, the lungs, and the beak.  The foetus now begins to move and to stretch out its head, though nothing but the viscera are yet formed; for the thorax, the abdomen, and all the external coverings of the fore part of the body, are still wanting. At the end of this day, or the beginning of the seventh, the claws begin to be visible; the chick opens and moves its beak; and the anterior parts of the body begin to cover the viscera.  On the seventh day, the chick is entirely formed; and, from this time till it issues from the egg, nothing happens but an expansion of all the parts it acquired during the first seven days.  The feathers appear on the 14^th or 15^th day; and, on the 21^st, it escapes from the egg, by breaking the shell with its bill.

These experiments of Harvey appear to have been made with the greatest exactness and fidelity.  In the sequel, however, we shall demonstrate their imperfection, and that the author has probably fallen into the common error of making experiments, with a view to establish is favourite hypothesis, that the first animated point which appeared was the heart.  But, before proceeding to this object, it is proper to give an account of his other experiments.

Every body knows the many experiments of Harvey made upon female deer.  They receive [94] the male about the middle of September.  A few days after copulation, the horns* of the uterus appear to be thicker and more fleshy than usual:  They are, at the same time, more lax and flabby; and, in each of their cavities, five carunculae are swelled nearly to the size and form of a nurse’s nipple.  On opening them with a scalpel, they appeared to be filled with an infinite number of white points.  Harvey pretends to have remarked, that, neither now, nor immediately after copulation, had the ovarium suffered any change; and that he never could discover, after repeated trials, the least drop of male semen in the uterus.

Towards the end of October, or the beginning of November, when the females are separated from the males, the thickness of the horns began to diminish; the internal surfaces of their cavities were swelled, and seemed to be glued together.  The carunculae still remained; and the whole resembled the substance of the brain, being so soft that it could not be touched.  Harvey tells us, that on the 13^th or 14^th of November, he perceived filaments, like those of a spider’s web, which traversed the cavities of the horns, and even that of the uterus itself.  These filaments arose from the superior angle of the [95] horns, and, by their number, formed a kind of membrane or empty coat.  A day or two afterwards, this coat or sac was filled with a white aqueous, viscid matter, and adhered to the uterus by means of a species of mucilage; and the adhesion was most sensible at the superior part of the uterus, where the rudiments of the placenta began then to appear.  In the third month, this sac contained an embryo of two fingers breadth in length, and also an internal sac, called the amnios, inclosing a transparent crystalline liquor, in which the foetus swam.  The foetus, at first, was only an animated point, like what appeared in the hen’s egg.  Every thing now proceeded and terminated in the same manner as described with regard to the chick, with this only difference, that the eyes of the chick appeared much sooner than those of the deer.  The animated point was visible about the 19^th or 20^th of November.  A day or two afterwards, the oblong body, which contained the rudiments of the foetus, made its appearance.  In six or seven days more, the foetus was so completely formed, that all its members, and even its sex, were distinguishable.  But the heart and viscera were still bare; and it was not till a day or two after, that they were covered with the abdomen and thorax.  This is the last work, the slating of the edifice.

From these experiments upon hens and deer, Harvey concludes, that all female animals have [96] eggs; that in these eggs a separation of a transparent crystalline liquor, contained in a sac (amnios), takes place, and that another external sac (chorion) incloses the whole liquors of the egg; that the first thing which appears in the crystalline liquor is an animated sanguineous point; and, finally, that the formation of viviparous animals is effected in the same manner with that of the oviparous:  The following is the account which he gives of the generation of both.

Generation, he observes, is an operation of the uterus alone; for not a drop of the male semen ever enters it.  The uterus conceives by a kind of contagion, communicated to it by the semen of the male, nearly in the same manner as the load-stone communicates a magnetic virtue to iron.  This male contagion  acts not only on the uterus, but on the whole body of the female, which is entirely fecundated, though the uterus alone possesses the faculty of conception, in the same manner as the brain has the sole power of conceiving ideas. The ideas conceived by the brain are similar to the images of the objects transmitted to it by the senses; and the foetus, which may be regarded as the idea of the uterus, is similar to that which produces it. This is the reason why children resemble their fathers, &c.

I will follow the system of our anatomist no farther: What has been said is sufficient to enable the reader to judge of it. But we have remarks of importance to make concerning his [97] experiments. He has represented them in a manner the most plausible and insinuating. He appears to have often repeated them, and to have taken every necessary precaution to avoid fallacy and deception; and, of course, we are led to think that he has seen every thing which possibly could be discovered. Uncertainty and obscurity, however, are perceptible in his descriptions. His observations are related from memory; and he seems, though he often maintains the contrary, to have made Aristotle, more than experience, his guide; for he has seen every thing in eggs, and very little more, than was mentioned by that philosopher. That the most material of his observations were made long before his own time, we shall be convinced by attending to what follows.

Aristotle knew, that the cords (chalazae) in eggs were of no use in the generation of the chick: “Quae ad principium lutei grandines haerent, nil conferunt ad generationem, ut quidam suspicantur.”* Parisanus, Volcher Coiter, Aquapendente, &c. had remarked the small cicatrice, as well as Harvey. Aquapendente believed it to be of no use; but Parisanus maintained that it was formed by the male semen, or, at least, that the white point in the middle of the cicatrice was the semen of the male, and that it was the rudiments of the foetus, “Estque,” says he, “illud galli semen alba et tenuissima tu- [98] nica abductum, quod substat duabus communibus toti ovo membranis,” &c. Hence the only discovery proper to Harvey is his having remarked the existence of this cicatrice, both in secundated and unsecundated eggs; for the other writers had observed, as well as he, the dilation of the circles, and the growth of the white point. These are all the remarks Harvey has made in his account of the two first days of incubation; what he mentions concerning the third day is only a repetition of what Aristotle delivers in the sixth book and fourth chapter of his history of animals: “Per id tempus ascendit jam vitellus ad superiorem partem ovi acutiorem, ubi et principium ovi est et foetus excluditur; corque ipsum apparet in albumine sanguinei puncti, quod punctum salit et movet sese instar quasi animatum; ab eo meatus venarum specie duo, sanguine pleni, flexuosi, qui, crescente foetu, feruntur in utramque tunicam ambientem, ac membrane sanguineas fibras habens eo tempore albumen continent sub meatibus illis venarum similibus; ac Paulo post discernitur corpus pusillum initio, omnino et candidum, capite conspicuo, atque in eo oculis maxime turgidis qui diu six permanent, sero enium parvi fiunt ac confidunt. In parte autem corporis inferiore nullum extat membrum per initia, quod respondeat superioribus. Meatus autem illi qui a corde prodeunt, alter ad cir- [99] cumdantem membranam tendit, alter ad luteum, officio umbilici.”

Harvey, because Aristotle says that the yolk rise to the small end of the egg, concludes that he had seen nothing himself, but had received his information from some other pretty accurate observer. In this accusation, Harvey evidently injures Aristotle, for the rising of the yolk to either end, solely depends upon its position during the time of incubation; for the yolk, being lighter than the white, uniformly mounts to the top, whether the large or the small end of the egg be uppermost. This observation we owe to William Langley, a physician in Dordrecht, who made experiments on the hatching of eggs in the year 1655, about 20 years before Harvey’s time.*

But, to return to the passage we have quoted. It is apparent, that the crystalline liquor, the animated point, the two circles, the two blood vessels, &c. are described by Aristotle in the same manner as they were seen by Harvey. This anatomist maintains, that the animated point is the heart, that the heart is the first part of the foetus which is formed, and that the viscera and other members succeed. All this has been mentioned by Aristotle, and seen by Harvey; and yet it is by no means consonant to truth. To be assured of this fact, we have only to repeat the same experiments, or to read with attention those [100] of Malpighius,* which were made about 50 years after the trials of Harvey.

