Meyer - Essays on the History of Embryology 3

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References - Essays on the History of Embryology  

Meyer AW. 1932 - Essays on the History of Embryology: Part I | Part II | Part III | Part IV | Part V | Part VI | Part VII | Part VIII | Part IX | Part X | Part XI | Arthur Meyer | Historic Embryology Papers

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Arthur William Meyer (1873 – 1966)
Arthur William Meyer (1873 – 1966)

Essays on the History of Embryology III

By A. W. Meyer, M. D.

Stanford University

This is the third paper of a. series of essays on this subject. Previous papers were printed in this journal as follows: Part I in December California and Western Medicine, page 447; Part II in January California and Western Medicine, page 40.

The Foundations of Morphologic Embryology

ONLY a few things on generation deserving of mention are known to have appeared during the long span of years between Galen and the seventeenth century - a period of about fifteen hundred years.

Leonardo Da Vinci 1452-1519

Since such a genius as Leonardo da Vinci belongs in this period, one is prompted to inquire regarding his ideas concerning generation. Although Leonardo’s interest in anatomy was artistic rather than scientific, a man of such great accomplishments cannot be overlooked. His anatomical drawings attest to his surpassing skill even if they do not have great scientific value and seem to have been largely without influence on the course of anatomy. McMurrich’s careful study clearly shows that Leonardo, like Galen, fell into errors because he transferred anatomical arrangements found in other mammals to man himself. Although he must have been familiar with the discoidal placenta, he nevertheless represented a full-term human fetus in an opened uterus, accompanied by an ungulate placenta. According to McMurrich the allantois accompanying the figure of a child is spoken of as passing “between the hands and knees of the child as it lies curled up, and it passes between the arms and the inner (silvestra) part of the thigh as far as the flanks and ties and encloses, making itself an imgastment for the child from its flanks downward.” He also spoke of a male and a female portion of the cotyledons and wondered which was expelled at birth.

Leonardo seems to have accepted traditional views, and when he departed from these his conceptions really do not represent an advance. Since the mother breathes for the child, he argued that the maternal heart also beats for the fetal heart and that the latter remains motionless until birth. He believed in maternal impressions and stated that the soul of the mother forms the fetus, the two having but one soul. He thought that the maternal emotional states not only may mark, but may kill the fetus. Like many others he bowed to religious authority in this connection, saying that he leaves to them “the rest of the definition of the soul,” since they know all secrets by inspiration.

Leonardo’s statement that although the fetal kidneys function, no urine is expelled because the fetal head presses upon the perineum, seems particularly strange since his drawings of fetuses do not show them in this position. He thought that the pressure of the head in this region forced the urine to escape through the urachus and then through the mouth of the uterus. These ideas of his-emphasize again that not even a great genius could correctly imagine and delineate the story of prenatal development.

Volcher Coiter’s Studies of Incubating Eggs

Early in the Seventeenth century Volcher Coiter, of whom Singer, in the “Evolution of Anatomy,” says, “So far as modern times are concerned, Coiter is unquestionably the father of anatomy,” opened incubating eggs daily and recognized the blastoderm as the rudiment of the chick, but he apparently saw many things incorrectly. It is possible that Coiter was overimpressed with the fanciful ideas of his teacher Aldrovandi, who, according to Harvey, held “that the yelk rises during the first days of the incubation into the sharp end of the egg, a proposition which no eyes but those of the blind would assent to; he thinks also that the chalazae are the semen of the cock, and that the chick arises from them, though it is nourished both by the yelk and the white. In this he is obviously in opposition to Aristotle, who held that the chalazae contributed nothing to the reproductive powers of the egg.”

Hieronymous Fabricius Ab Abquapendente

Hieronymous Fabricius ab Abquapendente, a pupil of Fallopius, also published illustrations on prenatal development of the chick, snake, hen, rat, and some of the domestic animals, and held that the chalazae do not represent the sperm of the cock but take part in the formation of the embryo. While professor of anatomy at Pavia, Fabricius published two editions, one in Venice in 1600 called “De Formato Foetu,” and a second at the time of his retirement in 1604, in Patavia. De formatione ovi et pulli tractatus accuratissimus, was published in the latter city after the death of Fabricius in 1621. According to Harvey, Fabricius and Aristotle “have written with so much accuracy on the generation of the chick from the egg that little seems left for others to do.”


