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[[Paper - An Early Human Ovum (Thomson) in situ]]
An Early Human Ovum (Thomson) in situ.
An Early Human Ovum (Thomson) in situ.
Odgers PN.
Odgers PN.

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Paper - An Early Human Ovum (Thomson) in situ

An Early Human Ovum (Thomson) in situ. Odgers PN. J Anat. 1937 Jan;71(Pt 2):161-168.3. No abstract available. PMID 17104634

An Early Human Ovum (Thomson) in situ

IN March 1913 the late Prof. Arthur Thomson received the uterus, which contained this ovum, with its adnexa from Prof. H. M. Turnbull of the LondonHospital. HebrieflydemonstratedittotheAnatomicalSectionofthe XVIIth International Congress of Medicine, which was held in London in the summer of that same year, but he never published any detailed description ofit.Somefiveyearsagohesuggestedtome thatitwaswellworthfurther examination,butitwasnotuntilafterhisdeaththattheslidesofthisspecimen with his serial microphotographs and notes about it were brought to my notice. Ishallcallitinthispaperafterhisname,andIhopethat,ifitisever referred to in the future, itmay be known as the Thomson ovum.

Prof. Turnbull discovered it in the decidua of the posterior wall of the uterus of an unmarried woman, aged 20, who died 5 hours after severe burns on 4 March 1913. The right ovary contained a corpus luteum, which measured 24*5x17-5mm. The woman's menstrual history was as follows. It first occurred at 15 years of age and had always been regular. Her last period commenced on3February,exactly29 daysbeforeherdeath. No datesofcoitus were available. The post-mortem examination took place 26 hours after death. The specimen was fixed in 10 per cent. formalin and cut into sections 10 thick.

From the menstrual history the maximal age of this ovum must be about 16 days. The inside measurements of the blastocyst are 2-1x 151 x 0-7 mm.; theembryonicdiscmeasures0-26x0-31(?)x0-16mm. (?).

In the following list it is placed among its contemporaries. DrS.Zuckerman has kindly computed for me from the inside measurements of the blastocyst cavity a rough estimate of its cubic capacity in the several ova, the cavities beingregardedforthispurposeasperfectspheres,ofwhichthediameterswere taken as the mean of the dimensions given. These figures are added in a separate column.

As is seen in the general view (PI. I, fig. 1), the blastocyst cavity and the trophoblast are well preserved, but the embryonic disc, particularly the ectoderm, has suffered a good deal of disorganization, the amniotic cavity being partly obscured by cellular detritus. While this forbids any detailed description of the disc itself, I wish to draw attention here to:

  1. the formation of the extra-embryonic coelom, and
  2. the wall of the yolk sac.


On either side of the amnio-embryonic vesicle a space is seen (P1. I, fig. 2), the one on the left being triangular in section, while the right one appears more quadrangular in shape. These are marked off from the rest of the blastocyst cavity by a regular layer - of mesothelial cels, which vary in differentsectionsintheirnumberandtheir shape, most of them being round, while aminorityareflatterandspindle-shaped. They are partially filed by coagulum similar to thatofthemagma. Ifthealmostsymmetricalchannelsthus formed are traced in one direction, they areseentocoalesceand surroundthisendoftheembryonicdisc(PI.I,fig.1), the common channel extending for thirteen sections beyond the disc: traced in the opposite direction they are observed to narrow and finallydisappear, the right before the left, sixteen sections from the disc, but here they are always separated from each other by a strand of mesenchyme and never join (PI.I,fig.4).

Text-fig. 1 is a diagram drawn roughly to scale to show the disposition of these channels (ExC) around the embryonic disc (ED) viewed from the dorsalaspect. ThelettersA,B,Ccorrespondtothelevelsofthemicro- photographs (PI. I, fig. 1; PI. I, fig. 2; and PI. I, fig. 4). While, as I have said, these channels are well marked out from the rest of the blastocyst cavity for the most part, there are in the case of either of them gaps in their parietes where they become continuous with the adjacent magma spaces. When tracedinserialsections,suchspacesareseentobeincreasinglyoutlined by mesothelialcelsso thateventuallytheyappear as litlebaysinthelateral wall of the channel which is thereby correspondingly enlarged.

The only other specimen which shows anything exactly like this one is the Peters ovum, but that of Tennant & Ramsey presents a condition very com- parabletoit.Theformerofthesewas re-examinedbyProf.0.Grosserin1908, andhe-hasbeengoodenoughtosendme hismicrophotographofthisovum andverykindlypermitsme toreproduceithereforcomparison(PI.I,fig.2).