Malpighius carefully examined the cicatrice, which is the essential part of the egg; he found that it was large in impregnated eggs, and small in those which had received no impregnation; and he discovered, that, in eggs which had never been sit upon, the white point, mentioned by Harvey as the first part that becomes animated, is a small purse or buddble swimming in the liquor bounded by the first circle; and that the embryo is visible in the centre of this purse. The membrane of the purse, which is the amnios, being exceedingly think and transparent, allowed him to see distinctly the foetus within it. Malpighius, from this first observation, concludes with propriety, that the foetus exists in the egg before incubation, and that the rudiments of the embryo are even then deeply rooted. It is unnecessary to mention how much this experiment differs from the opinion of Harvey; for he had observed nothing begun to be formed during the first days of incubation; and, in his estimation, the first vestige of a foetus is the animated point, which appears not till the third day. But Malpighius discovered that the rudiments of the whole foetus exist before incubation is commenced.

After ascertaining this important fact, Malpighius proceeded to examine the cicatrice of unimpregnated eggs, which, as formerly re- [101] marked is smaller than in those that have received an impregnation. Its margin is often irregular, and its texture sometimes differs in different eggs. Near its centre, in place of a bubble including the foetus, there is a globular mole or unorganized mass, which, when opened, presents nothing like regularity or arrangement of parts: It has only some appendages filled with a thick but transparent liquor; and this unformed mass is surrounded and enveloped in several concentric circles.

After six hours incubation, the cicatrice is considerably enlarged; and, in its centre, a bubble or globule formed by the anmnios is easily distinguishable. This globule is filled with a fluid, in the middle of which the head and back-bone of the chick visibly appear. Six hours after this, every thing is enlarged, and, of course, more apparent to the eye. In six hours more, that is, 18 hours after the commencement of incubation, the head is larger, and the spine is lengthened; and, at the end of 24 hours, the head of the chick appears, in a bended posture, and the spine is of a whitish colour. The vertebrae are ranged on each side of the spine, like small globules; and, nearly at the same time, the wings begin to sprout, and the head, neck, and breast, are lengthened. At the end of 30 hours, nothing new appears; but all the parts are enlarged, and especially the amnios. Round this membrane, may be remarked the umbilical [102] vessels, which are of a dark colour. In 38 hours, the chick has acquired more strength; its head is very large, and three vesicles appear in it surrounded with membranes, which likewise include the spine of the back, through which, however, the vertebrae are still visible. At the end of 40 hours, it was admirable to observe, continues our author, the chick living in the centre of the liquor of the amnios. The back-bone was increased, the head was bended, the vesicles of the brain were less bare, the rudiments of the eyes appeared, the heart beat, and the blood circulated. Here Malpighius describes vessels and the circulation of the blood; and he thought, with reason, that, though the heart did not beat till 38 or 40 hours after incubation was begun, it nevertheless existed before, as well as the other parts of the chick. But, on examining the heart in a dark chamber, he observed nothing like the luminous sparks issuing from it, as Harvey seems to insinuate.

At the end of the second day, the foetus appeared swimming in the liquor of the amnios; the head, which seemed to be composed of vesicles, was bended; the back-bone and vertebrae were lengthened; the heart, which hung out of the breast, beat three times successively, because the fluid it contains is pushed from the auricle into the ventricles, from the ventricles into the arteries, and, lastly, into the umbilical vessels. He remarks, that, having separated the [103] chick from the white of the egg, the motion of the heart continued for a whole day. In 14 hours more, or 62 hours from the beginning of the incubation, the chick, though stronger, remained still with its head bended in the liquor of the amnios: Veins and arteries were perceived among the vessels of the brain; and the lineaments of the eyes, and of the spinal marrow, appeared. At the end of three days, the body of the chick was crooked. Beside the two eyes, five vesicles filled with liquor appeared in the head; the rudiments of the thighs and of the wings were discernible; the body began to take on flesh; and the pupils of the eyes, and likewise the crystalline and vitreous humours, were distinguishable. At the termination of the fourth day, the vesicles of the brain were nearer each other; the processes of the vertebrae were longer; the wings and the thighs had become stronger, in proportion as they grew longer; the whole body was covered with an unctuous flesh; the umbilical vessels had pierced through the abdomen; and the heart was concealed within the breast, which was now shut up by a thin membrane. On the fifth, and at the end of the sixth day, the vesicles of the brain began to be covered; the spinal marrow, which was now more solid, was divided into two parts, and advanced along the trunk; the thighs and wings were longer, and the wings were unfolded; the abdomen was shut and tumified; the liver was distinctly visible, [104] and of a dark colour; the two ventricles of the heart beat; the body of the chick was covered with skin; and the points of the feathers began to appear. On the seventh day, the head was very large; the brain was covered with its membranes; the beak appeared between the two eyes; the wings, the thighs, and the legs, had acquired their perfect form; the heart seemed to be composed of two ventricles, like two contiguous globules, united at their superior part with the auricles; and two successive pulses were remarked both in the ventricles and auricles, as if there had been two separate hearts.

But I will follow Malpighius no farther. The remainder of the detail regards the growth and perfection of the parts till the chick breaks the shell in which it is inclosed, and becomes an inhabitant of a new world. The heart is the last part that assumes its proper figure, by the union of its ventricles, which happens not till the eleventh day.

We are now in a condition to form a distinct judgment concerning the value of Harvey’s experiments. It is probable that this celebrated anatomist did not make use of the microscope, (which was, indeed, very imperfectly known in his days), otherwise he never would have affirmed, that there was no difference between the cicatrice of impregnated and unimpregnated eggs; he never would have said, that the semen of the male produced no change upon the egg, [105] and particularly upon the cicatrice; he never would have advanced, that nothing was perceptible before the end of the third day; that the animated point appeared first; and that the white point was transformed into the animated point. He would have perceived that the white point was the bubble or globule which contained the whole apparatus of generation; and that all the rudiments of the foetus commenced there from the moment of receiving the impregnation of the cock: He would likewise have discovered, that, without this impregnation, it contains nothing but an unformed mass, which could never become animated; because, in fact, it is not organized like an animal, and because it is only after this mass, which ought to be regarded as a collection of the organic particles of the female semen, is penetrated by the organic particles of the male semen, that an animal is formed. This formation is instantaneous; but the motions of the new animal are imperceptible till 40 hours after the process of incubation has commenced: He would have not assured us, that the heart is first formed, and that the other parts are successively joined to it by juxta-position; since it is apparent, from the experiments of Malpighius, that the rudiments of all the parts are formed at once, but that they become perceptible only in proportion as they are successively unfolded: Lastly, if he had seen, as Malpighius saw, he would not have positively asserted, that no im- [106] pression of the male seed remained in the eggs, and that it was only by contagion that they were impregnated, &c.

