Phagocytella Theory

a hypothesis concerning the origin of multicellular animals proposed by Elie Metchnikoff (I. I. Mechnikov) between 1879 and 1886. According to the theory, a hypothetical animal called a phagocytella, or parenchymella, was the original multicellular organism. The structure of the phagocytella was held to be similar to that of the parenchymula, the larva of a lower multicellular organism. The phagocytella was thought to consist of a layer of ectodermal cells, called the kinoblast, and a mass of endodermal cells, called the parenchyma, or phagocytoblast. The kinoblast performed the functions of motility and exchange with the surrounding medium and of the establishment of boundaries, and the phagocytoblast was concerned with intercellular exchange and intracellular digestion. All the various forms of tissues of multicellular animal organisms were thought to have developed from the kinoblast and phagocytoblast in the course of evolution.