However, Harvey did not accept the idea of Aristotle that the first rudiment of the embryo appears on the pointed end of the egg and hence doubted whether Aristotle really saw the beginnings of the chick. Yet Harvey thought the hind and doe conceived “by a kind of contagion,” and says that Aristotle “did not sufliciently understand how the efficient cause (the seminal fluid of the cock) acted without contact; nor how the egg could of its own accord, without any inherent generative matter of the male, produce a chick.” But neither did Harvey know this although he rightly stated that no bird egg can develop an embryo without the “inherent generative matter of the male.” Yet Harvey wrote:

“Whoever has pondered with himself how the brain of the artist, or rather the_artist by means of his brain, pictures to the life things which are not present to him, but which he has once seen; also in what manner birds immured in cages recall to mind the spring, and chant exactly the songs they had learned the preceding summer, although meanwhile they had never practiced them; again—and this is more strange—how the bird artistically builds its nest, the copy of which it had never seen, and this not from memory or habit, but by means of an imaginative faculty (phantasia), and how the spider weaves its web, without either copy or brain, solely by the help of this imaginative power; whosoever, I say, ponders these things will not, I think, regard it as absurd or monstrous that the woman should be impregnated by the conception of a general immaterial ‘idea’ and become the artificer of generation... . “Since, then, nothing can be apprehended by the senses in the uterus after coition, and since it is necessary that there be something to render the female fruitful, and as this is probably not material, it remains for us to take refuge in the notion of a mere conception and of ‘species without matter’ (species sine materia), and imagine that the same thing happens here as everyone allows takes place in the brain, unless indeed there be someone ‘whom the gods have moulded of better clay,’ and made fit to discover some other efiicient cause besides any of those enumerated.”

Composition of Sperm

The idea that sperm is composed of a material and an immaterial part is an old one. The latter was spoken of as the aura spermatica and was sometimes looked upon as a vapor or volatile part which reached the ovary through the circulation or through the mouth and cavity of the uterus and the lumen of the tubes. The finding of narrow or obstructed vaginae in pregnant women, the smallness of the lumina of the tubes and failure to find sperm in the uterus and tubes in all cases were partly responsible for this idea. With what ingenuity Spallanzani attacked and settled this old problem by experiment will appear in the last essay. From a publication of A. Spigelius, 1631, largely on the pregnant state and fetal anatomy, entitled “De Formate Foetu,” and accompanied by fine but fanciful illustrations, we pass again to William Harvey, whose work on generation appeared in 1651. Harvey, who had been a pupil of Fabricius, was very loyal to his teacher. His greatest merit in regard to embryology lay in the fact that he systematically studied not only the incubating hen egg but the physiology of sex and mammalian propagation and supported the idea of epigenesis, or the gradual formation of the different parts of the embryo out of unformed material. This idea had been suggested by Hippocrates and Aristotle, but seems to have gained its first real support from Harvey’s work. Harvey, who used a lens in his studies, declared:

“Now it appears clear from my history that the generation of the chick from the egg is the result of epigenesis, rather than of metamorphosis, and that all its parts are not fashioned simultaneously, but emerge in their due succession and order; it appears, too, that its form proceeds simultaneously with its growth, and its growth with its form; also that the generation of some parts supervenes on others previously existing, from which they become distinct; lastly, that its origin, growth, and consummation are brought about by the method of nutrition; and that at length the foetus is thus produced.”

Fabricius, whom Singer regards as “the effective founder of modern embryology,” had expressed the opinion that most animals come from ova. Harvey likewise believed that some arise from ova and others from putrescent matter. He held that all perfect animals come from ova and unequivocally headed the sixty—second Exercitatio “Ovum esse primordium commune omnibus animalibus.” Although the word “ovum” was applied to the beginning of a being, the conceptus in utero was an ovum to Harvey, for the mammalia.n ovum was not discovered until almost two hundred years later. According to Whitman, Harvey objected to looking for any “prepared matter,” believing that every ovum arose de novo and that his conception of all animals arising from eggs and of epigenesis was merely that of Aristotle.

