Dictyostelium discoideum has been studied as a model for the developmental biology of complex organisms. Under optimum conditions, this organism lives as individual, amoeboid cells. When food is scarce, the cells stream together into a moving mass, resembling a slug that differentiates into a stalk with a spore-bearing body at its top. This structure releases spores that can grow into a new amoeboid cell. The development from identical, free-living cells to a multicellular organism simulates many of the properties of more complex and complicated organisms.