Eutely refers to the condition of having a body made up of a constant number of cells. Eutelic organisms, such as some rotifers, tardigrades, and nematodes, have cell division until they reach maturity, but then live out the rest of their lives with a fixed set of cells that do not replicate to cause further growth or to replace themselves. Any additional growth occurs through the enlargement of the existing cells. The number of cells in a mature individual is also common across all members of the species.