Since Harvey could not find substance in the uterus and tubes after coitus nor experimentally demonstrate the presence of a continuous passage through the female reproductive tract by injecting suspended material into the uterus, he concluded that male semen or something called female semen, arising from the ovary, could not enter the uterus and hence could play no part in conception. It was experimental evidence which caused him to turn to the wrong conception of fertilization through distant influence, and prompted him to conclude that the thing he called an ovum—that is, the chorionic vesicle——arose de novo in the uterus and was not nourished by it. The method of nourishment of the mammalian conceptus escaped Harvey and he was led astray by what he observed in the hen egg and deer. He concluded that a fetus the size of the thumb was “nourished only by the albumen that is contained in the conception; in the same way that we have seen the process go on in the hen’s egg. The mouths of the umbilical veins are lost and obliterated between the albumen and neighboring humours of the conception and their containing membranes; but nowhere is there as yet any connection with the uterus, although by these veins alone is nourishment supplied to the embryo.”

Harvey on Human Development

Fig. 1. After Malpighi. Chick after two days’ incubation. K. auricle; L. veins; M, right ventricle; N, left sinus; O, branches of umbilical arteries; P, umbilical arteries; Q, terminations of arteries; R, vesicle near right umbilical branch P is swollen with thin humor or ichor. (This vesicle must have been the extremity of the allantois.)

Regarding human development, Harvey wrote:

“For I rather think that during the first month there is scarcely anything of the conception in the uterus——at all events, I have never been able to discover anything. But the first month past, I have repeatedly seen conceptions thrown 0H, and similar to the one which Hippocrates mentions as having been voided by the female pipe—player, of the size of a pheasant’s or pigeon’s egg. Such conceptions resemble an egg without its shell; they are, namely, of an oval figure; the thicker membrane or chorion with which they are surrounded, however, is seen to be covered with a white mucor externally, particularly toward the larger end; internally it is smooth and shining, and is filled with limpid and sluggish waterit contains nothing else.”

It may be recalled in this connection that Aristotle said that the human embryo is as large as an ant at the end of the first month. Although I have been unable to obtain satisfactory information regarding the size of the ant Aristotle may have had in mind, it must undoubtedly have been a large ant, although the small-sized ant would suit the facts. It is extremely improbable that Aristotle could have seen and recognized a human embryo of one month, for the size of such was established only recently.

Harvey’s observations on pregnant deer also caused him to arrive at the conclusion that the uterus remains empty for a long time after coitus, for he wrote:

“Having frequently shown this alteration in the uterus to his majesty the king as the first indication of pregnancy, and satisfied him at the same time that there was nothing in the shape of semen or conception to be found in the cavity of the organ, and he had spoken of this as an extraordinary fact to several about him, a discussion at length arose: the keepers and huntsmen asserted at first that it was but an argument of a tardy conception occasioned by the want of rain. But by and by, when they saw the rutting season pass away, I still continuing to maintain that things were in the same state, they began to say that I was both deceived myself and had misled the king, and that there must of necessity be something of the conception to be found in the uterus. These men, however, when I got them to bring their own eyes to the inquiry, soon gave up the point. The physicians, nevertheless, held it among their aséva-pa —their impossibilities—that any conception should ever be formed without the presence of the semen masculinum, or some trace remaining of a fertile intercourse within the cavity of the womb. . .. In the dog, rabbit, and several other animals, I have found nothing in the uterus for several days after intercourse. I therefore regard it as demonstrated that after fertile intercourse among viviparous as well as oviparous animals, there are no remains in the uterus either of the semen of the male or female emitted in the act, nothing produced by any mixture of these two fluids. as medical writers maintain, nothing of the menstrual blood present as ‘matter’ iii the way Aristotle will have it; in a word, that there is not necessarily even a trace of the conception to be seen immediately after a fruitful union of the sexes. It is not true, consequently, that in a prolific connexion there must be any prepared matter in the uterus which the semen masculinum, acting as a coagulating agent, should congeal, concoct, and fashion, or bring into a positive generative act, or by drying its outer surface, include in membranes. Nothingcertainly is to be seen within the uterus of the doe for a great number of days, namely, from the middle of September up to the 12th of November.”

