the placental cushion is formed almost of foetal elements only. Figg. 5 and 6 may illustrate this. In the first-mentioned figure the whole gestationsack is presented. It is drawn in a low power and gives a schematic idea of the main facts. The wall of the germbladder consists for the greater part of trophoblast and hypoblast only, the formative epiblast and the somatic mesoblast having disappeared. At the upper side some traces of the ventral mesoblast are still visible and the huid side (left side of the drawing) of the umbilical vesicle is covered with the longitudinally stretched, narrow exocoeloma. The placental cushion is seen feebly projecting into this space. It consists mainly of enormous bloodlacunes surrounded by trophodermic tissue (hatched in the drawing). Laterally some trophospongial elements contribute to the structure. The trophodermal cone enters in the centre into the subjacent part of the placental pad. The latter consists of lacunar connective tissue with some syncytial clusters and a few degenerated and hypertrophied uterine glands. The false placental pad on the right side of the drawing shows the same features as in the previously treated sections.
In fig. 6 some more pecularities may be detected inconsequence of the use of a higher power of magnifying. We observe the finely dotted plasmoditrophoblast surrounding the bloodspaces as a narrow sheet. In some places it is cut tangentially and then it forms broad bands as on the right side of the placental cushion. The coarsely dotted cytotrophoblast has no connection with the bloodspaces or with the trophospongia, it is everywhere covered on its basal side by the syncytial layer of the plasmoditrophoblast. The large doublé hatched serpentine on the right side of the trophodermal cone is a region where the maternal tissue is degenerating and bloodlacunes are about to be formed. By want of means of distinction it is presented in the same manner as are the syncytial masses, which are seen mixed up with the trophospongia] clusters. To the left of the trophodermal cone a long stretched, hypertrophied uterine gland is present. To the right of it a gland is seen partly filled with blood. Finally we may remark that the syncytial masses and extravasates also extend into the layer of circular muscles.
As the sections have passed the middle of the placenta the exocoelomic space gradually contracts, retiring in ventro-dorsal direction. The result is that the placental cushion becomes connected with the hypoblast of the umbilical vesicle and that the mesoblastic covering disappears in ventro-dorsal direction (from right to left in the drawing). At last the whole surface of the cushion is covered by yolkhypoblast. However it is nowhere in contact with the bloodlacunes of the area vasculosa, the hypoblastic covering of this region being devoid of bloodspaces.
Fig. 7 gives a section through this region of the placenta. The exocoeloma has not yet disappeared totally, but still covers the dorsal (left) side of the placental cushion, the other half being bordered by the umbilical vesicle. The trophoderma has still a conical form and possesses large bloodspaces. In the central part of the placental pad we may distinguish large trophospongial clusters, empty spaces, blood lacunes and a few glands. The syncytial clusters are especially crowded round the margin of the cushion. Mind the large blood spaces and bloodvessels in the muscularis uteri.
At its proximal end the series shows in the main points the same pecularities as I have previously described at the distal one. As the exocoeloma has retired from the placental cushion, the syncytial masses of the false placental pad disappear and this side of the uterine mucosa' shows an increasing number of glands and obviously becomes thicker, while a deep groove appears within this glandular cushion, laying at a distance of ± 135° from the point of attachment of the mesometrium.
A few sections behind the disappearance of the mesoblast and the exocoeloma, the wall of the germbladder consisting throughout of trophoblast and hypoblast only, the placental cushion "separates from the placental pad and soon disappears. The latter still shows enormous syncytial masses and widened uterine glands begin to reappear in it. In the meantime the above mentioned antimesometral grove has become very deep and the mucosa pierces at