Meyer - Essays on the History of Embryology 5

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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 IV

By A. W. Meyer, M. D.

Stanford University

This is the fifth 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 number, page 40; Part III, in February number, page 105; Part IV, in March number, page 176.


Viewpoints of Haller and Bonnet

Fig. 6. Frontispiece. Harvey's first edition (after Malloch).
Fig. 7. The above figures are from Ledermuller, after Ruysch.
Fig. 1, a and b, are “rudimentary” human embryos. Fig . 2 The three spheres are said to be unfertilized human ova suspended by threads. They evidently must be immature Graaflan follicles. Fig. 3 An abortus slightly enlarged. fig. 5-An opened abortus said to still contain an embryo, the tail of which was attached and thought to be the rudiment of the umbilical cord. Fig. 6 A similar human embryo in which the head and abdomen are said to have differentiated and the umbilical cord shows further development. (This; to be sure. is a retained macerated, and probably abnormal, fetes.)

Many of the adherents of the preformation or old evolution theory, such as the great Swiss physiologist, Haller, did not accept it in its extreme form and application, but nevertheless supported it. He apparently found it incomprehensible that a force of nature should be able to build the organs out of unorganized material. Earlier, Haller was an epigenesist, but, strangely enough, was converted by his study of the development of the chick. Bonnet says that Haller wavered at one time in his adherence to preformation, but adds: “The chicken came to my assistance, and the great physiologist declared against epigenesis.” Haller, as Malpighi, knew that the cicatricula is present by the time the egg is laid, and he established the fact that the intestine and yolk sac are continuous. This was hailed as a great discovery and a crucial fact in support of preformation even by Spallanzani. Haller also thought that motion was discernible in the egg before fertilization and that the embryo, hence, must have existed previously and Bonnet referred to the “Hallerian doctrine of embryos lodged in the ovarium which cannot be fecundated artificially,” but Haller declared:

“Again, other anatomists, not less celebrated or less worthy of credit, have taught that the foetus existed in the mother and maternal ovary; which the male semen excites into a more active life, and likewise forms it variously, so as to show it just brought into life, and make its presence manifest. That yolks are also manifestly found in the female ovaries, even although they have not been impregnated with any male semen. But a yolk is known to be an appendix to the intestine of fowls; and to have its arteries from the mesenteric artery, and the covering of the yolk to be continued with the nervous membrane of the intestine, which is continuous with the skin of the animal. That along with the yolk, therefore, the foetus seems to be present in the mother hen, of whom the yolk is a part, and which gives vessels to the yolk.”


Since the last edition of Haller’s physiology appeared four years before Wolff’s work on the intestine it is of special interest to consider his ideas on generation. Haller stated that “The power of the male semen fecundates the ovum in the ovarian cells, as we see in the case of fetuses found in the ovaries in tubes; from the analogy of birds.” He stated that “The male semen fills the tubes themselves at the first impregnation, both in women and brute animals,” but he kept an open mind, as the following quotation shows:

“These changes, hitherto, which are proved at least by the testimony of our senses, may be either confirmed or corrected; those which follow are more conjectural; and the more difficult on account of experiments, and their difficulties and agreement with one another; and in the first place, it is a difficult question from whence proceed the first stamina of the new animal? Whether they are from both parents, and mixed into one animal by a conjunction of the seminal matter coming from the whole body, etc. . . . But no seed has ever certainly been observed in females; and innumerable examples show that the species of animals may be propagated without any mixture of seeds.”


In this connection Haller spoke of “animalcules that are everywhere spontaneously produced in other juices,” but he had formed a surprisingly good idea regarding the descent of the ovum, for he wrote:

“The extremity of the tube, therefore, surrounding and compressing the ovarium in a prolific congress, is thought to press out and swallow a mature ovum, from a fissure in the outer membrane, from whence it is continued down by the peristaltic motion of the tube, to the uterus itself; which peristaltic motion begins from the first point of contact with the ovum, and urges the ovum downward successively to the opening into the fundus uteri, which is very manifest in brute animals. The truth of this appears from the constant observation of a scar or fissure in the ovarium, which is produced there after conception; from a foetus being certainly found in quadrupeds, botl1 in the ovarium of the female, and in the tube-; from the analogy of birds, in which the descent of the ovum from the ovarium is very manifest. Yet we must acknowledge that a true ovum was never found in quadrupeds, unless after a long time. It is probable, that at the time of conception, the true ovum is almost fluid, very soft and pellucid, and cannot be distinguished from the mucus with which the tube is filled; likewise, that it is very small, on account of the narrowness of the tube.”


Haller regarded the blood vessels as the oldest part of the body, the veins appearing first and forming the arteries. One could easily select sentences from his writings that would imply that he was an epigenesist although he was that at first only.


