A simulation model of the evolution of a free-living bilayered animal is proposed. The model object developed two layers of cells. The inner layer was able to produce digestive enzymes, to split and absorb organic substances. The evolution of these model objects was accompanied by mutations resembling real adaptations in some coelenterates and placozoans. It was observed that the outer layer of the model produced cells capable of secretion of digestive ferments. This mutation was a principal apomorphy leading to the appearance of organisms with extraorganismal digestion. Visual Basic and STELLA modeling software were used for simulations. © MAIK Nauka 2008.