1. An Early Ovum imbedded in the Decidua (1908)

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The following memoir combines in one publication two separate papers which deal with the processes involved in the imbedding of the human ovum. They have been associated because of the complementary nature of the evidence they afford regarding the histological characters and the activities of the trophoblast. Each breaks new ground, in respect that while the first paper embodies a description of the earliest phase of the human ovum yet recorded, the second deals with the earliest case of ovarian pregnancy hitherto reported.

The fact that the extremely early ovum described in the first paper is a unique specimen presenting features which have not up to the present been observed, necessitated profuse illustration both by coloured plates and photographic figures. This has rendered the production a costly one, and we desire to express our obligations to the Carnegie Trust of the Scottish Universities for giving us a grant towards the expenses of publication.

University of Glasgow,

July 15th 1908.



Paper No I. An Early Ovum imbedded in the Decidua

History of the Specimen

Fixation of the Specimen

Dimensions of the Ovum

General Descriptions of the Sections

The Decidua

The Trophoblast

The Plasmodi-trophoblast

The Cyto-trophoblast

Layer of Large Free Cells

The Contents of the Blastocyst

The Mesoblast

The Embryonic Rudiment

Discussion of Data

Summary of Characters of the Ovum

Comparison with the Ova of Leopold and Peters

The Embryonic Rudiment

The Process of Imbedding

Comparative Data regarding Inbedding

Description of Imbedding of Human Ovum

Analogy with Imbedding of an Embolus of Chorion-epithelioma

Function of the Plasmodium

Fate of Early Plasmodium and Attachment of Ovum

The Age of the Ovum and Relation of Imbedding to Menstruation

Estimation of Age

Comparative Data

Comparison with other Cases

Summary of Dat«, regarding Selected Ova

Table of Selected Ova

Table showing Periods of Fertilization and Imbedding

Relation of the Menstrual Cycle to Oestrus Cycle

Meaning of Menstruation

Table of Menstrual Cycle

Ovulation and Menstruation

Nature of the Decidua

Paper No. II. An Early Ovarian Pregnancy


History of the Case

Naked-eye Description of the Specimen

Description of the Sections

Discussion of Data

Summary of some other Cases of Ovarian Pregnancy

Relations of Ovum to Lutein Tissue

Origin of Lutein C'ells in Human Subject

Process of Imbedding in Ovarian Pregnancy

Origin of Plasmodium

List of Works Cited


Very early stages of the human ovum are necessarily extremely rare. It is only by fortunate and fortuitous circumstances that an occasional specimen comes into the hands of the investigator. Within recent years a number of young ova have been described, which have considerably extended our knowledge, and have served to show that in certain respects the early stages of development in man differ materially from those in lower mammals. The ovum of Hubert Peters, of which an account was published in 1899, still represents the youngest phase known. A specimen described by Leopold in 1906 is certainly earlier than that of Peters, but no embryonic rudiment was present, and in several other respects it must be considered abnormal. On the other hand, the ova described by Graf v. Spee (1905), Beneke, and Jung amply confirm, though they do not extend, the data provided by Peters' specimen.

Considerable light has been thrown on the problems involved in early human development by recent comparative work, more especially that of Selenka and Keibel on monkeys and apes, and of Hubrecht on Tarsius spectrum. It is now known that the Primates, including Tarsius in that category, form embryologically a group by themselves. All have certain common and peculiar features. There is always present a mesodermic connecting-stalk (Ha/tstiel), through which the vessels of the embryo and chorion are connected without the medium of an allantois ; the yolk sac is very minute and is not coextensive with the blastocyst ; there is a precocious extra-embryonic coelom lined by middle-layer cells, which are present at a very early period before the appearance of the primitive streak or embryonic axis, and therefore before the formation of the dorsal mesoderm of the embryonic body.

