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Fig. 6. Section through the central region of the placenta, showing the spacious trophodermal bloodlacumar system surrounded by plasmoditrophoblast, the penetration of the trophodermal cone into the subjacent placental pad and the histological differentiation of the latter. Cytotrophoblast coarsely dotted, plasmoditrophoblast finely dotted, unchanged trophospongia single hatched, syncytial clusters doublé hatched, dermatic or trophospongial clusters hatched and dotted. X 50 (2k)-

Fig. 7. Section through the posterior (antembryonic) part of the placenta, showing the original connection of the yolk-hypoblast with the placental cushion. Trophospongia) or dermatic clusters presented by a dense dotting. X 50 (2/s)-

Fig. 8. Section through the true placental pad, showing the size of syncytial clusters. X 180 (2/3). Fig. 9. Section through the false placental pad, showing the transition of maternal capillaries into syncytial clusters. X 180 (2/3).

Fig. 10 & 11. Details from the same region drawn under high power. X 360 (V2).

N°. la of the catalogue.

Fig. 12 and 13. Two sections through the border of the placental pad and the muscularis uteri showing the communication and transition of maternal veins into the spaces of the syncytial clusters. The protoplasma of the clusters dotted. X 180 (2/3).

PLATE VI—VII. N°. la of the catalogue.

Fig. 14. Central section through the gestationsack in the embryonic and placental region. The embryo is cut in nearly sagittal direction. The yolksack and the wide opened enteron lie at the right side of the drawing, the placenta^ the exocoeloma and the back of the embryo are at the left side of it. Allantois and proamnion are present. The amnion-cavity and the neural tube are closed. The placental cushion projects far into the exocoeloma. X 35 (»/,).

Fig. 15. Section through the central part of the placenta. Mind the proximity of the placental surface and the area vasculosa. Trophoderma dotted, trophospongia single hatched, syncytial clusters doublé hatched. X 40 (2/3).

Fig. 16 and 17. Two sections through the central region öf the placenta, showing the direct communication of the maternal arteries with the trophodermal bloodlacunes. The black spots are clusters of highly coloured trophospongial cells. Cytotrophoblast densely, plasmoditrophoblast widely dotted. X 100 (3/4).

N°. 9 of the catalogue.

Fig. 18. Section through the gestationsack on the level of the headregion of the embryo and of the embryonic margin of the placental cushion, showing a rudiment of the proamnion, the closed brain tube, the separated foregut, the pericard with heartrudiment, the placental cushion with large central pit and the spongious placental pad. X 35 ('/,).

Fig. 19. Section through the midplacental region showing the narrow exocoeloma, the deep central pit bridged by a mesoblastic membrane and the nearly total syncytial degeneration of the spongious tissue of the placental pad. In the central part of the trophoderma a maternal artery is visible, in the muscularis a maternal vein communicates with a trophospongial lacune. X 50 (2/3).

Fig. 20. Section through the primitive streak and the closed tailamnion of the embryonic region and through the embryonic margin of the placenta. X 100 (2/3).

Fig" 21. Section through the central pit, showing the ingrowth of cytotrophoblastic villi and the coating of the trophodermic bloodspaces with plasmoditrophoblast, these two layers of the trophoderma being separated by narrow spaces. Observe the maternal artery in the basal part of the drawing. X 180 (2/3).

N°. 10 of the catalogue.

Fig. 22. Section through the gestationsack in the embryonic and placental region. The foetal membranes have been damaged in such a manner that the course of these 'structures cannot be determined exactly. The rolling up of the embryo is cause that it is cut thrice, once through the headregion, a second time through the posterior truncregion and a third time through the tailregion. Mind the communication of the exocoeloma with the embryonic coeloma. Through the pits and the cytotroblastic villi the bloodcapillaries of the exocoelomic mesoblast are penetrating into the trophoderma, forming a reticulum intermingling with that of the trophodermal (maternal) bloodlacunes. In the central region there is. a wide communication of the latter with an enormous arterial (?) bloodspacé in the placental pad. Rest of the communication of the yolksack with the enteron proper. X 35 (*/j)

Fig' 23. Section through the right half of the central placental region showing the same features as Fig. 22 under somewhat higher power. X 60 (2/3).

Fig. 24. Tangential section through the margin of the placental cushion, showing the intermingling of foetal capillaries and maternal bloodspaces, the latter lined by plasmoditrophoblastic pseudendothelium. X 180 (2/3).

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