Multicellular Organisms

animals and plants whose bodies consist of many cells and their derivatives (various forms of intercellular matter). A characteristic feature of multicellular organisms is the nonequivalence of the cells making up their bodies and the differentiation and segregation of the cells into groups of varying complexity (tissues, organs) that fulfill different functions throughout the organism. Multicellular organisms are characterized by individual development, or ontogeny, which generally begins (except in vegetative reproduction) with the division and differentiation of a single cell (sex cell, spore).