It is also proper to remark, that what Harvey has said concerning the parts of generation of the cock is by no means exact. He affirms, that the cock has no penis capable of entering the vagina of the hen. It is certain, however, that this animal, in place of one penis, has a couple, which both act at the same time; and this action is a vigorous compression, if not an actual copulation.* It is by this double organ that the cock throws his seminal liquor into the uterus of the hen.

Let us now compare Harvey’s experiments upon female deer with those of de Graaf upon female rabbits; and, though de Graaf believed as Harvey did, that all animals proceed from eggs, we shall find a very great difference in the manner in which these two anatomists have perceived the first formation, or rather the expansion, of the foetus of viviparous animals.

After exerting every effort to prove, by arguments drawn from comparative anatomy, that the testicles of viviparous females are true ovaria, Graaf explains the manner in which the eggs are detached from the ovaria, and fall into the horns of the uterus; and then re relates the remarks he made upon a rabbit which he dissected half an hour after copulation. The horns [107] of the uterus, he says, were uncommonly red; there was no change either in the ovaria, or in the eggs which they contained; and there was not the least appearance of semen in the vagina, in the uterus, or in the Fallopian tubes.

Having dissected another rabbit, six hours after copulation, he observed, that the follicles, or coats, which, in his estimation, contain the eggs in the ovarium, were become red; but he found no male semen either in the ovaria or any where else. Twenty hours after copulation, he dissected a third; he remarked in one ovarium three, and in the other five follicles much altered; for instead of being clear and limpid, they were become opaque and reddish. In another, dissected twenty-seven hours after copulation, the horns of the uterus, and the superior canals which teminate in them, were still more red, and their extremities embraced the ovarium on all sides. In another, which was opened forty hours after copulation, he found in one ovarium seven, and in the other three follicles changed. Fifty-two hours after copulation, he examined another, and found in one ovarium four changed follicles, and one in the other; and having opened these follicles he discovered in them a kind of glandular liquor, with a small cavity in the middle, where he could perceive no fluid, which made him suspect that the transparent liquor usually contained in the follicles, and which, he says, is inclosed in its own membranes, might [108] have been discharged by some kind of rupture. He searched for this matter in the canals which terminate in the horns of the uterus, and in the horns themselves; but he found nothing. He only remarked, that the membranes which line the horns of the uterus were much swelled. In another rabbit, dissected three days after copulation, he observed, that the superior extremity of the canal, which terminates in the horns of the uterus, straitly [sic] embraced the ovarium on every side: And, having separated it from the ovarium, he remarked, in the right ovarium, three follicles somewhat larger and harder than usual. After searching with great care the canals above mentioned, he discovered, he says, an egg in the right canal, and two more in the right horn of the uterus, so small that they exceeded not mustard seeds. These little eggs had each two membranes, and the interal one was filled with a very limpid liquor. Having examined the other ovarium, he found four changed follicles; three of them were whiter and had likewise some limpid liquor in their centres; but the fourth was of a darker colour, and contained no liquor, which made him suspect that the egg had escaped from it. He therefore searched the corresponding canal and horn of the uterus; he found an egg in the superior extremity of the horn, which was exactly similar to those he had discovered in the right horn. He alledges, that the eggs, when they are sepa- [109] rated from the ovarium, are ten times less than before their separation; and this difference in size, he imagines, is owing to the eggs, while in the ovarium, containing another matter, namely the glandulous liquor which he remarked in the follicles.

Four days after copulation, he opened another rabbit, and he found in one ovarium four, and in the other three follicles void of eggs: In the horns corresponding to the ovaria, he found four eggs on one side, and three in the other. These eggs were larger than those he had discovered three days after copulation. They were nearly the size of the lead-shot used for shooting small birds; and he remarked, that, in these egs, the interior membrane was separated from the exterior, and appeared as if a second egg was contained within the first. In another, dissected five days after copulation, he found five empty follicles in the ovaria, and an equal number of eggs in the uterus, to which they adhered very firmly. These eggs were as large as the shot employed for killing hares, and the internal membrane was still more apparent than in the last experiment. Having opened another rabbit, six days after copulation, he found in one of the ovaria six empty follicles, but only five eggs in the corresponding horn of the uterus, and they seemed to be all accumulated into one mass: In the other ovarium, he saw four empty follicles, and found but one egg in the [110] corresponding horn. These eggs were of the size of the largest fowling shot. Seven days after copulation, our anatomist opened another rabbit, and he found in the ovaria some empty follicles, which were larger, harder, and more red than those he had formerly observed; and he perceived as many transparent tumors in different parts of the uterus; and, having opened them, he took out the eggs, which were as large as small pistol bullets. The internal membrane was more distinct than formerly; and within this membrane he saw nothing but a very clear liquor. In another, dissected eight days after copulation, he found in the uterus the tumors or cells which contain the eggs; but they adhered so strongly to the uterus, that he could not detach them. In another, which he opened nine days after copulation, he found the cells containing the eggs greatly enlarged, and he perceived in the middle of the liquor inclosed by the internal membrane a small thin cloud. In another, which he opened ten days after copulation, the small cloud was thicker and darker, and formed an oblong body like a little worm. Lastly, twelve days after copulation, he distinctly perceived the embryo, which, though two days before, it was only an oblong body, was now so apparent, that he could distinguish its different members. In the region of the breast, he saw two red and two white points, and, in the abdomen, a mucilaginous reddish substance. Four- [111] teen days after copulation, the head of the foetus was large and transparent; the eyes were prominent; the mouth was open; the rudiments of the ears appeared; the back-bone was whitish, and bended towards the sternum, and small blood-vessels arose from each side of it, the ramifications of which extended along the back as far as the legs: The two red points were considerably enlarged, and appeared like the rudiments of the ventricles of the heart; on each side of the red points he saw two white ones, which were the rudiments of the lungs. In the abdomen he saw the rudiments of the liver, which was reddish, and a small body twisted like a thread, which was the stomach and intestines. After this, till the 31^st day, when the female rabbit brings forth, there was nothing to be remarked but the gradual expansion and growth of the parts which were already formed.

From these experiments, De Graaf concludes, that all viviparous females have eggs; that these eggs are contained in the ovaria or the testicles; that they cannot be separated till they are fecundated by the semen of the male; because, says he, the glandular liquor, by means of which the eggs are enabled to escape from their follicles, is not secreted till after an impregnation by the male. He alledges, that those who imagine they have seen pretty large eggs in three days, have been deceived; because, in his opinion, the eggs, though fecundated, remain longer in the ovarium, and, [112] in place of augmenting, they become ten times less than formerly, and they never begin to grow till after their descent from the ovaria into the uterus.

