ABSTRACT
One of the greatest and as yet unsolved problems of modern biology is morphogenesis, that is, the generation of new shapes and structures during development of organisms. Important evidence for the self-organizational properties of morphogenesis is its capacity to reduce the symmetry order without necessarily employing any discrete external "dissymmetrizators". Dissymmetrization, or symmetry breaking, is a remarkable natural process. The fundamental distinction is that embryos respond to any external influence, including mechanical, actively, that is, by generating their own internal mechanical force which tends to modify in some way the external mechanical stress. In vertebrate embryonic rudiments, pressure stresses are present but are due mostly to some other mechanisms, such as cell proliferation and cell intercalation. In hydroid polyps the cells of the tip region periodically swell and deswell due to osmotically driven water uptake and outflow.