There are other features, however, in which the several orders of the Primates differ inter se. In Tarsius the amnion is formed as in the rabbit, dog, etc., by secondary folds, while in monkeys, apes, and man it is already closed in the earliest stages known. The placentation again, in the monkeys (Old and New World), differs from that in the anthropoid apes and man. While the early phases in apes and monkeys, described by Selenka, confirm and explain the corresponding phases in the human subject, none of the stages known reach to the initial stages of the blastocyst, and therefore much is still left for conjecture. The extremely young ovum, which is the subject of the first of the papers in this memoir, represents the earliest stage of any primate form except Tarsius yet recorded, and merits careful and det<iiled description in respect that it pushes back the limits of the unknown in a sensible degree.

The age of young human ova is, of course, from the nature of the case, quite uncertain. It is usually calculated in terms of the conventional rule formulated by Professor His, but the results of the rule as applied to the youngest know^n specimens are unsatisfactory and contradictory. In the present case we are fortunate in possessing very accurate data, and an effort will be made by correlating the facts with those known for other specimens to revise the basis on which the age of early ova is calculated.

Not only do the structural features of the early primate blastocyst remain unknown, but the process of imbedding and the initial phases of placentation are also merely matters of surmise. All the ova described before the appearance of Hubert Peters' monograph were found completely imbedded in decidua, and the hypothesis that the ovum becomes surrounded by a process of circumvallation was generally accepted, though in more recent times the results yielded by comparative embryology had caused some doubt on the matter in the minds of a few observers.^ Several of

  • In William Hunter's Anatomy of the Oracid Uterus 1774, Plate 35, there is figured a complete decidual cast, in which an ovum about the size of a pea lies imbedded. In his diagrams William Hunter clearly indicated that the ovum is at this stage completely surrounded by the decidua, but he expresHed no opinion as to how it Injcomes implanted therein. The theory that the decidua covers the orifices of the Fallopian tubes, and is pushed out by the ovum as it entei-8 the uU.'rus, lias been erroneously attributed to him. (See Historical Introduction to the Catalogue of Um Anatomical ami Pathological Preparations of William Hunter. John H.

'*ie ova, such for instance as that described by Reichert, showed a small area of the decidua capsularis (formerly called reflexa) over the blastocyst, which was of a different nature from the rest of the capsule, and apparently composed of cicatricial tissue. They were, notwithstanding, completely enclosed by organised tissue. In Peters' ovum, however, and Ij^so in one described by Graf v. Spec (1905) there is a relatively large area from which decidua is absent, and its place is occupied by a mass of fibrin and blood-clot (the *' Gewebspilz "). The aperture in the wall of the implantation cavity occupied by this mass was considered by Peters, and also by Graf v. Spec, as the point of entrance of the ovum into the substance of the mucosa, but their preparations do not by themselves conclusively demonstrate the actual process by which the ovum is implanted. To prove how this is effected still earlier stages are required. Our young ovum is a further step in the direction of assured knowledge, and as w^ill be seen later necessitates some modification in the interpretation of the "Gewebspilz" completing the capsule in Peters' specimen, while our ovarian ovum, which is the youngest hitherto described implanted in the ovary, throws considerable light on the nature of the imbe^lding process.

In the absence of the early stages in the human subject it is necessary to make use, for the purposes of interpretation, of the data provided by Comparative Embryology, but the remarkable variability in the methods of implantation and in the details of placentation in the diflFerent mammalian orders, speaks for a certain specific character of the embryological processes involved. Caution, therefore, is required in grafting any data derived from the investigation of the conditions in lower mammals on to the facts known for the human ovum, and the more so as the young ovum we have to describe accentuates the very special features of the human blastocyst in its early phases.

