The developing embryo after implantation the embryo produce finger like processes called villi. these villi get embedded into the grooves called crypts.The developing embryo gets intimately connected with the uterine wall of the mother and this intimate connection is called as placenta. Placenta helps in the diffusion of nutrients and oxygen from the blood of mother to the blood of foetus.
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Embryo get nutrition from  the mothers blood with the help of a special tissue called placenta . this is a disc which is embended in the urine wall. it contains villi on the embryo side of the tissue. on the mothers side of the blood spaces ,which sourrended the villi. this provide a large surface area for glucose and O2 to pass from mothers blood embryo