By comparing these observations of Graaf with those of Harvey, we will easily perceive that the latter has missed the principal facts: And, though there are several errors both in the reasoning and in the experiments of De Graaf, this anatomist, as well as Malpighius, have discovered themselves to be better observers than Harvey. They agree in all fundamental points, and both of them contradict Harvey. He perceived not the alteration which take place in the ovaria; he saw not in the uterus those small globules which contain the materials of generation, and which are called eggs by de Graaf; he never suspected that the foetus existed in this egg; and, though his experiments give us tolerably exact ideas concerning what happens during the growth of the foetus, he furnishes no information concerning the commencement of fecundation, nor concerning the first expansion of the foetus. Schrader, a Dutch physician, who had a great veneration for Harvey, acknowledges that he cannot be trusted in many articles, and particularly in what relates to the first formation of the embryo; for the chick really exists in the egg before incubation; and, he says, that Joseph of Aromatarius was the first who [113] made this material observation.* Besides, though Harvey alledged that all animals proceeded from eggs, he never imagined that the testicles of females contained eggs; and it was only from a comparison between the sac, which he believed to be formed in the uterus of viviparous animals, with the growth and covering of the eggs in oviparous animals, that he maintained that all animals were produced from eggs; and even this is only a repetition of what Aristotle had said before him. Steno was the first who pretended to have discovered eggs in the ovaria of females. He says, that, in dissecting a female sea-dog [sic], he perceived eggs in the testicles, though this animal be viviparous; and he adds, that the testicles of women are analogous to the ovaries of oviparous animals, whether the eggs themselves fall into the uterus, or only the matter which they contain. Steno was the first who discovered these supposed eggs; De Graaf is willing to assume the discovery to himself; and Swammerdam warmly disputes the point with him, and alledges that Van-Horn had seen them before De Graaf.This last writer, it is true, has been accused of asserting many things which have been contradicted by experiments: He even pretended, that a certain judgment might be formed of the number of fetuses in the uterus, by the number of cicatrices or empty follicles in the ovaria. In this he is contradicted [114] by the experiments of Verrheyen,* by those of M. Mery⁺, and by some of his own, where he found fewer eggs in the uterus, than cicatrices in the ovaria.  Besides, we shall demonstrate that what he says concerning the separation of the eggs, and the manner in which they descend into the uterus, is by no means exact; that no eggs exist in the testicles of females; that what is seen in the uterus is not an egg; and that the systems which have been deduced from the observations of this celebrated anatomist are perfectly chimerical.

This pretended discovery of eggs in the testicles of females attracted the attention of most anatomists. They only found, however, in the testicles of viviparous females, small bladders; those they hesitated not to consider as real eggs, and, therefore, they called the testicles ovaria, and the vesicles eggs. They asserted also, like De Graaf, that these eggs differed in size in the same ovarium; that the largest in the ovaria of women exceeded not the bulk of a small pea; that they are very small in young girls; but that they increased with age and intercourse with men; that not above 20 could be reckoned in each ovarium; that these eggs are fecundated in the ovarium by the spirituous part of the male semen; that they then separate and fall into the uterus by the Fallopian tubes, where the [115] foetus is formed of the internal substance of the egg, and the placenta of its external part; that the glandulous matter, which exists not in the ovarium till after a fruitful embrace, compresses the egg, and excludes it from the ovarium, &c. But, though Malpighius, who examined matters more accurately, detected many errors committed by those anatomists even before they were received; yet most physicians adopted the opinion of De Graaf, without regarding the observations of Malpighius, which were nevertheless of the greatest importance, and which received much weight from the experiments of his disciple Valisnieri.

Malpighius and Valisnieri, of all naturalists, appear to have written with most judgment and acuteness on the subject of generation. We shall, therefore, give an account of their experiments and remarks.

Malpighius, having examined the testicles of a number of cows and other female animals assures us, that he found, in the testicles of all of them, vesicles of different sizes, whether the females were very young or adults. These vesicles are enveloped in a pretty thick membrane, the inside of which is interspersed with blood-vessels; and they are filled with a kind of lymph or liquor, which coagulates and hardens by the heat of a fire, like the white of an egg.

In process of time, a firm yellow body adheres to the testicles. It is prominent, and in- [116] creases to the size of a cherry, and occupies the greatest part of the ovarium. This body consists of several angular lobes, the position of which is very irregular, and it is covered with a coat or membrane interspersed with nerves and blood-vessels. The form and appearance of this yellow body varies considerably at different times. When it exceeds not the size of a grain of millet, it is roundish, and its substance, when cut, has a warty appearance. We often find an external covering round the vesicles of the ovaria, which consists of the same substance with the yellow bodies.

When the yellow body has become nearly of the size of a pea, it resembles a pear; and, in the centre of it, there is a small cavity filled with liquor. The same thing may be remarked when it as a large as a cherry. In some of these yellow bodies, after they have arrived at full maturity, Malpighius affirms that he saw, towards the centre, a small egg with its appendages, about the size of a millet seed; and, after they had discharged these eggs, they were flaccid and empty. They then resembled a cavernous canal; and the void cavities were as large as peas. He conceived that Nature designed this yellow glandular body for the preservation of the egg, and for making it escape from the testicles; and that, perhaps, it contributed to the formation of the egg; consequently, he remarks, the vesicles which are at all times found in the [117] ovarium, and always differ in size, are not the true eggs which receive the impregnation, but only serve to produce the yellow bodies in which the eggs are formed. Besides, though these yellow bodies are not always found in every ovarium; yet we always find the rudiments of them. Malpighius found the marks of them in new born heifers, in cows with calf, and in pregnant women; and, therefore, he properly concludes, that these yellow glandular bodies are not, as De Graaf asserts, an effect of impregnation. The yellow bodies, he remarks, produce unfecundated eggs, which fall out of the ovarium independent of any communication with the male, and also those which fall after impregnation. When the impregnated eggs fall in to the uterus, every thing proceeds in the manner described by De Graaf.

These observations of Malpighius demonstrate, that the testicles of females are not real ovaria; that the vesicles they contain are not eggs; that these vesicles never fall into the uterus; and that the testicles, like those of males, are only reservoirs containing a liquor which may be regarded as female semen in an imperfect state. This semen is matured in the yellow glandular bodies, of which it fills the internal cavities, and flows out after the yellow bodies have acquired their full size.

But, before we form a judgment concerning this important point, we must attend to the remarks of Valisnieri. [118]

In the year 1692, Valisnieri began his experiments upon the testicles of the sow. The testicles of the sow differ from those of cows, of mares, of sheep, of the she-asses, of female-dogs, of she-goats, of women, and of most viviparous animals; for they resemble a small bunch of raisin, the grains of which are round and prominent on the outside; between these grains are smaller ones, not yet arrived at maturity. These grains appear not to be covered with a common membrane. They are, says he, analogous to the yellow bodies observed in cows by Malpighius; they are round, and of a reddish colour; their surface is interspersed with blood-vessels, like the eggs of viviparous animals; and the whole grains together form a mass that is larger than the ovarium. With a little address, these grains may be separated from the ovarium, and each of them, after separation, leaves a nitch [sic] or depression.

These glandular bodies are not of the same colour in every sow. In some they are more red; in others more clear; and they are of all sizes, from the smallest seed, to that of a raisin. On opening them, a triangular cavity appears, filled with a limpid liquor, which coagulates with heat, and becomes white, like that which is contained in the vesicles. Valisnieri expected to find the egg in some of these cavities: But in this he was disappointed; though he made a careful search into all the glandular bodies of a [119] number of sows, and other animals, he could never discover the egg, which Malpighius affirms he found once or twice.

Under these glandular bodies, the vesicles of the ovarium appeared. They were more or less numerous according as the glandular bodies were larger or smaller; for, in proportion to the largeness of the glandular bodies, the vesicles diminished. Some vesicles were of the size of a lentil, and others exceeded not that of a millet seed. In the testicles, when raw, from 20 to 35 vesicles might be reckoned; but, when boiled, a much greater number appear, and they are so firmly attached, that they cannot be separated without breaking some of them.

