At this point a process called differentiation occurs by which each cell layer develops into different body systems. The endoderm develops into the inner lining of the digestive tract, glands including liver and pancreas, inner lining of the respiratory system. At this point further development occurs until the organism develops to the point of birth or hatching. Development then continues until the organism matures. In placental mammals the embryo implants into the wall of the uterus where a blood supply develops from the wall of the uterus called a placenta which meets with a blood supply from the embryo called the umbilical cord.
Diffusion occurs between the capillaries of the two blood supplies.
In other animals the yolk of the egg provides nutrients for the developing embryo which grows a blood supply into the yolk. Development begins at the point of fertilization. Angiosperms and gymnosperms then begin to form seeds.