maternal and foetal circulatory system are seen intermingling, centrad the trophoderma shows smaller and larger spaces partly filled with -maternal blood and partly empty.
In figg. 22 a large bloodspace of the placental pad probably of arterial character is seen in the centre communicating with the peripteral bloodspaces of the trophoderma. In fig. 22 on the other hand the same phenomenon is seen more laterally. Probably this is a connection of the maternal venous system with the trophodermal one through the intermediate of the trophospongial lacunes.
The placental pad is characterized by enormons spaces surrounded by syncytial masses and these spaces are partly filled with blood, partly empty. The muscularis underneath the placental pad also shows at several spots large accumulations of blood-coagulum and enormous empty spaces, this phenomenon being probably in connection with the large providing with blood of the placental region which is necessary to entertain the metabolism of the developing germbladder.
Finishing this description 1 will once more lay stress npon the circonstance that in Chrysochloris an intricate placental structure and bloodcirculation are formed without intermediate of the allantoic circulatory system, the development of placental cushion and pad depending only on the stimulus of the attachment of the germbladder to the uterine wall by the trophoblast.
1. In the pregnant uterus of Chrysochloris the uterine mucosa shows at both sides of the mesometrium two placental pads. These structures have not been preformed in the virginal or nonpregnant condition, the uterine mucosa then possessing an enormous and uniform thickness.
2. The medial pad is only slightly thick er than the remaining part of the mucosal wall, shows peculiar changes of the uterine glands and of the bloodcapillaries and never comes in contact with the wall of the germbladder. Therefore I call it the false placental pad.
8. The lateral one shows a much larger diameter and grows together with the wall of the germbladder to form the discoidal placenta. Therefore it may be called the true placental pad.
4. The embryonic area of the germbladder is lying at the mesometrical side of the uterus. Its caudal region with the ventral mesoderm and the exocoeloma is turned towards the true placental pad.
5. The part of the placental pad which grows together with the trophoblast, projects into the exocoelomic cavity and has been called placental cushion.
6. The placental cushion consists for the greater part of a large conical ingrowth of the trophoblast: the trophoderma s. ectoplacenta which differentiates into a thin outer syncytial coating of plasmoditrophoblast and inner epithelial proliferations of cytotrophoblast. The former gradually forms a pseudendothelial covering round the maternal bloodspaces which originally arise in the maternal trophospongia i. e. in the connective tissue of the uterine mucosa having taken a spongious character. In the first stages the trophospongia forms a saucerlike surrounding of the inverted trophodermal cone, in older one's it is pushed away by the lateral spreading of the latter. Thus the placental cushion consists in these stages of an enormous trophodermal pad which contains numerous maternal bloodlacunes surrounded by a plas modi trophoblastic pseudendothelium and a reticulum of cytotrophoblastic villi forming a conducting tissue for the foetal capillary system.
7. In the subjacent placental pad proper the tissue gradually becomes syncytial and large bloodspaces arise in various modes. The bulk of them are furnished by the hypertrophying of maternal bloodcapillaries forming spongious syncytial clusters, but concentration of nuclei of the connective tissue at definite spots causing the formation of spaces