The only differences in the appearance presented by these two sections are that in the Peters ovum (1) the lateral wall of the right channel has been torn away, (2) the containing wall of the intact left channel appears to be more celular, and (3) itextends on to the ventral wall of the yolk sac, while in the Thomson ovum, although they are wider, these channels are confined totheneighbourhoodoftheamnio-embryonicvesicle. Grosserdescribedthe channel in the Peters ovum as horseshoe-shaped; itsurrounds the cranial end of the disc as a small fissure. This is rather different from the wide com- munication presented by the present specimen.

Similarly, Tennant & Ramsey described "a space around the embryonic masswhichislimitedbyasinglelayerofflattenedmesodermalcellshavingthe appearanceofanendothelium(PI.II,fig.3).Thislayernotonlysurroundsthe space but likewise completely encloses those surfaces of the embryonic mass notdirectlyattachedtothemesenchyme." Intheirspecimen,too,thespace is horseshoe-shaped, as must be inferred from the fact that they found that "the left end of the embryonic disc stops bluntly and is entirely free of meso- thelial attachment while the right is completely encased in mesenchyme".

The three ova, Thomson, Peters and Tennant & Ramsey, seem to represent threestagesinthedevelopmentofthesechannels. Inthefirsttheyborder the amnio-embryonic vesicle only, in the second they have extended on to the lateralsideoftheyolksac,whileinthelasttheypracticallyenclosetheyolk saconallsides. Here,althoughtheauthorsdescribeaspace,Ithinkthereisa fine strand in the microphotograph they reproduce between the mesothelial layercoveringtheventralwalloftheyolksacandtheparietesofthespacetothe rightofthemidlinewhichmay indicateitsbilateralorigin(PI.II,fig.3),while in their reconstruction they show the ventral surface of the embryo as almost entirely free of mesenchyme, "with the exception of a small band of attach- ment extending about half way along this surface from the encapsulated end ".

In 1908 Keibel & Elze and Grosser described these channels as the com- mencement of the extra-embryonic coelom. Grosser (1924) suggested that theygraduallygrowventrallyroundtheyolksac,theiropposedwallspossibly forming, when they meet, the "distaler Nabelblasenfaden", the mesodermal strand which may connect the ventral pole of the yolk sac with the chorion. Further, he thought that these exocoelomic channels extend lateralwards by taking up the magma spaces nearest to them so that eventually the whole cavityoftheblastocystbecomestheextra-embryoniccoelom. Hewondered ifthelossofthelateralwallintheleftchannelinthePetersembryomightnot be due to its having already broken down so that on this side the exocoelom wascontinuouswiththeintercellularspacesofthemagma. Ihavementioned above that in the Thomson ovum there is evidence of the commencement of the same process, while Tennant & Ramsey wrote that in the specimen they described "on the surface towards the main chorionic cavity the continuity of thismembrane-likestructureislesswellmaintainedandirregularlydistributed openings in it offer probable avenues of communication between the larger and the smaller spaces ".

These three ova are peculiar then in being the only ones so far described which exhibit definite symmetrical coelomic channels.[1] The Fetzer (Grosser, 1924) and Herzog (Lewis, 1912) ova and the much more advanced embryo described by Waterston (Mall, 1916) have al been considered by these different observers to show something similar, but I would suggest that at al events the illustrations, which accompany the descriptions of these specimens, arefarfromconvincingfromthispointofview. Inalotherspecimensthe whole of the blastocyst cavity seems to represent the extra-embryonic coelom (Bryce,1924-5). An accumulationofmagmafluidappearsaccordingtothis author's account near its centre close to the embryonic disc, which gradually leads to the stretching and absorption of the mesodermal bands traversing itandtotheisolationoftheembryo,sothatultimatelyallthemagma spaces run together and the whole of the magma cavity becomes the exocoelom. Grosser (1913) and v. Mollendorif (1921) both suggested that there are thus two alternative ways in which this coelom may be formed.

It is, however, perhaps pertinent to observe that in the Peters ovum the trophoblast is already lined with "morula" mesoderm (Stieve, 1926), which also covers the ventral wall of the yolk sac beyond the limits of the exo- coelomic channel. The Thomson ovum presents the same appearance, although themesodermalcellscoveringtheyolksacarefew. Ineitherofthesecases, apparently, a gradual liquefaction of the magma would result in a perfect coelom lined with mesoderm without the help of the mesothelium of the channels at all.

With regard to the later fate of these exocoelomic channels there is only Grosser'ssurmisetoguideus,andonecannothelpthinkingthattheirformation as seen in the three specimens in which they occur serves no useful purpose. In any case their appearance in the Tennant-Ramsey and Thomson ova prove that the Peters ovum isno longer quite exceptional.