Having examined the testicles of a young sow, which had never brought forth, he found, as in the others, the glandular bodies; and their triangular cavities were likewise filled with lymph; but he could not discover any eggs either in the one or the other. The vesicles of this young sow were more numerous than in those which had brought forth, or those which were impregnated at the time of examination. In the testicles of another sow, which was far advanced in pregnancy, Valisnieri found two of the largest glandular bodies, which were flaccid and empty, and others, of a lesser size, in their ordinary state; and, in several others which he dissected when with young, he remarked, that the number of glandular bodies was always greater than the [120] number of fetuses. This confirms what we observed concerning the experiments of De Graaf, and proves that they are by no means exact. What he calls follicles of the ovarium are only the glandular bodies, the number of which always exceeds that of the fetuses. In the ovaria of a sow, two or three months old, the testicles were pretty large, and interspersed with vesicles of considerable size. Among the vesicles, the beginnings of four glandular bodies appeared in one testicle, and of seven in the other.

After these experiments upon sows, Valisnieri repeats those of Malpighius upon cows, and he found them to be exactly conformable to truth. He indeed acknowledges, that he was never able to discover the egg which Malpighius imagined he had seen once or twice in the interior cavity of the glandular bodies. After a fruitless search in the testicles of so many different females, it was natural to think, that Valisnieri would at least have doubted the existence of such eggs. But prejudice in favour of system made him admit, contrary to his own experience, the existence of eggs, which neither he nor any other man ever saw, or will see.

It is, perhaps, impossible to make a greater number, or more exact experiments, than Valisnieri has done. Among other animals, he examined the ewe, and found, that she has never anyh more glandular bodies in her testicles than [121] foetuses in the uterus. In young ewes, which were never impregnated, there is but one glandular body in each testicle, and, when one is emptied, it is succeeded by another; if a ewe has one foetus in the uterus, she has only one glandular body in her testicles; and if she has two fetuses, she has likewise two glandular bodies. This glandular body occupies the greatest part of the testicle; and, after it is emptied and disappears, another begins to grow for the purpose of a future generation.

In the testicles of a she-ass, he found vesicles as large as small cherries, which is an evident proof that they are not eggs, as it would be impossible for them to pass, by the Fallopian tubes, into the uterus.

The testicles of female wolves, dogs, and foxes, are covered with a membrane, like a purse, which is an expansion of that which surrounds the horns of the uterus. In a bitch which began to be in season, but had not been approached by the male, Valisnieri found the internal part of this purse, which does not adhere to the testicle, moistened with a liquor that resembled whey, and two glandular bodies in the right testicle, about two lines in diameter, and which occupied nearly the whole extent of the testicle. Each glandular body had a small nipple, with a distinct fissure, from which, without pressing it, there issued a liquor like clear whey; he therefore concluded, that this liquor was the same [122] which he found in the purse. He blew into this fissure with a pipe, and the whole glandular body immediately swelled; and, having introduced a bristle, he easily penetrated to the bottom of it. He opened the body on that side where he had introduced the bristle, and found an internal cavity which communicated with the nipple, and contained a considerable quantity of liquor. Valisnieri was always in hopes of discovering the egg; but these hopes, notwithstanding all his researches, were uniformly frustrated. He likewise found, in the left testicle, two glandular bodies, hoping, that, by this means, he might discover the egg, but still without any measure of success.

Having dissected another bitch four or five days after she had received the male, he found in the testicles three glandular bodies exactly similar to the former. He searched every where for the egg; but he was still disappointed. By the assistance of the microscope, he discovered the glandular bodies to be a net-work composed of an infinite number of globular vesicles, which served to filtre [sic] the liquor which issued through the nipple.

He then opened another bitch which was not in season, and having tried to introduce air between the testicle and the purse which covered it, he found that it dilated like a bladder filled with air. Having removed the purse, he disco- [123] vered two glandular bodies upon the testicles; but they had neither nipple nor fissure, and no liquor distilled from them.

In another bitch that had brought forth about five whelps two months before, he found five glandular bodies; but they were much diminished in size, and they began to disappear without leaving any cicatrices; there remained only a small cavity in their centre; but it contained no liquor.

Not satisfied with these and many other experiments, Valisnieri, who passionately desired to discover this pretended egg, called together the best anatomists his country afforded, and, among others, M. Morgagni; and, having opened a young bitch that was for the first time in season, and that had been covered three days before, they examined the vesicles of the testicles, the glandular bodies with their nipples, their canals, and the liquor in their internal cavities; but they could perceive no eggs. He then, with the same intention, made experiments on she-goats, foxes, cats, a number of mice, &c. In the testicles of all these animals, he uniformly found the vesicles, and frequently the glandular bodies with the liquor they contained; but no egg ever appeared.

In fine, being desirous of examining the testicles of women, he had an opportunity of opening a young country-woman, who had been some years married, and who was killed by a [124] fall from a tree. Though of a robust and vigorous constitution, she had never born any children. He endeavoured to discover if the cause of her barrenness existed in the testicles; and he found that the vesicles were all filled with a blackish and corrupted matter.

In a young girl of eighteen years of age, who had been brought up in a convent, and who had every appearance of real virginity, he found the right testicle a little longer than the left: It was of an oval figure, and its surface was somewhat unequal. This inequality was occasioned by five or six vesicles which protruded on the outside of the testicle. One of these vesicles, which was more prominent than the rest, he opened, and a quantity of lymph rushed out of it. This vesicle was surrounded with a glandular substance, in the shape of a crescent, and of a reddish yellow colour. He cut the testicle transversely, and found a number of vesicles filled with limpid liquor; and he remarked, that the Fallopian tube of this testicle was redder and somewhat longer than the other, as he had observed in other animals when they were in season.

The left testicle was whiter, and its surface more smooth; for, though some vesicles were a little prominent, none of them were in the form of nipples; they were all similar to each other, and the corresponding Fallopian tube was neither swelled nor red. [125]

In the testicles of a girl, aged five years, he found the testicle with the vesicles, their blood-vessels, and their nerves.

In the testicles of a woman of sixty years, he discovered some vesicles, and the vestiges of a glandular substance, like large points of an obscure yellowish brown colour.

From all these observations, Valisnieri concludes, that the work of generation is carried on in the female testicles, which he continued to regard as ovaria, though he never could find any eggs in them, and though, on the contrary, he had discovered that the vesicles were not eggs. He says, likewise, that, for the impregnation of the egg, it is not necessary that that the male semen should enter the uterus. He supposes, that the egg escapes through the nipple of the glandular body, after being impregnated in the ovarium; that it then falls into the Fallopian tube; that it gradually descends, and at last attaches itself to the uterus: He adds, that he is fully persuaded, that the egg is concealed in the cavity of the glandular body, though neither he nor any other anatomist was ever able to discover it.

In his estimation, the spirit of the male seed ascends into the ovarium, penetrates the egg, and gives motion to the foetus which previously existed in it. In the ovarium of the original mother of mankind, he observes, were eggs, which contained not only all the children she produced, but of the whole human race. If [126] this chain of infinite individuals contained in one, be incomprehensible to us, it is entirely owing to the imbecillity [sic] of our minds, of which we have daily proofs. But it is not, therefore, less consonant to truth, that all the animals which have existed, or can exist, were created at once, and were all included in their first mothers. The resemblance of children to their parents is owing, he continues, to the imagination, which acts so forcibly on the foetus as to produce stains, monstrosities, disorder of parts, and extraordinary concretions, as well as perfect similarities.

