At stage11 the flat cells of the amnioserosa cover the yolk between the dorsal and the ventral halves of the germ band.
  When the germ band retracts during stage 12 the cells of the amnioserosa still cover the cental yolk mass at the dorsal side of the embryo.
  When the dorsal closure progresses at stage 14 the amnioserosa occupies a small area at the dorsal surface.
  During dorsal closure at stage 14 the space covered by the amnioserosa becomes reduced. The cells of the amnioserosa now exhibit a columnar shape.
When the dorsal closure progesses at stage 15 the amnioserosa only occupies a small surface area. Eventually, the cells invaginate as the epidermis closes, coming to lie ventrally to the cardioblasts. Finally the amnioserosa cells degenerate and are phagocytosed at the end of embryogenesis.