“It appears, moreover, that all females do not shed seminal fluid into the uterus during intercourse; that there is no trace either of seminal fluid or menstrual blood in the uterus of the hind or doe, and many other viviparous animals. But as to what it is which is shed by women of warmer temperament no less than by men during intercourse, accompanied with failure of the powers and voluptuous sensations; whether it be necessary to fecundation, whether it be semen and prolific, is discussed by us elsewhere.”

Harvey’s treatise on the generation of animals contained forty pages of descriptive matter, no illustrations, and many philosophical reflections and contradictory statements. According to Brooks, his aim was to show that there is no physical continuity between parent and child and that fertilization is due to some mysterious “incorporeal” thing or influence such as a vital spirit from the stars. To Harvey the hen egg was not the product of ovary or uterus but of a vital principle. Harvey thought that conception was produced in the uterus “as an iron touched by a magnet is endowed with its own powers,” and there is ample justification for Huxley’s statement that Harvey also believed in spontaneous or equivocal generation. However, Harvey conceived many things correctly, and maintained, contrary to Aristotle and his followers, that the heart is not the source of the blood because “its parenchyma or proper substance arises some little time after the blood, and is superadded to its pulsating vesicles.” It is also well to recall that Harvey might have had other discoveries to his credit but for the loss of his notes and collections by mob violence. We can easily sympathize with him when he wrote:

“And whilst I speak of these matters, let gentle minds forgive me, if, recalling the irreparable injuries I have suffered, I here give vent to a sigh. This is the cause of my sorrow:—whilst in attendance on his majesty the king during our late troubles and more than civil wars, not only with the permission but by command of the Parliament, certain rapacious hands stripped not only my house of all its furniture, but what is subject of far greater regret with me, my enemies abstracted from my museum the fruits of many years of toil. Whence it has come to pass that many observations, particularly on the generation of insects, have perished, with detriment, I venture to say, to the republic of letters.”

Fig. 2. After Table 15 of de Graaf
Fig. 2. After Table 15 of de Graaf: A, a. testlculus secundum Iongitudlnlm apertus; B, ovum maximum seumaturum in estlculo adhuc contentum; CC, ova. mlnora seu immature in testlculo haerentla; DD membrana. testiculorum dartos appellata; E, ovum maximume e testiculo exemptuns; F, tuba talloplanae membranosa. expanslo; G. foramen coarctatum in tubae extremltate exlstens; H, tubae falloplanae extremltos; II, tubae pars rellqua; K, carnu uterinl pars abscissa; L, tubae llgamentum in homlnlbus alis vespertllionum asslmllatuns.

Had his collection been left him and had Harvey contented himself with observation and experiment and avoided what Willis rightly calls “wanderings in the labyrinth of the metaphysics of physiological science/’. his work on generation would be far more deserving. This biographer says he “did enough [speculating] to deter anyone from attempting to tread such barren ground again.” However, the errors of Harvey were not always due to pure speculation, but to faulty or inadequate observation, as the following quotation shows:

“In the deer as well as in the sheep, goat, and bisulcate animals generally, we find testicles; but these are mere little glands which rather correspond in their proportions to the prostate or mesenteric glands, the use of which is to establish divarications for the veins, and to store up a fluid for lubricating the parts, than for secreting semen, concocting it into fecundity, and shedding it at the time of intercourse. I am myself especially moved to adopt this opinion, as well by numerous reasons which will be adduced elsewhere, as by the fact that in the rutting season, when the testes of the buck and hart enlarge and are replete with semen, and the cornua of the uterus of the hind and doe are greatly changed, the female testicles, as they are called, whether they be examined before or after intercourse, neither swell nor vary from their usual condition; they show no trace of being of the slightest use either in the business of intercourse or in that of generation.”

Highmore a Contemporary of Harvey’s

In the same year that Harvey’s treatise on generation appeared a considerably younger countryman of his, Nathaniel Highmore, also published one on the same subject. Highmore contradicted some of Harvey’s ideas and insisted that male sperm actually gets into the uterus" and that sperm is not evaporated, as Harvey claimed, and incorporated into the body of the womb or into a more internal part and then redistilled into the womb again after a period of six weeks. He surmised that in the does or hinds in the womb of which Harvey found nothing before six weeks probably were barren. He emphasized that Harvey’s idea in this matter was like that of Fabricius, who thought that “an irradiating influence fecundates the Hen and makes fruitful all the eggs that shall for a long time after he produced, without any admixture of seed at all.” He says that Fabricius believed this because he found the mouth of the womb so small and because the cock had no intromittent organ.