As seen in PI. I, fig. 2, this appears as a space beneath the amnio-embryonic disc,outlinedfromtherestofthemagma cavitybyathinmembranous wall. Itisflatteneddorsoventrally. On theleftside,itsventralwalliscon- nected by an irregular strand of mesenchyme cels to the chorion, but this is the only evidence of a commencing "Nabelblasenfaden" so obvious in the Schlagenhaufer-Verocay specimen. While the dorsal wall of the yolk sac beneath the embryonic disc has a lining of cubical entodermal epithelium its lateral and ventral walls are formed by a sparse layer of flattened spindle- shaped cells mesothelial in character. These latter appear to be similar to many of the cels lining the extra-embryonic coelomic channels, and the coagulum within the yolk sac seems to be exactly like that filing these channels and the magma spaces. Clothingthelateralwallsandextendingon totheventralanglesofthesacareafewroundmesodermalcels. Itisinter- esting to compare the condition found here with that noted or illustrated in the other ova in the list given above.

Linzenmeier. There is no mention of this point in the text, but the accom- panying illustration shows flattened cells on the ventral side of the yolk sac with a cubical entoderm under the embryonic disc.

Stieve. "Theyolksacisoutlinedbyspindle-shapedmesodermcels,whilethe entodermisonlyrepresentedbyasinglelayerbeneaththeectodermofthedisc."

Peters. Herethewholesacislinedbyacubicalepitheliumofthesame typealround(P1.I,fig.2). InPeters'originaldrawingthecellsontheventral wall are more irregularly spaced than are those beneath the disc.

v.Milendorif,EiOP. "Initswholecircumferencetheyolksacislined withmarkedlyflattenedcellswithlens-shapednuclei." Hisfigureshowsa condition very much like that I have described in the Thomson ovum.

Fetzer.Thesacislinedexceptbeneaththediscwitha"thinlowentoderm". Sporadically the cells are larger, cubical or short cylindrical in type (Fetzer& Florian).

Falkiner. Hegivesnodescriptionofthispoint,buthisillustrationshows the lining of the yolk sac very much like that in the Thomson ovum.

Tennant& Ramsey. "Theyolksacislinedwithentodermalcels,whichare cuboidalonthedorsalsurfaceandflattenedontheventralsurface"(P1.I,fig.3).

Herzog. Lewis(1912)describedthesacinthisovumthus:"Overthegreater part of it the entoderm forms a very thin layer resembling endothelium."

Heine& Hofbauer.Theyolksacislinedbyasinglelayerofflattenedcells except under the disc.

Schlagenhaufer& Verocay.Theyolksacislinedthroughoutwithentoderm.

Jung. Theyolksacshowsasimplelayerofflatentodermcels.

