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Show 1 9 0 5 .] PLACENTA OF THE SPINY MOUSE. 2 8 5 The advancing edge of the trophoblast is sharply defined from the maternal tissue (text-fig. 44, T). The trophoblast is composed of a compact mass of cells with large nuclei and generally fairly well-marked cell-boundaries. It has, in fact, the character more of a cytotrophoblast than a plasmodi-trophoblast (text-fig. 44). The nuclei tend to arrange themselves in pairs. Text-fig. 45. A diagram of a section taken through the centre of the placenta of Acomys. The maternal channels are not much exaggerated in size, but the fcetal capillaries are considerably magnified. The trophoblast layer in the region of the foetal capillaries is not nearly so much attenuated as it should be. The foetal vessels are dotted, the channels containing maternal blood are white. The deep black is trophoblast. AA. Allantoic artery. AV. Allantoic vein. 1). Layer of cell-detritus probably foetal as well as maternal. FC. Foetal capillary. H. Hypoblast of the parietal wall of the yolk-sac. HH. Hypoblast of the proximal wall of the yolk-sac, very much folded. L. Lacuna? in trophoblast containing maternal blood, M. Muscle-coat of uterus. MA. Maternal artery. MES. Mesoblast of foetus. MV. Maternal vein. S. Line along which the placenta had been detached from the uterus. SP. Splanchnopleur layer of mesoblast. T. Trophoblast. TS. Trophospongia. VV. Approximate portion of the main vitelline vessels. Y. Cavity of the yolk-sac. YC. Klood-vessels of the yolk-sac circulation. This trophoblastic tissue, which in the figure (text-fig. 45) is shown as a thick black mass (T), is honeycombed by channels containing maternal blood (L), which channels become more broken and more numerous nearer to the foetal suiface, and the trophoblast consequently more attenuated. I think there are possibly other cavities m the tioplioblast-cells which are not blood-spaces. r 11 iis mass of tissue formed entirely of trophoblast and mateinal |
