primordium: origin] • The most rudimentary stage of an organ or other part.

an organ in its earliest stage of development; the foundation for subsequent development

An organ (eye) in its earliest stage of development.

A group of cells which gives rise to an organ.

large sack-like structure which develops prior to metamorphosis of some larvae (eg. crown-of-thorns starfish); thought to give rise to specific tissues or organs in the juvenile starfish

a very young, not differentiated basidiocarp.

(L., origin) the first group of cells in an embryo which constitutes a future organ, etc. (also see anlage).