This system of eggs, though it explains nothing, and has no foundation in Nature, would have obtained the universal suffrages of physicians, if, nearly about the same time, another opinion had not sprung up, founded upon the discovery of spermatic animals.

This discovery, which we owe to Leeuwenhoek and Hartsoeker, was confirmed by Andri, Valisnieri, Bourguet, and many other observers. I shall relate what has been advanced concerning those spermatic animals which are found in the semen of all males. Their number is so great, that the semen seems to be entirely composed of them; and Leeuwenhoek pretends to have seen many millions of them in a drop less than the smallest grain of sand. Though none of them appear in females, they are found in the emitted semen of all males, in the testicles, and in the vesiculae seminales. When the semen of [127] a man is exposed to moderate heat, it thickens, and the motion of all the animalcules is suddenly stopped. But, when allowed to cool, it dilutes and the animals continue in motion till the liquor again thickens by evaporating. The more this fluid is diluted, the number of animalcules are augmented; and, when greatly diluted by the addition of water to it, the whole substance of the fluid seems to be composed of animals. When the motion of the animalcules is about to cease, either on account of heat or of drying, they appear to approach nearer each other, to have a common circular motion in the centre of the small drop under observation, and to perish, all of them, at the same instant. But, when the quantity of liquor is greater, it is easy to distinguish them dying in succession.

These animalcules are said to be of different figures in different animals; but they are all long, thin, without any members, and move with rapidity in every direction. The fluid in which they are contained, as formerly remarked, is much heavier than blood. The semen of a bull, when chemically analyzed by Verrheyen, yielded first phlegm, then a considerable quantity of foetid oil, a very small proportion of volatile salt, and more earth than he expected.* This author was surprised that he could draw no spirit from the distillation of this liquor; and, as he imagined it contained a great quantity of [128] spirits, he attributed the evaporation of them to their subtility [sic]. But may we not suppose, with more probability, that it contains little or not spirits? Neither the consistence, nor the odor of this fluid, indicate the presence of ardent spirits, which never abound but in fermented liquors; and, with regard to volatile spirits, the horns, bones, and solid parts of animals, afford more of them than the fluids. What has received the appellation of seminal spirits, aura seminalis, among anatomists, has, perhaps, no existence; and it is certain, that the moving bodies apparent in the seminal fluid, are not agitated by these spirits. But, that we may be enabled to pronounce more clearly concerning the nature of the semen, and of its animalcules, we shall present the reader with the principal observations which have been made on the subject.

Leeuwenhoek, having examined the semen of a cock, perceived a number of animals similar to river eels; but they were so minute, that 50,000 of them were not equal in bulk to a grain of sand. Of those in the semen of a rat, it required, he says, many millions to make the thickness of a hair, &c. This excellent observer was persuaded, that the whole substance of the semen was only a mass of animalcules. He saw these animalcules in the semen of men, of quadrupeds, of birds, of fishes, and of insects. In the semen of a grass-hopper, the animalcules were long, and extremely thin. They appeared, [129] he says, to be attached by their superior end; and the other end, which he calls their tail, had a brisk motion, like that of the tail of a serpent when its head is fixed. In the semen of young animals, when examined before they have any sexual appetite, he alledges that he saw the same minute animals, and that they had no motion. But, when the season of love arrived, the animalcules moved with great vivacity.

In the semen of a male frog, he saw animalcules; but, at first, they were imperfect, and had no motion: Some time after, he found them alive. They were so minute, he observes, that ten thousand of them were only equal in bulk to a single egg of the female.

In the semen of a man and that of a dog, he pretended to see two species of animalcules, resembling males and female. Having shut up the semen of the dog in a small vial, he says, that a great number of animalcules died the first day; that, on the second and third day, still more of them died; and that few of them were alive on the fourth day. But, having repeated this experiment on the semen of the same dog, he found, at the end of seven days, the animalcules as brisk and lively as if they had been newly extracted from the animal: And, having opened a bitch that, some time before the experiment, had been three times covered by the same dog, he could not perceive, with his naked eye, any male semen in the uterus or its appendages; [130] but, but the assistance of the microscope, he found the spermatic animals of the dog in both horns of the uterus: In that part of the uterus which is nearest the vagina, he discovered great numbers, which evidently proves, says he, that the male semen enters the uterus, or, at least, that the spermatic animals of the dog had arrived their [sic] by their own motion, which enables them to pass over 4 or 5 inches in half an hour. In the uterus of a female rabbit, which had just received the male, he observed an infinite number of spermatic animals. He remarks, that the bodies of these animals are round; that they have long tails; and that they often change their figure, especially when the fluid in which they swim begins to dry up.

These experiments of Leeuwenhoek were repeated by several people, who found them exactly consonant to truth. But Dalenpatius, and some others, who were inclined to exceed Leeuwenhoek in acuteness of vision, alledged that, in the semen of a man, they not only found animals resembling tadpoles, who bodies appeared to be as large as a grain of corn, with tails about four times as long as their trunks, and who moved with great agility; but, what is still more amazing, Dalenpatius saw one of these animals break through its coat or covering: It was then no more an animalcule, but a real human body, in which he easily distinguished [131] the two arms and legs, the breast and the head.* But it is apparent, from the very figures, given by this author, of the embryo which he pretended to have seen escape from its covering, that the fact is absolutely false. He believed that he saw what he describes; but he was deceived; for this embryo, according to his description, was more completely formed, at the time of its transmigration from the condition of a spermatic worm, than it is in the uterus of the mother at the end of the fourth or fifth week. Hence this observation of Dalenpatius, instead of being confirmed by future experiments, has been rejected by all naturalists, the most acute of whom have only been able to discover in the seminal fluid of man, round or oblong bodies, which appear to have long tails, but no members of any kind.

One would be tempted to think that Plato had been acquainted with those spermatic animals which are transformed into men; for, at the end of his Timeaus,+ he says, “Vulva quoque matrixque in foeminis eadem ratione animal avidum generandi, quando procul a foetu per aetatis florem, aut ultra diutius ddetinetur, aegre fert moram ac plurimum indignatur, passimque per corpus oberrans, meatus spritus intercludit, respirare non finit, extremis vexat anguistiis, morbis denique omnibus permit, quosque u- [132] trorumque cupido amorque quasi ex arboribus foetum fructumve producunt, ipsum deinde decerpunt, et in matricem velut agrum inspargunt: Hinc animalia primum talia, ut nec propter parvitatem videantur, necdum appareant explicant, ingentia intus enutriunt, demum educunt in lucem, animaliumque generationem perficiunt.” Hippocrates, in his treatise De Diacta, seems likewise to insinuate that the semen of animals is full of animalcules. Democritus talks of certain worms which assume the human figure; and Aristotle tells us, that the first men issued from the earth in the form of worms. But neither the authority of Plato, or Aristotle, of Hippocrates, of Democritus, nor of Dalenpatius, will ever be able to bestow credibility on a notion which is repugnant to the repeated experience and observation of all those who have hitherto made inquiries into this subject.

