Presumptive Primordium

in embryology, the cell material from which the primordium of a particular organ (neural plate, cord, epidermis) forms during embryonic development. The position of a presumptive primordium is determined by marking. Charts of presumptive primordia in the early gastrula stage have been made for various cordate animals. In some worms and mollusks the position of the presumptive primordium has been traced up to early cleavage.