With the Peters and Schagenhaufer ova standing out as exceptions this analysisconfirmsBryce's(1924-5)statementthatinthefirstinstancetheyolk sacisalwayslinedwithflattenedendothelial-likecels. Inolderembryos,as Grosser (1924) pointed out, there is a complete change; in these (e.g. Rossen- beck, Grosser and Graf Spee ova) while the peripheral part of the sac is lined with cuboidal cells the portion of it beneath the disc has the flatter type of epithelium. SimilarlyFlorian& Hill(1934-5)describedtheyolksacwallin their specimen-" while the endoderm of its cranial and lateral walls is formed offlattenedcels,thatofitsventralwallisdistinctlyhigher." InattemptingtoexplainthesedifferencesStieveinterpretedtheappearance presented by the ovum (Werner) he described as follows. The future yolk sac ishererepresentedbyanenlargedmagma spacelyingbeneaththeembryonic disc and outlined by mesoderm cels. Later the entoderm of the disc must gradually grow ventrally and surround this space on its inner aspect and so form a definite yolk sac. He followed Corning (1925), who described the entoderminthehuman ovum asbeginningasan entodermalplate-thelowest layer of cels of the embryonic disc-rather than as an entodermal vesicle. In favour of such a conception are, I think, the following points: (1) Itbringstheformationofthehumanyolksacinlinewiththatwhich hasbeenfoundtooccurinmostothermammals (Stieve).Theonlyobservations incomparativeembryology,asfarasIam aware,whichsuggestthedevelop- ment of the yolk sac by the dehiscence or vacuolization of a primitively solid entodermal mass are those of Hubrecht (1889-90) in Erinaceus and Hill (1932)inNasalislarvatus. (2) The entodermal vesicle of the Teacher-Bryce ovum (TB. I.) lying in themagma anddivorcedfromtheamnio-embryonicvesiclemightverywellbe described as a magma space (Stieve). Bryce (1924-5) himself described it as beinglinedwithflattenedcelspreciselylikethoseformingthewallofthesac in Linzenmeier's embryo. (3) In the Tennant-Ramsey ovum the cubical entoderm appears to be surrounding the yolk sac and to have left only a portion of its ventral wall linedby flattenedcells(PI.I,fig.3). (4) Innearlyaltheearlyova theyolksac,linedwithflatmesothelial-like cels,isfiledwith a loose coagulum which seems to be indistinguishablefrom that of the magma spaces (Triepel, 1916). On the other hand Schlagenhaufer & Verocayfoundintheirovum thatthecontentsoftheyolksacstainedmore deeply with eosin than did that of the magma. Tennant & Ramsey described the yolk sac in their specimen as "partially filed by pink-staining finely granular material, while in other sections large yolk granules are present in thecavity". Petersfiguredsomedropsof(?)yolk-likematerialinhisoriginal drawingoftheyolksacinhisovum. Inallthesethreeinstances,ashasbeen notedalready,thesacislinedmore orlesscompletelywithacubicalentoderm. One might, therefore, suggest that there is some correlation between the character of the contents of the yolk sac and of its cellular lining. The appearance of the yolk sac in the Thomson ovum isvery much like that shown in Stieve's illustration. On Prof. J. P. Hill's advice I ventured to sendtheserialmicrophotographsofthisovum toProf.Grosser,andhewas kindenoughtogiveme hisopiniononthispointafterexaminingthem. His criticismofboththeThomsonandtheStievespecimenisthesame. Inboth, accordingtohim,theentodermalliningoftheyolksachasdisappearedexcept underthedisc. IconfessIthinkthisexplanationisadifficultone. Allowing that 26 hours elapsed between the woman's death and the fixation of the Thomson ovum, the entoderm could scarcely have vanished in this time withoutleavingatrace. Ifthecelshadbeenshed,theyortheirdebrisshould surelystilbefoundintheyolksac,unlessitswallswerebroken. Buttheyolk sacappearstobeintact,filedwithcoagulum,butcontainingonlyanoccasional detached cel. If there had been a dehiscence in itswall, the fluid content wouldcertainlyhaveescapedbeforeitscellularlining. Further,asIhave shownabove,inmostoftheearlyovathecelsliningtheyolksacaredescribed as being of this same character, and, while in different specimens they vary somewhat both quantitatively and qualitatively, most embryologists would followBryceindescribingthemasflattenedandendothelial-like. But,ifone accepts Grosser's explanation for the Stieve and Thomson ova, is one to condemnothersofaboutthesameagewhichshowasimilarcondition? One is left apparently with two alternatives. There is, on the one hand, the view generally held that these mesothelial-like cels lining the early yolk sac, so similar to many of those outlining the exocoelomic channels and to those scattered elsewhere throughout the blastocyst cavity, grow eventually into the cubical or low columnar ettoderm of the older sacs. On the other hand, there is the conception of Corning and Stieve of a yolk sac originally preformed asamagma spaceandoutlinedinmesoderm,whichlateracquiresanepithelial lining from the growing margins of an entodermal plate. This latter idea apparently has much to recommend itand I should prefer myself to interpret this specimen as rather corroborating it. While I realize to the full the weight that rightly should be attached to Prof. Grosser's opinion, I would suggest that the appearance of the cellular liningoftheyolksacinthisovum isnotsoremarkable. SUMMARY 1. The interior measurements of the blastocyst cavity in the Thomson ovum are 2-1x 1-51 x 07 mm.; itsmaximal age isabout 16 days. 2. Theextra-embryoniccoelomishereseentobecommencingasfairly symmetrical channels on either side of the amnio-embryonic vesicle. A com- parable appearance to this has been observed previously only in the Peters and Tennant-Ramsey ova. 3. Theyolksachasaliningofcubicalentodermbeneaththedisc;else- where it is merely outlined by a sparse layer of spindle-shaped mesothelial- likecels.Thisconditionisshown not tobeexceptionalintheearlierova and is held to corroborate Stieve's conception of an entodermal plate spreading ventrally to form the proper entodermal wall of the yolk sac as seen in later embryos. Iam verymuchindebtedtoProf.J.P.Hillforhiskindnessinexamining the slides of this specimen, and to Prof. 0. Grosser for giving me his opinion on the serial microphotographs of it, and for his kind permission to reproduce hisownphotographofthePetersovum. Imustalsothankthepublishersof Surgery,GynecologyandObstetricsforallowingme toreproducetheillustration, PI.I,fig.3,which appeared originallyin thatjournal. The other micro- photographs are the work of Mr W. Chesterman of this Department.


