[Concerning one obsolete tradition: does gastrulation in sponges exist?]

The analysis of comparative-embryological and molecular-biological data leads to the conclusion that universal basic mechanisms of morphogenesis occurred first in the evolution of animals in the ancestors of modern sponges and eumetazoans, which served as a basis of different evolution of individual development in Parazoa and Eumetazoa lines. In the former, morphogenesis in early embryogenesis led to formation of the water-current system as a means for capturing and delivery of food particles to different parts of the animal. In the latter, morphogenetic movements manifested themselves as gastrulation, during which the germ layers and the digestive system formed. The morphogenetic movements of cells in Metazoa emerged independently of cell specification. They are primary relative to cell differentiation. Theunity of all Metazoa is based on the similarity of mechanisms of morphogenesis rather than on the presence of germ layers.