Valisnieri and Bourguet perceived small worms in the semen of a rabbit: One of their extremities was longer than the other; they were very active in their motions, and beat the fluid with their tails: Sometimes they raised themselves to the top of the liquor, and sometimes sunk to the bottom; at other times they turned round, and twisted like serpents: In fine, says Valisnieri, I clearly perceived them to be real animals: “E gli riconobbi, e gli giudicai fenza [133] dubitamento alcuno per veri, verissimi, archiverissimi vermi.”* This author, though prejudiced in favour of the ovular system, admitted the actual existence of spermatic animals.

M. Andry pretends, that he could find no animals in human semen previous to the age of puberty; that they exist not in the semen of very old men; that there are few of them in those who are affected with the venerial [sic] disease, and that these few are in a languishing state; that none of them appear alive in impotent persons; and that the animalcules in the semen of men have a larger head than those of other animals, which corresponds, he observes, with the figure of the foetus and infant; and he adds, that those who use women too frequently have generally few or no animalcules in their semen.

Leeuwenhoek, Audry, and others, exerted every effort against the egg-system: They discovered in the semen of all males living animalcules; they proved that these animalcules could not be regarded simply as inhabitants of this fluid, since the quanitity of them was larger than that of the fluid itself; and since nothing similar to them existed either in the blood, or in any other of the animal fluids: They maintained, that, as females furnished no animalcules, their fecundity was solely derived from the males; that the existence of living animals in the semen throw more light upon the nature of gene- [134] ration than all the former discoveries on this subject; because the greatest difficulty in generation is to conceive how life is first produced, the future expansion and growth of the parts being only accessory operations; and, consequently, that not a doubt remained of these animalcules being destined to become men, or perfect animals, according to their species. When the improbability was objected to them, that millions of animalcules, all equally capable of becoming men, should be employed for this purpose, which only one of them was to enjoy the singular advantage of being admitted into the condition of humanity; when it was demanded of them, why this useless profusion of human germs? they [sic] replied, That it corresponded with the usual magnificence of Nature; that, in plants and trees, millions of seeds were produced, while only a few of them succeeded; and that, therefore, we ought not to be surprised at the prodigious number of spermatic animals. When the extreme minuteness of a spermatic worm, compared with the body of a man, was mentioned to them as a difficulty, they answered, that the seeds of trees, of the elm, for example, were equally minute, when compared with the perfect individuals; and they added, with equal propriety, metaphysical arguments, by which they proved, that largeness and minuteness were only relations, and that the transition from small to great, or from great to small, was performed by [135] Nature with greater facility than we could possibly imagine.

Besides, they asked, are there not frequently examples of the transformation of insects? Do we not daily see small aquatic worms, by simply throwing off their skin or covering, from which they received their external figure, transformed into winged animals? May not spermatic animalcules, by similar transformation, become perfect animals? Every thing, therefore, they conclude, concurs in establishing this system of generation, and in overturning that which is founded on the notion of eggs; and, though eggs really existed in viviparous animals, as well as in the oviparous, these eggs would only be the matter necessary for the growth and expansion of the spermatic worm, which enters by the pedicle that attaches the egg to the ovarium, where it finds abundance of nourishment prepared for it. All the worms which are so unfortunate as to miss this passage through the pedicle into the egg, perish, and that one alone which finds the proper road, is transformed into a perfect animal. The difficulty of finding this passage is sufficient to account for the great number and apparent profusion of the spermatic animals. It is a million to one against any individual worm’s finding this passage; but, to compensate this difficulty, there are more than a million of worms. When a worm has once got possession of an egg, no other can enter into [136] it; because, say they, the first worm shuts up the passage; or rather, there is a valve at the entry to the pedicle, which plays while the eggis not perfectly full; but, when the worm has filled the egg, this valve will not open, though pushed by a second worm. Besides, this valve is exceedingly well contrived; for, if the worm should chance to descend through the passage by which it entered, the valve prevents its escape, and obliges it to remain till it be transformed. The spermatic worm then becomes a real foetus; and it is nourished by the substance of the egg, and the membranes serve it for a covering; and, when the nourishment contained in the egg begins to fail, the foetus attaches itself to the internal surface of the uterus, and, by this means, extracts nourishment from the blood of the mother, till, by its weight, and the increase of its strength, it at last breaks off all connection with the uterus, and issues into the world.

According to this system, it was not the first woman, but the first man, who contained all mankind in his own body. The pre-existent germs are no longer inanimate embryos locked up in eggs, and included, in infinitum, within each other. They are, on the contrary, small animals, or organized living homunculi, included in each other in endless succession, and which, to render them men, or perfect animals, require nothing but expansion, and a transformation similar to that of winged insects. [137]

As physicians are at present divided between the system of spermatic worms, and that of eggs, and, as every new writer upon generation has adopted either the one or the other of these hypothesis [sic], it is necessary to examine them with care, and to show not only their insufficienty to explain the phaenomena of generation, but that they rest upon suppositions which are entirely destitute of probability.

Both systems suppose an infinite progression, which, as formerly remarked, is a mere illusion of the brain. A spermatic worm is more than a thousand million times smaller than a man. If, then, the body of a man be taken as an unit [sic], the body of a spermatic worm will be expressed by the fraction 1/1000000000, i.e., by a number consisting of ten cyphers [sic]; and, as a man is to a spermatic worm of the first generation in the same proportion as this worm is to a worm of the second generation, the size of this last spermatic worm will be expressed by a number consisting of 19 cyphers; for the same reason, the size of a spermatic worm of the third generation must be expressed by a number consisting of 28 cyphers, that of the fourth generation by 37 cyphers, that of the fifth generation by 46 cyphers, and that of the sixth generation by 55 cyphers. To form an idea of the minuteness represented by this fraction, let us take the dimension of the sphere of the universe from Sun to Saturn; and, supposing the Sun to be a [138] million times larger than the Earth, and distant from Saturn a thousand solar diameters, we shall find that 45 cyphers are sufficient to express the number of cubic lines contained in this sphere; and, if we reduce each line into a thousand million of atoms, no more than 54 cyphers will be necessary to express their number: Of course, a man will be proportionally greater, when compared with a spermatic worm of the sixth generation, than the sphere of the universe when compared to the smallest atom that can be seen with the assistance of a microscope. But, if this calculation were carried on to the 16^th generation, the minuteness would exceed all powers of expression. It is apparent, therefore, that the probability of this hypothesis vanishes in proportion as the object diminishes. This calculation applies equally to eggs as to spermatic worms; and the want of probability is common to both. It will, no doubt, be objected, that, as matter is infinitely divisible, this gradual diminution of size is not impossible. To this I reply, that all infinities, whether in geometry or in arithmetic, are only mental abstractions, and have no actual existence in Nature. If the infinite divisibility of matter is to be regarded as an absolute infinite, it is easy to demonstrate, that, in this sense, it has no existence; for, if we once suppose the smallest possible atom, by the very supposition, this atom must be indivisible; because, if it were divisible, [139] it would not be the smallest possible atom, which is contrary to the supposition. It is, therefore, apparent, that every hypothesis which admits an infinite progression ought to be rejected not only as false, but as destitute of every vestige of probability; and, as both the vermicular and ovular systems suppose such a progression, they should be excluded for ever from philosophy.

These systems are liable to another objection: In the ovular system, the first woman contained both male and female eggs; the male eggs could only give origin to males; but the female eggs behoved [sic] to contain millions of generations of both males and females: Hence every woman must have always contained a certain number of eggs capable of being unfolded in infinitum, and another number, which could only be unfolded once, and could have no farther operation in the series of existence. The same thing must take place in the vermicular system. Hence we may conclude, that there is not the smallest degree of probability in hypotheses of this nature.