The only competent analogy with the higher primate ovum among the lower mammals is to be found among the forms in which there is likewise a decidua capsularis, for instance the hedgehog among the insectivora, and the mice, rats, and guinea-pig among the rodents. It is to be noted that in these forms, as in the Primates, the amnion is closed from the first, and that the blastoderm shows the phenomenon, to a greater or less degree, of "inversion of the germinal layers." Two methods of imbedding, which will be dealt with in greater detail later, have been described in animals with a decidua capsularis. In the hedgehog, mice, and rats, the ovum is said to be received into a recess or fissure of the mucous lining of the uterus ; the epithelium disappears round the blastocyst ; the mucous membrane becomes greatly thickened to form the decidua capsularis ; and the fissure is cut off from the general cavity of the uterus by the fusion of the lips of the decidual swellings from which the epithelium has likewise vanished. In the guinea-pig the observations of Graf V. Spce seem to prove that the ovum, while still in the early blastocyst stage, destroys the epithelium of the surface at the spot where it becomes implanted, by the activity of its ectodermic cells, and then, by a continuance of the process of destruction and solution, imbeds itself in the connective tissue of the mucosa. One or other of these alternatives must apply to the human ovum, and we submit our two communications as a contribution towards the solution of the problem.

In regard to the initial stages of placentation a very large body of data has been accumulated by comparative embryology, and our views as to the deciduate placenta have undergone considerable modification. Apart from the general character of the placentation in the different orders of mammals, debate has centred on the nature of certain layers of cells which separate the foetal from the maternal blood in the placenta. It is unnecessary here to enter on any detailed account of the various and contradictory opinions which have been held on this histological detail, or of the several theories which have been put forward on the subject of the origin of these layers.^ It is now very generally admitted that the evidence afforded by both human and lower mammalian material is in favour of the foetal, i.e. chorionic origin of both layers covering the villi in the human placenta. No doubt appears to exist in the mind of anyone as to the cellular layer, generally known as Langhans* layer, but there is still a lack of decisive proof regarding the plasmodial investment of the villi, or syncytium. Certain authors have maintained that it owes its origin to the maternal tissues — some deriving it from the epithelium either of the surface or of the glands of the decidua, others holding that it represents maternal endothelium spread over the villi in the interlocking of foetal and maternal tissues, which has long- been considered to take place in the development of the placenta.

  • The different hypotheses are fully set forth by Hubert Peters, by Webster {Human Placentation)^ and by Strahl {Hertwt'ffs Uandhuch der EntwiclcduiKjitleJin') ; they have also been dealt with by Teacher in his papers on "Chorion-epithelioma," and are briefly summarised by Bryce in Quain^s Anatomy^ vol. i. 11th ed. 1908.

The idea that uterine epithelium is necessary for the production of the Plasmodium was finally excluded by Catherine Van Tussenbra^k when she demonstrated the existence of a syncytial layer on the villi of a chorionic vesicle imbedded in the ovary, and her observation has been confirmed by several investigators. It is just conceivable, however, that if a fertilized ovum developed in the interior of the GratHan follicle, the follicular epithelium might be responsible for the production of the Plasmodium ; but this cannot be the case if it be proved that the blastocyst may be imbedded in the ovarian stroma outside the corpus luteum. In the second communication embodied in this publication further proof will be provided that such a case may occur.

The theory that the plasmodial layer on the villi is derived from maternal endothelium has become practically untenable in view of the characters of the early ova described in recent years, but it is not quite so certain that it may not owe its origin to the maternal connective tissue in which the ovum is imbedded, altered by the biochemical activities of the ectodermic cells of the blastocyst. In this connection earlier stages in the development of the plasmodium than have been hitherto available in the human subject, are required for the complete demonstration of its foetal origin in the human placenta. Our young uterine ovum, in virtue of its stage of development, and our case of ovarian pregnancy, being a crucial experiment both on the nature of the imbedding process and on the origin of the plasmodium, bring critical evidence to bear on this question.

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Pages where the terms "Historic" (textbooks, papers, people, recommendations) 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, interpretations and recommendations may not reflect our current scientific understanding.     (More? Embryology History | Historic Embryology Papers)

Cite this page: Hill, M.A. (2021, February 27) Embryology 1. An Early Ovum imbedded in the Decidua (1908). Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/1._An_Early_Ovum_imbedded_in_the_Decidua_(1908)

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