“There are, therefore, in the primeval fetus, such as we first observe it, some things more perfect and conspicuous; others involved, and very small. The heart is the most perfect; it is the only movable and irritable part. . . . The embryo which we first observed in the uterus of the mother was a gelatinous matter, having scarce any proper shape, and of which one part could not be distinguished from another. . . . Again the more frequently, or the more minutely, we observe the long series of increase through which the shapeless embryo is brought to the perfection necessary for animal life, so much the more certainly does it appear that those things which are observed in the more perfect fetuses have been present in the tender embryo, although the situation, figure and composition seem at first to have been exceedingly different from what they show themselves to be at last; for an unwearied and laborious patience has discovered the intermediate degrees with which the situation, figure, and symmetry are insensibly reformed. Even the transparency of the primary fetus alone conceals many things which the color added a little after does not generate, but renders conspicuous to the eye. And it sufficiently appears that those parts which eminent anatomists have supposed in after times to be generated, and to be added to the primeval ones, have been all contemporary with the primeval parts, only small. some of it, and colorless.”

Haller carefully considered the possibility of the fetus’ swallowing amniotic fluid for purposes of nourishment and concluded that the evidences drawn, partly from birds and quadrupeds, favored the idea and that it did so. He believed that the maternal and placental circulations were continuous and gave as his reasons the suppression of menstruation during pregnancy, the loss of blood at birth, the exhaustion of fetal blood in case of hemorrhage on the part of the mother, the passage of water, mercury, tallow, and wax from the uterine arteries to the placenta, and because he thought that there is motion of blood in acardiac fetuses. It seems that Haller must have given some of these reasons upon hearsay or that he was deceived by his own eyes. However, he adopted a very fine attitude regarding all these things, for he wrote:

“Although it is not easy to explain everything mechanically, yet we ought to remember, that if indeed the new animal is truly, and shown by experience to be, present in the egg, those difficulties which are moved cannot overturn such things as have been truly demonstrated. although perhaps some things may re main, to which, in so great an infancy of human knowledge, we cannot yet give a full answer."


It seems especially strange that Spallanzani. Malpighi and Reaumur and Leeuwenhoek as well, supported this false theory of preformation and that the last named should have done so after the discovery of the spermatozoon by Hamm and himself. Yet we must remember that it does not tax the imagination much more to picture an endless number of human beings telescoped one within the other in the spermatozoon than in the Graafian follicle of the ovary. Although the latter is very much larger than the spermatozoon, the matter of size is not a crucial thing when such multitudes are concerned. Certain philosophers are said to actually have estimated the number of miniature human beings that must have been in the ovary of Eve at the hour of creation, and further tried to calculate the time when an ovum or spermatozoon would be depleted and human beings would, hence, cease to exist on earth. Hartsoeker, a man of science, estimated that the size relationship of the first grain of wheat to one after six thousand years would be inversely as unity to unity followed by thirty thousand zeros. He similarly estimated that if all rabbits born since the beginning had been enclosed in a rabbit living in his day the size relationship would be as one to this number followed by one hundred thousand zeroes, which must, of course, have seemed ridiculous. The philosopher Leibnitz gave the theory of preformation an entirely metaphysical interpretation, applying it to the soul and extending it to ridiculous lengths as Hartsoeker had done, and this helped to discredit it. But a greater difficulty confronting the preformationists lay in the fact that both ova and spermatozoa manifestly could not contain these minute forms of beings, for that would mean that every conception should result in a twin pregnancy. This dilemma resulted in the formation of two groups of preformationists, the ovists and the animalculists, accordingly as the ovum, or the spermatozoon was regarded as the germ of the future individual. Among the ovists were Cuvier, Harvey, Malpighi, Swammerdam, Spallanzani, and Littre ; and among animalculists, Andry, Boerhaave, and Erasmus Darwin, Leeuwenhoek, Lieutaud, Lancisi, Leibnitz, and others:


The expulsion of the male sexual products was such an obvious and striking phenomenon and the idea of male seed such an old one that the presence of spermatic animalculae in them seemed to be prima facie proof of the spermatic origin of the new individual. The occurrence of ovarian pregnancy was not regarded as disproving such an assumption, for the animalcules manifestly might be able to develop just as well in the ovary as in the uterus. It is interesting that it had been suggested as early as 1701, by Andry, that spermatozoa might enter the ovary, but that fact was not established until 1853, and the union of sperm and ovum was not observed until 1875. Both the ovists and the animalculists found it impossible to satisfactorily explain the occurrence of regeneration, deformities, variations and inheritance, but that did not deter one group from confronting the other with these objections. One of the chief objections to animalculism was that it seemed to violate the religious concept of a benign creator. It was regarded impossible to believe that all except one out of such myriads of spermatozoa, each of which was supposed to contain a preformed individual, should be preordained to perish, and Leeuwenhoek’s reference to the occurrence of similar things in plants and animals had little effect. The ovists, on the other hand, had to overcome the old belief that semen really represented the seed, and also the force of the old simile of the grain of wheat developing in the earth. Then, too, the very ancient observation that a woman might conceive while unconscious was taken to imply that she contributed nothing to procreation. It might seem that the discovery of the ovum by von Baer should have revived ovism, but von Baer himself decided against preformation and held that the embryo evolved slowly in the egg.