A third difficulty still remains, arising from the resemblance of children sometimes to the father, sometimes to the mother, and sometimes to both, and from the evident characters of specific differences in mules and other monstrous productions. If the foetus proceeds from the spermatic worm of the father, how comes the child to resemble its mother? If the foetus pre- [140] exists in the egg of the mother, how should the child resemble its father? And, if the spermatic worm of a horse, or the egg of a she-ass, be the origin of the foetus, how should the mule partake of the nature and figure both of the horse and ass?

These general objections, though perfectly invincible, are not the only difficulties with which these systems are embarrassed. May it not be demanded of those who embrace the vermicular system, how these worms are transformed, and wherein consist the analogy between this transformation and that which insects undergo? The caterpillar which is to become a butterfly, passes through a middle state, and, after it ceases to be a chrysalis, is completely formed, has acquired its full growth, and is instantly capable of generating: But, in the pretended transformation of the spermatic worm of a man, there is no middle or chrysalis state; and, supposing this to happen during the first days of conception, why is not the production of this chrysalis, in place of an unformed embryo, a perfect adult? Here all analogy ceases; and, of course, the notion of the transformation of the spermatic worm can receive no support from this quarter.

Besides, the worm which is to be transformed into a flie [sic] proceeds from an egg; this egg is produced by the copulation of the male and female, and it includes the foetus which is to pass [141] into a chrysalis, before it arrives at the perfect state of a flie, and before it acquires the power of generating. But the spermatic worm has no generative faculty; neither does it proceed from an egg: And, though it should be supposed that the semen contains eggs which produce the spermatic animals, the same difficulty still remains; for these supposed eggs are not a result of the copulation of two sexes, like those of insects. Consequently, the analogy fails here likewise; and the transformation of insects, in place of strengthening his hypothesis, seems entirely to destroy it.

The seeds of vegetables are resorted to, in order to account for the infinite number of spermatic animals: But this analogy does not apply; for, all the spermatic animals, one only excepted [sic], must absolutely perish. The seeds of vegetables, however, are not subject to the same necessity. When they become not vegetables themselves, they nourish other organized bodies, and serve the purposes of growth and of reproduction to animals. But the prodigious superfluity of spermatic animals can answer no end whatever. I make this remark, purely because I wish to omit nothing that has been advanced on the subject; for I acknowledge, that no argument drawn from final causes can either establish or destroy a physical theory.

The apparent equality in the number of spermatic animalcules in all animals, has also been [142] objected to by the supporters of this doctrine. If these animalcules are the immediate cause of generation, why is there no proportion between their numbers and those of the young, which are various in men, quadrupeds, birds, fishes, and insects? Besides, there is no proportional difference in most species of spermatic animals, those of a rat being nearly equal in size to those of a man. Even when a difference in size takes place, it has no proportion to the bulks of the animals. The spermatic animals of the calmar [sic], which is a small fish, are a hundred thousand times larger than those of a man or of a dog. This is an additional proof that these worms are not the sole and immediate cause of generation.

The particular objections to the ovular system are not less weighty. If the foetus existed in the egg before the junction of the male and female, why do we not see the foetus in the egg before impregnation, as clearly as after it? We formerly mentioned, that Malpighius always found the foetus in eggs which had received the impregnation of the male, and could discover nothing but an unformed mole or mass in the cicatrice of unimpregnated eggs. It is, therefore, evident, that the foetus is never formed till the egg has been impregnated.

Farther, we not only cannot discover the foetus in eggs before the intercourse of the sexes, but we have not been able to demonstrate the [143] existence of eggs in viviparous animals. Those physicians who pretend that the spermatic worm is the foetus inclosed in a coat or covering, are at least ascertained of the existence of spermatic worms; but those who maintain that the foetus pre-exists in the egg, have no evidence of the existence of the egg itself; for the probability of their non-existence in viviparous animals amounts almost to a certainty.

Though the partizans [sic] of the ovular system agree not as to what ought to be regarded as the real egg in the testicles of females, they all allow, however, that impregnation is accomplished in the testicle or ovarium. But they never consider, that, if this were the case, most foetuses would be found in the abdomen in place of the uterus; for, as the superior extremity of the Fallopian tube is unconnected with the ovarium, the pretended eggs would often fall into the abdomen. Now, we know this to be at least a very rare phaenomenon; and it is probable that it never happens but by means of some violent accident.

These objections and difficulties have not escaped the ingenious author of Venus Physique. But, as his work is in the hands of the public, and as it admits not of abridgement, we shall refer the reader to the book itself; and shall conclude with an account of a few particular experiments, some of which appeared to favour and others to contradict the above systems. [144]

In the history of the Academy of sciences [sic], ann. 1701, some objections are proposed by M. Mery against the egg-system. This able anatomist maintained, with propriety, that the vesicles found in the testicles of females are not eggs; that they adhere so firmly to the internal surface of the testicle, as not to admit of a natural separation; and that, though they could separate from the substance of the testicle, it was impossible for them to get out of it, because the texture of the common membrane inclosing the whole testicle is so firm and strong, that it is impracticable to conceive the possibility of its being pierced by a vesicle or round soft egg. And, as most anatomists and physicians were prepossessed in favour of the egg-system, and imagined that the number of cicatrices in the testicles corresponded with the number of fetuses, M. Mery showed such a quantity of these cicatrices in the testicles of a woman, as, upon the supposition of the truth of this system, would have argued a fecundity beyond the power of credibility. These difficulties stimulated other anatomists of the academy, who were partizans of the eggs, to make new researches. M. Duverney examined the testicles of cows and sheep, and maintained, that the vesicles were eggs, because some of them adhered less firmly to the testicles than others; and that it was natural to suppose that they separated altogether when they arrived at full maturity; especially as by blowing into [145] the cavity of the testicle, the air passed between the vesicles and the adjacent parts. M. Mery simply replied, that this proof was insufficient, as these vesicles were never seen separate from the testicles. M. Duverney farther remarked the glandular bodies upon the testicles; but he never considered them as parts essential to generation, but as accidental excrescences, like gall-nuts on the oak. M. Littre, whose prejudices in favour of eggs were still stronger, maintained, not only that the vesicles were eggs, but even assured us, that he discovered in one of them a well formed foetus, of which he could distinguish both the head and trunk; and he has even given their dimensions. But, admitting this wonder, which never appeared to any eyes excepting his own, to be convinced of the doubtfulness of the fact, we have only to peruse his memoir.* From his own description it appears, that the uterus was schirrous [sic], and the testicle very much corrupted; that the vesicle or egg, which contained the pretended foetus, was much less than common, &c.

Nuck furnishes us with a celebrated experiment in favour of eggs. He opened a bitch three days after copulation; he drew out one of the horns of the uterus, and tied it in the middle so as to prevent the superior part of the Fallopian tube from having any communication with the inferior part. After this he replaced the horn of [146] the uterus, and closed the wound. Twenty four days afterwards, he again opened the would, and found two fetuses in the superior part of the tube, that is, between the testicles and the ligature; and there was no foetus in the under part. In the other horn of the uterus, that was not tied, he found three fetuses regularly disposed; which proves, says he, that the foetus proceeds not from the male-semen, but th