BRYCE, T. H. (1924-5). Tranm. roy. Soc. Edinb. VOL. LM, pt. 3, p. 533. CORNING, H. K. (1925). Lehrbtuch d. Entwicklungsgesch. d. Menwchen, 2. Aufl. Munchen, S. 79. FAijWER, N. M. (1932). J. Obdtet. Gynaec. vol. XXXIX, p. 471. FETZER,M.(1910). Verh.anat.Ges.Bd.xxxvii,S.116.

FETZER, M. & FLORIAN, J. (1930). Z. miikr.-anat. Forsch. Bd. xxi, S. 351. FLORIAN,J.& HILL,J.P.(1934-5). J.Anat.,Lond.,Vol.LXIX,p.399. GROSSER,0.(1908). Vergleich.Anat.u.Entwicklungsgesch.d.Eihduteu.d.Placenta.Wienu. Leipzig. (1913). Anat.Hefte,Bd.XLVII,S.649. (1924). Z.ges.Anat.3Abt.Bd.xxv,S.391. (1927). Frilentwickllung, Eihautbildung u. Placentation d. menschen u. d. Sdugetiere. Munchen. HEINE & HOFBAUER, J. (1911). Z. Geburtsh. Gyndk. Bd. LXVIII, S. 665. HERZOG, M. (1909). Amer. J. Anat. vol. IX, p. 361. HILL,J.P.(1932). Philos.Trans.B,vol.CCXXI,p.108. HUBRECHT,A.A.W.(1889-90). Quart.J.micr.Sci.vol.XXX,p.283. JUNG,H.(1907). Mschr.Geburtsh.Gynak.Bd.XXV,S.901. KEIBEL, F. & ELZE, K. (1908). Normentafel z. Entwicklungsgesch. d. Menschen. Jena. LEWIS,F.T.(1912). ManualofHuman Embryology,vol.I,p.298. KeibelandMall. LINZENMEIER,G.(1914). Arch.Gynak.Bd.CI,S.1. MALL,F.P.(1916). Contrib.toEmbryology,vol.IV. V. MOLLENDORFF, W. (1921). Z. ges. Anat. Abt. 1, Bd. LXIT, S. 406. PETERS, H. (1899). Uber d. Einbettung d. menschlichen Eies. Leipzig u. Wien. SCHLAGENHAUFER & VEROCAY (1916). Arch. Gyndk. Bd. cv, S. 151. STIEVE,H.(1926). Z.Mikr.Anat.Bd.VI,S.295. (1931). Verh.anat.Ges.Bd.XL,S.44. TENNANT, R. & RAMSEY, E. M. (1934). Surg. Gynec. and Obstetr. vol. LVIII, P. 968. THOMSON,A.(1913). XVIIthInternat.CongressofMedicine,Section1,pt.2,p.28. TRIEPEL,H.(1916). Anat.Hefte,Bd.LIV,S.149.



Fig.1. Thesectionphotographedisthroughthemiddleoftheblastocystcavity(x44). Fig. 2. The same section as fig. 1 (x 100). This shows the exocoelomic channels, ExC, on either sideoftheembryonicdiscandventraltothistheyolksac,YS. Abovethediscistheamniotic cavity obscured by cellular debris which partially filsit. This section corresponds to the planeletteredB inText-fig.1.

PLATE II Fig.1. A section(x100)20,ubeyondoneextremityoftheembryonicdisc. Itcorrespondstothe planeA inText-fig.1andshowsthatthetwoexocoelomicchannelshavejoinedroundthis end of the disc. Fig.4. A section(x100)20/.zbeyondtheoppositeextremityofthediscshowingthetwochannels stilseparatefromeachother.ThiscorrespondstotheplaneC inText-fig.1. Fig.2. A photographofasection(x100)ofthePetersovum,kindlysentme byProf.0.Grosser. It shows the exocoelomic channel on the left intact, bordering the embryonic disc and the yolk sac, while that on the right has only its medial wall left. Fig. 3. A section (x 150 ?)ofthe Tennant-Ramsey ovum (reproduced by courtesy ofthe Editors

of Surgery, Gynecology and Obstetrics). It shows the amniotic cavity, the embryonic disc and the yolk sac surrounded on either side and ventrally by the extra-embryonic coelom.

  1. Since this was written K. Hiramatsu (Fol. Anat. Japon, 1936, Bd. XIV, p. 15) has published an account of the ovum, Ei-Ando. In this he describes two small cavities on either side of the dorsal portion of the yolk sac, which he thinks correspond to these exocoelomic channels.