Highmore insisted that only the womb was big enough to hold so large a quantity of sperm as is usually ejaculated, and continued:

“We shall find the material parts of the Male copied out to the life in the Fetus; even his marks, which never came under his sight or knowledge peradventure, to be branded on the young one; we must needs acknowledge something more than irradiation, or fecundating qualities, impressed on the womb by the Masculine seed; and more than phansie in the Females to produce such effects. A Hen trod by a Pheasant, though in a dark room that so she could never see his proportions or color, brings forth Chickens resembling both herself and the Pheasant. A Bitch lined with several kinds of Dogs, though in the dark, when her phansie could not operate to the assimilating of her births, brings forth her whelps fashioned and colored like to all those she coupled with. The Horse leaves some material impression of himself, on the Mule, which she begets on the Asse."

Highmore also controverted the idea of Fabricius that the cicatricula is a scar left by “breaking of the footstock, by which it was fastened to the Hen,” and added, “Parisanus thought it the seed of the cock, but I think it to be the seminal Atomes derived from both” the cock and hen for it is already present “when the eggs are but small little grains contained in the Egg-bag or Vitellary.”

Highmore’s treatise contains a number of illustrations on the early development of the chick and of plants and also an essay on Sir Gilbert Talbot’s powder of sympathy in the efficacy of which he fully believed. He stated his conceptions of generation of animals as follows:

“The first rank of Animals rises from corruption of other creatures (Eeles from Mud; Flies and Worms from Beasts; the Sarabeus from Oxen; Lice from the filth of most Creatures)."

This, to be sure, is a plain recognition of spontaneous generation such as is found in Harvey, and Highmore also holds that perfect animals do not arise in this way, but from “. . . Atomes by the testicles of both, thrown into the Matrix of the Female.” He insisted that both sexes must share in procreation because one of them must supply the role of the earth in regard to the seed, thus recurring to a very ancient concept. According to Cole, Highmore’s idea of generation lies between pangenesis and preformation, but preformation without emboitment and constituted by an orderly prearrangement of seminal atomes.

Shortly after the appearance of Harvey's book another contemporary of his, Joseph Needham, published a work also on the topic “De Formate Foetu,” which contained illustrations of mammalian embryos, but a far more substantial advance in embryology was made by the more detailed and comprehensive observations of Marcello Malpighi. His studies were accompanied by many illustrations of great merit. It is interesting that Harvey’s treatise on the circulation was published in Frankfurt in 1628, and that on generation in London and Amsterdam in 1651, while Malpighi’s was published by the Royal Society of London in 1672. The first of Malpighi’s contributions was entitled “De Formatione Pulli in Ovo,” and the second, “De Ovo Incubato.”

Heart Illustrations in Malpighi’s Treatise

Malpighi’s treatise contained twenty figures on the development of the heart alone. He recognized a difference in size of the cicatricula in the fertilized and unfertilized egg and, although they are very transient structures in the development of the vascular system, he saw and pictured the aortic arches. He further represented the neural groove, the head fold and the optic and cerebral vesicles, but contrary to the correct view of Harvey, Malpighi believed that some parts of the completed body preexist in the ovum and that others form during the course of development. However, in spite of this, Malpighi’s services to embryology were considerable, and it is significant that Sir Michael Foster generously regarded him rather than Harvey, as the founder of embryology. Cole also speaks of Malpighi’s “masterly analysis of the organogeny of the chick.”

Malpighi used a self-made microscope instead of a magnifying glass even in his young manhood, and had a great advantage over Harvey, who did his work with a poorer instrument, but, according to Cole, not in the later years of his life. Harvey's work on the circulation appeared the year Malpighi was born.

Stanford University.

(To be continued)

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Meyer AW. 1932 - Essays on the History of Embryology: Part I | Part II | Part III | Part IV | Part V | Part VI | Part VII | Part VIII | Part IX | Part X | Part XI | Arthur Meyer | Historic Embryology Papers

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