Endocytobiosis it's the intracellular association between two cells. It can be defined as the symbiotic relationship in which one symbiont inhabits in the cytoplasm of another. It is of two types: homologous and heterologous. If both the cells are derived from the same taxon or same biont (like e.g. synergides within the makrogametophyte of seed plants, it's called as homologous and if partner cells comes from the various taxa, then it's termed as heterogeneous. This special symbiotic association has the facultative ability to an evolutionary change of a dibiont-system into a replacement monobiont-system bearing a replacement cell organelle, the exogenosome. The best examples for this illustration are chloroplasts and mitochondria which are widely believed to be evolved from bacteria that when lived as endosymbionts within the cytoplasm of ancestors of eukaryotic cells