Erasmus Darwin as an Animalculist

Erasmus Darwin, whose Zoonomia was published in 1801, apparently was an animalculist in a modified sense, for he held that “At the earliest period of existence the embryo, as secreted from the blood of the male, would seem to consist of a living filament . . .” such as a “muscular fiber.” He stated that it was hard to conceive this, but repeatedly emphasized in the chapter on generation that the male plays a superior role and believed that the embryo is secreted by the glands of the male, for the cicatricula or germ disk was present only in hens that had been tread by the cock, writing:

“As the cicatricula of these eggs isgiven by the cook, and is evidently the rudiment of the new animal; we may conclude, that the embryon is produced by the male, and the proper food and nidus by the female.”

Darwin considered the objection that if only one out of so vast a number of spermatic animalculi or hominculi, as he called them, survives in man that the wastage must be very great, but he concluded this was Nature's way, as exemplified by trees and fish. He emphasized that “The embryo is secreted or produced by the male, and not by the conjunction of fluids from both male and female, appears from the analogy of vegetable seeds.” He referred to volvox globator in this connection, which “is said by Linnaeus to bear within it sons and grandsons to the fifth generation. These are probably living fetuses, produced by the father, of different degrees of maturity, to be detruded at different periods of time, like the unimpregnated eggs of various sizes, which are found in poultry; and as they are produced without any known copulation, contribute to evince that the living embryon in other orders of animals is formed by the male parent, and not by the mother, as one parent has the power to produce it.”

Darwin thought of the embryo as growing by “appositions of new parts and not by the distention of a primordial nest of germs, included one within another like the cups of a conjurer,” thus pronouncing against emboitment. He attributed an excess of parts to an excess of nourishment and “mules” among plants and animals to the stimulus of a different environment. In the last recapitulation in his chapter "on generation, he qualified his ideas somewhat and surmised that the animalcules found in semen of various animals are “produced by the stagnation of the semen in the vesiculae seminceles” and refers as evidence to “the spontaneous production of microscopic animals . . . in all solutions of decomposing vegetable and animal matter” within a few days even after boiling, as shown by the experiments of Reaumur and Baker.

In the chapter headed Reflections - on his experiments - Spallanzani says that, in his opinion, the immortal Haller alone has produced an insuperable objection against the spermatic worms being the authors of generation. Spallanzani apparently referred to the fact that Haller had shown that the yolk sac of the chick is continuous with the intestine. From this it was inferred that the chick must have existed in the hen before the latter had received the cock because the yolk existed in the egg. Although Bonnet realized the inadequacy of this observation, he wrote in a letter to Spallanzani:

“Haller was inclining to this hypothesis [epigenesis]. I had the courage to resist him, notwithstanding the impression his authority made on me. The chicken came to my assistance, and the great physiologist declared against epigenesis."

It is interesting that Spallanzani, himself, thought that no spermatic worms were present in his instances of artificial fertilization, and held that:

“This singular mode of impregnation equally demonstrates the falsehood of Epigenesis, or of that system, which has been raised from the dead, protected and caressed by Bufion; who, by means of his organic molecules, has created an imaginary organic world, as his countryman Descartes had before constructed the whole mass of existences, both organic and inorganic, with his subtle matter. The spermatic worms having first struck his senses, and being thence transferred to his fervid and creative fancy, lost their former name of animals, and acquired the new title of organic molecules.”

It is easy to realize the consternation created among the animalculists by the rediscovery of hermaphroditism in aphides by Bonnet about a century after the discovery of spermatozoa by Leeuwenhoek. If plant lice had an asexual as well as a sexual cycle; if ova could develop without the instrumentality of spermatozoa and perfect individuals nevertheless result, then the spermatozoon seemed to be ‘eliminated. Although these observations of Bonnet’s were at first doubted, they were confirmed and seemed to show clearly that the animalculists were in the wrong. They brought joy to the ovists, but their rejoicing was brief, for they too were soon to find that they also were in the wrong, although Gilis says the great Cuvier supported the preformation theory as late as 1830.


(To be continued)


Historic Disclaimer - information about historic embryology pages 
Mark Hill.jpg
Pages where the terms "Historic Textbook" and "Historic Embryology" appear on this site, and sections within pages where this disclaimer appears, indicate that the content and scientific understanding are specific to the time of publication. This means that while some scientific descriptions are still accurate, the terminology and interpretation of the developmental mechanisms reflect the understanding at the time of original publication and those of the preceding periods, these terms and interpretations may not reflect our current scientific understanding.     (More? Embryology History | Historic Embryology Papers)

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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